ECOLOGICAL DIVERSITYEcosystem diversityrefers to the diversity of a place at the level ofecosystems. Ecosystem diversity can also refer to the variety of ecosystems present in a biosphere, the variety of species and ecological processes that occur in different physical settings, variety of ecosystems in a biosphere orthe variety of species and ecological processes that occur in different physical settings.Biological diversity means the variability among living organisms from all sources including inter alia, marine, and other aquatic ecosystems and the ecological complexes of which they are part this includes diversity within species, between species, and of ecosystems. One way to gain an appreciation of the worlds most widely accepted meaning is to consider its evolution. In 1980, the term ecological diversity was used to describe the presumable ecological richness. Ecological diversityis the degree of variation ofecosystem present on the earth. It seems to be the result of the warm climate and high primary productivity.Marine biodiversity tends to be highest along coasts in the Western Pacific, where sea surface temperature is highest and in mid-latitudinal band in all oceans. It generally tends to cluster in hotspots,and has been increasing through time but will be likely to slow in the future. Rapid environmental changes typically causemass extinctions The earliest evidences forlife on Eartharegraphitefound to bebiogenicin 3.7 billion-year-oldmeta sedimentary rocksdiscovered inWestern Greenlandandmicrobial matfossilsfound in 3.48 billion-year-oldsand stone discovered inWestern Australia. Ecosystems are the combination of communities of living things with the physical environment in which they live. There are many different kinds of ecosystems, from deserts to mountain slopes, the ocean floor to the Antarctic, with coral reefs and rainforests being amongst the richest of these systems.Each ecosystem provides many different kinds of habitats or living places. The living things and the non-living environment (earth forms, soil, rocks and water) interact constantly and in complex ways that change over time, with no two ecosystems being the same.Although ecosystems are ever-changing and complex, some universal principles apply. One of these is that matter constantly cycles and recycles. Another principle is that energy moves through the cycle, being used, absorbed and stored.For example, forests act as filters for air, absorbing carbon dioxide and releasing oxygen. Seas are the great stabilizers of climates, with warm currents moderating temperatures on the land masses they pass. Mangroves and sea-grass beds are the nurseries for marine creatures. While the sun is a constant source of Earth's energy, energy is also available from geothermal processes. So while each ecosystem generates its own relationships, the Earth's environments are interrelated they all rely on the sun and the Earth's oxygen and water to survive.You can begin to appreciate how the elements in each ecosystem are connected to each other and the diversity that exists amongst Earth's ecosystems. Maintaining this ecological diversity isimportantfor the health of the planet.Climate change and other human-driven (anthropogenic) environmental changes will continue to cause biodiversity loss in the coming decades. In addition to the high rates of species extinctions already occurring worldwide. Ecological diversity is a term that can be used to describe ecological diversity at a variety of different scales, but in this context we will focus on the description of ecosystem diversity. Species play essential roles in ecosystems, so local and global species losses could threaten the stability of the ecosystem services on which humans depend. For example, plant species harness the energy of the sun to fix carbon through photosynthesis, and this essential biological process provides the base of the food chain for myriad animal consumers. At the ecosystem level, the total growth of all plant species is termed primary production, and as we'll see in this article communities composed of different numbers and combinations of plant species can have very different rates of primary production. This fundamental metric of ecosystem function has relevance for global food supply and for rates of climate change because primary production reflects the rate at which carbon dioxide (a greenhouse gas) is removed from the atmosphere. There is currently great concern about the stability of both natural and human-managed ecosystems, particularly given the myriad global changes already occurring. Stability can be defined in several ways, but the most intuitive definition of a stable system is one having low variability (i.e., little deviation from its average state) despite shifting environmental conditions. This is often termed the resistance of a system. Resilience is a somewhat different aspect of stability indicating the ability of an ecosystem to return to its original state following a disturbance or other perturbation. Most research on the relationship between ecosystem diversity and stability has focused on species richness, it is variation in species composition that provides the mechanistic basis to explain the relationship between species richness and ecosystem functioning. Species differ from one another in their resource use, environmental tolerances, and interactions with other species, such that species composition has a major influence on ecosystem functioning and stability.The traits that characterize the ecological function of a species are termed functional traits, and species that share similar suites of traits are often categorized together into functional groups. When species from different functional groups occur together, they can exhibit complementary resource-use, meaning that they use different resources or use the same resources at different times. For example, two animal predators may consume different prey items, so they are less likely to compete with one another, allowing higher total biomass of predators in the system. In the case of plants, all species may utilize the same suite of resources (space, light, water, soil nutrients, etc.) but at different times during the growing season for