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Why do trees die? Characterizing the drivers of background tree mortality
Adrian J Das1, Nathan L Stephenson1, Kristin P Davis2
1U.S. Geological Survey, Western Ecological Research Center, Three Rivers, California, 93271, USA.
Ecology
|November 19, 2016
Summary
Background tree mortality is primarily driven by biotic factors like insects and pathogens, not abiotic forces. Understanding these agents is crucial for accurate forest dynamics and future mortality predictions.
Area of Science:
- Forest Ecology
- Pathology
- Entomology
Background:
- Background tree mortality influences forest dynamics and responses to environmental change.
- Understanding biotic interactions is key to explaining geographical gradients in forest health.
Purpose of the Study:
- To identify the primary drivers of background tree mortality.
- To analyze the role of biotic factors in tree death rates.
Main Methods:
- Analysis of pathological data from 200,668 tree-years.
- 13-year observation period in Sierra Nevada old-growth forests.
- Recording 3,729 individual tree deaths.
Main Results:
- Biotic factors (insects, pathogens) caused 58% of tree deaths, especially in larger trees.
- Bark beetles were the most common biotic agent (40%), despite no outbreaks.
- Mortality factors showed little predictable co-occurrence on individual trees.
Conclusions:
- Background tree mortality is dominated by biotic agents, necessitating their inclusion in forest models.
- Biotic agents act opportunistically, often independently.
- Future research should consider biotic attacks on stems and roots, not just foliage.
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