Large, easily recognized terrestrial community units are known as biomes. In a given biome the life form of the climax vegetation is uniform, and is the key to recognition. Thus, the dominant chmax vegetation in the grassland biome is grass. Although the species of dominant grasses will vary in different geographical regions where the grassland biome occurs. Other types of vegetation will be included in the biome, as for example, ‘’weedy’’ seral stages in succession, forest subclimaxes related to local soil and ater condition crops, and other vegetation introduced by man.

    The distribution of six major biomes in relation to temperature and rainfall. If you will check the mean annual temperature and rainfall of your locality you can determine from which biomes you live in, even if you are now sitting in the middle of a city with no climax vegetation anywhere around. Several other biomes, such as chaparral, tropical savanna, thorn shrub, and tropical monsoon forests are related to seasonal distribution of rainfall rather than annual means.

   For the past 6 year most nations of the world have taken part in what is known as the ‘’international biological program’’ involving govermental grant support for interdisciplinary team research and systems modelling of major biomes. Both the ‘’modelling up’’ and the ‘’modelling down’’ approaches, as mentioned, are bing tested in fefforts to develop realistic working model that will help man better inderstand his impact on the matiral biome matrisx in which his civilization is embedded. For a brief rebiw of the inited states program and some of its accomplishments, see hammond (1974). Other natons have, in general, taken a less holistic approach with varying emphasis on such aspects as natural area inventory, impact of grazing animals, secondary production, detailed descriptive analysis of vegetation, environmental health, and preservation of genetic stocks of endangered wild and domestic organisms.

       Fresh water is very very important in our life. Much of what was said about estuaries also applied to freshwater marshes, they tend to be naturally fertile ecosystems. Tidal action, of course, is absent, but periodic fluctuation in water levels resulting from seasonal and annual rainfall variations often accomplishes the same thing in terms of maintaining longe range stability and fertility fires during dry periods consume accumulated organic matter thereby deepening the water holding basins and aiding subsequent aerobic decomposition and release of soluble nutrients, thus increasing the rate of production. In fact, if such events as drawdown and fire do not occur, the build up of sediments and peat (undecayed organic matter), tends to lead to the invasion of terrestrial woody vegetation. Where man controls water levels by dikes in marshes he generally finds that chemical herbicides or mechanical methods have to be used if the area is to continue to exist as a true freshwater marsh ecosystem suif able for ducks and other semiaquatic organisms.

    The general public prejudice against marshes is understandable, since they are sometimes the home of mosquitoes and other disease carriers and pests. Before much was known about the life history and ecology of the arthropods and anails as disease carriers, destroying their habitat (that is, draining the marsh) was about the only solution. Our present knoledge now makes it unnecessary to destroy the ecosystem in order to control undesirable species.

     In addition to producing ducks and fur bearers, marshes are valuable in maintaining water tables in adjacent ecosystems. The florida everglades are an exceptionally large and interesting stretch of freshwater marshes characterized by naturally fluctuating water levels. Complete drainage (even if possible or otherwise desirable) would not only ruin the area as a wildlife paradise but would also be  risky in that salt water might then intrude into the underground water supply needed by the large coastal cities. Likewise, complete stabilization of water levels would also destroy the unique features of the everglades, for reasons given at the beginning of this section.

     Finally, it is significant that rice culture, one of the most productive and dependable of agricultural systems yet devised by man, is actually a type of freshwater marsh ecosystem. The flooding, dranining, and careful rebuilding of the rice paddy each year has much to do with the maintenance of continuous of continuous fertility and high production of the rice plant, which, itself, is a kind of cultivated marsh grass. 

          Riverand Stream Ecosystems is very important in the world , The history of man has often been shaped by the rivers that provide water, transportation, and a means of waste disposal. Although the total surface area of rivers and streams is small compared to that of oceans and land mass, rivers are among the most intensely used by man of natural ecosystems. As in the case of estuaries, the need fo ‘’multiple use’’ (as contrasted to a ‘’single use’’ approach to such ecosystems as cropland) demands that the various areas (water supply, waste disposal, fish production, flood control, and so on) be considered together and not as entirely separate problems.

