Landscape dynamics and ecological change in the Southern Appalachians

Contacts

Monica Turner

Keywords

COWEETA LTER, historical land use, land-use change, Southern Appalachians

Research Overview

Our studies under the previous grant cycle documented differential responses among native herbs to historical land use and contemporary landscape patterns (Pearson et al. 1998). In the 2002-08 funding period, we extended that work to consider effects of land-use change on forest communities, to explore mechanisms that might explain the distributions of native forest herbs, and to relate distributions of non-native invasive plant species to land-use patterns. A key conclusion of our research to date is that historical land use has had a long-lasting legacy on the vegetation and soils of the Southern Appalachian forests. Using broad-scale analyses of the region, we intersected changes in housing density with the spatial pattern of forest communities, as dictated by the steep environmental gradients, to see whether there was differential risk.  Cove hardwood forest communities were found to be particularly vulnerable to increasing development, as these communities are naturally fragmented and located in sheltered slopes at middle elevations (Turner et al. 2003b). We also delved more deeply into the potential mechanisms that might explain the herb spatial distributions. Many species that were absent or rare in locations that were used historically for agriculture (e.g., bloodroot, bellwort, Trillium) were long-lived perennials dispersed by ants over short distances (< 2 m). We asked whether a lack of dispersers might explain the distribution of these herbs, but results showed that the species of ants required for dispersal were present across the study sites (Mitchell et al. 2002). Thus, lack of dispersers could not explain herb distributions—although dispersal rates would be slow, especially if populations had been locally extirpated and were distant from seed sources.

We focused next on whether soils and growing conditions might be affected by land-use history. Although there were some differences in mean size of nutrient pools with land-use history, there were striking differences in the variance of soil nutrients (Fraterrigo et al. 2005). In previously farmed sites, there was less total variance, and most variance was among plots rather than within plots. In reference sites, total variance was greater, and most variance was within plots (thus at finer scales) not among plots. Thus, it was the spatial structure of soil nutrients that revealed a key land-use legacy. Spatial variation in plant densities were largely driven by soil patterns because detrending the patterns with soil nutrients removed the effects of different land-use histories on the spatial patterns of the herbaceous species (Fraterrigo et al. 2006c). Soil microbial communities were also distinct among land-use histories. Previously farmed sites have less fungi, more Gm- bacteria, whereas reference sites have more fungi (Fraterrigo et al. 2006a). These differences were present even though total microbial biomass and litterfall did not vary. Finally, we found that herbaceous plants exhibit different patterns of growth and biomass allocation at sites with different land use histories.  In references sites where total herb cover is higher, plants allocate more biomass to stems rather than leaves compared to sites previously used for agriculture or logging (Fraterrigo et al. 2006b).  Conversely, there is more allocation to leaves, and less to stems in previously farmed areas (where total herb cover is lower and soil phosphorus is higher). In sum, these studies clearly demonstrated long-term effects of historical land use manifest in soils and forest herbs.

Additionally, support from the LTER program is acknowledged in several general articles that are not tied directly to our empirical studies.  These include a contribution to the special feature about LTER in BioScience (Turner et al. 2003a), an invited annual review article on landscape ecology (Turner 2005a) and a contribution to a special feature in Ecology on landscape ecology in North America (Turner 2005b).

Most recently, we extended our vegetation studies to non-native invasive plants that are shade tolerant and hence have the potential to impact this densely forested region. Our field data revealed that Celastrus orbiculatus (oriental bittersweet, a woody vine native to east Asia) and Microstegium vimineum (Japanese stiltgrass, a shade-adapted C-4 grass) were the invasives that were encountered most freqeuntly. As part of his doctoral dissertation, Tom Albright found that oriental bittersweet was more likely to be found in locations closer to its introduction locus (near Asheville, NC), at lower elevations, with greater forest edge habitat and near roads (Albright 2007). Furthermore, oriental bittersweet appears to be expanding its distribution in the Southern Appalachians. 

