Current status and future prospects of Zoige Marsh in Eastern Qinghai-Tibet Plateau

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Current status and future prospects of Zoige Marsh in Eastern Qinghai-Tibet Plateau Shuang Xiang a , Ruqing Guo b , Ning Wu a , Shucun Sun b,a,∗ a b

Chengdu Institute of Biology, Chinese Academy of Sciences, Chengdu 610041, China Department of Biology, Nanjing University, Nanjing 210093, China

a r t i c l e

i n f o

a b s t r a c t

Article history:

Zoige Marsh, located in the Northeastern Qianghai-Tibet Plateau, is the largest highland

Received 31 August 2007

marsh in the world. The marsh is one of the hotspots for biodiversity, harboring many

Received in revised form

endemic and endangered species, including Grus nigricollis, the only plateau crane. Zoige

20 February 2008

Marsh has a large area of high-quality grasslands, serving as the fifth largest livestock base

Accepted 27 February 2008

in China, and it is also the major water source to the headstream of the Yellow River. However, due to global warming and unwise use of the marsh resources, including ditching for grassland enlargement, peat exploitation, and livestock grazing, since the 1970s, Zoige

Keywords:

Marsh has suffered severe ecosystem degradations such as vegetation recessive succession,

Zoige Marsh

biodiversity loss, soil deterioration, and rodent disasters. It is therefore imperative to restore

Biodiversity

the damaged marsh. We propose in this paper that ecological engineering and livestock

Ecosystem degradation

population control must be taken as measures for ecological restoration and biodiversity

Ecological restoration

protection.

Qinghai-Tibet Plateau

1.

Introduction

Zoige Marsh, located in the northeast corner of Qinghai-Tibet Plateau (101◦ 36 –103◦ 55 E, 32◦ 20 –34◦ 05 N), is the largest highland marsh in the world. It covers 7.08 × 105 hm2 (Fei, 2006), spanning Sichuan and Gansu Provinces of China, with an altitude between 3400 m and 3900 m above sea level (Fig. 1). Zoige Marsh National Natural Reserve was established by the Chinese government in 1994 to protect the marsh and the surrounding areas. Zoige Marsh has many special functions of ecosystem service as suggested for other wetlands (Mitsch and Gosselink, 1993). First, it is one of the most important sources of the headwater of Yellow River and Maqu Marsh in Gansu Province. Measurements indicate that Zoige Marsh accounts for about 40% and 30% of the total flow of the headstream in dry seasons

© 2008 Elsevier B.V. All rights reserved.

and rainy seasons, respectively (SAFS, 2006). Second, Zoige Marsh is a key region for biodiversity protection in China, harboring a number of endemic and endangered species, which is of great economic and ecological significance (Liu and Bai, 2006). Third, Zoige Marsh has a vast area of grasslands, providing high quality and huge quantity of fodder to livestock and thus making it one of the five largest rangelands in China (Zhou and Li, 2003). Additionally, Zoige Marsh has the largest peat deposition in China, with an estimate of about 1900 million tons in dry weight, which could be invaluable to multiple uses (He and Zhao, 1999). Therefore, Zoige Marsh is not only related to the ecological security of the Yellow River drainage basin, but also crucial to the sustainable development of the local area (Zhang et al., 2005). Because of the unique service functions, Zoige Marsh has attracted a lot of attention from ecologists and geologists

∗ Corresponding author at: Department of Biology, Nanjing University, 22 Hankou Road, Nanjing 210093, China. Tel.: +86 25 83686670; fax: +86 25 83592684. E-mail address: [email protected] (S. Sun). 0925-8574/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.ecoleng.2008.02.016

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e c o l o g i c a l e n g i n e e r i n g 3 5 ( 2 0 0 9 ) 553–562

Fig. 1 – Sketch map showing marsh distribution in Zoige Marsh.

(Zhao, 1999). Recently, there has been a growing number of studies focusing on the ecosystem degradation of Zoige Marsh (e.g., Wang et al., 2006; Gao, 2006; Yang, 1999). It is well recognized that the trend of land desertification is becoming apparent and the local area is facing an unprecedented ecological crisis. It is urgently needed to find out the causes of the marsh degradation and to rehabilitate the damaged ecosystem. Many studies have been conducted in the marsh area, mostly dealing with physical geography, biogeography, palaeogeography and sediment deposition (e.g., Yan et al., 1999; Sun et al., 2001). Moreover, numerous studies have dealt substantially with global-class wetlands, for example, the US Everglades National Park and the Great Lakes (e.g. Mitsch and Gosselink, 1993). However, there is no systematic international report on the ecology of the marsh so far. In this paper, we first provide an overview of the marsh biodiversity, and then show the current status of the marsh degradation and point out the causes of degradation. Finally, we propose a future perspective for the ecosystem restoration.

2.

Biodiversity in Zoige Marsh

2.1.

