A ten-year woodland restoration trajectory

Leighton Reid describes a long-term ecological research project at Shaw Nature Reserve (Franklin County, Missouri, USA). To learn more, read the new research paper (email the author for a pdf copy – jlreid@vt.edu) or tune in for a webinar from the Natural Areas Association on April 21 (register here).

In 2000, the Dana Brown Woods were dark and dense. Brown oak leaves and juniper needles covered the sparsely vegetated ground, and invasive honeysuckle was creeping in around the edges. Biologically, the woodland was getting dormant.

In contrast, the woods today are lit by sunlight everywhere except the lowest-lying streambanks, and the ground is hardly visible beneath a green layer of diverse, ground-level foliage. These changes were most likely caused by two actions: burning the woods, and cutting out invasive trees and shrubs.

Many practitioners have seen woodlands recover to some extent when they are burned, but few have documented the recovery as thoroughly and over so long a period of time as Nels Holmberg and James Trager.

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Nels Holmberg (left) discussing the finer points of Rubus identification with Quinn Long in the Dana Brown Woods.

Nels is an ecologist and sheep farmer in Washington, Missouri. He has inventoried the plants at several state parks and natural areas. In 2000, Nels teamed up with Shaw Nature Reserve’s resident natural historian, James Trager, and together they designed a study to describe how ecological restoration was changing the woodland flora at the reserve. They picked the Dana Brown Woods as their study area.

In a nutshell, Nels and James chose 30 random points on a map. They divided the points evenly across three ecological communities. They placed 10 points in mesic woodlands – the gently sloping parts of the property where white oak and shagbark hickory were most prevalent. Ten points were in areas dominated by eastern red cedar – mostly thin-soiled ridgetops that faced the south, and ten points were in forest – the lower, thicker-soiled toe slopes where northern red oak and Shumard oak were dominant in the canopy with paw paws and spicebush down below.

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Three ecological communities in the Dana Brown Woods: (A) red cedar dominated areas which, after removing red cedar, looked more like dolomite glades in some parts; (B) mesic woodlands with lots of oak and hickory in the canopy; and (C) forest – which had a much darker understory.

At each point, Nels hammered in a t-post, then walked 50 m in the steepest direction and hammered in another t-post. This was his transect. Every year for more than a decade (2000-2012), Nels walked the transects and recorded every stem of every species that was inside of 10 0.5-m2 study plots. Actually, he did this twice per year – once in the spring to capture the ephemeral plants, and once in early summer. Over the course of the study he spent more than 200 days in the field.

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Dana Brown Woods before (left) and after (right) red cedar removal, with Nels’s 30 transects. The horizontal axis of the image is about 0.9 km. Imagery is from Google Earth.

During this time the stewards at Shaw Nature Reserve were busy restoring the woods. From 2001-2012, they burned the woods five times. This amounted to about one fire every three years. In 2005-2006, they brought in a logging crew to remove all of the eastern red cedars.

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James Trager lights a fire in a woodland at Shaw Nature Reserve.

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One of several thousand red cedar stumps from trees that were harvested from the Dana Brown Woods in 2005-2006.

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One of Nels’s sampling quadrats in the Dana Brown Woods. Photo: Nels Holmberg.

I met Nels and James in 2014. I had just joined Missouri Botanical Garden’s Center for Conservation and Sustainable Development as a postdoc, and I was looking for a local research project. I heard that Nels Holmberg had a giant dataset about woodland restoration, so I called him and asked if I could look at it. Nels said “Sure!”. I imagined he would send me an Excel file. Instead he brought in a giant cardboard box full of yellow legal pads where he had recorded his data.

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One of hundreds of datasheets where Nels recorded his detailed observations.

It took a long time to digitize all of the data. There were more than 50,000 data points. But once we had it all together, this is what we learned:

After eleven years of restoration, the number of native plant species in Dana Brown Woods increased by 35%, from 155 species in 2001 to 210 species in 2012. This increase was linear. That is, the number of native species was still increasing at the end of the study. If we repeated the study today, we expect the number of native species would be even greater than in 2012.

The number of native species increased at different speeds and to different degrees in different ecological communities. In the lower and wetter forest areas, the numbers didn’t really shift very much. They jumped around but not in one direction. In the woodland areas, the number of native species increased by about 23% in the first three years and then leveled out. But in the higher and drier areas where red cedars had been dominant, the number of plants increased linearly by 36%.

Native Species Richness

Changes in the number of native plant species recorded over time in the Dana Brown Woods. On the left are overall changes for the whole management unit. On the right are changes for different ecological communities within the management unit. The management interventions are shown in gray.

The plant species that benefited from the restoration were mostly forbs and grasses. A couple of the biggest “winners” were black snakeroot (Sanicula odorata) and nodding fescue (Festuca subverticillata). There were also some “losers”: Virginia creeper (Parthenocissus quenquefolia) and spring beauty (Claytonia virginica) both declined over time. Relatively few of the species that became more common were “conservative” – i.e., dependent on intact habitat. Mostly they were more widespread and tolerant species.

