Natural History of Ecological Restoration

Tag: Woodland

  • Understanding the role of soil microbial communities in oak woodland restoration using DNA metabarcoding

    Understanding the role of soil microbial communities in oak woodland restoration using DNA metabarcoding

    By: Rachel Brant

    Rachel is a postdoctoral fellow in the Missouri Botanical Garden’s Center for Conservation & Sustainable Development whose research focuses on plant-pollinator interactions and using eDNA to advance the conservation and restoration of biodiversity.

    Oak-dominated ecosystems occur in many areas of the northern hemisphere, support considerable biodiversity, and provide vast benefits to humans. Although notably absent from the southern hemisphere, oak-dominated or mixed-oak dominated forests are found across much of southern and central Europe, northeast Asia, and the eastern and central United States. Oak ecosystems range from closed forests with a dense midstory to open forests or woodlands with continuous canopy or widely spaced trees and dominance of herbaceous vegetation in the understory.

    Around 80% or more of the plant diversity in oak forest and woodland ecosystems in the eastern US, including a large proportion of rare species, resides in the herbaceous layer, which contributes significantly to nutrient cycling and overall ecosystem function. However, these forests and woodlands have suffered significant degradation over the past century, resulting in dramatic shifts in species composition and structure due to human land-use activities, invasive species, and alterations in disturbance regimes. In particular, fire exclusion has led to the encroachment of fire-intolerant tree species and nonnative shrubs, decreasing both understory light availability and the abundance and diversity of herbaceous plant species.

    Restoration of oak ecosystems usually involves prescribed burning or a combination of burning, canopy thinning, and control of undesirable woody vegetation. Although these restorative practices encourage the passive recovery of herbaceous flora, restored oak woodlands often lack conservative species in the understory. Unlike matrix or ruderal plant species, conservative plant species are those that depend on high-quality or minimally damaged sites and rapidly disappear with degradation. In addition, they often fail to recolonize sites naturally, making them potentially important targets for reintroduction.

    (Top) Degraded oak woodland at Missouri Botanical Garden’s Shaw Nature Reserve infested with nonnative shrubs and fire-sensitive tree species and (Bottom) Adjacent restored oak woodland after mechanical control of woody encroachment and six prescribed burns. Note the minimal sunlight penetrating the woodland floor and lack of herbaceous species in the degraded woodland relative to the restored woodland. Photo: (Top) Brad Delfeld and (Bottom) Matthew Albrecht.

    Conservative species are notoriously challenging to reintroduce in restoration projects, with soil microbes emerging as a key factor influencing their success. Arbuscular mycorrhizal fungi (AMF) are particularly crucial in this context; they enhance nutrient uptake and improve stress resistance, benefits that are especially valuable for conservative plant species with specific habitat requirements. For example, one study found that conservative species were more dependent on AMF and exhibited higher habitat specificity compared to less conservative species (Bauer et al. 2018). The practice of soil inoculation with whole soil, which presumably contains beneficial mutualists like AMF, is increasingly employed to boost plant growth and survival in restoration projects. Despite its growing popularity, though, the effects of soil inoculation on the establishment of herbaceous species in oak-dominated ecosystems remain poorly tested.

    Another factor that may affect the establishment of conservative plant species is the timing of reintroduction. Environmental conditions are predicted to be more favorable for the establishment of conservative species later in restoration, in part because soil symbionts facilitating plant establishment may only be found in later-successional sites. Alternatively, early restorations may lack the establishment barriers potentially encountered later in restoration, such as competition with established vegetation or soil legacies from early-arriving species, but could be deficient in important microbial mutualists often required by conservative plant species.

    To test these hypotheses, we examined the potential role of soil microbial communities on the performance of conservative herbaceous species using an oak woodland restoration chronosequence at the Missouri Botanical Garden’s Shaw Nature Reserve. First, we collected bulked field soil samples from three sites representing different restoration ages (young, intermediate, and old) based on their onset since restoration began (7, 16, 29 years ago) with prescribed burning, selective tree thinning, and non-native shrub control. We quantified several soil abiotic properties (e.g., pH, phosphorus, potassium, and nitrogen) and employed DNA metabarcoding to describe the microbial composition of the soil. DNA metabarcoding is a cutting-edge technique that identifies many taxa from an environmental sample by sequencing specific genetic markers from extracted DNA. This method provides a comprehensive snapshot of the microbial diversity present, allowing one to better understand otherwise cryptic below ground communities. 

    Conservative perennial forbs used in a greenhouse study to test the effects of soil inoculation young, intermediate, and old restored woodlands on plant growth: Geum virginianum (left), Solidago argute (center), and Solidago caesia (right). Photo credit: Gerrit Davidse (left) and Missouri Botanical Garden (center and right).

    Next, we conducted a greenhouse study with three conservative forb species, Geum virginianum, Solidago arguta, and Solidago caesia, testing their growth responses to soil inoculum from sites that differ in restoration age. These species are components of the regional species pool, but absent from restored oak woodlands at Shaw Nature Reserve. We placed germinated seeds of each species in quart-sized pots filled with a sterilized topsoil mix that mimic oak woodland soils. Each sterile pot (270 in total) was then inoculated with 10 mL of the bulked live field soil (approx. 1% by volume) sourced from one of the three restored sites. Plants were grown for 12 weeks in standard greenhouse conditions and then evaluated for growth using nondestructive measurements.

    Planting seeds of conservative forb species into soil inoculum treatments in a greenhouse study. Photo credit: Leighton Reid

    Tree species and soil microbial communities in restored oak woodlands 
    Not surprisingly, we found that younger restored oak woodlands, with historically fewer prescribed fires, had a greater abundance of fire-sensitive tree species (e.g., sugar maple, Acer saccharum) than the intermediate and older restored sites. However, younger restored woodlands also exhibited lower levels of soil phosphorus compared to older sites, consistent with previous studies that have shown greater levels of potassium and phosphorus in soils post-burning. Other soil abiotic properties, however, did not differ across the restoration chronosequence. 

    A grove of sugar maples (Acer saccharum) during autumn in the young restoration site at Shaw Nature Reserve. Photo credit: Mike Saxton

    Bacterial and fungal communities varied in composition across the restoration chronosequence. For example, Firmicutes, a phylum of bacteria noted for surviving in extreme conditions, such as in severely burned areas, was more abundant in soils from the oldest restored woodland, which experienced a greater number of prescribed fires than the other sites. In contrast, the fungal phylum Ascomycota was more abundant in restored woodlands of young and intermediate age. Members of Ascomycota include decomposers that break down organic materials and endophytes that form mutualistic or commensal associations with plants. 

    Plant-soil interactions in response to soil inoculation
    After 12 weeks of plant growth in the greenhouse, we found that forbs tended to grow larger leaves when grown in soil inoculum from the younger restoration site compared to the intermediate restoration site. Additionally, S. arguta and S. caesia grew longer leaves in soil inoculated from the intermediate compared to the old site, while G. virginianum plants tended to produce longer leaves when grown in inoculum from young relative to the old restoration site.

    Leaf length (cm) of three native forbs after 12 weeks of growth in whole-soil inoculations from young, intermediate, and old restored oak woodlands at Shaw Nature Reserve. Geum virginianum (GV), Solidago arguta (SA), and Solidago caesia (SC).

    Results from the DNA metabarcoding provide a clue as to why the soil inoculum treatments induced different plant-growth responses. Soils from the young restoration exhibited increased relative abundance of mutualistic microbes, including AMF and cyanobacteria, and decreased pathogenic taxa after conditioning by each of the three species. In contrast, the oldest restoration site had the greatest relative abundance of pathogens and the lowest relative abundance of mutualists. This enhanced microbial profile in young restorations may facilitate better nutrient uptake, and disease and stress resistance in plants. From a practical perspective, early-stage restorations may provide the most favorable soil microbial community for the establishment of conservative plant species in these oak ecosystems. One possible reason for this could be a shift in the increased relative abundance of AMF-associating tree species (e.g., maple) from older to young restored woodlands. AMF-associating tree species may harbor unique AMF taxa that resulted in increased herbaceous plant growth and AMF colonization for plants conditioned with young soil inoculum.

    Interestingly, although some microbial taxa exhibited consistent patterns across all plant species within an inoculation treatment, each plant species also associated with unique microbial taxa when grown in the same soil inoculum treatment. For example, the Glomeraceae, which includes AMF, was marginally more abundant after S. caesia was grown in young inoculum, whereas Ascobolaceae – fungi that feed on decaying and dead matter – was significantly abundant only when G. virginianum was grown in old soil inoculum. This means that species reintroduced during different stages of oak ecosystem restoration could influence key ecological functions by selecting for or against certain microbes, including pathogens that regulate plant community dynamics, decomposers involved in nutrient cycling, and mutualists that enhance plant performance. 