         From the energetic standpoint rivers and streams are incomplete ecosystems; that is, some portion, often a large protion, of the biological energy flow is based on organic matter imported from adjacent terrestrial ecosystems, or sometimes from adjacent lakes. Although streams are naturally adapted waste treatment systems for degradable wastes (recall our frequent comment about ‘’free sewers’’) almost all of the world’s great rivers are severely over loaded with the residues of man’s civilization. As geographer M. G, Wolman (1971) has concluded, ‘’demands on water resources are increasing at a rate that exceeds the rate of installation of waste treatment facilities.’’ This is another one of those ‘’mismatched rates’’ that are at the heart of man’s troubles with his environment. In all parts of the world man has so extensively dammed, diked, and channelized rivers that it is getting hard to find a truly wild river of any size. It is turning out that some of these manipulations bring only temporary or local benefits at great cost, and create additional problems costing still more money to correct (as in the case of some flood control projects). Accordingly, flood damages that used to be considerednatural disaster’s (and therefore, unavoidable) are more and more proving to be man – made disasters (and, therefore, avoidable). In the future, proposed alterations will have to be subjected to a more thorough cost – benefit analysis than was the case in the past. More about this in the next post.

         The stream ecologist finds it convenient to consider flowing water ecosystems under two subdivisions: (1) streams in which the basin is eroding and the bottom, therefore, is generally firm; and (2) streams in which material is being deposited and, therefore, the bottom is generally composed of soft sediments. In many cases these situations alternate in the same stream, as may be seen in the ‘’rapids’’ and ‘’pools’’ of small streams. Aquatic communities are quite different in the two situations owing to the rather different conditions of existence. The communities of pools resemble those of ponds in that a considerable development of phytoplankton may occur and the species of fish and aquatic insects are the same or similar to those found in ponds and lakes. The life of the hard bottom rapids, however, is composed of more unique and specialized forms, such as the ner spinning caddies (larvae of insects called caddies flies or trichoptera), which constructs a fine silk net that removes food particles from the flowing waters.

        The load of sediment discharged into the oceans by the great rivers of the world tell us something about man’s treatment of the land. The rivers of Asia, the continent with the oldest civilizations and the most intense human pressure on the land, discharge 1500 tons of soil per square mile of land area annually.

      Between the seas and the continents lies a band of diverse ecosystems that are not just transition zones but have ecological characteristics of their own. Whereas physical factors such as salinity and temperature are much more variable near shore than in the sea itself, food conditions are so much better that the region is packed with life. Along the shore live thousands of adapted species that are not to be found in the open sea, on land, or in fresh water. A rocky shore, a sand beach, a sand beach, an intertidal mud flat, and a tidal estuary dominated by salt marshes are shown in this post illustrate four kinds of marine inshore ecosystems. The word ‘’estuary’’ (from Latin aestus, tide) refers to a semi enclosed body of water, such as a river mouth or coastal bay where the salinity is intermediate between the sea and fresh water, and where tidal action is an important physical regulator and energy subsidy.

Estuaries and inshore marine waters areamong the most naturally fertile in the world

       Estuaries and inshore marine waters are among the most naturally fertile in the world. Three major life forms of autographs are often intermixed in an estuary and play varying roles in maintaining a high gross production rate; these are (1) phytoplankton; (2) benthic micro flora – algae living in and on mud, sand, rocks or other hard surfaces, and bodies or shells of animals; and (3) macroflora – large attached plants – the seaweeds, submerged eel grasses, emergent marsh grasses, and , in the tropics, mangrove trees. An estuary is often an efficient nutrient trap that is partly physical (differences in salinities retard vertical but not horizontal mixing of water masses) and partly biological, as was illustrated by the example of the mussel population. As discussed in the next post this property enhances the estuary’s capacity to absorb nutrients in wastes provided organic matter has been reduced by secondary treatment estuaries peovide the ‘’nursery grounds’’ (that place for young stages to grow rapidly) for most coastal shellfish and fish that are harvested not only in the estuary but offshore as well.

