Urbanization, agriculture, and invasive species are transforming and fragmenting remnant oak and hickory forests of the upper Midwest, altering stress and disturbance regimes. Fire suppression has reduced the frequency of fires, leading to denser forest canopies and damper, shadier conditions. This study examines the impacts of these processes on the taxonomic and functional diversity of forest trees and carabid beetles.
Carabid beetle diversity was assessed using pitfall traps along two transects at 18 sites, with bi-weekly collections. Beetles were curated and identified, and plant composition was analyzed using 50m circular plots and line-point intercepts along six transects. Various analyses, including non-metric multidimensional scaling ordination, fourth corner analysis, and cluster analysis, identified patterns in taxonomic and functional trait diversity. Multi-response permutation procedures tested for differences in plant and beetle compositions, and Indicator Species Analysis highlighted species and traits associated with each site group. ArcGIS calculated measures of forest patch fragmentation, disturbance, and stress.
Four groups of sites were identified with distinct taxonomic and functional diversity (MRPP A-Statistic = 0.89, p < 0.001 for trees; A-statistic = 0.05, p = 0.001 for beetles), differing in environmental and fragmentation measures (MRPP A-statistic = 0.07, p = 0.01). Group one patches were dominated by diverse mature and sapling tree species, fire and drought-tolerant, with diverse seed sizes and dispersal strategies. These patches had the highest carabid diversity. Other groups varied in dominance by native or non-native species, canopy openness, and carabid community composition, reflecting differences in disturbance tolerance and life history strategies.
.png)
