Mountain Pastures of Qilian Shan: Plant Communities, Grazing Impact and Degradation Status (Gansu Province, NW China)

15/2 • 2016, 21–35 DOI: 10.1515/hacq-2016-0014 Mountain pastures of Qilian Shan: plant communities, grazing impact and degradation status (Gansu province, NW China) Alina Baranova¹,*, Udo Schickhoff¹, Shunli Wang² & Ming Jin² Key words: alpine vegetation, Abstract altitudinal gradient, Detrended Environmental degradation of pasture areas in the Qilian Mountains (Gansu Correspondence Analysis (DCA), province, NW China) has increased in recent years. Soil erosion and loss of Indicator Species Analysis (ISA), biodiversity caused by overgrazing is widespread. Changes in plant cover, overgrazing, pasture degradation, however, have not been analysed so far. The aim of this paper is to identify plant species diversity. communities and to detect grazing-induced changes in vegetation patterns. Quantitative and qualitative relevé data were collected for community classification Ključne besede: alpinska vegetacija, and to analyse gradual changes in vegetation patterns along altitudinal and grazing višinski gradient, korespondenčna gradients. Detrended correspondence analysis (DCA) was used to analyse variation analiza z odstranjenim trendom in relationships between vegetation, environmental factors and differential grazing (DCA), analiza indikatorskih vrst pressure. The results of the DCA showed apparent variation in plant communities (ISA), pretirana paša, degradacija along the grazing gradient. Two factors – altitude and exposure – had the strongest pašnikov, vrstna pestrost. impact on plant community distribution. Comparing monitoring data for the most recent nine years, a trend of pasture deterioration, plant community successions and shift in dominant species becomes obvious. In order to increase grassland quality, sustainable pasture management strategies should be implemented. Izvleček Degradacija pašnih površin v gorovju Qilian (provinca Gansu, SZ Kitajska) se je v zadnjih letih močno povečala. Erozija tal in izguba biotske pestrosti sta se zaradi pretirane paše zelo razširili. Do sedaj še nismo analizirali sprememb v pokrovnosti rastlin. V članku smo opisali rastlinske združbe in označili spremembe vegetacije zaradi paše. Združbe smo klasificirali na podlagi kvantitativnega in kvalitativnega popisnega gradiva in analizirali postopne spremembe v vegetacijskem vzorcu vzdolž gradienta višine in paše. Vegetacijo smo klasificirali z metodo združevanja. Za analizo variabilnosti odnosov med vegetacijo, okoljskimi dejavniki in različno intenzivnostjo paše smo uporabili korespondenčno analizo z odstranjenim trendom (DCA). Rezultati analize DCA so pokazali očitno raznolikost rastlinskih združb vzdolž gradienta paše. Največji vpliv na razširjenost rastlinskih združb sta imela višina in ekspozicija. S primerjavo podatkov monitoringa zadnjih devetih let Received: 28. 11. 2015 smo ugotovili, da se zaradi paše očitno slabša sukcesija rastlinskih združb, prihaja Revision received: 18. 04. 2016 pa tudi do sprememb dominantnih vrst. Za izboljšanje kakovosti travišč bo Accepted: 21. 04. 2016 potrebno uvesti trajnostne načine gospodarjenja. 1 University of Hamburg, Institute of Geography, CEN Center for Earth System Research and Sustainability, Hamburg, Germany. E-mail: udo.schickhoff@uni- hamburg.de, [email protected]* 2 Academy of Water Resource Conservation Forest of Qilian Mountains (AWRCFQM), Zhangye, Gansu Province, China. E-mail: [email protected], [email protected] * Corresponding author - 10.1515/hacq-2016-0014 Downloaded from PubFactory at 08/13/2016 05:09:27PM 21 via free access A. Baranova, U. Schickhoff, S. Wang & Ming Jin 15/2 • 2016, 21–35 Mountain pastures of Qilian Shan: plant communities, grazing impact and degradation status (Gansu province, NW China) the forests and grasslands have been replaced by second- Introduction ary vegetation, with a considerable percentage of unpal- atable, toxic and often thorny or spiny shrub and herb The impact of grazing on plant communities has been species that have a lower grazing value and rarely form a the focus of a multitude of studies all over the globe. Re- closed vegetation cover, at least in drier areas. sults showed that effects of grazing vary strongly between Only very few preliminary studies on vegetation and regions with different precipitation regimes and types of its degradation in the Qilian Mountains are available in pasture lands, and depend on the scale and specific site the literature, most of them in Chinese. A phytosocio- conditions (Vetter 2005, Metera et al. 2010). Direct ef- logical study was conducted by Kürschner et al. (2005), fects of grazing are associated with a change in canopy giving an overview of vegetation patterns and floristic height, habit and shoot architecture of plants, whereby composition, formed