Structure and Function in Agroecosystem Design and Management - Chapter 6 doc

126 Biophysical Interactions at the Ecosystem Level: Exploratory Studies at Iseilema Grasslands of Ujjain, India.. A survey of this literature points out that althoughmuch information is

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

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

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 occurringunderground In fact, these latter changes are more important when theimpact on the system is considered, such as changes in soil-water-energy, theexuberance and extinction of microbial populations, the growth and vanish-ing of roots, and other such related processes Having taken notice of themyriad changes taking place in response to the seemingly probabilisticchanges leading to a complexity, one needs to view the whole process as atotal system (Van Dyne et al., 1978) in view of biological interactions In thischapter, 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 atmany places, due to recurring biotic operations, such as grazing, fire, andscrapping 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 oforganic matter and the production processes Odum (1971) asserted that themost 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 thedetritus 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 ditions Singh and Yadava (1974), Sims et al., (1978), Sims and Singh (1971,1978a, 1978b, and 1978c) have presented illuminating accounts of the biomassstructure, productivity, and energy compartmental transfers, as well as theaccumulation 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 amodeling approach for the evaluation of the uptake, transfer and release ofthe system state variables Yadav and Singh (1977) have described a thoroughlegend of the grasslands of India, while others (Coupland, 1979) have ade-quately dealt with the structure and function of the grasslands of India andthe world, including an illustrative account of the decomposer kinetics in thegrazing land ecosystems A survey of this literature points out that althoughmuch information is available on production dynamics and the aspects of thegrazing land ecosystems, there is a wide lacuna in our understanding of thebiological interaction in tropical grassland ecosystems

Fossil record shows that tropical grasslands originated as long ago as 6 to

12 million years The environment remained in its pristine purity and niality as man stayed in the hunting and gathering stage However, manentered the pastoral age and domesticated animals and then graduallypassed 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 “breadbaskets” of the world exist on soils developed under centuries of grasslandcover Grasslands in tropics have mainly originated from the destruction ofpermanent woody vegetation and are thus bio-edaphic sub-climaxes.Tropical and subtropical grasslands are located in the plains and mountainswithin 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 theworld’s population (FAO, 1995) The extent of tropical grasslands and live-stock population is summarized in Table 6.1, which illustrates the livestockdependence on grasslands The number of livestock has increased, and at thesame time the area of grasslands has decreased around the world (except inBrazil), indicating intensification of grassland usage by livestock It is esti-mated that over 90% of the feed for livestock on a world-wide basis comesfrom grasslands/rangelands With continued human population growth,there will be increased demand for milk and meat, resulting in even moreintensive grassland utilization Greater intensity of grassland utilization willrequire more knowledge of the functional ecology and biological interactions

conge-in grassland ecosystems

Successional Levels

Every living being is surrounded by materials and forces that constituteits environment and through which it meets its needs Nothing can escape itsenvironment, no animal or plant can live completely sealed off from theworld, and all living things must make exchanges with their environment interms of energy, matter, and waste elimination All living beings are interde-pendent and must absorb energy, termed as natural resources, more or lesscontinuously to fuel their life process The grasslands are renewable naturalresources and are one of a number of seral phases of vegetation Their struc-ture is dynamic rather than static One ecological association follows uponand grows in consequence of its predecessor in a well-marked and orderlysequence 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 characteristicphases of the sere which may thus end at a subclimax rather than at its

Table 6.1 Land Area, Permanent Pastures, and Livestock Population of the

Tropical and Subtropical Countries*

Land area Permanent pastures Livestock*

* 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 ofvegetation 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 grazinganimals (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, themost important constraint affecting grassland is its extreme fragility Thismeans that the landscape, vegetation, and soil cover degrade much morequickly than in more favored habitats; fragility affects the biological system

and hence sustainability or, in ecological parlance, homeostasis—the dency of a biological system to resist change and remain at a stage of dynamicequilibrium or relative consistency This is because a grassland ecosystem iscapable of self regulation due to biological interactions as a law of nature.

