Potential changes in cloud patterns due to global warming are of critical importance because of their strong influence on sunlight, temperature, and precipitation experienced by plant communities. Plants are especially sensitive to changes in cloud cover because sunlight, temperature, and water availability are important factors driving photosynthetic carbon gain, growth, reproduction, and spatial distribution patterns. The most dramatic response to changes in cloud patterns are projected for plant communities currently characterized by frequent cloud cover (e.g. mountain cloud forests, temperate and tropical rainforests). The purpose of this project is to use field measurements of photosynthesis, water stress, leaf temperature, and growth of native tree species in the Southern Appalachians Mountains (eastern US) and the Rocky Mountains (western US) under a range of naturally-occurring cloud regimes. From these data, a model will be developed that predicts long term effects of changing cloud-cover patterns on future growth and survival. These forest ecosystems represent two common types of mountain cloud regimes found across the globe?morning cloud-immersion and afternoon broken clouds, respectively. These forest tree species are physiologically adapted to their current climactic conditions, and it is anticipated that predicted changes in cloud cover may result in increased water, sunlight, and leaf temperature stress, leading ultimately to geographic and altitudinal migration, and/or extinction. Loss or decline of these high-mountain forests would have major impacts on such important features as timber production, snow accumulation, and corresponding water supply for agricultural and municipal use. This project will involve a collaborative effort between a university with a strong graduate program (Wake Forest University) and a local liberal arts college lacking the facilities and equipment to facilitate undergraduate research (High Point University). Three undergraduates from HPU (from underrepresented groups in science) have committed to the project and are highly motivated to become graduate students.