Effects of projected climate change on vegetation in the Blue Mountains ecoregion, USA

We used autecological, paleoecological, and modeling information to explore the potential effects of climate change on vegetation in the Blue Mountains ecoregion, Oregon (USA). Although uncertainty exists about the exact nature of future vegetation change, we infer that the following are likely to occur by the end of the century: (1) dominance of ponderosa pine and sagebrush will increase in many locations, (2) the forest-steppe ecotone will move upward in latitude and elevation, (3) ponderosa pine will be distributed at higher elevations, (4) subalpine and alpine systems will be replaced by grass species, pine, and Douglas-fir, (5) moist forest types may increase under wetter scenarios, (6) the distribution and abundance of juniper woodlands may decrease if the frequency and extent of wildfire increase, and (7) grasslands and shrublands will increase at lower elevations. Tree growth in energy-limited landscapes (high elevations, north aspects) will increase as the climate warms and snowpack decreases, whereas tree growth in water-limited landscapes (low elevations, south aspects) will decrease. Ecological disturbances, including wildfire, insect outbreaks, and non-native species, which are expected to increase in a warmer climate, will affect species distribution, tree age, and vegetation structure, facilitating transitions to new combinations of species and vegetation patterns. In dry forests where fire has not occurred for several decades, crown fires may result in high tree mortality, and the interaction of multiple disturbances and stressors will probably exacerbate stress complexes. Increased disturbance will favor species with physiological and phenological traits that allow them to tolerate frequent disturbance.