BALANCE OF NATURE

Plants, animals, and other organisms that live together in the same area-such as a forest or a pond-form a community. Within a community, the members of one species make up a population. The size of each population stays fairly stable unless some change alters conditions in the community. Biologists refer to the relative stability of each population within a community as the balance of nature.


Maintaining the balance

All living things are closely related to their environment. Any change in one part of nature-for example, a natural increase or decrease in a population of any species of animal or plant-causes reactions in several other parts. In most cases, these reactions work to restore the balance of nature.

Ecosystems. An ecosystem consists of the biological and physical environments of an area. The biological environment is made up of all living things in the community. The physical environment includes air, soil, water, and weather. All these biological and physical factors interact within an ecosystem. They compose a network of complex relationships that control population growth.

Each organism is related to a variety of the biological and physical factors of its ecosystem. For example, rabbits need air and water from the physical environment to breathe and drink. They also need biological features, such as plants, for food and cover  (shelter). On the other hand, rabbits are eaten by foxes and other predators (flesh-eating animals). In addition, several kinds of parasites live in and on rabbits.

The relationship among rabbits, plants, and foxes can be shown by an example of an ecosystem that includes these three organisms. Assume that during a certain year, the temperature and rainfall within this ecosystem are ideal for plant growth. As a result, rabbits have a more plentiful supply of food than usual. The female rabbits are well-fed and healthy, and most of them produce large litters. The young rabbits have enough food, and nearly all of them survive. In time, the area becomes overpopulated with rabbits, and they continually compete with one another for food and cover. The losers become weak and unprotected, and they may fall victim to disease and parasites. They also become easy targets for foxes, and so the rabbit population decreases.

More rabbits means more food for foxes. The foxes respond in much the same way as the rabbits did to an increased food supply-their population grows. But more foxes means that even more rabbits are hunted, and so the number of rabbits shrinks even further. The rabbit population will continue to decrease until it again comes into balance with the ecosystem's ability to support it-an ability known as the ecosystem's carrying capacity. Similar controls govern plant populations. On a small scale, such actions and reactions go on every day.

Competition plays a major role in controlling population growth. An ecosystem has limited amounts of the food and cover necessary for each population. Therefore, individual members of the same population must compete for those necessities. But competition is much less intense between different populations. For example, deer and rabbits are herbivores (plant-eating animals), but they usually eat different kinds of plants.

Competition for food. If a population becomes too large for the available supply of food, many of the weaker members will starve. Others may migrate into another ecosystem, but they may not survive. Still others, weakened by hunger, may die from disease and parasites, or they may be killed by predators.

Competition for cover. Competition for cover. Cover is a requirement for most populations. Only a certain number of rabbits can live in a given brier patch, and only so many foxes can occupy the available den sites. If the rabbit population becomes too large for the brier patch, competition will force some individuals to live in poorer cover. There, they will be more likely to be attacked by predators or by disease and parasites.

Predators can help maintain the quality of their prey population if the two species have lived for a long time in the same ecosystem. Under such conditions, the prey species learns to deal with the predators. Therefore, predators normally kill only the weakest and least desirable members of the prey population. The prey population thus stays in a healthy state.

Disease and parasites can reduce or even wipe out a population. But most pathogens (diseases and parasites) have been present throughout history. Most host (infected) species have become adapted to living with their pathogens. Disease and parasites serve as important population controls primarily in the presence of other factors, such as competition for food or cover.

Behavior helps govern the size of some animal populations. Three behavioral factors may be important: (1) territoriality, (2) dominance hierarchy, and (3) stress.

Territoriality occurs among animals that require a certain minimum amount of space, regardless of the available food and cover. Among such species, one animal or a group of animals establishes a territory. No other members of the species are allowed in this area, and breeding is usually restricted to the animals with territories. Such behavior ensures that the strongest members of the population-the animals with territories-survive and produce offspring.

Dominance hierarchies, often called "pecking orders," occur among many types of social animals. Within populations of such animals, the stronger individuals dominate the weaker ones. These dominant animals get the best food, cover, and breeding places. Weaker individuals are forced into areas with poorer food and cover, and some do not survive. The offspring of dominant parents also have the best chance to survive. The traits of the strongest individuals thus are passed on to the next generation of the species.

Stress occurs among crowded populations of animals. Stressed animals become aggressive and irritable, and they often fight with one another. Some individuals do not breed, and those that do breed produce small litters. Many females do not take care of their young. Diseases and parasites spread rapidly among crowded animals, further reducing their number.

Upsetting the balance

Natural factors and human factors may alter the relationships within an ecosystem. Earthquakes, floods, and fires started by lightning are natural factors that may upset nature's balance. Human factors that may do so include logging and livestock grazing. As a result of these and other factors, entire populations may be wiped out or may grow suddenly at an astounding rate.

A historical example illustrates a change in balance. During the early 1900's, a stable population of about 4,000 mule deer lived on the Kaibab Plateau in northwestern Arizona. Beginning in 1907, human hunters began killing the deer's natural predators-coyotes, mountain lions, and wolves. As a result, the population of deer on the plateau increased to about 100,000 by 1924. But there was not enough food for so many deer, and thousands of deer starved. Balance did not return to the ecosystem of the Kaibab Plateau until 1939.

In another case, a chain of events known as the ripple effect began when fishing crews apparently overharvested fish populations in the northern Pacific Ocean. As a result, seals and sea lions, which eat fish, declined. In 1998, biologists reported that killer whales, which normally prey on seals and sea lions, had begun to prey on sea otters. The killer whales sharply reduced some sea otter populations. Next, sea urchins, a major food of the otters, increased. The sea urchins consumed huge amounts of a type of algae known as kelp. They reduced the ocean's kelp beds, which provide habitat for many other species. Beginning with fewer fish, an entire marine ecosystem-seals and sea lions, killer whales, sea otters, sea urchins, and kelp beds-was upset. No one knows when balance will return.

