Environmental Stressors

California’s Central Valley and San Francisco Bay Estuary have a long history of mercury contamination from past mercury mining and gold extraction. Waterbirds are particularly susceptible to mercury because of their use of wetland habitats where methylmercury (the most toxic and biologically available form) is produced and relatively low methylmercury exposure can reduce reproductive success...

The desert tortoise is listed as “threatened” under the Endangered Species Act. USGS WERC scientists, along with project partners have been conducting long-term analyses on how changes in the southwestern deserts of the United States can affect desert tortoise populations. Dr. Todd Esque and his team are investigating how habitat disturbances and restoration projects influence tortoise populations...

Dr. Nathan Stephenson and colleagues seek to determine what changes are occurring in forests, why they are occurring, and what they mean. For example, they have documented a long-term, apparently climatically-induced increase of tree mortality rates in otherwise undisturbed old forests across the western U.S., implying that these forests could become net sources of atmospheric carbon dioxide.

Coastal estuaries that contain marshes and mangroves are currently being reshaped by changing ocean and atmospheric conditions through prolong drought, sea-level rise and increased extreme storm events. Many projected increases in sea-level are expected to result in loss of tidal wetlands and their component species. In addition, changing sediment loads, extreme tide and storm events, and shifting...

This project improves our understanding of the ecology of amphibians in northern California and evaluates methods of managing landscapes and these imperiled species. In particular, Dr. Brian Halstead examines the distribution and demography of amphibians to understand factors that affect where amphibians are found and how populations change. He further explores the relationships of amphibians with...

Dr. Kathleen Longshore’s goal is to understand how predator/prey relationships, disease and human-caused disturbance work separately and synergistically to impact bighorn sheep populations under variable ecological stress. Information from this project will provide managers with an understanding of specific and regional impacting factors that contribute to impact variation in population trends.

Dr. Kathleen Longshore, in collaboration with Dr. Todd Esque, provides information to project the possible conflict between losses of habitat for foraging involved in the proposed development of alternative energy installations in the Mojave Desert and help develop advanced conservation efforts for the golden eagle. Information from this project will also inform California’s Desert Renewable...

How will increased drought affect forest fire severity? WERC’s Dr. Phil van Mantgem is testing the idea increased drought stress may affect forest fire severity independent of fire intensity. Drought stress prior to fire can affect tree health, potentially resulting in a higher sensitivity to fire-induced damage. Thus, with drought there may be ongoing increases in fire severity (the number of...

The community's ability to understand and predict changes in forests and their feedbacks to the global carbon cycle increasingly relies on models spanning several scales of biological organization – from tree leaves to entire forested landscapes. Yet many model assumptions about key processes – such as tree growth and mortality – require long-term data that are sometimes difficult and time...

Wetlands provide numerous ecosystem services, but also can be sources of methylmercury production and export. Click the next tab to learn how WERC's Dr. Josh Ackerman is evaluating the ecological factors that drive contaminant bioaccumulation in wetland-dependent fish and wildlife.

With sea level rise, how will the coastal habitats of the San Francisco Bay Estuary change over the next 100 years? Mapping and modeling studies by Dr. Karen Thorne, WERC scientists, and partners have produced scenarios for this important coastal ecosystem.

There is a growing consensus among resource managers to use native plant materials for ecological restoration of degraded drylands. Some plant species may be suitable for re-introduction across broad environmental gradients. Other species may fail under narrower conditions, or their re-introduction may have genetic consequences for local ecotypes, particularly when adapting to future climate...