Ecological species groups of landform-level ecosystems dominated by jack pine in northern Lower Michigan, USA

Abstract

A combination of field and tabular methods and multivariate analyses were used to develop groups of ground flora species (i.e., ecological species groups) that characterize and distinguish highly disturbed, landform-level ecosystems dominated by jack pine in northern Lower Michigan. The endangered Kirtland's warbler formerly or currently occupied the large glacial landforms for which species groups were developed. Eight such ecological species groups were created using 31 woody and herbaceous species sampled in 144 plots within a 20,000 km2 geographic region of uniform climate and regional physiography. The groups were initially constructed using subjective, observation-based groupings of species with similar presence and abundance along soil moisture and fertility gradients. Species groups were corroborated using TWINSPAN and detrended correspondence analysis, and the environmental conditions indicated by each were described and contrasted based upon field observations and canonical correspondence analysis. Two of the eight species groups indicated very dry, infertile sites, and one was indicative of a very broad range of sites dominated by jack pine. The remaining five groups reflected a relatively gentle environmental gradient within the set of ecosystems we sampled, indicating small differences along a soil moisture gradient and less so along a soil fertility and light availability gradient. The groups were applied successfully for the majority of an area that had been repeatedly logged and/or burned for at least 120 years. In addition, the groups were successful when tested on sites with highly disturbed upper soil strata furrowed for the establishment of plantations between the 1960s and 1980s. Within the boundaries of the regional ecosystems for which they were developed, ecological species groups reflect the integrated effects of multiple site factors that control the height growth rates of jack pine trees that, in turn, determine the duration of Kirtland's warbler occupancy. While usually applied at the scale of ecosystem types, our results demonstrate that ecological species groups may also provide the ecological basis for distinguishing ecosystems at broader scales. When examined simultaneously in the field with physiography, microclimate, and soil factors, the groups are therefore useful in identifying and classifying ecosystem units at the scale of landforms, the appropriate scale of management for the Kirtland's warbler.