Treesearch

Climate classifications supply climate visualization with inference about general vegetation types. The Köppen classification system of thermal classes and an arid class is widely used, but options are available to strengthen climate change detection. For this study, I incorporated temperature and aridity information into all climate classes to isolate climate change, added a hypertropical class to better detect warming and drying in tropical zones, and developed a consistent ruleset of thermal classes with one temperature variable for streamlined application, yet maintained primary Köppen...

Present-day species distributions modeled with climate variables cannot provide potential future climate space for species that have contracted in range due to extirpations, regardless of abundant sample sizes within current ranges. My objective was to examine effects of range contractions on modeling of species to determine suitable space under climate change, exploring different approaches to modeling based on historical range maps. As examples of this issue, I estimated the current and future bioclimate envelopes of American bison (Bison bison) and elk (Cervus elaphus) from their...

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...

Climate change is associated with shifts in the geographic range of trees and other taxa globally. In North America and elsewhere tree species’ ranges are expected to shift at rates of meters to kilometers annually. However, empirically detecting a shift in the range of a tree species may be difficult due to the lack of quality long-term regional or national data. Evidence of range shifts is further confounded by apparently contradictory findings from separate studies that use different methods to evaluate species responses. In this study we examine U.S. Forest Service Forest Inventory...

Dispersed recreation is an important use of national forests, including in experimental forests where long-term research is conducted to evaluate effects of environment and disturbances on ecosystems. Recreation has markedly increased in Bent Creek Experimental Forest since it was established in 1925. The objective of this investigation was to quantify visitors, their activities, and associated vehicular traffic to provide a baseline for evaluating the effects of recreation on the experimental forest environment and to identify potential research opportunities. In a core study conducted...

Prescribed fall burning is commonly used worldwide on rangeland sites to enhance vegetation resources and restore disturbed ecosystems, but little is known about how it may alter microbial communities and insect activities. We used two site treatments (low- to moderate-burn severity plots and unburned control plots) at a high-elevation (2 100 m above sea level) shrub-steppe rangeland site. Four yr after the prescribed burn, captured insects primarily consisted of Coleoptera (beetles), Hymenoptera (ants, bees, and wasps), and Orthoptera (grasshoppers and crickets) species with similar or...

Great Basin bristlecone pine (Pinus longaeva D.K. Bailey) presence in the Stansbury Mountains of north-central Utah has been reported prior to the year 2020, but these reports lack adequate population characterization and the delineation of distinct stands of trees. In summer 2020, we identified and documented the presence of 5 separate stands of bristlecone pine in the Stansbury Mountains. These stands are removed from the nearest bristlecone populations in other mountain ranges by a distance of approximately 120 km; as such, they represent a unique outlier population of the species. We...

High-severity fires and short-interval reburns strongly influence forest structure and composition and may overwhelm forest ecosystem resilience and catalyze persistent shifts to non-forest conditions. Recent increases in annual area burned and severity in the western United States (US) highlight the need to better understand the long-term effects of high-severity fire, including interactions with subsequent fires. In the early 20th century, the northern US Rocky Mountains experienced several fire seasons with widespread, high-severity fires, under fire weather comparable with extreme...