Baseline levels of tree mortality can, over time, contribute to high snag densities and high levels of deadwood (down woody debris) if fire is infrequent and decomposition is slow. Deadwood can be important for tree recruitment, and it plays a major role in terrestrial carbon cycling, but deadwood is rarely examined in a spatially explicit context. Between 2011 and 2019, we annually tracked all trees and snags ≥1 cm in diameter and mapped all pieces of deadwood ≥10 cm diameter and ≥1 m in length in 25.6 ha of Tsuga heterophylla / Pseudotsuga menziesii forest. We analyzed the amount, biomass, and spatial distribution of deadwood, and we assessed how various causes of mortality that contributed uniquely to deadwood creation. Compared to aboveground woody live biomass of 481 Mg ha−1 (from trees ≥10 cm diameter), snag biomass was 74 Mg ha−1 and deadwood biomass was 109 Mg ha−1 (from boles ≥10 cm diameter). Biomass from large-diameter trees (≥60 cm) accounted for 85%, 88%, and 58%, of trees, snags, and deadwood, respectively. Total aboveground woody live and dead biomass was 668 Mg ha−1. The annual production of downed wood (≥10 cm diameter) from tree boles averaged 4 Mg ha−1 yr−1. Woody debris was spatially heterogeneous, varying more than two orders of magnitude from 4 to 587 Mg ha−1 at the scale of 20 m × 20 m quadrats. Almost all causes of deadwood creation varied in importance between large-diameter trees and small-diameter trees. Biomass of standing stems and deadwood had weak inverse distributions, reflecting the long period of time required for trees to reach large diameters following antecedent tree mortalities and the centennial scale time required for deadwood decomposition. Old-growth forests contain large stores of biomass in living trees, as well as in snag and deadwood biomass pools that are stable long after tree death. Ignoring biomass (or carbon) in deadwood pools can lead to substantial underestimations of sequestration and stability.

中文翻译：

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大直径树木对产生障碍物和枯木生物量的重要性

如果不常发生火灾且分解缓慢，则树木死亡率的基线水平会随着时间的流逝而导致较高的树突密度和大量的枯木（木屑下沉）。枯木对于树木的募集可能很重要，它在陆地碳循环中起着重要作用，但是很少在空间明确的背景下检查过枯木。在2011年至2019年之间，我们每年追踪25.6公顷的Tsuga heterophylla / Pseudotsuga menziesii森林中直径≥1cm的所有树木和障碍物，并绘制所有直径≥10cm且长度≥1m的枯木。我们分析了阔叶树的数量，生物量和空间分布，并评估了造成死角树的独特原因的各种死亡原因。与481 Mg ha-1的地上木质活生物量（来自直径≥10 cm的树木）相比，粗枝生物量为74 Mg ha-1，沉材生物量为109 Mg ha-1（来自直径≥10 cm的树干）。大直径树木（≥60厘米）的生物量分别占树木，粗枝和枯木的85％，88％和58％。地上木质生，死生物量总计为668 Mg ha-1。从树bo砍伐的木材（直径≥10厘米）的年产量平均为4 Mg ha-1 yr-1。木质碎片在空间上是非均质的，在20 m×20 m的方柱上，从4到587 Mg ha-1变化超过两个数量级。在大径树和小径树之间，几乎所有造成死木的原因的重要性都有所不同。立茎和枯木的生物量逆分布较弱，反映了因树木死亡而使树木达到大直径所需的长时间以及枯木分解所需的百年尺度时间。古老的森林在活着的树木以及树死后很长一段时间内稳定的粗枝和沉材生物量库中包含大量生物量存储。忽略枯木池中的生物量（或碳）会导致对螯合和稳定性的严重低估。