example, early- and late-season grasses in prairies. Increasing species diversity can influence ecosystem functions such as productivity by increasing the likelihood that species will use complementary resources and can also increase the likelihood that a particularly productive or efficient species is present in the community. For example, high plant diversity can lead to increased ecosystem productivity by more completely, and/or efficiently, exploiting soil resources (e.g., nutrients, water). While primary production is the ecosystem function most referred to in this article, other ecosystem functions, such as decomposition and nutrient turnover, are also influenced by species diversity and particular species traits.Theoretical models suggest that there could be multiple relationships between diversity and stability, depending on how we define stability. Stability can be defined at the ecosystem level for example, a rancher might be interested in the ability of a grassland ecosystem to maintain primary production for cattle forage across several years that may vary in their average temperature and precipitation. Plant community can stabilize ecosystem processes if species vary in their responses to environmental fluctuations such that an increased abundance of one species can compensate for the decreased abundance of another. Biologically diverse communities are also more likely to contain species that confer resilience to that ecosystem because as a community accumulates species, there is a higher chance of any one of them having traits that enable them to adapt to a changing environment. Such species could buffer the system against the loss of other species. In this situation, species identity and particular species traits are the driving force stabilizing the system rather than species richnessA wealth of research into the relationships among diversity, stability, and ecosystem functioning has been conducted in recent years. The first experiments to measure the relationship between diversity and stability manipulated diversity in aquatic microcosms miniature experimental ecosystems containing four or more trophic levels, including primary producers, primary and secondary consumers, and decomposers. These experiments found that species diversity conferred spatial and temporal stability on several ecosystem functions. Stability was conferred by species richness, both within and among functional groups. When there is more than one species with a similar ecological role in a system, they are sometimes considered "functionally redundant." But these experiments show that having functionally redundant species may play an important role in ensuring ecosystem stability when individual species are lost due to environmental changes, such as climate change.More recently, scientists have examined the importance of plant diversity for ecosystem stability in terrestrial ecosystems, especially grasslands where the dominant vegetation lies low to the ground and is easy to manipulate experimentally. In 1995, David Tilman and colleagues established 168 experimental plots in the Cedar Creek Ecosystem Science Reserve, each 9 x 9 m in size, and seeded them with 1, 2, 4, 8 or 16 species drawn randomly from a pool of 18 possible perennial plant species. Plots were weeded to prevent new species invasion and ecosystem stability was measured as the stability of primary production over time. Over the ten years that data were collected, there was significant inter-annual variation in climate, and the researchers found that more diverse plots had more stable production over time. In contrast, population stability declined in more diverse plots. These experimental findings are consistent with the theory described in the prior section, predicting that increasing species diversity would be positively correlated with increasing stability at the ecosystem-level and negatively correlated with species-level stability due to declining population sizes of individual species.Experiments manipulating diversity have been criticized because of their small spatial and short time scales. In a 24-year study of naturally assembled Inner Mongolia grassland vegetation, scientists observed variation in the biomass of species, functional groups, and the whole community in response to strong inter-annual variation in growing-season precipitation. They found that while the abundance of individual species fluctuated, species within particular functional groups tended to respond differently such that a decrease in the abundance of one species was compensated for by an increase in the abundance of another. This compensation stabilized the biomass productivity of the whole community in a fluctuating environment. These findings demonstrate that local species richness both within and among functional groups confers stability on ecosystem processes in naturally assembled communities.Experiments in aquatic ecosystems have also shown that large-scale processes play a significant role in stabilizing ecosystems. A whole-lake acidification experiment in Canada found that although species diversity declined as a result of acidification, species composition changed significantly and ecosystem function was maintained. This suggests that given sufficient time and appropriate dispersal mechanisms, new species can colonize communities from the regional species pool and compensate for those species that are locally lost. This observation emphasizes the importance of maintaining connectivity among natural habitats as they experience environmental changes.Evidence from multiple ecosystems at a variety of temporal and spatial scales, suggests that biological diversity acts to stabilize ecosystem functioning in the face of environmental fluctuation. Variation among species in their response to such fluctuation is an essential requirement for ecosystem stability, as is the presence of species that can compensate for the function of species that are lost. While much of the evidence presented here has focused on the consequences of changes in species diversity on primary production in natural ecosystems, recent research has found similar relationships between species diversity and ecosystem productivity in human-managed ecosystems.

