Data for: Tree species size class patterns portend compositional shifts and low resilience in managed northern hardwood forests

Declining biodiversity is a global challenge to sustainability and resilience of ecosystems facing multiple novel stressors, including climate change and invasive pests-pathogens. Northern hardwood forests (NHF) of the Great Lakes region have experienced declines in canopy tree diversity since European colonization, with current tree regeneration patterns in some areas suggesting perpetuation of this trend. However, regional (106 ha) patterns and possible causes are underexplored. To address this information gap, we used data from 141 managed NHF stands, Michigan, USA to examine diversity indices across tree size classes (seedling, sapling, and canopy); stand-level drivers of regeneration (seedling and sapling) diversity and individual species density; and patterns among species in relative abundances across size classes. Diversity was similar across size classes (mean asymptotic species richness of 6 – 7 species and <3 effective common species); however, some species contributing to..., Our data are from 141 managed northern hardwood forest stands distributed throughout northern Michigan. Data were collected from a systematic grid of 25 survey points within a 12-ha square within each stand and collected species-level data in the following plots at each survey point. We counted all tree seedlings shorter than 50 cm and ocularly estimated percent cover of shrubs and groundcover composition (e.g., hardwood litter, bare mineral soil, downed woody material) within 2 quadrats, each 1 m2 (50 m2 total per stand). Within a 2 m radius circular plot (314 m2 total per stand) we tallied stems 50 to 137 cm tall and tallied and measured DBH for stems > 137 cm tall and < 5 cm DBH. Within a 6 m radius circular plot (2,827 m2 total per stand), we tallied and measured DBH for all stems > 5 cm DBH. From these data we established the following size classes: seedlings, 0 – 137 cm tall; saplings, > 137 cm tall and < 10 cm DBH; canopy trees, ≥ 10 cm DBH.. For all size classes w..., Excel