In 1825, the French
naturalist Adolphe Dureau de la Malle first used the term ecological succession
to describe the growth of vegetation after forest clear-cutting. Henry Chandler
Cowles reintroduced this term in 1899 in his doctoral dissertation at the University
of Chicago to describe the succession of vegetation and soil on the Indiana
sand dunes, located on the southern end of Lake Michigan. Cowles, who became an
early leader in the emerging study of ecology, wrote about ecological
succession as the history of the ecosystem from its birth to maturity: changes
occur in the species community, with some becoming less abundant over time, and
replaced by more plentiful species.
Frederic Clements was a
contemporary of Cowles, classmate of the writer Willa Cather at the University
of Nebraska, and a leading early plant ecologist. Based on his studies of
vegetation in his native state of Nebraska and the western United States, in
1916 he proposed that vegetation gradually changes over time in a sequence of
predictable and deterministic stages—which he likened to the development of an
individual organism—toward a mature climax stage. This concept was a dominant
theory through much of the twentieth century.
Primary succession refers to
plant communities occupying sites that had not been previously vegetated and
include sandy or rocky surfaces or those covered by lava flow. The earliest
signs of vegetation include lichens and grass (pioneer plants), which require
few nutrients and use the minerals from rocky surfaces to survive. These are
succeeded by small shrubs, trees, and then animals in the climax stage, forming
a fully functional ecosystem. By contrast, secondary succession occurs in an
area that has undergone a major disturbance or removal of a preexisting vegetative
community because of fire, flood, hurricane, or such human factors as logging
or agricultural activities. Secondary succession proceeds much more rapidly to
the climax stage. Cowles referred to these intermediate stages progressing
toward the climax community as sere. As each new plant species grows, it
modifies the habitat to permit and facilitate the growth of the subsequent
species.
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