15 Grassland Ecosystem

Renuka Gupta

epgp books

 

Module27: Grassland Ecosystem

LEARNING OBJECTIVES

  • Definition and characteristics of grassland ecosystems
  • The distribution of world’s grassland ecosystem
  • The Abiotic environment
  • Biodiversity and Community Composition Ecosystem functions
  • Human impacts on Grasslands Grassland Management

27.1. Introduction

 

Grassland ecosystems are ecologically and economically important, and are of widespread occurrence. The productivity of grasslands provides important services to humanity, including feed for livestock and the regulation of carbon and water cycling. Grasslands (also called rangeland) provide forage and habitat to domestic animals and wildlife. Most grassland coevolved with large grazers, and herbivory has been found to affect ecological processes at levels ranging from individual plants to ecosystem processes and landscape patterns (Blair et al., 2014). The soils of grassland ecosystems store large quantities of carbon and other nutrients and play a major role in global biogeochemical cycles. Temperate grasslands are the third largest global store of carbon in soils and vegetation after wetlands and boreal forests.

 

There is also a long and complex relationship between grasslands and humans. The fertile soils that developed under many types of grasslands have been plowed and the nutrients mined to support agricultural production. It is estimated that about one billion people depend directly on grasslands for their livelihoods worldwide (Suttie et al., 2005). Grasslands rank among the most critically endangered biomes due to widespread conversion for multiple anthropogenic uses, including 70% of global agriculture (Hoekstra et al., 2005), besides increased pressures from people and livestock populations. In India, grasslands generally occur in areas receiving between 250 mm and 900 mm annual precipitation. There is a variety of grassland communities in India with different dominants, in response to variability in environmental conditions including grazing, in each of the grassland type (Singh and Gupta, 1992).

 

27.2. Definition and Characteristics of Grassland Ecosystems

 

The potential distribution of grassland ecosystems to a large extent is determined by climatic variables, principally temperature and precipitation. Three factors including drought, fire, and grazing by large ungulate herbivores, distinguish grasslands from other ecosystem types. They are located in areas in which water availability is below the requirement for the forest at some time during the year but is sufficient to support grasses as the dominant plant type.

 

In a comprehensive review of major grasslands of the world, Coupland (1979, p. 22) defined grasslands as “ecosystems in which the dominant vegetative component is comprised of herbaceous species”. Sometimes the term grassland is used to encompass herbs and shrubs (White et al., 2000), grasses and shrubs can form complex mixes, and dominance may alternate between the two within the span of years or decades.

 

The term grassland can also be used in a broader sense to encompass ecosystems with a significant grass cover interspersed with varying degrees of woody vegetation, and some deserts and shrub grasslands having a significant cover of grasses interspersed with succulent plants and/or shrubs (Blair et al., 2014).

 

According to Dixon et al. (2014), a grassland is defined as “a non-wetland type with at least 10% vegetation cover, dominated or co-dominated by graminoid and forb growth forms, shrubs have < 25% canopy cover and where the trees form a single-layer canopy with either less than 10% cover and 5 m height (temperate) or less than 40% cover and 8 m height (tropical)”.

 

General Characteristics of Grasslands

 

Climatically climax grasslands are those that result from prevailing climatic conditions, whereas the managed grasslands (pastures or lawns) represent intermediate successional stages. In climatically climax grasslands, seasonal water deficits and periodic droughts prevent the establishment of forests in those regions. Some important characteristics of grasslands are as follows:

 

  1. Climate, fire, and grazing are three key factors that are responsible for the origin, maintenance, and structure of the most extensive natural grasslands globally.
  2. Grasslands can vary in the relative abundance of grasses and other plant life forms, such as trees and shrubs.
  3. Grasslands are characterized by high allocation of plant biomass belowground.
  4. There is a large input of plant root litter to the soil resulting in high fertility of grasslands soils, particularly in temperate regions.
  5. Roots of most species in all prairies penetrate (up to 2 m), and root weight in climax perennials is several times more than that of shoots.
  6. Some of the grasses such as big bluestem (Andropogon gerardii), wheat grass (Agropyron smithii) and buffalo grass (Buchloe dactyloides) have underground rhizomes and are thus sod-formers.

 

Some characteristics of temperate steppes and prairies and tropical grasslands are summarized in Table 27.1.

