CHAPTER 6 Biological Interaction in Tropical Grassland Ecosystems Panjab Singh and S.D. Upadhyaya CONTENTS Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114 Nature of Tropical Grasslands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115 Origin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116 Successional Levels. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116 Diverse Grassland Communities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118 Biodiversity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118 Species Diversity in the World . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119 Community Diversity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120 Ecosystem Diversity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121 Structure of Tropical Grassland . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121 Abiotic Characteristics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123 Biotic Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123 Production Strategy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124 Primary Productivity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125 Secondary Productivity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126 Biological Interactions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126 Biophysical Interactions at the Ecosystem Level: Exploratory Studies at Iseilema Grasslands of Ujjain, India . . . . . . . . . . . . . . . 127 Interspecific and Intraspecific Interactions. . . . . . . . . . . . . . . . . . . . . 131 Biophysical Interactions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131 Interaction of Trees and Grasses. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133 Aboveground Interactions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133 Belowground Interactions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 134 113 0-8493-0904-2/01/$0.00+$.50 © 2001 by CRC Press LLC 920103_CRC20_0904_CH06 1/13/01 10:51 AM Page 113 114 STRUCTURE AND FUNCTION IN AGROECOSYSTEMS DESIGN AND MANAGEMENT Grass-Legume Interactions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135 Trees-Grass-Livestock Interactions . . . . . . . . . . . . . . . . . . . . . . . . . . . 135 Tree/Grass-Legume-Animal Interactions. . . . . . . . . . . . . . . . . . . . . . 136 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139 INTRODUCTION The grassland biome is characterized by grasses and their relatives where the dominant life forms are mixed with herbaceous plants. Grassland ecosys- tems consist of many interacting environmental forces, local combinations of organisms, and the impacts of use by an increasing number of people. These systems remain primarily under the control of overall environment, although use and management of grassland ecosystems alter populations of organ- isms, change the rate of physical and biological inputs, and account for about 25% of earth’s natural vegetation. Grassland ecosystem components include soil, vegetation, populations, communities, and animals. Most of the exten- sive areas of existing natural grassland have undergone changes through man-tree-grass-animal interactions. Significant impact from grazing and fire has been noticed. Plants are often adapted to fast, scattered fires that burn the tops of plants but leave seeds, roots, or other resistant structures intact. Examples include the tall grass prairie of the U.S. and Canada, the steppes of Central Asia, and the plains of Africa. Because these areas are often suitable for cultivation or livestock grazing, a great deal of this biome around the world has been highly modified, often for many centuries or millennia. The existence of grassland, i.e., the great bread baskets of the world, and grazing animals extends back into the geological history (Box et al., 1969). The grasslands have been one of the most precious of natural wealth since times immemorial to man, which is supported by fossil records of grasses observed in the cretaceous, or even earlier when flowering plants were spreading throughout the biosphere. The precipitation-evaporation ratio and precipitation-seasonality ratio are important biophysical factors in produc- ing different types of grasslands and in the delineation of the grasslands. Grasslands occur over a wide range of mean annual temperatures, occurring in near tropical situations as well as extremely cold climates, having been classified as steppes, prairies, and savannas, and temperate, semi-arid, desert, alpine, and tundra grasslands, depending on their environment and the vegetational characteristics at their place of occurrence. One of the main aims of the international biological program (IBP) has been the evaluation of the terrestrial productivity, the main theme having been the synthesis of the grassland ecosystem to examine the “biological