Taxonomic and phylogenetic shifts following an inland derecho

Abstract

In 2009, a derecho occurred in southern Illinois, affecting large areas of the regional forest systems. Previous research reported multi-strata species compositional shifts post-derecho at LaRue Pine Hills/Otter Pond Research Natural Area but did not investigate how these changes varied within the RNA. These observations are expanded here to include phylogenetic and spatial relationships to show how compositional shifts can vary within a landscape. Surveys were conducted the year before and after the derecho. Univariate and multivariate analyses identified elevation as an environmental driver of diversity and community composition. Spatial analyses identified spatial patterns in taxonomic (TSR) and phylogenetic (PSR) species richness, and metrics of phylogenetic clustering and overdispersion (net relatedness index and nearest taxon index; NRI and NTI, respectively), in seedling, sapling, and tree communities. Tree TSR and PSR and sapling PSR decreases and sapling NTI increases occurred post-derecho. Seedling diversity-elevational relationships exhibited humped-backed relationships, while saplings showed positive linear relationships between phylogenetic metrics and elevation. Local Moran’s I analysis showed post-derecho clustering in the north-central extent for seedling, sapling, and tree strata. Co-Kriging interpolation predicted seedling diversity increases in the southwestern extent, with sapling and tree diversity increases in the eastern extent and the north-central extent respectively post-derecho, indicating competitive interactions at lower elevations and environmental filtering at higher elevations. Seedling and tree NRI and NTI increased in the southern extent, whereas sapling clustering increased in the northeastern extent. These relationships indicate how community assembly processes (i.e., competition or environmental filtering) are altered following large-scale disturbance.