Basic physical geography

The climate of Zoige Marsh is of the mild, cold temperate continental monsoon type. The annual mean temperature is

about 0.7–1.1 ◦ C, with the highest monthly mean being 10.8 ◦ C in July and the lowest being −10.6 ◦ C in January. The annual mean precipitation is 656.8 mm, 86% of which occurs between April and October. The non-frozen period ranges between 16 and 25 days, and the accumulative temperature of higher than 10 ◦ C is only about 630 ◦ C. The total sunshine time reaches 2400 h per year, and the total irradiance is about 580 kJ cm−2 . The mean relative humidity maintains at about 65%. The growing season of the marsh is very short, usually 5 months, from May to September. The main geomorphologic types of Zoige Marsh include hills, river valleys, and terraces. The majority of the rivers in the marsh area belong to the drainage basin of Yellow River, and they are mostly characterized by flat valleys, serpentine channels, and low drainage capacity. In this paper, unless specified otherwise, Zoige Marsh denotes an integration of several different types of ecosystems, including freshwater marshes, meadows (grasslands), and sandy areas (the desertification area). That is to say, Zoige Marsh is composed of a core area of marsh ecosystems and its surrounding areas. The main soil types of Zoige Marsh include highland meadow soil, highland marsh soil, and highland peat soil. Water covers the soil all year round or seasonally, and therefore peat decomposition rates are low. The depth of peat soil is quite considerable, with a mean depth being 3 m and the utmost reaching 10 m. Organic matter occupies more than half

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of soil dry weight. pH value of the soil is generally between 7.0 and 8.0. The gley is quite deep and the mother matter of the soils is mostly flour sand or sub-clay. Such climatic, geomorphologic, and edaphic features are believed to be fit for the marsh development (Yang et al., 2002).

2.2.

Vegetation types and plant species diversity

In the Zoige Marsh Nature Reserve, owing to habitat differences along elevational gradients, vegetation changes gradually, showing a vertical zonation pattern. Three vegetation types, alpine boskage, alpine meadow, and marsh, can be classified from bottom of valleys to mountaintops in the reserve (SAFS, 2006). Previous surveys indicated that the marsh vegetation in the marsh area was simple and 13 community associations could be identified (Table 1; Tian, 2005). There are 71 vascular plant species belonging to 25 families in the marsh. The families containing the largest number of species are Cyperaceae (13 species), and then Ranunculaceae (7), and Asteraceae (5), Umbelliferae (4) and Gramineae (4) come next, followed by Chenopodiaceae (3), Juncaceae (3) and Scrophulariaceae (3), and Primulaceae (2) (Fei, 2006). A recent survey showed that there were 118 vascular plant species on the alpine meadow, belonging to 27 families and 83 genera (Wang et al., 2002). Among them, Asteraceae has 2 genera and 19 species; Gramineae has 2 genera and 14 species; Ranunculaceae has 7 genera and 9 species; and the other 16 families have only 1 species. At the genus level, Gentiana has 7 species; Polygonum has 5 species; Potentilla and Saussurea both have 4 species; Pedicularis, Kobresia and Artemisia all have 3 species (Wang et al., 2002). According to the “list of national protected wild plants”, three species belonging to three different families and genera, Pomatosace filicula, Anisodus tanguticus, and Meconopsis punicea, are classified as the second-class protected species (SAFS, 2006).

2.3.

2.4.

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Endangered species and economic species

Due to the unique climatic, geomorphologic, and edaphic features, many species are endemic to Zoige Marsh, such as Caltha scaposa, Kobresia tibetica Maxim, Carex muliensis, and Blysmus sinocompressus (He and Zhao, 1999). Many species become rare and endangered. For instance, Sinocarum coloratum, Scrophularia chinensis, Scrophularia chinensis, Rheum palmatum have been listed as endangered species by the Environmental Protection Agency of China. The species that have been categorized as vulnerable species in the marsh include Potamogeton filiformis var. applanatus, P. heterophyllus, P. gramineus, P. pectinatus, P. crisps, Hippuris vulgaris, Utricularla intermedia, U. minor, Menyanthes trifoliata, and Equisetum fluviatile. Furthermore, Isoetes hypsophila, Eleochalis valleculosa, Polygonum sieboldi, Callitriche hermaphroditica have been listed as rare species. There are also many endemic and highly endangered animal species in Zoige Marsh. Eight species including Grus nigricollis, Ciconia ciconia, C. nigra, Haliaetus leucoryphus have been listed as national first-class protected animals, and 27 species were listed as national second-class protected animals, including Lutra lutra, Procapra picticaudata (Table 2). The national first-class protected bird and the world-class endangered species Grus nigricollis is a crane endemic to Qinghai-Tibet Plateau. Besides those phylogenetically important endangered species, there are many economically important animals and plants. According to a preliminary report, the number of plants species that can be used as forage is 1208 in Zoige Marsh Natural Reserve, belonging to 573 genera of 131 families (SAFS, 2006). There are also abundant medicinal plants in the marsh, and the representative species include Cordyceps sinensis, fritillary (Fritillaria cirrhosa), Notopterygium incisum, Angelica pubesce, astragalus root (Astragalus membranaceous), Chinese goldthread (Coptis chinensis), largeleaf gentian root (Gentiana macrophylla) and rhubarb (Rheum rhabarbarum).