basis of productivity in human welfare.” The synthesis of grassland ecosys- tem analysis usually involves various statistical and mathematical models. According to Van Dyne et al. (1978), grassland ecosystems are dynamic and 920103_CRC20_0904_CH06 1/13/01 10:51 AM Page 114 BIOLOGICAL INTERACTION IN TROPICAL GRASSLAND ECOSYSTEMS 115 not static. In the grassland ecosystem, we see various dynamic phenomena, such as changes in the biomass of plants and animals and phenological pro- gression, as well as the less noticeable but still significant changes occurring underground. In fact, these latter changes are more important when the impact on the system is considered, such as changes in soil-water-energy, the exuberance and extinction of microbial populations, the growth and vanish- ing of roots, and other such related processes. Having taken notice of the myriad changes taking place in response to the seemingly probabilistic changes leading to a complexity, one needs to view the whole process as a total system (Van Dyne et al., 1978) in view of biological interactions. In this chapter, an analysis is made of research results obtained on the main interac- tions identified in tropical grassland ecosystems, and their potential signifi- cant impact is discussed. NATURE OF TROPICAL GRASSLANDS Tropical grasslands are seral in nature, attaining a status of disclimax at many places, due to recurring biotic operations, such as grazing, fire, and scrapping. They owe their origin either to deforestation or to shifting culti- vation by nomadics, with the species composition of these grasslands vary- ing with the intensity of grazing and harvesting. The important functions of the grassland ecosystems are the dynamics of organic matter and the production processes. Odum (1971) asserted that the most important functional properties of ecosystems are energy flow, biogeo- chemical cycles, and biological regulation. A major portion of the energy fixed by the photosynthetic canopy of green plants ultimately finds its way into the detritus component (Macfadyen, 1963). A considerable amount of information is available about organic matter production and the processes associated with it in different grassland ecosystems of the world, under varying climatic con- ditions. Singh and Yadava (1974), Sims et al., (1978), Sims and Singh (1971, 1978a, 1978b, and 1978c) have presented illuminating accounts of the biomass structure, productivity, and energy compartmental transfers, as well as the accumulation and disappearance of organic matter in grazing land ecosystems. Bokhari and Singh (1975), Billore and Mall (1976), Pandey (1975), Upadhyaya (1979), and Paliwal and Karunaichamy (1999) have adopted a modeling approach for the evaluation of the uptake, transfer and release of the system state variables. Yadav and Singh (1977) have described a thorough legend of the grasslands of India, while others (Coupland, 1979) have ade- quately dealt with the structure and function of the grasslands of India and the world, including an illustrative account of the decomposer kinetics in the grazing land ecosystems. A survey of this literature points out that although much information is available on production dynamics and the aspects of the grazing land ecosystems, there is a wide lacuna in our understanding of the biological interaction in tropical grassland ecosystems. 920103_CRC20_0904_CH06 1/13/01 10:51 AM Page 115 116 STRUCTURE AND FUNCTION IN AGROECOSYSTEMS DESIGN AND MANAGEMENT ORIGIN Fossil record shows that tropical grasslands originated as long ago as 6 to 12 million years. The environment remained in its pristine purity and conge- niality as man stayed in the hunting and gathering stage. However, man entered the pastoral age and domesticated animals and then gradually passed from the nomadic stage to settled cultivation. Grasslands were impor- tant to man before plants were ever domesticated. In the late 1800s the impor- tance of grasslands and the grass plant were recognized. The great “bread baskets” of the world exist on soils developed under centuries of grassland cover. Grasslands in tropics have mainly originated from the destruction of permanent woody vegetation and are thus bio-edaphic sub-climaxes. Tropical and subtropical grasslands are located in the plains and mountains within 28°N and 30°S of the equator (Thomas, 1978). This land mass of trop- ics and subtropics accounts for 38% of the earth’s surface and 45% of the world’s population (FAO, 1995). The extent of tropical grasslands and live- stock population is summarized in Table 6.1, which illustrates the livestock dependence on grasslands. The number of livestock has increased, and at the same time the area of grasslands has decreased around the world (except in Brazil), indicating intensification of grassland usage by livestock. It is