    Overall, our study demonstrates how restoration age can shape interactions between soil microbes and herbaceous plant species in restored oak woodlands. By better understanding these interactions, we can enhance the restoration and recovery of degraded oak ecosystems. However, an important and lingering question from our study is whether differences in plant growth and microbial communities observed in the greenhouse persist after the focal plant species are transplanted into the field. A study currently underway at Shaw Nature Reserve is addressing this question across different restoration ages and competition treatments. Our study reinforces global calls that emphasize the need for more research on the dynamic nature of plant-microbe relationships and interactions over time during restoration. Advancing scientific research on the relationship between the soil microbiota and ecological restoration practices is crucial for meeting local, regional, biome level and global restoration goals.

    If you want to learn more about microbial-herbaceous plant interactions in restored oak woodland, we invite you to read our recent paper in Ecology and Evolution.

  • Reconstructing and reconnecting native habitats post-pipeline construction at the Litzsinger Road Ecology Center

    Reconstructing and reconnecting native habitats post-pipeline construction at the Litzsinger Road Ecology Center

    By James Faupel & Caity Sims 

    James Faupel is the urban ecology restoration supervisor at the Litzsinger Road Ecology Center (LREC) and Caity Sims is the Project Clear restoration coordinator. The LREC is a private, urban outdoor education site in the heart of Metropolitan St. Louis, Missouri that is managed by the Missouri Botanical Garden for educational programming with K-12 teachers and students, and supported by many local university-based researchers.

    Part 1: by James Faupel

    Anticipating Loss

    In September of 2018, when I took on the lead restoration ecologist role at the  Litzsinger Road Ecology Center (LREC), I was aware of the impending utility pipeline project (Project Clear) that would impact around a quarter of this education center’s restored habitats and the adjoining urban Deer Creek. The 15.8-hectare (39-acre) ecology center combines a mix of reconstructed bottomland prairie and restored riparian woodlands, with a stretch of urban creek in surprisingly good ecological condition. I knew this was a unique opportunity to set up a long-term study to examine the processes of reconstructing tallgrass prairie following major anthropogenic soil and landscape disturbance, a topic with little previous research, especially in urban areas.

    The 6.3 km (3.9 mile) long Deer Creek branch of Project Clear was slated to dissect a 0.8 km (0.5 mile) long swath of LREC’s restored habitats – a pretty significant amount of collateral damage. To be clear, the purpose behind Project Clear’s sanitary pipeline path is well intentioned. The Metropolitan St. Louis Sewer District’s (MSD) Project Clear is a six billion dollar, 28-year long initiative to improve water quality and alleviate many wastewater concerns related to the frequent sewage overflows of the legacy sewer system of the St. Louis region. Cleaner water in Deer Creek would mean healthier breeding and feeding conditions for a wide variety of wildlife that live in or rely on the water of the creek, as well as healthier adjoining ecosystems, and much healthier domestic water supplies for human residents of St Louis County. The collateral damage of the MSD Deer Creek branch was 6.3 km (3.9 mile) of riparian habitat was damaged, degraded or destroyed.

    In 2019, the Litzsinger Road Ecology Center (LREC)’s oldest prairie reconstruction and woodlands were dissected by the Project Clear pipeline path. The LREC is an outdoor educational facility of the Missouri Botanical Garden, and relies on functional ecosystem services to introduce children to the intricacies of nature. The pipeline project construction equipment would directly impact the LREC’s grounds and classes for three years, but its impact to the habitats here will be felt for generations. Photo by James Faupel.

    As discussed in a previous NHER blog post on the topic, urban prairie reconstructions are important tools in the toolbox of prairie education to the general public and in saving North America’s prairie remnants. Remnant prairies are invaluable fragments of a once vast grassland ecosystem of the Midwest and are now one of the most endangered ecosystems in the world. Getting the chance to expand the area covered by reconstructed prairie at an educational site like LREC was an opportunity that I did not want to miss. The downside was that the LREC restoration team would have only one year to gather baseline data before the sanitary pipeline construction began, and I also had to fit in learning all of the other ins and outs of my new role.

    Throughout 2019, with the assistance of LREC volunteers, interns, and partner researchers from local universities and organizations, we were able to gather a wide array of baseline data that could be used as a comparison in the years ahead, once the future restored prairies are older. In 2019, the previously restored habitats at LREC were 30 years old, among some of the oldest restored habitats in the St. Louis region. Restoration projects of this age are incredibly valuable for ecological research projects looking to better understand anthropogenic impacts on the environment around urban centers and to learn best practices for effective, long-lasting restoration efforts. They are priceless.

     During the growing season of 2019, we were able to survey all the vascular and nonvascular plant species growing in the proposed pipeline path and adjoining areas, as well as survey for birds, bees, spiders, ants, and algae thanks to the varied expertise of all involved. Baseline samples were collected of the upper soil horizons along the entire pipeline path, in addition to a complete inventory of all of the trees and shrubs that would be removed during construction so we could assess their value. The most significant baseline dataset is that of Elizabeth Hasenmueller and her Lab at Saint Louis University, who had been studying the water quality of Deer Creek at LREC for five years prior to the sanitary pipeline installation and are excited to continue this research, hoping to capture more data and test hypotheses concerning the hydrology and geochemistry of this urban stream as water quality improves with the removal of the sewage overflows from the creek.

    LREC volunteers assisted staff in a tree inventory of 746 native trees and shrubs ahead of the pipeline installation in 2019. The canopy trees were measured and their value assessed using the US Forest Service’s iTree database. The USFS’s estimated replacement value of the 289 mature canopy trees was half a million US dollars. This dollar value is in addition to the countless ways the ecological and environmental services provided by these trees could be valued. Photo by James Faupel.

    Deconstruction of Habitat

    On September 30th, 2019, construction vehicles arrived on the grounds of LREC, and began the month-long habitat removal on site. In what felt like the blink of an eye, a large section of one of the oldest prairie reconstructions in the St. Louis region, along with 746 individual native trees and shrubs, were gone and no longer providing any ecological or educational services. It was quick, like a bandage being ripped from the skin.

    Before and after the 0.8 km (0.5 mile) MSD pipeline construction path on the property of the LREC. 
    Left: October 2018. Right: August 2020 (Google Earth 2019, 2021).

    The pipeline installation process, from start to finish on LREC property, lasted nearly three years. Following the removal of all the preexisting habitat, work began on trenching the ground open, dynamiting the bedrock, installing the sewer pipe, reworking the now homogenized limestone bedrock/C horizon soil mix back into the trenches, restabilizing the streambanks from their stream crossings, and finally grading the soil out to pre-construction elevations. We knew from the beginning of their trenching process that we would ultimately be trying to grow native prairie plants in a “novel ecosystem” with soil conditions that would never co-occur with them in nature. 

    Throughout the construction process, there was plenty of time for planning how we would restore the land once it came back into our hands, as well as how we would monitor it long term. There is little research that has been done on the topic of prairie reconstruction following major anthropogenic soil disturbance. Initially we thought it would be beneficial to test many different methods of soil remediation ahead of the seeding of native prairie plants in different study plots. However, during the three year construction period, there were several major flooding events from the adjacent Deer Creek that changed our minds. The regularity and increasing frequency of these flash flood events of this urban creek made us take pause and the aforementioned research idea was scrapped. These events aren’t likely to lessen anytime soon, as the area covered by impervious surfaces in the surrounding watershed continues to grow. Future flooding events would introduce too many confounding variables to any kind of research that compared the outcomes of various soil remediation methods to make it a worthwhile investment of our time and resources.

    Left: Throughout the construction of the pipeline path (2019-2022), the path was impacted by Deer Creek flooding beyond its banks 11 times. It was completely covered by 4 major flash flood events as seen here. Right: The pipeline path a few months after construction had finished in late summer of 2022, covered in a growing season’s worth of early successional species. Here a contractor puts down the first annual cover crop to help break up the compacted soils and help hold the soil in place during rain events. Photos by James Faupel.

