New Biomass Estimates for Chaparral-Dominated Southern California Landscapes

Abstract

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.

The effects of prolonged drought on vegetation dieback and megafires in southern California chaparral

“…Remote sensing has been used to assess the impacts of drought on chaparral communities (Dong et al, 2019), estimate changes in biomass (Schrader‐Patton & Underwood, 2021), and monitor changes over time (Coates et al, 2015; Gillespie et al, 2018). To assess the spatial extent of chaparral dieback that occurred following the drought of 2011–2017, and prior to the Thomas and Woolsey Fires, we used Landsat 4/5/7/8 surface reflectance NDVI data (normalized difference vegetation index) data to quantify changes in green biomass or living vegetation.…”

Food for all? Wildfire ash fuels growth of diverse eukaryotic plankton

“…For example, in the nearshore SBC surface waters, atmospheric nitrogen deposition from natural and anthropogenic sources was estimated to account for the largest annually integrated nitrogen flux (430 kg N km −2 yr −1 ) [ 52 ]. Spatio-temporal complexity of atmospheric aerosol deposition precludes precise quantification of Thomas Fire ash deposition to the SBC; however, based on the area burned [ 8 ], average above-ground live biomass (4.2 kg m −2 ) [ 54 ], and assuming 75–100% of vegetation was consumed with 50–80% of biomass undergoing complete combustion [ 40 ] we estimate that 0.7 × 10 9 –2.4 × 10 9 kg of ash was produced by the Thomas Fire. If all ash produced was deposited throughout the SBC (approx.…”

Biomass Assessment and Carbon Sequestration in Post-Fire Shrublands by Means of Sentinel-2 and Gaussian Processes

“…After a fire occurrence, different development stages of the shrub vegetation can be found: areas with low shrub development, others with high shrub development, and areas with only short shrubs or only high size shrubs. Regardless of the stage and structure, remote sensing and field data were used to estimate biomass in shrub areas in Portugal [8] and California [38], to identify changes in aboveground biomass after fire in the Amazon [39], and to evaluate vegetation recovery after fire in Siberia [40]. In this line, the methods can be considered suitable for the proposed objectives of the manuscript as it accurately estimated the carbon stock in small coppice areas.…”