Fire and the Distribution and Uncertainty of Carbon Sequestered as Aboveground Tree Biomass in Yosemite and Sequoia & Kings Canyon National Parks

Abstract

Abstract:Fire is one of the principal agents changing forest carbon stocks and landscape level distributions of carbon, but few studies have addressed how accurate carbon accounting of fire-killed trees is or can be. We used a large number of forested plots (1646), detailed selection of species-specific and location-specific allometric equations, vegetation type maps with high levels of accuracy, and Monte Carlo simulation to model the amount and uncertainty of aboveground tree carbon present in tree species (hereafter, carbon) within Yosemite and Sequoia & Kings Canyon National Parks. We estimated aboveground carbon in trees within Yosemite National Park to be 25 Tg of carbon (C) (confidence interval (CI): 23-27 Tg C), and in Sequoia & Kings Canyon National Park to be 20 Tg C (CI: 18-21 Tg C). Low-severity and moderate-severity fire had little or no effect on the amount of carbon sequestered in trees at the landscape scale, and high-severity fire did not immediately consume much carbon. Although many of our data inputs were more accurate than those used in similar studies in other locations, the total uncertainty of carbon estimates was still greater than ±10%, mostly due to potential uncertainties in landscape-scale vegetation type mismatches and trees larger than the ranges of existing allometric equations. If carbon inventories are to be meaningfully used in policy, there is an urgent need for more accurate landscape classification methods, improvement in allometric equations for tree species, and better understanding of the uncertainties inherent in existing carbon accounting methods.

Global importance of large‐diameter trees

“…We note that this calculation of the size of the plot required is a measure of spatial variation within the forest, and does not depend on the accuracy of the allometric equations used for calculating each tree's biomass. Allometric equations can be imprecise for large‐diameter trees, both because of their structural variability and the enormous sampling effort, and therefore our estimates of overall biomass could be off by ± 15% (Lutz et al, ).…”

Fixing a snag in carbon emissions estimates from wildfires

“…United States indicate actual combustion is nearly nonexistent for mature trees in fire-prone ecosystems (Campbell, Alberti, Martin, & Law, 2009;Lutz et al, 2017).…”

“…The largest discrepancies between modeled and observed combustion of aboveground biomass exist for live, mature trees, which are the dominant pool of aboveground carbon across western US forests (Ghimire, Williams, Collatz, & Vanderhoof, ; Hudiburg et al, ; Wilson, Woodall, & Griffith, ). Default values for live tree bole (stem) combustion can range from 30%–80% (S1 and S2) in high‐severity events, but post‐fire observations in the western United States indicate actual combustion is nearly nonexistent for mature trees in fire‐prone ecosystems (Campbell, Alberti, Martin, & Law, ; Campbell, Fontaine, & Donato, ; Lutz et al, ). Field experiments show that there is inadequate prolonged heat to facilitate combustion of live tree stems, even at the highest fire intensities (Smith et al, ; Sparks et al, ).…”

“…is in conflict with observations (Lutz et al, 2017). It is important to rectify overestimates because governments are currently using mortality and emissions estimates from fire to inform land management decisions intended to mitigate climate change (California, Executive Department, 2018;Fears & Eilperin, 2019;Nunez, 2006;Oregon, 2005;UNFCCC, 2015; U.S. Executive Office of the President, 2018), emphasizing the need for model improvement using field observations.…”

Advancing Fire Science with Large Forest Plots and a Long-Term Multidisciplinary Approach

“…Fine-scale spatial pattern plays an important role in mediating post-fire effects, either through density-dependent mortality or aggregated post-fire forest development [20,21]. The importance of spatial heterogeneity to the correct calculation of landscape carbon [22][23][24] and remnant forest patches (e.g., refugia [25][26][27][28]) has been well established, but the spatial distribution of fire-caused mortality remains understudied. When spatial patterns of fire mortality are considered, they are usually inferred from Landsat-derived spectral changes at a 900 m 2 grain [29][30][31][32], but this scale is almost certainly too coarse to determine causes and consequences of tree mortality (Figure 1).…”