    In late summer of 2022, the property was handed back to the staff at LREC to begin the habitat reconstruction work. By this point in time, I had been promoted to a supervisor position at LREC and had many more responsibilities that took me away from being able to dedicate significant time to the Project Clear pipeline restoration project. Our two summer interns that year assisted with the second round of soil sampling for comparison to the baseline soil data and an inventory of all of the plants that naturally colonized the disturbed areas along the entirety of the pipeline path that year. For information from that botanical inventory, you can read our article that was published in the 2022 volume of Missouriensis. Our immediate reconstruction plans were to bring in a contractor that could quickly get annual cover crops down and hopefully germinate and root into the compacted soil before any fall or winter flooding events occurred. We also planned for a major seed collecting effort in 2023, so that we could sow a wide variety of early successional native species onto the pipeline path in late fall of 2023, or before the first snow of winter.

    With my role having been redirected away from the pipeline path reconstruction, I lobbied for a new staff member that could replace me and focus all their efforts on the reconstruction, research, and monitoring of this important project. Caity Sims was hired for the role of coordinator of the project in January of 2023 and hit the ground running. It has been an incredible year mentoring her throughout this process and I look forward to exploring the reconstructed prairie habitat she will be establishing and chaperoning with our amazing team of volunteers, staff, and interns over the next few years.

    Part 2: by Caity Sims 

    Before Reconstruction Began

    I was fortunate enough to witness the LREC before Project Clear as a summer intern in 2019. That summer, I assisted with collecting pre-deconstruction baseline data on trees and the algae found in Deer Creek. After my internship, I left St. Louis for Jonesboro, Arkansas to earn a master’s degree focused on botany in the Mississippi Alluvial Plain. Ready to apply my botanical and research skills in the working world, I returned to the LREC in January 2023 as the Project Clear restoration coordinator. I was shocked to finally see first-hand the impact the pipeline construction project had had on the riparian, woodland, and prairie ecosystems of LREC. What seemed in my memory like a maze of bottomland woodland was reduced to a scanty wooded edge surrounded by a sparsely vegetated brown strip of fallow land. 

    Before I joined the LREC team, a cover crop of common wheat (Triticum aestivum) had been seeded onto a majority of the pipeline path in winter 2022. Around the same time, a six-species cover crop mix, consisting of crop grasses, common pea, and field mustard (Brassica rapa) was seeded onto the southern section of the path. Cover crops mend the soil by adding nutrients, perforating the soil for better water infiltration, outcompeting weedy species, and preventing erosion of bare soil. 

    Unfortunately, the first round of cover crop mixes did not do well, and by mid-April the common wheat was barely a foot tall and had already gone to seed. The mixed species cover crop did not grow on most of the seeded area of the southern section due to flooding washing away a majority of the seeds. The path desperately needed a second cover crop at that point, so we hired contractors to seed the warm season crop, Sudan grass (Sorghum bicolor), onto the majority of the path again and a nine species cover crop mix onto the southern section. The Sudan grass did much better, growing to heights of over six feet in some areas. Although the mixed species cover crop seemed to do better, the extreme summer heat drying out the compacted soils resulted in depauperate mature plants. There were many areas directly over the pipeline that seemed unlikely to hold any vegetation at all. 

    Cover crop comparison between common wheat, taken on May 23, 2023 (A) and Sudan grass taken on August 3, 2023 (B); both photos were taken from about the same position on the path, but facing in opposite directions. Pictured in panel C are size comparisons of common wheat individuals on May 26, 2023, the two on the left were collected from the middle of the pipeline and the one on the right from the outer edge of the pipeline path. Note the numerous bare patches of soil in panels A and C. Photos: Caity Sims.

    Despite environmental conditions being heavily anthropogenically impacted, a good number of native early successional and bottomland species grew alongside the cover crops on the path. I was surrounded by many familiar disturbance-prone and riparian species, as my master’s thesis had focused on plants growing on Mississippi River islands. I recorded 310 species growing on the entire path after completing vegetation surveys in 2023. As I expected, some of the most common species were yellow foxtail grass (Setaria pumila), southern crabgrass (Digitaria ciliaris), barnyard grass (Echinochloa crusgalli and E. muricata), hairy seed crowngrass (Paspalum pubiflorum), late boneset (Eupatorium serotinum), and tall goldenrod (Solidago altissima), all of which thrive in disturbed environments. 

    As I work toward reconstructing the land to improve structure and function of the ecosystem for many native organisms, I need to quantify the results of this effort. To measure the changes in plant communities along the pipeline path over time, I established dozens of permanent vegetation monitoring plots along the path that will be monitored every summer. For each plot, I collect the presence and percent cover of each species in the plot. I am hopeful that by 2027, native prairie plants will constitute 75% of the flora and vegetation in every plot. 

    Summer interns, Karen (left) and Cicely (right), learning to identify plants from a vegetation monitoring plot on the pipeline path. Photo: Adam Rembert.

    Also found post-pipeline construction were two species new to Missouri:  Centaurium pulchellum, and Myosotis arvensis, and three new to St. Louis County records: Sesamum indicum, Cyclospermum leptophyllum, and Krigia cespitosa. All record species are not native to Missouri except K. cespitosa, which has been recorded from neighboring counties. It’s not uncommon to find new state or county records in disturbed areas. For more detailed information about those species, their identification, and potential explanations for their introduction to the LREC, check out my article in the 2023 volume of Missouriensis. 

    We have classified several different habitat types on the pipeline path including wet depressions and ephemeral ponds, rocky upland (i.e., “glade”), creek bank, woodland edge, and fallow ground. Due to a permanent pipeline access easement built and maintained by the Metropolitan St. Louis Sewer District (MSD), we cannot reconstruct the bottomland woodland that was destroyed. However, we can reconstruct a bottomland prairie on a majority of the path where the fallow ground with rocky and compacted soil are the most prominent. In the wider southern section, we will reconstruct a savanna that will include tree plantings outside of the MSD’s easement. 

    Going Forward

    Staff and volunteers collected seed throughout the 2023 growing season. We focused on collecting species with Coefficient of Conservatism (C-Value) ranks of six or below, which is consistent with the range of C-values observed in the 2022 vegetation survey of the path. The coefficient of conservatism (or C-scores) is an index ranging from 0-10, representing a species’ fidelity to intact remnant or long-restored habitats, as determined by local botanical experts. Species with higher C-scores are less tolerant of environmental degradation and increasingly restricted to high quality sites. Species with C-Values from 0-6 are likely to be found in disturbed and early successional environments, while species with C-Values from 7-10 are more likely to be found in near-pristine and remnant environments (Ladd and Thomas 2015). High C-Value species are harder to establish in restored and reconstructed habitats. 

    Summer and fall interns focused mainly on seed collection, cleaning, and organization to prepare for the 2023/2024 winter seeding. It was a monumental effort with amazing results. We collected seeds from 96 species in 2023 for a total weight of 49 kg (108 lbs) of mostly Pure Live Seed (PLS), with some chaff. In addition to collecting seeds, contractors have drilled 39 prairie species onto the pipeline path seeding a total of 16 kg (36 lbs) of PLS. We also added seeds collected in previous years that were housed in seed storage at the LREC. Including the 2023 collected seed, the PLS from contractors, and the previously collected seed, a total of 189 species with a total weight of 74 kg (164 lbs) was seeded on the pipeline path. To view the results of our seed collecting effort in 2023, please see our interns’ compiled end of season unpublished report.

    Boxes of Culver’s root (Veronicastrum virginicum) seed ready to be cleaned (A), fall intern, Cailyn, posing with seed to be added to the broadcasting mix (B), staff and volunteers mixing seed in preparation for broadcasting the pipeline path on January 5, 2024 (C), and staff and volunteers broadcasting the “glade” mix onto the most well-drained and rocky portion of the pipeline path on January 11, 2024 (D). Top photos by Adam Rembert, bottom photos by Caity Sims.

    I am hopeful that the seedings will be successful and signs of a prairie will begin to emerge this year. However, flooding and poor soil conditions are major issues on the pipeline path. I have already dealt with the aftermath of floods washing away cover crops and soil, and remaining soils lacking suitable nutrients and structure for plant growth. These are out of my control, so all I can do is accept them, keep trying, have patience, and not let frustration get the best of me. 

    In three years, I anticipate less introduced and early successional species as they fail to compete with the maturing perennial natives. I envision more pollinator observations on the former pipeline path as the prairie species begin to bloom. After the third growing year, we may be able to burn the young prairie and savanna. In 30 years, I hope to return to see restored prairie, savanna, woodland, and creek habitats functioning as home to a diversity of plants, insects, birds, reptiles, amphibians, mammals, and microbiota like the undisturbed LREC habitats do today. 

    Staff and volunteers broadcasting a spring and summer flowering seed mix onto the pipeline path on October 13, 2023. Photo: Tom Kibby.