under long-term grazing pressure. short, prostrate and rosette plant forms are less sensitive Wang (2002) and Wang et al. (2002) studied distribu- to grazing (Diaz et al. 2006). In general, grazing favours tion patterns of vegetation along an elevational gradient annual over perennial plants (Diaz et al. 2006), and in- and detected peaks in species richness and species diver- creases the abundance of low-growing forbs compared to sity at intermediate positions of this gradient. Plant spe- grass and tall forb species (Metera et al. 2010). Generally, cies composition is also reported to vary between north- the effect of grazing is connected with the disappearance facing and south-facing slopes (Wang et al. 2002, Wang of good forage grasses and an increase in the proportion 2002, Huang et al. 2011). Chang et al. (2004) reported of invasive species (Zhou et al. 2006). a decline in biodiversity and found that more than 50% According to the intermediate disturbance hypothesis of the pasture communities are composed of toxic plant (Connell 1978, Kershaw & Mallik 2013), the diversity species. In overgrazed conditions, total nitrogen and total of grazed plant communities varies along a gradient of phosphorus of the alpine pastures decreased significantly, grazing pressure. Extensive (or moderate) grazing was whereas pH and soil bulk density significantly increased shown to be an effective tool to maintain genetic and bi- (Sheng et al. 2009). However, there are so far no detailed otic diversity of grasslands, while species richness is lower studies focusing on vegetation-environment relationships under the complete exclusion of livestock as well as under and on variation of vegetation patterns with changing site overgrazing (Wu et al. 2009, Metera et al. 2010, Török et conditions and differential grazing impact. al. 2014). Moderate grazing was found to be optimal to In order to fill this research gap, the objectives of this retain high plant species diversity (Zhou et al. 2006). Low study are to clarify hitherto unknown implications of grazing intensity was recommended to sustain the highest increased grazing intensity for rangelands in the Qil- levels of plant functional diversity, while intensive graz- ian Mountains. We hypothesize that the habitat quality ing was shown to decrease the proportion of characteristic and biodiversity of grazing lands are declining due to grassland species (Török et al. 2016). increased use intensity under the conditions of recent In the Qilian Mountains (Heihe River Basin, Gansu socio-economic change in NW China. We focus (1) on Province, NW China) overgrazing has been identified the main environmental variables influencing vegeta- as the core environmental problem of the region (Li et tion patterns along the altitudinal gradient, and (2) on al. 2003, Li et al. 2004), corroborating the general view the assessment of the pasture quality according to species among county officials that overgrazing is threatening for- composition and grazing impact in montane and alpine est and rangeland sustainability. Uncertainties regarding grasslands of the Qilian Mountains. rights of access and use of grazing resources hinder the establishment of proper rangeland management (Ding- guo 1992, Li et al. 2003). Sheep, goats and yak graze al- Methods most everywhere in the forests and adjoining rangelands, Study area which seems to be the prime cause preventing natural regeneration of trees and shrubs. Uncontrolled increases The Heihe River Basin, 97°24'–102°08' E to 37°44'– in the number of animals exceeds the carrying capacity 42°42' N, is the second largest inland river basin in the of grazing lands. Grazing pressure is extraordinarily high arid regions of northwestern China (Zhao et al. 2006). It on montane pastures, which are grazed in spring and au- belongs to the middle part of the Hexi corridor, which tumn, when alpine pastures are still or already snow-cov- is a 40–80 km wide tectonic depression between the ered. Pasture lands are insufficient in area, and intensive Longshou Mountains in Inner Mongolia and the Qil- grazing on spring, autumn, and summer pastures inhibits ian Mountains along the border of the Tibetan Plateau plant growth and reproduction (Dingguo 1992). Most of (Figure 1). The Qilian Mountains are of extraordinary - 10.1515/hacq-2016-0014 22 Downloaded from PubFactory at 08/13/2016 05:09:27PM via free access A. Baranova, U. Schickhoff, S. Wang & Ming Jin 15/2 • 2016, 21–35 Mountain pastures of Qilian Shan: plant communities, grazing impact and degradation status (Gansu province, NW China) importance as a water source region for the lower reaches soils and alpine cold desert soils near the summit, and of Heihe, Shiyang, and Shule rivers, supplying 4 million brown-desert soils at lower elevations (Wu 1980, Wang

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