ten-Diverse Grassland Communities

Most developing countries are in the tropics, where grasslands are themajor feed resources (over 40%) for livestock rearing Due to enormous bioticactivities, 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 based savannas are common in India Most of the Japanese grasslands repre-sent semi-natural grasslands created and maintained by man Around theworld, 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 alsodiverse heterogeneity in nature because of the great variation in climate, soil,and physiography Dabadghao and Shankarnarayan (1973) have identified

Bamboo-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 grasslandcommunities The grazing pressure is very high, 1 –4 ACU/ha, against thenormal 0.2–0.5 ACU/ha in the arid and semi-arid areas of India (Shankar andGupta, 1992)

BIODIVERSITY

The variety of all life forms—the different plants, animals, and ganisms, the genes they contain, and the ecosystems of which they form apart—is termed biological diversity or biodiversity (Wilson, 1992) Grasslandbiodiversity is not a fixed entity, but constantly changing; it is increased bygenetic change and evolutionary processes and reduced by extinction andhabitat degradation The concept emphasizes the interrelatedness of biomeand biological interactions Grassland biodiversity is also a limited and a

microor-Table 6.2 Tribes and Genera of the Family Gramineae (Grasses)

Andropogoneae Andropogon, Bothriochloa,Chrysopogon, Colix, Cymbopogon,

Dichanthium, Hemarthria, Heteropogon, Hyparthenia, Hyperthelia, Imperata, Ischaemum, Iseilema, Lasiurus, Saccharu, Sehima, Sorghum, Themeda, Trachypogon, Tripsacum, Vetiveria, Vossia, Zea

Eragrostideae Dactyloctenium, Diplachne, Eleusine, Eragrostis,Triodia

Digitaria, Echinochloa, Eriochloa, Hymenachne, Melinis, Panicum, Paspalidium, Paspelum, Pennisetum, Setaria, Spinifex, Stenotaphrum, Tricholaena, Urochloa

perishable natural resource It has three components, namely: species sity, community diversity, and ecosystem diversity

diver-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, ingeneral, is dominated by therophytes and cryptophytes (Singh and Yadav,1974) The preponderance of therophytes results from a strong periodicity inbiotope and biocoenosis The loss of a species reduces species diversity andthreatens 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 largetropical 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 distributionclosely 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 oftribes (Table 6.2) found in tropical grasslands, which are unevenly distrib-uted in world grasslands (Figure 6.1)

Figure 6.1 Percentage distribution of tribes/grass in World Grassland Ecosystem.

Indian tropical grasslands consist of 245 genera and 1256 species ofgrasses (Bor, 1960); out of these, 139 species are reported to be endemic(Mehra and Magoon, 1974) Indian grassland legumes consist of 167 generaand about 1150 species, including cultivated, introduced as wild species(Singh and Morrison, 1998)

Community Diversity

The International Biological Programme (IBP) analyzed world grasslandcommunities, including natural grasslands, tundras, deserts, savannas,prairies, steppes, and other grasslands derived from forests, and cautionedabout 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 ofnew herbivores, replacement of native grasses/legumes by exotics, deliber-ate incorporation of trees, etc Permanent pastures occupy approximately25% of the earth’s land area (Table 6.1): 3395 million hectares of permanentpastures of the world provide forage and habitat for some 4204 million live-stock In the tropical and subtropical regions of the world, approximately23% is grazing land communities (‘t Mannetje, 1978), mostly savannas withvarying proportions of trees and shrubs Many of the large grassland com-munities are climax formations determined by soil and climate; others are ofmore recent origin and have replaced forest communities destroyed mainly

by cutting and fire, and these have been maintained largely through grazinganimals (Barnard and Frankel, 1964) Hence, fire and grazing have been very important features associated with the community diversity Naturalcommunities converted into grasslands are greatly influenced by biologicalinteractions

