Crowding and sulfur pollution outweigh climate in forest change
Kling MM, Burnham PA, Dube MP, McGill BJ, McLaughlin BP, Miller SN, Waring TM, Gotelli NJ.
Climate Adaptation
The thinning canopy gaps and seedling struggles you might notice on a forest walk aren't just about warmer weather, they're tied to how dense the woods have become and to sulfur pollution drifting in from miles away.
Scientists tracked 100 tree species across the US for over two decades and asked what's really driving changes in how trees sprout, grow, and die. Climate change gets most of the attention, but it turns out that how crowded a forest has become and pollution in the air, especially sulfur, are actually bigger factors. New seedlings turned out to be the most sensitive part of the whole system, and across the country forests are generally slowing down, growing and regenerating less than they used to.
Key Findings
Analyzed 2002-2024 forest inventory data covering recruitment, growth, and mortality of 100 tree species against six environmental variables (climate, pollution, forest density)
Forest density changes and sulfur pollution deposition showed stronger links to tree demographic rates than climate variables, driven by both higher exposure and greater species sensitivity
Recruitment (new seedling establishment) was the most sensitive demographic process to all six environmental drivers, and recruitment, growth, and mortality rates have declined on average nationwide, with regional and species variation
chevron_right Technical Summary
A massive 22-year study of US forests found that trees growing too crowded and air pollution (especially sulfur) are affecting tree growth, death, and reproduction even more than climate change does, and overall forest activity is slowing down across the country.
Abstract Preview
Original paper
Forest Densification and Pollution Rival Climate in Driving US Tree Demographic Change.
Forests play critical roles in biodiversity, climate regulation, and human well-being, yet their responses to simultaneous environmental changes remain poorly understood. Across the United States, ...
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