Unreasonable human disturbance shifts the positive effect of climate change on tree-ring growth of Malus sieversii in the origin area of world cultivated apples

Abstract

The wild apple (M. sieversii) in Xinjiang is the ancestor of the world cultivated apple, and its death and decline have aggravated the degradation of wild fruit forests in the Tianshan Mountains. However, the reasons of degradation of the wild fruit forest is not clear. Therefore, we hypothesized that human disturbance shifts the positive effects of climate change on tree-ring growth of wild apple. We tested this hypothesis by answering two scientific questions. (1) Does climate change have a significant impact on tree-ring growth of wild apple trees? (2) Has unreasonable human disturbance altered the effect of climate change on tree-ring growth? We chose wild apples at different degenerate levels to contrastively analyze the effects of climate change on the tree-ring growth of M. sieversii using analysis of wavelet coherence and Pearson correlation, and quantifying the effect of climate changes on tree-ring of M. sieversii with periodic superimposed trend models. We confirmed the effects of human disturbance on tree-ring of wild apple using mixed linear models. The result showed climate change contributed to a 50.9% increase in the tree-ring chronology of wild apple in non-degraded areas after 2008. However, unreasonable human disturbance resulted in a significant decrease (P < 0.01) to tree-ring chronology of wild apple in degenerate areas. We determined that unreasonable human disturbance altered the positive effects of climate change on tree-ring growth of wild apple. Therefore, we concluded that the main reason for degradation of wild fruit forests was unreasonable human disturbance. Moreover, the effect of pest control measures on promoting tree-ring growth was not significant in the recent short term, suggesting that pest control and management of wild fruit forest should be further strengthened. Our research comprehensively considered the effects of both climate change, anthropogenic activities, pests and diseases on wild apple in a wild fruit forest, and confirmed the main reason for degeneration of wild fruit forests. These results not only determined the influence of two key factors on the growth of M. sieversii, but also provided a scientific basis for the ecological conservation of wild apple trees in the future.