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).

Drought, flood, and fire: an unexpected habitat recipe for at-risk bats

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.

A female Indiana bat, “Celeste”, captured during mist netting surveys at Shaw Nature Reserve in 2017 and 2019. Photo credit: Cassidy Moody.

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.

The audio signature of an Indiana bat, captured by detectors at Shaw Nature Reserve. Courtesy: Wildheart Ecology.

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.

Indiana bat roost site at Shaw Nature Reserve. Photo credit: Cassidy Moody.

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.

Indiana bat roost habitat along the Meramec River at Shaw Nature Reserve in Gray Summit, Missouri. Photo credit: Cassidy Moody.

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.

According to the U.S. Fish and Wildlife Service population status update, the states with largest net loss of Indiana Bats since 2007 (% decline since 2007) includes:

1. Indiana: -53,220 (-22%)
2. New York: -39,367 (-75%)
3. Missouri: -18,157 (-9%)
4. Kentucky: -15,220 (-21%)
5. West Virginia: -14,125 (-96%)
6. Tennessee -6,509 (-73%)
7. Ohio: -4,739 (-62%)
8. Pennsylvania: -1,027 (-99%)

What Can Be Done

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.

Notes on dolomite glade natural history and restoration

In early October, CCSD scientists Leighton Reid, Matthew Albrecht, and James Aronson and Shaw Nature Reserve naturalist James Trager toured several dolomite glades with Greg Mueller (Chicago Botanic Garden) and Betty Strack (Field Museum). We used the opportunity to discuss glade natural history and restoration.

In his book The Terrestrial Natural Communities of Missouri, Paul Nelson describes glades as:

“…open, rocky, barren areas dominated by drought-adapted forbs, warm-season grasses and a specialized fauna. They appear as small or large essentially treeless openings within landscapes primarily dominated by woodlands.”

Missouri glades are characterized by their geology. Many occur on southwestern-facing slopes with outcrops of sedimentary rocks, like dolomite and sandstone. But some also occur with igneous rocks in the St. Francis Mountains and Tom Sauk Mountain.

For some, glades seem like miniature deserts, complete with cacti, collared lizards, tarantulas, and even roadrunners in southwestern Missouri.

But glades are also like islands. To many of the organisms adapted to these sunny, rocky environments, the dark, duffy woodlands that surround them may seem like an oceanic barrier to movement. Dispersal events between glades can be rare. For collared lizards, dispersal is contingent on landscape fire to temporarily make the surrounding woodlands more easily traversable.

Glades are rarely cultivated, but many have been grazed. Cattle degrade glades by eroding and compacting their thin, precious soil. Some glades are also maintained by fire, which keeps woody trees and shrubs from crowding out the forbs and grasses. When people suppress fires, some glades become overrun with trees – especially eastern redcedar (Juniperus virginiana).

Shaw Nature Reserve contains a kind of chronosequence of glade restorations. Near the Maritz Trail House, Crescent and Long Glades were restored in the 1990s by clearing out the encroaching redcedar, establishing a fire regime, and reintroducing forbs and grasses – some of which were sourced from the remnant prairie at Calvary Cemetery in St. Louis. Other glades at Shaw Nature Reserve were restored in the 2000s and 2010s using similar techniques. So it might be possible to study changes in restored glades over time by comparing older restored glades to younger ones.

Could better-conserved dolomite glades serve as a reference to guide restoration at Shaw Nature Reserve? Beautiful dolomite glades are conserved at Valley View Glades Natural Area, Victoria Glades Conservation Area, and Meramec State Park. Some of these have plant species that are missing from Shaw Nature Reserve, possibly because they once existed at Shaw Nature Reserve and were extirpated, or possibly because glades at Shaw Nature Reserve lack appropriate ecological conditions for these plants. For example, prior grazing may have stripped the soil of some vital mycorrhizal fungi. Either way, the lack of some rare plants at Shaw Nature Reserve is probably exacerbated by fragmentation – a remnant plant population at Valley View Glades Natural Area would probably have trouble dispersing seeds 28 kilometers (17 miles) to Shaw Nature Reserve.

Further reading

Nelson P. (2010) Terrestrial Natural Communities of Missouri. 550 pages.

