RELEASE-2022

Coarse Downed Wood bulk density samples are collected from terrestrial sites with qualifying logs where repeat CDW Survey sampling is performed. CDW Bulk Density sampling is implemented twice per site, the first time within the first three years of data collection at a site, and the second time 5-6 years after the first sampling event. When possible, the same logs are targeted for sampling at both sampling time points. Sampling may occur in up to 20 Distributed Plots and all Tower Plots, and unlike all other NEON TOS sampling, collection of disks may also occur outside of NEON plot boundaries, due to the sparsely distributed nature of target logs. Logs sampled for bulk density are parsed into five decay categories that broadly match existing USFS definitions, three size categories (2-5 cm, 5-10 cm, and greater than 10 cm diameter), and are identified to the highest taxonomic resolution possible according to the USDA Plants database. The bulk density sampling effort is inherently variable from site to site, as it is driven by the number of 'decayClass x sizeCategory x taxonID' (DST) combinations, which is strongly dependent on site-level tree diversity. For each site, sampling is considered complete once all rank-ordered DSTs that cumulatively make up 80% of the total tallies have been sampled. Target disk sample size per DST is n=10 for DSTs >= 10 cm diameter, and n=5 for DSTs < 10 cm diameter.

粗死木质残体（Coarse Downed Wood，CDW）容重样本采集自拥有合格枯木且需开展重复CDW调查采样的陆地样地。每个样地需开展两次CDW容重采样：首次采样在样地数据收集的前三年内完成，第二次采样则距首次采样事件间隔5至6年。若条件允许，两次采样将针对同一批目标枯木进行。采样可覆盖最多20个分布式样地（Distributed Plots）及全部塔式样地（Tower Plots）；与NEON所有其他TOS采样不同，由于目标枯木分布较为稀疏，圆盘样本的采集也可在NEON样地边界外开展。用于容重采样的枯木被划分为5个腐烂等级，大致匹配美国林务局（United States Forest Service，USFS）现有分类标准；同时分为3个径级：2–5 cm、5–10 cm及直径大于10 cm；并依据美国农业部（United States Department of Agriculture，USDA）植物数据库，尽可能鉴定至最高分类学分辨率水平。容重采样的工作量因样地而异，其核心驱动因素为“腐烂等级×径级×分类单元ID（decayClass x sizeCategory x taxonID，简称DST）”的组合数量，而该组合数强烈依赖于样地尺度的树木多样性。对于每个样地，当累计占总记录数80%的所有排序后DST组合均完成采样时，即认为该样地的采样工作完成。针对每个DST组合的目标圆盘样本量为：径级≥10 cm的组合采样n=10个圆盘，径级<10 cm的组合采样n=5个圆盘。