27.3. Distribution of World’s Grasslands

 

Grasslands in the wider sense are among the largest ecosystems in the world; their area is estimated to be 40.5 percent of the terrestrial area excluding Greenland and Antarctica (World Resources Institute, 2001, based on IGBP data; White et al., 2000). The distribution of temperate and tropical grasslands is shown in Fig. 27.1. According to White et al. ( 2000), grasslands are most common in semi-arid zones (28% of the world’s grasslands), followed by humid (23%), cold (20%), and arid zones (19%) ; Sub-Saharan Africa and Asia have the largest total area in grassland; The five countries with the largest grassland area are Australia, the Russian Federation, China, the United States, and Canada.

 

 

27.3.1 Temperate Grasslands

 

Major grasslands in the temperate regions of the world include the steppes of central Eurasia, the velds of the high plateaus of southern Africa, the pampas of Argentina, and the prairies of North America (Fig.27.2). Recent research confirms that, of all the world’s 14 biomes, temperate grasslands are at greatest risk, as these systems are highly altered while being the least protected. Temperate grasslands cover about 8% of the Earth’s terrestrial surface.

 

Fire has helped grasses to outcompete woody plants that invade the grassland. Forbs (composites, legumes, etc.) are constantly present, but are always less important constituents of prairies (Blair et al 2014). The tall-grass prairies of North America or the velds of South Africa, are thought to be as disturbance-dependent communities (Blair et al 2014). Smaller areas occur in southeastern Australia and the drier parts of New Zealand. In these grasslands, periodic fires, droughts, and the activities of grazers are essential to prevent grassland transforming to other ecosystem types.

27.3.2 Tropical Grasslands and Savannas

 

Tropical grasslands are located near the equator, between the Tropic of Cancer and the Tropic of Capricorn. They cover much of Africa as well as large areas of Australia, South America, and India (Fig.27.3). The term Campos refers to grasslands or pastures of South America with vegetation cover comprising mainly grasses and herbs; scattered small shrubs and trees are occasionally found, generally near the banks of streams. The Llanos, located in the Orinoco River Basin, which runs between Colombia and Venezuela in northern South America, are some of the world’s richest tropical grasslands. Termites are especially abundant in the tropical grasslands of the world.

Savannas in Africa have world’s richest fauna of grazers and browsers (e.g., zebra and giraffe); there also occur predators such as lions.

 

Terai-Duar savannas and grasslands  occur in southern Asia including Bangladesh, Bhutan, India, and Nepal (http://wwf.panda.org/about_our_earth/ecoregions/teraiduar_savannas_grasslands.cfm) Flooded grasslands and savannas as large complexes occur in the Everglades, Pantanal, Sahelian flooded savannas, Zambezian flooded savannas, and flooded grasslands of Rann of Kutch, Gujarat, India.

27.3.3 Managed grazing systems

 

Managed grazing lands, designed for the production of animals for consumption, cover about 25% of the global land surface and has larger geographic extent than any other form of land use (Asner et al. 2004).

 

27.3.4 Grasslands of India

 

In India, the area under various kinds of grass cover, including fallow and wastelands, is estimated to be about 18% of the total land area. If the forested area (about 19% of total land) is included, most of which also supports grazing, about 37% of land can be said to be available for grazing. The average annual production of dry grass or hay in India is about 250 million tons.

Most of the grasslands in India are of anthropogenic in origin and seral in nature because of the influence of livestock grazing, fire, deforestation, drought, and abandonment of cultivation (see Singh and Gupta, 1992). Five major grass cover types of India have been recognized (Dabadghao and Shankarnarayan, 1973), which are: Sehima–Dichanthium type; Dichanthium–Cenchrus–Lasiurus type, Phragmites–Saccharum–Imperata type; Themeda–Arundinella type; Temperate-Alpine Grasslands According to Rawat and Adhikari (2015), some important grasslands of India are: alpine moist meadows of Central Himalaya, alpine arid pastures of Trans Himalaya, Terai grasslands of Gangetic and Brahmaputra plains, floating grasslands of Manipur, Banni grasslands of Rann of Kutch, Gujarat, and, shola grasslands of western Ghats. The Shola grasslands are unique as they are restricted in their distribution to the high altitude (>1700 m) in the Western Ghats and interspersed with tropical forests (generally found in the mountain folds and valleys). Shola grasslands are maintained by fire and frost and have an ancient and geographic relict species of ungulate, Niligir Tahr.

