Spatio-temporal variations and drivers of ecological carrying capacity in a typical mountain-oasis-desert area, Xinjiang, China

Highlights

• Spatial pattern of ecological carrying capacity (ECC) is shaped largely by altitude.

• ECC decreases from west to east, and shows increase in some prefectures.

• Good ECC exist mainly in the mountains and oasis with increasing trends.

• Temperature is a better driver of ECC improvement than precipitation.

• Agriculture, water and urban developments may continue to depress ECC.

Abstract

The aggravation of climate change and human activities have challenged the fragile ecology of the arid and semi-arid Xinjiang in Northwest China. The concept of ecological carrying capacity (ECC) refers to the ability of an ecosystem to support the healthy development of the human social system and provide adequate resources and enabling environmental conditions. A comprehensive evaluation of ECC could rationalize ecological restoration and sustainable development. This study evaluates the ECC of Xinjiang's unique landscape structure of mountain-oasis-desert ecosystems from 1982 to 2017, using remote sensing data such as vegetation and evapotranspiration and geographic information system technology, and index evaluation method. The ECC patterns and change trends were explained from multidisciplinary perspectives, and the internal drivers of ECC spatio-temporal variations were evaluated by partial correlation analysis and residual analysis. The results showed an average ECC value at the median level of 0.29. For spatial distribution, ECC value decreased from west to east, the median ECC area was the most widespread, and the poorest ECC area was concentrated mainly in Southern Xinjiang's deserts. From the analysis of the significance of the change, ECC in Xinjiang had generally declined, with the decreasing areas exceeding the increasing areas. The driver analysis found temperature exerting a greater impact than precipitation on ECC improvement, and human activities positively impacted ECC. Altitude was closely associated with ECC distribution with better ECC in high elevation areas. The positive correlation between urbanization and ECC level was significant. The findings provide a relatively comprehensive and synoptic framework for ecological assessment in arid and semi-arid areas to inform sustainable development and ecological restoration in Xinjiang.

Introduction

Ecological carrying capacity (ECC) was developed based on the carrying capacity concept, with its origins from Malthus's “population theory”, which describes the limitation of food supply on population growth (Seidl and Tisdell, 1999). Ecologists have adopted this concept to describe the relationship between population, environment, and social economy that an ecosystem can support. It is the ability to provide adequate resources and enabling environmental conditions for the healthy development of the human social system (Jin et al., 2018; Martire et al., 2015).

In recent decades, China's economy and population have experienced fast growth. During this period, in the relatively less-developed northwest region of Xinjiang, the Chinese government has implemented successively economic development policies such as “China's Western Development Policy” and “Silk Road Economic Belt” (Central Government Portal of China, 2014), bringing rapid social and economic development. Meanwhile, climate change is affecting all regions of the world (El-Beltagy and Madkour, 2012; Ripple et al., 2020), accentuating the impacts of human activities in Xinjiang. To achieve regional sustainable development, it is critical to balance economic development and environmental wellbeing (Miao et al., 2016; Shi et al., 2020).

Xinjiang is located in the arid and semi-arid region of Northwest China, with a fragile ecology and limited natural resources. Ecological problems such as land desertification (Li et al., 2014; Li et al., 2013) and salinization (Zhuang et al., 2021) are prominent. Due to the extensive distribution and complex evolution mechanisms of environmental impacts, it is difficult to evaluate quantitatively the overall regional ecological status. It is similarly challenging to analyze quantitatively the synergy of various driving factors on temporal and spatial changes. Lacking such knowledge could compromise the ecological restoration efforts (Ge et al., 2015). Dang and Liu (2012) observed that the primary problem in formulating a regional-scale ecological restoration plan is how it will affect the carrying capacity and sustainability of the target area. Zhang et al. (2020b) realized that the primary premise of ecological restoration is ascertaining the ecological carrying capacity (ECC) as the basis to formulate a detailed regional ecological restoration plan. It is also critical to monitor ECC decline in tandem with the continual population and economic growth (Skonhoft and Solem, 2001). Hence, the ECC concept offers a powerful tool to monitor and evaluate sustainable development, especially in ecologically stressed and fragile areas (Kessler, 1994; Świąder, 2018; Yue, 2012).

The ECC techniques have been applied to different situations in many regions. The data sources include Statistical Yearbook (Wei et al., 2020; Ariken et al., 2021), field measurements (Bu et al., 2020), and remote sensing (Wu et al., 2020). The common ECC evaluation methods include ecological footprint (Solarin and Bello, 2018; Swiader et al., 2020), net primary productivity (NPP) (Ren et al., 2020), state space model (Mao and Yu, 2001), and “3S” (remote sensing, geographic information system and global positioning system) technology comprehensive analysis (Wu and Hu, 2020; Yue, 2012). Despite the diverse data and methods, ECC research in China is still beset by limitations. Most data sources are statistical data. Due to inherent data limitations, the whole administrative region is often taken as the basic research unit. The study indicators often ignore intrinsic ecosystem attributes and focus on people-centered ones, such as gross land area per capita, waste treatment capacity, and industrial CO₂ emission. The bias towards large-scale statistical data tends to restrict the studies to the provincial administrative units and broad-brush indicators, thus neglecting the complex local ecological reality (Wei et al., 2020; Ariken et al., 2021). In addition, a large amount of measured data has been used in studies related to water ecological carrying capacity (WECC). The measured data allows monitoring the ecological water health and the stresses caused by human activities, but they are limited to the county scale and water-resource perspective (Bu et al., 2020). Overall, many studies are one-sided, lack regional relevance and integration, and do not fully consider the innate study-area characteristics.

The rapid development of Xinjiang is closely associated with utilizing its scarce water resource to exacerbate the ecological crisis. The intensification of salinization and desertification has exerted undue pressure on the environment (Zhang and Huisingh, 2018; Zhou et al., 2020). The constrained consideration of a single ecological factor (e.g., water resources, vegetation, or land), the entire administrative division, and the short duration cannot fully reflect Xinjiang's ecological stresses, let alone understanding the trends and causes of ECC changes. Recent advances in research techniques for temporal and spatial analysis of ECC and availability of new data offer opportunities to strengthen relevant studies (Wan et al., 2017; He and Xie, 2019). The results may offer an important theoretical and practical basis for Xinjiang's ecological restoration and sustainable development.

This study evaluated ECC's spatio-temporal characteristics and internal drivers in Xinjiang from 1982 to 2017. A series of research techniques and data sources were applied in an integrated manner to conduct the research, including: (1) remote sensing data and geographic information system technology; (2) Global Inventory Modelling and Mapping Studies (GIMMS) Normalized Difference Vegetation Index (NDVI); (3) evapotranspiration data; (4) meteorological data; (6) statistical data on socio-demographic and economic domains; and (6) findings and data of previous studies of arid and semi-arid areas for a comprehensive assessment of the natural conditions of the study area (Wu et al., 2020).

The specific study objectives were to: (1) explore the spatio-temporal patterns and changes of ECC in Xinjiang using the remote sensing evaluation model; (2) analyze the status and multi-year changes of ECC in various prefectures using the cluster heat-map; and (3) explain the internal drivers of spatio-temporal ECC changes based on meteorological and human factors using partial correlation analysis and residual analysis. This study could provide a basis to inform the sustainable development of Xinjiang as a typical ecological vulnerable area. It could offer reference value for implementing ecological and environmental protection policies in similar areas in China and other countries.