Lines of woody vegetation on dolomite glades correspond to the local stratigraphy; plants like gum bumelia (Sideroxylon lanuginosum) and eastern redbud (Cercis canadensis) accrue on slightly deeper-than-average soils. (Crescent Glade, Shaw Nature Reserve)

In this regularly burned glade at Shaw Nature Reserve, there is a fairly seamless transition between the open glade with abundant Rudbeckia and Silphium and the adjacent oak/hickory woodland. In other places, such glade/woodland transitions are marked by a dense thicket of vegetation, often with a strong component of eastern redbud or eastern redcedar. (Crescent Glade, Shaw Nature Reserve)

Gattinger’s goldenrod (Solidago gattingeri) is an open-panicled goldenrod found on dolomite glades in the northern Ozarks and, disjunctly, in the cedar barrens of central Tennessee. This one was growing just above a transition from dolomite to sandstone substrate on Crescent Glade at Shaw Nature Reserve.

A short-winged meadow katydid (Conocephalus brevipennis) rests on a seed head of Missouri coneflower (Rudbeckia missouriensis). These black seed heads were abundant across Crescent Glade in early October.

Barn glade has been restored much more recently. A line of green, resprouting brush (including invasive Lonicera maackii and Ailanthus altissima) is visible where woody vegetation was recently removed. Blue flags in the foreground mark an experimental population of endangered Pyne’s ground plum (Astragalus bibullatus).

A denizen of barn glade – the lichen grasshopper. (Shaw Nature Reserve)

The quality of Valley View Glades Natural Area is evident in the abundant and diverse fall wildflowers that were present in early October. Could regional dolomite glades like this one serve as references to guide glade restoration at Shaw Nature Reserve?

 

 

Microstegium population distribution (and control) along Brush Creek

Restoration specialist, Mike Saxton, describes his observations on the distribution of invasive Japanese stiltgrass along a creek running through Shaw Nature Reserve.

Brush Creek (blue) runs eastward through Shaw Nature Reserve in Gray Summit, Missouri. Gray Summit Road is in the upper right.

July 28, 2017

Yesterday, Adam and I put in to Brush Creek at the Old Gray Summit Rd. bridge and headed upstream spraying Microstegium vimenium (Japanese stiltgrass). This was the second time through this area this year and I made this sweep solo 3 times last season. My first outing last season, I used 3 gallons of herbicide before I finished the first wetland cell…this year it’s been much, much lighter. Last year, with only 1 person spraying, I was hard pressed to leave the creek bed because there was so much to spray directly along the accessible banks. And in our first outing this season, Catherine and I stayed completely within in the creek, rarely going up on the banks.

However, yesterday Adam and I abandoned the creek bed and went crashing through the brushy banks, finding more Microstegium than I had anticipated. What was interesting was that pockets of stiltgrass followed a predictable pattern of distribution. In many areas, one creek bank will be severely down cut, perhaps 15 ft sheer banks, while the opposite bank is tapered with a more gradual slope. This is where you find the Microstegium. I posit that floodwaters do not over-top the high bank but rush over the lower bank depositing sediment and seed. Almost without fail, the lower bank, if totally brushy, would have scatted Microstegium. However, if the lower bank was open or had open pockets of sunlight, those pockets would be dense thickets of stiltgrass. We observed a nearly 1-to-1 correlation between bank height and stiltgrass presence/absence and open sunlit patches having dense patches of stiltgrass on the lower banks.

I was covering a roughly 20 ft swath out from the bank edge before it dropped into the creek bed.  I did go further from the creek a number of times but wasn’t finding much (if any) the further I got from the creek.

Management considerations

Based on these observations, I believe that our current strategy of managing downstream from the “head waters” is prudent. Based on the diminished population this year and because the species has a 5-year seed viability, we should continue to see diminishing populations if we continue to be methodical and thorough with our management.

We repeatedly found dense patches of Microstegium in high light availability openings/tree fall gaps. This suggests to me that if we open up the brush creek corridor with forestry mowing/brush cutting, the increased light levels and soil disturbance might cause a spike in Microstegium populations.  While the brush creek corridor isn’t priority #1, I know we’ll get there some day. Before we aggressively start clearing brush in this area, I’d like to have 3-5 years of aggressive Microstegium management under our belts. We have observed diminished populations in the wildflower garden, along Paw Paw Creek, and along Brush creek with just one year of management. Coupled this with a short seed viability…and we might have a winning strategy.

 

Large patch of Japanese stiltgrass (Microstegium vimenium) along Brush Creek at Shaw Nature Reserve.