ELIMINATING SMOKE DOES NOT NECESSARILY CUT CARBON EMISSIONS

Land-clearing techniques exist that do not produce smoke, including biological methods to accelerate decomposition and various mechanical techniques that chip or shred biomass, either for mulching on the site or for transport off site for disposal or sale. All of these `no-burn' techniques presently are more expensive than burning. Moreover, as noted above, burning produces many benefits for land users.

Research may be able to reduce the economic and technical disadvantages (compared to burning) of certain techniques, such as mulching. If they are feasible, policies to regulate the timing of burning and new techniques for land clearing without burning could-over time- address part of the regional smoke problem.

However, it must be emphasized that unless a significant portion of the biomass from land clearing is used to manufacture wood products with a long useful life (instead of simply decaying), these measures will only have a short-term effect on C emissions.

Moreover, the attractiveness of technological alternatives to clear land without burning, or the level of subsidies required for adoption of these techniques, also are infuenced by national policies, such as timber export taxes.

THE EFFECTS OF SLASHING DAN BURNING OF LAND MANAGEMENT

Slashing and burning is the preferred method of land clearing in the tropics for smallholders and large companies alike because it is cheaper, at least from a private perspective, and easier than available alternatives. In addition, fire eliminates field debris, reduces problems with weeds and other pests and diseases, makes nutrients available in the form of ash and loosens the soil to make planting easier. In some ways it is preferable environmentally compared to some other land-clearing methods.


For example, bulldozers and other heavy machinery cause soil compaction and erosion. Fire has many distinct advantages for low-income households: all other methods are more expensive; fire kills crop pests and diseases; and the ash provides much-needed fertilizer. Results of field experiments and surveys in Sumatra Indonesia demonstrate the key role that phosphorus (P) plays in resource management. Burning at low or medium intensity releases P into soil solution, but high-intensity fires reduce P levels. With greater fuel supply, hence hotter fires, the negative effects of heat on soil mineralogy offset the positive effects of additional ash.

DEFINITION OF FOREST STANDS | FOREST PATCHES

Definition of Forest Stands or Forest Patches refer to the ecosystem scale at which a relatively homogenous forest unit can be identified. The composition, structure, and ecological functions within a stand are similar enough that an ecologically responsible forest use prescription can be applied uniformly within the stand, without encountering changes in ecological parameters that may produce unexpected or undesirable results.

In conventional forestry, “stands” have largely been defined by narrow timber characteristics, which were in turn driven by short-term economic variables. However, in order to plan and carry out ecologically responsible forest uses within an ecosystem-based approach, stands must be defined in relation to whole ecosystem factors that are required to maintain fully functioning forests at the landscape and stand levels.

In other words, the boundaries of a stand are not determined by rigid human management criteria such as timber size and timber quality, but by the full spectrum of ecosystem parameters that have been shaped by natural disturbance patterns and that reflect the movement of energy, nutrients, water, and animals into and out of a particular ecosystem.

Human scales are closest to forest scales at the stand or patch level. For example, the stand or patch level is the scale where visible human modification occurs. However, an ecosystem-based approach must always consider that what occurs at the stand or visible scale will also have impacts on a variety of other scales, from the large landscape to the microscopic.

DEFINITION OF FOREST LANDSCAPE

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Definition of forest landscape is the large-scale view of a forest. When industrial timber managers use the term “forest landscapes,” they are usually concerned with scenery and visual impacts. In the context of an ecosystem-based approach, however, a forest landscape is a mosaic of interconnected, interdependent stands or patches that are repeated in a pattern across the larger landscape. This pattern has both spatial and temporal components.

An ecosystem-based approach requires that all planning and activities begin at the regional/landscape level. When planning for human use, landscape level decisions are made for watersheds of small to moderate size (less than 5,000 hectares to about 50,000 hectares, or 12,000 to 125,000 acres). In sub-regional or regional planning processes, forest landscape level considerations are expanded to large watersheds encompassing hundreds of thousands of hectares/acres.

In planning and carrying out forest uses, particularly timber management, many people tend to focus on small forest parcels. This is a result of our limited spatial view, short time frames, and cultural conditioning. In contrast, an ecosystem-based approach requires that all planning and activities start at the landscape level. The character and condition of the forest landscape dictate what is ecologically possible at the stand level.

The character of a forest ecosystem refers to how a forest works, from the landscape level to the stand or patch. For example, forests that have frequent fires have a different character than forests where wind and root decay are the primary agents of disturbance. Some forests are characterized by steep slopes, shallow soils, and well-defined drainage patterns, while other forests have gentle slopes, cold soils, and diffuse drainage patterns.

Forests of a different character will have different composition and structures, and therefore differences in how they function. Different composition, structures, and functioning lead to different kinds of ecological limits to human use. Ecological limits are natural factors or processes that are easily damaged or degraded if modified by human uses. For example, steep and/or wet slopes impose ecological limits because, if disturbed, they are likely to erode, causing problems like soil loss and siltation of streams. Cold soils are an ecological limit because nutrient cycling occurs in shallow organic layers which may be easily damaged by many types of human activities.

The condition of a forest describes how human uses have modified forest functioning from the landscape level to the stand or patch level. Conventional timber management frequently results in negative impacts, like fragmentation, loss of old growth, and soil degradation. An ecosystem-based approach protects forest composition and structure and respects the ecological limits of forests to various human uses. By respecting ecological limits ecosystem-based approaches avoid degradation of short- and long-term forest functioning.
Ecological limits to human use are determined by describing and interpreting the character and condition of, first, the forest landscape, and then the forest stand or patch.