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 ofgrazing animals Similarly, many of the world’s original forests have beenconverted to grasslands Many desert areas are also utilized seasonally forgrazing Collectively, about 40% of the earth’s ecosystem with normal spec-trum of tribes and genera of the family Gramineae (grasses) is used by grazinganimals The four main elements of grassland ecosystem, namely abiotic sub-stances, producer organisms, consumers, and decomposer organisms, havegreat diversity in world grasslands Living organisms (plants, animals, andmicroorganisms) are taken as a whole while studying interactions with thenonliving environment in the ecosystem It is mostly an open system compris-ing plants, animals, organic residues, atmospheric gases, water, and mineralsthat are involved together in the flow of energy and circulation of matter Aconceptual model of organic matter storage, flow, and biological interactionswhich help in nutrient cycling and CO2fertilization is shown in Figure 6.2 Theboxes in the figure represent organic matter accumulation, and the arrowsshow 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, soilnutrients, and climate A grassland ecosystem is inherently “leaky”: at a mini-mum, energy and nutrients move in and out More likely, individual organismsmove 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 ious pools such as the soil, litter, and urine A common type of interactionamongst different tropic levels and total quantity of mineral flow from source

var-to sink are depicted in Figure 6.2 Detailed analysis of mineral/energy reservesdescribes the system organization and provides a base for the study of mineralcycling/energy flow through the system and the biological groups responsiblefor transformations which will facilitate the grassland management in a sus-tainable manner The annual cycle of plant biomass accumulations and litterdecomposition has received much attention With the development of concepts

of ecosystem structure and function, many grassland ecologists assorted thecarbon fixation by grasses and its later circulation in the ecosystems

STRUCTURE OF TROPICAL GRASSLAND

Tropical natural grasslands structurally and physiognomically are acterized by mixed herbaceous plants (dominated by grasses), trees, and a

char-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 representingdisclimax have been derived after the destruction of forests and are main-tained due to regular biotic interference Such vegetation is normally termedsavanna (Moore, 1970) In the course of time, the grasslands have undergonesignificant changes, due to the human population pressure, in terms ofdeclining area, carrying capacity, and productivity Structure and function of

tropical grasslands need to be improved by enhancing the potential of logical interactions and matter cycling.

bio-Abiotic Characteristics

Tropical grasslands are characterized by a climate that shows distinct wetand dry (cyclical) seasonal patterns Mean annual precipitation in tropicaland subtropical grasslands usually ranges 600–1500 mm and the length ofactive growing season ranges 120–190 days (rainy season) Temperaturebecomes the controlling factor for biological interactions in a tropical grass-land ecosystem The mean monthly variation of temperature between thewarmer and colder seasons in a tropical area is 5°C; for every 100 m increase

in elevation there is a decline of 0.8°C in the mean annual temperature Thesoils of tropical grassland are highly leached, and there is rapid decay (due tohigh temperatures) with low levels of humus accumulation with reddish oryellowish color Abundant groups of microorganisms in tropical grasslandsoils are bacteria, actinomycetes, and fungi A number of different types ofdecomposer organisms are recognized on a functional basis (Clark and Paul,1970)

In order to consider abiotic characteristics from an ecological point ofview, Walter (1973) proposed the climate diagram which gives informationconcerning the mean temperature, precipitation, relative humidity, and aridseasons Based on the climate diagram, different ecological zones of tropicaland subtropical grasslands are abiotically characterized as semihumid, semi-arid, subarid, euarid, and perarid grasslands, depending on hot/wet/dryseason duration

Biotic Characteristics

If the grasslands are to be maintained as seral stages of ecological opment, the biotic components (producer, consumers, and decomposers)must interact with each other, at the expense of solar energy, into a form inwhich they are to be reused Producers, consumers, and decomposers arewell organized grazing and detritus food webs

devel-A biotic model (Figure 6.3) depicting biophagic and saprophagic ways describes the food web, and utilization of biological interactions and car-bon cycling in tropical interactions will lead to a sustainability of grazing landresources Producers in tropical grasslands are mainly graminoides (grasses

path-and sedges) of Andropogoneae, Paniceae, path-and Cyperaceae groups which often

furnish 90% contribution The fauna consists of invertebrate and vertebratepredators, small herbivores, and very few carnivores Microarthropods andmicrobes (mostly bacteria) comprise the group of developers which help inoperating the detritus food web In addition to the role of reducers anddecomposers, the microbes also play a vital role in biological nitrogen fixation

Consumer ll (Carnivores)

