Rubenstein School of Environment and Natural Resources, University of Vermont, Burlington, Vermont, 05405, USA.
Gund Institute for Environment, University of Vermont, Burlington, Vermont, 05405, USA.
Ecol Appl. 2018 Apr;28(3):798-815. doi: 10.1002/eap.1691. Epub 2018 Mar 26.
Wind is one of the most important natural disturbances influencing forest structure, ecosystem function, and successional processes worldwide. This study quantifies the stand-scale effects of intermediate-severity windstorms (i.e., blowdowns) on (1) live and dead legacy structure, (2) aboveground carbon storage, and (3) tree regeneration and associated stand dynamics at four mature, mixed hardwood-conifer forest sites in the northeastern United States. We compare wind-affected forests to adjacent reference conditions (i.e., undisturbed portions of the same stands) 0-8 yr post-blowdown using parametric (ANOVA) and nonparametric (NMS ordination) analyses. We supplement inventory plots and downed coarse woody detritus (DCWD) transects with hemispherical photography to capture spatial variation in the light environment. Although recent blowdowns transferred a substantial proportion of live overstory trees to DCWD, residual live tree basal area was high (19-59% of reference areas). On average, the initial post-blowdown ratio of DCWD carbon to standing live tree carbon was 2.72 in blowdown stands and 0.18 in reference stands, indicating a large carbon transfer from live to dead pools. Despite these dramatic changes, structural complexity remained high in blowdown areas, as indicated by the size and species distributions of overstory trees, abundance of sound and rotten downed wood, spatial patterns of light availability, and variability of understory vegetation. Furthermore, tree species composition was similar between blowdown and reference areas at each site, with generally shade-tolerant species dominating across multiple canopy strata. Community response to intermediate-severity blowdown at these sites suggests a dynamic in which disturbance maintains late-successional species composition rather than providing a regeneration opportunity for shade-intolerant, pioneer species. Our findings suggest that intermediate-severity wind disturbances can contribute to stand-scale structural complexity as well as development toward late-successional species composition, at least when shade-tolerant regeneration is present pre-blowdown. Advance regeneration thus enhances structural and compositional resilience to this type of disturbance. This study provides a baseline for multi-cohort silvicultural systems designed to restore heterogeneity associated with natural disturbance dynamics.
风是影响全球森林结构、生态系统功能和演替过程的最重要的自然干扰因素之一。本研究量化了中强度风灾（即倒伏）对（1）活的和死的遗留结构、（2）地上碳储存以及（3）树木再生及其相关林分动态在四个成熟的美国东北部混合硬木-针叶林林分站点的影响。我们通过参数（方差分析）和非参数（NMS 排序）分析，将受风影响的森林与相邻的对照条件（即同一林分中未受干扰的部分）进行比较，这些对照条件的时间范围为风灾后 0-8 年。我们用半球摄影补充清查样地和倒下的粗木质残体（DCWD）样带，以捕捉光环境的空间变化。尽管最近的倒伏将大量活的上层树木转移到了 DCWD 中，但残留的活立木基面积仍然很高（对照区域的 19-59%）。平均而言，风灾林分中 DCWD 碳与活立木碳的初始风灾后比值为 2.72，而对照林分为 0.18，表明活的和死的碳库之间有大量的碳转移。尽管发生了这些剧烈的变化，但风灾区域的结构复杂性仍然很高，这表现在上层树木的大小和物种分布、健全和腐烂的倒下木材的丰度、光可用性的空间模式以及林下植被的变异性上。此外，每个站点的风灾和对照区域的树种组成相似，通常耐荫物种在多个树冠层中占主导地位。这些站点的中等强度风灾的群落响应表明，在这种情况下，干扰维持了晚熟物种的组成，而不是为不耐荫的先锋物种提供了再生机会。我们的研究结果表明，至少在风灾前存在耐荫更新的情况下，中等强度的风干扰可以促进林分尺度的结构复杂性，并促进向晚熟物种组成的发展。因此，提前更新增强了对这种干扰的结构和组成弹性。本研究为旨在恢复与自然干扰动态相关的异质性的多林分抚育系统提供了基线。
