Drivers of epiphyte recovery in secondary forests in southeastern Brazil

Alex Fernando Mendes is an undergraduate researcher in the Tropical Silviculture Lab at the University of São Paulo, Brazil. He describes his thesis project, undertaken in dozens of forest fragments in the endangered Atlantic Forest biome. Currently, Alex is analyzing his data as a visiting researcher in the Center for Conservation and Sustainable Development.

Historically, intensive agriculture in the Brazilian Atlantic Forest has caused large-scale deforestation of this biome. However, new legal requirements, land exhaustion, and the shifting priorities of farmers have recently allowed forests to regenerate on some formerly farmed lands. Given the unique nature of the Atlantic Forest, its high species endemism, and its potential for providing ecosystem services, the Tropical Silviculture Lab (LASTROP) at the University of São Paulo, coordinated by Prof. Pedro Brancalion and its partners, initiated a project in 2014 to better understand the structure and composition of these new forests.

However, forests aren’t made solely of trees. Among the plant components of a forest, there are others life forms such as epiphytes, lianas, and herbs that contribute to biodiversity and provide food, water, and shelter for many animal species. Epiphytes are plants that use other plants as support. Due to their sensitivity to environmental changes, epiphytes can be used as bioindicators. Therefore, we asked how these plants are doing in these young regenerating forests. And what landscape and local attributes facilitate or hinder their recolonization?

image1.jpg

Epiphyte species found in second-growth forests of the Atlantic Forest – A) Philodendron bipinnatifidum Schott; B) Lepismium houlletianum (Lem.) Barthlott.; C) Ionopsis utricularioides (Sw.) Lindl.; D) Catasetum fimbriatum (E. Morren) Lindl. & Paxton; E) Aechmea bromeliifolia (Rudge) Baker; F) Billbergia sp.

 

To try to answer these questions, we are studying the epiphyte communities in 40 second-growth forests (i.e., forests that were once completely cut down). We are considering three landscape drivers (distance from watercourses, distance from forest edge and forest cover in a 1-km buffer around the remnant) and four local drivers (previous land use, forest age, liana abundance, and tree basal area). We expect that forests close to watercourses would provide the moisture required by epiphytes. We expect to find more epiphytes further from the forest edge since forest cover in more conserved forests may limit their establishment. Since our forests regenerated from abandoned eucalyptus plantation and pastures, we want to check if the non-native eucalyptus could act as a filter preventing epiphytes recolonization. We also expect that older forests and forests with more basal area could house more epiphytes than young forests. Finally, field observations made us wonder if lianas could compete with epiphytes by occupying the same niche.

Of the more than 6,000 phorophytes (trees that could support epiphytes) sampled in these 40 forests we found 398 epiphytes belonging to 21 morphospecies distributed in 4 families (Araceae – 1 species, Bromeliaceae – 14 species, Cactaceae – 5 species, Orchidaceae – 5 species). Only three species, Tillandsia pohliana, Tillandsia tricholepis, and Ionopsis utricularioides, represented more than half (59.5%) of all epiphytes found in second-growth forests. The genus Tillandsia was expected to be abundant in these young forests, since these are disturbance-adapted species that can even be found growing on power lines in cities.

Image2

Epiphytes of the genus Tillandsia (Bromeliaceae) are often found in extreme microenvironments in urban areas (Photos by A. Mendes, 2017).

Our analysis is in progress, but our preliminary observations suggest that forests closer to watercourses and closer to forest edge are more likely to have epiphyte recolonization than forests far from edge and watercourses. Forests regenerated on pastures have more epiphytes than those on abandoned eucalyptus plantation. Our dataset will soon be upgraded with new forest types: conserved and disturbed old-growth forests, and mixed tree plantings for forest restoration, totaling approximately 70 forests with epiphyte samples.

With this research, we hope to find out the local and landscape factors that contribute to epiphyte recolonization in second-growth forests. In practice, this will allow us to locate sites with limited potential for spontaneous colonization of this life form to take actions that promote colonization and establishment, such as introducing individuals. Finally, by identifying epiphytes species that are more sensitive to disturbance, we can focus our reintroduction interventions.

Landscape

Small, remnant forests are surrounded by cattle pastures in southern Brazil.

Note: The image of Philodendron bipinnatifidum featured at the top of this post was taken by David Stang. 

Advertisements

Homemade mycorrhizal inoculum improves seedling growth for some native Malagasy trees

MBG Madagascar’s Chris Birkinshaw and Dinasoa Tahirinirainy describe exciting, preliminary results from a forest restoration experiment in highland Madagascar.

