Response of altitudinal vegetation belts of the Tianshan Mountains in northwestern China to climate change during 1989-2015

Abstract

Within the mountain altitudinal vegetation belts, the shift of forest tree lines and subalpine steppe belts to high altitudes constitutes an obvious response to global climate change. However, whether or not similar changes occur in steppe belts (low altitude) and nival belts in different areas within mountain systems remain undetermined. It is also unknown if these, responses to climate change are consistent. Here, using Landsat remote sensing images from 1989 to 2015, we obtained the spatial distribution of altitudinal vegetation belts in different periods of the Tianshan Mountains in Northwestern China. We suggest that the responses from different altitudinal vegetation belts to global climate change are different. The changes in the vegetation belts at low altitudes are spatially different. In high-altitude regions (higher than the forest belts), however, the trend of different altitudinal belts is consistent. Specifically, we focused on analyses of the impact of changes in temperature and precipitation on the nival belts, desert steppe belts, and montane steppe belts. The results demonstrated that the temperature in the study area exhibited an increasing trend, and is the main factor of altitudinal vegetation belts change in the Tianshan Mountains. In the context of a significant increase in temperature, the upper limit of the montane steppe in the eastern and central parts will shift to lower altitudes, which may limit the development of local animal husbandry. The montane steppe in the west, however, exhibits the opposite trend, which may augment the carrying capacity of pastures and promote the development of local animal husbandry. The lower limit of the nival belt will further increase in all studied areas, which may lead to an increase in surface runoff in the central and western regions.

Figure 1

Location of the study area and the composition of the altitudinal vegetation belts. (a) The areas enclosed by the red rectangles are our study area. The rectangle on the left is Zhaosu county; the middle is Hutubi county; and the right is Yiwu county. (b) The altitudinal vegetation belts in Tianshan Mountains; (I), (II), and (III) indicate Yiwu county, Hutubi county, and Zhaosu county, respectively.

Figure 2

Spatial variation of temperature and precipitation [(a) indicated spatial variation of precipitation in Tianshan Mountains and surrounding areas; and (b) indicated spatial variation of temperature in Tianshan Mountains and surrounding areas]. (c) Indicated the changing trend of temperature and precipitation in the study area during 1989–2015. The Mann Kendall (MK) trend test was used to identify the climate change (i.e., temperature and precipitation) trend of the Tianshan Mountains during 1981–2015.

Figure 3

Changes of altitudinal vegetation belts in the study area from 1989–2015. All Y-axis represent anomalies values. Because the upper limit of the cushion vegetation is the lower limit of the nival belt, we only show the trend of the lower limit of the nival belt.

Figure 4

Temporal variation of precipitation. To better compare the variation trend of altitudinal vegetation belt, temperature and precipitation, we normalized the data of temperature, precipitation, and altitudinal belt spectrum. The normalized range of all data is [− 1, 1].

Figure 5

Temporal variation of temperature. [(a) Yiwu county; (b) Hutu bi county; and (c) Zhaosu county].