Post-landslide interactive effects of plant facilitation and rill erosion on tree seedling colonization toward restoration

Abstract

Landslides are some of the primary causes of forest disturbances, and their frequency is increasing globally due to climate changes. The recruitment and colonization processes of seedlings are pivotal in forest restoration after landslides. However, the effects of new biotic and abiotic environmental conditions generated by landslides on subsequent seedling performance remain poorly understood. Specifically, this study addresses the following questions: 1) how newly recruited seedlings form spatial distribution patterns, 2) how the spatial distance between conspecific and heterospecific seedlings affect the survival and growth of seedlings, 3) what roles rill erosion plays in post-landslide sites on the process of seedling colonization, and 4) whether the distance of seedlings from neighbors and from the rill boundary interactively shapes seedling performance. To address these questions, we conducted surveys at three artificial landslide sites in northern temperate forests. During the first growing season following landslides, the spatial positions of all newly recruited seedlings of two dominant species, as well as the boundaries of rill erosion, were marked. Then, the survival and growth rate of seedlings were monitored. In the post-landslide area, newly recruited seedlings primarily exhibited spatial clustering with conspecific neighbors and demonstrated significantly higher abundance around rills. At the scale of several centimeters, neighboring seedlings influenced the performance of focal seedlings. Proximity to conspecific and heterospecific neighbors significantly enhanced focal seedling survival and growth. The survival of seedlings near rills decreased, and this response varied by species. The proximity of a seedling to heterospecific neighbors attenuated the negative influences of being near rills. Our study indicates that there were conspecific and heterospecific facilitative effects on seedling survival at a post-landslide habitat, but the relative importance of the two effects could be dependent on the degree of rill erosion. We suggest that the effects of plant-plant facilitation, together with the fine-scale geomorphological heterogeneity, shape seedling performance, thereby influencing the forest restoration process.