Vegetation community change over decadal and century scales in the North Carolina piedmont

Abstract

This thesis examines vegetation community change at two temporal scales in the Piedmont of North Carolina. Using long-term plots in the Duke Forest, I examine decadal-scale changes in community composition of the forest understory and shed light on the potential drivers of that change. Using historical data from colonial survey records, I study presettlement forest communities of the Piedmont and attempt to reconstruct Piedmont forests as they may have been in the time before European arrival. The pattern of successional change in southeastern United States Piedmont forests has been assumed from chronosequence studies over the last half century. However, these assumptions for forest understory herb-layer populations and communities have not been tested using long term data sets. Using permanently marked plots in the Duke Forest (Durham, NC, USA) re-censused after a 23 year time step, species richness and community changes at 25m2 and 1000m2 scales are examined. I look at changes across life forms and examine these changes in relation to measured stand and environmental factors. Although total species richness stayed relatively constant through the 23 year step, herb richness declined with a concomitant increase in woody richness. Plot composition change was remarkably consistent and this change was not correlated to any measured stand or environmental factors. These community-level changes are consistent with previously reported changes in the understories of hardwood dominated stands in the Duke Forest, suggesting that landscape scale drivers may be more important than within-stand successional processes in patterning herbaceous communities at this time. Combined with growing evidence from other studies, this work indicates that forests in the temperate region may be experiencing changes different from those predicted by successional chronosequence studies. It indicates that one of the primary drivers of this change is the explosive growth of deer populations in the last two decades. Witness trees recorded in historical surveys have been used to reconstruct presettlement vegetation in many parts of North America, leading to a better understanding of vegetation patterns before the effects of Europeans. For some parts of North America, Government Land Office records make the process of reconstructing vegetation patterns easier - thus more is known about these areas. Because of the unique and unplanned nature of settlement in the southeastern U.S., less is known about the presettlement vegetation in this area of the country. Using a reconstructed cadastral map of a section of the North Carolina Piedmont, I was able to plot the positions of trees on the historical landscape. These data were then used to understand and reconstruct the composition of presettlement forests. Although the vegetation of some areas of the Piedmont is similar to what was expected, I find significant differences with the expected presettlement composition. In particular, pine species were common in some areas and rare in others, indicating that different disturbance regimes were active on the landscape.