esti- mated that over 90% of the feed for livestock on a world-wide basis comes from grasslands/rangelands. With continued human population growth, there will be increased demand for milk and meat, resulting in even more intensive grassland utilization. Greater intensity of grassland utilization will require more knowledge of the functional ecology and biological interactions in grassland ecosystems. Successional Levels Every living being is surrounded by materials and forces that constitute its environment and through which it meets its needs. Nothing can escape its environment, no animal or plant can live completely sealed off from the world, and all living things must make exchanges with their environment in terms of energy, matter, and waste elimination. All living beings are interde- pendent and must absorb energy, termed as natural resources, more or less continuously to fuel their life process. The grasslands are renewable natural resources and are one of a number of seral phases of vegetation. Their struc- ture is dynamic rather than static. One ecological association follows upon and grows in consequence of its predecessor in a well-marked and orderly sequence. One association therefore acts as a nursery to its immediate suc- cessor. This series of orderly sequence from the first to the last is referred to as the sere. The successional levels of tropical grasslands are characteristic phases of the sere which may thus end at a subclimax rather than at its 920103_CRC20_0904_CH06 1/13/01 10:51 AM Page 116 BIOLOGICAL INTERACTION IN TROPICAL GRASSLAND ECOSYSTEMS 117 Table 6.1 Land Area, Permanent Pastures, and Livestock Population of the Tropical and Subtropical Countries* Land area Permanent pastures Livestock* (M ha) (M ha) (M) Region 1979 1994 1979 1994 1989 1994 World Total 13040.9 13045.4 3265.0 3395.2 4164.3 4204.3 Africa 2963.5 2963.5 892.7 883.5 609.5 641.3 Asia 2679.0 2679.0 686.4 792.1 1697.0 1880.9 Brazil 845.6 845.6 170.1 185.0 224.3 236.2 Australia 764.4 764.4 436.3 414.5 191.6 149.9 India 297.3 297.3 112.1 111.4 440.4 454.5 Sudan 237.6 237.6 98.0 110.1 59.0 65.1 Indonesia 181.0 181.0 12.0 11.8 38.8 44.3 Chad 125.9 125.9 45.0 45.0 10.1 11.1 South Africa 122.1 122.1 81.4 81.3 53.0 50.3 Ethopia 110.1 110.1 45.4 44.9 — 77.8 Venezuela 88.2 88.2 17.1 17.8 — — Pakistan 77.0 77.0 5.0 5.0 101.1 117.2 Nigeria (Kenya) 56.9 56.9 21.3 21.3 55.2 64.4 Cameroon 46.5 46.5 2.0 2.0 12.8 13.9 Nepal 13.6 13.6 1.8 2.0 — — Bangladesh 13.0 13.0 0.6 0.6 — — Sri Lanka 6.4 6.4 0.4 0.4 3.2 3.3 Bhutan 4.7 4.7 0.2 0.2 0.6 0.7 Pacific Islands (Fiji) 1.8 1.8 0.1 0.1 0.5 0.7 * Livestock numbers include horses, mules, asses, cattle, buffaloes, camels, pigs, sheep, and goats * Based on FAO Production Yearbook data, 1995 climax, e.g., grassland of arid and semi-arid tropics (low rainfall areas). Monsoonal grasslands in the tropics are the stabilized successional stages of vegetation. In areas of higher rainfall, the successional levels terminate in for- est as a climax stage. Here, the biological interaction determines the charac- ter of vegetation and also the successional level of the ecosystem. The grazing animals (biotic pressure) maintain the successional level of grasslands (Barnard and Frankel, 1964). Grasslands are maintained as such due to bio- edaphic pressures. Similarly the use of fire has also been a very important fea- ture associated with development of tropical grasslands. Besides these, the most important constraint affecting grassland is its extreme fragility. This means that the landscape, vegetation, and soil cover degrade much more quickly than in more favored habitats; fragility affects the biological system 920103_CRC20_0904_CH06 1/13/01 10:51 AM Page 117 118 STRUCTURE AND FUNCTION IN AGROECOSYSTEMS DESIGN AND MANAGEMENT and hence sustainability or, in ecological parlance, homeostasis—the ten- dency of a biological system to resist change and remain at a stage of dynamic equilibrium or relative consistency. This is because a grassland ecosystem is capable of self regulation due to biological interactions as a law of nature. Diverse Grassland Communities Most developing countries are in the tropics, where grasslands are the major feed resources (over 40%) for livestock rearing. Due to enormous biotic activities, the grassland communities have undergone significant changes. The tropical and subtropical grasslands of the southern hemisphere are rep- resented by savannas with low vegetation and scattered trees, while steppes in Asia are generally grassy and without trees. Africa is covered with more than one third grassland of Acacia-based savannas. The savannas in Australia are dominated by Eucalyptus and Acacia both equally. In India, Burma, and Indonesia, grassland savannas occur in the tropical rain forests. Bamboo- based savannas are common in India. Most of the Japanese