Analysis of the regional carbon balance of Pacific Northwest forests under changing climate, disturbance, and management for bioenergy

Atmospheric carbon dioxide levels have been steadily increasing from anthropogenic energy production, development and use. Carbon cycling in the terrestrial biosphere, particularly forest ecosystems, has an important role in regulating atmospheric concentrations of carbon dioxide. US West coast forest management policies are being developed to implement forest bioenergy production while reducing risk of catastrophic wildfire. Modeling and understanding the response of terrestrial ecosystems to changing environmental conditions associated with energy production and use are primary goals of global change science. Coupled carbon-nitrogen ecosystem process models identify and predict important factors that govern long term changes in terrestrial carbon stores or net ecosystem production (NEP). By quantifying and reducing uncertainty in model estimates using existing datasets, this research provides a solid scientific foundation for evaluating carbon dynamics under conditions of future climate change and land management practices at local and regional scales. Through the combined use of field observations, remote sensing data products, and the NCAR CESM/CLM4-CN coupled carbon-climate model, the objectives of this project were to 1) determine the interactive effects of changing environmental factors (i.e. increased CO₂, nitrogen deposition, warming) on net carbon uptake in temperate forest ecosystems and 2) predict the net carbon emissions of West Coast forests under future climate scenarios and implementation of bioenergy programs. West Coast forests were found to be a current strong carbon sink after accounting for removals from harvest and fire. Net biome production (NBP) was 26 ± 3 Tg C yr⁻¹, an amount equal to 18% of Washington, Oregon, and California fossil fuel emissions combined. Modeling of future conditions showed increased net primary production (NPP) because of climate and CO₂ fertilization, but was eventually limited by nitrogen availability, while heterotrophic respiration (R[subscript h]) continued to increase, leading to little change in net ecosystem production (NEP). After accounting for harvest removals, management strategies which increased harvest compared to business-as-usual (BAU) resulted in decreased NBP. Increased harvest activity for bioenergy did not reduce short- or long-term emissions to the atmosphere regardless of the treatment intensity or product use. By the end of the 21st century, the carbon accumulated in forest regrowth and wood product sinks combined with avoided emissions from fossil fuels and fire were insufficient to offset the carbon lost from harvest removals, decomposition of wood products, associated harvest/transport/manufacturing emissions, and bioenergy combustion emissions. The only scenario that reduced carbon emissions compared to BAU over the 90 year period was a 'No Harvest' scenario where NBP was significantly higher than BAU for most of the simulation period. Current and future changes to baseline conditions that weaken the forest carbon sink may result in no change to emissions in some forest types

Climate Change, Woodpeckers, and Forests: Current Trends and Future Modeling Needs

The structure and composition of forest ecosystems are expected to shift with climate‐induced changes in precipitation, temperature, fire, carbon mitigation strategies, and biological disturbance. These factors are likely to have biodiversity implications. However, climate‐driven forest ecosystem models used to predict changes to forest structure and composition are not coupled to models used to predict changes to biodiversity. We proposed integrating woodpecker response (biodiversity indicator) with forest ecosystem models. Woodpeckers are a good indicator species of forest ecosystem dynamics, because they are ecologically constrained by landscape‐scale forest components, such as composition, structure, disturbance regimes, and management activities. In addition, they are correlated with forest avifauna community diversity. In this study, we explore integrating woodpecker and forest ecosystem climate models. We review climate–woodpecker models and compare the predicted responses to observed climate‐induced changes. We identify inconsistencies between observed and predicted responses, explore the modeling causes, and identify the models pertinent to integration that address the inconsistencies. We found that predictions in the short term are not in agreement with observed trends for 7 of 15 evaluated species. Because niche constraints associated with woodpeckers are a result of complex interactions between climate, vegetation, and disturbance, we hypothesize that the lack of adequate representation of these processes in the current broad‐scale climate–woodpecker models results in model–data mismatch. As a first step toward improvement, we suggest a conceptual model of climate–woodpecker–forest modeling for integration. The integration model provides climate‐driven forest ecosystem modeling with a measure of biodiversity while retaining the feedback between climate and vegetation in woodpecker climate change modeling

Ds01_supportingdataset_firehistoryrecord

Fire history record used as input for fire occurrence in DayCen

Thinning effects on forest productivity: Consequences of preserving old forests and mitigating impacts of fire and drought

