Centurial changes in forest structure and composition in southwestern Japan based on historical data

AimsThe impacts of anthropogenic activities, such as deforestation and land-use change, and climate change on forest ecosystems have intensified in recent years. To predict future dynamics and guide management, it is crucial to clarify forest structure and composition prior to these disturbances; however, few studies have analyzed data recorded before major human and climate-related impacts. Here we analyzed forest inventory data (467,809 trees ≥ 7.5 cm in diameter at breast height at 534 plots) from the 1920s–1930s to evaluate these long-term effects.LocationAlmost all forest vegetation plots in southwestern Japan.MethodsTo assess centurial changes in forest structure and composition, we calculated aboveground biomass (AGB), size structure, species richness, and species composition for historical and current forest plots. We further examined the effects of anthropogenic activity on the density of large-diameter trees.ResultsThe average density of large-diameter trees and species richness in historical forests were significantly 2.4 and 1.3–1.4 times higher, respectively, than in current forests, but average AGB was similar. The effect of anthropogenic activity was larger in historical forests than current forests. In historical forests, species typical of old-growth forests were dominant, while species typical of human-managed and early successional forests were dominant in current forests.ConclusionOverall, our results indicate that, over the past century, forests in southwestern Japan have been shaped more strongly by human activities than by climate change, resulting in pronounced changes in forest structure and species composition. The stability of AGB despite these changes suggests that AGB alone is insufficient to characterize forest functioning. The reconstructed forest status from a century ago offers valuable insights for future forest management and restoration efforts to achieve nature positive.研究目的 近年来，人为活动（如森林砍伐与土地利用变化）及气候变化对森林生态系统的影响日益加剧。若要预测森林未来动态并指导经营管理，明确干扰发生前的森林结构与组成至关重要；然而目前鲜有研究对重大人为与气候干扰前记录的相关数据开展分析。本研究针对1920至1930年代的森林清查数据（共534块样地内的467809株胸径≥7.5cm的林木）进行分析，以评估上述长期干扰的影响。 研究区域 日本西南部几乎所有的森林植被样地。 研究方法 为评估森林结构与组成的百年变化，我们分别计算历史样地与当前样地的地上生物量（aboveground biomass, AGB）、径级结构、物种丰富度及物种组成，并进一步探讨人为活动对大径级林木密度的影响。 研究结果 历史森林的大径级林木平均密度与物种丰富度分别显著高于当前森林的2.4倍与1.3~1.4倍，但二者的平均AGB并无显著差异。人为活动对历史森林的影响程度大于当前森林。历史森林以原始林典型物种占优，而当前森林则以人工经营林与早期演替林的典型物种为主。 研究结论 总体而言，本研究结果表明，在过去一个世纪中，日本西南部森林受人类活动的塑造作用远强于气候变化，进而导致森林结构与物种组成发生显著变化。尽管森林经历了上述变化，AGB仍保持稳定，这说明仅依靠AGB不足以表征森林生态系统功能。百年前的森林现状重建结果可为未来森林经营与修复工作（以实现自然向好目标）提供宝贵的参考依据。