Southern mesic forests historically occupied close to ten percent of Wisconsin’s total land area. Clearing of land for agriculture and infrastructure has resulted in a limited number of highly fragmented remnant forests remaining. Fragmentation and succession are driving compositional shifts in these remnant forests, resulting in a loss of diversity across all strata. The primary objective of this research was to determine how species composition has shifted in one upland southern mesic forest, Abraham’s Woods State Natural Area (SNA), over 70 years. We resampled permanent plots to quantify changes in structure and composition between establishment in 2008 and 2018. We also compared these two sampling periods to historical data from 1949. We hypothesize: (1) forest composition is shifting to an increased dominance in Acer saccharum in all strata, while (2) Quercus and Carya species fail to recruit, and (3) understory richness and floristic integrity decline.
Results/Conclusions
Our results indicate that over the past decade, Abraham’s Woods SNA has seen an increase in importance value of overstory A. saccharum (10%). As older, large diameter canopy trees senesce (Quercus spp. and Ulmus rubra), shade tolerant species are being recruited into canopy gaps. A. saccharum is the most commonly recruited species due to its dominance across all size classes. As forest succession continues, A. saccharum will likely dominate all size classes in this forest in the future, though other mesic, shade tolerant associates will likely persist (Tilia americana and Ostrya virginiana). Between 2008 and 2018, Quercus rubra and Carya cordiformis saplings experienced 100% mortality across these plots, while A. saccharum remained the dominant species in the sapling layer. This further indicates a shifting composition in this forest. Between 1948 and 2018, understory species richness at Abraham’s Woods SNA decreased by 19 species and the floristic quality index decreased by 10, indicating a decline in overall site intactness. Our findings support our hypotheses that species composition is shifting in Abraham’s Woods SNA and understory richness and floristic integrity are declining. These results suggest that overall site diversity in Abraham’s Woods SNA will continue to decline over time.