Carbon fluxes across three climatically-distinct forest chronosequences in Oregon Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/ng451n854

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  • Biometric and gas exchange techniques were used to measure soil respiration (soil surface CO₂ efflux) and NEP (Net Ecosystem Production) across three climatically-distinct forest chronosequences in Oregon. Results indicate significant forest type, age, and forest type x age interaction effects on annual soil respiration. A regional age class distribution skewed away from the youngest and oldest forests moderate regional variation in soil respiration. Sensitivity analysis suggests that the regional variation in annual soil respiration is most dependent on summer base rates (i.e. soil respiration normalized to a common temperature) and much less dependent on site-specific temperature response curve (to which annual rates are relatively insensitive) and soil degree-days (which vary only 10% among sites). Across all plots, annual soil respiration was not correlated with aboveground net primary production (ANPP, R²=O.06, p>0.1) but it was correlated with belowground net primary production (R²=0.43, p<0.001). Despite the wide range in temperature and precipitation regimes experienced by these forests, all exhibited similar soil respiration per unit fine root biomass, (R²=0.45, p<0.00l). Forest floor mass and mineral soil carbon were only weakly coupled to soil respiration (R²=0.14, and 0.12, respectively). Trends between soil respiration, production, and root mass among age classes within cover type were inconsistent and do not always reflect cross-site trends. NEP was highly negative immediately following stand replacing disturbance in all forests and recovered to positive values by 10, 20, and 30 years of age for the mild and mesic Coast Range, West Cascades and East Cascades, respectively. The response of stand-level NEP to individual disturbance events is greater than that attributable to edaphoclimatic differences between forest type. However, when successional trends in NEP are weighted by current age class distributions, the variability in landscape-level NEP attributable to whole disturbance regimes is equivalent to that attributable regional edaphoclimatic differences between forest types. Simulations of age class distribution under varying disturbance frequencies suggest that the sensitivity of landscape-level NEP to changes in disturbance regime varies among forest types and is linked to both remnant detritus and photosynthetic recovery rate that are partly a function of long-term edaphoclimatic differences.
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