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ARS Home » Plains Area » Las Cruces, New Mexico » Range Management Research » Research » Publications at this Location » Publication #131598

Title: COMMUNITY STRUCTURE ALONG ELEVATION GRADIENTS IN HEADWATER REGIONS OF LONGLEAF PINE SAVANNAS

Author
item Drewa, Paul
item PLATT, WILLIAM
item MOSER, E.

Submitted to: Journal of Plant Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/1/2002
Publication Date: 5/1/2002
Citation: DREWA, P.B., PLATT, W.J., MOSER, E.B. COMMUNITY STRUCTURE ALONG ELEVATION GRADIENTS IN HEADWATER REGIONS OF LONGLEAF PINE SAVANNAS. JOURNAL OF PLANT ECOLOGY. 2002. V. 160(1). P. 61-78.

Interpretive Summary: The makeup of savanna plant communities and their relationships with the environment are rarely characterized locally. Our primary goal was to examine the composition and abundance of herbs, as well as shrubs/trees, along local elevation gradients in headwater regions of longleaf pine savannas in the southeastern United States. We also examined whether mathematically-defined herb communities were similar to those of shrubs/trees along the same elevation gradients and whether they were both influenced by soil characteristics and elevation. Abundance data were collected within quadrats placed along transects from upslope savannas through mid-slope seepage bogs into lower-slope shrub/tree zones within Louisiana and Florida. Beta-flexible cluster analysis and nonmetric multidimensional scaling were used to describe herb communities while only the latter was performed on shrub abundance data. Cluster analysis results sbased on herbs were used also to describe shrub/tree communities. This provided an indirect way of comparing how herbs and shrub/trees changed along the same elevation gradients in terms of their composition and abundance. In Louisiana, diagrams of these mathematical descriptions revealed 3 distinct herbaceous plant communities that changed abruptly along elevation gradients of several meters and were strongly influenced by changes in soil moisture. In Florida, 3 similar herb communities changed with elevation gradients of only <1m, but were not as clearly defined. In both regions, shrub/tree communities were much broader and appeared less sensitive than herbs to changes in elevation and soil characteristics. Years of fire suppression and dormant-season fires may have resulted in the spread of shrubs/trees across these elevation gradients but not herbs.

Technical Abstract: Quantitative descriptions of vegetation patterns and relationships with substrate characteristics at localized scales have received less attention than regional levels. Our primary objective was to examine the distributions of herbs and shrubs/trees along local topographic gradients in headwater regions of longleaf pine savannas in the southeastern United States. We also examined whether herb patterns were structurally similar to those of shrubs/trees along the same topographic gradients and whether patterns were correlated with edaphic factors. Abundance data were collected within quadrats placed along transects from upslope savannas through mid-slope seepage bogs into lower-slope shrub/tree zones within Louisiana and Florida. Beta-flexible cluster analysis and nonmetric multidimensional scaling were used to delineate herbaceous species communities. Ordination was performed separately on shrub/tree abundance data. The herb-based classifications were also used to delineate shrub/tree communities, providing an indirect means of comparing herb to shrub/tree distributions. In Louisiana, 3 herbaceous communities were sharply delineated along elevation gradients of several meters and were strongly correlated with soil moisture. In Florida, 3 similar herbaceous communities were less discrete along elevation gradients of <1 meter. In both regions, shrub/tree distributions were much broader and appeared less sensitive than herbs to changes in environmental gradients. Coefficients of variation indicated that herbaceous species were more narrowly distributed than shrubs/trees along localized elevation gradients in both Louisiana and Florida. Alterations of fire regimes may have resulted in expanded distributions of shrubs/trees but not herbs.