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Pacific Northwest Research Station

  • New biomass estimates for chaparral-dominated Southern California landscapes

    Chaparral shrublands are the dominant wildland vegetation type in Southern California and the most extensive ecosystem in the state. Disturbance by wildfire and climate change have created a dynamic landscape in which biomass mapping is key in tracking the ability of chaparral shrublands to sequester carbon. Despite this importance, most national and regional scale estimates do not account for shrubland biomass. Employing plot data from several sources, we built a random forest model to predict aboveground live biomass in Southern California using remote sensing data (Landsat Normalized Difference Vegetation Index (NDVI)) and a suite of geophysical variables. By substituting the NDVI and precipitation predictors for any given year, we were able to apply the model to each year from 2000 to 2019. Using a total of 980 field plots, our model had a k-fold cross-validation R2 of 0.51 and an RMSE of 3.9. Validation by vegetation type ranged from R2 = 0.17 (RMSE = 9.7) for Sierran mixed-conifer to R2 = 0.91 (RMSE = 2.3) for sagebrush. Our estimates showed an improvement in accuracy over two other biomass estimates that included shrublands, with an R2 = 0.82 (RMSE = 4.7) compared to R2 = 0.068 (RMSE = 6.7) for a global biomass estimate and R2 = 0.29 (RMSE = 5.9) for a regional biomass estimate. Given the importance of accurate biomass estimates for resource managers, we calculated the mean year 2010 shrubland biomasses for the four national forests that ranged from 3.5 kg/m2 (Los Padres) to 2.3 kg/m2 (Angeles and Cleveland). Finally, we compared our estimates to field-measured biomasses from the literature summarized by shrubland vegetation type and age class. Our model provides a transparent and repeatable method to generate biomass measurements in any year, thereby providing data to track biomass recovery after management actions or disturbances such as fire.

    Content Type: Publications

  • Riverine dissolved organic carbon and freshwater export in the eastern Gulf of Alaska

    The coastal zone of southeast Alaska contains thousands of streams and rivers that drain one of the wettest, carbon‐rich, and most topographically varied regions in North America. Watersheds draining temperate rainforests, peatlands, glaciers, and three large rivers that flow from the drier interior of the Yukon Territory and British Columbia discharge water and dissolved organic carbon (DOC) into southeast Alaskan coastal waters. This area, which we have designated the southeast Alaska drainage basin (SEAKDB), discharges about twice as much water as the Columbia or Yukon Rivers. An understanding of the timing, location, and source of water and DOC guides research to better understand the influence of terrestrial outputs on the adjacent marine systems. Additionally, a spatially extensive understanding of riverine DOC flux will improve our understanding of lateral losses related to terrestrial carbon cycling. We estimate 1.17 Tg C yr−1 of DOC enters the adjacent marine system along with 430 km2 of freshwater that influences estuary, shelf, and Gulf of Alaska hydrology. We estimate that 23% to 66% of the DOC entering coastal waters is bioavailable and may influence metabolism and productivity within the marine system. The combination of the large and spatially distributed water and DOC input, long and complex shoreline, large enclosed estuarine volume, and bounded nearshore coastal currents suggests that the physiographic structure of southeast Alaska may have a significant impact on the metabolism of riverine DOC in coastal marine ecosystems.

    Content Type: Publications

  • Planting trees to mitigate climate change: Policy incentives could lead to increased carbon sequestration

    The 741 million acres of forestland in the United States play a role in mitigating the effects of climate change by sequestering nearly 16 percent of the atmospheric carbon dioxide emissions produced annually in our country. Reducing the conversion of forestland to other uses and planting even more trees, whether through afforestation or reforestation, would increase the nation’s carbon storage capacity. The U.S. Department of Agriculture (USDA) has several incentive programs to accomplish these goals.

    Researchers with the USDA Forest Service and Portland State University modeled various scenarios to determine how carbon sequestration would increase if the agency increased its financial investment in these tree planting and forest conservation programs. They also modeled how a 10-percent reduction in the area burned by stand-replacing wildfires could affect carbon sequestration. Because increasing levels of atmospheric carbon has a social cost, they calculated the monetary value of the carbon sequestrated.

    The research team found that afforestation and reforestation policies yielded the greatest return in carbon sequestration. By 2050, 469 teragrams (Tg) of carbon dioxide equivalent per year (CO2 eq/yr) could be sequestered compared to a baseline scenario of 323 Tg CO2 eq/yr. They estimated the cost of expanding afforestation and reforestation programs at $6.5 billion, far less than the estimated $93.6 billion in monetary benefits that the increased carbon sequestration from expanding these programs was projected to yield.

    Content Type: Publications

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