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.
Highlights
The remains of dead trees and large branches on the forest floor, known as downed coarse woody debris (DCWD), contribute to the structure and function of forest ecosystems
When the collapse ratio was included in the DCWD calculation, the mean volume was 9% less (31.2 m3/ha) with a range in reduction of 1 to 33% across plots, and the carbon storage was 7% less (4.6 Mg C/ha) with a range of 0 to 30%
Results of our analysis using Forest Inventory and Analysis (FIA) data from the northeastern US indicate that the uncertainty in estimates of DCWD carbon storage is large, mostly due to uncertainty in the density of DCWD
Summary
The remains of dead trees and large branches on the forest floor, known as downed coarse woody debris (DCWD), contribute to the structure and function of forest ecosystems. There has been growing recognition of the influence of DCWD on many. Manuscript received 22 August 2018; revised 30 October 2018; accepted 4 December 2018. Ecological Applications Vol 29, No 2 long-term carbon storage pool. Dead wood comprises 8% of the carbon stock in the world’s forests (Pan et al 2011), but quantities vary considerably across and within forest types (Harmon and Hua 1991). In temperate forests of the northeastern United States, DCWD amounts to ~20% of the aboveground biomass (Currie and Nadelhoffer 2002, Fahey et al 2005, Bradford et al 2009)
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