R1

R2

R3

Figure 6.3 Grazing (Biophagic pathway) and detritus (Saprophagic pathway) food

web in a tropical grassland ecosystem R1, R2, and R3represent the piratory losses from trophic levels.

res-Production Strategy

The grassland ecosystem contains a complex mixture of carbon nents in a continuous state of creation, transformation, and decomposition.This dynamic state is maintained through the ability of grasses (C3 and C4),forbs, shrubs, and trees in grassland to capture the solar radiation and utilize

compo-it to transform carbon dioxide (and water) into organic molecules of richdiversity This interaction between the living (plants) and nonliving (abiotic)environments is known as biophysical interaction Many interesting interac-tions between animals within the grassland system form feedback loopsrelated to the food chain (Figure 6.2) Animals (herbivores and carnivores) ofthe tropical grasslands vary from the lowly insects (invertebrates) to magnif-icent vertebrates Ants and termites are often abundant among the verte-brates, and the large mammal herbivores dominate, with predators makingonly a small contribution to the average annual biomass Where autotrophsare measured in thousands of kilogram biomass per hectare, the annual

standing crops are in the order of hundreds of grams per hectare Theaverage biomass of invertebrates below ground may be ten times that which

is above ground Based on studies of several types of grassland ecosystems.Wiegert and Evans (1967) concluded that (1) stable natural grasslands can beutilized to an extent approaching 0.3–0.45 range of herbivore ingestion/netprimary production ratios determined for managed grasslands; (2) the level

of utilization with the presence of large livestock, and (3) ecosystems nated by invertebrates may be exploited at very low levels, but secondaryproductivity is high when calculated per unit standing crop basis Where netprimary productivity is very high, the secondary productivity of invertebrateherbivore populations may be greater, on a per unit area basis, than that ofthe large mammal herbivore population In tropical grassland ecosystems,the large animal biomass is higher as compared to temperate grasslandecosystems Man’s domestic animals make up the greatest part of the largeanimal biomass in the developing tropics Much of the natural grasslandshave been replaced by man-managed rangelands and are deteriorating day

domi-by day because of erosion, recurring drought, and abusive grazing Bioticoperations also change the production strategy of tropical grasslands favor-ably It is thus essential to promote studies on biological interactions andcause-effect relationships operating among biotic organisms and abioticenvironmental variables (Shiyomi, 1997)

Primary Productivity

Synthesizing information and analyzing data on standing state biomass,energy flow, nutrient cycling, and primary productivity are of immense valuefor understanding biological interactions Figure 6.2 simulates the grasslandecosystem-level model used to explore the interactions of producers, herbi-vores, carnivores, and decomposers within an environment The biologicaland biophysical interactions of elevated CO2 and elevated solar radiationchange grassland production, decomposition rates, and nutrient uptake, andtransfer and release functions It is one of several large models that derive theinteractions in the ecosystem level model (ELM) By computing differentcomponents and functions of ELM and their relationship with drivingvariables (i.e., daily precipitation, weekly max/min temperatures, windspeed, relative humidity, monthly mean soil temperature) and state variables(i.e., soil and inorganic ammonium, nitrate data, and growth parameters),one can predict grassland ecosystem dynamics that could be attended bychanges in temperature, elevated CO2concentrations, changes in precipita-tion, and ultimately changes in grassland productivity Energy fixed by theproducer component as total net primary production is dissipated to herbi-vores—carnivores—decomposer via litter and root decomposition The pro-ducers also absorb nutrients from soil and incorporate these in their biomass

These nutrients are then transferred through dry matter to consumers anddecomposers and ultimately are released to soil through biological phenom-ena Primary productivity, nutrient status, and turnover have been studied

by various workers in tropical grasslands (Singh, 1976; Billore and Mall, 1976;Singh and Yadav, 1974; Karunaichamy and Paliwal, 1995; Paliwal andKarunaichamy 1999) and temperate grasslands (Bokhari and Singh, 1975;and Sims and Singh; 1978)