 

27.4. The Abiotic Environment : Climate and Soils

 

Grasslands occur under a very broad range of mean annual temperature and rainfall. The climates of grasslands vary from temperate to tropical with annual rainfall ranging from about 250 mm/year in  arid grasslands to more than 1,000 mm/year in mesic grasslands. The precipitation generally occurs as frequent light rains over an extended period (90 days or more).

 

The prairies of North America occupy areas where rainfall (250 to 750mm per year) is intermediate between those of deserts and forests (Blair et al., 2014). The tropical and subtropical grasslands, savannas, and shrub lands are characterized by rainfall levels ranging from 900-1500mm per year. Grasslands often experience very high intra- and inter-annual variability in rainfall. Many grasslands experience periodic droughts and a dormant season based on seasonal dry or cold conditions. At local scales, soil water availability in grasslands is often highly correlated with plant physiological processes, plant productivity, and soil microbial activity.

Temperate grasslands can occur on a variety of different soil types. The characteristic dark, rich soils are known as Mollisols in the US Soil Taxonomy system. Soil Profile of a Mollisol for mixed temperate grassland is shown in Fig. 27.5. Soils associated with temperate grasslands are usually deep (over 2 m), loamy textured, high in organic matter, and very fertile. These characteristics make these soils highly suitable for cultivation but prone to wind erosion if ecosystem balance is not maintained.

Many tropical and subtropical types of grassland occur on soils that are geologically much older and therefore more highly weathered, depleted in cations and have lower phosphorus availability. Continuous weathering in Tropical Grassland and Savannas has produced nutrient-poor Oxisols, which are particularly deficient in phosphorus. In sandy arid areas (less than 300 mm of annual precipitation), soils (less than 60cm deep) often support grassland, while deeper soils on the surrounding area support shrubland. Alfisols are common in the drier savannas, whereas Entisols are associated with the driest savannas. The grasslands of India occur on a wide variety of soils including alluvial, coastal alluvial, red, laterites, black, and desert soils.

 

27.5. Biodiversity and Community Composition

 

The herbaceous layer of grasslands is usually grasses and several other plant types. Halophytes belonging to Chenopodiaceae, both herbaceous and shrubby, are important on alkaline and saline soils in many arid and semi -arid grazing lands. In tundra, lichens, especially Cladonia rangifer, and mosses provide reindeer feed.

Grasses provide the matrix in which other plant species such as annual and perennial forbs (non-graminoid, non-woody plants), shrubs, and trees co-occur in a grassland ecosystem. In most of the world’s major grasslands, perennial grasses are dominant. Some grasslands are dominated by grass species having underground rhizomes and thus are “sod-forming” grasses, while other grasslands are dominated by species that grow in densely packed clumps of tillers and are bunchgrasses. The graminoid flora of grasslands can be quite species rich. For example, in the Konza Prairie (native tallgrass prairie preserve jointly owned by The Nature Conservancy and Kansas State University in USA), the grasses co-occur with over 400 species of forbs and woody plants, which provide much of the floristic diversity characteristic of the prairie (Blair et al. 2014).

 

The Daurian Steppe extends across Russia, China and Mongolia, it contains one of the world’s last intact temperate grassland ecosystems in the world (Box 27.1).

 

The Agulhas Plain grassland, part of the Cape Floristic Province of South Africa. This constitutes one of the world’s 36 biodiversity hotspots for conservation (Myers et al., 2000; http://www.cepf.net/resources/hotspots/Pages/default.aspx), contains a flora of 1751 species, including 23.6% regional endemics and 5.7% local endemics (see Blair et al. 2014). It is one of the largest extant storehouses of lowland fynbos and is recognized as a centre of endemism ’

 

The high elevation (montane and alpine) grasslands and shrublands, include the puna and paramo in South America, subalpine heath in New Guinea and East Africa, steppes of the Tibetan plateaus, as well as other similar subalpine habitats around the world. The montane grasslands of the Tibetan Plateau still support relatively intact migrations of Tibetan antelope (Pantholops hodgsoni) and Tibetan wild ass (Equus hemionus). A unique feature of many tropical paramos of the northern Andes is the presence of giant rosette plants from a variety of plant families.