TYPES OF ECOSYSTEM DIVERSITY:Some important type of Ecosystem diversity are discussed below:1. AQUATIC ECOSYSTEM:Anaquatic ecosystemis anecosystemin abody of water.Communitiesoforganismsthat are dependent on each other and on their environment live in aquatic ecosystems. The two main types of aquatic ecosystems aremarine ecosystemsandfreshwater ecosystems. i. MARINE ECOSYSTEM:Marine ecosystems cover approximately 71% of the Earth's surface and contain approximately 97% of the planet's water. They generate 32% of the world's netprimary production.[1]They are distinguished from freshwater ecosystems by the presence of dissolved compounds, especiallysalts, in the water. Approximately 85% of the dissolved materials inseawateraresodiumandchlorine. Seawater has an average salinity of 35parts per thousand(ppt) of water. Actual salinity varies among different marine ecosystems. Marine ecosystems can be divided into many zones depending upon water depth and shoreline features. Theoceaniczone is the vast open part of the ocean where animals such as whales, sharks, and tuna live. Thebenthiczone consists of substrates below water where many invertebrates live. Theintertidalzone is the area between high and low tides; in this figure it is termed the littoral zone. Other near-shore (neritic) zones can includeestuaries,salt marshes,coral reefs,lagoonsandmangroveswamps. In the deep water,hydrothermal ventsmay occur wherechemosyntheticsulfurbacteriaform the base of the food web.Classesof organisms found in marine ecosystems includebrown algae,dinoflagellates,corals,cephalopods,echinoderms, andsharks. Fishes caught in marine ecosystems are the biggest source of commercial foods obtained from wild populations.[1]Environmental problems concerning marine ecosystems include unsustainable exploitation of marine resources (for exampleoverfishingof certain species),marine pollution,climate change, and building on coastal areas.[1]ii. FRESHWATER ECOSYSTEM:Freshwater ecosystems cover 0.80% of the Earth's surface and inhabit 0.009% of its total water. They generate nearly 3% of its net primary production.[1]Freshwater ecosystems contain 41% of the world's known fish species.[3]There are three basic types of freshwater ecosystems: Lentic: slow moving water, includingpools,ponds, andlakes. Lotic: faster moving water, for examplestreamsandrivers. Wetlands: areas where the soil is saturated or inundated for at least part of the time.

LENTICLake ecosystems can be divided into zones. One common system divides lakes into three zones. The first, the littoral zone, is the shallow zone near the shore. This is where rooted wetland plants occur. The offshore is divided into two further zones, an open water zone and a deep water zone. In the open water zone (or photic zone) sunlight supports photosynthetic algae, and the species that feed upon them. In the deep water zone, sunlight is not available and the food web is based on detritus entering from the littoral and photic zones. Some systems use other names. The off shore areas may be called the pelagic zone, and the aphotic zone may be called the profundal zone. Inland from the littoral zone one can also frequently identify a riparian zone which has plants still affected by the presence of the lakethis can include effects from windfalls, spring flooding, and winter ice damage. The production of the lake as a whole is the result of production from plants growing in the littoral zone, combined with production from plankton growing in the open water.Wetlands can be part of the lentic system, as they form naturally along most lakeshores, the width of the wetland and littoral zone being dependent upon the slope of the shoreline and the amount of natural change in water levels, within and among years. Often dead trees accumulate in this zone, either from windfalls on the shore or logs transported to the site during floods. This woody debris provides important habitat for fish and nesting birds, as well as protecting shorelines from erosion,Two important subclasses of lakes areponds, which typically are small lakes that intergrade with wetlands, and waterreservoirs. Over long periods of time, lakes, or bays within them, may gradually become enriched by nutrients and slowly fill in with organic sediments, a process called succession. When humans use the watershed, the volumes of sediment entering the lake can accelerate this process. The addition of sediments and nutrients to a lake is known as eutrophication. PONDSPonds are small bodies of freshwater with shallow and still water,marsh, andaquatic plants.[5]They can be further divided into four zones: vegetation zone, open water, bottom mud and surface film.[6]The size and depth of ponds often varies greatly with the time of year; many ponds are produced by spring flooding from rivers. Food webs are based both on free-floatingalgaeand uponaquatic plants. There is usually a diverse array of aquatic life, with a few examples including algae, snails, fish, beetles, water bugs, frogs, turtles, otters and muskrats. Top predators may include large fish, herons, or alligators. Since fish are a major predator upon amphibian larvae, ponds that dry up each year, thereby killing resident fish, provide important refugia for amphibian breeding.[7]Ponds that dry up completely each year are often known asvernal pools. Some ponds are produced by animal activity, including alligator holes and beaver ponds, and these add important diversity to landscapes.

