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Using High-Quality Vegetation Plot Datasets to Restore Ecosystems: An Example from the Coastal Plain of the Southeastern United States M. Forbes 1 Boyle , Robert K. 1 Peet , and Thomas R. 2 Wentworth 1 University of North Carolina, Dept. of Biology; 2 North Carolina State University, Dept. of Plant Biology Abstract Introduction The success of restoration efforts is typically based on the successional trajectory of a site to its predefined target condition. Varying processes can determine the target condition, but a poor description of the target within the region of study may ultimately hinder the restoration effort. Reference sites of undisturbed, late-seral-stage ecosystems are needed to quantitatively define regional (> km²) community types, which can then be used to successfully determine target conditions for restoration efforts. Over the past twenty years, the Carolina Vegetation Survey (CVS) has acquired high-quality biotic and abiotic records from over 6,000 vegetation plots distributed across North and South Carolina, United States of America (US). Recently, we used these data to assess the ability of an existing classification, the US National Vegetation Classification Standard (NVCS), to define target conditions for restoration. We focused on nonalluvial wetland community types in the southeastern Coastal Plain of the Carolinas, a region largely defined by its complex distribution of unique wetlands. Over half of the association-level vegetation units currently recognized by the NVCS for the Coastal Plain of the Carolinas are wetlands. These systems vary considerably in terms of species richness, geomorphology, soil, hydrology, and disturbance history. We classified 184 plots containing 601 species using hierarchical cluster analysis techniques and then used non-metric multidimensional scaling to define groups based on soils and geomorphology. Our analyses indicated a need for substantial revision of the NVCS classification. Of the 56 associations recognized in the current study, 21 are newly described, 30 have complex relationships with one or more previously-described associations, and only 5 remain unchanged from their original NVCS delineations. We were unable to assess 37 associations because we were lacking appropriate data. The Carolina Vegetation Survey (CVS) is a multi-institutional collaborative research program established in 1988 to document the composition and status of the natural vegetation of North and South Carolina, United States of America (US), for purposes of inventory, assessment of conservation status, and monitoring of environmental impacts. Data collection methods are standardized and are widely employed across the southeastern US (Peet et al. 1998). Over the past 20 years, CVS has acquired high quality, quantitative records from over 6,000 vegetation plots distributed across the Carolinas. These data have allowed for the first time an accurate documentation of the natural communities and species habitats from this region (Figure 1). Ultimately, we designed a hierarchical framework to guide restoration efforts using the newly described classification units. Once defined, these classification units were mapped and identified to a biogeographic region. Regardless of seral-stage, restoration sites were delineated into specific classification units by identifying environmentally stable discriminants. Classification models were used to select the appropriate composition of species within a restoration site. Finally, monitoring plots were established to ensure that the successional trajectory of a restored site would reach its predefined target condition. This hierarchical framework provided a necessary platform to filter a rigorous community classification dataset into a usable structure that restoration managers could use to guide successful and ecologically meaningful restoration efforts. In May 2005, CVS initiated a partnership with the North Carolina Ecosystem Enhancement Program (EEP)—a state agency created for the purpose of wetland habitat restoration—with goals designed to benefit the two organizations in terms of generation, management, and distribution of vegetation data from both natural and mitigation sites. The CVS data management system has been designed to ensure accurate collection, reporting and transmission of vegetation monitoring data from field collection to raw datasheets to insertion into the CVS-EEP data archive, and then accurate reporting to EEP and future contractors. The degree to which restoration efforts are deemed successful is typically based on the successional trajectory of a site to its predefined target condition. Brinson and Rheinhardt (1996) emphasized the critical roles of reference wetlands in compensatory mitigation, whereby successful restoration involves establishment of goals (restoration targets), development of templates for the targets, and tracking the success rate of the endeavor. Information gathered from CVS database can be used to define site-specific reference conditions (Figure 2). EEP contractors can use these data to establish restoration targets specific to designated project sites. Furthermore, quantitative assessment from these high-quality vegetation plots can provide a better understanding of lower-order community structure and composition for the US National Vegetation Classification Standard (NVCS) (Federal Geographic Data Committee 2008). STUDY OBJECTIVES Utilize high-resolution vegetation data from the CVS database in order to assess the ability of the NVCS to define target conditions for restoration Figure 1. Distribution of established plots by the Carolina Vegetation Survey as of 2007 within North and South Carolina, US. Orange dots represent plots occurring in nonalluvial wetland communities of the southeastern US Coastal Plain (green shading). Vegetation – Environmental Plot Database Create higher-order levels based on: 1) physiognomic level 2) upland vs. wetland 3) open vs. closed forest Quantitative assessment