Current work

Our studies of non-native species are ongoing. We are currently completing analyses of the regional distribution of Microstegium using data from the Carolina Vegetation Survey in collaboration with Bob Peet of the University of North Carolina; former postdoc Dean Anderson is leading this effort.  Current doctoral student Tim Kuhman completed a 2006 field study of the effects of land-use history on invasive species presence and abundance at the Bent Creek Experimental Forest, for which land-use history is well known and mapped.  These data revealed a very strong positive association between land-use history and invasive species occurrence, along with intriguing differences in both overstory composition and the evergreen understory (which is drastically reduced in areas that were farmed historically). During summer 2007, Kuhman sampled 25 watersheds varying in housing development patterns to determine whether recent exurban development is facilitating the spread of non-native invasive plants.

Read more on Tim Kuhman’s studies…

Future directions

CWT research has focused extensively on understanding the patterns and ecological implications of natural disturbances and land-use changes throughout the Southern Appalachian region. However, potential climate change effects have received less attention.  The steep environmental gradients that characterize the Southern Appalachians provide an outstanding opportunity for studying climate effects on vegetation and how climate and land-use change will interact. During the 2008-2014 funding cycle, we propose research that will contribute to key elements of this interaction, including (1) understanding the effects of projected climate and land-use changes on biodiversity, emphasizing native herbs, non-native invasive forest plants, birds, and forest diseases; and (2) understanding how changes in climate and forest communities will influence ecosystem processes, particularly carbon and nitrogen dynamics, and how these ecosystem processes may feedback to affect the future forest community. 

For the southern Appalachians and Piedmont, projections of land-cover change with global warming indicate strong sensitivity to increasing aridity.  Forests are expected to expand under more moderate scenarios, where moisture stress is less severe, but decline under more extreme climate scenarios. Temperate deciduous forest communities are likely to be replaced by southeast mixed forests in most scenarios, but if moisture is sufficiently limiting, replacement by savanna/woodland may occur. Mammal and bird richness are also predicted to decline in much of the southern US.  Few (if any) studies have been considering understory species, however.  We propose a set of linked studies that evaluate the joint effects of climate and land-use change on native forest herbs, invasive plant species and vertebrates (especially birds). 

Selected Publications

Completed Dissertations

Albright, T. P.  2007.  Invasive plant distributions: lessons from native and exotic ranges.  PhD dissertation, University of Wisconsin, Madison, WI.

Fraterrigo, J. M.  2005.  Influence of land-use change on the long-term persistence of forest underestory herbs in the southern Appalachian highlands.  PhD dissertation, University of Wisconsin, Madison, WI.

Journal articles

Fraterrigo, J. M., M. G. Turner, S. M. Pearson, and P. Dixon.  2005.  Effects of past land use on spatial heterogeneity of soil nutrients in Southern Appalachian forests.  Ecological Monographs 75:215-230.

Fraterrigo, J. M., T. C. Balser and M. G. Turner. 2006a. Microbial community variation and its relationship with nitrogen mineralization in historically altered forests. Ecology 87:570-579.

Fraterrigo, J. M., M. G. Turner and S. M. Pearson.  2006b.  Plant allocation and growth in the herb layer of historically altered forests.  Journal of Ecology 94:548-557.

Fraterrigo, J. M., M. G. Turner and S. M. Pearson.  2006c. Interactions between past land use, life-history traits and understory spatial heterogeneity.  Landscape Ecology 21:777-790.

Hicks, N. G. and S. M. Pearson.  2003.  Salamander diversity and abundance in forests with alternative land-use histories in the southern Blue Ridge Mountains.  Forest Ecology and Management 177:117-130.

Mitchell, C. E., M. G. Turner and S. M. Pearson. 2002. Effects of historical land use and forest patch size on myrmecochores and ant communities. Ecological Applications 12:1364-1377.

Pearson, S. M., A. B. Smith, and M. G. Turner.  1998.  Forest fragmentation, land use, and cove-forest herbs in the French Broad River Basin.  Castanea 63:382-395.

Turner, M. G. 2005a. Landscape ecology: what is the state of the science?  Annual Review of Ecology, Evolution and Systematics 36:319-344.

Turner, M. G. 2005b. Landscape ecology in North America: past, present and future. Ecology 86:1967-1974.

Turner, M. G., S. Collins, A. Lugo, J. Magnuson, S. Rupp and F. Swanson.  2003a. Long-term ecological research on disturbance and ecological response. BioScience 53:46-56.

Turner, M. G., S. M. Pearson, P. Bolstad and D. N. Wear. 2003b.  Effects of land-cover change on spatial pattern of forest communities in the southern Appalachian Mountains (USA). Landscape Ecology 18:449-464.