 

 

Soil and vegetation recovery on burn pile scars at Shaw Nature Reserve

Claire Waldman is a senior at Centre College. This summer, she worked with CCSD scientist Matthew Albrecht to study the legacy of burn pile scars – the ashy leftovers from burning thinned tree trunks – in a restored woodland at Shaw Nature Reserve as part of MBG’s NSF-funded Research Experience for Undergraduates (REU) program.

In December 2016, the staff at Shaw Nature Reserve began a major restoration project focusing on 60 acres of woodland that were heavily invaded by bush honeysuckle (Lonicera maackii), Japanese privet (Ligustrum japonicum), and other invasive shrubs. This work, funded by the Institute of Museum and Library Services, commenced with removal of the invasive shrubs and thinning the canopy through selective tree cutting to promote a more open woodland structure. An open canopy structure allows for future use of prescribed burns in the area to help maintain the open canopy and facilitate diverse understory vegetation.

Canopy thinning left land managers with excess woody debris – that is, there were many large, fallen trees covering the forest floor. Rather than use heavy machinery to remove the logs (which often creates a large amount of soil disruption), the wood was stacked into piles and burned. These slash pile burns create an extremely localized but intensive disturbance. The soil at the burn site becomes sterilized and covered in a layer of ash. These sites are referred to as burn scars. The layer of ash that remains, as well as the absence of vegetation, make burn scars easily identifiable.

Slash pile burn at Shaw Nature Reserve, December 2016 (left). Barren sampling plot in a burn scar six months later (right).

Slash pile scars were distributed across the restored site at Shaw Nature Reserve. Previous research has suggested the combustion of biomass and extreme temperatures of the burns can be lethal to the soil seedbank, alter soil structure, moisture, and nutrient availability. The rate of native vegetation recovery on slash pile scars depends on burn intensity, pile area, and properties of the surrounding plant community. The native plant community in burn pile scars, without active seed addition by people, are expected to recover slowly. If the native plant community recovers slowly over time, it raises the concern that slash pile scars could serve as foci for the reestablishment and spread of invasive or undesirable species.

This summer, as part of the NSF-funded Research Experience for Undergraduates program at the Missouri Botanical Garden, I worked under the guidance of Matthew Albrecht to further our understanding of these slash pile burn scars.

First we developed a field experiment focused on native vegetation recovery in slash pile burns. In order to characterize the changes in soil nutrients, compaction, and moisture that occur in these burn piles, we took soil samples from the burn piles as well as adjacent control areas and sent them to the University of Missouri Soil and Plant Testing Laboratory. The results we obtained from this soil analysis were dramatic. Soil pH, P, Ca, Mg, and K were all significantly higher in the burn pile. Soil compaction and soil organic matter were both significantly lower in the burn pile.

Soil chemical properties from samples of the top 4 cm of burn pile and control soil (Albrecht et al. Unpublished data).

While there was an apparent flush of nutrients available in these burn piles, in the first growing season after a burn occurred, we found that burn scars remained essentially bare. We created experimental burn scar plots in which we seeded six native species. The six species sown into the plots were Bromus pubescens (grass), Chasmanthium latifolium (grass), Lespedeza violacea (legume), Senna marilandica (legume), Solidago ulmifolia (composite), and Symphyotrichum drummondii (composite).  We also seeded these species in adjacent unburned control plots. We then monitored plant occupancy in these plots over the course of eight weeks.

Six native plant species seeded into the burn pile scars and adjacent control areas.

We found four of the six species established significantly better in the control plots relative to the burn scar plots. These results support that while there is a significant influx of nutrients in the burn scars, there are other factors that are limiting native species establishment in the burn scars.

Vegetation cover in a burn plot six months after a slash pile burn (left) and an adjacent, unburned control plot (right).

Average percent native vegetation cover (± 1 standard error) in burned plots and unburned control plots (Albrecht et al. Unpublished data).

There are restoration implications of our results. We found, of the six species sowed into the burn plots, native grasses established best. While the microenvironment created by slash pile burns presents a barrier to the restoration of native vegetation in burn pile scars, seed additions of native grasses provide a practical management strategy for promoting native vegetation recovery in burn pile scars.

Average plot occupancy for six native herbaceous plant species in burned plots and unburned control plots. Error bars denote 1 standard error. P-values were derived from a generalized linear mixed effects model. Brpu = Bromus pubescens, Chla = Chasmanthium latifolium, Levi = Lespedeza violacea, Sema = Senna marilandica, Soul = Solidago ulmifolia, Sydr = Symphyotrichum drummondii. (Albrecht et al. Unpublished data).

