Estimating uncertainty in the volume and carbon storage of downed coarse woody debris

Abstract

Downed coarse woody debris, also known as coarse woody detritus or downed dead wood, is challenging to estimate for many reasons, including irregular shapes, multiple stages of decay, and the difficulty of identifying species. In addition, some properties are commonly not measured, such as wood density and carbon concentration. As a result, there have been few previous evaluations of uncertainty in estimates of downed coarse woody debris, which are necessary for analysis and interpretation of the data. To address this shortcoming, we quantified uncertainties in estimates of downed coarse woody debris volume and carbon storage using data collected from permanent forest inventory plots in the northeastern United States by the Forest Inventory and Analysis program of the USDA Forest Service. Quality assurance data collected from blind remeasurement audits were used to quantify error in diameter measurements, hollowness of logs, species identification, and decay class determination. Uncertainty estimates for density, collapse ratio, and carbon concentration were taken from the literature. Estimates of individual sources of uncertainty were combined using Monte Carlo methods. Volume estimates were more reliable than carbon storage, with an average 95% confidence interval of 15.9 m3/ha across the 79 plots evaluated, which was less than the mean of 31.2 m3/ha. Estimates of carbon storage (and mass) were more uncertain, due to poorly constrained estimates of the density of wood. For carbon storage, the average 95% confidence interval was 11.1 Mg C/ha, which was larger than the mean of 4.6 Mg C/ha. Accounting for the collapse of dead wood as it decomposes would improve estimates of both volume and carbon storage. On the other hand, our analyses suggest that consideration of the hollowness of downed coarse woody debris pieces could be eliminated in this region, with little effect. This study demonstrates how uncertainty analysis can be used to quantify confidence in estimates and to help identify where best to allocate resources to improve monitoring designs.

Carbon fractions in the world’s dead wood

“…There remain several known sources of uncertainty in dead wood C assessments, such as variability in dead wood tissue-density measurements, or limited dead wood inventory data 11 . When compared to these other sources of variability, dead wood CFs can be a minor consideration 11 .…”

“…There remain several known sources of uncertainty in dead wood C assessments, such as variability in dead wood tissue-density measurements, or limited dead wood inventory data 11 . When compared to these other sources of variability, dead wood CFs can be a minor consideration 11 . Yet, because both inter- and intraspecific variation in wood CFs can be accurately accounted for through accurate measurements 20 , 38 and representative sampling designs, these overestimates are systematic and easily corrected.…”

“…Given its importance in the global C cycle, robust methods for quantifying C in dead woody material are critical for estimating forest C stocks and fluxes at multiple scales. However, there remain several critical large sources of uncertainty surrounding estimates of dead wood C stocks and fluxes 11 . One important consideration in estimating dead wood C fluxes that has received limited attention is the proportion of C in dead wood, as it is used to convert dead wood biomass into C stocks 12 .…”

Carbon Storage Dynamics of Secondary Forest Succession in the Central Loess Plateau of China

“…CWD has a slow decomposition rate and can last for decades or even hundreds of years, thus forming a long-term carbon pool. According to Pan's research [11], dead wood accounts for approximately 8% of the world's forest carbon stocks, and the stock of dead wood varies depending on the forest-forming tree species and the forest type [26]. However, these variations are often not taken into account in the estimation of ecosystem carbon stocks, thus leading to little knowledge of the extent to which CWD carbon dynamics affect the ecosystem carbon balance [27].…”

Archaeological documentation of wood caribou fences using unmanned aerial vehicle and very high-resolution satellite imagery in the Mackenzie Mountains, Northwest Territories

“…The CWD-MBG was divided by the FTL (MBG/FTL) to provide a measure as to how tight CWD objects were spatially arranged when caribou structures were represented as continuous lines. Structure-specific and total network volume of CWD was approximated by assuming cylindrical wooden shapes (squaring the average radius, multiplied by total structure length and π), without correcting for stages of decay, hollowness, collapse ratio, or the more tapered morphology of conifer trees (Husch et al 2002;Campbell et al 2019).…”