Which native legume or non-legume nitrogen-fixing tree is more efficient in restoring post-landslide forests along an environmental gradient?

Abstract

Under climate change, heavy precipitation is predicted to trigger frequent shallow landslides. To accelerate vegetation recovery after landslides, planting nitrogen (N)-fixing trees is a promising technique. However, a comparison of the performance of non-legume and legume N-fixing species planted across a wide range of environments after landslides has not been conducted, which is problematic for determining the most efficient tree species for restoration. We planted the seedlings of a native legume (Lespedeza bicolor) and a native non-legume (Alnus hirsuta) tree species and monitored their survival in 15 landslide forests artificially established across a variety of environments in northern Japan. The landslides were mimicked by removing standing trees and surface soil with heavy machinery from the sites. There was a significant difference in the survival rate of seedlings between the two species. The survival rate was significantly higher for L. bicolor than for A. hirsuta. Furthermore, the performance of the two species differed along the environmental gradient of post-landslide forests. Interestingly, L. bicolor seedlings survived better in the steeper post-landslide forests, probably due to less exposure to ungulate herbivory. On the other hand, the warmer air temperature and serpentine soil negatively influenced the survival of A. hirsuta, which indicates different environmental preferences of N-fixing plants in post-landslide forests. Our results suggest that for efficient forest restoration after landslides, careful selection of N-fixing plants based on slope conditions is essential.