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Co-author Olivia Hajek demonstrates a hog peanut (Amphicarpaea bracteata) – a good representative of the type of species that benefited most from the restoration. Hog peanut is an herbaceous legume that is common in many woodlands, including disturbed ones.

Our study did not include a control treatment, but counterfactuals exist at Shaw Nature Reserve (although they are becoming fewer and fewer with the excellent stewardship of Mike Saxton and many others). There are still thick patches of eastern red cedar covering remnant glades on parts of the property. Woodlands that have not been regularly burned are now filled with bush honeysuckle (Lonicera maackii), wintercreeper (Euonymus fortunei), and other invaders. And low-lying forest that has not been restored is very dark with fire-intolerant sugar maple (Acer saccharum) casting much of the shade. If we had included a control treatment in our experiment, these are probably the trends we would have found – definitely not a spontaneous resurgence of diverse native plants.

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Fragrant sumac (Rhus aromatica) was present at the outset of restoration and remained relatively stable.

Why does this work matter? The biggest value of this study is that it shows a relatively long-term restoration trajectory, and it does so in fine botanical detail. Many managers and scientists already have data to show that fire and tree thinning increase woodland plant diversity. This study adds another dimension. It shows how quickly plant diversity recovered. It also shows how the speed and shape of the recovery varied across the landscape. We hope that other scientists and practitioners will compare the recovery trajectories in the Dana Brown Woods to their own natural areas. To facilitate that, we have made all of the underlying data freely available online.

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Buffalo clover (Trifolium reflexum) is a conservative species that is present in Dana Brown Woods but was not detected in any of the survey plots.

One of the next steps for this research is to figure out how and when to re-introduce some more conservative plants. Although the Dana Brown Woods became much more diverse as it was being restored, most of the plants were early successional or generalist species. We found very few habitat specialists that cannot tolerate disturbance, which suggested to us that some of these species may have been lost from the site at some time in the past. To learn how conservative plants might be re-introduced, we have started a new experiment testing the effects of soil microbes, competition, and time since the start of restoration on the success of introduced seedlings from seven conservative plant species. In the next year or two, we hope to have new information and recommendations for restorationists looking to add more specialized biodiversity to their woodlands.

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Freemont’s leather flower (Clematis fremontii) is a restricted species occurring on dolomite glades in southeastern Missouri. Although it is present at Shaw Nature Reserve less than one kilometer from Dana Brown Woods, it has not colonized the restored glade habitats there. This photo is from Valley View Glade near Hillsboro, Missouri.

To learn more about this research, you can read the original research paper in Natural Areas Journal. Email me for a pdf copy (jlreid@vt.edu). You can also tune in on April 21 for a webinar on this work. Register here.

Cove forests on the southern Cumberland Plateau are losing trees

Rich, cove forests are losing tree species faster than sandy, upland forest, according to long-term research in Sewanee, Tennessee led by Jon Evans (University of the South), Callie Oldfield (University of Georgia), and Leighton Reid (Virginia Tech).

The southern Cumberland Plateau in Sewanee, Tennessee is a ribbon of stacked limestone and sandstone rising above the valley by some 275 m, about four-fifths the height of the Eiffel Tower. From above, the plateau’s forests stand out dark green against the surrounding farmlands and give the impression of a large, homogeneous block of habitat.

The reality is somewhat different. The forests of the southern Cumberland Plateau are botanically distinct, and they are changing differentially over time.

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The southern Cumberland Plateau near the borders of Tennessee, Alabama, and Georgia. Imagery © Google Earth 2019.

The plateau’s sandstone cap is dry and craggy. Blueberries thrive in acidic soil under a canopy of oaks and hickories. Where the soil is especially shallow, the forest opens up onto exposed outcrops with fence lizards and prickly pear cacti. Just a stone’s throw away, the cove forests are a world apart. Wet and calcareous, the plateau’s deep, dark coves are famous for limestone caves and ephemeral wildflowers. Even though they are close neighbors, the two dominant forest communities of this region share less than 25% of their plant species.

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Upland forest on the top of the Cumberland Plateau, underlain by the sandstone. Photo by Jon Evans.

As part of a long-term forest change study, in 2014 we surveyed tree communities in upland and cove forests that had been previously surveyed in 1995 and 2005. Our results, published in the Natural Areas Journal, showed that upland forests maintained the same suite of tree species in roughly the same numbers, but cove forests became considerably less diverse. For example, we detected nine fewer tree species in the plots in 2014 compared to 1995. Understory trees were hardest hit – less than 1/3 of the species that were present in 1995 were still represented in the understory in 2014.

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Cove forest in Thumping Dick Hollow, underlain by limestone. Photo by Jon Evans.

Being neighbors, upland and cove forests have been subjected to similar disturbances over the past few decades. For example, both forests have comparable exposure to wind storms, pathogens, and herbivores – particularly deer. White-tailed deer have become overpopulated due to the loss of their natural predators, and few tree seedlings escape their browsing. We have seen PVC plot markers chewed to the ground by ravenous deer. Our observations suggest that cove forest tree species are less resistant to these disturbances than their upland counterparts.