of vegetation – environmental datasets (e.g. cluster analysis, ordination, indicator species analysis, discriminant analysis) Identify classification units based on similar vegetation, abiotic conditions Map units onto biogeographic region Improve upon classification scheme of southeastern US Coastal Plain nonalluvial wetlands Design a hierarchical framework to guide restoration efforts using newly defined classification units Provide restoration managers localized, high-resolution targets for restoration Improve upon lower-order levels within the National Vegetation Classification Standard Figure 2. Flow-diagram depicting how plot data from the Carolina Vegetation Survey database are organized to produce high-resolution community classification with quantitative descriptions and defined environmental settings. Results The southeastern Coastal Plain of the United States is home to a diverse array of nonalluvial wetlands. Distribution of these systems is related to the presence of poorly drained soils, topographical depressions, and the abundance of peat accumulations, while differing fire regimes maintain species structure. Clockwise from upper left: Depression pond hardwood forest, bay forest, Atlantic white cedar forest, and low pocosin. Approach I. II. Classified 184 plots containing 601 species using hierarchical cluster analysis (BrayCurtis, flexible beta) and non-metric multidimensional scaling. Mapped clusters into higher-order hierarchical bins (Vegetation of the Carolinas 2008) and used qualitative techniques to map individual plots to nearest NVCS-defined Association(s). A three-level scale was used to assess the degree to which these units corresponded to an Association: 1) Poor: these communities are newly described 2) Complex: these communities could be mapped to at least one other Association 3) Good: these communities corresponded well with current Association descriptions Used Indicator Species Analysis to identify diagnostic species of unique classification units (NVCS Associations). Compared diagnostic species with those specified in the existing unit definition. Discriminant analysis was used to determine critical abiotic variables between clusters. III. Designed a hierarchical framework to guide restoration efforts using the newly described classification units. BAY FORESTS / NONRIVERINE SWAMPS / HARDWOOD FLATS PONDS & MARSHES / AQUATIC VEGETATION POCOSINS / PONDPINE WOODLANDS Figure 3. Hierarchical cluster analysis of Carolina Coastal Plain plots obtained by the Carolina Vegetation Survey (Distance Measure: Bray – Curtis, Linkage Method: Flexible Beta, beta = -0.25). CVS plots from nonalluvial wetlands of the Carolina Coastal Plain formed classification units based on similar vegetation patterns arising from hydrologic and soil gradients (Figure 3). We determined there was a substantial need to revise the current NVCS classification of these systems based on the lack of fit between our quantitative data and qualitative descriptions of NVCS vegetation associations. Of the 93 associations recognized as nonalluvial from the study area, 21 are newly described, 30 have complex relationships with one or more previously described association, and 5 remain unchanged from their original NVCS delineations. We were unable to assess 37 associations because we were lacking necessary plot data. Community descriptions of eight of these associations are given in Figure 4. Coastal Plain hardwood flats NVCS Associations: Depression ponds NVCS Associations: 1) Quercus michauxii - Quercus pagoda / Clethra alnifolia Leucothoe axillaris Forest Assessment – Good Description: 1) Dichanthelium wrightianum – Dichanthelium erectifolium Herbaceous Vegetation Assessment – Complex Description: This community occurs on seasonally to nearly permanently saturated flats over mineral soils characterized with having a high water table. Canopy dominants include Quercus michauxii, Quercus laurifolia, Quercus pagoda, Liquidambar styraciflua, Liriodendron tulipifera, Acer rubrum, and Fraxinus pennsylvanica. Subcanopy trees include Carpinus caroliniana var. caroliniana and Ilex opaca var. opaca. A dense shrub stratum is composed of Arundinaria tecta and Vaccinium fuscatum. Herbs found in this community are diverse and can include Dichanthelium dichotomum var. ramulosum, Woodwardia areolata, Thelypteris noveboracensis, and Carex laxiflora. This community association is usually found on middle topographic positions of limesink ponds, and thus less influenced by saturation. Dominant species found in these plots include Lachnanthes caroliniana, Centella erecta, Panicum virgatum, and Pinus taeda. Although these plots fit with the described geomorphology of the NVCS community type, they lack the nominal species necessary for accurate characterization. Limesink communities within the study area are in need of further examination to enhance the NVCS understanding of Coastal Plain ponds and marshes. 2) Quercus pagoda – Quercus michauxii – Quercus alba / Arundinaria tecta – Sabal minor / Chasmanthium laxum Forest Assessment – Complex Description: This oak-dominated wet swale association is described from the Outer Coastal Plain of South Carolina and Georgia. It is composed of both upland and bottomland species, and probably experiences flooding only during severe (e.g. hurricane) rain events, and then without significant overland flow. Canopy species diversity is high; species include Quercus pagoda, Quercus michauxii, Quercus falcata, Quercus alba, and Quercus phellos. Other canopy trees include Fraxinus americana, Acer floridanum, Carya ovata, and Fagus grandifolia var. caroliniana. The subcanopy and shrub strata are sparse within this association. Species include Ulmus alata, Ilex decidua var. decidua, and Liquidambar styraciflua. Unlike the NVCS community description, these plots do not contain either Arundinaria tecta or Sabal minor. Furthermore, these plots have much higher species richness values than acknowledged by the described community type. Herbaceous species found in these plots include Poa cuspidata, Chasmanthium sessiliflorum var. sessiliflorum, Viola affinis, and Chasmanthium laxum. 