  • Land Abandonment, Succession, and Restoration: The Wolf Run Grassland Restoration Project at the Missouri Botanical Garden’s Shaw Nature Reserve

    Land Abandonment, Succession, and Restoration: The Wolf Run Grassland Restoration Project at the Missouri Botanical Garden’s Shaw Nature Reserve

    By: Mike Saxton and Calvin Maginel

    Mike Saxton (mike.saxton@mobot.org) is the Manager of Restoration and Land Stewardship, and Calvin Maginel (cmaginel@mobot.org) is the Ecological Resource Scientist at Shaw Nature Reserve. 

    Since 1950, over 1-billon acres of agricultural land have been abandoned worldwide. In certain landscape contexts, unassisted spontaneous recovery of high levels of native biodiversity in abandoned fields is possible while in others, like the Midwest USA, fallow fields rarely develop into biologically rich habitats. To achieve the ambitious goals of the UN Decade of Ecosystem Restoration, land managers and ecologists need to better understand how to assist the regeneration and ecological restoration of these highly altered landscapes. 

    In 1925, the Missouri Botanical Garden purchased 1,300 acres of battered farm ground in Gray Summit, MO – approximately 35 miles (56 km) west of St. Louis – to escape the deleterious impact urban air pollution was having on horticultural collections in St. Louis City. The intended uses of this acreage were to: (1) propagate and grow plants, trees, and shrubs for the main Garden’s displays and (2) establish an arboretum focusing on woody plant collections. The site was officially named the Shaw Arboretum in 1933. After decades of development, many non-essential operations at the Arboretum were eliminated in 1958 and many fields were abandoned to allow spontaneous successional change. In 2000, the Shaw Arboretum was renamed Shaw Nature Reserve to reflect its contemporary mission to demonstrate, test, and inspire responsible stewardship practices through education, restoration, and protection of natural habitats and public enjoyment of the natural world. Today the Nature Reserve consists of 2,400 acres of varied habitat in various stages of restoration and revised management, including the use of prescribed fire.  

    Prior to European settlement, the natural plant communities and ecosystems of the area were fire adapted, open oak-hickory woodlands and xeric glades with gallery forests along riparian corridors. Post-settlement, woodlands were clear-cut with some woodlots left to passively regenerate while others were converted to row crop agriculture. 

    Wolf Run Grassland Restoration 

    In 2016, Nature Reserve staff set an ambitious goal to bring all 2,400 acres of the site into active management to promote native biodiversity by the year 2030. This effort will include restoring open pastures and former row crop fields, a relatively simple process. A much more challenging effort will be reclaiming 120 acres of old fields with 60+ year successional development, which is our current Wolf Run Grassland Restoration project. The 120 acre project area was initially “wasted farm ground” that had erosion gullies “where a freight train could pass without you seeing it”, according to August Beilmann, former Arboretum Director from 1941 to 1956. The entire project area was re-sculpted and smoothed by a bulldozer in 1953 and then converted to bluegrass (Poa pratensis). “Every piece of this land that looks so likely to be just right was laboriously rebuilt,” said Beilmann in a 1974 interview.

    Wolf Run Grassland Restoration project area in ca. 1945 showing open fields (light green) maintained through cattle grazing and mowing with trees occupying wet-weather streams and ditches (dark green). Photo: MBG Archives.

    Since 1958 when areas including the Wolf Run Grassland Restoration were removed from mowing and grazing, the site was encroached upon and became dominated by eastern red cedar (Juniperus virginiana), the non-native invasive shrubs Amur honeysuckle (Lonicera maackii), and border privet (Ligustrum obtusifolium), as well as slippery elm (Ulmus rubra), shingle oak (Quercus imbricaria) and ash (Fraxinus) species, the latter of which which are in severe decline due to the emerald ash borer. 

    These degraded woodlands had little native ground flora and were highly infested with non-native shrubs. Tree abundance and species composition had no historic analog. When setting ecological restoration goals for the area, staff determined that much of the site could not be managed as an open oak-hickory woodland, which would have existed at the site pre-settlement.  A new vision was needed. 

    Goals for the Wolf Run Grassland Restoration project

    • Establish a mosaic of 80 acres (~32 ha) of prairie, 15 acres (~6 ha) of savanna and 25 acres (~10 ha) of oak-hickory woodlands
    • Maximize native flora diversity and aggressively control invasive shrub species 
    • Manage with periodic, dormant-season prescribed fire 

    In 2021, Nature Reserve staff marked hundreds of native trees to retain including white, red, bur and black oaks (Quercus alba, Q. rubra, Q. macrocarpa, Q. velutina) and shagbark hickory (Carya ovata) and bitternut hickory (C. cordiformis). Drainages and wet weather streams were left with a 50 ft. (~15 m)  untreated buffer zone while a perennial creek flowing through the unit retained a 150 ft. (~46 m) untouched buffer. A logger removed unmarked trees from the area, with the commercial value of the timber offsetting the cost of the removal. Following US Fish and Wildlife Service recovery management guidelines for the Indiana bat (Myotis sodalis) — a federally endangered species — trees were only removed from November 1st to April 1st.

    Wolf Run Grassland Restoration project area pre-thinning (2021), approximately 60 years after land abandonment. Note the dark green areas are dominated by eastern red cedar (Juniperus virginiana), a native tree that rapidly colonizes abandoned or disturbed lands in the Midwest. Historically, this fire-sensitive tree species primarily occurred on rocky outcrops and bluffs that served as refugia from periodic fires that were common in the pre-European settlement landscape. Photo: ESRI
    Wolf Run Grassland Restoration project area post-thinning (2023). Photo: ESRI
    Forestry contractor equipment was used to remove most woody biomass greater than 4.5 in. (~11 cm) in diameter and left behind mostly small-diameter slash. A bulldozer was used to collect the debris into 600 piles that were subsequently burned. Photo: Mike Saxton

    The Restoration team has spent the last 9 months focusing on the removal of stumps for the project area. Stumps can be a substantial hazard for vehicles, equipment and staff safety. To seed native species and effectively manage the area for invasive species in perpetuity, the stumps must be ground down or cut flush to the ground.

    Skid loader mounted stump grinder removing stumps. Photo: M. Saxton

    Concurrent to this effort has been the site preparation step of chemically treating all of the invasive species and the disturbance driven annual vegetation that emerged post-land clearing [primarily fireweed (Erechtites hieraciifolius), mare’s tail (Erigeron canadensis), ragweed (Ambrosia artemisiifolia) and fox tail (Setaria pumila)]. This step is necessary because diverse, healthy native plant communities have not existed in these areas in more than 100 years. Consequently, there is no native seedbank to support the unassisted spontaneous recovery of native perennial herbaceous species in these highly degraded acres. 

    In areas where stumps have not been cleared, traditional equipment (tractor boom sprayers and UTV mounted spray rigs) for applying herbicide are ineffective. The Nature Reserve hired a contractor that specializes in drone-assisted aerial herbicide applications. The drone flies 12 ft. (~37 m) above vegetation and can self-navigate around trees and other hazards. The unit carries a total of 8 gallons (~30 L) and sprays approximately 3 gallons of herbicide per acre. The effective width of each pass is 25 ft. (~8 m). A single battery powers the drone, with a flight time of 7.5 minutes and a re-charge time of 6 minutes. When the herbicide tank runs out, the drone re-deploys to the fill up location, is refilled by the contractor, and then returns to where it left off. 

    Aerial drone sprayer used to eliminate undesirable vegetation. Photo: M. Saxton

    The last step after the undesirable trees have been removed, biomass/debris has been burned, the stumps have been ground and invasive species have been controlled, is the final ground preparation. Currently, in 2023, we are again smoothing out erosion gullies and clearing away the last remnants of woody debris with a bulldozer. This effort will ensure effective seed-to-soil contact when we sow native seed in January 2024 and will enhance our ability to successfully search for invasive species in the coming years by eliminating deep ruts and rills.  

    Above: Bulldozer in 1953 eliminating erosion rills in Wolf Run Grassland Restoration project area. Below: Bulldozer completing site preparation for native seed addition (2023).  Top Photo: St. Louis Globe Democrat, Bottom Photo: M. Saxton

    Native Seeding and Experimentation to promote Biodiversity Recovery 

    During the growing season of 2023, the Restoration team at the Nature Reserve has been feverishly collecting seed for this 2024 seeding effort. More than 1,100 lbs. (~500 kg) of bulk, milled seed from ~200 locally collected native tallgrass prairie and open oak-hickory woodland species will be used in the restoration planting. Additionally, these acres are enrolled in the Environmental Quality Incentives Program, EQIP – part of the Natural Resources Conservation Service, and we must purchase viability-tested seed to meet the minimum required specifications of the contract. The hand-collected seed together with the pure live seed (PLS) – percentage of viable seed in a seed lot – purchased from commercial vendors will provide us with ample species and volume of seed to effectively cover the 40 acres (~16 ha) to be planted this winter. 