Background: Management strategies have been proposed to minimise the effects of climate change on forest resilience. Aims: We investigated the Pacific Northwest US region forest carbon balance under current practices, and changes that may result from management practices proposed for the region’s 34 million ha of forests to mitigate climate change effects. Methods: We examined the relationship between NPP and biomass, using plot data, and estimated the effects of proposed clear-cut harvest of young mesic forests for wood products and bioenergy while preserving mesic mature/old forests for biodiversity (Sparing), thinning all forests (Sharing), and a combination of sparing mesic mature and old, clearing mesic young, and thinning dry forests (Sparing/Sharing). Results: The forests of the region were found highly productive (NPP 163 Tg C year⁻¹) and a strong carbon sink with NEP of 45 Tg C year⁻¹. Observations indicated the relationship between NPP and biomass was not significantly different for thinned versus unthinned stands, after accounting for site quality and precipitation effects. After simulating proposed management to mitigate climate change, regional NPP was reduced by 35% (Sparing), 9% (Sharing), and 29% (Sparing/Sharing) compared with current practices. Conclusions: Applying management practices appropriate for current forest conditions to mitigate future climate change impacts can be accomplished, but at a cost of reducing NPP. Sparing all forests >50 years old resulted in the largest NPP reduction, but the impact could be reduced by clearing only a subset of young forests.Keywords: fire, harvest, drought, disturbance, forest carbon processe

Thinning effects on forest productivity: consequences of preserving old forests and mitigating impacts of fire and drought

International audienceBackground: Management strategies have been proposed to minimise the effects of climate change on forest resilience.Aims: We investigated the Pacific Northwest US region forest carbon balance under current practices, and changes that may result from management practices proposed for the region's 34 million ha of forests to mitigate climate change effects.Methods: We examined the relationship between net primary production (NPP) and biomass, using plot data, and estimated the effects of proposed clear-cut harvest of young mesic forests for wood products and bioenergy while preserving mesic mature/old forests for biodiversity (Sparing), thinning all forests (Sharing) and a combination of sparing mesic mature and old, clearing mesic young and thinning dry forests (Sparing/Sharing).Results: The forests of the region were found highly productive (NPP 163 Tg C year−1) and a strong carbon sink with net ecosystem production of 45 Tg C year−1. Observations indicated the relationship between NPP and biomass was not significantly different for thinned versus unthinned stands, after accounting for site quality and precipitation effects. After simulating proposed management to mitigate climate change, regional NPP was reduced by 35% (Sparing), 9% (Sharing) and 29% (Sparing/Sharing) compared with current practices.Conclusions: Applying management practices appropriate for current forest conditions to mitigate future climate change impacts can be accomplished, but at a cost of reducing NPP. Sparing all forests >50 years old resulted in the largest NPP reduction, but the impact could be reduced by clearing only a subset of young forests

DayCent .100 files

Parameterization/Input files for DayCent simulation

Model Output

output used to create figures and computation

Model Climate Input

Climate forcing data for DayCen

Data from: Fire-regime variability impacts forest carbon dynamics for centuries to millennia

Wildfire is a dominant disturbance agent in forest ecosystems, shaping important biogeochemical processes including net carbon (C) balance. Long-term monitoring and chronosequence studies highlight a resilience of biogeochemical properties to large, stand-replacing, high-severity fire events. In contrast, the consequences of repeated fires or temporal variability in a fire regime (e.g., the characteristic timing or severity of fire) are largely unknown, yet theory suggests that such variability could strongly influence forest C trajectories (i.e., future states or directions) for millennia. Here we combine a 4500-year paleoecological record of fire activity with ecosystem modeling to investigate how fire-regime variability impacts soil C and net ecosystem carbon balance. We found that C trajectories in a paleo-informed scenario differed significantly from an equilibrium scenario (with a constant fire return interval), largely due to variability in the timing and severity of past fires. Paleo-informed scenarios contained multi-century periods of positive and negative net ecosystem C balance, with magnitudes significantly larger than observed under the equilibrium scenario. Further, this variability created legacies in soil C trajectories that lasted for millennia. Our results imply that fire-regime variability is a major driver of C trajectories in stand-replacing fire regimes. Predicting carbon balance in these systems, therefore, will depend strongly on the ability of ecosystem models to represent a realistic range of fire-regime variability over the past several centuries to millennia

Belowground Carbon Allocation in a Mixed Conifer Forest in the Northern Rockies

Understanding how the exchange of carbon dioxide between vegetation and the atmosphere contributes to climate change is becoming an increasingly important issue for scientists, policy makers, and land owners. Forest ecosystems store approximately 50% of global terrestrial carbon with a significant amount in belowground pools. Knowledge about the amount of carbon allocated to belowground pools is lacking, especially seasonal allocation to fine root biomass and baseline values of forest soil carbon prior to management or land use change. We are collecting field observations to establish baseline soil carbon densities and seasonal fine root allocation in a mixed conifer forest of Northern Idaho. The observations will be analyzed for differences due to canopy cover, species composition, and soil moisture gradients. This project is part of a larger field experiment studying the effects of thinning on forest biogeochemical cycling. Data is forthcoming and we expect it to contribute to scientific knowledge about forest carbon storage in temperate coniferous forests