Data from: Long-term impacts of variable retention harvesting on ground-layer plant communities in Pinus resinosa forests

Concerns about loss of biodiversity and structural complexity in managed forests have recently increased and led to the development of new management strategies focused on restoring or maintaining ecosystem functions while also providing wood outputs. Variable Retention Harvest (VRH) systems, in which mature overstorey trees are retained in various spatial arrangements across harvested areas, represent one potential approach to this problem. However, long-term evaluations of the effectiveness of this strategy at sustaining plant community composition are needed as this strategy is increasingly applied in managed forest landscapes throughout the world. The forest ground layer plays a central role in forest ecosystem functioning and we evaluated the long-term (11+ year) dynamics in ground-layer plant communities in response to VRH study in Pinus resinosa Aiton. forests. This large-scale, manipulative study included four overstorey (control, small gap-aggregated, large gap-aggregated and dispersed) and two understorey (ambient and reduced shrubs) treatments replicated four times in 16 ha stands. Changes in ground-layer community composition were apparent 11 years following harvest, regardless of live-tree retention pattern. Richness and diversity increased and were driven by introduction and colonization of ruderal species, while forest interior species continued to persist across treatments. All life-forms responded positively to harvest with the exception of moss and clubmoss species. The lack of effect of spatial pattern of retention on ground-layer plant communities was likely related to the presence of a dense and persistent shrub layer, a result of decades of fire suppression. In particular, the greatest responses to overstorey retention pattern occurred in areas receiving shrub reduction treatments, indicating this recalcitrant layer likely filtered response to retention pattern. Synthesis and applications. Overall, this work highlights flexibility in choosing a Variable Retention Harvest (VRH) approach when sustaining ground-layer plant community diversity and composition are goals, but altered disturbance regimes (e.g. fire suppression, timber harvesting) that have facilitated the presence or formation of recalcitrant understories, need to be considered. The legacy effects of historical land use and alterations to natural disturbance regimes on the understorey in northern temperate forests are of equal, if not greater importance to overstorey retention patterns, in eliciting desired responses to VRH and need to be more carefully considered in future applications of this method.

近年来，人们对人工经营林生物多样性丧失与结构复杂性下降的担忧日益加剧，由此催生了一批兼顾木材产出与生态系统功能修复或维持的新型森林经营策略。可变保留采伐（Variable Retention Harvest, VRH）系统即在采伐区域内以多种空间配置模式保留成熟上层林木，正是解决该问题的潜在方案之一。然而，随着该策略在全球人工林景观中应用愈发广泛，仍需开展长期评估以验证其维持植物群落组成的有效性。

森林地被层在森林生态系统功能中发挥核心作用，本研究针对北美红松（Pinus resinosa Aiton）林开展VRH试验，评估了地被层植物群落长达11年以上的动态变化。这项大型操控性试验在16公顷的林分中设置了4种上层林处理（对照、小斑块聚集、大斑块聚集以及均匀分散）与2种下层林处理（自然灌丛、灌丛缩减），每种处理均重复4次。

采伐11年后，无论活立木保留模式如何，地被层群落组成均出现显著变化。群落物种丰富度与多样性均有所提升，这一变化由杂草类物种的引入与定植所驱动，而森林内部物种在各处理组中均持续留存。除苔藓与石松类物种外，所有生活型类群均对采伐呈现正向响应。活立木保留空间模式对地被层植物群落未产生显著影响，这可能与数十年森林防火导致的致密且稳定的灌丛层存在有关。具体而言，上层林保留模式的最大响应出现在灌丛缩减处理区域，表明这一顽性灌丛层可能会过滤保留模式所带来的群落响应。

研究总结与应用启示：总体而言，当以维持地被层植物群落多样性与组成为目标时，本研究证实可变保留采伐（VRH）策略具备选择灵活性，但同时需考虑到已促使致密下层林形成或存续的干扰制度改变（如森林防火、木材采伐）所带来的影响。在诱导VRH达到预期效果方面，北温带森林下层林所受的历史土地利用遗留效应与自然干扰制度改变的影响，至少与上层林保留模式同等重要，甚至更为关键，因此在该方法的未来应用中需予以更审慎的考量。