    Concurrent with the preparation effort, we initiated a research study, which will help inform our work and the broader research community on plant recruitment amongst scraped soils that have been inoculated with mycorrhizal fungi and those that have not. This study includes paired species from the same genus that have different CC-values, short for coefficients of conservatism, which represents a species’ tolerance of environmental degradation, or its fidelity to intact remnant or long-restored habitats, as determined by local botanical experts. Ecologists generally expect species that are dependent on stable intact communities (higher CC-values) to be more reliant on mycorrhizae connections to establish and flourish. Species with high CC-values tend to establish poorly in restoration sites, which is one of the reasons to pursue this study. Some examples from the ten herbaceous pairs of native species include sedges (Carex bushii [CC = 4] and Carex bicknellii [CC = 10]), grasses (Sporobolus compositus [CC = 3] and Bouteloua curtipendula [CC = 7]), and forbs (Oligoneuron rigidum [CC = 5] and Oligoneuron album [CC = 9]).

    We added all 20 species at the same rate of pure live seed to provide each species an equal opportunity to establish. Initial analyses after one growing season indicate that low CC-value species germinated more successfully, producing more seedlings and greater percent cover than the high CC-value species, regardless of inoculation. We expect the addition of mycorrhizal fungi to have the greatest effects on species during the first couple of years after germination. If the mycorrhizae associate with the roots of the high-CC species more than the low-CC species, this may help them grow faster or be more resistant to future stress. Future monitoring will show us if there are long-term effects of inoculation.

    To check for updates on restoration activities and results from experimental studies, please visit our webpage.

    Barrels of hand-collected seed connected to a seed dryer, which pumps air through tubes into the barrels to eliminate mold & moisture. Photo: M. Saxton
  • Seed additions facilitate herb-layer restoration in a temperate oak woodland

    Seed additions facilitate herb-layer restoration in a temperate oak woodland

    By Andrew Kaul, a Restoration Ecology Post-doc in the Center for Conservation and Sustainable Development at the Missouri Botanical Garden. His new, open-access paper in Ecological Solutions and Evidence is available here.

    Throughout most of the eastern United States, oak woodlands were once a widespread and dominant ecosystem. These woodlands experienced periodic fires, which prevented woody trees and shrubs from growing so densely that the overstory canopy became closed. The partly open canopy allowed light to reach the ground, supporting a diverse community of herbaceous plants including wildflowers, grasses, and sedges. However, over the past two centuries, human induced changes including fire suppression, invasion by non-native shrubs, and other factors have caused most woodlands to become overgrown, and lose much of the diversity of plant species in the herbaceous ground layer.

    Research on how to manage and restore these woodlands has shown that cutting down some trees to thin out the woodland, as well as removing non-native shrubs, and reintroducing periodic fires, are all strategies that help improve the quality of these habitats. However, even after employing all of these management strategies, many desirable plant species may still not return on their own. Ecosystem restoration often involves re-introducing plant species as a seed mix distributed over a cleared area, and this method can be very effective for grassland and savanna habitats that contain few trees. Restoring wildflowers and grasses in wooded areas with the addition of a seed mix could drastically improve the diversity and quality of the herbaceous community, but this approach has not been experimentally studied, and little is known about how to select the right species for re-introduction this way.

    To address these knowledge gaps, scientists and land managers at the Missouri Botanical Garden started an experiment at the Shaw Nature Reserve in 2016, where highly diverse seed mixes of native plants were added to a degraded woodland undergoing active restoration. Throughout late 2016 and much of 2017, crews of managers and volunteer land stewards worked to thin the canopy by removing less desirable tree species, especially the aggressively fast growing native conifer, Eastern Redcedar (Juniperus virginiana). After thinning the canopy, crews used a combination of mechanical removal and herbicides to control the dense non-native shrubs. Fire was reintroduced through controlled burns starting in late 2017.

    Large Eastern Redcedars dominate a degraded woodland at Shaw Nature Reserve in Gray Summit MO. The understory is overgrown with non-native woody species including bush honeysuckle (Lonicera maackii), privet (Ligustrum obtusifolium), and wintercreeper (Euonymus fortunei). The lack of recent fire has led to a build up in leaf litter, and native herbaceous species are mostly absent. Photo: CCSD & SNR staff.

    After the woodland was thinned, in January of 2018, we added seed mixes to three different management units, along a gradient of lower/wetter to higher/drier parts of this landscape. The seed mixes contained between 79 and 93 species, and all of the seed was collected from plants growing at the nature reserve. In order to track how these seed additions influenced the establishment of the herbaceous community, we collected data on the composition of the plant communities in areas that received seed and areas that did not. We sampled the plant community in 2017 before the seed additions and in the following two years, 2018-2019.

    Top: Woodland under management at Shaw Nature Reserve in March of 2017, after selective thinning of trees to open up the canopy and removal of most woody shrubs. Leaves of some persistent bush honeysuckle can be seen. Bottom: Same woodland in June of 2019 after the addition of a seed mix in 2018. Photo: CCSD & SNR staff.

    In both the seeded and non-seeded woodlands, the effect of management actions was very clear and positive, since both the number and cover of herbaceous species dramatically increased from the sample in 2017 to later sample dates. This is consistent with previous research showing that thinning the canopy, removing shrubs, and reintroducing fire promote restoration of herbaceous plants.

    We also found substantial benefits from reintroducing species with seed mixes. The areas that received seed had about 10 more plant species present within a one square meter area, than the areas that did not get seed. We were also interested in the quality of the kinds of species that were establishing based on coefficients of conservatism, which denote how sensitive species are to human disturbances. We found that areas with seed added, contained fewer plants that were weedy ruderals, and more that were conservative and generally found only in high-quality intact habitat. Interestingly, areas that got seed additions were also more dominated by grasses and the areas that did not receive seed, although less rich in species, tended to have more abundant wildflowers (forbs). Specifically, common grasses that were sown at high rates tended to dominate areas that received seed additions, including river oats (Chasmanthium latifolium), hairy woodland brome (Bromus pubescens), and bottlebrush grass (Elymus hystrix). The restored areas that did not get a seed addition were dominated by ruderal (low conservatism) forbs such as jumpseed (Persicaria virginiana), white snakeroot (Ageratina altissima), and common yellow woodsorrel (Oxalis stricta).

    A representative area that had seed added (top) and an area that did not (bottom) in June of 2019. In the non-seeded area, a large patch of the weedy native composite, giant ragweed (Ambrosia trifida), can be seen in the foreground. Photo: CCSD & SNR staff.

    Our final goal was to examine the recruitment success of the over 100 different plant species that we added as seeds, to see if there were patterns in which kinds of species tended to establish best. Perhaps surprisingly, over half of the species we added were never detected in vegetation samples. These species might not have been sown into favorable conditions, or potentially, the quality of the seed might have been poor, since it came from wild populations and the seeds might not have been viable or mature. Still, some seeds may be dormant for many years, and more added species may break dormancy and recruit later. Among the species that did establish from added seeds, we found that recruitment was much higher for species that were sown at higher rates, suggesting that some species might have benefitted from a higher seeding rate. Both grasses and forbs tended to recruit well when sown at high rates, but the 25 sedge species we added had little or no recruitment success.

    Based on our results, future research on woodland restoration should address why sedges are difficult to restore and methods to remedy this deficit. Additionally, it will be interesting to track the development of these herbaceous communities into the future, to examine how sown and unsown areas resist re-invasion by shrubs while they are continually managed with periodic burns. Our seed mixes dramatically improved the diversity and floristic quality of the herb layer in this woodland, however many species did not recruit, and key functional groups including sedges and forbs were underrepresented in their abundance. Future research should investigate what ratios of functional groups in seed mixes produce the best restoration outcomes, since conventions established for grassland restoration may not be the best approaches for restoring herbaceous species under a tree canopy. If you are interested in learning about this project in greater depth, the paper is freely accessible here. If you have any questions, feel free to contact Andrew (akaul@mobot.org).

  • How does prescribed fire affect a threatened terrestrial orchid?

    How does prescribed fire affect a threatened terrestrial orchid?

