Matthew Albrecht is a Scientist in the Center for Conservation and Sustainable Development at Missouri Botanical Garden. Here he describes a recent fieldtrip to the Ouchita Mountains to study outlying populations of the federally threatened Missouri bladderpod, Physaria filiformis.
Situated between Rocky Mountains to the west and the Appalachians to the east lies the often overlooked Ouachita (pronounced WAH-shi-tah) Mountains of central and western Arkansas and adjacent Oklahoma. Unlike the Rocky and Appalachian Mountains, the Ouachitas are a relatively small mountain chain that trends primarily east-west. Despite occupying a relatively small area, the Ouachitas harbor a large proportion of the region’s plant diversity and represent a remarkable center for endemism including many rare plants species with extremely narrow distributions.
On a recent spring afternoon, Christy Edwards and I had the opportunity to visit the relatively rare and poorly studied shale outcroppings of the Ouachitas with botanists Brent Baker and Diana Soteropoulos of the Arkansas Natural Heritage Commission. In the Ouachitas, shale formations outcrop on gentle to steep south- or west-facing slopes and occasionally on gently sloping drainages. Upon first glance, these outcroppings with exposed fragments of thin, black shale and patches of sparse vegetation cover appear somewhat other worldly. Upon closer inspection, one finds tucked between shale fragments a number of xeric-adapted herbaceous species capable of surviving in this harsh environment, where the dark, sun-scorched shale at the surface creates extreme ecological conditions.
Shale barrens and glades are mosaic plant communities consisting of a remarkable number of endemic, rare, and narrowly-distributed species. According to NatureServe, 36 plant species of state conservation concern and more than 20 globally critically imperiled, imperiled, or vulnerable species occur in this system. New species are still occasionally discovered and a few species remain undescribed in the Ouachita shale barrens. For example, we saw a striking purple-flowered undescribed species of wild hyacinth (Camassia sp. nova) during our visit.
The star of the show that day and the focus of our research expedition to the Ouachitas was the federally threatened Missouri bladderpod (Physaria filiformis). Many members of the genus Physaria – commonly known as bladderpods due to their inflated seed pods – are recognized for their narrow distributions and edaphic endemism, or restriction to unusual soils. As a small-statured winter annual, Missouri bladderpod showcases brilliant yellow flowers in early spring and specializes on thin-soiled calcareous (dolomite and limestone) outcrops in northern Arkansas and southwestern Missouri. However, at its southern range limit in the Ouachitas, Missouri bladderpod is known from just a few isolated shale glades and barrens.
Prior to visiting the Ouachitas I wondered how a presumed calciphile like Missouri bladderpod existed on shale formations, which typically produce acidic soils. Perhaps like a few other species of rocky outcrops in the region – such as Sedum pulchelum (widow’s cross), and Mononeuria patula (lime-barren sandwort) which occur on both acidic and calcareous substrates – I surmised MO bladderpod may also tolerate a broader range of edaphic conditions than previously thought. However, I soon learned the shale outcroppings we visited were interbedded with limestone and supported other calciphilic indicator species such as Ophioglossum engelmannii.
A case of cryptic speciation in the Ouachitas
Once known only from limestone glades in southwestern Missouri, botanists over the years have discovered populations of Missouri bladderpod on limestone, dolomite, and shale outcroppings in scattered locations throughout Arkansas, denying Missouri’s claim of its only endemic species. A recent study led by Christy Edwards at the Missouri Botanical Garden examined range-wide (Arkansas and Missouri) genetic variation in Missouri bladderpod and the degree of genetic differentiation among populations on limestone, dolomite, and shale. Interestingly, genetic data showed isolation by distance – meaning that as geographic distance increased among populations so too did genetic differentiation. Most strikingly, the geographically isolated shale populations in the Ouachitas were highly genetically divergent from dolomite and limestone glade populations further north in Arkansas and Missouri. This strong pattern of genetic differentiation points to a possible cryptic speciation event in the Ouachitas and a previously unrecognized extremely rare species. On one hand, the genetic data was somewhat surprising given there are no obvious morphological differences among Ouachita shale populations and P. filiformis. Conversely, the data do support the remarkable pattern of narrow-endemism observed throughout the Ouachita Mountains.
As we trekked across Arkansas for a few days – along with Brent and Diana who generously shared their time and expertise – collecting fresh material of Missouri bladderpod for a deeper research dive into whether morphological traits differentiate this previously unrecognized cryptic species in the Ouachitas, the need to conserve and restore glade habitat became ever clearer. At present, there are only three known Ouachita populations, making this cryptic species extremely rare and vulnerable to extinction. Many shale glade and barrens systems are now severely damaged or have been destroyed by mining activities. Fortunately, the largest population we visited consisted of thousands of plants scattered across a shale glade and barrens complex that has been restored and managed with fire and woody thinning by the Ross Foundation. In the absence of periodic, appropriately-timed prescribed burning, glades and barrens slowly become encroached with woody species that eventually choke-out sun-loving plants like Missouri bladderpod.
Other populations of Missouri bladderpod eek out an existence on small stretches of outcrops on roadsides or private property maintained as cattle pasture. These sites prove challenging to conserve and restore. Sadly, we did visit some sites where populations were barely surviving due to degraded habitat conditions. However, two sites we visited gave us a glimmer of hope that Missouri bladderpod will continue to survive and thrive. First was a newly discovered dolomite glade population on private property in north-central Arkansas. The property owners recently thinned woody vegetation and began prescribed burning to restore their glade and woodland ecosystem. When we visited, Missouri bladderpod was thriving after a recent prescribed burn. Similarly, the second site we visited on public property had been thinned and burned in recent years, resulting in a diverse plant community and flourishing Missouri bladderpod population. These success stories illustrate the importance of restoring degraded habitat to conserve our rarest components of biodiversity.
To learn more about the Missouri bladderpod, read the new, open access paper by Christy Edwards, Matthew Albrecht and others.
Rakan “Zak” Zahawi is the executive director of the Charles Darwin Foundation in Galápagos, Ecuador. He and his collaborator, Rebecca Cole, partnered with a coffee processing plant to repurpose farm waste and help restore a rainforest. Read more about the project in an open access article in Ecological Solutions and Evidence.
From the very first time I saw the results of the orange peel project on the ground back in 2004 I was sold! What a brilliant idea I thought – use the waste products generated from the production of orange juice (and any related citrus products) to regenerate degraded habitats where expansive dry forests were once found. The idea was Dan Janzen’s, an ecologist at the University of Pennsylvania who has worked in northern Costa Rica for the better part of 50 years. At the time I was working for the Organization for Tropical Studies (OTS) and given that I work as an ecologist in forest restoration, a colleague thought I might be interested.
The idea is simple, take truckloads of agricultural waste (in this case orange peels) and spread them in a layer ~0.5 m thick across hectares of extremely degraded land dominated by forage grasses. Under the tropical sun this layer generates an enormous amount of heat, and in the process of ‘cooking’ down it asphyxiates and kills the forage grass that is notoriously difficult to eradicate. At the same time, birds and other seed dispersers visit the site, attracted by the abundant larvae helping to decompose the material. The net result is a lot of organic material and nutrients and many seeds dispersed combining to help jump-start the recovery of a degraded habitat and return it to a forested state.
