Post‐settlement ecological changes in the forests of the Great Lakes National Parks

Abstract

Abstract National parks of the United States seek to preserve the natural and cultural heritage of the United States, yet parks in the eastern and Midwestern United States were established after periods of human settlement and disturbance. In the Great Lakes region, fire and windfall originally dominated as disturbance agents, driving dynamics in prairies, savannas, and in many forested ecosystems. However, fire suppression over the last century has radically lengthened fire return intervals. Additionally, widespread logging, slash burning, mining, and agricultural settlement successively shifted the dominant forms of land use, greatly altering these forests. From 2008 to 2014, the National Park Service's Great Lakes Inventory and Monitoring Program surveyed vegetation in nine Great Lakes National Parks. We compared these surveys with data derived from the mid‐ to late‐1800s Public Land Survey ( PLS ) to assess shifts in forest composition. Community composition has changed dramatically since the mid‐19th century. Preferred timber species (e.g., Pinus strobus and Tsuga canadensis ) and fire‐adapted species (e.g., Quercus macrocarpa and Pinus banksiana ) have declined across the region, while aspen ( Populus spp.) and/or maple ( Acer spp.) have consistently increased. Ordinations reveal both these general trends and substantial divergence in composition within particular parks since the PLS . Past logging practices and mesification following fire suppression account for most general trends across the region, while local differences in edaphic conditions, ungulate herbivory, and disturbance regimes account for many park‐to‐park differences. Understanding how these factors, alone and in combination, have affected forests in these parks provides both a picture of regional forest dynamics and tools that improve our ability to manage these parks. Continuing to monitor forest vegetation in these parks will allow us to test our understanding of forest dynamics and to use these parks as the “land laboratories” that Leopold envisioned.