Fauna and animal species diversity

Zoige Marsh is very rich in animal resources. There are 38 mammal species belonging to 15 families of 5 orders. Among them, there are two insectivore species belonging to Soricidae and 16 carnivore species of 3 families, and 5 Artiodactyla species of 4 families, and 11 rodent species of 5 families, 4 lagomorpha species of 2 families. There are 137 bird species belonging to 28 families of 13 orders. Among them, 58 species belongs to Passeriformes and 79 species from other taxa. There are 3 reptile species belonging to 3 families of 2 orders, Phrynocephalus hongyuanensts, Scincella tsinlingensis, and Gloydius strauchii. There are 3 amphibian species belonging to 2 families of 1 order, Bufo minshanicus, Rana kukunoris, and Nanorana pleskei. There are 15 fish species belonging to 2 families of 1 order (Nemachilinae and Schizothoracinae). There are 61 arthropod species (Siphonaptera not included) belonging to 31 families of 8 orders, and they mostly belong to Lepidoptera, Coleoptera, and Diptera. Other invertebrates include Radix ouricuaria, R. swenhoi, Haemolaelaps glasgowi, H. kitanoi, H. ivanoi, H. tangkensis, and Gammarus sp. (He and Zhao, 1999).

3. Current status of Zoige Marsh degradation Zoige Marsh kept a primary landscape until the 1960s, when population increase was rapid and resource exploitation was encouraged. Drought stress and shrinkage of Zoige Marsh became apparent in the 1970s, after which the marsh degradation was accelerated. Today, it is believed that the degradation is naturally irreversible (Wang et al., 2002). This section provides a big picture of the current status of Zoige Marsh degradation.

3.1.

Shrinking of marshes

Before the 1950s, the water table of the marsh ranged between 20 cm and 40 cm on average and even reached 1 m in some places (An, 2002). However, nowadays, the water table is mostly below 15 cm in summer, whereas some sites are just wet and sometimes even in drought. Due to the decline in water table, the total wetland area of Zoige Marsh has decreased by more than 30% in the past 30 years, and most

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Table 1 – The main types of marsh plant communities in Zoige Marsh (rebuilt based on Tian (2005) and Fei (2006)) No.

Community type (association)

Habitat

1

Potamogeton-Algae

Perennial, deep soak (50–120 cm)

2

Carex lasiocarpa-Menyanthes trifolia

Perennial, shallow soak (20–40 cm)

3

Carex lasiocarpa-Utricularia intermedia

Perennial, shallow soak (10–30 cm); 20–30 cm thick soil

4

Carex muliensis-Eriophorum latifolium

5

Carex meyeriana

Perennial, shallow soak (10–20 cm), 4–5 m thick turf bed Crumby hillock, perennial or seasonal soak (5–20 cm), 5–9 m thick turf bed

6

Carex muliensis-Cremanthodium stenactlninm

7

Carex muliensis-Callha scaposa

8

Blysmus sinocom-Kobresia capillifolia

Reticulate or trench meadow hillocks, temporary soak (3–5 cm), 2–3 m thick turf bed

9

Kobresia tibetica-Kobresia capillifolia

Meadow hillocks, humid soil

10

Kobresia tibetica-Trollius ranunculoides

No meadow hillock, humid soil

11

Potentilla anserine-Kobresia capillifolia

Flat surface, humid soil

12

Elymus nutans-ruderal

Flat or relief surface, moderate moisture

13

Poa-Kobresia-ruderal

Subalpine slope, moderate moisture

Latticed or reticulate meadow hillocks, perennial or seasonal soak (5–10 cm), 2.5–5 m thick turf bed Reticulate or trench meadow hillocks, seasonal or temporary soak (3–10 cm), 0.5–4.5 m thick turf bed

of the lost wetlands, especially lake and river wetlands, have transformed into sandy lands (Table 3). A recent survey showed that there were more than 200 sandy sites originating from wetlands, and that the total area of sandy sites and potential desertification sites were 4091 hm2 and 12,023 hm2 ,