    By Leighton Reid and Ryan Klopf

    Leighton Reid is an assistant professor of ecological restoration in the School of Plant and Environmental Sciences at Virginia Tech. Ryan Klopf is the Mountain Region supervisor and natural areas science coordinator for the Virginia Natural Heritage Program. They describe a new research project that aims to understand how an important restoration tool impacts the population dynamics of federally threatened small whorled pogonia orchids. This project has an open PhD position available to start in January 2023; details can be found at the end of this post.

    Deep in the heart of Virginia’s Shenandoah Valley, nestled against the western edge of the Blue Ridge Mountains, two clusters of small, green orchids grow in the dappled sunlight of a woodland understory. The orchids are small whorled pogonias (Isotria medeoloides) – a rare species that is considered threatened by the United States government because its population is declining so quickly that it could become endangered in the foreseeable future. We have monitored these populations for the past two summers, keeping tabs on every individual, to learn how this species is affected by one of the most important restoration tools in North America – prescribed fire.

    A small whorled pogonia orchid with two flowers at Mount Joy Pond Natural Area Preserve. Photo: Lindsay Caplan.

    Small whorled pogonia

    As their name implies, small whorled pogonias are small (≤25 cm) and whorled (their leaves radiate outward from the stem). This species is a member of the Pogonieae, an orchid tribe that includes species in Asia and eastern North America. Its closest relative is the large whorled pogonia (I. verticillata) which sometimes grows alongside small whorled pogonia, but is distinguished by its purplish stem (small whorled pogonia has a whitish green, glaucous stem).

    Small whorled pogonia (left) with a whitish, glaucous stem compared to large whorled pogonia (right) with a purplish stem base. Photos: Sara Klopf (left) & JL Reid (right).

    Small whorled pogonias emerge from the leaf litter in late spring and in some years produce one or two solitary greenish yellow flowers, particularly when plants are exposed to more sunlight. Their flowers do not require any help with pollination; they produce the same amount of seed whether they are cross-pollinated or pollinate themselves.

    The seeds themselves are tiny – like vanilla seeds, which are in the same orchid sub-family (Vanilloideae). The parent plant (which is usually both a mother and a father) provides almost no resources at all to its offspring. Each seed’s fate is closely linked to whether or not it finds a mycorrhizal fungus in the Russulaceae family to help it acquire the resources that it needs to survive and grow. In a typical relationship between plants and mycorrhizal fungus, the fungus scours the soil for nutrients like nitrogen and phosphorus and provides them to the plant in return for energy in the form of carbohydrates, which the plant produces through photosynthesis.

    A developing fruit on a small whorled pogonia orchid at Mount Joy Pond Natural Area Preserve in June 2022. Photo: Andres Cunningham.

    Fire and water at Mount Joy Pond

    The story of this research project begins about 80 years ago, in a DuPont chemical plant in Waynesboro, Virginia. In the 1930s-1950s, the DuPont facility used mercury to produce rayon – a synthetic, silk-like fiber. Some of the mercury escaped from the plant and leaked into the South River – a tributary of the Shenandoah River. Mercury is a neurotoxin, and in the environment it can accumulate to dangerous levels in animals that are higher on the food chain, like fish. For many years, people living along the South River have been warned about the poor water quality and advised not to eat the fish.

    In 2016, DuPont reached a $50 million USD settlement with the United States Department of Justice, the Department of the Interior, and the Commonwealth of Virginia to restore habitat for wildlife in the South River watershed, enhance water quality, and improve recreational areas. This settlement represented one of the largest environmental damage settlements in United States history.

    Some of the DuPont settlement money was allocated to the Virginia Natural Heritage Program, a division of the Virginia Department of Conservation and Recreation that uses science-based conservation to protect Virginia’s plants and animals. Specifically, funds were provided to allow the Virginia Natural Heritage Program to protect and restore woodland habitat surrounding a unique wetland at the Mount Joy Pond Natural Area Preserve in Augusta County.

    Briefly, Mount Joy Pond is a Shenandoah Valley Sinkhole community; that is, it is a groundwater-controlled wetland that floods intermittently when water percolates up through underlying carbonate rocks and then floods over the top of a clay lens perched in a layer of soil derived from the overlying sedimentary rocks. When this happens, the water becomes trapped, like water in a saucer. This unique situation creates wetland habitats which have persisted for the past 15,000 years and contain numerous rare and disjunct species, including the globally rare Virginia sneezeweed (Helenium virginicum). There are several dozen Shenandoah Sinkhole ponds, but only a handful of them are protected.

    Virginia sneezeweed, an endemic species in the southeastern United States with disjunct populations in Virginia’s Shenandoah Valley sinkhole ponds and in a similar wetland situation in the Ozark Mountains of southern Missouri. Photo: JL Reid.

    In the past, Mount Joy Pond filled with water every few years, but in recent decades it has filled up less and less often. To restore the wetland’s hydrology, the Virginia Natural Heritage Program set out to thin the surrounding forest and re-introduce fire to prevent fire intolerant trees, such as red maple, from regenerating. This may sound counterintuitive to some, but the logic is this:

    • Each tree is like a drinking straw sucking water out of the ground and releasing it into the air via transpiration. If there are a lot of trees, the groundwater may stay too low to fill up the pond.
    • Fire used to be much more common in the Shenandoah Valley. Prior to European colonization, Indigenous People burned the landscape and maintained much of it as savanna and open woodland – ecosystem types that have fewer trees than present day forests.
    • By removing some trees and reintroducing a regular fire cycle, land managers at Mount Joy Pond Natural Area Preserve can restore an open woodland and raise the groundwater level, causing the pond to flood more often.

    The Virginia Natural Heritage Program began to implement this restoration project in 2017, and the first thinning operations and burn were a success. In the years since, the groundwater level appears to have gone up, suggesting that the hydrological restoration plan is working.

    Small whorled pogonia discovery

    In the first spring after that first fire, a botanist was surveying the burned woods near the pond and found something unexpected – a small population of small whorled pogonia orchids, which had not been seen previously in the preserve despite extensive surveying by the Virginia Natural Heritage Program’s inventory team. Were the orchids there all along and nobody noticed them? Maybe. Or maybe the fire helped the orchid population emerge after years of suppression in the dense leaf litter in the shady understory.

    Our team uses a grid sweep survey to search for new small whorled pogonia individuals in June 2022. Photo: JL Reid.

    The story became more complicated later that summer when a more intensive search turned up a second population of small whorled pogonia orchids on the preserve – this one in an area that had not been burned.

    The immediate consequence of discovering the new pogonia populations was that the United States Fish and Wildlife Service expressed concerns that future fire management might be detrimental to this threatened species. Nobody had studied how small whorled pogonia responds to fire, and there was a chance that burning could damage the population, even if it was good for the nearby pond’s hydrology. Of course, there was also a chance that not burning could damage the population. With fire, inaction is still an action.

    To help settle the issue, the United States Fish and Wildlife Service agreed to sponsor a PhD student to study the small whorled pogonias at Mount Joy Pond and figure out how their population dynamics are impacted by prescribed fire.

    Lindsay Caplan and Jimmy Francis monitor a population of small whorled pogonias at Mount Joy Pond Natural Area Preserve in June 2022. Photo: JL Reid.

    Effects of prescribed fire on small whorled pogonia orchids

    The main goal of our ongoing research is to understand how prescribed fire impacts small whorled pogonias. To do this, we will map and monitor the two subpopulations and the woodland plant communities in which they live. Over the next two years, one of the two subpopulations will be burned during a winter or early spring prescribed fire, and we will continue monitoring to document changes in plant vigor, reproduction, and population size. We will pay special attention to the light environment, which seems to be important for small whorled pogonia reproduction, and to the diversity and composition of soil fungi, which are important for small whorled pogonia emergence. We will also conduct annual surveys of the entire reserve to search for additional populations.

    Ethan Dunn uses a canopy imager to measure canopy cover, photosynthetically active radiation, and leaf area index over a tiny small whorled pogonia individual in July 2021. Photo: JL Reid.

    This project is just beginning. To date, we have monitored the two populations for two growing seasons (2021, 2022). There is still much work to be done. One of the next steps will be to produce an accurate map of each plant’s location, which will require centimeter-level precision using high-quality GPS equipment under a forest canopy.

    We are currently seeking a PhD student to lead this research project starting in January 2023. A description of this opportunity is below. This project is an excellent opportunity for a student to develop expertise in ecological restoration and threatened species conservation from both a scientific perspective and an on-the-ground land management perspective.

    Ultimately, the results of from this study will inform management of natural areas and small whorled pogonia restoration projects throughout the species’ wide range – from Ontario to Georgia.