LOTICThe major zones in river ecosystems are determined by the river bed's gradient or by the velocity of the current. Faster moving turbulent water typically contains greater concentrations of dissolved oxygen, which supports greater biodiversity than the slow moving water of pools. These distinctions forms the basis for the division of rivers intoupland and lowlandrivers. The food base of streams within riparian forests is mostly derived from the trees, but wider streams and those that lack acanopyderive the majority of their food base from algae.Anadromous fishare also an important source of nutrients. Environmental threats to rivers include loss of water, dams, chemical pollution andintroduced species.A dam produces negative effects that continue down the watershed. The most important negative effects are the reduction of spring flooding, which damages wetlands, and the retention of sediment, which leads to loss of deltaic wetlands. WETLANDSWetlands are dominated byvascular plantsthat have adapted to saturated soil. There are four main types of wetlands: swamp, marsh, fen and bog (both fens and bogs are types ofmire). Wetlands are the most productive natural ecosystems in the world because of the proximity of water and soil. Hence they support large numbers of plant and animal species. Due to their productivity, wetlands are often converted into dry land withdykesanddrainsand used for agricultural purposes. The construction of dykes, and dams, has negative consequences for individual wetlands and entire watersheds.Their closeness to lakes and rivers means that they are often developed for human settlement.Once settlements are constructed and protected by dykes, the settlements then become vulnerable to land subsidence and ever increasing risk of flooding.The Louisiana coast around New Orleans is a well-known example:the Danube Delta in Europe is another. 2. TERRESTRIAL ECOSYSTEM:Aterrestrial ecosystemis an ecosystem found only on landforms. Six primary terrestrial ecosystems exist:tundra,taiga,temperate deciduous forest,tropical rain forest,grasslandanddesert. A community of organisms and their environment that occurs on the land masses of continents and islands. Terrestrial ecosystems are distinguished from aquatic ecosystems by the lower availability of water and the consequent importance of water as a limiting factor. Terrestrial ecosystems are characterized by greater temperature fluctuations on both a diurnal and seasonal basis than occur in aquatic ecosystems in similar climates. The availability of light is greater in terrestrial ecosystems than in aquatic ecosystems because the atmosphere is more transparent in land than in water. Gases are more available in terrestrial ecosystems than in aquatic ecosystems. Those gases include carbon dioxide that serves as a substrate for photosynthesis, oxygen that serves as a substrate in aerobic respiration, and nitrogen that serves as a substrate for nitrogen fixation. Terrestrial environments are segmented into a subterranean portion from which most water and ions are obtained, and an atmospheric portion from which gases are obtained and where the physical energy of light is transformed into the organic energy of carbon-carbon bonds through the process of photosynthesis.Terrestrial ecosystems occupy 55,660,000 mi2 (144,150,000 km2), or 28.2%, of Earth's surface. Although they are comparatively recent in the history of life (the first terrestrial organisms appeared in the Silurian Period, about 425 million years ago) and occupy a much smaller portion of Earth's surface than marine ecosystems, terrestrial ecosystems have been a major site of adaptive radiation of both plants and animals. Major plant taxa in terrestrial ecosystems are members of the division Magnoliophyta (flowering plants), of which there are about 275,000 species, and the division Pinophyta (conifers), of which there are about 500 species. Members of the division Bryophyta (mosses and liverworts), of which there are about 24,000 species, are also important in some terrestrial ecosystems. Major animal taxa in terrestrial ecosystems include the classes Insecta (insects) with about 900,000 species, Aves (birds) with 8500 species, and Mammalia (mammals) with approximately 4100 species.Organisms in terrestrial ecosystems have adaptations that allow them to obtain water when the entire body is no longer bathed in that fluid, means of transporting the water from limited sites of acquisition to the rest of the body, and means of preventing the evaporation of water from body surfaces. They also have traits that provide body support in the atmosphere, a much less buoyant medium than water, and other traits that render them capable of withstanding the extremes of temperature, wind, and humidity that characterize terrestrial ecosystems. Finally, the organisms in terrestrial ecosystems have evolved many methods