I never forgot that visit and over the years that I worked in southern Costa Rica as Director of the Las Cruces Biological Station (a field station run by OTS) I always thought of trying the study there. The difference was that there was no orange production in the region but another agricultural byproduct was widely available – coffee pulp waste! I wondered – could the results of the orange project be replicated with another agricultural waste product? While the idea was always on my mind, it took more than a decade for me to actually test it after Rebecca Cole, a long-term research colleague who was based at the University of Hawaii expressed interest in collaborating.
With funds secured from the March Conservation Fund, we setup a modest pilot study with a 35 × 45 m plot buried half a meter deep. That’s 30 dump trucks – or 360 m3 of material! As with the orange peel study, this land was primarily degraded pasture and would have been slow to recover on its own. We monitored this and an adjacent similar-sized plot for 2 years and the results were nothing short of spectacular. While the control treatment languished with overgrown grasses with a few shrubs, the coffee waste plot was completely transformed. The grass was smothered and in its place a patch of young trees. All species were pioneers but they are nonetheless critical to the recovery process – and the fact that they dominated the entire plot was really promising. With time it is hoped that more mature forest species will come into this system and establish – and with a young canopy of pioneers providing a little shade, the conditions are perfect for this to happen!
This study is a small pilot project, but the results speak for themselves. So does the coffee industry! Every year, millions of tons of coffee pulp waste are generated and finding a way to not only dispose of this waste in an ecologically sound manner, but also use it for habitat recovery is a win-win for everybody. It is exceedingly rare for industry to be able to pair up so seamlessly with conservation and restoration that it is hard to believe. Of course, there are hurdles – such as governmental regulations that manage such waste products, but the potential here is enormous. And the next challenge before us is to see if we can bring this idea to scale and test the methodology across big areas of degraded habitat in the tropics. We will keep you posted!
Read more about this project in a recent open-access article published in Ecological Solutions and Evidence.
Holly Bradley, Bill Bateman, and Adam Cross (Curtin University) describe the natural history and conservation of the Western Spiny-tailed Skink, an Australian lizard with a mixed history of translocation success. For more information, read their 2020 review on migration translocations in Conservation Biology.
Australia harbors approximately 10% of the Earth’s reptile species, and over 96% of all lizards and snakes occurring there are found nowhere else in the world. However, this incredible and irreplaceable biodiversity is under threat. Australia is one of the highest contributors to species losses globally, with over 1700 species and ecological communities threatened with extinction. In the last 20 years alone the number of threatened reptiles has nearly doubled, with 61 species now federally listed.
The Western Spiny-tailed Skink (Egernia stokesii badia) is just one example of a unique, endemic reptile threatened with extinction in Australia. Continued habitat degradation from practices such as grazing and mineral extraction (largely iron ore) are some of the major contributors to population decline.
Western Spiny-tailed Skinks are one of the most social of all snake and lizard species – an uncommon trait among reptiles. Colonies of the skinks reside together in log ‘castles’, consisting of hollow logs and fallen branches. These natural structures provide a year-round residence for the skinks, who create latrine piles in select areas outside of the logs in order to keep the hollows clean.
As well as being an ecologically unique threatened subspecies, with distinct spined scales particularly on their tails, and occurring only in a small region of Western Australia, spiny-tailed skinks are also culturally significant. PhD researcher Holly Bradley met with Badimia elder Darryl Fogarty to discuss the cultural significance of the skinks in her study area, the southern region of the Mid West. Elder Darryl Fogarty informed the local name of the skinks to be meelyu, and for some members of the regional community they represent a sacred totem. Totemic animals are common for many Indigenous groups across Australia and are linked with the worldview that people are an integral part of nature, belonging to a network of spiritual and physical entities.
Often, a totem will represent one’s connection with one’s nation, clan or family group. With a preordained totem comes a spiritual responsibility, where a person is accountable for the stewardship of their totem, meaning it is protected and passed down to the next generation. For many groups, this means that a person cannot eat the animal totem. Before Europeans colonized Australia, this traditional practice contributed to maintaining biodiversity and ensuring an abundance of food supplies; part of ‘caring for country,’ or maintaining ecosystem health.
The reverence with which totemic species were regarded helped to prevent significant declines in certain animal population numbers in the past. However, after the imposition of European land management into Western Australia, changes have occurred to the ecosystem balance. For example, large areas of native vegetation have been cleared, largely for urban development and agriculture, and the introduction of hoofed livestock has degraded and compacted soils. Introduction of domestic animals has also led to feral cat invasion across over 99.8% of the Australian land mass, which has led to wildlife devastation. For the skink, these changes have meant significant population declines throughout its Mid West range.
In the face of continued transformation, habitat loss, and landscape-scale degradation, one of the ways in which Australia is trying to combat biodiversity loss is by relocating wildlife away from areas where they are likely to be (or definitely will be) impacted by these threats. Under Commonwealth regulation, if a proposed action by a mining company, such clearing of native vegetation, causes significant impact to a threatened species, approval may be conditional upon mitigation or offset measures, such as the translocation of individuals away from the threat. However, translocation is rarely a condition included as part of a decision notice without a high degree of certainty of success.
For non-threatened species, there are no Commonwealth laws which require a standard for translocations, and decisions are made on an ad hoc basis, generally with assisted relocation of larger charismatic mammals such as kangaroos and quenda, allowing local cities or councils a social license to continue urban development, without providing ongoing funding to monitor the long-term success of these translocations. After analyzing the outcomes of hundreds of translocation efforts around the world, we (Bradley et al. 2020) urge all land managers to shift their thinking away from what appears to be a poorly effective strategy. Although removing animals from areas destined for clearing might appear a simple resolution to the threats posed by activities such as urban sprawl or mining, it does not actually guarantee the survival of the individuals that are ‘saved’. In fact, our review of this practice indicates that there is little follow-up on the success of translocation and many translocations may result in the eventual death of the translocated individuals.
To be successful, translocations need to ensure not only that relocated individuals survive but also that they contribute to the long-term persistence of a self-sustaining, reproducing population. Many mitigation-motivated translocations, i.e., relocations that respond to an immediate threat to individuals, have only the single goal of moving an individual or population away from the immediate danger. However, for these animals to actually survive and persist, it is critical that the design of translocation efforts be informed by sound science and an understanding of the complex ecology of the different species targeted for “saving”. Crucially, it is essential to monitor the translocated animals to understand their behaviour in the new location, estimate likely population viability in that location, and better understand and communicate how translocation efforts might be improved in the future.
We have just entered the United Nations Decade on Ecosystem Restoration, which represents a growing global commitment towards preventing, halting and reversing the degradation of ecosystems. However, for there to be the restoration and protection of fully functioning, healthy ecosystems, it is important for translocations to target a suite of ecologically significant species, rather than just the larger, charismatic mammals. Current biases generally exclude consideration of reptiles within assessments of mine site restoration success, despite their particularly high diversity and abundance within the arid mining regions of Australia, and their occupation of important ecological niches. The well-known ‘Field of Dreams’ idea, presented as one of the abiding myths of restoration ecology, assumes native animals will return on their own after revegetation of a site but, in practice, it doesn’t always work out that way.
