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.
Intellectual Merit. This project (Research at Undergraduate Institutions -RUI Award #1122092) has resulted in a new perspective regarding the importance of cloud regimes to the physiology and ecology of the vast majority of mountain forest tree species that experience daily clouds. By contrasting the southern Appalachian Mountains with the southern Rocky Mountains of the US, we found a strong physiological dependence on both morning cloud cover typical of the Appalachians and the afternoon cloud patterns characteristic of the more continental Rocky Mountains. In both cases, the dominant tree species showed improved water status and, thus, greater photosynthetic performance generated by their contrasting cloud patterns. For the Appalachian tree species we discovered that the typical morning immersion in clouds enabled water uptake by leaves that added to the improved water relations during afternoon periods, simply due to the fact that daily transpiration is much reduced during morning cloud immersion. Moreover, this reduction led to lower water stress in the afternoon and a corresponding increase in photosynthetic carbon gain. Similarly for the Rocky Mountain tree species, afternoon clouds resulted in a significant savings in water loss and increases in photosynthesis. In addition, rapid changes in heavy cloud cover and clear-sky intervals did not result in significant declines in photosynthesis due to such rapid and extreme changes in incident sunlight. Given current scenarios for climate warming and probable alterations in cloud regimes for the US. Overall, these data are predictive of possibly serious ecophysiological impacts on these forest trees under current scenarios of continued climate warming and probable changes in cloud regimes for these regions. Broader Impacts. A total of eight undergraduate students, four PhD graduate students, and two assistant professors were involved in this project. Four of the undergraduate students are considered underrepresented in the area of science, engineering, and mathematics. Four of the undergraduates have gone on to graduate two of the PhD students now have postdoctoral positions. In addition, this research has received attention by several media outlets, including dissemination on a web site linked to the major social media outlets. This work has also been presented at three different meetings of national/international research societies, e.g. The Ecological Society of America (ESA). Five publications in internationally refereed journals have also resulted directly from this research, including co-authorships for several of the undergraduate students involved in the field and laboratory work. The collaborator from the RUI institution (Dr. Niky Hughes) recently received a scholarship award from her university (High Point University, High Point, NC) that was bolstered substantially by this award-- a rare NSF grant for this institution designed primarily for undergraduate teaching, i.e. an RUI institution.