of transporting gametes in environments where fluid flow is much less effective as a transport medium.The organisms in terrestrial ecosystems are integrated into a functional unit by specific, dynamic relationships due to the coupled processes of energy and chemical flow. Those relationships can be summarized by schematic diagrams of trophic webs, which place organisms according to their feeding relationships. The base of the food web is occupied by green plants, which are the only organisms capable of utilizing the energy of the Sun and inorganic nutrients obtained from the soil to produce organic molecules. Terrestrial food webs can be broken into two segments based on the status of the plant material that enters them. Grazing food webs are associated with the consumption of living plant material by herbivores. Detritus food webs are associated with the consumption of dead plant material by detritivores. The relative importance of those two types of food webs varies considerably in different types of terrestrial ecosystems. Grazing food webs are more important in grasslands, where over half of net primary productivity may be consumed by herbivores. Detritus food webs are more important in forests, where less than 5% of net primary productivity may be consumed by herbivores.There is one type of extensive terrestrial ecosystem due solely to human activities and eight types that are natural ecosystems. Those natural ecosystems reflect the variation of precipitation and temperature over Earth's surface. The smallest land areas are occupied by tundra and temperate grassland ecosystems, and the largest land area is occupied by tropical forest. The most productive ecosystems are temperate and tropical forests, and the least productive are deserts and tundras. Cultivated lands, which together with grasslands and savannas utilized for grazing are referred to as agroecosystems, are of intermediate extent and productivity. Because of both their areal extent and their high average productivity, tropical forests are the most productive of all terrestrial ecosystems, contributing 45% of total estimated net primary productivity on land. The primary types of terrestrial ecosystems have been described belowi. TUNDRAInphysical geography, atundrais abiomewhere thetreegrowth is hindered by low temperatures and short growing seasons. The termtundracomes through, "treeless mountain tract". There are three types of tundra:arctic tundra, alpine tundra, andAntarctic tundra. In a tundra, thevegetationis composed of dwarfshrubs,sedgesandgrasses, mosses, andlichens. Scattered trees grow in some tundras. Theecotone(or ecological boundary region) between the tundra and the forest is known as thetree lineor timberline.ii. ARCTICArctic tundra occurs in the farNorthern Hemisphere, north of thetaigabelt. The word "tundra" usually refers only to the areas where the subsoil ispermafrost, or permanently frozen soil. (It may also refer to the treeless plain in general, so that northernSpmiwould be included.) Permafrost tundra includes vast areas of northernRussiaandCanada. The polar tundra is home to several peoples who are mostly nomadicreindeer herders, such as theNganasanandNenetsin the permafrost areaThe tundra is a very windy area, with winds often blowing upwards of 50100km/h (3060mph). However, in terms of precipitation, it is desert-like, with only about 1525cm (610in) falling per year (the summer is typically the season of maximum precipitation). Although precipitation is light, evaporation is also relatively minimal. During the summer, the permafrost thaws just enough to let plants grow and reproduce, but because the ground below this is frozen, the water cannot sink any lower, and so the water forms the lakes and marshes found during the summer months. There is a natural pattern of accumulation of fuel andwildfirewhich varies depending on the nature of vegetation and terrain. Research in Alaska has shown fire-event return intervals, (FRIs) that typically vary from 150 to 200 years with dryer lowland areas burning more frequently than wetter highland areas. Thebiodiversityof the tundras is low: 1,700 species of vascular plants and only 48 species of land mammals can be found, although millions of birds migrate there each year for the marshes. There are also a few fish species such as theflatfish. There are few species with large populations. Notable animals in the Arctic tundra includecaribou(reindeer),musk ox,arctic hare,arctic fox,snowy owl,lemmings, andpolar bears(only near ocean-fed bodies of water). Tundra is largely devoid ofpoikilothermssuch as frogs or lizards.Due to the harsh climate of the Arctic tundra, regions of this kind have seen little human activity, even though they are sometimes rich in natural resources such asoilanduranium. In recent times this has begun to change in Alaska,Russia, and some other parts of the world.

