Forest health and drought response

Science Center Objects

Forests provide society with economically important and often irreplaceable goods and services, such as wood products, carbon sequestration, clean water, biodiversity, and recreational opportunities.  Yet hotter droughts (droughts in which unusually high temperatures exacerbate the effects of low precipitation) are projected to increase in frequency and intensity in coming decades, potentially threatening forest sustainability.  Using a number of complementary data sets, this project treats California’s recent hotter drought as a potential preview of the future, with the ultimate goal of providing forest managers with the information and adaptation tools they need to increase forest resistance and resilience to extreme droughts of the future.

Statement of Problem:

Ongoing global changes – particularly interacting changes in climate, land use, and disturbance regimes – are rapidly altering forests, often in undesirable ways.  Such changes have been particularly evident in the western United States.   This project explores the effects of climatic drivers on forest vegetation, ecological disturbance processes, mountain hydrology, and the coupled ecohydrological responses that determine vulnerability of western U.S. mountain landscapes to change.


Why this Research is Important:

Forests sequester the majority of the terrestrial biosphere’s carbon, making them key components of the global carbon cycle.  For society to anticipate, mitigate, and adapt to these increasing threats to forests, we must improve our ability to understand and forecast forest response to environmental changes and management actions.  We thus work closely with forest managers – particularly in the National Park Service and U.S. Forest Service – to provide concepts and tools for wise management of the nation’s forests.  Our primary insights come from intensive, place-based study of a globally unique network of forest research plots in California’s Sierra Nevada mountain range, in which the fates of tens of thousands of trees have been followed for up to 36 years.  Insights from this network, in turn, catalyze regional and global syntheses.

Linked to the Western Mountain Initiative (WMI) since 2003, this project explores effects of climatic drivers on forest vegetation, ecological disturbance processes, mountain hydrology, and the coupled ecohydrological responses that determine vulnerability of western U.S. mountain landscapes to change (see figure below).

WMI Diagram

(Credit: Baron. Public domain)


The effects of California’s extreme 2012-2016 drought were exacerbated by abnormally high temperatures, resulting in historically unprecedented tree mortality.  To capture scientific information needed to prepare forest managers for similar events in the future, we launched the Leaf to Landscape project in 2014, with core funding from USGS, NPS, and USFS.  Our 2014-2017 collection of “perishable” data was coordinated across spatial scales, from tree leaves to entire forested landscapes.  Our globally-unique network of permanent forest plots in the Sierra Nevada has been a key component of this interdisciplinary effort.


Our primary goal for the next five years is to apply our existing Leaf to Landscape data and continued documentation of forest drought response and recovery to provide forest managers with key information and tools, as outlined the following six objectives:

Objective 1:  Create and validate empirically derived, species-specific forest vulnerability maps, letting the trees themselves reveal which parts of the forested landscape are likely to be most vulnerable to future hotter droughts.

Objective 2(i) Empirically identify areas that served as hydrologic refugia during the drought, (ii) quantify the extent to which they protected tree species, and (iii) determine whether tree species differed in the extent to which refugia protected them.

Objective 3Provide a first real validation test of a state-of-the-art forest vulnerability model, determining how well it predicted actual patterns of tree mortality during the hotter drought

Objective 4:  Empirically quantify the effectiveness – or lack thereof – of past forest treatments in increasing tree survival during extreme drought

Objective 5Determine the species-specific timing, magnitude, and nature of lagged tree mortality following extreme drought

Objective 6Create and validate empirically derived giant sequoia vulnerability maps, and determine the role of bark beetles in drought-induced sequoia mortality