Climax communities
Climax communities refer to mature ecosystems that represent the final stage in a natural succession process, characterized by a stable and balanced assortment of plant and animal species adapted to their environment. These communities are crucial reservoirs of biodiversity, providing a rich habitat for various life forms. The concept originated in 1916 from forestry biologist Frederic E. Clements, who suggested that specific vegetation types emerge given particular climatic and topographical conditions. However, contemporary ecological understanding has shifted towards viewing these communities as dynamic systems, constantly evolving rather than fixed entities.
Different subtypes of climax communities exist, including polyclimax, where multiple stable assemblages can exist in an area, and plagioclimax, which reflects human-influenced ecosystems. Notably, climax communities are particularly vulnerable to human disturbances, which can lead to their contraction and loss. Preservation efforts aimed at protecting entire ecosystems have shown greater success in maintaining biodiversity compared to those focused solely on individual species. Overall, while many climax communities persist in regions like the Amazon rainforest and North American coniferous forests, their stability and diversity remain threatened by human activities and environmental changes.
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Subject Terms
Climax communities
DEFINITION: Assemblages of plants and animals representing the end point in a successional sequence; mature communities in equilibrium with their environment
Climax communities are reservoirs of biological diversity. As levels of human disturbance increase, climax communities contract in area and begin to disappear. Efforts to preserve endangered species that focus on entire communities are more likely to be successful, especially at preserving unrecognized threatened species, than efforts that focus on one species alone.
The concept of a climax was first proposed in 1916 by forestry biologist Frederic E. Clements in a monograph on the vegetation of Washington State. Clements postulated that there is a unique, discrete vegetation type for a given climate and topography, and that type will occur if succession is allowed to proceed to its end point. This concept has fallen into disfavor among theoretical ecologists and conservationists since World War II. A more modern view, based on numerous detailed studies, views communities as being in a state of constant flux that decreases in amplitude with time. The terms “mature,” “late successional,” and “old-growth” are used to describe what formerly was called a climax community.
Subtypes of climax communities sometimes recognized include polyclimax, where several different assemblages of plants and animals can represent a stable end point for a given area; subclimax, where the usual vegetation remains in a late stage of succession because of regular, infrequent disturbance; and plagioclimax, where the stable vegetation of a region has been shaped by human activity over a long period of time. An example of a plagioclimax is the species-rich oak savanna of Oregon and northern California, which was maintained by periodic burning in prehistoric times and grazing after European settlement. Excluding both fire and cattle results in overgrowth by conifers and a precipitous decline in diversity of herbaceous plants and insects.
Following massive disturbance, whether natural or caused by humans, the vegetation of an area experiences succession as early colonizing species modify the in ways that allow other species to colonize. Over time, the spatial complexity, species diversity, primary productivity, and stored of the vegetation increases, as do the species diversity and food-web complexity of animals. In addition to being much richer biologically, mature communities are more resistant to external disruption than are early successional ones.
Climax communities include prairie and savanna vegetation as well as forest, but these and other vegetation types ideally suited to human exploitation persist mainly as small tracts deliberately preserved from development. Such preservation of fragments of an originally more extensive is typically only partially successful in preserving stability and species diversity, because the complexity of an ecosystem depends on its size as well as lack of disturbance. Preserving small, widely separated tracts of virgin rain forest in the Amazon basin has, for example, led to the loss of larger predators from much of their original range, and this in turn has disrupted populations of prey species. Extensive areas of mature climax communities relatively free of human disturbance still extant in the early years of the twenty-first century include the rain forest of the Amazon basin, coniferous forests of North America and Siberia, and the Arctic tundra.
Bibliography
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