grasslands repre- sent semi-natural grasslands created and maintained by man. Around the world, the grassland communities consist of 22% high grass savannas, 31% tall grass savannas, 13% tall grass prairies, 10% short grass prairies, 18% grasslands and savannas, and 6% mountain grasslands, (Shantz, 1954; Whyte, 1960). Tropical grasslands of India are rich in biodiversity and also diverse heterogeneity in nature because of the great variation in climate, soil, and physiography. Dabadghao and Shankarnarayan (1973) have identified five major grass covers of India—Sehima-Dichanthium, Dichanthium- Cenchrus-Lasiurus, Phragmites-Saccharum-Imperata, Themeda-Arundinella and Temperate Alpine distributed in elevation from 150 to 2100 m and rainfall ranges from 100 to 3750 mm. Over 40% of the total geographical area of India is available for grazing by over 400 million livestock under diverse grassland communities. The grazing pressure is very high, 1–4 ACU/ha, against the normal 0.2–0.5 ACU/ha in the arid and semi-arid areas of India (Shankar and Gupta, 1992). BIODIVERSITY The variety of all life forms—the different plants, animals, and microor- ganisms, the genes they contain, and the ecosystems of which they form a part—is termed biological diversity or biodiversity (Wilson, 1992). Grassland biodiversity is not a fixed entity, but constantly changing; it is increased by genetic change and evolutionary processes and reduced by extinction and habitat degradation. The concept emphasizes the interrelatedness of biome and biological interactions. Grassland biodiversity is also a limited and a 920103_CRC20_0904_CH06 1/13/01 10:51 AM Page 118 BIOLOGICAL INTERACTION IN TROPICAL GRASSLAND ECOSYSTEMS 119 Table 6.2 Tribes and Genera of the Family Gramineae (Grasses) Tribe Genera Andropogoneae Andropogon, Bothriochloa,Chrysopogon, Colix, Cymbopogon, Dichanthium, Hemarthria, Heteropogon, Hyparthenia, Hyperthelia, Imperata, Ischaemum, Iseilema, Lasiurus, Saccharu, Sehima, Sorghum, Themeda, Trachypogon, Tripsacum, Vetiveria, Vossia, Zea Aristidae Aristida Arundineae Phragmites Arundinelleae Loudetia, Tristachya Chlorideae Asterbla, Chloris, Cynodon, Enteropogon Eragrostideae Dactyloctenium, Diplachne, Eleusine, Eragrostis,Triodia Oryzeae Leersia, Oryza Paniceae Acroceras, Anthephora, Axonopus, Brachiaria, Cenchrus, Digitaria, Echinochloa, Eriochloa, Hymenachne, Melinis, Panicum, Paspalidium, Paspelum, Pennisetum, Setaria, Spinifex, Stenotaphrum, Tricholaena, Urochloa Sporoboleae Sporobolus Zoysieae Leptothrium perishable natural resource. It has three components, namely: species diver- sity, community diversity, and ecosystem diversity. Species Diversity in the World The strong impact of climate throughout the world also manifests itself in marked species diversity in world grasslands. The flora of grasslands, in general, is dominated by therophytes and cryptophytes (Singh and Yadav, 1974). The preponderance of therophytes results from a strong periodicity in biotope and biocoenosis. The loss of a species reduces species diversity and threatens the functioning of ecological communities. Grassland is one of a number of serial phases of vegetation (grass, shrub, and trees), which has dynamic rather than static structure. Many of the large tropical grasslands from west to east are dominated by the species of tribes: Paniaceae characterized by high temperature and low rainfall, Andropogoncae characterized by rainfall varying from 125 to 2250 mm and distribution closely related to temperature. They are abundant in the tropical savannas of India, Africa, and South America. Eragrostideae tribe is distributed abun- dantly where yearly winter temperature is above 10°C and rainfall is about 1000 mm (Skerman and Riveros, 1990). There are ten common groups of tribes (Table 6.2) found in tropical grasslands, which are unevenly distrib- uted in world grasslands (Figure 6.1). 920103_CRC20_0904_CH06 1/13/01 10:51 AM Page 119 120 STRUCTURE AND FUNCTION IN AGROECOSYSTEMS DESIGN AND MANAGEMENT Figure 6.1 Percentage distribution of tribes/grass in World Grassland Ecosystem. Indian tropical grasslands consist of 245 genera and 1256 species of grasses (Bor, 1960); out of these, 139 species are reported to be endemic (Mehra and Magoon, 1974). Indian grassland legumes consist of 167 genera and about 1150 species, including cultivated, introduced as wild species (Singh and Morrison, 1998). Community Diversity The International Biological Programme (IBP) analyzed world grassland communities, including natural grasslands, tundras, deserts, savannas, prairies, steppes, and other grasslands derived from forests, and cautioned about change in communities due to biological interactions. Man has modi- fied grassland communities for intensification of animal and plant produc- tivity through prudent use of fire, conversion to