Biomes and environmental issues

DEFINITION: Major ecological zones shaped primarily by climate and characterized by the types of plant and animal life they support

The complexity of biomes exposes them to varying and sometimes cascading changes from both natural and human-initiated events. The consequences for the larger environment can range from minimal to catastrophic.

Biomes and environmental issues

Each of the Earth’s biomes has a typical ecological pattern, with its flora and fauna sharing similar characteristics, such as leaf forms and survival strategies. A study of any biome, on any continent, will show multiple ways its species carry out the essential tasks of life. Biomes are large and complex, with species forming intricate networks of life within subsets of the biomes.

Land-based major biomes include: tropical rain forest, tropical dry forest, savanna or tropical grassland, desert, temperate grassland, Mediterranean scrub or chaparral, temperate deciduous forest, temperate mixed and coniferous forest, boreal forest or taiga, and Arctic tundra. Marine biomes are basically characterized as oceanic or freshwater, although the lack of vegetation-climate links and the gradients between coastal and deep-sea habitats make the simplicity of this scheme problematic. Finally, human activities have so transformed large portions of the planet that some biologists treat anthropogenic (human-dominated) biomes as a separate concept. These biomes range from dense settlement patterns in urban landscapes to cropland, rangeland, and forest.

Influences on Biomes

Biomes are sometimes viewed as giant ecosystems. Because of biomes’ size and complexity, however, both scientists and lay observers find it more useful to view biomes as made up of many different ecosystems and habitats.

Land-based biomes are shaped largely by their climates. The most important climatic factors are latitude and humidity—total precipitation, seasonal rainfall patterns, ambient moisture—elevation can also be important. Cross-cutting these climatic factors, though influenced by them, are features such as terrain, soil type and nutrient status, and prevailing winds. All these affect the kinds of vegetation that can flourish in a region, thus determining the types and amounts of animal life the plant cover will support.

Generally, biomes closer to the equator support more biodiversity in the form of different species. From 40 to 75 percent of all animal species on the Earth are indigenous to tropical rainforests. An estimated 50 percent of all life forms are native to tropical forests. Tropical rainforests are also home to two-thirds of all flowering plant species. Tropical rainforests also have many layers of life systems, from the canopy ecosystems with their monkeys, marmosets, and tropical birds, such as macaws, down through several canopy-gap layers that shelter opossums and woodpeckers, to the forest floor, the base station for jaguars and frogs, among other jungle dwellers. However, tropical rainforests lack a rich nutrient base. Since they have poor soil quality, most of the biome's available nutrients are held within the trees themselves.

In contrast, temperate deciduous forests lack the great biodiversity found in tropical rainforests. The life processes in temperate deciduous forests are highly regulated by seasonal temperature changes. As leaves fall to the ground, they carry calcium and other minerals to the forest floor; this litter turns into humus and becomes the nutrient-rich soil on which broad-leaved trees thrive.

Another mix of resources and life strategies is found in desert biomes. Most deserts do get some water and support some life, but anything growing there must adapt to little moisture and hot, unshaded land that is poor in nutrients. Desert plants store nutrients in underground organs such as their root systems, and cacti have expandable stems for storing water from sudden but infrequent downpours. Desert dwellers such as the kangaroo rat get their moisture from eating seeds. Their underground burrows retain three times as much humidity as exists aboveground.

Environmental Issues and Biomes

For the nonhuman organisms living in a given biome, the environmental features of that biome are essential to life. Human beings, in contrast, interact with biomes by finding ways to use the biomes’ natural resources to sustain them. However, human technologies and dense human populations can upset a delicately balanced biome far beyond its ability to recover. Even in the ancient world, large-scale grazing and firewood collection apparently turned once-wooded coastal areas into the Mediterranean scrub that bears that region’s name.

Throughout history, humans have cleared forests or modified grasslands for use in agriculture. Sometimes the environmental damage done by such processes is limited. For example, the prairie grasslands of the American Great Plains were originally roamed by bison, and the cattle herds that replaced the bison filled the same ecological niche. Other human-caused changes have brought near disaster to entire biomes.

Human activities have altered every one of the Earth’s biomes. Among the direst changes has been the destruction of tropical forests caused by timber harvesting and by the clearing of trees and other plant life to make way for ranching or industry. The damage caused when a biome is altered is not confined to the loss of diverse natural resources within that biome; rather, such change threatens the entire biosphere because it interferes with the role the biome plays in balancing the Earth’s systems. The loss of rainforests, for example, damages the atmosphere because of the accompanying loss of oxygen renewal that was provided by the trees.

The ocean biome is central to regulating heat and rainfall around the world, and, through its plankton, is the source of most photosynthesis on the Earth. The crumbling of coral reefs and the huge trash vortex reported in the North Pacific in the late 1990s were early warning signals about the environmental threats to this biome’s future. Freshwater bodies are susceptible to damage from industrial and fertilizer runoff. Other natural biomes face their own unique threats of rapid environmental degradation.

Global climate change has had an impact on many biomes. For example, climate changes have affected many tree species. The sugar maple is dying out in many of the southernmost reaches of its growth zone but thriving in cooler Canadian territories. In other areas, warmer and drier seasons have increased the frequency and intensity of wildfires.

Anthropogenic biomes are, by definition, shaped by human activity, but humans can make conscious decisions that can reduce the negative impacts of such activity on the environment. Within cities, for example, humans can counter the effects of vast, heat-retaining stretches of pavement by creating rooftop gardens, rain gardens, and other green spaces.

Bibliography

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