Secondary Productivity

Tropical grasslands constitute a significant community type in the energyeconomy of the biosphere Grassland systems are managed primarily for thedevelopment of plant materials for the production of livestock (cattle, sheep,goats, and other herbivores) utilized by man as food or byproducts Secondaryproductivity of grasslands, defined as the calorific equivalent of consumerprotoplasm produced per unit time, is dependent on primary productivity ofthe system and also on the assimilation/ingestion (a/i) and/or produc-tion/assimilation (ps/a) efficiency of the consumers Consequently, the com-munity with the highest primary productivity possesses the capabilities forthe greatest secondary productivity The degree of utilization of primary pro-duction by herbivores (grazing pathway) and its further ingestion by carni-vores and decomposer (detritus pathway) are two different forms of energyflows (Figure 6.3) Based on the population of consumers, the a/i efficiencyand ps/a efficiency may vary independently with each other Odum et al.(1962) noted that grasslands can be utilized sustainably to an extent of herbi-vore ingestion/net primary production ratio of 0.3 to 0.45 Surprisingly,information on the sustainable utilization of tropical grasslands with specialreference to optimization of consumers’ interactions is meager Studies areneeded on complex, indirect biological interactions in tropical grasslandecosystems

BIOLOGICAL INTERACTIONS

The literal meaning of “interaction” is reciprocal action or influence oneach other In grassland ecosystems, various types of grasses (different tribesand species) are grown in close proximity to one another and also to other

herbaceous plants (other than the gramineae family), and in some cases (such

as in savannas) with woody perennials Invertebrates (including arthropodsand microbes) and vertebrates (including livestock) also live together ingrasslands Various interactions take place between the species (plants andanimals) and within the species through the media of soil and microclimateand may exert favorable or adverse effects on each other and also on envi-ronment Nair (1993), Ong and Huxley (1997), and Rao et al (1997) discussed

various tree-crop and biophysical interactions in agroforestry These tions take place both above- and belowground and include a complete set ofsystems relating to radiation exchange, water and nutrient budget, and car-bon budget Tropical grasslands have all kinds of interactions categoricallydefined as (1) physical environment affecting biological environment andvice versa, (2) interspecific and intraspecific interaction, (3) biophysical inter-action, (4) tree/grass interaction, (5) grass/legume interaction, and (6)tree/grass-livestock interaction.

interac-Biophysical Interactions at the Ecosystem Level: Exploratory Studies

at Iseilema Grasslands of Ujjain, India

The organic matter budget has been intensively studied in Iseilemagrassland community at Ujjain, located tropically (23°11 N and 75°43 E) inIndia The grasslands of Ujjain are tropical and are seral in nature, owingtheir origin to the biotic perturbations The driving variables of the siteincluded precipitation (AR), humidity (ARH), temperature (AT), and solarradiation (ASR) The climate, essentially monsoonic, is characterized by threedistinct seasons in a year—rainy, winter, and summer seasons The climaticdata of the area revealed the average annual rainfall during the last 10 years

to be 928 mm, while the mean minimum and mean maximum air ture during the same period ranged from 24°C to 32°C and 12°C to 16°C,respectively Likewise, the mean relative humidity of the area under investi-gation was found to be 41.12% at 4.30 p.m while 70.25% at 8.30 a.m Themonsoonic climate of the area is paralleled by dry subhumid and megather-mal conditions The hydrological processes model revealed a little water sur-plus during the period of the investigation Biotic state variables revealed asignificant positive correlation between these variables and the total viablemicrobial populations in the grazing lands under study Having observedduring the different seasons significant variations in the edaphic variables,such as soil moisture, bulk density, pH, organic matter, and high amounts oforganic phosphate content of the soil, it is concluded that the soils of the pres-ent study exhibit a greater degree of fertility

tempera-As a sequel to a detailed study of the organic matter dynamics and otheraspects in these grazing lands, a brief investigation of the community struc-ture and floristic composition of these grasslands was made It revealed that

there were 42 species: 30 were grass species (most were Andropogoneae and

Paniceae), 5 were legumes, and 7 were species of forbs Iseilema had the

est important value index among the grasses, while Indigofera had the

high-est important value index among the legumes

The above- and belowground vegetational productive patterns tuted the input parameters, and the output variables comprised root decom-position, litter decomposition and the total soil respiration The productiondynamics patterns were evaluated by taking the biomass estimation and the