 

Ankafobe Forest on Malagasy highlands - experiment located on grassy ridges

This sliver of riparian forest is one of the last vestiges of Madagascar’s highland forests. Decades of Missouri Botanical Garden research in Madagascar have shown that more than 80% of all plant species on the island exist nowhere else. Many are threatened with extinction due to habitat loss. Several previous posts have described forest restoration efforts at this site, home to the largest population of the endemic sohisika tree (Schizolaena tampoketsana) – a species that belongs to a family (Sarcolanaceae) that only exists on Madagascar.

A small number of forest restoration projects in Madagascar routinely inoculate the tree seedlings in their nurseries with a homemade mycorrhizal inoculum. While the nurserymen are convinced that this technique promotes growth and survival of tree seedlings, there seems to be no published data objectively demonstrating these positive outcomes. In an effort to provide the evidence to justify investment in this technique, we designed a simple experiment that will compare the survival and growth under four treatments of young plants of six native trees planted in grassland adjacent to the Ankafobe Forest on the central Malagasy highlands.

Table – Four experimental treatments to test the effects of mulch and mycorrhizal inoculum on native tree seedling growth in highland Madagascar

  Inoculated Not inoculated
Mulched Treatment 1 Treatment 2
Not mulched Treatment 3 Treatment 4 (control)

In our experiment, fifteen seedlings of each of six native tree species will be grown under each of the four treatments listed above. The mycorrhizal inoculum was made by filling a pit (150 cm long × 50 cm wide × 30 cm deep) lined with sacks with topsoil collected from around the roots of three native tree species, then growing maize and beans in this soil for three months before cutting these plants down and letting the substrate dry out for two weeks. The substrate remaining in the pit is the inoculum and was used by adding one tablespoon to each seedling container.

Making the inoculum

Beans and maize are grown in topsoil collected from a remnant forest to amplify local mycorrhizae populations. This enriched soil (i.e., inoculum) is then added to seedling containers.

The tree seedlings that received mycorrhizal enrichment were inoculated in November 2017, and all of the seedlings were otherwise grown under the same conditions in the nursery until January 2018 when they were planted out into an experimental plot at Ankafobe. Half of the tree seedlings were surrounded by a thick layer of grass-based mulch (~30-cm deep). The comparison of seedling performance with and without the addition of mulch is interesting because of the possibility that mulch helps to maintain a relatively cool and moist environment in which the mycorrhizae can flourish.

Table – Mean difference in tree seedling height (cm) between seedlings inoculated versus not inoculated with homemade mycorrhizae, after two months in the nursery (N = 30 seedlings per species).

Species Inoculated seedling height Non-inoculated seedling height t p1
Aphloia theiformis 29.5 ± 10.2 33.4 ± 6.5 -1.75 1.0000
Baronia tarantana 18.1 ± 6.1 11.4 ± 3.5 5.21 <0.0001
Brachylaena ramiflora 27.2 ± 6.0 31.8 ± 6.5 -2.87 1.0000
Craspidospermum verticillatum 43.0 ± 5.9 42.6 ± 3.7 0.37 1.0000
Macaranga alnifolia 34.8 ± 8.6 39.2 ± 5.2 -2.43 1.0000
Uapaca densifolia 23.0 ± 7.9 11.5 ± 2.6 7.58 <0.0001

1 t and p values are from a one-tailed student’s t-test asking whether inoculated seedling height was greater than non-inoculated seedling height. P values are adjusted for multiple comparisons with Bonferroni correction.

Although we plan to measure seedling survival and growth 12 months from the time when they were planted (i.e., in January 2019), we were interested to see that for two of the species the height of inoculated seedlings was significantly greater than the height of non-inoculated seedlings after a mere two months in the nursery. On average, inoculated seedlings of Baronia tarantana are 1.6× taller than non-inoculated seedlings; while the seedlings of Uapaca densifolia are a full 2× taller. For the other species there was no significant difference between the height of the inoculated and non-inoculated plants.

Experiment showing line of seedlings some with and some without mulch (1)

Tree seedlings are planted out in a field experiment at Ankafobe in January 2018. These seedlings are planted adjacent to a line of “green manure” (i.e., nitrogen-fixing Tephrosia shrubs planted to improve the degraded highland soil prior to planting native tree seedlings).

 

What happened to the Bahama Nuthatch?