iii. ANTARCTICAntarctic tundra occurs onAntarcticaand on several Antarctic and Sub-Antarctic islands, includingSouth Georgia and the South Sandwich Islandsand theKerguelen Islands. Most of Antarctica is too cold and dry to support vegetation, and most of the continent is covered by ice fields. However, some portions of the continent, particularly theAntarctic Peninsula, have areas of rocky soil that support plant life. The flora presently consists of around 300400 lichens, 100 mosses, 25liverworts, and around 700 terrestrial and aquatic algae species, which live on the areas of exposed rock and soil around the shore of the continent. Antarctica's two flowering plant species, the Antarctic hair grass(Deschampsia antarctica) andAntarctic pearlwort(Colobanthus quitensis), are found on the northern and western parts of the Antarctic Peninsula. In contrast with the Arctic tundra, the Antarctic tundra lacks a large mammal fauna, mostly due to its physical isolation from the other continents. Sea mammals and sea birds, includingsealsandpenguins, inhabit areas near the shore, and some small mammals, likerabbitsandcats, have been introduced by humans to some of the sub Antarctic islands. TheAntipodes Sub Antarctic Islands tundraeco regionincludes theBounty Islands,Auckland Islands, Antipodes Islands, theCampbell Island group, andMacquarie Island.[13]Species endemic to this eco region includeNematoceras dienemumandNematoceras sulcatum, the only Sub Antarctic orchids; theroyal penguin; and the Antipodean albatross. The flora and fauna of Antarctica and the Antarctic Islands (south of 60 south latitude) are protected by theAntarctic Treaty. iv. ALPINEAlpine tundra does not contain trees because the climate and soils at high altitude block tree growth. Alpine tundra is distinguished from arctic tundra in that alpine tundra typically does not have permafrost, and alpine soils are generally better drained than arctic soils. Alpine tundra transitions to subalpine forests below thetree line; stunted forests occurring at the forest-tundraecotoneare known asKrummholz.Alpine tundra occurs in mountains worldwide. The flora of the alpine tundra is characterized by dwarf shrubs close to the ground. The cold climate of the alpine tundra is caused by the low air pressure, and is similar topolar climate.v. TAIGATaiga, also known asboreal forest, is abiomecharacterized byconiferousforestsconsisting mostly ofpines,sprucesandlarches.The taiga is the world's largestterrestrialbiome. InNorth Americait covers most of inlandCanadaandAlaskaas well as parts of the extreme northern continental United States (northernMinnesotathrough the Upper Peninsula of MichigantoUpstate New Yorkand northernNew England) and is known as theNorthwoods.InEurasia, it covers most ofSweden,Finland, much ofNorway, some lowland/coastal areas of Iceland, much ofRussiafromKareliain the west to thePacific Ocean(including much ofSiberia), and areas of northernKazakhstan, northernMongolia, and northernJapan(on the island ofHokkaid). However, the main tree species, the length of the growing season and summer temperatures vary. For example, the taiga of North America mostly consists of spruces;ScandinavianandFinnishtaiga consists of a mix of spruce, pines andbirch; Russian taiga has spruces, pines and larches depending on the region, the Eastern Siberian taiga being a vast larch forest.A different use of the term taiga is often encountered in the English language, with "boreal forest" used in the United States andCanadato refer to only the more southerly part of the biome, withtaigaused to describe the more barren areas of the northernmost part of the biome approaching thetree lineand thetundrabiome. Hoffman (1958) discusses the origin of this differential use in North America and why it is an inappropriate differentiation of the Russian term.vi. TEMPERATURE DECIDIOUS FORESTTemperate deciduous forestsortemperate broad-leaf forestsare dominated by trees that lose their leaves each year. They are found in areas with warm, moist summers alternate and mild winters. The three major areas of this forest type occur in the northern hemisphere: easternNorth America,eastern Asia, andEurope. Smaller areas occur inAustralasiaand southernSouth America. Examples of typical trees includeoak,maple, beech, andelm. The diversity of tree species is higher in regions where the winter is milder, and also in mountainous regions that provide an array of soil types and microclimates.One of the world's great protected examples of this forest type