Graduate Thesis Or Dissertation
 

Remote sensing of radiation intercepted by vegetation to estimate aboveground net primary production across western Oregon

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/z029p689h

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  • Remote sensing of variables necessary to estimate net primary production of vegetation over large temporal and spatial scales has been a goal of climate change research. This thesis consists of two studies that address the reliability of satellite and airborne sensors to quantify a basic component of all production models, the amount of light intercepted by vegetation canopies throughout the year. The studies focus on an empirical model of net primary production: NPP = [IPAR*f(T)*f(D)*f(V)]*εu, where IPAR is the amount of incident photosynthetically active radiation intercepted by vegetation during the year, and environmental limits to production are freezing temperatures (T), drought (D), and high vapor pressure deficit (D). A relatively constant energy-use efficiency coefficient (En) would allow broad application of this model to a wide variety of natural vegetation types and climate conditions. The first study showed that the normalized difference vegetation index (NDVI), calculated from field spectrometry, provided a good linear estimate of the fraction of incident PAR intercepted by constructed canopies of bitterbrush (R2 = 0.83) and manzanita shrubs (A2 = 0.86) at an open canopy ponderosa pine site. In the second study, Thematic Mapper Simulator NDVI explained 97% of the variation in %IPAR by shrub and forested sites across Oregon. These studies demonstrated the general ability to estimate %IPAR from remotely sensed observations. The second study showed that the fraction of light intercepted by forest and shrub vegetation, coupled with meterological station measurements of total annual incident radiation, explained 70% of the variation in primary production. Additional limitations on the utilization of light should be considered to estimate production. Constraints on the ability of each species to use intercepted light, as defined by freezing temperatures, drought, and vapor pressure deficit, were quantified from hourly meteorological station measurements and physiological measurements in the field. The environmental limits to light capture by photosynthesis, however, did not improve the ability to explain variation in above-ground NPP across the forested and shrub sites. Differences in carbon allocation patterns among plant life forms appear to be important to fully test primary production models.
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