Download The effect of grazing on plant species richness on the Qinghai

The effect of grazing on plant species richness on the Qinghai Plateau, Tibet
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Jianjun Cao1, Nicholas M. Holden2, Guozhen Du1*
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1. The Key Laboratory of Arid Agro-ecology of the Ministry of Education, Lanzhou
University
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2. UCD Bioresources Research Centre / Biosystems Engineering, UCD School of
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Agriculture, Food Science and Veterinary Medicine, University College Dublin, Belfield,
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Dublin 4, Ireland
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Abstract
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In Maqu County in the Gansu Province of China there are two predominant forms of grazing
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managements. Under multi-household (MH) management, grassland is jointly managed by
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two or more households without fences between household pastures. Under single-household
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(SH) management fenced-off parcels of grassland are separately managed by one household.
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Resource management policy in the area assumed that MH management would subject a
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parcel of land to more grazing pressure than SH use because no individual was responsible
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for the resource. However, the consequences of this difference in land ownership are not clear
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in terms of biodiversity and overall agro-ecology, and differences in plant species richness
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between MH and SH could have long term implications for the region. Comparable land
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parcels subject to MH and SH were identified and surveyed by quadrat analysis and the data
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summarized using the Gleason Index. MH land had a greater index values than SH but the
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differences were not significant. A further analysis of the plant species richness data indicated
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that the number of households using MH land influenced the species richness. Land used by 3
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to 7 households had significantly lower index values than land used by 8 to 15 households,
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which in turn had significantly lower index values than land used by >15 households. There
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was also evidence to suggest that the quality of the forage available deteriorated under SH
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management. It was concluded that MH grazing resulted in greater species richness than SH
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and is perhaps an important contributor to biodiversity conservation and grassland
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management for the region.
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Keywords
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Multi-household grazing management; Single-household grazing management; Plant species
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richness; Gleason Index; Maqu County; Gansu Province
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Introduction
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Anthropogenic land use, whether converting natural landscapes for human use or changing
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management practices on human-dominated land has transformed large proportion of the
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planet’s land surface (Foley et al., 2005). Research has revealed the environmental impacts of
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anthropogenic land use ranging from changes in atmospheric composition (IPCC, 2000) to
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extensive modification of Earth’s ecosystems. Although land-use practices vary greatly across
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the world, the ultimate outcome is generally the same: the acquisition of natural resources for
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immediate human needs, often at the expense of degrading environmental conditions. (Foley
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et al., 2005). Land use change and land management has in some cases caused a decline in
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biodiversity (Maurer et al, 2006) and change in vegetation composition (AO et al., 2008)
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through the loss, modification, and fragmentation of habitats, degradation of soil and water,
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and overexploitation of native species (Pimm, and Raven, 2000). Land use change is not only
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the main cause of the soil degradation, but it also generates pressure on local, and perhaps
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fragile, economies (Wang et al., 2004). At present, land use change is a major threat to
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species diversity of grasslands throughout the world (Maurer et al, 2006), thus developing an
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understanding grassland ecosystem response to land use change is required in order to
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manage and prevent land degradation (Zhou et al., 2002) because maintaining plant diversity
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is a central goal of global biodiversity management (Olff & Ritchie, 1998). Linking
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ecological theories of species diversity to land management has become a research and
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management priority for promoting species diversity and sustainable use of natural systems
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(Bestelmeyer et al., 2003).
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China encompasses enormous variations in topographical features, with high mountain
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ranges and extensive plateaus, resulting primarily from the collision of the Indian
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subcontinent with the Asian continent. The resulting habitat heterogeneity contributes to the
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maintenance of high biodiversity by providing many niches and opportunities for speciation.
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The estimated number of vascular plant species is nearly 33,000, with 30,000 angiosperms,
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250 gymnosperms and 2600 pteridophytes, ranking third in plant biodiversity in the world
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(Lopez-Pujol et al. 2006; Shimono et al., 2010). The Qinghai–Xizang (Tibetan) plateau
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occupies 2.5 million km2, approximately 25% of the area of the People’s Republic of China.
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An estimated 70% of the plateau is high altitude grasslands, considered as cold alpine
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rangelands extend from the moist sub-humid grasslands of the eastern plateau to the
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semi-arid alpine desert steppe in the west, and display a diverse array of plant and wildlife
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species (Smith & Foggin, 1999; Richard et al., 2006). According to Lopez-Pujol et al. (2006)
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more than 12,000 species in 1,500 genera of vascular plants have been identified on the
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plateau, including 3,500 species that are endemic to the plateau. Therefore, maintenance of
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plant richness on the Tibet Plateau is of both national and global importance. However, these
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distinctive flora and fauna – many of which are endangered (Smith & Foggin, 1999) – are
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declining due to many causes of degradation (Richard et al., 2006) including climate change
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(drying), human population increase, increase in burrowing mammal populations due to
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ineffective control and hunting of predators, increasing concentration of livestock near winter
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settlements, reduced mobility due to restrictive pasture tenure, breakdown of traditional
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regulatory mechanisms, and lack of government investment in rangeland and livestock
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infrastructure. Some researchers (Gimenez, 2002; Richard et al., 2006; Yang, 2007; Zhang
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and Li, 2008) have suggested that changes in land use have caused degradation and reduced
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plant biodiversity, but no field experiments have been conducted to demonstrate these effects.