is found inGreat Smoky Mountains National Park.vii. TROPICAL RAIN FORESTTropical rainforestscan be characterized in two words: warm and wet. Mean monthly temperatures exceed 18C (64F) during all months of the year. Average annual rainfall is no less than 168cm (66in) and can exceed 1,000cm (390in) although it typically lies between 175cm (69in) and 200cm (79in). This high level of precipitation often results in poor soils due to leaching of soluble nutrients.Tropical rainforests exhibit high levels of biodiversity. Around 40% to 75% of all bioticspeciesareindigenousto the rainforests. Rainforests are home to half of all the living animal and plant species on the planet. Two-thirds of all flowering plants can be found in rainforests. A single hectare of rainforest may contain 42,000 different species of insect, up to 807 trees of 313 species and 1,500 species of higher plants. Tropical rainforests have been called the "world's largest pharmacy", because over one quarter of naturalmedicineshave been discovered within them. It is likely that there may be many millions of species of plants, insects and microorganismsstill undiscovered in tropical rainforests.Tropical rainforests are among the most threatened ecosystems globally due to large-scale fragmentation due to human activity.Habitat fragmentationcaused by geological processes such as volcanism and climate change occurred in the past, and have been identified as important drivers of speciation. However, fast human driven habitat destruction is suspected to be one of the major causes of species extinction. Tropical rain forests have been subjected to heavyloggingandagricultural clearancethroughout the 20th century, and the area covered by rainforests around the world is rapidly shrinking.viii. GRASSLANDGrasslandsare areas where thevegetationis dominated bygrasses(Poaceae), however sedge (Cyperaceae) and rush (Juncaceae) families can also be found. Grasslands occur naturally on all continents exceptAntarctica. Grasslands are found in mosteco-regionsof theEarth. For example there are fiveterrestrial eco-regionclassifications (subdivisions) of thetemperate grasslands, savannas, and shrub landsbiome('ecosystem'), which is one of eightterrestrial eco zonesof the Earth's surface.ix. DESERT:Adesertis a barren area of land where littleprecipitationoccurs and consequently living conditions are hostile for plant and animal life. The lack of vegetation exposes the unprotected surface of the ground to the processes ofdenudation. About one third of the land surface of the world isaridor semi-arid. This includes much of the Polar Regions where little precipitation occurs and which are sometimes called "cold deserts". Deserts can be classified by the amount of precipitation that falls, by the temperature that prevails, by the causes of desertification or by their geographical location.Deserts are formed byweatheringprocesses as large variations in temperature between day and night put strains on the rocks which consequently break in pieces. Although rain seldom occurs in deserts, there are occasional downpours that can result in flash floods. Rain falling on hot rocks can cause them to shatter and the resulting fragments and rubble strewn over the desert floor is further eroded by the wind. This picks up particles of sand and dust and wafts them aloft in sand ordust storms. Wind-blown sand grains striking any solid object in their path can abrade the surface. Rocks are smoothed down, and the wind sorts sand into uniform deposits. The grains end up as level sheets of sand or are piled high in billowing sand dunes. Other deserts are flat, stonyplainswhere all the fine material has been blown away and the surface consists of amosaicof smooth stones. These areas are known asdesert pavementsand little furthererosiontakes place. Other desert features include rock outcrops, exposed bedrock and clays once deposited by flowing water. Temporary lakes may form and salt pans may be left when waters evaporate. There may be underground sources of water in the form of springs and from aquifers. Where these are found,oasescan occur.Plants and animals living in the desert need special adaptations to survive in the harsh environment. Plants tend to be tough and wiry with small or no leaves, water-resistantcuticlesand often spines to deterherbivory. Some annual plantsgerminate, bloom and die in the course of a few weeks after rainfall while other long-lived plants survive for years and have deep root systems able to tap underground moisture.

