RELEASE-2021

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.

粗倒木（Coarse Downed Wood, CDW）体积密度样本采集于符合条件的陆地样地，此类样地需开展重复CDW调查采样。CDW体积密度采样在每个样地分两次实施：首次采样需在样地数据收集的前三年内完成，第二次采样则与首次采样事件间隔5至6年。条件允许时，两次采样的目标均为同一批倒木。
采样可覆盖最多20个分布式样地及所有塔基样地；与NEON TOS其他所有采样方案不同，鉴于目标倒木分布稀疏，圆盘样本的采集也可在NEON样地边界外进行。
用于体积密度采样的倒木被划分为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；同时划分3个尺寸等级：直径2~5cm、5~10cm及大于10cm，并依据美国农业部植物数据库（USDA Plants Database）尽可能鉴定至最高分类学分辨率。
体积密度的采样工作量存在固有样地差异，其驱动因素为「腐烂等级×尺寸类别×分类单元ID（decayClass x sizeCategory x taxonID, DST）」的组合数量，而该数量强烈依赖于样地的树木多样性。对于每个样地，当累计占总采样数80%的全部按秩排序的DST组合均完成采样时，即认为该样地的采样工作完成。
针对各DST组合的目标圆盘样本量为：直径≥10cm的DST组合n=10，直径<10cm的DST组合n=5。