  • Identifying regional and restoration species pools for the Ozark Highlands

    Identifying regional and restoration species pools for the Ozark Highlands

    Andrew Kaul is a Restoration Ecology Post-doc in the Center for Conservation and Sustainable Development working with Matthew Albrecht at the Missouri Botanical Garden, and Michael Barash is a junior Biology major at Washington University in St. Louis. Here they describe Michael’s undergraduate research on commercial native seed availability for woodland restoration.

    One of the largest barriers to restoration of degraded terrestrial habitats is availability of seed for use in reintroduction of desirable native plant species. Over the past few decades, the industry of native plant seed production has grown rapidly, but most native species in the US (and globally) are still not commercially available, and there can be strong biases in which types of species tend to be selected by seed producers.

    In ecological parlance, a “species pool” represents all of the species which can colonize and occupy a certain region. Not all of the species in a regional species pool are available commercially, which is how many restoration practitioners acquire seeds, so the subset of species pool that contains only the species that are commercially available in a given region is sometimes called the “restoration species pool”.

    For most ecosystems around the world, it is not well documented what proportion of the species pool is commercially available, and why these species have been selected for commercial trade. The few studies that have been conducted on commercial seed availability for restoration have found consistently that herbaceous (rather than woody) and rare species (rather than common ones) are less likely to be available, and there are strong taxonomic biases in which plant families are more represented. In the US, these studies have focused on open-canopy habitats with few trees, such as grasslands, rather than on more closed-canopy systems like woodlands and forests.

    An open rocky glade (left), and a glade to woodland transition (middle), a woodland understory (right; Shaw Nature Reserve, Gray summit MO).

    To address this information gap, we assessed the capacity of the native seed industry to support ecological restoration across terrestrial habitats in the Ozark region of the midcontinent USA. The use of seed additions to accelerate recovery of plant diversity in Ozark woodlands and forests is not well studied, and little information is available on how to best select species for reintroduction from seed. The specific goals of this project were to:

    1) Identify the species pool of native herbaceous (non-woody) vascular plants appropriate for restoration of glades, woodlands, and forests in the Ozark Highlands;

    2) Define the restoration species pool by identifying which of these species are commercially available;

    3) Quantify biases in this restoration species pool with respect to growth form, rarity, habitat affinity, and a few important functional traits;

    4) Identify candidate species which are not available from seed vendors, but should be a priority for seed production due to their importance for Ozark habitats.

    The spatial scope of this study is the Ozark Highlands, level III ecoregion 39, which covers all of Southern Missouri, as well as parts of Northern Arkansas, and NE Oklahoma.

    We began this project by developing a targeted species list of 1,178 herbaceous species native to upland habitats in the Ozark region, based on existing datasets from the Ecological Checklist of the Missouri Flora, the Flora of Missouri, and the Biota of North America Program (BONAP).

    We predicted there would be selection, implicit or explicitly, by seed producers for species based on their growth form, conservatism score wetness rating, rarity, and functional traits. Each species’ physiognomy (growth form), conservatism score (that is, sensitivity to disturbance), and wetness ratings (a type of habitat affinity) were included in the Missouri Checklist. For each species in our pool, we compiled data on two measures of rarity including a qualitative measure –  the official Missouri State conservation ranking, and a quantitative measure – the range size of the species in the US, as measured by the number counties in the nation where there have been recorded occurrences in the BONAP database. We compiled trait data on height of adult plants, and bloom timing and duration from species descriptions in the Flora of Missouri. For each grass species, we compiled data on photosynthetic pathway from published literature.

    We made predictions that species with certain growth strategies, traits, range sizes, and habitat preferences would be under- or over-represented in the pool of species produced by seed vendors. We predicted that compared to other growth forms, perennial forbs would be over-represented in the restoration species pool because the aesthetic value of restoration projects is often a high priority, and perennial forbs with their big flowers, are “showier” and will return year after year. Similarly, taller species, and those with a longer bloom period may be selected preferentially because their blooms are more noticeable. We expected that species which have a smaller range or are not abundant in sites where they do occur are less likely to be in demand by restoration practitioners, so are less likely to be commercially available. Based on this pattern we expected species with a lower conservatism score, larger range size, and higher conservation rank (less concern for conservation) to be more commonly produced by seed vendors.

    We predicted that species with a larger range such as pale purple coneflower (Echinacea pallida; map on the left), would be more likely to be available from at least one producer than species with a smaller range, such as the related yellow coneflower (Echinacea paradoxa; right). Maps are from BONAP, and light green areas denote counties where the species has been reported.

    The cottage seed industry for prairie plants has grown especially rapidly in recent years, so we expected that species which are generally found in more open habitats like glades, prairies, and savannas, would more likely to have been selected by at least one producer than the species which occur mostly in shady habitats like woodlands and forests. Similarly, since open habitats tend to have drier soils than shaded ones, we predicted there may be a bias toward species with a higher (drier) wetness rating. Many grass species that grow in open habitats have evolved a more efficient way of conducting photosynthesis under hot sunny conditions. There are fewer of these “warm-season” grasses than “cool-season” ones, but we predict that proportionally more warm-season grasses will be commercially available, because they are common in the prairie seed market.

    Inflorescences of big bluestem (Andropogon gerardii), and Indian grass (Sorghastrum nutans) can be seen at this glade to woodland transition at Victoria Glades Conservation Area in Hillsboro, MO. These warm-season grasses are dominant in many prairies and common in glades, but generally do not occur under the canopy of wooded areas.

    In order to test these predictions, we needed to compile information on which species in our pool are available from seed vendors. We identified ten seed vendors that are likely potential sources of seed materials for species native to the Ozark Highlands. These include five seed vendors within Missouri, four large regional seed vendors located in Iowa, Minnesota, and Kentucky, and one very large seed vendor that produces seed for regions all across all the US. We were able to get information on which species each vendor produces from their website, or if they did not have a website, then through personal communication. Many vendors sell a combination of seeds and potted plants, with most species only being available in one form or the other. For this study, we were only interested in seed products because restoration of herbaceous communities through seed additions is the most common and affordable approach.

    Based on preliminary analyses, we found that 501 (43%) species were commercially available from at least one vendor. We found the strongest trends supporting the prediction that species differ in their likelihood of commercial availability based on physiognomy or “growth form”. Perennial species were twice as likely to be available as shorter-lived annual or biennial species, and as predicted, forbs were better represented in seed vendor catalogues than grasses or sedges.

    We predicted that more common species would be better represented in the restoration species pool and our results somewhat support this prediction. Conservatism scores are assigned to species by expert botanists in each region, so they reflect how rare and how disturbance tolerant species are within local areas. In the US, these scores are often assigned at the state level. In order to avoid over-interpreting these designations, we binned scores into three groups including ruderal (0-3), matrix (4-6), and conservative (7-10) for use in our analysis. We found that “matrix” species with middling conservatism scores were more likely to be available than conservative or ruderal species. This may be because ruderal species can be somewhat weedy and may be expected to recruit into restored areas as volunteers. And on the other hand, highly conservative species may be difficult to grow for seed production, or have a small range, and thus limited restoration potential or demand. The state of Missouri has designations for the conservation concern of all native species. We found that species classified as “vulnerable” (S3), “imperiled” (S2), or “critically imperiled” (S1) were less likely to be available from seed vendors, as species classified as “secure” (S5) or “apparently secure” (S4). And finally, as predicted, we found that species with larger ranges are more likely to be commercially available.

    We expected species which mostly occur in open habitats with little tree cover to be more likely to be commercially available. We classified each species as belonging to one of three habitat affinity groups, being an open habitat specialist, closed habit specialist, or a generalist. We found no bias in species availability based on habitat affinity or based on the wetness rating for Missouri. Based on the prediction that the prairie-focused seed market would promote availability of warm-season grasses, we thought they would have greater proportional representation in the seed market, but we also did not find evidence for that prediction. Warm and cool season grasses were equally likely to be available, with about a third of all species belonging to each group being available.

    While we did not find that species with affinity to open habitats were more likely available from at least one producer than species from closed habitats, we did notice that the species which were sold by the most producers tended to be “prairie species” like butterfly milkweed (Asclepias tuberosa; left), which was available from 9 of the 10 vendors we surveyed, or stiff goldenerod (Solidago rigida; right), which was available from 8 vendors.

