Treesearch

Whitebark pine (Pinus albicaulis Engelm.) has experienced rapid population declines and is listed as threatened under the Endangered Species Act in the United States. Whitebark pine in the Sierra Nevada of California represents the southernmost end of the species' distribution and, like other portions of its range, faces threats from an introduced pathogen, native bark beetles, and a rapidly warming climate. Beyond these chronic stressors, there is also concern about how this species will respond to acute stressors, such as drought. We present patterns of stem growth from 766 large...

The dominant chemical form of nitrogen pollution in the atmosphere in the U.S. is shifting from oxidized nitrogen, primarily from combustion of fossil fuels, to reduced nitrogen from agricultural animal waste and fertilizer applications. Does it matter to lichens? In this synthesis, we characterize U.S. air concentrations of the most ubiquitous gaseous forms of reduced and oxidized nitrogen, NO2 and NH3, respectively, and their direct effects on lichens. In the U.S., the 3-year average (2017–2019) of the annual mean for each monitoring site ranges up to 56.4 μg NO2 m−3 (∼30 ppb) and 6 μg...

Historical land and fire management practices coupled with climate change and modern human development pressures are contributing to larger, more frequent, and more severe wildfires across Western U.S. forests. Human ignitions are the predominant cause of wildfire throughout the United States, necessitating wildfire management strategies that consider both the causes of human ignitions and the factors that influence them. Using a dataset of over 104,000 ignitions from 1992 to 2018 for Oregon and Washington (U.S), we examine the major causes of wildfire ignitions and build regression models...

Recruiting beavers—or building structures that mimic beaver dams—is an increasingly popular method for restoring streams and floodplains in the American West. Doing so can boost the growth of vegetation for cattle forage and improve habitat for fish and wildlife. But with a nature-based solution for stream restoration, anything can happen. Gordon Grant and Susan Charnley, scientists with the USDA Forest Service Pacific Northwest Research Station, studied beaver-related restoration projects throughout the U.S. West. This research revealed uncertainties and unintended consequences involved...

Background: Wildfire is a major contemporary socio-ecological issue facing the people and natural resources of Southern California, and the prospect that a warming climate could lead to a higher probability of fire in the future is cause for concern. However, connecting climate change to projected burn probability is complex. While most models generally show temperature increasing in the future, changes in humidity and precipitation are less certain, and these changes interact to generate projections of future climates that are sometimes, but not always, more conducive to wildfire. We ran...

Models that simulate ecosystems at local to regional scales require relatively fine resolution climate data. Many methods exist that downscale the native resolution output from global climate models (GCM) to finer resolutions. NASA NEX-DCP30 is a statistically downscaled 30 arcsecond resolution climate dataset widely used for climate change impact studies in the conterminous USA (CONUS), but it did not include vapor pressure data which is essential for many types of models. We downscaled vapor pressure data from 28 global climate models included in the Coupled Model Intercomparison Project...

In the Willamette River, OR, main channel temperatures can be too warm for cold water fishes, causing fish to concentrate in secondary channel features that provide thermal refugia. However, temperature regimes vary among and within features. Improved understanding of physical processes controlling thermal regimes is needed. This study developed a dimensionless index for assessment of thermal refugia on the upper Willamette River. The novel hyporheic insolation (HIN) index uses minimal field measurements to predict thermal refugia resulting from buffering. Continuous water temperature...

Predicted increases in extreme droughts will likely cause major shifts in carbon sequestration and forest composition. Although growth declines during drought are widely documented, an increasing number of studies have reported both positive and negative responses to the same drought. These divergent growth patterns may reflect thresholds (i.e., nonlinear responses) promoted by changes in the dominant climatic constraints on tree growth. Here we tested whether stemwood growth exhibited linear or nonlinear responses to temperature and precipitation and whether stemwood growth thresholds...

Climate change is driving widespread changes in ecological communities. Warming temperatures often shift community composition toward more heat-tolerant taxa. The factors influencing the rate of this “thermophilization” process remain unclear. Using 10-y census data from an extensive forest plot network, we show that mature tree communities of the western United States have undergone thermophilization. The mean magnitude of climate warming over the 10-y study interval was 0.32 °C, whereas the mean magnitude of thermophilization was 0.039 °C. Differential tree mortality was the strongest...

Climate change is increasing the severity and duration of drought events experienced by forest ecosystems. Because water is essential for tree physiological processes, the ability of trees to survive prolonged droughts will largely depend on whether they have access to reliable water sources. While many woody plant species exhibit the ability to shift water sources between different depths of soil and rock water in response to changes in climate and water availability, it is unclear if Sierra Nevada conifers exhibit this plasticity. Here we analysed the δ18O and δ13C values of annual tree...