Dominant species Hippuris vulgaris, Myriophyllum verticillatum, Potamogeton pusillus, P. maackianus, P. pectinatus, Utricularia intermedia, U. gibba, Phragmites communis Carex lasiocarpa, Cicuta virosa, Glyceria aquatica, Menyanthes trifolia Carex lasiocarpa, Equisetum helaochoris, Polygonum amphibium, Triglochin maritimum, Utricularia intermedia Carex muliensis, Eriophorum latifolium Anemone trullifolia, Blysmus sinocom, Carex meyeriana, Leptodictyum riparium, Sanguisorba Carex muliensis, Cremanthodium stenactlninm, Pedicularis longiflora Callha scaposa, Carex muliensis, C. ennrvis, Chamaesium thalistrif, Deschampsia caespitosa, Festuce ovina, Juncus concinnus, K. capillifolia, K. setchwanensis, Kobresia tibetica, Poa pratensis, Trollius ranunculoides Aster alpinus, Blysmus sinocom, Callha scaposa, Chamaesium thalistrif, Parnassia trinervis, Potentilla anserine, Ranumculus longicaulis Blysmus sinocom, Carex ennrvis, C. atrofusca, Dschampsia caespitosa, Kobresia tibetica, K. capillifolia, K. humilis, K. kansuensis, K. setchwanensis, K. parva, Polygonum viviparum, Potentilla enserina Carex muliensis, Gentianopsis paludosa, Kobresia tibetica, Morina alba, Trollius ranunculoides Callha scaposa, Carex muliensis, Chamaesium thalistrif, Deschampsia caespitosa, Kobresia capillifolia, K. tibetica, Koeleria cristata, Polygonum sphaercstachyum, P. viviparum, Potentilla anserine Agrostis schneideri, Anemone rivularis, Anopholis lacteal, Astragalus luteolus, Deschampsia caespitosa, Deyeuxia sylvatlca, Dianthus chinensis, Elymus nutans, Festuca chinensis, Gentiana leucomelaena, G. straniinea, Geranium pylzowianum, Geuldenstaedtia diversifolia, Lathyruss pratensis, Leontopodium nanum, Oxytropis ochrocephala, Poa pachyantha, Potentilla anserine, P. fifurca, Ranunculus brotherusii, Roegneria nutans, Saussurea nigrescens, Taraxncum sp., Trisetum clarkei Agrostis limprichtii, Anemone geum, Deschampsia caespitosa, Elymus nutans, Euphorbia pekinensis, Festuca chinensis, Hedysarum sikkimense, Kobresia pygmaea, K. setchwanensis, Roegneria nutans, Stipa aliena, Trisetum clarkei, Veronica ciliate

respectively (Yang, 1999). As a result of the increase in sandy area, only in Ruoergai County of Sichuan Province, pasture lands decreased by 419 hm2 on average per year and the edge of sandy area moved forward 16.4 m per year in past 30 years (Yang, 1999).

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Table 2 – Species list of the first and second-class China national protection animals in Zoige Marsh (rebuilt from SAFS (2006)) Species Aves 1 Ciconiiformes 1.1 Ciconiidae 1.1.1 Ciconia nigra 2 Anseriformes 2.1 Anatidae 2.1.1 Cygnus cygnus 2.1.2 C. olor

Biogeographic realm

Paleartic

Protection class

IUCN-2003

I I

Paleartic Paleartic

II II

Paleartic Paleartic Paleartic Paleartic Paleartic Paleartic Paleartic Paleartic Paleartic Cosmopolitan Cosmopolitan Cosmopolitan Paleartic

II II II II II I II I I II II I II

Paleartic Paleartic Paleartic Paleartic Cosmopolitan

II II II II II

4 Galliformes 4.1 Tetraonidae 4.1.1 Bonasa seweraowi

Oriental

II

LR/nt

5 Gruiformes 5.1 Gruidae 5.1.1 Grus grus 5.1.2 G. nigricollis

Paleartic Paleartic

II I

VU

6 Strigiformes 6.1 Strigidae 6.1.1 Glaucidium cuculoides 6.1.2 Glaucidium brodiei 6.1.3 Athene noctua

Oriental Oriental Paleartic

II II II

Oriental

II

VU

Paleartic

II

VU

Paleartic Paleartic Paleartic

II II II

VU NT NT

Paleartic

I

LR/nt

Paleartic Oriental

II II

VU

3 Falconiformes 3.1 Accipitridae 3.1.1 Milvus migrans 3.1.2 M. korschun 3.1.3 Buteo lagopus 3.1.4 B. hemilasius 3.1.5 B. buteo 3.1.6 Aquila chrysaetos 3.1.7 A. rapax 3.1.8 Haliaeetus leucoryphus 3.1.9 H. albicilla 3.1.10 Aegypius monachus 3.1.11 Gyps himalayensis 3.1.12 Gypaetus barbatus 3.1.13 Circus cyaneus 3.2 Falconidae 3.2.1 Falco cherrug 3.2.2 F. peregrinus 3.2.3 F. subbuteo 3.2.4 F. columbarius 3.2.5 F. tinnunculus

Beast 1 Carnivora 1.1 Canidae 1.1.1 Cuon alpinus 1.2 Mustelidae 1.2.1 Lutra lutra 1.3 Felidae 1.3.1 Felis bieti 1.3.2 F. manul 1.3.3 F. lynx 2 Artiodactyla 2.1 Moschidae 2.1.1 Moschus sifanicus 2.2 Bovidae 2.2.1 Procapra picticaudata 2.2.2 Capricornis milneedwardsi

VU LR/nt LR/nt

Note: IUCN: International Union for the Conservation of Nature and Natural Resources; UV: vulnerable; LR/nt: low risk/near threatened.

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Table 3 – Temporal change in land use of Zoige Marsh (rebuilt from Gao (2006)) Area (hm2 )

Land use type

Marsh Lake wetland River wetland Sandy land

3.2.

