Graduate Thesis Or Dissertation

 

Carbon storage and fluxes in forests of western Oregon : successional patterns and environmental controls Public Deposited

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/sb397c022

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  • In this study we use a combination of data from forest inventories, intensive chronosequences, extensive sites, and remote sensing, to make estimates of biomass and net primary production (NPP) for the forested region of Western Oregon. Plot-level forest inventory data were provided by the USDA Forest Service through their Forest Inventory and Analysis and Current Vegetation Survey programs. We also use the light use efficiency model 3-PGS to estimate net primary production (NPP) of the forests of western Oregon. We evaluate the performance of the model using the forest inventory NPP dataset as well as with estimates of productivity from eddy flux towers. We also evaluate the belowground carbon allocation scheme employed in the 3-PGS model. The forest age distributions differ by geographic location with fewer old stands in the Coast Range and the East Cascades, and a relatively uniform distribution of ages from 0 to greater than 800 in the West Cascades. Age distributions also differ by land ownership, with fewer old stands on non-federal lands than on national forest lands (maximum ages ~ 250 and >800 respectively). The timing and magnitude of maximum net primary production varies by ecoregion, with high-productivity sites reaching a maximum NP of ~2kg C m⁻² y⁻¹ at about 30 years of age, and low-productivity sites (East Cascades) reaching a maximum NPP ~0.8 kg C m⁻² y⁻¹ between 80 and 100 years. Measurements of additional carbon budget components combined with inventory data provide estimates of carbon storage and fluxes that may be useful for forest management and validation of regional model simulations. A forest productivity model, 3-PGS, was evaluated with NPP data and used to quantify controls on NPP in each of the ecoregions. Overall the 3-PGS model tends to overestimate NPP at high productivity sites and underestimate productivity at moderate and low productivity sites. Overestimates of NPP in the Coast Range are partially a function of the model, in effect, using fPAR to detect successional changes in NPP. Belowground allocation as estimated by the model does not compare well with belowground allocation estimates from forest inventory data and intensive site measurements. The model suggests that NPP is most constrained by environmental factors in the East Cascades (~20% of potential NPP), less constrained in the West Cascades (~45% of potential NPP), and least constrained in the Coast Range (~60% of potential NPP). Coastal Range forests tend to be most limited by temperatures sub-optimal for photosynthesis and summer VPD constraints. East Cascades forests are limited by soil fertility, temperature, VPD, and strong soil water deficits throughout much of the year. Carbon cycle research has reached a point where both small and large scale datasets of carbon storage and fluxes are necessary. There is an increased interest in understanding carbon cycling at regional to global scales and the combined power of large and small scale studies of carbon cycling help us to improve our understanding of successional carbon dynamics. Calibration and evaluation of modelling at these scales could be aided by data collected at equivalent scales.
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