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In this paper the effect of changing land management (i.e. a land use change) on plant
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richness on the Qinghai Tibet plateau will be examined.
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Grassland use change on Qinghai Tibet plateau
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For thousands of years cold-tolerant livestock grazing by nomadic Tibetan herders on the
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Qinghai plateau was the dominant and apparently environmentally sustainable land use (Yan
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et al., 2005). However, in the late 1970s, policy reform led to settling of nomadic farmers,
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livestock being divided among then and individual family leasing of state owned pasture
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(Manderscheid, 2001). The rationale for privatizing rangeland in China was the belief that
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open access of privately owned livestock to common rangeland had led to rangeland
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degradation and that elimination of open-access property rights could solve the problem
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(Gadgil et al., 1993; Yan et al., 2005), known more generally as the “Tragedy of the
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Commons” (Hardin, 1968; Ashenafi & Williams, 2005; Wang, 2009). In Hardin’s (1968)
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theory, the individual will maximize utilization of common land even if this results in
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degradation because the individual achieves short-term benefits and the longer-term burdens
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are distributed amongst all with right of access. The suggested solution is private land
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ownership, which theoretically encourages the owner to utilize the resource sustainably.
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There is evidence however that suggests the theory is not universal (Crépin and Lindahl,
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2009) and that common ownership, in the right social setting might be environmentally
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beneficial. In China, Grassland Supervisor Stations assign rangeland use rights to individual
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households, establish boundaries by fencing, and set, monitored and enforced stocking rates
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for individual household pastures (Ranks, 2004). About 70 per cent of usable rangeland was
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leased through long-term contracts by 2003, of which 68 per cent was contracted to
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individual households and the rest to groups of households or to villages (Yao, 2003).
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There are predominantly two land use types since the implementation of this system
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single-household (SH) use and multi-household (MH) use. For MH, grassland is jointly
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managed by two or more households without boundaries between household pastures, while
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for SH, grassland is fenced-off and managed by one household. If the number of households
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is larger enough, MH grassland management is similar to historical nomadic land use while
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SH represents the ideal for the theory of individual ownership to drive sustainable
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management.
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The objective of this paper is to examine the effect on plant richness of grazing management
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under single household ownership (less likely to cause degradation according to theory) and
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under multiple household ownership that closely resembles historical nomadism (more likely
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to cause degradation according to theory). The work addresses the question of whether SH
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management results in greater or lesser plant species richness, used as an indicator of
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biodiversity (Ma & Liu, 1994; Fang et al., 2004) compared to MH management.
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Materials and Methods
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The Maqu grassland ecosystem, located Maqu County in the Gansu Province of China is on
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the eastern Qinghai-Tibet plateau, (101°E; 34°N). The altitude ranges from 2900 m to 4000 m
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with an annual rainfall of 450 to 780 mm, an annual average temperature of 1.8 oC (ranging
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from minima of -10.7 oC in January to 11.7 oC in July, and a growing season maxima of 23.6
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oC
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59 % is highly productive alpine meadow. The grassland types include mainly alpine meadow
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(59%), brushy meadow (33%), woodland meadow <1%), saline meadow (<1%), swampy
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meadow (6%) and upland grass (1%)(Bu et al., 2006). The estimated number of vascular
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plant species is over 530, with 57 families and 204 genera.
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to 28.9 oC) and 270 frost days annually. The grassland area is about 870,000 ha of which
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Historically, nomadic grazing with common ownership was the dominant livestock
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management system in the Maqu. Since 1995 grassland has been progressively allocated to
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individual households with the intention of maintaining rangeland health and promoting
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livestock production (Yan et al., 2005). The original nomadic grazing system was replaced by
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SH and MH grazing systems. In Maqu, the development of MH reflects a long social history
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of collective living, family relationships, limitation of water resources and a lack of
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infrastructure (Cao et al., 2009) that represents a compromise between people and
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government that allow both to progress. A typical household grazes sheep and Yak, with
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stocking rates of around 2 animals per hectare. When nomadic grazing stopped, herders
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usually choose winter grasslands as their home place because these grasslands are productive
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under natural conditions and trafficable at most times of the year. Summer grasslands are
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difficult to access so less desirable for permanent residence. Generally livestock are
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transferred in June from winter grasslands to summer grasslands, back to winter grasslands in
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August, to summer grasslands in September and returned winter grasslands in October.
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All experiments were conducted on winter grassland after herders had transferred to summer
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grasslands at the beginning of July. Only land managed by farmers who had transferred their
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livestock at the same time, had similar stocking rates (2 sheep per Ha as overseen by
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Government) and had the same grassland type was selected. All sampling was conducted over
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1 week in dry weather on 30 SH and 30 MH plots. Within each plot sampled, 3 sub-plots
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were identified and three 50cm2×50cm2 quadrats were laid out at randomly selected locations
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and orientations. The species richness based on species count per quadrat was expressed
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using the Gleason Index (G) calculated as (Ma, 1994):
G = S/lnA
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(1)
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where S = number of species in the quadrat and A = area of quadrat,. The coverage of
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individual species was also visually estimated by the same observer for each plot. Land
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management was classified by the number of households with right of access and an analysis
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by household pressure (number of households with access to the land parcel) was conducted
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using SPSS 15.0 statistical software. ANOVA was used to determine the significance of any
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differences.
