Drivers of woody canopy water content responses to drought in a Mediterranean-type ecosystem

Severe droughts increase physiological stress in woody plant
species, which can lead to mortality,
fundamentally altering the composition, structure, and biogeography of forests
in many regions. Little is known, however, about the factors determining
the physiological response of woody plants to drought at landscape scales. Our
objective was to understand woody plant species responses to ongoing changes in
climate, using remotely sensed canopy water content (CWC) as an indicator of
plant physiological and phenological status. We
used fused imaging spectroscopy and light
detection and ranging (LiDAR) from the
Carnegie Airborne Observatory (CAO) to quantify the
factors affecting species compositional changes in CWC in a diverse
Mediterranean-type ecosystem (Jasper Ridge Biological Preserve, CA) between 2013 and 2015. Mapped CWC was spatially
variable in both of the observation years, and proved to be most closely tied
to species composition and distribution across the landscape. The secondary
predictors of CWC were elevation and soil substrate. In contrast, we found that
CWC change was much more related to environmental factors than to the species
composition. We suggest that the effect of environment on CWC change is
mediated through species resistance and resilience to drought. Monitoring CWC
change with imaging spectroscopy is a powerful approach to identifying species-level
responses to climatic events and long-term change, which may provide support for policy decisions and conservation
at large spatial scales.