croplands, introduction of new herbivores, replacement of native grasses/legumes by exotics, deliber- ate incorporation of trees, etc. Permanent pastures occupy approximately 25% of the earth’s land area (Table 6.1): 3395 million hectares of permanent pastures of the world provide forage and habitat for some 4204 million live- stock. In the tropical and subtropical regions of the world, approximately 23% is grazing land communities (‘t Mannetje, 1978), mostly savannas with varying proportions of trees and shrubs. Many of the large grassland com- munities are climax formations determined by soil and climate; others are of more recent origin and have replaced forest communities destroyed mainly by cutting and fire, and these have been maintained largely through grazing animals (Barnard and Frankel, 1964). Hence, fire and grazing have been very important features associated with the community diversity. Natural communities converted into grasslands are greatly influenced by biological interactions. 920103_CRC20_0904_CH06 1/13/01 10:51 AM Page 120 BIOLOGICAL INTERACTION IN TROPICAL GRASSLAND ECOSYSTEMS 121 Ecosystem Diversity Ecosystem or ecological diversity of grasslands is changing day by day. Many of the world’s original grasslands have been largely converted to crop- lands or to seeded pastures, although these regions carry large numbers of grazing animals. Similarly, many of the world’s original forests have been converted to grasslands. Many desert areas are also utilized seasonally for grazing. Collectively, about 40% of the earth’s ecosystem with normal spec- trum of tribes and genera of the family Gramineae (grasses) is used by grazing animals. The four main elements of grassland ecosystem, namely abiotic sub- stances, producer organisms, consumers, and decomposer organisms, have great diversity in world grasslands. Living organisms (plants, animals, and microorganisms) are taken as a whole while studying interactions with the nonliving environment in the ecosystem. It is mostly an open system compris- ing plants, animals, organic residues, atmospheric gases, water, and minerals that are involved together in the flow of energy and circulation of matter. A conceptual model of organic matter storage, flow, and biological interactions which help in nutrient cycling and CO 2 fertilization is shown in Figure 6.2. The boxes in the figure represent organic matter accumulation, and the arrows show pathways of transfer from one sink to another. Alphabetical symbols (u: uptake; t: transfer; r: release) denote biophysical or biological functions of inter- actions. The biochemical and physical factors include sunlight, rainfall, soil nutrients, and climate. A grassland ecosystem is inherently “leaky”: at a mini- mum, energy and nutrients move in and out. More likely, individual organisms move in and out as well. Within each grassland ecosystem, there are a myriad of well-defined groups of living organisms—producers (plants), consumers (animals), and decomposers (bacteria and fungi)—interacting with each other. Interactions of herbiovores, carnivores, and decomposers provide many routes of nutrient transfer and release, describing the quantities of minerals in the var- ious pools such as the soil, litter, and urine. A common type of interaction amongst different tropic levels and total quantity of mineral flow from source to sink are depicted in Figure 6.2. Detailed analysis of mineral/energy reserves describes the system organization and provides a base for the study of mineral cycling/energy flow through the system and the biological groups responsible for transformations which will facilitate the grassland management in a sus- tainable manner. The annual cycle of plant biomass accumulations and litter decomposition has received much attention. With the development of concepts of ecosystem structure and function, many grassland ecologists assorted the carbon fixation by grasses and its later circulation in the ecosystems. STRUCTURE OF TROPICAL GRASSLAND Tropical natural grasslands structurally and physiognomically are char- acterized by mixed herbaceous plants (dominated by grasses), trees, and a 920103_CRC20_0904_CH06 1/13/01 10:51 AM Page 121 122 STRUCTURE AND FUNCTION IN AGROECOSYSTEMS DESIGN AND MANAGEMENT Figure 6.2 Box and arrow diagram of ecosystem level model of mineral cycling and energy flow in grassland ecosystem to study the impact of biological interactions (r-release, t-transfer, u-uptake). low plant cover of non-woody species. Unstable grasslands representing disclimax have been derived after the destruction of forests and are main- tained due to regular biotic interference. Such vegetation is normally termed savanna (Moore, 1970). In the course of time, the grasslands have undergone significant changes, due to the human population pressure, in terms of declining area, carrying capacity, and productivity. Structure and function of 920103_CRC20_0904_CH06 1/13/01 10:51 AM Page 122 [...]