Vegetation Dynamics and Responses to Climate Change and Human Activities in Central Asia
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Science of the Total Environment 599–600 (2017) 967–980 Contents lists available at ScienceDirect Science of the Total Environment journal homepage: www.elsevier.com/locate/scitotenv Vegetation dynamics and responses to climate change and human activities in Central Asia Liangliang Jiang a,b,Guli·Jiapaera,⁎, Anming Bao a,HaoGuoa,b, Felix Ndayisaba a,b a State Key Laboratory of Desert and Oasis Ecology, Xinjiang Institute of Ecology and Geography, Chinese Academy of Sciences, Urumqi 830011, China b University of Chinese Academy of Sciences, Beijing 100049, China HIGHLIGHTS GRAPHICAL ABSTRACT • The contributions of climate change and human activities were determined for different vegetation types. • Drought is the main factor affecting veg- etation degradation in the Kyzylkum Desert. • Increased irrigation was an important cause of the vegetation degradation around the Large Aral Sea in study period. • The effects of human activities on vege- tation changed from negative to posi- tive in eastern Central Asia. article info abstract Article history: Knowledge of the current changes and dynamics of different types of vegetation in relation to climatic changes Received 6 February 2017 and anthropogenic activities is critical for developing adaptation strategies to address the challenges posed by cli- Received in revised form 29 April 2017 mate change and human activities for ecosystems. Based on a regression analysis and the Hurst exponent index Accepted 1 May 2017 method, this research investigated the spatial and temporal characteristics and relationships between vegetation Available online xxxx greenness and climatic factors in Central Asia using the Normalized Difference Vegetation Index (NDVI) and – Editor: D. Barcelo gridded high-resolution station (land) data for the period 1984 2013. Further analysis distinguished between the effects of climatic change and those of human activities on vegetation dynamics by means of a residual anal- Keywords: ysis trend method. The results show that vegetation pixels significantly decreased for shrubs and sparse vegeta- Vegetation dynamics tion compared with those for the other vegetation types and that the degradation of sparse vegetation was more NDVI serious in the Karakum and Kyzylkum Deserts, the Ustyurt Plateau and the wetland delta of the Large Aral Sea Climatic change than in other regions. The Hurst exponent results indicated that forests are more sustainable than grasslands, Human activities shrubs and sparse vegetation. Precipitation is the main factor affecting vegetation growth in the Kazakhskiy Hurst exponent Melkosopochnik. Moreover, temperature is a controlling factor that influences the seasonal variation of vegeta- tion greenness in the mountains and the Aral Sea basin. Drought is the main factor affecting vegetation degrada- tion as a result of both increased temperature and decreased precipitation in the Kyzylkum Desert and the northern Ustyurt Plateau. The residual analysis highlighted that sparse vegetation and the degradation of some shrubs in the southern part of the Karakum Desert, the southern Ustyurt Plateau and the wetland delta of the Large Aral Sea were mainly triggered by human activities: the excessive exploitation of water resources in the up- stream areas of the Amu Darya basin and oil and natural gas extraction in the southern part of the Karakum De- sert and the southern Ustyurt Plateau. The results also indicated that after the collapse of the Soviet Union, ⁎ Corresponding author. E-mail addresses: [email protected] (Guli·Jiapaer), [email protected] (A. Bao), [email protected] (H. Guo). http://dx.doi.org/10.1016/j.scitotenv.2017.05.012 0048-9697/© 2017 Elsevier B.V. All rights reserved. 968 L. Jiang et al. / Science of the Total Environment 599–600 (2017) 967–980 abandoned pastures gave rise to increased vegetation in eastern Kazakhstan, Kyrgyzstan and Tajikistan, and abandoned croplands reverted to grasslands in northern Kazakhstan, leading to a decrease in cropland greenness. Shrubs and sparse vegetation were extremely sensitive to short-term climatic variations, and our results demon- strated that these vegetation types were the most seriously degraded by human activities. Therefore, regional governments should strive to restore vegetation to sustain this fragile arid ecological environment. © 2017 Elsevier B.V. All rights reserved. 1. Introduction In addition to climate change, human activities are a key factor af- fecting vegetation growth. After the disintegration of the Soviet Union Global temperatures in the past century have increased by approxi- in 1991, politics and the economic development model in Central Asia mately 0.74 °C, and the intensity of precipitation events is expected to were changed to varying degrees, resulting in large-scale rural–urban increase, especially in wet regions. Decreases in mean precipitation in migrations, broad-scale private ownership, and an economic develop- most mid-latitude and arid areas contribute to drying during the sum- ment model that transformed from a planned economy to a free market mer, indicating a great risk of drought in these areas (IPCC and WGI, economy. The management model of agriculture and animal husbandry 2007; Meehl et al., 2007). According to forecasts, dryland regions will also switched from state-owned and collective farming to private and become warmer and drier, and wet regions will become warmer and free market farming. Indeed, changes in the method and scale of moister (Guli·Jiapaer et al., 2015; Lioubimtseva et al., 2005; Ndayisaba human activities inevitably impacted vegetation growth (Hostert et et al., 2016; Yu et al., 2003). Moreover, Central Asia is located in a al., 2011). There are three important aspects of these changes that mid-continental region and contains one of the world's largest arid may control vegetation greenness in Central Asia: (1) extensive derelict areas. Precipitation has exhibited a slight decreasing trend in this region lands restored to other vegetation types; (2) the expansion of irrigated with spatially heterogeneous changes (Li et al., 2015; Mannig et al., agriculture resulting in vegetation degradation, such as the environ- 2013; Sorg et al., 2012). The temperature in Central Asia has been rising mental disaster of the Aral Sea Basin; and (3) the collapse of animal hus- rapidly, particularly since the mid-1990s, and it is presently higher than bandry in Central Asia (Klein et al., 2012; Lioubimtseva and Henebry, at any other period in recorded history (Davi et al., 2015; Hu et al., 2014; 2009; Xi and Sokolik, 2016). Thus, in the broader context of sustainable Li et al., 2015). In this region, vegetation ecosystems typically lack biodi- development, a more profound understanding of vegetation dynamics versity and stability and have been susceptible to high climatic variabil- following the disintegration of the Soviet Union is vital for planning ity in recent decades (Bohovic, 2016; de Beurs et al., 2009; Han et al., strategies to adapt to concurrent climatic fluctuations. However, despite 2016; Zhou et al., 2015), especially in three temperate deserts: the the great social and economic changes that have occurred, the different Muyunkum Desert, Karakum Desert and Kyzylkum Desert (Fig. 1)(C. mechanisms that drive vegetation changes in response to climate Zhang et al., 2016). Vegetation in drylands is ecologically beneficial, change have received little consideration in Central Asia. not only sustaining domestic and wild animals but also providing im- Generally, vegetation changes triggered by climatic factors and portant ecological functions, such as the prevention of soil desertifica- human activities, separately or together, influence vegetation greenness tion (Lioubimtseva, 2014; Tao et al., 2017). Thus, the responses of on regional and global scales (Breshears et al., 2005; King et al., 2015; dryland vegetation to climate change are emerging as a research focus Nezlin et al., 2005; Sun et al., 2015; Wang et al., 2015; Y. Zhang et al., worldwide. 2016). Thus, understanding vegetation dynamics and its response to Fig. 1. Topographical map of the nations of Central Asia. .