Translocation case study: spiny-tailed skinks
As iron ore extraction continues in Western Spiny-tailed Skink’s habitat throughout the Mid West region, future translocations of colonies of this endangered reptile are likely. Understanding the basic requirements for establishment and persistence is crucial, and gathering this knowledge requires significant investment in research and monitoring. For example, detailed studies are required of the diet and habitat log pile characteristics needed for colonies to thrive. As these skinks are shy and observational records are difficult to obtain, this means other research methods are required, such as collecting scats for visual and genetic analysis of the invertebrate and plant contents of their diet. A more informed understanding of diet can help improve translocation site selection, as it is important to know what plant and animal species are important food sources that must be present or else be planted or reintroduced in restoration sites for successful recolonization.
Another example of critical information to promote successful translocations is understanding the key predation threats to the Western Spiny-tailed Skink. Despite the protection of their unique spined tails which allow them to lodge tightly into crevices and act as a defensive mechanism against attack, they are still at risk of decline from predation. One method to understand the key predators of skinks within the Mid West has been to place camera traps at active colony sites. Below is an example of an image captured of a feral cat with an adult skink in its mouth, indicating that control of feral predators, particularly cats, is likely to be critical in ensuring the initial survival of relocated skink individuals.
It is also important to understand how translocated individuals integrate within the recipient ecosystem, and that they do not introduce any non-native parasites, or outcompete any native species for food resources. Research by Bradley et al. (2020) shows that those who undertake mitigation translocations rarely consider the long-term impacts of how translocated animals affect the recipient ecosystem, and if the carrying capacity of the translocation site has space for the introduction of new individuals.
Translocation can be expensive (for example, the relocation of cheetahs (Acinonyx jubatus) in Namibia cost about $2800 USD per individual), and the continued funding and implementation of ad hoc species relocations to justify continued habitat loss may be both wrong-headed and a waste of limited conservation dollars. Translocation is also a highly stressful practice for the animals, and it is counter-productive to go through such efforts if there are no territories or food resources available for their survival.
To improve the outcome of future translocations of the Western Spiny-tailed Skink, it is also important to understand the complexity of the recipient ecosystem and how best to help translocated individuals assimilate there. Detailed habitat assessment and locating appropriate log pile structures can determine if the recipient site is appropriate for the skinks, and targeted surveys can determine if skinks are already present within the area. Selection of translocation sites as close as possible to the source location will prevent the co-introduction of non-native parasites or diseases.
The way forward
Less than half of all published studies undertaking translocations compared or tested different techniques (Bradley et al. 2020). Without a comparison of different techniques, such as whether supplementary feeding during an ‘acclimation’ phase at the translocation site or if the establishment of temporary fencing might help population establishment compared with simply releasing animals into new habitat, it will be very difficult to improve translocation practices for the future. Given current success rates are less than 25% for mitigation translocations around the world (i.e., the number resulting in self-sustaining populations), there is huge room for improvement. A holistic approach to land management considering both ecological and cultural significance can both protect and restore community wellbeing, as well as promote the return of functional, self-sustaining ecosystems in restoration practice.
For more information, read our 2020 review of migration translocation success in Conservation Biology: Bradley H, Tomlinson S, Craig M, Cross AT, Bateman B. 2020. Mitigation translocation as a management tool. Conservation Biology https://doi.org/10.1111/cobi.13667.
Mike Saxton is an ecologist restoration specialist at Shaw Nature Reserve, a 10 km2 mosaic of restored and reconstructed woodlands, prairies, wetlands, and riparian forest along the Meramec River in Gray Summit, Missouri.
For most land managers, there aren’t enough hours in the day. Between invasive species management, native seed collection and prescribed fire implementation, there are never enough boots on the ground. Add in equipment break downs, erratic weather and administrative tasks and it’s no surprise that with so many balls in the air, something gets dropped. Far too often, we drop the ball on science and monitoring, which are critically important for biodiversity-driven ecosystem management and restoration. Research and monitoring can, in some cases, be expensive; usually they take a certain amount of specialization, and they most certainly take time. For these reasons and many others, land managers build partnerships with universities, collaborate with outside agencies, and engage the public in community science to meet research and monitoring needs.
What follows is an example of a highly successful partnership between non-profit organizations, a private consulting group, and a federal agency to better understand and protect a federally endangered species.
In 2017, Shaw Nature Reserve hosted a Bioblitz partnering with the non-profit Academy of Science, St. Louis. For two days, participants combed the area looking for as many plant and animal species as they could find. A single federally endangered Indiana bat (Myotis sodalis) was captured during an evening mist netting session along a riparian corridor, marking the first time this species was documented at the Nature Reserve.
Wildheart Ecology, the local consulting firm which carried out the Bioblitz bat survey, returned in the summer of 2018 to deploy acoustic detectors to further document bat populations at the Nature Reserve. The data revealed the presence of nine different species, including the Indiana bat, the endangered gray bat (Myotis grisescens), and several other species of conservation concern.
After these surprising and impressive findings, scientists at the U.S. Fish and Wildlife Service carried out mist netting in summer 2019 at the Nature Reserve to gather more information about the federally endangered population of Indiana bats. Netted individuals were tagged and fitted with tiny transponders. Using telemetry, USFWS staff were able to locate a maternal roost colony tree in the Meramec River flood plain. After multiple emergence sampling events conducted at dusk, the population is estimated to be 150+ individuals, making it one of the largest recorded in Missouri.
So how did Shaw Nature Reserve end up with one of the state’s largest populations of at-risk bat species? The story begins in fall 2015, when a major flooding event on the Meramec River deposited large amounts of woody biomass and created logjams in the Nature Reserve’s floodplain. Another major flooding event in the spring 2017 compounded these conditions. In the fall of 2017, moderate drought gripped the region, drying leaf litter and woody fuels on the forest floor. In November of that year and on a low humidity day in drought conditions, we conducted a prescribed fire that thoroughly burned the floodplain forest, which normally does not carry fire. The flames crept into flood-debris logjams, causing a major conflagration. Dozens of floodplain forest trees died — mostly silver maple, elm and cottonwood— leaving an open patch of larger-diameter snags, or upright dead trees. It is in these snags where the federally-endangered Indiana bats have found a home. Turns out, the serendipitous convergence of flood, drought, and fire created just the ideal conditions. Couple that with high-quality foraging areas across a healthy, diverse, managed landscape and this population is thriving.
Current status of Indiana Bats
Unfortunately, like many bat species, the Indiana bat has been in decline and imperiled by human disturbance and disease. According to the U.S. Fish and Wildlife Service, hibernating Indiana bats are especially vulnerable to disturbance, since they often congregate in large numbers – from 20,000 to 50,000 – to overwinter. A large number of deaths can occur if humans disturb these caves during hibernation. While other factors are also responsible for their decline, the devastating wildlife disease known as white-nose syndrome — discovered in 2006 — is a serious threat to the long-term survival of the species.