 

Terai-Duar savannas and grasslands contain the world’s tallest grasses and have the greatest densities of tigers, rhinos, and ungulates. The dominant grass of the floodplains is Saccharum, or elephant grass, which grows each year to heights over seven meters and supports a number of habitat specialists such as the Bengal Tiger (Panthera tigris) and its prey base, the Chital (Axis axis).

 

Serengeti National Park savanna: The most famous savannas are in Africa, Serengeti National Park, located in north-central Tanzania, has three distinct types of savanna grassland, i.e., long-grass, intermediate grass, and short grass. In the vast plains of Serengeti National Park, comprises 1.5 million hectares of savanna. The annual migration of two million wildebeests plus hundreds of thousands of gazelles and zebras, followed by their predators in their annual migration in search of pasture and water, is one of the most important aspects in the natural world. The biological diversity of the park is very high with at least four globally threatened or endangered animal species, i.e., black rhinoceros, elephant, wild dog, and cheetah.

 

Diversity of Wildlife in the Indian grasslands

 

Some important ungulates in Indian grasslands on a regional basis are given in Table 27.3. Some of the rarest species of wildlife are found in the Indian grasslands, many of them totally dependent on them. The Bengal Florican, One-horned Rhinoceros, Pygmy Hog, Hispid Hare, Wild Buffalo, Hog Deer, Swamp Deer in terai grassland, the Great Indian Bustard in dry, short grasslands, the Lesser Florican in monsoonal grasslands of western India, and the Nilgiri Tahr in the shola grasslands of the Western Ghats are some examples (Anonymus, 2006). Pygmy hogs have been reported to be sensitive indicator species, because a decline in their population indirectly shows that there is imbalance in the biodiversity of the ecosystem; being critically endangered shows that the entire area where they are found is a threatened habitat.

 

The great Indian bustard inhabits dry grasslands and scrublands on the Indian subcontinent; its largest populations are found in Rajasthan. The Great Indian Bustard, one of the heaviest flying birds, it is considered to be the flagship grassland species. The great Indian bustard (Ardeotis nigriceps) is a tall, long legged bird; it is classified as Critically Endangered (CR) on the IUCN Red List. The Bengal florican has a very small, rapidly declining population largely as a result of widespread loss of its grassland habitat. It is therefore Endangered C1 Vulnerable. Lesser Florican (Sypheotides indica) is endangered because it has a very small, declining population, primarily a result of loss and degradation of its dry grassland habitat. The rate of decline is predicted to increase in the near future as pressure on the remaining grasslands intensifies (Zafar-ul Islam and Rehmani, 2002)

 

27.6. Ecosystem Functions

27.6.1. Productivity of Grassland Ecosystems

 

The ‘rate at which energy is stored by green plants in the form of organic substances’ and is generally expressed as net primary productivity (NPP) in terms of biomass, or carbon sequestration,, per unit area per unit time , after subtracting respiration (R) losses during the measurement period from the total energy fixed (i.e., gross primary productivity, GPP). In western North American temperate grasslands, above-ground primary production (ANP) ranged from186 to 330 876 g m- 2 yr- 1 ( Sims and Singh 1978), Fig. 27.6. Net root production (RP) ranged from 96 to 876 g m – 2 yr- l. Total net primary productivity (TNP) ranged from 282 to 1203 g m-2 yr- l. Approximately 34% and 81% of allocation of productivity was belowground in these temperate grasslands, Fig. 27.6.

Tropical savannas can be remarkably productive, with a net primary productivity that ranges from 1 to 12 t C ha-1year-1(Grace et al. 2006). The lower values are found in the arid and semi-arid savannas occurring in extensive regions of Africa, Australia and South America. The global average of the tropical savanna productivity was 7.2 t C ha-1year-1. The carbon sequestration rate (net ecosystem productivity) averaged 0.14 t C ha-1year-1

 

Two decades ago, an important study reported that the ecosystem productivity of diverse grassland was more resistant (changing less during drought), and more resilient, recovering more quickly after drought, than that of species poor communities (Tilman and Downing, 1994). Large-scaled experiments have shown significant positive impacts of plant diversity and composition on ecosystem processes such as biomass production, nutrient use, and decomposition. Results from a network of experiments carried out on five continents on 42 grassland types suggest that two or more nutrients often constrain aboveground net primary productivity of these globally significant ecosystems ( Fay et al. 2015).