IMPORTANCE OF ECOSYSTEM DIVERSITY:At the ecosystem level, biodiversity provides the conditions and drives the processes that sustain the global economy and our very survival as a species. The benefits and services provided by ecosystems include:

1. GENERATION OF SOILS AND MAINTENANCE OF SOIL QUALITYThe activities of microbial and animal species including bacteria, algae, fungi, mites, millipedes and worms condition soils, break down organic matter, and release essential nutrients to plants. These processes play a key role in the cycling of such crucial elements as nitrogen, carbon and phosphorous between the living and non-living parts of the biosphere.2. MAINTENANCE OF AIR QUALITYPlant species purify the air and regulate the composition of the atmosphere, recycling vital oxygen and filtering harmful particles resulting from industrial activities.3. MAINTENANCE OF WATER QUALITYWetland ecosystems (swamps, marshes, etc.) absorb and recycle essential nutrients, treat sewage, and cleanse wastes. In estuaries, molluscs remove nutrients from the water, helping to prevent nutrient over-enrichment and its attendant problems, such as eutrophication arising from fertilizer run-off. Trees and forest soils purify water as it flows through forest ecosystems. In preventing soils from being washed away, forests also prevent the harmful siltation of rivers and reservoirs that may arise from erosion and landslides.4. PEST CONTROLAround 99 per cent of potential crop pests are controlled by a variety of other organisms, including insects, birds and fungi. These natural pesticides are in many ways superior to their artificial equivalents, since pests can often develop resistance to chemical controls.

5. DETOXIFICATION AND DECOMPOSITION OF WASTESSome 130 billion metric tons of organic waste is processed every year by earths decomposing organisms. Many industrial wastes, including detergents, oils, acids and paper, are also detoxified and decomposed by the activities of living things. In soils, the end product of these processes a range of simple inorganic chemicals is returned to plants as nutrients. Higher (vascular) plants can themselves serve to remove harmful substances from groundwater.6. POLLINATION AND CROP PRODUCTIONMany flowering plants rely on the activities of various animal species bees, butterflies, bats, birds, etc. to help them reproduce through the transportation of pollen. More than one-third of humanitys food crops depend on this process of natural pollination. Many animal species have evolved to perform an additional function in plant reproduction through the dispersal of seeds.7. CLIMATE STABILIZATIONPlant tissues and other organic materials within land and ocean ecosystems act as repositories of carbon, helping to slow the build-up of atmospheric carbon dioxide, and thus contributing to climate stabilization. Ecosystems also exert direct influences on regional and local weather patterns. Moisture released into the atmosphere by rainforests, for example, causes regular rainstorms, limiting water loss from the region and helping to control the surface temperature. In cold climates, meanwhile, forests act as insulators and as windbreaks, helping to mitigate the impacts of freezing temperatures.

8. PREVENTION AND MITIGATION OF NATURAL DISASTERSForests and grasslands protect landscapes against erosion, nutrient loss, and landslides through the binding action of roots. Ecosystems bordering regularly flooding rivers (floodplain forests and wetlands) help to absorb excess water and thus reduce the damage caused by floods. Certain coastal ecosystems (salt marshes, mangrove forests, etc.) prevent the erosion of coastlines.

9. PROVISION OF FOOD SECURITYBiodiversity provides the vast majority of our foodstuffs. The annual world fish catch, for example (averaging 100 million metric tons), represents humanitys most important source of wild animal protein, with over 20 per cent of the population in Africa and Asia dependent on fish as their primary source of protein. Terrestrial animals, meanwhile, supply an array of food products: eggs, milk, meat, etc. Wild biodiversity provides a wide variety of important foodstuffs, including fruits, game meats, nuts, mushrooms, honey, spices and flavorings. These wild foods are especially important when agricultural supplies fail. Indeed, wild biodiversity guards against the failure of even the most advanced agricultural systems. For example, the productivity of many of the developed worlds agricultural crops is maintained through the regular assimilation of new genes from wild relatives of these crops. These wild genes offer resistance to the pests and diseases that pose an ever-evolving threat to harvests.

10. PROVISION OF HEALTH CAREThe World Health Organization estimates that 80 per cent of people in the developing world that rely on traditional medicines derived mainly from plants.18