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Results
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The ten most common plant species found on the observation plots (Table 1) vary by land
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management. Under SH management quality forage typified by Poaprafensis is no longer
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common. Ligularia virgaurea, Anemone rivularia and Herba Taraxaci have become more
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common species and are regarded as an indicator as degradation because they are poisonous
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weeds that exploit bare soil surface exposed by intensive grazing pressure (Zhang et al., 2003;
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Xie et al., 2010). When summarized by Gleason Index, the species richness of MH (24.4 ±
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4.2) was marginally higher than that of SH (22.2 ± 3.9), but the difference in species richness
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was not significant. The results do indicate however that since 1998 two species seem to have
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been lost with the change to SH management. It is not possible to establish whether this is a
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progressive tend that might indicate further species decline.
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Household access within MH management was clustered into three classes: 3-7 households;
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8-15 households; and >15 households. Species richness was positively correlated (r=0.51,
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p<0.001) with increase in household access and there were significant differences by
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household access and management type (Figure 1). The SH and 3-7 household MH plots had
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lower species richness compared to the MH with >8 households.
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Discussion
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The results indicate that grassland species richness is linked to household access and the
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intensity with which animals graze the grassland resource on a year round basis. SH
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landholdings have little access to a range of pastures so the land has to be used at times when
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it would traditionally be vacated (e.g. the shift from winter to summer grazing grounds and
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vice versa) while MH landholdings can be managed in a more traditional manner with land
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allocated to the most suitable grazing season. Therefore there is more sustained grazing
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pressure on the plant assemblage in SH plots than in MH plots due to trampling (Ao et al.,
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2008) and non-selective grazing (Milchunas et al., 1998). The MH plots permit animals to be
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more selective in their grazing choices as they have greater areas to forage over and the
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owners have more management options for optimizing grazing (Richard et al., 2006;
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Gimenez, 2002). It would also appear that the social pressure assumed by the theory of the
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“tragedy of the commons” has not applied. Individuals seem not to have taken personal
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short-term benefits at the expense of those neighbors they share with. This presumeably
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reflects a tradition of nomadic cooperation. At the smaller management scale associated with
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SH, decreased resource heterogeneity may have contributed to decreased niche dimensions
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leading to the loss of grassland species richness (Olff and Ritchie, 1998; Spiegelberger et al.,
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2006; Harpole & Tilman, 2008) and to introduction of new species due to bare soil being
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exposed.
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Conclusion
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The results of this study indicate that having a choice of grazing land associated with natural
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seasonality, and sufficient area to permit selective grazing will protect plant diversity on
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Qinghai-Tibet Plateau. Under MH (or even nomadic management), livestock can use
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abundant low-quality food and while creating frequent but small disturbances across the
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landscape, which is efficient for seed dispersion, provides niche openings for plant
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development and facilitates spatially heterogeneous urine and dung deposition thus increasing
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regeneration and soil heterogeneity (Olff & Ritchie, 1998). To achieve sustainable rangeland
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management, lessons from traditional management (Yan et al., 2005) can be adapted to
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permit controlled development of the resource without unwanted side-effects. The results of
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this study indicate that Single household grassland management will probably cause a
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decrease in plant diversity by focusing grazing pressure on small areas of grassland rather
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than permiting a more sustainable dispersion over a wider area as can occur under multiple
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household management.
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Acknowledgements
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Our work is funded by Ford Foundation (grant 1085-0629) “Grassland management research
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based on livelihood of herders: A case study from the key water supplement area (Maqu) to
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Yellow river”.
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Table 1: The 10 most common species found in winter grassland of SH and MH in the Maqu County survey
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Rank order
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2
3
4
5
6
7
8
9
10
3
4
5
6
7
16
Species
Kobresia capillifolia
Scirpus pumilus
Potentiual
Festucaovina
Kobresia Wild
Elymusnutans
Ligularia virgaurea
Anemone rivularia
Herba Taraxaci
Kobresia humilis
SH
22(+/- 21)
19(+/- 17)
15.6(+/-11)
14(+/-8)
13(+/-8.1)
13(+/-16)
11.9(+/-13.7)
5.9(+/-3.6)
5.3(+/-3.4)
4.1(+/-1.7)
Species
Scirpus pumilus
Festucaovina
Kobresia capillifolia
Tibeta himalaica(Bakerer) Tsui
Poaprafensis
Lancea tibetica Hook.F.Et Thomas
Elymusnutans
Potentiual
Kobresia Wild
Ranun Culus
MH
26(+/- 15)
25(+/-11)
24 (+/- 20)
22(+/-14)
20(+/- 12)
19.3(+/-10.7)
19(+/-15)
16.1(+/-11.5)
15 (+/-12.2)
12(+/-9)
1
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