With thoughtful management and strategic planning, conservation practitioners can conserve and restore bat habitat. Providing a continuous supply of roosting trees and maintaining a habitat structure to facilitate foraging are key aspects of restoration and management plans for bats. According to the Beneficial Forest Management Practices for White Nose Syndrome-affected Bats, below are some best-practice guidelines for achieving these goals:
Harvest timber during the hibernation period to eliminate or significantly reduces the likelihood of direct fatality or injury to tree-roosting bats.
Create large-diameter snags and canopy gaps, via girdling or chemical (e.g., “hack and squirt”) methods, to increase sun exposure to existing and potential roost trees.
Increasing midstory openness to facilitate travel corridors and foraging opportunities via increased mobility and insect prey detection.
Retain or create large-diameter snags during forest regeneration harvests or when managing stands affected by windthrow or disease/insect outbreaks.
Limit aerial or broadcast spraying near known hibernacula, maternity sites, and surface karst features, unless it can be demonstrated that it would have no adverse impact on bat populations or habitat.
Avoid disturbances near maternal roost sites or colonies when possible.
Fell hazard trees that appear to provide bat roosting habitat and do not pose an imminent danger to human safety or property during winter (hibernation period) and avoid removing them during June and July when non-flying bat pups may be present.
Avoid burning during cold periods since this can be detrimental to colonies of some species if individuals cannot escape smoke and heat from fires.
Apply low-intensity fires when possible since high-intensity fires are more likely to cause injury.
Account for caves, mines, important rock features, bridges, and other artificial structures when developing burn plans since these locations are often occupied by roosting or hibernating bats.
Remove hazard trees and construct fire-lines during winter, when possible, to reduce chances of removing occupied roost trees or disturbing maternity colonies.
Protect known maternity roost trees and exceptionally high-quality potential roost trees (e.g., large snags or large-diameter live trees with lots of exfoliating bark) from fire by removing fuels from around their base prior to ignition.
Limit management activities and disturbances near cave entrances.
Eradicate and control invasive plants to improve habitat quality for bats.
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.
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.
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?
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).
Dr. Matthew Albrecht is an associate scientist in conservation biology in the Center for Conservation and Sustainable Development at Missouri Botanical Garden. He describes the ecology of the endangered Pyne’s ground-plum (Astragalus bibullatus).
Formed from the fossilized remains of an ancient tropical sea, the Nashville Basin encompasses the geographic center of Tennessee, stretching north to southern Kentucky and south to northern Alabama. Celebrated by some as the “home of country music,” many of us prefer to revel in the region’s unique flora and fauna associated with the globally rare limestone glades, or limestone cedar glades. Here, thin, rocky soils interspersed with flat, exposed limestone bedrock support sun-loving herbaceous plants adapted to the scorching temperatures and parched soils of summer followed by near-permanently saturated soils in winter. Trees and other woody vegetation struggle to take hold here, creating an open, desert-like ambience.
Treasured for their unique flora, limestone glades feature over two dozen endemic or near-endemic species along with several unusual disjuncts – known mainly from grasslands far west of Mississippi River. Glade endemics such as Nashville Breadroot (Pediomelum subacaule) and Gattinger’s prairie clover (Dalea gattingeri), occur in open, shallow-soil communities dominated by C4 annual grasses and C3 winter annuals, including several members of Leavenworthia spp. Most of these glade-restricted species are widespread throughout the Nashville Basin. However, several of the disjuncts and endemics are extremely rare, such as the federally endangered Pyne’s ground-plum (Astragalus bibullatus). Known from just a few sites in a single-county, Pyne’s ground-plum teeters perilously close to the brink of extinction.
Why are Pyne’s ground-plum and a few other endemics and disjuncts so rare? At first glance, the obvious culprit appears to be habitat loss from the unrelenting sprawl of Nashville. Just take a drive from Nashville to Murfreesboro on I-24 and you will encounter an uninterrupted sea of strip malls and tract housing. In the late 1800’s, famed botanist Augustine Gattinger collected a specimen of Pyne’s ground-plum much farther north than where present-day populations are found, in a spot now inundated by the J. Piercy Priest Dam and Reservoir near Nashville. Constructed on the Stones River in the 1960s, the dam flooded thousands of acres for “recreational enjoyment” and hydroelectric power generation. Undoubtedly, other rare plant populations, unknown at the time, faced a similar fate. Over time, humans have abused many glades, using them as trash dumps or for off-road vehicle recreation, which could have also led to their demise.
Our long-term research with Pyne’s ground-plum also points to additional factors. In 2010, we began a demographic monitoring study on Pyne’s ground-plum populations to understand how we could reverse this species’ decline. Most remaining populations occupy slightly deeper soil pockets on glade edges where perennial C4 grasses and forbs form narrow, linear bands that abruptly transition into impenetrable thickets of woody vegetation – mostly of eastern red cedar (hereafter “cedar”). In a few cases, Pyne’s ground-plum grows in small, rocky openings surrounded by dense, dark cedar-hardwood forest.
At the time, the long-standing paradigm was that Pyne’s ground-plum – and some other extremely rare plants like Trifolium calcaricum – thrive in the partial shade cast by these adjacent cedar trees and woody vegetation at the glade edge. As the story goes, some endemics were less hardy and required some shade as a buffer from the extreme microclimate on the thin-soil outcrops. Much of the early, pioneering work on glade ecology by Elise Quarterman and her students – described stable plant communities under edaphic control of the thin, rocky soil. As was typical of that era, they described plant communities on deeper soils according to classical climax theories of eastern deciduous forest succession.
However, several years of careful monitoring and experimentation in my lab began to reveal other factors at play. Initially considered an outlier, one of our monitored populations occurs beneath a utility right-of-way, which rapidly succeeds to woody vegetation in the absence of periodic mowing. Our data showed that plants here grew larger and usually produced far more flowers and fruits compared to shaded sites. After measuring soil properties, light availability, and other vegetation properties in permanent plots, our analyses indicated that the amount of woody vegetation cover rather than edaphic conditions drove growth and reproduction in Pyne’s ground-plum. Follow-up experiments conducted by then REU student, Rachel Becknell, confirmed light-conditions that mimic cedar resulted in reduced growth of Pyne’s ground plum.
With fresh eyes, we began to scrutinize the dense thickets of cedar at our study sites. Upon closer inspection, we noticed the occasional, gnarled, and open-grown (i.e., wolf tree) chinkapin or post oak jutting above the younger, even-aged thickets of redcedar. Chinkapin and post oaks grow slowly in these thin, rocky soils, but their low-lying branches in multiple directions suggest these wolf trees once grew in conditions more open in the distant past. Historical aerial imagery dating back to the 1950’s confirmed that some of these forested sites were once more open, with far fewer cedars.
We speculate that disturbances from prior land-use activities probably kept these deeper soil areas around glade openings in a more savanna-like or open woodland state. In their absence, opportunistic woody vegetation – especially fast-growing cedar – colonized all but the thinnest soils in the limestone glades. Over time, this led to the development of multilayered forests and dense shrub layers that now surround the thin-soil glade openings at many of our study sites.