       Organisms have evolved many adaptions to cope with tidal cycles, thereby enabling them to exploit the many advantages of living in an estuary. Some animals, such as fiddler crabs, have internal ‘’biological clocks’’ that help to time their feeding activities to the most favorable part of the tidal cycle. If such animals are experiment tally removed to a constant environment they continue to exhibit rhythmic activity synchronous with the tides. Estuaries have been traditionally the most used, but least appreciated, free sewers for man’s great coastal developments. As symptoms of overuse appear (the decline in seafood yield is often a first symptom) government becomes concerned with ‘’coastal management.’’ An economic approach to proper evaluation of estuaries is discussed in the next post.

        The major oceans (Atlantic, pacific, Indian, arctic, and antarctic) and their connectors and extensions cover approximately 70% of the earth’s surface physical factors dominate life in the ocean. Waves, tides, currents, salinities, temperatures, pressures, and light intensities largely determine the makeup of biological communities that, In turn, have considerable influence on the composition of bottom sediments and gases in solution. The food chains of the sea begin with the smallest know autographs and end with the largest of animals (giant fish, squid, and whales). The study of the physics, chemistry, geology, and biology of the sea are combined into a sort of ‘’super science’’ called oceanography, which is becoming increasingly important as an international force. Although exploration of the sea is not quite as expensive as exploration of outer space, a considerable outlay of ships, shore laboratories, equipment, and specialists are needed. Most research is of necessity carried out by a relatively few large institutions backed by government subsidies, mostly from the affluent nations.

         To fully appreciate both the promise and the problems involved in man’s use of the sea we need to look at the contour of the sea bottom which also gives standard oceanographic nomenclature for zones of the sea. According to the now widely accepted ‘’continental drift theory,’’ some of the continents, especially Africa and south America as one pair and Europe and north America as another, were once quite close together and have drifted apart through the ages. The mid – Atlantic ridge is , according to this theory, the line of former contact between continents now hundreds of miles apart. As a citizen you will be hearing a lot about the continental shelf, that sloping plateau that borders the continents. Located here are the bulk of undersea oil and mineral wealth. From the edge of the shelf, which varies greatly in width from location to location, the continental slope drops off rapidly into the true of the sea. The topography of the continental slope is very rugged with huge canyons and ridges that are constantly changing under the forces of volcanic action and underwater ‘’landslides’’

         Since there are likely to be phytoplankton under every square meter and since life in some form extends to the greatest depths, the seas are the largest and ‘’thickest’’ of ecosystems. They are also biologically the most diverse. Marine organisms exhibit an incredible array of adaptations, ranging from flotation devices that keep the tiny planters within the upper layers of water, to the huge mouths and stomachs of deep sea fish that live in a dark, cold world where meals are bulky but few and far between. As shown in this post the continental shelf areas are fairly productive, seafood harvested here is an important source of protein and minerals for man. The most productive areas and largest fisheries are those that benefit from nutrients carried up by upwelling currents, a form of energy subsidy. Strong upwelling occurs in certain areas along the west coasts of the several continents. The Peruvian upwelling region, one of the most productive natural areas in the world, was singled out for special discussion on this post. The vast stretches of the deep sea, however, are mostly semi desert with considerable total energy flow. (because f the large area) but not much per unit of area. The autotrophic layer (phonic zone) is so small in comparison with the tropospheric layer that the nutrient supply in the former is limiting. A number of schemes have been proposed, and there are now several experiments under way, to tap the potential energy of vertical temperature differences to create artificial upwelling. Even if man is not able to obtain much food from the deep – sea area it is nevertheless very important to him, for the seas act as a giant regulator that helps to moderate land climates and maintain favorable concentrations of carbon dioxide and oxygen in the atmosphere.

       International conferences are now being scheduled to discuss the thorny problem of setting up international law with rules and regulations for exploiting seabed minerals and energy resources. Since, as we have noted, most mineral wealth, as well as most exploitable food, is located near shore, it would seem reasonable for each country to assume stewardship of the shelf area adjacent to its land territory, but the large differences in width of the shelf make such a simple solution difficult, perhaps impractical. Most objective assessments (see, for example, cloud,1969) warn against undue optimism that the deep sea is a vast storehouse just waiting to be exploited. Recovering such resources as there are will be even more expensive than getting minerals and oil from the shelf where costs are indeed huge. Remember that sea is more important as a life support and climate regulator than it is as a supply depot. Anything we do to exploit the latter must not jeopardize the former (recall our point about ‘’gross and net’’energy).