Restoration Prospects for Heitutan Degraded Grassland in the Sanjiangyuan

J. Mt. Sci. (2013) 10(4): 687–698 DOI: 10.1007/s11629-013-2557-0 Restoration Prospects for Heitutan Degraded Grassland in the Sanjiangyuan LI Xi-lai1*, PERRY LW George2,3, BRIERLEY Gary2, GAO Jay2, ZHANG Jing1, YANG Yuan-wu1 1 College of Agriculture and Animal Husbandry, Qinghai University, Xining 810016, China 2 School of Environment, University of Auckland, New Zealand Private Bag 92019, Auckland, New Zealand 3 School of Biological Sciences, University of Auckland, New Zealand Private Bag 92019, Auckland, New Zealand *Corresponding author, e-mail: [email protected] © Science Press and Institute of Mountain Hazards and Environment, CAS and Springer-Verlag Berlin Heidelberg 2013 Abstract: In many ecosystems ungulates have yield greatest success if moderately and severely coexisted with grasslands over long periods of time. degraded areas are targeted as the first priority in However, high densities of grazing animals may management programmes, before these areas are change the floristic and structural characteristics of transformed into extreme Heitutan. vegetation, reduce biodiversity, and increase soil erosion, potentially triggering abrupt and rapid Keywords: Heitutan degraded grassland; Alpine changes in ecosystem condition. Alternate stable state meadow; Restoration/rehabilitation; Sanjiangyuan; theory provides a framework for understanding this Qinghai-Tibet Plateau (QTP) type of dynamic. In the Sanjiangyuan atop the Qinghai-Tibetan plateau (QTP), grassland degradation has been accompanied by irruptions of Introduction native burrowing animals, which has accentuated the loss of ground cover. Severely degraded areas of Environmental damage resulting from alpine meadows are referred to as ‘Heitutan’. Here, using the framework of alternate stable state theory, population pressure, intensifying land-use and we describe the proximate and ultimate drivers of the climate change, alongside many other factors, has formation of Heitutan on the QTP, and we assess been accompanied by a progressive depletion of prospects for recovery, in relation to the degree of natural resources. The Global Assessment of biophysical alteration, of these alpine meadows. Human-Induced Soil Degradation concluded that Effective rehabilitation measures must address the “approximately 23% of the world’s used terrestrial underlying causes of degradation rather than their area was degraded: 38% was lightly degraded; 46% symptoms. Heitutan degradation is not uni-causal. moderately degraded; and 16% strongly to Rather it reflects different mechanisms operating at extremely degraded” (Oldeman and van Lynden different spatio-temporal scales across this vast 1997). Grazing lands are possibly “the most region. Underlying causes include overly aggressive degraded land use type in the world” (Papanastasis exploitation of the grasslands (e.g. overgrazing), 2009), and grassland degradation is a world-wide amplification of grazing and erosion damage by small mammals when outbreaks occur, and/or climate problem (Kessler and Laban 1994; Muller et al. change. Given marked variability in environmental 1998; Carrick and Krüger 2007). conditions and stressors, restorative efforts must vary Grassland refers to expansive and mostly across the region. Restoration efforts are likely to unimproved land that supports natural vegetation such as grasses or grass-like plants, including forbs Received: 24 October 2012 Accepted: 6 July 2013 and shrubs (Li et al. 2013). Grassland, rangeland 687 J. Mt. Sci. (2013) 10(4): 687–698 and pasture are loosely synonymous terms used in opposite effect. Thus, the extent to which changes different parts of the world to refer to a similar set in grazing pressure lead to changes in ecosystem of environmental conditions where ecosystems condition does not solely depend on the number produce forage (Ren 2000). In this paper we use (biomass) of livestock, but also on the pattern of the term ‘grassland’ throughout. Grassland their grazing (Oesterheld et al. 1992). degradation is characterised by reduced In this paper we describe the proximate and productivity, fragmentation of grass cover, ultimate drivers of the formation of grassland reduction in soil fertility, soil compaction, an degradation on the Qinghai-Tibet Plateau (QTP) in increase in unpalatable grass species, or a western China. We appraise prospects for recovery in combination of some or all of these factors (Li relation to the degree of biophysical alteration of 1997). As grassland ecosystems provide a wide these alpine meadows. We place these long-term range of ecological goods and services, including spatio-temporal dynamics in the context of current animal habitat, soil-related services, grazing interest in the dynamics and restoration of ecological resources for livestock and carbon storage (White systems showing alternative stable states. Better et al. 2000; Lund 2007; Wen et al. 2013), understanding of regional variability in drivers of degradation affects the livelihood of the grassland degradation can contribute to protection pastoralists who depend on them (Harris 2010). and management of these fragile alpine ecosystems. White et al. (2000) suggest that the extent and severity of soil degradation in grassland areas has increased markedly in recent decades. 