    Traits of species may also contribute to seed vendors’ interest in propagating them. We found evidence that within perennial wildflowers (forbs), species with a taller maximum height are more likely to be available. We also predicted that species with a longer potential bloom period would be better represented in the seed market, but surprisingly our data shows a negative relationship, where species that can bloom for many months are less represented in the restoration species pool. This pattern may be driven by differences between functional groups or plant families and deserves further investigation.

    The final goal of this project was to identify candidate species to recommend to seed producers as valuable for restoration potential. We identified such species based on the highly detailed descriptions provided in a keystone reference for this region, Paul Nelson’s The Terrestrial Natural Communities of Missouri (2005). This book describes the geologic, climatic, and natural features of natural community types in Missouri. We only considered habitats within the broad designations of forests, woodlands, savannas, prairies, and glades, and we narrowed our focus to only habitat types that occur within the Ozark Ecoregion. For each of these 37 Ozark habitats, this reference provides lists of plant species that are “dominant”, “characteristic”, or “restricted” to that habitat. We propose that a good starting place in assessing the capacity of the native seed industry to support ecological restoration across terrestrial habitats in the Ozark region is to examine whether all of the “dominant” plant species in habitats within the Ozarks are available from vendors. Of the 120 species identified by Nelson as “dominant” in Ozark habitats, 80 of them (66%) were commercially available. This is encouraging, since it is higher than the overall availability rate of 43%, however there are still 40 species which would be difficult for restoration practitioners to acquire without hand collecting from wild populations. This highlights how biases in the restoration species pool could potentially make assembling a high-quality seed mix more difficult, if the species for sale represent those which are easiest to cultivate, rather than being the ones which have the most biological significance to restoration.

    Birdfoot violet (Viola pedata) is classified as a dominant species for dry sandstone woodlands and is common on dolomite glades. Fortunately, we found it is commercially available from two vendors. Two other violets, wood violet (Viola palmata), and arrowleaf violet (Viola sagittata) are dominant in other Ozark habitats, but are not available from any of the vendors we surveyed.

    Here, we are only scratching the surface in terms of identifying ways in which the seed production industry may inadvertently be biasing the restoration species pool and consequently the diversity and composition of restored plant communities. In the future we recommend continued collaboration between seed producers, restoration practitioners, and conservation scientists, to identify the limitations of available seed stocks and better align supply and demand for native seeds. Most seed vendors do not label products at taxonomic designations below the species level. However, conservation goals are sometimes identified for subspecies or varieties. The extent to which these taxa are commercially available is difficult to assess. Additionally, many restoration projects call for seed from a local provenance, but obtaining information on ecotypes of native seed lots from vendors can be difficult. While nearly 40% of our species pool for restoration projects in the Ozark Highlands are commercially available, the proportion of those species that are available from an Ozark ecotype is likely much lower.

    We are currently preparing this project for publication. If you are interested in learning more, or have any questions, feel free to email Andrew (akaul@mobot.org).

  • Torrey’s mountain mint – an oddball species?

    Torrey’s mountain mint – an oddball species?

    In a state whose flora has been studied for hundreds of years, grassland conservation and restoration are still hindered by a need for better understanding of basic plant ecology and systematics. Leighton Reid, Jordan Coscia, Jared Gorrell, and Bert Harris contributed to this post.

    All ecologists deal with puzzling groups of plants. In eastern North America, sedges (genus Carex) and panic grasses (genus Dichanthelium) are notorious for having many species with similar characteristics. In Central America, tree seedlings in the avocado family (Lauraceae) can be tricky to separate.

    Sometimes we also encounter oddballs – plant species that it’s hard to see where they fit into the contemporary landscape.

    Torrey’s mountain mint (Pycnanthemum torreyi) is a bit of both – an oddball species whose relationships to other mountain mints is not yet worked out.

    Late-season aspect of Torrey’s mountain mint. Photo credit: B. Harris.

    Like others in its genus, Torrey’s mountain mint is an aromatic herb that grows (mostly) in more-or-less open areas. Its crushed leaves have a delightful minty smell. In summer, it produces clusters of small, white flowers that are visited by a variety of pollinators.

    Unlike some other mountain mints, Torrey’s is also rare. NatureServe ranks it as a G2, meaning that it is imperiled throughout its range – which extends sporadically from New Hampshire to Kansas.

    Virginia has more Torrey’s mountain mint populations than the other states. The Flora of Virginia describes its habit as “dry, rocky, or sandy woodlands and clearings.” In some places, like the Piedmont, it occurs mainly on basic soils, whereas in other places, like the Coastal Plain, it lives in sandy, acidic soils. In the mountains it has been found also in limestone seepages.

    An oddball species

    While restoring natural areas in Chicagoland in the 1980s, Stephen Packard described some of the plants he saw as “oddball species”. Species like purple milkweed (Aslcepias purparescens) and cream gentian (Gentiana alba) grew neither in closed forest nor in open prairie, so where did they belong? These species preferred intermediate levels of light, such as would be found beneath a spreading burr oak. Packard’s observation that these species preferred savanna conditions sparked his realization that savanna had once been a frequent component of the Chicago landscape.

    Matthew Albrecht has considered a similar possibility in Tennessee for Pyne’s ground plum (Astragalus bibullatus). This species grows on so-called cedar glades around Nashville, but it does not grow right in the middle. It prefers the edges where there is intermediate light. This suggests that these cedar glades may once have had softer edges that tapered slowly from exposed, rocky glade into open woodland. With modern fire suppression, these edges have become hard; many glades are now bordered by dense forests of eastern red cedar.

    Could our own Pycnanthemum torreyi fall into the same category? An “oddball species” with a preferred niche that is neither full sun nor full shade? In our fieldwork on the northern Virginia Piedmont, we encountered several populations of Torrey’s mountain mint, all of which were growing in edgy sites, like powerline right of ways, or the edge of an old apple orchard.

    A small population of Torrey’s mountain mint grows along one edge of this field near the forest edge, not in the open center of the field. Is this typical of this species’ preferred light environment?

    Last summer, one of us (Leighton) tested P. torreyi’s habitat affinities inadvertently and with a very small sample size. He planted three seedlings in his small, Blacksburg, Virginia yard – one in an exposed spot on the south side of the house and two in a partially-shaded spot on the north side of the house. The plant in the more open, southerly spot grew okay, but it was somewhat stunted – like a spider plant that has been left out in the sun. Its stem and leaves grew short and tough. In contrast, the two plants on the north side of the house grew full and spread out, both flowering and fruiting in their first season. They also remained green late into the season, even after nearby P. tenuifolium and P. incanum had senesced. If this was a species desirous of full sun, shouldn’t it be doing better in the exposed position in the back by the parking lot?

    Two Torrey’s mountain mints growing well and flowering in partial shade on the north side of JL Reid’s home in Blacksburg, Virginia.

    Clearly Leighton’s sample is way too small to draw any conclusions, but it does make us wonder if Torrey’s mountain mint prefers and intermediate level of light, such as would be found in a savanna or an open woodland. These disturbance-dependent habitats were once widespread but are excluded today in much of the eastern United States. Maybe Torrey’s mountain mint is an oddball species whose habitat preferences will eventually lead us to design new restoration targets in Virginia, but we’ll have to study its ecology in a bit more detail first.

    A “Problematic Species”

    The Flora of Virginia also highlights that Torrey’s mountain mint is a “problematic species”, whose interpretation is “confounded by its similarity to Pycnanthemum verticillatum and its hybridization with other species.”

    During our fieldwork in 2020, we were able to positively identify all of the individuals that we encountered, differentiating P. torreyi from P. verticillatum by characteristics of their flowers and leaves. Still, the possibility that Torrey’s mountain mint is not a well-differentiated species is troubling. Several landowners in our area are conserving open habitat in part because this rare species occurs there, so it would be nice to know if it is a good species.

    I asked Gary Fleming, a Vegetation Ecologist for the Virginia Natural Heritage Program, for his thoughts. “Well, the entire genus Pycnanthemum is a bit problematic!” Gary wrote me in an email. He explained that the problem is that nobody has studied this genus using molecular phylogenetics, that is, using DNA to reconstruct the evolutionary relationships between species. As a result, our understanding of how species in this genus relate to each other is pretty fuzzy.

    “Personally, I think P. torreyi is a good species,” Gary continued, “Over the years, I’ve observed it in numerous places state-wide and it appears to be morphologically very consistent.”

    In a state whose flora has been studied for hundreds of years, apparently the Pycnanthumum nut has not yet been cracked. Hopefully some enterprising botanist will take this up soon (and maybe Packera while they’re at it).

    Torrey’s mountain mint flowers. Photo credit: JL Reid.

    Note: Part of this blog post represents a USDA NIFA Hatch project.