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, management, and forest type influences on carbon dynamics of West-Coast US forests

Net uptake of carbon from the atmosphere (net ecosystem production, NEP) is dependent on climate, disturbance history, management practices, forest age, and forest type. To improve understanding of the influence of these factors on forest carbon flux in the western U.S., a combination of federal inventory data and supplemental ground measurements was used to estimate several important components of NEP in forests in Oregon and Northern California during the 1990’s. The specific components studied were live and dead biomass stores, net primary productivity (NPP), and mortality. In the semi-arid Northern Basin and mesic Coast Range, mean total biomass was 4 and 24 Kg C m-2, and mean NPP was 0.28 and 0.78 Kg C m-2 y-1, respectively. These values were obtained using species- and ecoregionspecific allometric equations and tended to be higher than those obtained from more generalized approaches. There is strong evidence that stand development patterns of biomass accumulation, net primary production, and mortality differ due to climate (ecoregion), management practices (ownership), and forest type. Among those three factors and across the whole region, maximum NPP and dead biomass stores were most influenced by climate, while maximum live biomass stores and mortality were mostly influenced by forest type. Live and dead biomass, NPP, and mortality were most influenced by forest type. Decrease in NPP with age was not general across ecoregions, with no marked decline in old stands (>200 years) in some ecoregions, and in others, the age at which NPP declined was very high (458 years in East Cascades, 325 in Klamath Mountains, 291 in Sierra Nevada). There is high potential for increasing total carbon storage by increasing rotation age and reducing harvest rates in this region. Only 1% of forest plots on private lands were >200 years old, whereas 41% of the plots were greater than 200 years old on public lands. Total carbon stocks could increase from 3.2 Pg C to 7.3 Pg C and NPP could increase from 0.109 Pg C y-1 to .168 Pg C y-1 (a 35% increase) if forests were managed for maximum carbon storage by increasing rotation age.Keywords: climate, forests, carbon, inventor

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

An integration framework for linking avifauna niche and forest landscape models.

Avian cavity nesters (ACN) are viable indicators of forest structure, composition, and diversity. Utilizing these species responses in multi-disciplinary climate-avian-forest modeling can improve climate adaptive management. We propose a framework for integrating and evaluating climate-avian-forest models by linking two ACN niche models with a forest landscape model (FLM), LANDIS-II. The framework facilitates the selection of available ACN models for integration, evaluation of model transferability, and evaluation of successful integration of ACN models with a FLM. We found selecting a model for integration depended on its transferability to the study area (Northern Rockies Ecoregion of Idaho in the United States), which limited the species and model types available for transfer. However, transfer evaluation of the tested ACN models indicated a good fit for the study area. Several niche model variables (canopy cover, snag density, and forest cover type) were not directly informed by the LANDIS-II model, which required secondary modeling (Random Forest) to derive values from the FLM outputs. In instances where the Random Forest models performed with a moderate classification accuracy, the overall effect on niche predictions was negligible. Predictions based on LANDIS-II simulations performed similarly to predictions based on the niche model's original training input types. This supported the conclusion that the proposed framework is viable for informing avian niche models with FLM simulations. Even models that poorly approximate habitat suitability, due to the inherent constraints of predicting spatial niche use of irruptive species produced informative results by identifying areas of management focus. This is primarily because LANDIS-II estimates spatially explicit variables that were unavailable over large spatial extents from alternative datasets. Thus, without integration, one of the ACN niche models was not applicable to the study area. The framework will be useful for integrating avifauna niche and forest ecosystem models, which can inform management of contemporary and future landscapes under differing management and climate scenarios

Evaluating the Impacts of Seasonal Root and Litter Quality and Biomass on Belowground Carbon Dynamics

Soil carbon is the largest terrestrial carbon sink in the biosphere. Heterotrophic soil respiration (Rh) is one terrestrial to atmospheric flux path for carbon, an important component in climate change. While the relationship of soil respiration with soil temperature and moisture is well studied, less is known about the impact of seasonally available soil organic matter (SOM). This project aims to better understand Rh, specifically its relationship with seasonal forest litter and root variation. Through biannual root and monthly litter biomass collections, as well as seasonal measurements of carbon and nitrogen ratios (CN), we will determine the impact root and litter quantity and quality has on Rh. We anticipate that root biomass die-off and litter accumulation during the fall will increase Rh. Further, we expect fall CN ratios to decrease, resulting in higher carbon use efficiency in microbial decomposers and increased Rh compared to the spring. This would suggest seasonal variations in SOM CN may amplify Rh flux patterns resulting from seasonal biomass differences. This project seeks to verify the impact of seasonal biomass on Rh , and determine if biomass alone is an effective tool for modelling soil respiration factors, or if seasonal CN differences must also be accounted for

Interactive Effects of Environmental Change and Management Strategies on Regional Forest Carbon Emissions

International audienc

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