 

The biomass production ranged from 2 to 5711 g m−2 in different grassland community types, including natural and managed (pastures and meadows) grasslands over a wide range of climatic zones (temperate, Mediterranean, and tropical), and altitudes (lowland to alpine) (Fraser et al. 2014).The results of their study based on 30 sites in 19 countries and six continents strongly support the humped-back model (HBM) of the plant richness-productivity relationship (Fig. 27.7). The HBM suggests that plant diversity peaks at intermediate productivity because at low productivity few species can tolerate the environmental stresses, and at high productivity a few highly competitive species dominate (Grime, 1973; Fraser et al. 2014).

 

27.6.2. Food Chain and Food Web

 

An organism that makes its own food is called a producer. Examples of producers in the prairie are grasses, forbs and wild flowers because they use the solar energy to make their own food through a process of photosynthesis. An organism that depends on others for food is called a consumer. Examples of consumers in the prairie include grasshoppers, harvester ants, mice and prairie chickens. Gray fox an omnivore that eats both plants and animal material ( Fig.27.8). Examples of decomposers in the prairie are earthworms, fungi and bacteria. Recycling of nutrients occurs in the prairie through decomposition.

27.6.3. Nutrient Cycling

 

Grassland ecosystems contain cycles of nitrogen, and other plant nutrients, such as phosphorus and potassium. Nutrients are derived from weathered rock or dissolved in rainfall. The nutrients may be lost from the system by leaching, or in runoff or through harvesting of plants. Most nutrients are recycled within the system through plant uptake, leaf fall and litter decomposition. Nutrients are stored in the biomass, the litter and the soil in variable quantities depending on the type of grassland ecosystems and seasonality of climate.

 

Ecosystem nutrient budgets can also be presented in the form of compartment models as shown in Figure27. 9. In this model, the standing state of nutrients are given in compartments and flux rates on the arrows connecting one compartment with the other. The proportion of N cycled through the root compartment in the short-grass prairie is substantially greater than the proportion cycled through the shoot compartment.

27.7. GOODS AND SERVICES OF GRASSLANDS

 

Grassland is a renewable resource; productivity is variable and determined by climate, soil, topography. These systems provide many goods and services that are important to humans. Grasslands are an important source of food resources, namely meat, milk or honey. The most widespread use of grassland worldwide is in the production of domestic livestock (principally mammalian herbivores: cattle, sheep, goats, horses, water buffalo, and camels). A large numbers of wild herbivores also depend on grasslands, and in many cases share the land with domestic herds. There is a large variety of forage plants, and for the most part they are grasses or legumes Semi-natural grasslands are significant source of many medicinal plants.

Grasslands provide critical ecosystems services that regulate, support and underpin the environment that we live in. These include climate regulation, water storage, nutrient cycling, erosion control or soil stabilization, pollination and biodiversity (Table27.2). Climate regulation via soil carbon storage and sequestration is highly valued. Temperate grasslands are the third largest global store of carbon in soils and vegetation (after wetlands and boreal forests), the amount of C that could be stored in the world’s grazing lands is considerable and presents a potentially large mitigation opportunity.

 

Table 27.2. Grassland Ecosystem Services (based on MA 2005; TEEB 2010)

27.8. HUMAN IMPACTS ON GRASSLANDS

 

Grasslands are being modified by conversion of land to agriculture, urbanization/human settlements, desertification, fire suppression, overgrazing by livestock, habitat fragmentation, climate change, the introduction of invasive (non-native) species, and woody plant expansion (White et al., 2000; Blair et al, 2014). All these factors have been found to influence the functioning of grassland ecosystems. Some impacts on grassland systems are discussed as follows.