Area change (hm2 )

October 1975

November 1986

October 2001

433902.47 2507.63 18789.12 3174.57

383652.49 2175.53 11621.96 8079.79

346270.52 1643.05 9764.81 14342.97

−87631.95 −864.58 −9024.31 11168.4

Recessive succession of Zoige Marsh

Vegetation of Zoige Marsh presents a tendency of recessive succession. With the decline of water table, in most wetlands, hydrophytes disappeared gradually, and mesophytes invaded and became dominants. A typical recessive succession mode is marsh → marsh meadow → meadow under the circumstance of water partly drained and peat partly mined (Liu and Bai, 2006). However, if water is drained drastically and peat is totally mined, the mode may be marsh → meadow. Under the condition that vegetation is artificially cleared, the mode may be marsh → marsh meadow → meadow → xeric land → desert. During the recessive succession, community structure and species composition changed dramatically. For example, in Riganqiao marsh, its typical vegetation was Carex muliensis ca. 30 years ago, but at present, it is dominated by C. meyeriana that competitively displaced C. muliensis (Fei, 2006). Overall, in Zoige Marsh, the abundance of mesophytes is growing, while the distribution area of hydrophytes is declining rapidly (Zhao, 1995). Moreover, the distribution area and abundance of forbs and poisonous plant species have increased drastically. In the 1960s, forbs species occupied less than 20% of the marsh. Today, however, the proportion has reached 70%, whereas that of high-quality grasses has decreased from 60% to 10% (Yang, 1999). More than 35 poisonous species, belonging to 12 families, have been recorded in the marsh. These species include Stellera chamaejasme, Anemone obtusiloba, Del-

Mean annual change (hm2 )

Percentage of annual change (%)

−3370.46 −33.25 −347.09 429.55

−3.85 −3.85 −3.85 3.85

Percentage of total change (%)

−20.20 −34.48 −48.03 351.81

phinium tatsienense, Aconitum gymnandrum, and Thalictrum sp., which are mostly deleterious to livestock. In addition, the decline of species diversity is obvious in Zoige Marsh during the recessive succession. Many precious wild animals have disappeared or decreased drastically in abundance and distribution area. For example, there were 710 Grus nigricollis before the 1980s, but this number was about 300 during the 1980s and decreased to 15 in a census of 1997 in the Waqie area of the marsh (Yang, 1999).

3.3.

Soil degradation

There are three major soil types in Zoige Marsh. Because peat and mire are covered with water seasonally or all year round, and also because the vegetation is dominated by hydrophytes and hydro-mesophytes, the soil is inundated over a long period of time and the decomposition of plant litter is very slow. Therefore, peat soil is actually a huge amount of organic matter reserve. Meadow soil is a transitional type. The water table and organic matter content are lower in meadow soil than that of peat and mire. The soil surface is just in a humid state and the vegetation is dominated by mesophytes and hydro-mesophytes. Aeolian sandy soil is of a degenerated type. The surface is always in the drought state and the vegetation is mainly dominated by xero-mesophytes. Because plant litter is not rich in the soil and the decomposition rate is relatively high, there is little organic matter content in the soil. Generally, the increase of water table in the soils

Fig. 2 – Schematic graph showing a sere in which vegetation, soil types, and water levels co-vary in Zoige Marsh (rebuilt from Fei (2006)).

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facilitates the accumulation of organic matter and vice versa (Fig. 2). Due to the decline of water table and the changes in vegetation structure and species composition, soil degradation has also been observed (Tian, 2005). A typical mode of soil degradation is peat soil → mire soil → meadow soil → aeolian sandy soil (Fig. 2). During soil degradation, besides the gradual decrease in organic matter and water table, some mineral nutrient elements, such as N, P, and K, change obviously. It has been found that the total content of humid acid, N, and P decreased while total content of K and the soil alkalinity increased (Zhao and He, 2000; Tian et al., 2004), suggesting a decreasing soil fertility. Furthermore, the variation magnitude of soil temperature has much increased apparently due to the decline in vegetation coverage and density. In addition, water quality of Zoige Marsh has deteriorated. For example, COD, pH, total alkalinity, and the degree of mineralization increase (Zhao and He, 2000), and the content of NH4 + and NO3 − increase dramatically in many rivers and lakes of the marsh.

4.

Causes of Zoige Marsh degradation

4.1.

Global warming and neotectonic uplifting

Because Zoige Marsh is located on Qinghai-Tibet Plateau, it is assumed to be more sensitive to global warming. The temperature of Zoige Marsh has increased gradually in the past years. According to data from the weather station of Hongyuan County, mean annual temperature of the latest 20a is higher than 1 ◦ C, whereas before 1978, it was lower than 1 ◦ C (Wang et al., 2006), indicating an increased potential evapotranspiration. The data collected by Zoige County climate station show that mean annual temperature increased by 0.0173 ◦ C in the latest 50a (Gao, 2006). However, mean annual precipitation has decreased a little in the marsh (Zhang et al., 2005; Wang et al., 2006). Therefore, relative humidity has decreased and the tendency to dryness has emerged. A 30,000-year pollen and carbon stable-isotope record of two lacustrine sections from the Zoige Plateau also apparently indicated a long-term trend towards aridity in the study area (Yan et al., 1999). The consequences of these climatic changes include the decline in water table, frozen soil mitigation, and plant drought-stress, thereby resulting in the vegetation’s recessive succession and in soil degradation. Neotectonic uplifting of earth crust may be also possibly responsible for the marsh degradation although it is very slow (Sun et al., 2001). Zoige Marsh originated from the uplifting of Qinghai-Tibet Plateau. However, continuous uplifting would make Zoige Marsh too high for the southwestern monsoon to bring rainfall and to nourish the marsh (Gao, 2006). Meanwhile, uplifting of the lithosphere would deepen the rivers of the marsh and make the groundwater table descend. This likely accelerates soil drying. Moreover, it is suggested that the crust movement has changed the river flow path and directions, and have made old riverbeds the sources of sands (Wang et al., 2002; Tian, 2005). The sand sources, along with the windy weather, produce sandstorms almost every year in the marsh,

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and this will certainly be a strong impetus for desertification, water loss and soil erosion.