On January 6-10, CCSD scientist Leighton Reid joined Bert Harris, Kelly Farrell, and David Wilcove on a search for what has become one of the rarest bird species in the western hemisphere.

Maker:L,Date:2017-8-24,Ver:5,Lens:Kan03,Act:Kan02,E-ve

Grand Bahama Island, only known home of the Bahama Nuthatch.

The Bahama Nuthatch (Sitta insularis) is or was a bird found nowhere except on Grand Bahama Island, a thin, 153-km long piece of weathered limestone lying 84 km east of Palm Beach, Florida.

 

The Bahama Nuthatch differs from a widespread southeastern US species, the Brown-headed Nuthatch (S. pusilla) in having a longer bill and a distinctive, high-pitched warbling call. It is a denizen of the Caribbean pine (Pinus caribaea) forests that cover about 60,000 ha of Grand Bahama Island. Perhaps always rare, the species was a lot more common in the 1960s than 30 years later in the early 1990s. Ten years ago, a nearly island-wide survey found only 14 individuals in a single tract of forest east of Freeport, the island’s largest settlement. A local nature guide, Erika Gates, regularly found one to three individuals of the species in this area through June 2016, but in early October 2016, Hurricane Matthew (Category 5) blew across the island, causing significant damage. The Bahama Nuthatch has not been detected since June 2016 despite Ms. Gates and others searching in its previous locations. It is considered “endangered” by the IUCN.

Maker:L,Date:2017-8-24,Ver:5,Lens:Kan03,Act:Kan02,E-ve

A postage stamp sheet commemorating the Bahama Nuthatch (Sitta insularis), an extremely rare species known only from a single island in the Bahamas.

Maker:L,Date:2017-8-24,Ver:5,Lens:Kan03,Act:Kan02,E-ve

Bert Harris plays the distinctive warbling call of the Bahama Nuthatch through a speaker into a very quiet Caribbean pine forest.

For six days in early January, four of us intensively searched the area around the two most recent sightings, the ones from May and June 2016. We focused on the core area at first and gradually expanded outwards as it became clear that we were finding no individuals at the former sites. We estimated that we searched an area of roughly 4600 hectares of pine forest over a period of 26 hours (88 person-hours). We travelled approximately 92 km of roads and trails, both driving and walking. Many of these were old logging roads, which crisscross the entire island. While driving, we stopped every 0.4 km (0.25 mi) and played a recording of the nuthatch’s distinctive call. While walking, we played the call more frequently.

We did not find any Bahama Nuthatches. We think that our group, the first to search for multiple days for this species since 2016, was also the first to fail to find it. Perhaps the species’ conservation status should be changed from endangered to critically endangered. Ideally, some Bahamian ornithologist will be able to survey again for the species during the coming breeding season, and if the species is rediscovered, its remaining habitat will be protected, restored, and expanded.

This slideshow requires JavaScript.

In addition to the Bahama Nuthatch, we noted that several birds which breed exclusively in the pine forests were also very rare or absent. Bahama Yellowthroats (Geothlypis rostrata), Bahama Warblers (Setophaga flavescens), and Olive-capped Warblers (S. pityophila) were relatively abundant during surveys in 1968 and 2007, but Bahama Yellowthroats were totally absent from our search, and we found only a handful of Bahama Warblers and Olive-capped Warblers, making them even rarer in our survey than the nuthatch was in 2007 (though we searched during some relatively cold weather and during the non-breeding season). We also failed to detect a single Bahama Swallow (Tachycineta cyaneoviridis). Looking through historical records on eBird we noted that the West Indian Woodpecker (Melanerpes superciliaris) was formerly abundant across the island but has not been recently seen.

The causes of decline for the Bahama Nuthatch and perhaps for other breeding birds of the pine forests are mysterious. Grand Bahama Island has been extensively logged, initially for large diameter timber (prior to 1900) and later (1940s-1970s) for pulpwood. The expansion of the city of Freeport and tree-killing inundation by seawater over large areas have both reduced the potential habitat area. Feral cats, introduced raccoons, and corn snakes introduced in the 1990s could be predating native birds. We saw at least nine raccoons during our short time on Grand Bahama. Altered fire frequency and the increased frequency of Atlantic hurricanes may also be impacting the species, possibly by removing snags that are required for nesting.

Erika_Nuthatch3Bus

As recently as 2011, 65 Caribbean ornithologists were able to view the Bahama Nuthatch simultaneously and within three meters of a tour van. Photo by Erika Gates.

