Seasonal and Topographic Variation in Net Primary Productivity and Water Use Efficiency in a Southwest Sky Island Fores
Abstract
Western North American Forests represent an uncertain sink for atmospheric carbon. While understanding of the physical drivers of productivity in these forests has grown in the last decade, the relative influence of topographic position in the complex terrain of montane systems remains understudied. The high-latitude mixed conifer forest ecosystems of the southern Arizona Madrean Sky Islands are characterized by low precipitation, high annual variation in temperature, and heterogeneous topography. Eddy covariance measurements these forests show distinct seasonal trends due to temperature and bi-modal precipitation patterns, but these measurements are unable to resolve potential differences in physiological function on opposing north and south aspects within the footprint of the tower. Most of the year, north aspects receive less energy input due to the oblique angle of incoming solar radiation, leading to a divergence in soil moistures and temperatures. However, overall movement of energy and material is much higher on these north aspects on an annual basis. The implications of these differences for net primary productivity (NPP) and water use efficiency (WUE) are poorly addressed in the literature. We evaluated the relative control that topography has on the physical environment (soil moisture and temperature) and how these factors affect water stress, NPP, and WUE. We combined leaf-level measurements of photosynthesis and transpiration with other physiological and meteorological measurements to determine how the dominant vegetation functions as a result of microclimatic conditions. Initial results from the spring and summer measurement periods suggest topographical differences in microclimate, resulting in differences in NPP in the spring, but not the summer. Also, each of the three species on the same aspect responded differently to the same microclimatic conditions, underscoring interspecific variation at the site. How might these patterns change throughout an annual cycle of sun angles that differentially influence the soil surface? A more complete picture of seasonal behavior will be developed with the addition of fall and winter measurements. These conclusions should provide a more complete picture of ecosystem function to the benefit of foresters and modelers.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2016
- Bibcode:
- 2016AGUFM.B11B0456M
- Keywords:
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- 0426 Biosphere/atmosphere interactions;
- BIOGEOSCIENCESDE: 0428 Carbon cycling;
- BIOGEOSCIENCESDE: 1813 Eco-hydrology;
- HYDROLOGYDE: 1818 Evapotranspiration;
- HYDROLOGY