Michigan Forests Face Triple Threat From Climate, Deer, and Disease

A new dataset tracking forest seedling establishment across Michigan shows that young trees are struggling to survive the compounding stresses of warmer winters, elevated deer browsing pressure, and spreading fungal and bacterial diseases. The data matters because seedling survival is the canary metric for long-term forest viability: a forest that cannot regenerate its understory will age out and collapse over decades even if its mature canopy looks healthy today.

The interaction effects between the three stressors are the alarming finding. Climate change weakens tree immune responses and shifts species range boundaries, making forests more susceptible to diseases that historically stayed confined to warmer zones. Deer populations — elevated in part because milder winters reduce winter mortality — then browse the weakened seedlings before they can establish. No single management intervention addresses all three simultaneously: reducing deer through culling is politically contentious, disease treatment is expensive at landscape scale, and climate change is not a locally controllable variable.

Michigan's forestry managers now face the question of whether to prioritise 'assisted migration' — deliberately planting species adapted to future conditions rather than historical ones — or to double down on defending existing species composition. The answer will determine what the Great Lakes forests look like in 2075.