Claire Waldman recording  plant occupancy in an experimental plot at Shaw Nature Reserve.

Does fire affect Eastern Bluebird nest success at Shaw Nature Reserve?

Joseph Smith is a rising senior at Lake Superior State University. This summer, he studied the effect of prescribed fire on Eastern Bluebird nesting success at Shaw Nature Reserve as part of  MBG’s NSF-funded Research Experience for Undergraduates (REU) program.

Among the rich plant diversity at Shaw Nature Reserve are a wide range of animal species, including the Eastern Bluebird (Sialia sialis). The Nature Reserve is home to an extensive bluebird trail consisting of 86 nest boxes in the north-central region of the reserve. This summer, I have been working with Dr. Leighton Reid and a citizen scientist, Lynn Buchanan, in an effort to understand the effects that land management practices have on bluebird nest success.

Prescribed fire is one of the most important management practices used at Shaw Nature Reserve. In the 2016-2017 burn season, for instance, nature reserve staff set fire to 306 ha (756 acres) of woodlands, prairies, and glades to restore and maintain open vegetation structure and a high diversity of native plants. However, it was unclear what effect these fires might have bluebirds.

Hypothetical effects of prescribed fire on Eastern Bluebird nest success. +/- symbols denote the short-term effect of fire on snakes and arthropods, and the effect of snakes and arthropods on bluebird nest success. Photo credits: (1) Black rat snake (Pantherophis obsoletus) by John Mizel CC BY-NC-SA 2.0, (2) Bluebird eggs by Bailey & Clark (2014); (3) Red-legged grasshopper (Melanoplus femurrubrum) by Gilles Gonthier; (4) Prescribed fire courtesy of Shaw Nature Reserve.

We hypothesized that fire might affect bluebird nesting success in two ways. First, fire could reduce the food supply for nesting birds. When understory vegetation burns, many arthropods are also killed, and it takes some time for their populations to rebound. During the lag, bluebirds might have less to eat, which could result in poorer nest success.

Second, fires could increase nest success by reducing the risk of snake predation. Bluebird boxes at Shaw Nature Reserve are equipped with baffles to prevent snakes from getting in, but snake predation still occurs sometimes. After a fire, there is less vegetation to hide snakes from their own predators, like raptors, and we surmised that fewer snakes could mean more successful bluebird nests.

The Bluebird Trail at Shaw Nature Reserve. Bluebird nest boxes are shown in yellow.

We tested our hypotheses using a long-term dataset collected by volunteers. Over the past eight years, Lynn Buchanan and her team have monitored the nest boxes on the bluebird trail and kept records of their observations. Each week during the breeding season, they peek into all of the boxes and record the number of eggs and nestlings, how many nestlings fledged, and whether or not the nest was predated.

With statistical help from Washington University researcher Joe LaManna, we found that prescribed fire had little or no effect on bluebird nesting. We compared areas that were burned with areas that were mowed, and we also compared burned areas at different time intervals since the most recent fire (0-3 years). Likewise, we found no effect of prescribed fire on the rate of snake predation.

Species	Probability of nest success (%)*	Probability of snake predation (%)*	Did nest success change from 2009-2016?	Did prescribed fire have an effect on nest success?
Eastern Bluebird	90.8 ± 0.5	4.6 ± 0.3	No	No
House Wren	92.1 ± 0.1	4.0 ± 0.3	No	No
Tree Swallow	92.1 ± 0.1	4.8 ± 0.4	No	No

*Standard errors are shown

While the lack of significant results can be slightly disheartening after an entire summer of work, it is reassuring that the bluebird population is thriving at Shaw Nature Reserve. Overall, we calculated that 90.8 ± 0.5% of bluebird nests produced at least one fledgling. In addition, two other species (House Wrens and Tree Swallows) that commonly use bluebird boxes also had high nest success.

There are more aspects of bluebird nesting to look at. For instance, the time from when an egg hatches until the chick leaves the nest could be longer in recently burned areas if there is less food (i.e., arthropods) available. In the meantime it appears the bluebirds are living well at Shaw Nature Reserve.

Eastern Bluebird (left) and bluebird nest box (right) at Shaw Nature Reserve. Photo credits: (L) Bluebird by Andy Reago & Chrissy Mclarren; (R) bluebird nest box by Rachel Weller.

Monitoring Breeding Birds at Shaw Nature Reserve

The best time to start a long-term dataset is 25 years ago. The second-best time is now!

