Ecological resilience to ungulate overbrowsing is an important issue in forest ecosystems. After chronic herbivory, the recovery rate of understory vegetation and its related functions can be slow even with decreasing grazing intensity; thus, detecting elasticity during alternative successional trajectories is fundamental to understanding state perturbations. In this context, we focused on physical plant-soil feedback (functional interactions between plant growth and soil physical conditions) and evaluated elasticity and recovery processes according to deer density. The effects of 40 years of chronic herbivory by sika deer (average density 14.7 individuals km-2 ) on the recovery of understory plant communities and associated changes in soil physical properties in headwater catchments were assessed. Using 8 years of catchment-wide exclusion (fenced) and reduction (only culled; average 4.3 individuals km-2 ) treatments, plot sampling was conducted in 2010 (before treatment) and 2018 (after treatment). The recovery of vegetation and soil physical properties were evaluated, and functional plant-soil relationships and spatial variability were assessed to detect recovery processes during alternative successional trajectory. Woody species increased only under the exclusion treatment and the average soil bulk density was lower than that under reduction treatments. Soil bulk density was negatively correlated with root biomass in the fenced catchment, and root biomass was positively associated with woody species richness. Reduced soil bulk density (~0.5 g cm-3 ) was observed with greater root biomass and woody species richness on upper hillslopes in the deer-excluded catchment where plant coverage was minimal. Successional failure under the reduction treatment suggested slow recovery with a depressed threshold according to deer density, indicating a clockwise hysteretic response to deer density. Unlike plant coverage during the earlier period of overbrowsing, woody species root development led the recovery of functional physical plant-soil feedback; however, this was probably limited by the higher soil erosion rate in riparian areas and an under-developed herb layer. Our results highlight an alternative recovery trajectory of physical plant-soil feedback driven by an alternative plant element (woody roots) to recovery trajectory with increasing plant cover. However, riparian erosion and herb layer would still suppress recovery. Therefore, recovery might be slower at the landscape scale.

中文翻译：

---

物理植物-土壤反馈对慢性鹿食草的生态恢复：缓慢、部分但功能恢复。

有蹄类动物过度浏览的生态恢复力是森林生态系统中的一个重要问题。长期食草后，即使放牧强度降低，林下植被及其相关功能的恢复速度也会变慢；因此，在替代连续轨迹期间检测弹性对于理解状态扰动至关重要。在这种情况下，我们专注于物理植物-土壤反馈（植物生长和土壤物理条件之间的功能相互作用），并根据鹿密度评估弹性和恢复过程。评估了梅花鹿（平均密度 14.7 人 km-2）40 年的慢性食草对林下植物群落恢复以及源头流域土壤物理特性相关变化的影响。使用 8 年的全流域排除（围栏）和减少（仅剔除；平均 4.3 个人 km-2 ）处理，在 2010 年（处理前）和 2018 年（处理后）进行了小区抽样。评估植被和土壤物理特性的恢复，评估功能性植物-土壤关系和空间变异性，以检测替代演替轨迹期间的恢复过程。木本物种仅在排除处理下增加，平均土壤容重低于还原处理。围栏流域的土壤容重与根系生物量呈负相关，而根系生物量与木本物种丰富度呈正相关。降低土壤容重（~0. 5 g cm-3 ) 在植物覆盖最小的鹿排除流域的上山坡上观察到更大的根生物量和木本物种丰富度。还原处理下的连续失败表明恢复缓慢，根据鹿密度降低阈值，表明对鹿密度的顺时针滞后反应。与过度浏览早期的植物覆盖不同，木本植物根系发育导致功能性物理植物-土壤反馈的恢复；然而，这可能受到河岸地区较高的土壤侵蚀率和不发达的草本层的限制。我们的结果强调了由替代植物元素（木本根）驱动的物理植物-土壤反馈的替代恢复轨迹，以随着植物覆盖度的增加而恢复。然而，河岸侵蚀和草本层仍会抑制恢复。因此，景观规模的恢复可能会较慢。