Sampling system for estimating woody debris in an urban mixed tropical forest

Abstract Woody debris, defined as standing and downed deadwood, consists in an essential component of the forest carbon stock. However, few studies have been carried out to get an efficient and accurate sampling procedure for estimating it. This work proposes two methodologies to estimate the woody debris volume in a Brazilian mixed tropical forest: 1) two-stage systematic sampling, using a mixed methodology, in which the Strand’s method is applied to standing dead trees and stumps, and line intercept sampling is used to fallen trees and branches; and 2) ratio estimate of the sum of cross-sectional areas of deadwood pieces and forest basal area, aiming to obtain the total woody debris volume indirectly in the natural forest. Conversions for biomass and carbon stocks were made applying the mean basic density on the estimates of deadwood volumes. Both methodologies are accurate for woody debris volume estimates, with a sampling error equal to 16.1% (methodology 1) and 5.7% (methodology 2), at a 95% probability level. Thus, the methodology 2 has potential to be used in strategic forest inventories of woody debris, such as in National Forest Inventories, due to increasing importance of its quantification in all forest ecosystems.

摘要：枯木质残体（Woody debris），定义为立枯木与倒枯木，是森林碳库的核心组成部分。然而，目前针对其高效精准估算的采样方法相关研究仍较为匮乏。本研究针对巴西混合热带林提出两种木质残体蓄积量估算方法：1）两阶段系统抽样法：采用混合采样策略，对立枯木与伐桩应用斯特兰德法（Strand’s method），对倒木及枝条则采用截线抽样法（line intercept sampling）；2）残体横截面积总和与森林断面积的比率估计法：旨在间接估算天然林内木质残体总蓄积量。研究通过将平均基本密度应用于残体蓄积量估算结果，完成生物量与碳储量的转换计算。两种方法均能精准估算木质残体蓄积量，在95%置信水平下，方法1的抽样误差为16.1%，方法2为5.7%。鉴于木质残体量化在各类森林生态系统中的重要性日益提升，方法2具备应用于木质残体战略森林调查（如国家森林清查）的潜力。