Agriculture: Grasslands have historically been an area of expansion for human land use, and much of the world’s highly productive grassland has been converted to crops, mixed farming and artificial pastures (Suttie et al., 2005). In temperate grasslands, this conversion occurred prior to the 1950s (Millennium Ecosystem Assessment, 2005). Currently, agricultural expansion is occurring in the tropics, as a result of which many tropical savannas and grasslands in South America, southern Africa, and Asia are undergoing change (Gibbs et al., 2010). Future threats to grasslands also appear high for providing food to a rapidly growing human population (Foley et al., 2011). Conversion of grasslands to croplands or seeded pastures has exerted a major impact on biodiversity and ecosystem function; in many cases these converted grasslands have become net sources of carbon and nutrients leading to global change

 

Human Settlements and Urbanization: The conversion of grassland to agricultural land and for human settlement, have greatly modified these ecosystems. The prairies of North America were home to many early European settlers. More people live in grasslands than forests.

 

Grazing: Grasslands and populations of wild ungulates have coexisted for millions of years. Wild ungulates are an essential component of energy and nutrient flows in grassland ecosystems. Large populations of herbivores, including bison of North America, wildebeest and zebra of Africa, and Tibetan antelope of Asia have been characteristic of the world’s major grasslands. It is estimated that 50% of all temperate grasslands are utilized as pastures, and in many regions, overgrazing is common (Ramankutty et al.,2008).

Desertification may be the most severe modification of grassland ecosystems. Widespread desertification of North America’s semi-arid grasslands has already occurred.

Fire is an important factor in maintaining grassland ecosystems. Despite providing important services for maintaining natural and human-influenced grasslands, fire can be harmful, especially when very hot and frequent, fire can destroy vegetation and increase soil erosion. Fire has caused degradation of grasslands because of improper fire regimes and overstocking.

Grassland fragmentation is caused by agriculture, road building, fencing and woody invasion.

Impacts of climate change on Grasslands: Grassland function is directly dependent upon temperature, precipitation, and soil moisture. Climate change will affect the goods and services that grassland areas provide, including carbon storage, nitrate filtration, water quality, crop yield, and forage for livestock and wildlife (IPCC, 2007).

Invasion of Exotic Species: Within the span of the last two centuries, exotic species have overtaken vast expanses of grasslands in Australia, South America, and parts of North America (see Seabloom et al., 2013). Grasses comprise the most aggressive invaders.

 

27.9. GRASSLAND MANAGEMENT

The majority of the world’s grasslands are considered to be degraded to some degree. Depending on the desired use, grasslands are managed for one of several goals, including production of forage for raising domestic and wild animals, carbon sequestration, and biodiversity conservation, production of biofuels, enhancing the environment or conservation of natural areas (Gibson, 2009). The global potential for C sequestration in the soils of the world’s grazing lands is 352 Tg CO2 yr _1 through improved grazing management in rangelands and pasturelands, and the sowing of legumes in pasturelands (Henderson et al., 2015).

 

Grassland  management  involves  social,  economic,  cultural  and  technical  factors.  The  grassland components are to be managed in way so as to obtain the optimum combination of goods and services for society on a sustained basis. Many natural areas require management intervention because natural disturbance regimes have been disturbed or no longer in place in highly degraded grasslands.  Some of the strategies for grassland management based on Suttie et al. (2005) and Gibson (2009) are outlined as follows:

 

  1. Managing the plant/animal system by maintaining the desirable plant species, and defining the appropriate level of utilization, and the state of plants as an indicator of system ‘health.
  2. To improve the grassland ecosystem by retaining species and managing water, nutrient and energy cycles with reasonable efficiencies, and maintaining suitable levels of production.
  3. Stocking rates need to be maintained in the case grazing for forage and livestock production in a particular environment and the plant community; intermediate level of grazing could be practiced to maximize primary production and the stocking rate.
  4. Fire in the form of prescribed burning is also a powerful tool in grassland management.
  5. To protect and enhance the soil and vegetation complex. Improvement of the pastoral vegetation in extensive grasslands through manipulation of grazing pressure and the use of controlled fire.
  6. Growing of fodder crops can be useful for favoured areas in extensive grassland systems,
  7. Some management strategies including regulation of grazing, protection of vegetation, and reseeding for Indian grasslands are summarized in Box 27.2.

