Widespread tree mortality mapping suggests size-dependent risk for extreme drought stress
Abstract
Forest ecosystems are one of the single greatest global contributors to ecosystem services and wildlife habitat, but uncertainty about future climate brings these benefits under threat. Drought poses a serious risk to forested ecosystems by disrupting water availability, reducing photosynthetic rates, and increasing leaf mortality. Over time, tree death propagates through ecosystems as trees succumb to pests that take advantage of weakened individuals, resulting in widespread tree mortality. Large trees in forests provide the most benefits to humans and wildlife, but may be the most vulnerable. The U.S. Forest Service estimates that over 66 million trees have died off in California since the severe 2010 drought. The future of forests in this region is unclear, presenting the need for a more thorough understanding of which trees are experiencing high mortality and what might be the landscape-scale drivers of this trend. We investigated whether larger trees have higher mortality in the dry forested areas of the southern Sierra Nevada. We used LiDAR to detect single tree crowns and measured height of over 350,000 individuals. NAIP imagery provided the basis for crown-level mortality mapping over an 8 year time period, with a validated accuracy of over 80%. Over half of all measured trees in this study were dead and taller on average than the live population (p < 0.001). Dead trees clustered in valley bottoms and mountain slopes had a higher proportion of living trees. Time since drought was a major control over the size dependent mortality relationship. Our findings add robust landscape-scale evidence for the higher risk of large individuals in dry forest ecosystems and a method for future monitoring of size-dependent tree mortality for improved management.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.B24B..02S
- Keywords:
-
- 0414 Biogeochemical cycles;
- processes;
- and modeling;
- BIOGEOSCIENCESDE: 0439 Ecosystems;
- structure and dynamics;
- BIOGEOSCIENCESDE: 1640 Remote sensing;
- GLOBAL CHANGEDE: 1817 Extreme events;
- HYDROLOGY