Summer solstice is the height of the bird breeding season at Shaw Nature Reserve. Dozens of species are singing, from Dickcissels in the open prairies, to Prothonotary Warblers in the damp forests along the Meramec River, to near-ubiquitous Blue-gray Gnatcatchers, seemingly everywhere.

 

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For six days this month, two students and I are counting birds systematically across Shaw Nature Reserve to learn how they are influenced by ecological restoration. Birds are a common focus for monitoring restoration projects because they can be observed efficiently over large areas, and because they often respond quickly to changes in ecosystem structure. Ovenbirds, for instance, prefer the dark shade of closed-canopy forests, whereas Kentucky Warblers replace them in woodlands that have been burned (fire is a common restoration strategy in many Missouri ecosystems).

Locations of bird counting stations at Shaw Nature Reserve. Each point is at least 100 meters from the edge of a management unit and at least 200 meters from any other station.

A typical bird survey goes like this:

• 4:20 AM. I pour a travel mug of coffee, pick up a student to help record data, and drive to Shaw Nature Reserve in the dark. There are way too many deer along the side of I-44.
• ~5:00 AM. We arrive at Shaw Nature Reserve in twilight and hear a cacophony of birds singing over one another. Indigo Buntings scatter from the loop road ahead of our car.
• ~5:15 AM. We arrive at the first bird counting station and record the temperature, cloud cover, and wind speed. For five minutes, we write down each bird that we hear or see. Sometimes during these early morning counts, nocturnal birds, like Chuck-will’s-widow, are still calling.
• ~5:30-10:00 AM. After we finish a point, I set my GPS to navigate to the next point on our route and we continue to record birds until mid-morning, by which time it is warm and many birds have stopped singing (although the Red-eyed Vireos are still going strong).

Leighton Reid (left) listens to Wood Thrushes and Northern Parulas while REU student Joseph Smith (Lake Superior State University, right) records data. As indicated by the abundant bush honeysuckle (Lonicera maackii; e.g., by Leighton’s right leg), this particular part of the reserve has yet to be restored.

This is our inaugural bird survey at Shaw Nature Reserve. Unlike many of my projects, this one does not have explicit apriori hypotheses; I’m not trying to “test” anything. Instead, I intend for these data to be used for monitoring and demonstrating progress. Over time, I hope and expect these observations to provide a record of biodiversity change as portions of the reserve are restored and managed.

Counting Common Yellowthroats, Dickcissels, and Red-winged Blackbirds at dawn at the Wetland Mitigation Bank.

For more information on breeding birds at Shaw Nature Reserve, you can explore citizen science observations on eBird, including this printable checklist of birds recorded in June during the past 10 years.

Environmental determinants of plant community change during restoration at Shaw Nature Reserve

Olivia Hajek spent 10 weeks this summer studying woodland restoration at Shaw Nature Reserve with CCSD scientist Leighton Reid. She participated in MBG’s NSF-funded Research Experience for Undergraduates (REU) program.

Wildflowers in the restored Dana Brown Woods: purple milkweed (Asclepias purpurescens; left) and buffalo clover (Trifolium reflexum; right).

During my ten weeks in Missouri, I completed a research project evaluating the role environmental conditions play in restoration at Shaw Nature Reserve.  Specifically, I worked in the Dana Brown Woods management unit, a part of the Missouri Ozark foothills that features diverse plant communities across its heterogeneous landscape.  Sixteen years ago, the Dana Brown Woods was a closed-canopy woodland highly invaded by eastern red cedar.  However, restoration practices including reintroduction of fire and mechanical removal of woody shrubs like eastern red cedar have dramatically changed plant communities since 2000.  I was very fortunate coming into this project because there was extensive data about the plant communities in the Dana Brown Woods from 2001-2012 while restoration was occurring.  A local botanist, Nels Holmberg, monitored understory plants beginning a year before the first fire, creating complete information about the plant community before restoration and as it changed over time.

We wanted to see how different environmental conditions affect how plant communities change over time in response to restoration.  To answer this question, we visited 300 points across the woodland and measured several environmental parameters, including aspect, slope, rockiness, elevation, and juniper stump density (juniper stumps decay slowly, so many of the trees cut in 2006 were still visible).

Fieldwork in Dana Brown Woods. Olivia makes friends with a hog peanut (Amphicarpaea bracteata).

