Modeling leaf area as an input to transpiration models in aspen-conifer forests in Big Cottonwood Canyon, Utah using remotely sensed data and geographic information systems

Quaking aspen (Populus tremuloides Michx.) is a major community type in the Intermountain West. Aspen covers approximately 1.29 million hectares throughout the Colorado Plateau, of which 0.291 million are located in Utah. As aspen forests convert to conifer, water runoff is decreased significantly. Part of this decrease in runoff is due to the increased water loss through yearly transpiration of conifers as compared to aspen. A spectrally based model for leaf area index (LAI) has been developed as an input to a transpiration model of aspen stands. The generation of a leaf area model for broadleaf species has not met with the success of similar attempts with conifers. A variety of problems associated with spectrally based LAI measurements include variable canopy structure, the position of communities on various slope aspects that interfere with the spectral sensor's ability to distinguish between varying canopies, and understory leaf area. Slope aspect was a major issue in the development of the reflectance model. A radiance model composed of a combination of radiances received at the sensor and potential irradiance on a slope shows promise in correcting remotely sensed spectral data for variations in slope aspect.