To dig a bit deeper in time, my colleague, Dr. Quinn Long, and I also examined early land survey records dating back to the late 1700’s. Surveyors would delineate property boundaries based on the tree species (i.e., witness trees). If no tree species were present, surveyors used stakes (or sometimes stacks of rocks) to mark off the property boundary. In the records we examined, eastern redcedar represented just 2% of all witness tree species while oaks and stakes represented a majority of the records. Now, cedars are probably the most abundant tree in the Nashville Basin.
Although we interpret historical data with caution, these multiple lines of evidence imply a historically more open landscape in the Nashville Basin with far fewer cedars. Cedars are fire intolerant, and we hypothesize that periodic fire – naturally set by lightning and Native Americans – maintained historically lower densities of woody vegetation and promoted grassland species surrounding the glade pavement openings. Genetic analyses by our collaborators Dr. Ashley Morris (Furman University) and colleagues show widespread admixture among populations of Pyne’s ground-plum, which also supports a historically open landscape mosaic that facilitated gene flow among remnant populations via pollinator or animal movement.
Admittedly, we were not the first to propose a paradigm shift in the ecology of the Nashville Basin. We soon realized a few other astute botanists long before us advocated for the use of fire management to create more open habitat around glades, but with limited data these recommendations never gained widespread traction among land managers or found their way into the scientific literature. Another issue was that ecologists and botanists tended to focus almost exclusively on the plant communities of open, thin-soil glades – which are clearly not fire-dependent – rather than on the matrix plant communities of slightly deeper soil surrounding them.
Not surprisingly, our ideas faced much skepticism and many questions: Hasn’t cedar always been the dominant tree of the Nashville Basin? After all, the Cedars of Lebanon State Park and State Forest – the largest remaining tract of Nashville Basin Glades and Woodlands under public protection – was named after the towering eastern red cedars that reminded early settlers of the Biblical cedar forests around Mount Lebanon.
At about the same time of our research discoveries, Dr. Dwayne Estes, botanist and Director of the Southeastern Grasslands Initiative, also began developing transformative ideas about the Nashville Basin. Like us, he hypothesized that the glades were historically embedded in a savanna and open woodland landscape rather than dense forests as they are now. Unfortunately, there are few historical descriptions of the Nashville Basin before early settlers radically altered the landscape via farming, pasturing, and logging. Estes speculates that lack of detailed naturalist descriptions of the Nashville Basin prior to the Civil War resulted in a misunderstanding of its historical condition. The earliest reports after the Civil War describe a largely forested region with large cedars, which could have easily developed over the 80-year period between the time of settlement and the mid-1800’s.
Long before settlement, we know that American bison and other large mammalian grazers also crisscrossed this landscape along ancient traces or megafauna highways that connected mineral licks and water sources. Formerly known as French lick, what is now present day downtown Nashville contained a large salt lick, once visited by herds of bison and elk according to early accounts. Disturbance associated with grazing and large-animal activity combined with periodic fire and drought probably kept the Nashville Basin in a more open state. Interestingly, Pyne’s ground-plum’s presumed closest relative, Astragalus crassicarpus, is widespread throughout grasslands in the Great Plains. Commonly known as buffalo pea, it also produces large plum-colored fruits eaten by Native Americans and presumably bison. In many years of monitoring, we rarely find that animals eat Pyne’s ground-plum fruits, which slowly dehisce releasing their hard seeds next to mother plants. Seeds contain a double seed coat making them challenging to germinate. After years of experimentation, we have found that exposing seeds to high concentrations of sulfuric acid followed by a short period of cold stratification results in consistently high germination compared to other treatments. We now wonder whether this germination strategy might be linked to ancient relationships with mammalian grazers who possibly dispersed the fruits and scarified the seeds.
How does Pyne’s ground-plum inform restoration of degraded woodland and savanna-like systems in the Nashville Basin? Thanks to the prodigious efforts of conservation agencies, several remnant limestone glades have been protected. However, until recently, the dense, cedar-hardwood forest surrounding open glades received little attention from land managers. In 2012, we along with collaborators at the Tennessee Department of Environment and Conservation (TDEC) and United States Fish and Wildlife Service began thinning woody vegetation in the most shaded Pyne’s ground-plum populations. After a few years, we noticed increased flowering at the most shaded sites. To reestablish a more open woodland and savanna-like structure in protected areas throughout the Nashville Basin, TDEC began widespread thinning of woody vegetation around glade openings and reinitiating the key ecological process of fire.
On a warm, sunny afternoon this past October, my colleague, Noah Dell, and I set out to survey restored areas that might be suitable for establishing Pyne’s ground-plum populations. Hiking through recently restored areas we noticed grassland- and savanna-associated species slowly beginning to rebound and increase in abundance. Compared to previous years, it was much easier to find open, deeper soils on well-drained sites that are needed to reestablish Pyne’s ground-plum. With time and continued restoration of ecological processes, we are optimistic that this and many other rare species will continue towards path of recovery in the Nashville Basin.
Adam Cross and Thilo Krueger describe the natural history and conservation of carnivorous plants. Adam is a research fellow at Curtin University , Western Australia and Science Director for the EcoHealth Network. Thilo is a masters student in Adam’s research group and is researching prey spectra and other plant-animal interactions of carnivorous plants.
Carnivorous plants are a unique and fascinating group that have captivated scientists and the public, as well as inspired writers and film makers, for well over a hundred years. During his seminal 1875 work Insectivorous Plants, while studying one of the sticky-leaved Sundews (Drosera), British naturalist Charles Darwin once famously and not at all exaggeratedly wrote “I care more about Drosera than the origin of all the species in the world”. These incredible species have flipped the traditional perception of plants as immobile producers, and possess highly modified leaves that have evolved to attract, capture and digest animal prey – mostly small insects, but for some species occasionally also birds and small mammals.
Capturing prey allows carnivorous plants to obtain nutrients in habitats where soils are extremely nutrient-poor, and they thrive in areas like swamps, rocky seepages and dripping rock walls, seasonally-flooded lowlands and even the canopies of tropical rainforests. Many species of these predatory plants grow in almost pure sand or in laterite soils, which are notoriously low in important nutrients for plants such as nitrogen and phosphorus. In these habitats, carnivory represents a very effective strategy for competition and survival.
While there are several very well-known carnivorous plants, such as the Venus Flytrap (Dionaea) and Trumpet Pitcher Plants (Sarracenia) of North America, there are in fact over 860 species that are currently described world-wide. Incredibly, carnivory has independently evolved at least 11 times in different plant lineages, and at many different points in time. This evolutionary development has led to a wide diversity not only in the size and form or carnivorous plants, but also their function and biology. While some species are not much larger than a single grain of sand (such as the diminutive Utricularia simmonsii, one of the smallest of all flowering plants), the largest species are vines growing up to 60 m into rainforest canopies (Triphyophyllum peltatum). Many species are terrestrial, occurring in habitats ranging from mountain tops to Mediterranean scrubland to seasonally-wet swampland, and numerous species have become partially or even fully aquatic. Within tropical rainforests, there are even a number of epiphytic carnivorous plants – species growing high in the canopy on the mossy trunks or branches of trees.
