Approaches to forest management have changed markedly in the Pacific Northwest in recent decades, yet legacies of past management persist on the landscape. Following clearcut logging, woody residues were typically burned to reduce future fire hazard, create planting spots, facilitate natural recruitment, and retard growth of competing vegetation. We asked whether legacies of broadcast burning persist in the forest understory during the early stages of stand closure, how they manifest structurally or compositionally, whether they are altered by subsequent management (pre-commercial thinning), and how they vary with gradients in the physical environment or stand structure. We used data from 44 pairs of burned and unburned plots sampled 37–42 years after clearcut logging of mature and old-growth forests in western Oregon and Washington. Burning had persistent, but mostly subtle effects on community structure and composition. Burned plots had greater cover of early-seral species and lower cover of woody forest species. Among the latter, tall shrubs showed consistently negative responses to burning. Smaller-statured woody and herbaceous species were more variable in their responses, reflecting a greater diversity of regenerative traits. For some understory attributes, effects of burning were contingent on thinning history. For example, burning enhanced species richness and reduced species evenness, but only in unthinned sites. Conversely, burning increased the spatial variability of tall shrub cover, but only in thinned sites. In some instances, thinning compounded the effects of burning, resulting in a four-fold increase in cover of early-seral herbs and a 50% reduction in cover of forest tall shrubs relative to plots that received neither treatment. For most understory attributes, regional variation in the magnitude of the burn effect was not easily explained by burn severity, site environment, or stand structure. Collectively, our results highlight the persistent, but highly variable, effects of broadcast burning on the post-harvest development of the forest understory. They suggest that, where it is feasible, controlled burning can be used in regeneration-harvest units to achieve a variety of management objectives, with minimal effect on the forest understory.

中文翻译：

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广播燃烧对林下组成和结构具有持久但微妙的影响：西部喀斯喀特森林的长期研究结果

近几十年来，太平洋西北地区的森林管理方法发生了显着变化，但过去管理的遗留问题仍然存在。砍伐完后，木质残留物通常会被焚烧，以减少未来的火灾危险，创造种植点，促进自然补充，并延缓竞争植被的生长。我们询问，在林分关闭的早期阶段，广播燃烧的遗留物是否仍然存在于林下林下，它们在结构或成分上如何表现，它们是否会因后续管理（商业化前的间伐）而改变，以及它们如何随着物理梯度的变化而变化。环境或展位结构。我们使用了俄勒冈州西部和华盛顿州成熟森林和古老森林砍伐后 37-42 年采样的 44 对烧毁和未烧毁地块的数据。燃烧对群落结构和组成具有持续但大多微妙的影响。烧毁的土地上早期系列物种的覆盖率较高，而木本森林物种的覆盖率较低。在后者中，高灌木对燃烧始终表现出负面反应。身材较小的木本和草本物种的反应变化更大，反映出再生特征的多样性。对于某些林下属性来说，燃烧的影响取决于稀疏历史。例如，燃烧提高了物种丰富度并降低了物种均匀度，但仅限于未间伐的地点。相反，燃烧增加了高灌木覆盖的空间变异性，但仅限于稀疏地区。在某些情况下，间伐加剧了燃烧的影响，导致与未接受任何处理的地块相比，早期系列草本植物的覆盖率增加了四倍，而森林高灌木的覆盖率则减少了 50%。对于大多数林下属性来说，烧伤效应程度的区域差异很难用烧伤严重程度、场地环境或林分结构来解释。总的来说，我们的结果强调了广播燃烧对森林林下植被收获后发育的持续但高度可变的影响。他们建议，在可行的情况下，可以在再生收获单位中使用受控燃烧，以实现各种管理目标，同时对森林林下层的影响最小。