The effects of the human footprint and soil properties on the habitat suitability of large old trees in alpine urban and periurban areas

Large old trees contribute to ecosystem integrity and biodiversity in urban and periurban areas. Quantifying the factors influencing the suitable habitats of large old trees is critical for management. Because tree species are sensitive to changes in the human footprint and soil properties in alpine regions, understanding the effects of these on the habitat suitability of large old trees is crucial for ecological management in urban and periurban areas of alpine regions. Here, we used a habitat suitability model to project the distributions of suitable habitats of six large old tree species (Salix matsudana, Picea crassifolia, Picea wilsonii, Populus cathayana, Populus simonii, and Ulmus pumila) in urban and periurban areas of Qinghai Province, China, based on climate, the human footprint, and soil variables. Then, we used jackknife methods and effect size analysis to quantify the effects of the human footprint and soil properties on the habitats of large old trees. Our results showed that the human footprint and soil properties, especially cation exchange capacity, affected the habitat suitability of the large old trees in Qinghai Province. The tree species in Chengzhong, Chengxi, Ping'an, Guide, and Qilian were all greatly affected by the human footprint and soil properties. We propose the following management strategies based upon our data: 1) protected areas should be established for large old trees where soil nutrient levels are high to ensure the protection of small groups of scattered trees and single isolated trees; and 2) Chengzhong, Chengxi, Huangzhong, Ping'an, Ledou, Minhe, Xunhua, and Guide should be used as recruitment areas of large old trees based on their suitable climate and soil properties in Qinghai Province. Our study provides insight into the effective management of large old trees in alpine regions.