 

 

27.10. Summary

 

  • Grasslands are defined as “ecosystems in which the dominant vegetative component is comprised of herbaceous species”; also encompass ecosystems with a significant grass cover interspersed with varying degrees of trees and shrubs.
  • Climate, fire, and grazing are three key factors that are responsible for the origin, maintenance, and structure of the most extensive natural grasslands globally.
  • Major grasslands in the temperate regions of the world include the steppes of Eurasia, the ‘velds’ of southern Africa, the pampas of Argentina, and the prairies of North America, cover 8% of the Earth’s terrestrial surface.
  • Grasslands and savannas are of widespread occurrence within the subtropics and tropics such as the bushvelds of Africa, and the compos and llanos of South America, Terai-Duar savannas and grasslands in southern Asia, and flooded grasslands and savannas
  • In India, grasslands generally occur in areas receiving between 250 mm and 900 mm annual precipitation. About 37% of land can be said to be available for grazing. The average annual production of dry grass or hay in India is about 250 million tons.
  • Major grassland types of India include Sehima–Dichanthium type, Dichanthium–Cenchrus–Lasiurus type, Phragmites–Saccharum–Imperata type, Themeda–Arundinella type, and Temperate-Alpine Grasslands.
  • Grasslands occur under a very broad range of mean annual temperature and rainfall, and soil types. Grasses provide the matrix in which other plant species such as annual and perennial forbs (non-graminoid, nonwoody plants), shrubs, and trees.co-occur in a grassland ecosystem.
  • Grasslands provide critical ecosystems services that regulate, support and underpin the environment that we live in. These include climate regulation, water storage, nutrient cycling, erosion control or soil stabilization, pollination and biodiversity.
  • The biomass production ranges from 2 to 5711 g m−2 in different natural and managed (pastures and meadows) grasslands over a wide range of climatic zones (temperate, Mediterranean, and tropical), and altitudes (lowland to alpine).
  • Grasslands are being modified by conversion of land to agriculture, urbanization/human settlements, desertification, fire suppression, overgrazing by livestock, habitat fragmentation, climate change, the introduction of invasive non-native species, and woody plant expansion.
  • The strategies for grassland management include managing the plant/animal system, improving the grassland ecosystem, maintaining the stocking rates at intermediate level of grazing, prescribed burning, conserving wildlife and biodiversity, protection of vegetation, and reseeding.
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REFERENCES

 

