Abstract
A simulation model to estimate net primary productivity (NPP) has been combined with in situ measurements of soil carbon dioxide (CO2) emissions and leaf litter pools in three coast redwood forest stands on the central California coast. Monthly NPP was predicted from the CASA model using 250-meter resolution vegetation index (VI) inputs. Annual NPP was predicted to vary from 380 g·C·m-2·yr-1 to 648 g·C·m-2·yr-1 at central coast redwood sites over the years 2007 to 2010. Measured soil respiration rates at between 0.5 to 2.2 g·C·m-2·d-1 were slightly below the range of measurements previously reported for a second-growth mixed (redwood and Douglas-fir) conifer forests. Although warm monthly temperatures at the southern-most redwood forest sites evidently results in elevated stress levels to sustained redwood growth into the dry summer months of June and July, these redwood stands appear to sequester CO2 from that atmosphere into forest biomass for a net positive ecosystem carbon balance each year.
Highlights
We present the results of the NASACASA (Carnegie-Ames-Stanford Approach) model, which predicts net primary productivity (NPP) fluxes using inputs of climate and satellite imagery as a means to understand coast redwood carbon cycling at the landscape level
Production of plant biomass is estimated as a product of time-varying surface solar irradiance, Sr, and the Enhance Vegetation index (EVI) from MODIS satellite data [22], plus a constant term for maximum light utilization efficiency that is modified by time-varying stress scalar terms for temperature (T) and moisture (W) effects (Eq.1)
Annual NPP was predicted to vary from 380 g·C·m−2·yr−1 to 648 g·C·m−2·yr−1, with the lowest productivity consistently each year estimated for the southern-most Big Creek site and intermediate annual productivity values estimated for the Brazil Ranch site
Summary
The coast redwood is the tallest living tree species and notably long-lived [2]. The historical and cultural significance of coast redwood makes the conservation and scientific study of these forests a continuing priority for ecologists [3,4]. The redwood ecoregion has been identified by the World Wildlife Fund as being in the highest conservation priority class among ecoregions in the United States, based on biological uniqueness, conservation status, and impending threats [2,5]. Climate change may be among the most serious threats to the remaining Pacific coast redwood forests. Johnstone and Dawson [7] reported physiological evidence that coast redwood and other ecosystems along the United States west coast may be increasingly drought stressed under a summer climate of reduced fog frequency and greater evaporative demand. Understanding the current rates of redwood forest productivity and carbon cycling are essential as baseline values against which future changes can be evaluated
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