US tree demography is shifting with forest crowding and pollution changes as strongly as with climate
WHAT THE EVIDENCE SAYS
Using nationwide forest-inventory observations from 2002–2024, researchers compared how recruitment, growth and mortality in 100 tree species responded to six environmental variables representing climate, atmospheric pollution and forest density. Changes in forest density and pollutant deposition—particularly sulfur—showed stronger associations with all three demographic rates than the climate variables tested, reflecting both species sensitivity and the magnitude of exposure change. Recruitment probability was the most sensitive demographic process. Across the country, recruitment, growth and mortality all slowed on average, with substantial species and geographic variation.
WHY IT MATTERS / OUR READ
A forest can be climate-stressed and still be responding more immediately to crowding, regeneration bottlenecks or the legacy of changing air pollution. That matters for diagnosis: a management response aimed only at temperature and precipitation can miss drivers that are locally stronger and more tractable. Recruitment deserves particular attention because it responded most strongly across the tested pressures.
CAVEATS / UNCERTAINTY
This is an observational attribution framework using inventory and environmental-change data; stronger association does not establish a single causal driver. Declining sulfur deposition is an environmental change, not evidence that current sulfur pollution is uniformly worsening forests. Species, regions and demographic rates differ substantially, so the national average should not become a universal silvicultural prescription.
SOURCE
Global Change Biology — primary study
View original evidence ↗
Nationwide inventory data for 100 species show forest density and sulfur-deposition change had stronger associations with recruitment, growth and mortality than the climate variables tested; recruitment was the most sensitive process.
Read the Wild Lands assessment →