However, perhaps most incredibly, there are many different structures and methods that plants have evolved for carnivory. A range of genera, including Byblis(Byblidaceae), Drosera(Droseraceae), Drosophyllum (Drosophyllaceae), Pinguicula (Lentibulariaceae) and Triphyophyllum (Dioncophyllaceae) employ sticky leaves to capture prey, relying upon mucilage produced by specialized sessile or motile glands containing digestive enzymes to snare and absorb nutrients from insects. Philcoxia (Plantaginaceae) also produces sticky leaves, but holds these beneath the soil surface to capture small nematodes and other small subterranean fauna. Some species produce leaves modified to form pitchers of varying complexity with slippery walls to prevent the escape of captured prey, which drown and are digested in pools of water and enzymes (BrocchiniaandCatopsis[Poaceae], Cephalotus[Cephalotaceae], Nepenthes[Nepenthaceae], andDarlingtonia, Heliamphora, Sarracenia [Sarraceniaceae]). Still others utilize quick-moving, snapping lobed traps (Dionaea and Aldrovanda[Droseraceae]), and many species even produce highly complex subterranean corkscrew and suction traps (GenliseaandUtricularia[Lentibulariaceae]). Some of these structures are capable of making among the fastest movements in the plant kingdom.
A number of carnivorous plants also exhibit amazing biological mutualisms, being rather paradoxically reliant upon animals for their growth and survival.Roridula (Roridulaceae) produces sticky resin from glands on its leaves, but lacks the capability to produce any digestive enzymes and instead relies upon a unique digestive mutualism with a Hemipteran bug (Pamerideaspecies) to absorb nutrients from captured prey, as these bugs can move among the resinous glands without being captured and defecate onto the leaf surface. Similar digestive mutualisms are known for Hemipteran bugs of the genus Setocoris with Byblis and some species of Drosera. The digestive fluid of the pitcher plant Cephalotus follicularisprovides crucial breeding habitat for a species of stiltfly (Badisis ambulans), while Nepenthes hemsleyanaprovides a safe roosting site for Hardwicke’s bat and in return benefits from digesting the ablutions of roosting bats in addition to capturing insect prey. Other Nepenthes, such as the Bornean N. lowii, produce an appealing food for tree shrews on the underside of the pitcher lid, which has a laxative effect and results in the shrew depositing a package of nutrients into the pitcher ‘latrine’ in return for the feed. It has even been proposed that the squat pitchers of Nepenthes ampullaria, which are open to the rain and catch falling leaf detritus, could be vegetarian.
These predatory plants can be found on every continent except Antarctica, but there are distinct “hotspots” of carnivorous plant diversity in South America, South Africa, Southeast Asia and Australia. Almost a quarter of all currently described carnivorous plants can be found in the ancient, nutrient-poor landscapes of Western Australia, for example. Unfortunately, many of these areas are also experiencing some of the world’s highest rates of habitat destruction – in the southwest of Western Australia, where approximately 120 species of carnivorous plants occur, approximately 70% of all native vegetation (and up to 97% in some regions) has been cleared for agriculture and urban development. What little native vegetation remains is often isolated, heavily fragmented, and significantly degraded from weed invasion and poor fire management.
Carnivorous plants have been described as harbingers of ecosystem integrity, as they are often the first to disappear after disturbance. As might be expected given their unique ecologies, most carnivorous plants have very small ecological niches and are extremely sensitive to environmental change. Given that they often rely on habitats such as nutrient-poor wetlands, which are particularly vulnerable to human impacts and represent some of the most threatened ecosystems globally, carnivorous plants face an existential threat in the 21st Century.
A recent international study by Cross et al. (2020) examining the conservation status and threats faced by carnivorous plants found approximately a quarter of all species around the world were at risk of extinction. The highest numbers of critically endangered species occurred in Australia, Brazil, Indonesia, Philippines, Cuba and Thailand – in many cases, the same areas regarded as the most significant hotspots of carnivorous plant diversity. Importantly, 89 species of carnivorous plants (over 10% of all species) are only known from a single location, making them particularly vulnerable to any disturbances, and particularly rapid impacts, to their habitats.
Due to their unique insect-capturing traits and often spectacular appearance, many carnivorous plants are very popular with horticulturists and hobby plant collectors. Unfortunately, this has created a significant market for illegal collection – also known as poaching – of carnivorous plants and several species have already been driven to the brink of extinction by poachers. Pitcher Plants such as Tropical Pitcher Plants from south-east Asia and the Albany Pitcher Plant from Western Australia are particularly affected by poaching but even the iconic Venus Flytrap from the United States continues to be plagued by unscrupulous poachers. There must be immediate and concerted global action to cease the illegal collection of wild plants, and much greater regulatory enforcement of biodiversity protection laws to end carnivorous plant poaching.
Cross et al. found that the continuing clearing of natural vegetation for agriculture, urban development and mining projects represented by far the most severe and immediate threat to carnivorous plants. In just the past two decades, massive areas of pristine habitat have been converted into oil palm plantations in Southeast Asia, cattle farms in Brazil, or suburban housing and industrial development in Australia. For example, two of the last remaining populations of the Critically Endangered rainbow plant (Byblis gigantea) in Perth, Western Australia, were destroyed for the construction of a liquor supermarket and a logistics distribution centre. Several populations of sundews (Drosera) near the town of Hermanus, in South Africa, are rather paradoxically being lost to the development of a settlement known as “Sundew Villas”. Much stronger protections are required to ensure that remnant carnivorous plant habitats are protected and conserved.
Climate change poses another significant threat to carnivorous plants, especially the many species occurring in Mediterranean climate regions where warming, drying trends are already becoming evident. Extreme and prolonged drought conditions, such as have been recently experienced in many Mediterranean climate regions around the world, can not only impact directly upon species and communities, they can also fuel high-intensity and aseasonal fires. Although fire forms a natural part of the ecology of many ecosystems in which carnivorous plants occur, fire regimes have been increasingly altered by climate change and inadequate fire management practices. The effect of altered fire regimes on carnivorous plants is complex, idiosyncratic and often still poorly understood; while some species (especially geophytes such as tuberous Drosera) may benefit from high-intensity fires that remove competition from other vegetation, the same fire can have devastating impacts on other species lacking underground structures for resprouting. For example, an extreme summer bushfire in 2006 near Perth, Western Australia, fuelled by record drought conditions at the time, reduced the only known population of the critically endangered Drosera leioblastus from several thousand individuals to just 11 plants, while simultaneously inducing mass-flowering of most tuberous Drosera in the same area. The complex effect of fire and the need for sound fire management policies is highlighted by the Albany Pitcher Plant (Cephalotus follicularis), which is threatened both by prescribed burning at short fire intervals as well as long-term fire suppression. Weed invasion can further exacerbate fire management, and Cross et al. (2020) suggest that simultaneous prioritisation should be afforded to invasive species management and the maintenance and preservation of natural ecosystem processes such as fire regimes and hydrological functioning.