We speculate that some trees on the sandy uplands might be pre-adapted to the new deer browsing regime. Several upland tree species are clonal. For example, sassafras, sourwood, and chestnut oak trees can share resources with smaller seedlings that sprout from their bases or roots. The parental subsidy might help these species maintain their populations in the droughty, acidic upland soils of the Cumberland Plateau. It could also help seedlings keep growing after they have been munched by a deer.

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Sassafras (Sassafras albidum) is a clonal tree species common in upland forests on the Cumberland Plateau. Photo by Callie Oldfield.

Clonal species are less common in the cove forest. There the dominant trees like sugar maple and tulip poplar typically reproduce via seeds. Paw paw is one of the few clonal species that grows in the cove forest, and it is also one of the few species that increased in abundance there from 1995-2014.

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Leighton Reid (left) and Callie Oldfield (right) survey tree communities on the southern Cumberland Plateau in 2005 and 2014, respectively. Photos by Jon Evans.

The southern Cumberland Plateau is regarded by some conservation groups as a resilient southeastern landscape, and indeed its variable topography and large extents of natural habitat may help many species resist or respond to new environmental challenges. However, our research highlights that the two dominant tree communities of the southern Cumberland Plateau respond to disturbances differently and may have a limited capacity to buffer one another from ongoing change.

 

For more information, see our new paper in Natural Areas Journal. To request a pdf, email jon.evans@sewanee.edu.

It’s Complicated: Trees and Ecological Restoration

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The best time to plant a tree was twenty years ago. The second best time is now.
-Anonymous

Addendum: That is, unless the tree will grow just fine without your help or the tree doesn’t really belong there. In that case, the best time might be never.

Planting a tree is rejuvenating. It gets you outside, it’s good exercise, and it’s often good for the planet. Really, trees give us an awful lot and don’t ask for much in return. Among their many gifts are food, shade, animal habitat, building materials, erosion control, and fuel. Trees also filter our water and suck carbon out of the air. In cities, trees collect grit and grime that would otherwise coat our lungs.

But tree planting is not the same as restoration. Ecological restoration is the process of assisting the recovery of a damaged ecosystem. Trees are integral to many ecosystems, like forests…

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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.

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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)

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.

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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.

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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.

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

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…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.

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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!

Endemic Flora in the Ouachita Mountains

Some 300 million years ago, the South American plate collided with the North American continental crust. The resultant buckling formed the dramatic topography of the Ouachita Mountains, which extend from southwestern Arkansas into eastern Oklahoma, defining the southern extent of the Interior Highlands of mid-continental North America.

The fold belt topography of the Ouachita Mountains

The fold belt topography of the Ouachita Mountains

Although the Ozark region, which forms the northern portion of the Interior Highlands, has received more attention in terms of both scientific literature and public familiarity, the Ouachita Mountains have a larger number of endemic plant taxa. In total, fourteen endemic plant taxa have been documented from the Ouachita Mountains, several of which have only been described in recent decades. As a member of the Center for Plant Conservation network of botanical gardens, we work to conserve imperiled plant species in the southeastern United States through seedbanking, reintroduction, and research to better understand the ecology and life history of these species. This research ranges from experiments to understand the ecological conditions necessary to break dormancy and induce germination, to field experiments that aim to provide guidance for ecological restoration and management of the communities and ecosystems in which these taxa occur.

Scenic vista in the southern Ouachita Mountains

Scenic vista in the southern Ouachita Mountains

Ouachita mountain goldenrod (Solidago ouachitensis) is one of the rare and endemic taxa which we are working to conserve in this region. Recently, during the week of November 17th-21st, Matthew Albrecht and I traveled to the Ouachita Mountains to collect seed of S. ouachitensis. A minor snowfall preceded our arrival, bringing with it unseasonably low temperatures. The snow remained for several days on north facing slopes, which increased both the scenic beauty of the region and the difficulty of traversing steep terrain.

Collecting seed of Solidago ouachitensis with a light dusting of snow

Collecting seed of Solidago ouachitensis with a light dusting of snow

The trip was perfectly timed to coincide with the peak of seed maturation, which made for a successful collection effort. Solidago ouachitensis occurs predominantly in two distinct habitat types – mesic oak dominated forest near the summit of slopes and also mixed hardwood forest of riparian toe slopes. Several populations occur along the Talimena National Scenic Byway, where the ridge tops are dominated by a dwarf forest comprised of a near continuous canopy of gnarled, windswept white oak. Solidago ouachitensis occurs on several north-facing aspects down slope from these dwarf forest. Populations vary greatly in size, from no more than several individuals up to thousands of individuals. It appears that the most robust populations (in terms of total population size, the proportion of the population producing seed, and the reproductive output of individual plants) occur in areas with evidence of recent fire. Prescribed fire is used as a management tool in the Ouachita National Forest, which appears to be beneficial for Solidago ouachitensis. To further explore this, we’re initiating experiments to examine whether chemical compounds in smoke enhance germination.

– Quinn Long

Solidago ouachitensis with mature seed. A charred log in the background provides evidence of recent fire.

Solidago ouachitensis with mature seed. A charred log in the background provides evidence of recent fire.