Carbon fractions in the world\u2019s dead wood

Adam R Martin,Grant M Domke,Mahendra Doraisami,Sean C Thomas

doi:10.1038/s41467-021-21149-9

Abstract

A key uncertainty in quantifying dead wood carbon (C) stocks—which comprise ~8% of total forest C pools globally—is a lack of accurate dead wood C fractions (CFs) that are employed to convert dead woody biomass into C. Most C estimation protocols utilize a default dead wood CF of 50%, but live tree studies suggest this value is an over-estimate. Here, we compile and analyze a global database of dead wood CFs in trees, showing that dead wood CFs average 48.5% across forests, deviating significantly from 50%, and varying systematically among biomes, taxonomic divisions, tissue types, and decay classes. Utilizing data-driven dead wood CFs in tropical forests alone may correct systematic overestimates in dead wood C stocks of ~3.0 Pg C: an estimate approaching nearly the entire dead wood C pool in the temperate forest biome. We provide for the first time, robust empirical dead wood CFs to inform global forest C estimation.

Highlights

A key uncertainty in quantifying dead wood carbon (C) stocks—which comprise ~8% of total forest C pools globally—is a lack of accurate dead wood C fractions (CFs) that are employed to convert dead woody biomass into C
Dead wood carbon fractions compared to IPCC protocols and live wood
The average estimated dead wood CFs are significantly larger than live wood CF that averages 47.2 ± 0.8% (F1, 3392.7 = 67.7, p < 0.001; Fig. 1)

Summary

Introduction

A key uncertainty in quantifying dead wood carbon (C) stocks—which comprise ~8% of total forest C pools globally—is a lack of accurate dead wood C fractions (CFs) that are employed to convert dead woody biomass into C. Global forest C sinks owe to high net uptake in regenerating forests of ~1.3 Pg C year−1; intact forests contribute an additional sink of 0.85–2.4 Pg C year−1 1,2, recent evidence indicates that the strength of this sink is declining in the tropics[3] and across North America[4]. These sinks are offset by losses of C due to deforestation and forest degradation, in tropical regions where forest loss accounts for ~0.43–1.3 Pg C year−1 on average[2,5]. Dead wood C dynamics are sensitive to fine-scale disturbances such as harvesting, windstorm impacts, wildfires, and pest or pathogen outbreaks (e.g., refs. 9,10)

Methods

Results

Conclusion