Ecological restoration offers not only hope for the return of many carnivorous plant species to regions from which they have been lost, but also an effective mechanism by which ecosystem functioning and natural processes like fire and hydrology can be reinstated in degraded landscapes where these processes have been impaired. While there is growing urgency to conserve what little natural carnivorous plant habitat remains, Cross et al. (2020) highlight the growing imperative to begin scaling up restoration efforts in areas where habitat loss and ecosystem disturbance have been most severe, in order to concomitantly provide new habitat for these species and provide buffers for protected areas. Far too often remnant habitats are not only highly fragmented but also abut farmland or urban developments, and the restoration of ecological corridors and buffer zones will confer resilience and greater ecological integrity to these increasingly beleaguered ecosystems.
The loss of carnivorous plants would not only be a devastating loss for future generations, but could potentially have detrimental effects across ecosystems. They have captivated scientists and the public for hundreds of years, from their portrayal as horrifying monsters in popular films to providing inspiration for the development of non-stick surfaces. But they are integral parts of ecosystems, important cogs in the complex biodiverse systems in which we live and upon which we rely, and we must preserve them. The number of vulnerable, endangered and extinct species continues to grow despite conservation efforts around the world, and it is clear that we must begin investing significantly in the restoration of carnivorous plant habitats, particularly in regions such as Australia, Brazil, South Africa, southeast Asia and North America, if they are to survive for future generations to marvel at.
Our global review of the conservation status of carnivorous plants can be read in full, open access, here. To learn more about the unique and incredible biology of our carnivorous plant heritage, see a recent international monograph about their ecology, biology and evolution to which the present authors were contributors. The authors have also recently written books on some of the most amazing carnivorous plant species, including the Waterwheel Plant, Aldrovanda vesiculosaand the Albany Pitcher Plant, Cephalotus follicularis.
Andrew Kaul is a new Restoration Ecology Post-doc in the Center for Conservation and Sustainable Development at the Missouri Botanical Garden. Here he describes some projects from his dissertation work conducted with Brian Wilsey at Iowa State University.
Tallgrass prairies once covered most of the central United States, but much of this historic ecosystem was lost to agriculture during the 19th and early 20th Centuries. Iowa sits at the heart of the tallgrass prairie range and lost more of its prairie than any other state except Illinois.
Throughout the Midwest, prairie restoration efforts have become increasingly common, and after several decades of research, the practice of prairie restoration has become increasingly complicated. We now know that restoration outcomes can be highly variable, and it is difficult to predict the outcome of any given restoration because there are so many factors that have been documented to influence restoration success, in terms of species diversity and establishment of target species from the seed mix.
For my PhD at Iowa State I studied 93 grassland restoration projects across Iowa. Previous work on grassland restoration had included careful experiments and thorough investigations of novel restoration techniques. What hadn’t been done before was to treat existing restorations each as their own little experiment and to sample broadly across the wide diversity of restorations in the real world. This approach allowed us to describe general patterns across many sites and to investigate which of the many potentially important processes tended to drive restoration outcomes.
With this project, my advisor Brian Wilsey and I sought to test which factors are the best predictors of restoration success in terms of species diversity, degree of invasion, and establishment of sown species. We considered factors including management history, the diversity of the seed mix, land use history of the site, site size and shape, soil characteristics, and weather during the first couple years of vegetation development. We took a retrospective approach to answer these questions, using existing restorations, which were highly variable in their age and how they were undertaken. We sampled vegetation at 93 restoration sites across Iowa over two summers and interviewed the managers of each of those sites afterwards to get information on when the restoration was started, what seed was used, and how it had been managed. We also sampled 5 prairie remnants, as a reference.
We found that by far the strongest predictor of plant diversity and recruitment of species from the seed mix was the degree of invasion by exotic species, where the more heavily invaded a site was, the lower the plant diversity and recruitment of target species. The influence of exotic species was more important than soil type, site management, restoration age, or any other aspects of the restoration, indicating control of exotic species is key to restoring prairies, and other temperate grasslands. The degree of invasion was higher in more linear shaped sites, sites with higher soil organic matter, and sites with fewer species in the seed mix, so we found that these variables were negatively related to our restoration success measures because of their indirect effects through exotic species. More linear habitats tend to have more “edge effects” where there are more colonization opportunities for exotic species. The higher invasion rates we found in sites with greater soil organic matter indicate the exotic species are better able to take advantage of nutrient availability. The lower invasion rates in sites seeded with more prairie species indicate that these mixes contain species that together, occupy more niche space and leave less open niches for exotic species to colonize. We also found that sites mowed during the first two years of establishment had higher diversity and establishment of sown species. This practice is supposed to suppress the annual weeds, which start growing before the seeded prairie species can establish.
Another goal of this project was to examine the ecology of milkweeds in prairie habitats. Milkweeds are obligate host plants for larvae of the monarch butterfly (Danaus plexippus), and in recent years, conserving and restoring milkweed populations in service of monarchs has become a major conservation priority in North America, especially in the Midwest, where many of the migratory monarchs breed. We counted milkweed stems within a meter of our sample quadrats at each prairie, and used these count data to examine what prairie habitats have the highest milkweed abundances, and what features of a prairie habitat best predict stem density. Specifically, we tested whether stem densities were different between remnant prairies, roadside restorations, and the non-roadside “conservation” restorations, most of which are managed by the Iowa Department of Natural Resources.
Milkweeds were far more abundant in remnants than restorations. Among restorations, roadsides had higher milkweed densities. Remnant prairies also had a higher diversity of milkweeds, so they are clearly an important habitat for this forb assemblage. Most of the milkweeds we sampled in restorations were common milkweed, even though it is rarely planted. On the other hand, Swamp milkweed (Asclepias incarnata) and butterfly milkweed (Asclepias tuberosa) are often included in restorations seed mixes, but were not nearly as abundant as volunteer common milkweeds.
Across all the restorations, we tested whether milkweed stem density was related to management (burning and/or mowing) or environmental variables including soil characteristics, plant diversity, degree of invasion, and site shape (linearity). We found that milkweeds were more abundant in more linear and invaded sites, and sites with lower soil density, and higher soil pH. These factors indicate that milkweeds are more abundant in areas with more soil disturbance. This is not surprising, considering the “weedy” ruderal nature of many milkweeds, especially common milkweed. The relationship with pH was a novel discovery, and future work will be needed to experimentally test whether milkweed germination or growth is higher in more basic soils, which is what our study indicates.
I am continuing my research on tallgrass prairie restoration with new projects examining plant functional traits to help understand why certain species are under- or over-represented in restorations. We have collected data on plant and leaf functional traits for over a hundred prairie plants and will test how the mean traits of plant communities differ between seed mixes, restorations, and remnants. Additionally, I am working with the Wilsey Lab on a related project examining phenological differences between plant communities in remnant and restored prairies.
To learn more, follow me on Twitter @andrew_kaul and check out our milkweed paper in Restoration Ecology. The prairie restoration study was recently accepted in Ecological Applications, under the title, “Exotic species drive patterns of plant species diversity in 93 restored tallgrass prairies.” Look for it to come out soon!
Leighton Reid describes a field trip to a unique, natural community with Tom Wieboldt, retired curator of the Massey Herbarium at Virginia Tech.