4.2.

Artificial drainage and peat exploitation

Artificial drainage is often regarded as the most important cause for Zoige Marsh degradation. It is usually conducted to enlarge pastures and to tap peat resources. In the 1970s, the total length of ditches was 320 km, with 30% of the total area negatively affected and 57% marshes transformed into meadow. In the 1990s, an additional 51 km-long ditch was created so that 83% of the total area showed degradation syndrome (Liu and Bai, 2006). Drainage has drastically decreased groundwater depth, and it has also destroyed the integrality of Zoige Marsh by transforming the marshes into meadows or sands, thereby leading to landscape fragmentation. Because there are not enough hydropower resources and mineral resources such as coal and oil, local people use peat as their major energy source. A previous survey indicated that there were 138 large peat mines and 82 medium-scale mines scattering over Zoige Marsh (Liu and Bai, 2006). Moreover, local people always mine peat privately to supply energy resource for factories, schools, and apartments. In addition, some factories collect peat from Zoige Marsh in recent years, to produce compound chemical fertilizer. This kind of peat exploitation not only physically destroys local vegetation and soils, but also indirectly increases the number and length of ditches, changing hydrology of the marsh (Fig. 3).

4.3.

Livestock overgrazing and rodent disaster

Stockbreeding has developed at a high speed in the Zoige Marsh area since the 1970s, resulting in a serious conflict between livestock populations and pasture lands (Fig. 3). Surveys conducted by Zoige County show that current livestock population and average livestock population per hm2 are 5 and 4 times higher than those of 40 years ago, respectively. A model calculation suggested that the theoretical livestock carrying capacity of Ruoergai County is 1865 thousand units (a sheep a unit), but the actual population is 2855 thousand units in 2000 (Gao, 2006). Overgrazed and trampled by these livestock, the pasture lands are hard to regenerate naturally and recessive succession is unavoidable (Zhou and Li, 2003). Rampant increase in wild rats is not only an aftereffect of the marsh degradation but also an important cause as well (Fig. 3). Possibly due to the loss of predators, the population increase of wild rats is apparent in recent years (Jiang, 2004). The recorded density of rats on the pasture lands is quite striking. For example, the density of Myaspalax sp. is 25.24/hm2 , the density of Marmota himalayana is 45/hm2 , and astonishingly, the density of Ochotona sp. is as high as 450/hm2 in Hongyuan County. The wild rats deteriorate pasture lands barbarically. According to a survey conducted in Hongyuan County, the total pasturelands damaged by the rodents is 16,299 hm2 , accounting for 2.18% of usable lands (Liu and Bai, 2006). Moreover, the rodents inhibit the regeneration of pasture lands and accelerate the ecosystem degradation. In general, the deterioration of Zoige Marsh is triggered by both natural evolution and human activities, but anthropogenic disturbance is certainly more important. During the

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Fig. 3 – Schematic graph showing the causes of Zoige Marsh degradation and possible restoration strategies. For more detail, see text.

latest 1000 years, the temperature has been continuously increasing (Bai and Chen, 1996). However, the degradation of Zoige Marsh became obvious only after the 1950s, which coincides with the timing of people beginning to disturb it. The worst condition of Zoige Marsh has occurred in the most recent years, when human interference has historically been the greatest.

5.

Future prospect for ecological restoration

How to restore a wetland ecosystem is a complicated problem. The most important is apparently to restore the wetland hydrology. However, many other important factors should also be taken into account (Mitsch and Wilson, 1996; Zedler, 2000; Patterson and Cooper, 2007). It is well recognized that landscape setting, habitat condition, soil properties, topography, nutrient supplies, disturbance regimes, invasive species, seed banks and declining biodiversity can constrain the restoration process (Zedler, 2000). Moreover, social and economic background is critical to wetland restoration. A review of the data on patterns of wetland conservation in Austria, Ando and Getzner (2006) found that conservation decisions are guided at least in part by variation in economic cost, and if there was a marked bias against conserving lands that happen to be privately owned, the bias against protecting private land is likely to be cost-ineffective. To restore the degraded Zoige Marsh, we think that the first priority is to recover hydrology, and then vegetation, and finally fauna that have recently been considered indicators of successful ecological restoration (Kentula, 2000). In addition, since a major goal of protecting the crane, Grus nigricollis, could be carried out only when diverse habitats of the crane were meet, we also think that the marsh restoration should be conducted at the landscape level, as strongly suggested by several recent studies (Simenstad et al., 2006; Niggebrugge et al., 2007; Simmons et al., 2007). We propose that ecological engineering measures should be conducted first to restore

the marsh hydrology and vegetation, and we also propose to control livestock population size to facilitate progressive successions of the ecosystem. In the long run, we believe that setting up an ecological monitoring system is a must for the marsh protection as a whole.