Just from field observations, we could see noticeable differences in the environment and plant community composition across the woodland.  Higher slopes were rockier, covered in old juniper stumps, and rich in sunflowers, whereas the lower regions near the Meramec River floodplain had deeper soil and more mesic plant species, like spicebush.

Data analysis confirmed that environmental gradients moderated plant community change over time. Higher, rockier areas experienced greater plant species turnover and greater increases species richness and abundance from 2001-2012, whereas shaded valleys changed relatively little.

Plant composition change from 2001-2012 increased with elevation, particularly during spring surveys. BC = Bray-Curtis dissimilarity, which measures the difference in plant species composition between a plot in 2001 and itself in 2012. Juniper, red oak, and white oak were subjectively determined habitat classifications at the outset of the study.

Our observations were likely driven by differential fire behavior across the woodland. Historically, fires were a frequent disturbance in the Ozark foothills. Four prescribed fires from 2001-2012 probably had larger impacts on the drier upland areas than in the wet lowlands, which would not have burned as well.

Quantifying how ecological restoration practices, like prescribed fire, vary across environmental gradients is important for land management planning, especially in the Ozark foothills where the landscape is so heterogeneous.

Leighton stood by while Olivia presented her research to the public at Sensational Summer Nights.

Vegetation changes at Shaw Nature Reserve

CCSD scientists Leighton Reid, Matthew Albrecht, and Quinn Long are teaming up with restoration ecologist James Trager and botanist Nels Holmberg to learn how ecological restoration has affected herbaceous plant communities in an eastern Missouri woodland.

What happens to Missouri’s grasses and forbs when you remove invasive shrubs? When you return prescribed fire to a degraded woodland? How do restoration impacts differ for summer-blooming plants and spring ephemerals? For dry hilltops versus mesic hollows? These are a few of the questions that we hope to address with a long-term dataset from Shaw Nature Reserve.

Nels Holmberg (left) and Quinn Long (right) discuss the finer points of blackberry identification at Shaw Nature Reserve.

Shaw Nature Reserve encompasses 10 km² of woodlands and glades along the Meramec River in eastern Missouri. Missouri Botanical Garden purchased the land in 1925 when coal pollution in Saint Louis was so bad that it was killing plants; the garden decided to move its collections to the country where the air was pure. Ultimately the city cleaned up, the collections stayed in Saint Louis’s Tower Grove neighborhood, and the property along the Meramec became a nature reserve and popular hiking area.

Like other ecosystems in the Missouri Ozark foothills, Shaw Nature Reserve changed considerably during the last century. Fire, once a regular disturbance, became scarce, allowing junipers to crowd in on the glades. Invasive species, like Amur honeysuckle, spread into the woodlands and created dense, understory thickets.

Blue wood aster (Symphyotrichum cordifolium) – a late bloomer in the Dana Brown Woods.

Twenty five years ago, Shaw Nature Reserve began to counteract these changes through ecological restoration. Staff and volunteers cleared invasive shrubs and began to periodically burn the landscape.

In 2000, restoration ecologist James Trager and botanist Nels Holmberg designed a study to monitor restoration effects on herbaceous vegetation. Holmberg surveyed 30 transects twice per year from 2000-2012, recording the abundances of more than 360 plant species. Restoration in this area started in 2003, so the first two years of Holmberg’s transects represent a pre-restoration baseline against which we can compare data from the subsequent decade.

Holmberg’s dataset contains more than 50,000 rows. Thanks to Christian Schwarz for digitizing them!

Recently, we plotted Holmberg’s transects on Google Earth. The images show clear changes since restoration began almost 15 years ago.

Holmberg’s transects transposed on a 1995 aerial photo of Shaw Nature Reserve – zoomed in on the Dana Brown Woods. This photo was taken in early spring before most trees leafed out. Dark vegetation is predominantly eastern red cedar (Juniperus virginiana). Holmberg originally grouped the transects into three classes based on the dominant vegetation.

Juniper clearing began in 2006. This is what the summer-time forest looked like the year before…

…and after juniper clearing. By 2006 the Dana Brown Woods had been burned twice with prescribed fires, and a lot of the junipers had been cut out. Compare the open/brown areas in this photo with the solid green canopy in 2005.

The most recent imagery, from October 2014, shows some fall color. Note that “red oak” mostly refers to upland Shumard oak, Quercus shumardii.

Our plan for 2016 is to analyze changes in understory vegetation composition over twelve years. Stay tuned for more information in this ongoing project!