Native tree rehabilitation in Costa Rica’s biggest urban park

During a recent trip to Costa Rica, CCSD scientist Leighton Reid toured La Sabana, Costa Rica’s largest urban park, with Wilmar Ovares, an instructor at the Universidad Estadal a Distancia who has been studying the recovery of bird diversity following large-scale replacement of exotic trees with native ones.

The first time I visited La Sabana Metropolitan Park in downtown San Jose was in 2005. At that time it was essentially a eucalyptus woodland; the tall trees with peeling bark stretched upwards above the soccer fields and hiking trails. No longer. La Sabana has gotten a makeover in the last few years – and for the better.

20171209_103908 (1)

The old La Sabana (exotic eucalyptus trees in background – slated for removal in the near future) and the new (native trees and a eucalyptus stump in the foreground). The tree at right (unidentified species; Solanaceae) is a natural recruit, dispersed to the site by a bird or a bat. The slightly curved tree at center-right has died, but it can still serve as a bird perch and might facilitate the dispersal and establishment of a new, native tree in its place.

The project was initiated as a collaboration between three institutions: the National Biodiversity Institute (INBio), the National Sports and Recreation Institute (ICODER), and Scotiabank. Beginning in 2010, this collaborative removed most of the exotic trees in La Sabana and replaced them with more than 5000 native trees, representing 234 species. Not all of the species are native to the central valley, but all are native to the country.

Although the planted trees are still quite small, one short-term indicator of project success is the recovery of bird diversity in the park. On my first visits to La Sabana prior to 2010, the birding was slow, with occasional excitement when I would stumble on a eucalypt in flower – abuzz with warblers, orioles, and hummingbirds. Now, Wilmar Ovares finds that the number of bird species has increased by more than a third. Many of the new species are migrants, which breed in North America and winter in Central America. Others have drifted in from nearby riparian forests along the Rio Torres and the Rio Maria Aguilar. In some cases, birds and other animals have carried in and deposited native tree seeds, complementing the plantings.

20171209_104803 (1)

Vainillo (Tecoma stans, Bignoniaceae), a beautiful, native addition to La Sabana.

20171209_105009 (1)

This Annona cherimola (Annonaceae) recruited on its own at this site in La Sabana. Its large seed may have been dispersed by a bird, a squirrel, a raccoon, or even a human. The source of the seed may have been the Rio Torres, which flows through a riparian forest not far from the park. This tree species is a conservation priority species in the Central Valley.

To be clear, this project is not strictly ecological restoration; below the new trees is a manicured lawn, and it is likely to remain that way for some time. The work is better classified as rehabilitation – a return of some elements of the local biodiversity, but by no means all of it. This approach is sensible given that the park is a resource for human recreation – not just a habitat for plants and animals. Still, if the park administration wished to go further, they could consider introducing some native, understory shrubs, ground-layer plants, and epiphytes, all of which would enhance bird diversity and enrich the experience of visitors.

JicaroMosaic

Jicaro (Crescentia alata, Bignoniaceae) is a champion of forest restoration efforts in Guanacaste, and it looks good in La Sabana as well. The large flowers are pollinated by nectar-eating bats, and the fruits are used by some indigenous people as water canteens.

BarbadosCherryMosaic

Acerola (Malpighia glabra, Malpighiaceae) in a recent planting in La Sabana. This tree/shrub produces edible fruits, which are not very sweet. (Thanks to Amy Pool for correcting a previous misidentification!)

20171209_111359 (1)

The last vestiges of the old La Sabana. This area near the stadium is dominated by eucalyptus (from Australia) and Cupressus lusitanica (from Mexico and northern Central America). Wilmar Ovares finds a lower diversity of bird species in these exotic tree groves, despite their much greater stature. Though it cannot be denied that when the eucalyptus are flowering, warblers, orioles, hummingbirds and others may be found in large numbers feeding on the nectar and nectar-eating insects.

20171209_104456 (1)

Wilmar Ovares has been monitoring changes in the bird community in La Sabana as a result of the native tree rehabilitation.

 

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.

CrescentGladeSoilLine

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)

20171002_124035

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)

SpecialGoldenrodCrescentGlade

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.

KatydidCrescentGlade

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.

BarnGlade

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).

LichenGrasshopper

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

ValleyViewOverlook

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.

Map_Mike

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.

 

JSG-min

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.

BurnPileMontage

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.

SoilProperties

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.

SpeciesII

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.

BareGroundReVeg

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

PercentPlantCov

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.

PlotOccupancy

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

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