1 Cause of Grassland Degradation in the In many ecosystems ungulates have coexisted Sanjiangyuan with grasslands over long periods of time. However, the viability of some of these ecosystems is 1.1 Grassland resources and degradation threatened by recent changes in stocking rates in China arising from domestication programmes. High densities of grazing animals may alter the floristic Most of China’s rich grassland resources are and structural characteristics of vegetation, reduce distributed in the west and northwest, in biodiversity, and increase soil erosion. Hence, environmental settings that include alpine meadow, humans can affect the condition of grassland tundra and steppe. Collectively, these rangelands ecosystems through modification of the grazing cover 41.7% (400 million ha) of China’s land area regime. The impacts of domestic animals may be (Ren et al. 2008). The QTP is a vast, elevated either positive or negative, reflecting different plateau in western China, bordering India in the stocking densities and behaviours (Sankey et al. west, and the Kunlun, Arjin and Qilian Mountains 2009). A comparison of the grazing of grasslands in the northeast and northwest. The Sanjiangyuan by wild ungulates and domestic livestock lies at the heart of the QTP in the southern part of underlines important transformations in grassland Qinghai province (latitude 31o39’-36o12’N, ecosystems. The primary goal of domestic animal longitude 89o45’-102o23’ E; Li et al. 2012a). husbandry is to maximise animal biomass. Humans have used alpine meadows Oesterheld et al. (1992) found that, after dominated by Kobresia spp. (Cyperaceae) for controlling for primary productivity, the biomass of livestock grazing for more than 8,000 years (Kaiser domestic animals can be up to an order of et al. 2008; Miehe et al. 2008, 2009). Prior to the magnitude higher than that of wild grazers. At high mid-Holocene climatic optimum, landscapes of the densities, domestic grazing animals can change QTP were more heavily forested but were then vegetation composition and structure, reduce cleared (largely by fire) and Kobresia subsequently biodiversity, and increase soil erosion; in extreme became established. If grazing pressures are situations, grazing may eliminate much vegetation removed, Kobresia pastures disappear. The alpine cover (Evans 1998). Paradoxically, at ecosystems in the region are locally threatened by (appropriately) high densities wild animals can increases in human population and uncontrolled have a positive impact on ecosystem structure and production activities (Ma et al. 2000; Du et al. function, but domestic animals appear to have the 2004; Zhou et al. 2005; cf., Harris 2010; Li et al. 688 J. Mt. Sci. (2013) 10(4): 687–698 2013). Removal of vegetation has reduced the Sanjiangyuan can be considered to be degraded water-retention capacity of the region and lowered (Fan et al. 2010). the capacity of the environment to cope and Areas of degraded alpine meadows on the QTP recover in periods of stress (Li 2007). Today, are referred to as ‘Heitutan’ (see Figure 1; Li et al. between 26-46% of the total grassland area in the 2012b). Increased proportions of bare (a) Alpine meadow: high density Kobresia populations are highly resilient (b) Severely degraded Heitutan: severe small mammal damage and soil erosion extend across around 40% of the area covered by alpine meadow Figure 1 Various stages and states of Heitutan formation from (a) intact through (b) severely degraded to (c) extremely degraded in the Sanjiangyuan (photos: Li Xi-lai 2007). Figures on the right show a close view of grassland conditions in each condition. 689 J. Mt. Sci. (2013) 10(4): 687–698 ground/eroded ground, less palatable herbage and degraded ground and subsequently Heitutan. Over more unpalatable plant species in these areas have time, the loss of vegetation, possibly amplified by accelerated rates of water and soil erosion. Nearly small mammal activity, can negatively impact 14 % (49,000 km2) of the Sanjiangyuan has been grasslands and promote a regime shift towards degraded to Heitutan grassland (Li et al. 2013). Heitutan (Shang et al. 2006; Li et al. 2013). In Given their black colour and geographic location, areas of Heitutan, the loss of palatable forage these areas

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