... of livestock in the world (Table 6. 4) The importance of the pasture-cattle-coconut system in southeast Asia and the Pacific (Reynolds, 1995), silvipastoral systems in Africa 920103_CRC20_0904_CH 06 1 36 1/13/01 10:51 AM Page 1 36 STRUCTURE AND FUNCTION IN AGROECOSYSTEMS DESIGN AND MANAGEMENT (Le Houerou, 1980), silvipasture in India (Singh and Roy, 1998), pasture under cashew plantation in Kenya (Goldson,... Sims, P.L and Singh, J.S., 1971 Herbage dynamics and net primary production in certain ungrazed and grazed grasslands in North America, in Preliminary Analysis of Structure and Function in Grasslands, N.R French (Ed.) Range Sci Deps, 5 Sci Ser No 10 Colorado State University Fort Collins 59–124 Sims, P.L and Singh, J.S., 1978a The structure and function of ten western North American grasslands II Intraseasonal... transfer functions J Ecol 66 :983 –1009 Sims, P.L., Singh, J.S., and W.K Launnroth, 1978 The structure and function of ten western North American grasslands I Abiotic and vegetation characteristics J Ecol 66 :251 –285 Singh, P and Roy, M.M., 1998 Agroforestry and rangeland development, in Fifty Years of Agronomic Research in India R.L Yadav, P Singh, R Prasad, and IPS Ahlawat ISA, New Delhi Singh, P and Upadhyaya,... Trees-Grass-Livestock Interactions Associations among livestock, grasses, and trees are intense The livestock component of the grassland may be herds and flocks grazing and browsing in the vicinity of grazing lands and a mutually beneficial association (fodder-grassland manuring) In man-managed grounds or a silvipastoral system, trees or shrubs (collectively called trub) are combined with livestock and. .. studies in tropical rangelands, in Sixth Int Rangeland Cong Proc., Queensland Australia Vol 1, 132–133 Singh, J.S., 19 76 Structure and function of tropical grassland vegetation of India Pol Ecol Stud 2:17 –34 Singh, J.S and Yadav, P.S., 1974 Seasonal variation in composition, plant biomass and net primary productivity of a tropical grassland at Kurukshetra, India Ecol Monogr 44:351 –3 76 Singh, J.S and. .. prerequisites Mechanistic and process-based uptake transfer and release functions of ecosystem level components (Figure 6. 2) and interlinked resource use efficiency must be worked out for understanding the mechanisms of component-component interactions Interaction of Trees and Grasses The interaction of trees and grasses is a kind of intergeneric interaction in which microclimate and soil are the two important... Riha, S.J., Ali, A.R., and Mwonga, S.M., 1989 The effects of trees on their physical, chemical and biological environments in a semi-arid savanna in Kenya J Appl Ecol 26( 3):1005 –1024 Billore, S.K and Mall L.P., 19 76 Nutrient composition and inventory in a tropical grassland Plant and Soil 45:509 –520 Bokhari, U.G and Singh, J.S., 1975 Standing state and cycling of nitrogen in soil-vegetation components... 142 1/13/01 10:51 AM Page 142 STRUCTURE AND FUNCTION IN AGROECOSYSTEMS DESIGN AND MANAGEMENT Shelton, H.M., 1990 Using legumes to sustain pasture systems J Aust Inst of Agric Sci 3(3):34 –40 Shiyomi, M., 1997 Utilization of biological interactions and matter cycling in agricultural ecosystems Innovative Strategies for Linking Agricultural and Environmental Education in Asian-Pacific Countries for the... gramineae family), and in some cases (such as in savannas) with woody perennials Invertebrates (including arthropods and microbes) and vertebrates (including livestock) also live together in grasslands Various interactions take place between the species (plants and animals) and within the species through the media of soil and microclimate and may exert favorable or adverse effects on each other and. .. productivity, nutrient status, and turnover have been studied by various workers in tropical grasslands (Singh, 19 76; Billore and Mall, 19 76; Singh and Yadav, 1974; Karunaichamy and Paliwal, 1995; Paliwal and Karunaichamy 1999) and temperate grasslands (Bokhari and Singh, 1975; and Sims and Singh; 1978) Secondary Productivity Tropical grasslands constitute a significant community type in the energy economy . 13045.4 3 265 .0 3395.2 4 164 .3 4204.3 Africa 2 963 .5 2 963 .5 892.7 883.5 60 9.5 64 1.3 Asia 267 9.0 267 9.0 68 6.4 792.1 169 7.0 1880.9 Brazil 845 .6 845 .6 170.1 185.0 224.3 2 36. 2 Australia 764 .4 764 .4 4 36. 3. (Coupland, 1979) have ade- quately dealt with the structure and function of the grasslands of India and the world, including an illustrative account of the decomposer kinetics in the grazing land. the biological interaction in tropical grassland ecosystems. 920103_CRC20_0904_CH 06 1/13/01 10:51 AM Page 115 1 16 STRUCTURE AND FUNCTION IN AGROECOSYSTEMS DESIGN AND MANAGEMENT ORIGIN Fossil record shows