2) Panicum hemitomon – Eleocharis equisetoides – Rhynchospora inundata Herbaceous Vegetation / Lyonia lucida Forest Assessment – Complex Description: This community is found over outer Coastal Plain limesink ponds, usually at lower topographic positions. The only dominant species found across these plots is Panicum hemitomon. Other species found include Cephalanthus occidentalis, Amaranthus cannabinus, Azolla caroliniana, Rhynchospora inundata, Nymphaea odorata ssp. odorata, Lachanthes caroliniana, Eriocaulon decangulare var. decangulare, and Rhexia cubensis. Each sampled limesink pond in this NVCS-described community type had its own unique vegetation composition. There is a clear need for study of the broad range of limesink and other temporarily ponded depressions of the Carolina Coastal Plain. Conclusions The use of high-quality plot data from CVS improves upon reference information, target design, monitoring, and data management - analysis. Finer-scale classification levels of nonalluvial wetlands of the southeastern US Coastal Plain need revision within the NVCS. Implementation of a hierarchical framework is necessary to bridge the gap between rigorous data analysis and model-building procedures advocated by academic institutions AND the results they generate that can be used by restoration managers: • Perform quantitative analysis on high-quality plot data to determine classification units and to improve upon existing classification schemas • Map classification units within a biogeographic region • Identify environmentally stable discriminants in order to delineate restoration sites into defined classification units • Use species lists determined from classification models to select the appropriate composition of species within a restoration site • Establish monitoring plots within restoration sites to ensure that the successional trajectory of a restored site would reach its predefined target condition Bay forests NVCS Associations: Pocosins NVCS Associations: 1) Gordonia lasianthus - Magnolia virginiana - Persea palustris - Sphagnum spp. Forest Assessment – Poor Description: 1) Pinus serotina / Zenobia pulverulenta - Cyrilla racemiflora – Lyonia lucida Wooded Shrubland Assessment – Complex Description: This community is found on peaty seepage depressions on landforms with a high water table. The canopy in all of these plots is dominated by a mixture of Gordonia lasianthus, Persea palustris, and Magnolia virginiana var. virginiana. Other canopy species include Acer drummondii, Acer rubrum, and Nyssa biflora. The shrub and vine component of these plots is patchy to dense, and includes Lyonia lucida, Clethra alnifolia, Cyrilla racemiflora, Ilex coriacea, Gaylussacia frondosa, Leucothoe axillaris, Smilax laurifolia, Vitis rotundifolia var. rotundifolia, and Toxicodendron radicans var. radicans. The high variability of the shrub and herb component of these plots warrants an examination of the NVCS schema for this community type. This typical high pocosin of the Atlantic Coastal Plain is composed of a very dense shrub stratum, up to 3 meters tall. Typical shrub species include Lyonia lucida, Zenobia pulverulenta, Cyrilla racemiflora, Ilex coriacea, Ilex glabra, and Persea palustris. An open canopy of Pinus serotina, Taxodium ascendens, and Nyssa biflora are characteristic of these plots. The presence of these latter two species explains the inconsistency between some of these plots and the NVCS description of this community type. Brinson, M.M., and R. Rheinhardt. 1996. The role of reference wetlands in functional assessment and mitigation. Ecological Applications 6(1):69-76. 2) Cyrilla racemiflora – Zenobia pulverulenta Shrubland Assessment – Good Description: Peet, R.K., T.R. Wentworth, and P.S. White. 1998. A flexible, multipurpose method for recording vegetation composition and structure. Castanea 63:262-274. 2) Magnolia virginiana – Persea palustris / Lyonia lucida Forest Assessment – Complex Description: This saturated forest represents an intergrade to a shrub-dominated high pocosin of the Outer Coastal Plain of the southeastern United States. The open canopy of this community is composed of both Acer rubrum var. trilobum and Magnolia virginiana var. virginiana. The shrub stratum is dense and composed of many species. These include Ilex coriacea, Lyonia lucida, Clethra alnifolia, and Ilex laevigata. These plots differ from the NVCS community description by having a diverse shrub stratum and by having a significant amount of Arundinaria tecta in the herb-shrub strata. These plots are also significantly north of the documented range of this association. The next closest match would be the Gordonia-type described above, though these plots completely lack Gordonia sp. This community is defined as a low pocosin of peat domes within the outer Coastal Plain of North Carolina. A mixture of both evergreen and deciduous species is found within this community, and canopy heights are generally low (< 15m for the scattered trees and ~ 2m for the dominating shrubs). In these plots, the open canopy is composed of Pinus serotina, Gordonia lasianthus, Ilex laevigata, and Acer drummondii. The extremely dense shrub stratum is composed of Zenobia pulverulenta, Ilex coriacea, Smilax laurifolia, and Kalmia cuneata. Figure 4. Plots were identified to associations following the US National Vegetation Classification Standard (NVCS). The ‘association’ is defined as a group of plots having similar species composition, structure, and habitat. This is the lowest, finest level of the NVCS hierarchy. Citations Federal Geographic Data Committee. 2008. National Vegetation Classification Standard http://www.fgdc.gov/standards/projects/FGDC-standards-projects/vegetation Acknowledgements We would like to acknowledge all the many field and data workers who collectively provided the plot data for this analysis. Other support, including funding, was provided by the following institutions: