Constantz Brook M, Stella John C, Holl Karen D
Environmental Studies Department, University of California, Santa Cruz, California, USA.
Department of Sustainable Resources Management, State University of New York College of Environmental Science and Forestry, Syracuse, New York, USA.
Ecol Appl. 2025 Apr;35(3):e70043. doi: 10.1002/eap.70043.
The classic restoration ecology model of ecosystem recovery predicts that restoring the initial conditions of a formerly degraded site will facilitate recovery and convergence with a reference site. Few restoration studies have long-term longitudinal data to evaluate recovery trajectories, which typically vary among different aspects of ecosystem structure and composition. We used repeat surveys to evaluate if the trajectory of vegetation structure and community composition in restored and reference forests converged from recovery of restored forest or degradation of reference forest, and whether patterns differed for forest overstories and understories. We measured vegetation communities 9-16 years after prior surveys and 21-30 years after planting in 11 restored and 8 reference forest sites along a 100-km span of the Sacramento River, California. We used generalized linear mixed models and nonmetric multidimensional scaling to evaluate convergence in overstory structure, overstory composition, understory cover, and understory composition. Restored forest structure became more similar to reference forests over time, converging on a basal area of ca. 20 m ha around 25 years and densities of stems around 35 years. In contrast, overstory species composition remained distinctive, primarily due to the different initial tree-species composition and limited overlap in new species recruitment in restored and reference forests. Restored understories had lower native and higher exotic cover than reference sites in both surveys. Restored understory composition became more similar to reference sites as shade-intolerant exotic species cover declined. However, understory composition in restored sites remained distinct from reference sites due to the increased woody cover, primarily from the invasive, shade-tolerant shrub Rubus armeniacus, which increased from 2% to 23% mean site cover between the two surveys. Path analysis showed that in restored forests, R. armeniacus cover was negatively related (R = -0.51) to native understory cover, suggesting that it impedes forest recovery. Our results suggest that this system has converged with reference forest in overstory structure but not yet in overstory or understory composition. We found substantial degradation of restored forest understories over time due to R. armeniacus spread; redirecting this trend would require substantial, ongoing intervention.
生态系统恢复的经典恢复生态学模型预测，恢复一个曾经退化场地的初始条件将促进其恢复并与参照场地趋同。很少有恢复研究拥有长期纵向数据来评估恢复轨迹，而恢复轨迹通常在生态系统结构和组成的不同方面有所差异。我们利用重复调查来评估恢复森林和参照森林中植被结构与群落组成的轨迹是否从恢复森林的恢复或参照森林的退化开始趋同，以及森林上层和下层的模式是否不同。我们在加利福尼亚州萨克拉门托河100公里跨度范围内的11个恢复森林和8个参照森林场地，在之前调查后的9 - 16年以及种植后的21 - 30年对植被群落进行了测量。我们使用广义线性混合模型和非度量多维标度法来评估上层结构、上层组成、下层覆盖度和下层组成的趋同情况。随着时间推移，恢复森林的结构变得与参照森林更为相似，在约25年时基部面积趋近于约20平方米/公顷，在约35年时茎密度趋近。相比之下，上层物种组成仍然有差异，主要是由于恢复森林和参照森林初始树种组成不同以及新物种招募的重叠有限。在两次调查中，恢复森林的下层本土覆盖度较低，外来物种覆盖度较高。随着不耐阴外来物种覆盖度下降，恢复森林的下层组成变得与参照场地更为相似。然而，由于木本覆盖度增加，主要是来自入侵的耐阴灌木亚美尼亚悬钩子，其在两次调查之间平均场地覆盖度从2%增加到23%，恢复场地的下层组成与参照场地仍然不同。路径分析表明，在恢复森林中，亚美尼亚悬钩子的覆盖度与本土下层覆盖度呈负相关（R = -0.51），表明它阻碍森林恢复。我们的结果表明，该系统在上层结构上已与参照森林趋同，但在上层或下层组成上尚未趋同。我们发现由于亚美尼亚悬钩子的扩散，恢复森林的下层随时间有显著退化；扭转这一趋势将需要大量持续的干预。
