Department of International Environmental and Agricultural Science, Tokyo University of Agriculture and Technology, Fuchu, Japan.
Faculty of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Japan.
Ecol Appl. 2022 Oct;32(7):e2656. doi: 10.1002/eap.2656. Epub 2022 Jun 19.
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 ) 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 ) 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 ) 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.
食草动物过度啃食对生态系统的抵抗力是森林生态系统中的一个重要问题。在慢性食草作用之后，即使放牧强度降低，林下植被及其相关功能的恢复速度也可能很慢；因此，检测替代演替轨迹中的弹性对于理解状态干扰至关重要。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 40 年来梅花鹿（平均密度为 14.7 只 km ）慢性食草作用对溪流集水区林下植物群落恢复及其相关土壤物理性质变化的影响。使用 8 年的集水区范围（围栏）和减少（仅剔除；平均 4.3 只 km ）处理，于 2010 年（处理前）和 2018 年（处理后）进行了样地采样。评估了植被和土壤物理性质的恢复情况，并评估了功能植物-土壤关系和空间变异性，以检测替代演替轨迹中的恢复过程。仅在排除处理下木本物种增加，平均土壤容重低于减少处理。在围栏集水区，土壤容重与根生物量呈负相关，根生物量与木本物种丰富度呈正相关。在鹿排除集水区的上山坡，由于植物覆盖率最小，观察到土壤容重降低（约 0.5 g cm ），根生物量和木本物种丰富度增加。减少处理下的土壤容重（约 0.5 g cm ）降低（约 0.5 g cm ），根生物量和木本物种丰富度增加，表明根据鹿密度恢复缓慢，阈值降低，表明对鹿密度的顺时针滞后响应。与过度啃食早期的植物覆盖率不同，木本物种根发育引领了功能物理植物-土壤反馈的恢复；然而，这可能受到河岸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，而不是随着植物覆盖度增加的恢复轨迹。然而，河岸侵蚀和草本层仍会抑制恢复。因此，在景观尺度上恢复可能会更慢。