5.1.

Ecological engineering

Construction work is considered an important measure for the restoration of wetland ecosystems (Pedersen et al., 2007). It is imperative to take ecological engineering measures to impede Zoige Marsh degradation, because some parts of the marsh have been seriously damaged and are naturally irrecoverable. For example, the sandy and desertification areas serve as a source of sand for sandstorms, and it is almost impossible to self-recover. One effective rehabilitation method is to plant grass or transplant turf in the rainy seasons to stabilize sand dunes and then facilitate progressive succession. Moreover, the nutrient retention function of soil is important for the maintenance and restoration of ecosystems (Schrautzer et al., 1996). Peat has been suggested to cover the sandy areas due to its fertility and heat-holding ability, which may favor seed germination and seedling establishment of plants (He and Zhao, 1999). Peat covering could be a good measure because it can combine resource exploitation with ecological restoration. A previous study even suggested planting a wind-proof forest (He and Zhao, 1999), but the feasibility of this suggestion is not clear yet. Additionally, ecological engineering must be implemented to eliminate any factors that systematically degrade the marsh ecosystem, for instance, the ditches. Refilling the ditches could elevate the groundwater level and facilitate the progressive succession from sandy vegetation to meadow and then marsh vegetation (Fig. 3). Presently, in a program supported by the Global Environment Facility, more than 200 km ditches within Zoige Marsh have been refilled, allowing 50,000 hm2 marshes and about 1000 hm2 lake wetlands to be recovered (Wang et al., 2006).

e c o l o g i c a l e n g i n e e r i n g 3 5 ( 2 0 0 9 ) 553–562

Under the policy of Western Exploitation called for by the Chinese central government, the local government has raised some funds to restore Zoige Marsh, and most of the funds will be directed to ecological engineering projects. More engineering measures will be carried out in the future.

5.2.

Livestock population control

One way to eliminate overgrazing is to decrease livestock population to the level below the carrying capacity of the grassland (Fig. 3). However, this will certainly decrease the income of local people, and therefore aid from the local and central government is needed. Another way to improve environmental quality and to mitigate livestock impact is to switch from the traditional mode of livestock culturing to a sustainable one (Fig. 3). For example, summer and winter pasturelands can be arranged alternatively to feed livestock, resulting in a rotation for grassland use, thus lessening the impact of overgrazing on grasslands. Proper livestock grazing could improve the efficiency of the nutrient cycle and energy flow of the grassland ecosystem, and increase plant species diversity (Wang et al., 2006). Furthermore, other human activities such as peat exploitation and tourist development need to be controlled and well managed.

5.3.

Ecological monitoring and biodiversity protection

Before any restoration measures are taken, it is necessary to understand in detail the current situations and to determine the changing tendency of Zoige Marsh, and to determine where biodiversity protection and ecological restoration are the most urgent; therefore, it is of importance to establish a comprehensive monitoring system and a geographic information system. After the establishment of Zoige Marsh Nature Reserve in 1994, the marsh environmental quality has improved greatly (Wang et al., 2006). Up to now, 7 additional reserve areas have been established surrounding Zoige Marsh and the total protection area reaches 1.60 × 107 hm2 (Zhang et al., 2005). However, since 1960s, the biodiversity and geographic information has not been systematically gathered and therefore a decision-making expert system for ecological risk assessments is still difficult to implement at present.

Acknowledgements Thanks are due to the staff of the Zoige Marsh National Protection Reserve for permitting this study to be conducted. We also thank Luo Peng and Yan Li for providing materials on Zoige Marsh. The research was funded by the Chinese Ministry of Science and Technology (2006BAD09A04-03-01) and the Chinese Academy of Sciences (KZCX2-XB2-02).

references

An, S.Q., 2002. Ecological Engineering in Wetlands. Chemical and Industrial Press, Beijing (in Chinese).