From southwestern Virginia to central Pennsylvania, ancient shale formations jut out of the mountains at wonky angles. Loose and crumbly, the rocks bake in the sun. Surface temperatures can reach 60° C (140° F) – comparable to a desert. Rocks slip and tumble easily on the steep slopes. Few eastern plants are tough enough to hack it under these conditions. Among those that can, a few are globally unique.
On a warm day in August, I had the opportunity to botanize one such place – a central Appalachian shale barren in Craig County, Virginia – with Tom Wieboldt, retired curator of the Massey Herbarium at Virginia Tech (VPI), and a leading authority on shale barren flora. As we hiked and photographed plants, we talked about the conservation and potential for ecological restoration of these rare communities.
The gems of the shale barrens are the endemics. Amazingly, 22 species are found mostly or exclusively on central Appalachian shale barrens. Another seven species are rare or disjunct from the rest of their range – typically far to the west. For example, the closest population of chestnut lip fern (Cheilanthes castanea) outside of Virginia and West Virginia is in Oklahoma.
Shale barren plant communities exist in a dynamic equilibrium. The steep, brittle shale formations often are under-cut by rivers, which carry away rocks and cause further erosion. In essence, the entire slope is constantly slipping downwards. Successful plants find the most stable areas and send down deep roots to try to keep their place on the rocky conveyor belt.
Why do shale barrens occur only in the Central Appalachians and not also in the Southern Appalachians? Tom gave me two reasons. First, the shale deposits in the Central Appalachians get thinner south of Montgomery County, Virginia, where Virginia Tech is located. Second, the high Allegheny Mountains in West Virginia create a rain shadow over parts of the Central Appalachians, more so than the more southern and shorter Cumberland Mountains. Drier conditions in the Allegheny rain shadow contribute to the shale barrens’ uniquely western ambiance.
Inhospitable as they are, shale barrens are not immune from human pressures. They are sometimes crossed by roads or utilities, and shale banks are sometimes quarried for road-building material. Livestock and overpopulated white-tailed deer browse the plants and catalyze erosion, while also adding nitrogen and foreign seeds to the sparse soil.
Can disturbed shale barrens be restored?
When Reed Noss visited a Virginia shale barren for his book Forgotten Grasslands of the South, he found traversing the slippery slopes, lurching from one scattered red cedar to another, “close to suicidal”. I had similar thoughts following Tom up the mountainside. He climbed like a mountain goat, wandering out on thin ledges to collect interesting looking mosses.
As we walked, Tom wondered aloud whether it would even be possible to restore such a fragile plant community if it was destroyed. Wouldn’t it be better just to leave these places alone?
Undoubtedly leaving these places alone would be better. But I enjoyed thinking about how one might restore a shale barren that had already been destroyed – by quarrying, for instance. A first step might be to recontour the slope, aiming to reestablish a dynamic equilibrium with some areas eroding more actively than others. Perhaps this could be done by a skilled operator with some of the same quarrying equipment that had previously exploited the loose shale.
To revegetate such a place would require a source of propagules. I am teaching a course on Plant Materials for Environmental Restoration, so I put it to my students to find out whether shale barren plants were available from two major conservation seed suppliers. The results were not promising. Out of 86 native, non-woody angiosperms found in central Appalachian shale barrens*, less than a quarter (23.3%) could be purchased from any major seed supplier, and only 2.3% were available as seed collected from Virginia. None of the endemics were available.
As far as I can tell, few shale barren restorations have been undertaken, but I did read about one attempt in a shale barren in Green Ridge State Forest, Maryland. Whereas some shale barrens are actively threatened by acute pressures, like quarrying, this small (0.6 ha) barren was passively threatened by steady encroachment from the surrounding forest. Trees, especially pignut hickory (Carya glabra), were growing into a formerly open barren, stabilizing the soil and cutting off direct sunlight to plants closer to the ground. Managers restored the site in 2010-2011 by removing some of the pignut hickories and by burning the area during the winter. Together, these actions resulted in greater herbaceous vegetation cover and greater species diversity.
*For the seed availability exercise, we used the list of plants recorded by the Virginia Natural Heritage Program in their description of Central Appalachian Shale Barren (Shale Ridge Bald / Prairie Type) CEGL008530. We excluded woody plants, non-native plants, and ferns.
Kathlynn Lewis is an undergraduate researcher in the School of Plant and Environmental Sciences at Virginia Tech. She is studying soil carbon storage as part of a larger project on grassland floristics, conservation, and restoration in northern Virginia. Keep up with her research on Twitter by following @KathlynnLewis.
How many rare or “cool” plants do you drive by every day without noticing? Do you brake for Buchnera americana? Do you pull over for Pycnanthemum torreyi? This is something not a lot of people think about, and I didn’t think about either until very recently. The answer is that there are more cool plants along roadsides than you would think. Some of the rarest grassland plants in Virginia have found a home in roadside clearings and powerline cuts where regular removal of trees has created an opening for them to grow and sometimes thrive.
Many of the native vegetation surveys have taken us to the locations people might expect to find high-quality grassland plants, such as parts of Manassas Battlefield National Park where the soil and ecosystem have remained relatively undisturbed for almost 80 years. Other areas are much less expected. Rare plants also show up in power line right of ways and strips of roadside with tire tracks crisscrossing them in every direction and markers stuck in the ground indicating the soil was completely displaced to bury utility lines.
During June, we collected samples from 29 sites to compare plant species diversity with the amount of carbon stored in the soil. We also sampled soils from grassland restoration plantings and pastures “improved” with tall fescue (Schedonorus arundinaceus) to compare the effect of different management practices and ecological restoration on soil carbon sequestration. The soil work is my part of the project. My prediction is that soil carbon storage will be greatest in diverse, native grasslands and lowest in degraded fescue fields. I expect that restored grasslands will be intermediate.
Power line right of ways are an interesting focus of this study because they present both opportunities and challenges for plant conservation. Power companies keep these areas open by cutting out trees and spraying young sprouts with herbicide. This management is the only reason that grasslands exist in these places today, but the rare plants that live there are at constant risk of collateral damage. At least two of the areas that we sampled in June were sprayed in July, harming populations of rare plants like Torrey’s mountain mint (Pycnanthemum torreyi) and stiff goldenrod (Solidago rigida).
The vegetation surveying team has already observed over 450 species across the 29 sites sampled. Not all of these species are a welcome presence though. Invasive species appear to pose one of the largest threats to Virginia grassland ecosystems we have observed in the field. A newly emerging and particularly aggressive invader is joint-head grass (Arthraxon hispidis) which we have found in many of the sites we are sampling. This annual grass is similar to Japenese stiltgrass (Microstegium vimineum) but there is very little information about its effects on grassland ecosystems or methods for controlling it.
The plant survey team is now doing a second round of sampling to identify later-blooming species, and they are collating information about the land use history at each of our study sites. The soil samples we collected are currently being analyzed (by me) in a lab at Virginia Tech. We will start analyzing data in the fall and hope this summer’s fieldwork will help inform future research projects and the conversation around land management in Virginia grasslands.
To find out how ecological restoration affects grassland soil carbon storage in northern Virginia, follow the author on Twitter @KathlynnLewis.