  • Anonymus, (2006). Report of the Task Force on Grasslands and Deserts. Planning commission, Government of India, New Delhi.
  • Asner, GP, Elmore, AJ, Martin, RE and    Olander, LP(2004). Grazing systems, ecosystem responses, and global change. Annual Review of Environment and Resources 29:11.1–11.39.
  • Bailey, RG (1989). Explanatory Supplement to ecoregions map of the continents. Environmental Conservation 16: 307-309.
  • Blair JM., Nippert J and Briggs,J (2014). Grassland Ecology. Pages 389-423 In The Plant Sciences – Ecology and the Environment Volume 8 (R. Monson, ed.), Springer Reference Series, Springer-Verlag, Berlin.
  • Coupland, RT (1979) Grassland Ecosystems of the World. Cambridge University Press, Cambridge, UK.
  • Dabadghao, PM and Shankarnarayan, KA (1973). The Grass Cover of India. Indian Council of Agricultural Research, New Delhi.
  • Dixon, AP, Faber-Langendoen, D, Josse, C, Morrison, J and Loucks, CJ (2014). Distribution mapping of world grassland types. Journal of Biogeography, 41: 2003-2019.
  • Fay, PA et al. (2015). Grassland productivity limited by multiple nutrients. Nature Plants, 1 (7). ISSN 2055-026X
  • Foley, JA , Ramankutty, N, Brauman, KA et al. (2011). Solutions for a cultivated planet. Nature, 478: 337-342.
  • Fraser, LH, Jentsch, A. and Sternberg, M (2014), What drives plant species diversity? A global distributed test of the unimodal relationship between herbaceous species richness and plant biomass. J Veg Sci, 25: 1160–1166.
  • Fraser, LH. et al. (2015). Worldwide evidence of a unimodal relationship between productivity and plant species richness. Science 349: 302-305.
  • Gibbs, HK, Ruesch, AS, Achard, F, Clayton, MK, Holmgren, P, Ramankutty, N, and Foley, JA (2010). Tropical forests were the primary sources of new agricultural land in the 1980s and 1990s. Proceedings of the National Academy of Sciences USA, 107(38): 16732- 16737.
  • Gibson DJ (2009). Grasses and Grassland Ecology. Oxford University Press Oxford, UK.  305 pp.
  • Grime JP (1973). Control of Species Diversity in Herbaceous Vegetation. Journal of Environmental Management 1: 151-167.
  • Henderson, BB, Gerber, PJ, Hilinski, TE, Falcucci, A, Ojima, DS, Salvatore, M, Conant, RT (2015) Greenhouse gas mitigation potential of the world’s grazing lands: Modeling soil carbon and nitrogen fluxes of mitigation practices. Agriculture, Ecosystems & Environment 207: 91–100.
  • Hoesktra, JM., Boucher, TM., Ricketts, TH and Roberts, C (2005) Confronting a biome crisis: global
  • disparities of habitat loss and protection. Ecology Letters 8: 23–29.
  • IPCC (Intergovernmental Panel on Climate Change). (2007). Climate Change 2007: Synthesis Report. Contribution of Working Groups I, II and III to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change (AR4). Core Writing Team, R.K. Pachauri and A. Reisinger (eds.). IPCC, Geneva, Switzerland, 104 pp.
  • Millennium Ecosystem Assessment (2005). Ecosystems and Human Well-Being: Current State and Trends, Vol. 1. Island Press, Washington, DC.
  • Myers, N., Mittermeier, RA, Mittermeier, CG, da Fonseca, GAB and Kent, J(2000). Biodiversity hotspots for conservation priorities. Nature 403: 853-856.
  • Olson, DM., Dinerstein E., Wikramanayake E D, Burgess, N D, Powell, G V N, et al.  (2001).
  • Terrestrial ecoregions of the world: a new map of life on Earth. BioScience 51:933-938.
  • Orgiazzi, A, Bardgett RD, Barrios E. et al. (Eds.)(2016). Global Soil Biodiversity Atlas. European Commission, Publications Office of the European Union, Luxembourg. 176 pp.
  • Ramankutty N., Evan AT, Monfreda C and Foley JA (2008). Farming the planet: 1. Geographic distribution of global agricultural lands in the year 2000. Global Biogeochemical Cycles 22: GB1003. DOI: 10.1029/2007GB002952.
  • Rawat, GS and  Adhikari BS (Eds.). (2015). Ecology and Management of Grassland Habitats in India,
  • ENVIS Bulletin. Wildlife and Protected Areas. Vol. 17. Wildlife Institute of India, 240pp.
  • Rodgers, WA (1988). The wild grazing ungulates of India: an ecological review. In: ( P. Singh and P.S. Pathak, eds) Rangelands – resource and management. Rangeland Management Society of India, Jhansi. pp. 9–21
  • Seabloom, EW et al.    (2013). Predicting invasion in grassland ecosystems: is exotic dominance the real embarrassment of richness? Global Change Biology: doi: 10.1111/gcb.12370
  • Singh, JS and Gupta, SR (1992). Grasslands of Southern Asia. In: Ecosystems of the World, Volume 8
  • Natural Grasslands:  Eastern  Hemisphere  and  Resume,  Coupland,  R.T.  (ed).  Elsevier Science Publishers, Amsterdam, The Netherlands.pp83-123.
  • Singh JS, Singh SP, Gupta SR (2015). Ecology, Environmental Science and Conservation. S. Chand, New Delhi, India.
  • Suttie JM, Reynolds SG, Batello C, eds (2005). Grasslands of the World. Food and Agriculture Organization of the United Nations, Plant Production and Protection Series (Food and Agriculture Organization, Rome), No. 34.
  • Tilman,D, and Downing, JA(1994). Biodiversity and stability in grasslands. Nature 367 : 363-365.
  • White, R., Murray, S. and Rohweder, M. (2000).Pilot analysis of global ecosystems: Grassland ecosystems. World Resources Institute, Washington, DC.
  • Whittaker, RH (1975). Communities and Ecosystems. Second Edition. MacMillan, New York.
  • Zafar-ul Islam M and Rahmani A (2002). Threatened Birds of India. BUCEROS: Envis Newsletter: Avian Ecology & Inland Wetlands. Vol.7 No.1&2. pp.23