561

Ando, A.W., Getzner, M., 2006. The roles of ownership, ecology, and economics in public wetland-conservation decisions. Ecol. Econ. 58, 287–303. Bai, M.T., Chen, J.M., 1996. Official History of Ruoergai County. Ethnologic Press, Beijing (in Chinese). Fei, S.M., 2006. A background study of the wetland ecosystem research station in the Ruoergai Plateau. J. Sichuan Forest. Sci. Technol. 27, 21–29 (in Chinese). Gao, J., 2006. Degradation factor analysis and solutions of Ruoergai Wetland in Sichuan. Sichuan Environ. 25, 48–52 (in Chinese). He, C.Q., Zhao, K.Y., 1999. The conservation of wetlands biodiversities and their sustainable utilization in Roige Plateau. J. Nat. Resour. 14, 238–244 (in Chinese). Jiang, D.K., 2004. Studies on the construction and protection of Hongyuan Grassland. Sichuan Grassland 104, 42–43 (in Chinese). Kentula, M.E., 2000. Perspectives on setting success criteria for wetland restoration. Ecol. Eng. 15, 199–209. Liu, H.Y., Bai, Y.F., 2006. Changing process and mechanism of wetland resources in Ruoergai Plateau, China. J. Nat. Resour. 21, 810–818 (in Chinese). Mitsch, W.J., Gosselink, J.G., 1993. Wetlands, 2nd edn. Wiley, New York. Mitsch, W.J., Wilson, R.F., 1996. Improving the success of wetland creation and restoration with know-how, time and self-design. Ecol. Appl. 6, 77–83. Niggebrugge, K., Durance, I., Watson, A.M., Leuven, R.S.E.W., Ormerod, S.J., 2007. Applying landscape ecology to conservation biology: spatially explicit analysis reveals dispersal limits on threatened wetland gastropods. Biol. Conserv. 139, 286–296. Patterson, L., Cooper, D.J., 2007. The use of hydrologic and ecological indicators for the restoration of drainage ditches and water diversions in a mountain fen, cascade range, California. Wetlands 27, 290–304. Pedersen, M.L., Andersen, J.M., Nielsen, K., Linnemann, M., 2007. Restoration of Skjern River and its valley: project description and general ecological changes in the project area. Ecol. Eng. 30, 131–144. SAFS (Sichuan Academy of Forest Science), 2006. Scientific Investigation Report on Zoige Marsh. Sichuan Science and Technology Press, Chengdu (in Chinese). ¨ Schrautzer, L., Asshoff, M., Muller, F., 1996. Restoration strategies for wet grasslands in northern Germany. Ecol. Eng. 7, 255–278. Simenstad, C., Reed, D., Ford, M., 2006. When is restoration not? Incorporating landscape-scale processes to restore self-sustaining ecosystems in coastal wetland restoration. Ecol. Eng. 26, 27–39. Simmons, M.T., Venhaus, H.C., Windhager, S., 2007. Exploiting the attributes of regional ecosystems for landscape design: the role of ecological restoration in ecological engineering. Ecol. Eng. 30, 201–205. Sun, G.Y., Luo, X.Z., Turner, R.E., 2001. A study on peat deposition chronology of holocene of Zoige Plateau in the northeast Qinghai-Tibetan Plateau. Acta Sedimentologica Sinica 19, 177–206 (in Chinese). Tian, Y.B., 2005. Restoration succession of wetland soils and their changes of water and nutrient in Ruoergai Plateau. Chin. J. Ecol. 2, 1–5 (in Chinese). Tian, Y.B., Xiong, M.B., Song, G.Y., 2004. Study on change of soil organic matter in the process of wetland ecological restoration in Ruoergai Plateau. Wetland Sci. 2, 88–93 (in Chinese). Wang, Q., Bao, W.K., Yan, Z.L., Timo, K., Alfred, C., Angela, M., 2002. Basic types and characters of the western Zoige Meadows and their changes in recent decades. J. Appl. Environ. Biol. 8, 133–141 (in Chinese).

562

e c o l o g i c a l e n g i n e e r i n g 3 5 ( 2 0 0 9 ) 553–562

Wang, Y.C., Gan, Y.M., Zhang, J.H., Yan, J.J., Liu, R.F., 2006. Degradation factor analysis and protect solutions of Zoige plateau wetland in Sichuan. Sichuan Anim. Vet. Sci. 33, 6–9 (in Chinese). Yan, G., Wang, F.B., Shi, G.R., Li, S.F., 1999. Palynological and stable isotopic study of palaeoenvironmental changes on the northeastern Tibetan plateau in the last 30,000 years. Palaeogeogr. Palaeoclimatol. Palaeoecol. 153, 147–159. Yang, X., Zhai, X.L., Yu, G.Y., 2002. Current situation of Zoige plateau wetlands biodiversity and their conservation countermeasures. J. Changchun Univ. 12, 16–20 (in Chinese). Yang, Y.X., 1999. Ecological environment deterioration, mire degradation and their formation mechanism in the Zoige Plateau. J. Mt. Sci. 17, 318–323 (in Chinese). Zedler, J.B., 2000. Progress in wetland restoration ecology. TREE 15, 402–407.

Zhang, X.Y., Lu, X.G., Gu, H.J., 2005. To analyze threats, to describe present conservation situation and to provide management advices of the Ruoergai marshes. Wetland Sci. 3, 292–297 (in Chinese). Zhao, K.Y., 1999. Marsh Records of China. Science Press, Beijing (in Chinese). Zhao, K.Y., He, C.Q., 2000. Influence of human activities on the mire in Zoige Plateau and countermeasure. Scientia Geographica Sinica 20, 444–449 (in Chinese). Zhao, R.C., 1995. Desertification of Roergai grassland and its preventive countermeasure. Sichuan Environ. 14, 15–20 (in Chinese). Zhou, G.J., Li, H., 2003. Desertification and preventive countermeasure of Zoige Grassland. Sichuan Grassland 1, 35–36 (in Chinese).