Successional Change In Community Structure

Relatively predictable changes in community structure occur over periods of decades to centuries as a result of succession on newly exposed or disturbed sites. New habitats become available for colonization as a result of tectonic activity, glacial movement, sea level change, and sediment deposition or erosion. Species colonizing newly exposed surfaces usually are small in stature, tolerant of exposure or able to exploit small shelters, and able to exploit nonorganic or exogenous resources. Disturbances to existing communities affect each species differently, depending on its particular tolerances to disturbance or postdistur-bance conditions (see Chapter 2). Often, legacies from the predisturbance community (such as buried rhizomes, seed banks, woody litter, and animals surviving in protected stages or microsites) remain following disturbance and influence the trajectory of community recovery.

The process of community development on disturbed or newly exposed sites is called ecological succession. The succession of populations and communities on disturbed or newly exposed sites has been a unifying concept in ecology since the time of Cowles (1911) and Clements (1916). These early ecologists viewed succession as analogous to the orderly development of an organism (ontogeny). Succession progressed through a predictable sequence of stages (seres), driven by biogenic processes, which culminated in a self-perpetuating community (the climax) determined by climatic conditions. Succession is exemplified by the sequential colonization and replacement of species: weedy annual to perennial grass to forb, to shrub, to shade-intolerant tree, and finally to shade-tolerant tree stages on abandoned cropland. Succession following fire or other disturbances shows a similar sequence of stages (Fig. 10.2).

Although the succession of species and communities on newly exposed or disturbed sites is one of the best-documented phenomena in ecology, the nature of the community and mechanisms driving species replacement have been debated intensely from the beginning. Gleason (1917,1926,1927) argued that succession is not directed by autogenic processes but reflects population dynamics of individual species based on their adaptations to changing environmental conditions. Egler (1954) further argued that succession could proceed along many potential pathways, depending on initial conditions and initial species pools. E. Odum (1969) integrated the Clementsian model of succession with ecosystem processes by proposing that a number of ecosystem properties, including species diversity, primary productivity, biomass, and efficiency of energy and nutrient use, increase during succession. Drury and Nisbet (1973) viewed succession as a temporal gradient in community structure, similar to the spatial gradients discussed in Chapter

Spruce Forest Succession

26-50

51-100

100-200

200-500+

Diagrammatic representation of upland white spruce forest succession in Alaska following fire. From van Cleve and Viereck (1981) with permission from Springer-Verlag. Please see extended permission list pg 571.

Forest floor -,

26-50

51-100

100-200

200-500+

Diagrammatic representation of upland white spruce forest succession in Alaska following fire. From van Cleve and Viereck (1981) with permission from Springer-Verlag. Please see extended permission list pg 571.

9, and argued that species physiological tolerances to environmental conditions were sufficient to explain species replacement. More recently, the importance of disturbances and heterotroph activity in determining successional processes and preventing ascension to the climatic climax has been recognized (e.g., Davidson 1993, MacMahon 1981, Ostfeld et al. 1997, Pickett and White 1985, Schowalter 1981,1985, Willig and Walker 1999).

The concept of succession as goal-oriented toward a climax has succumbed to various challenges, especially recognition that succession can progress along various pathways to nonclimatic climaxes under different environmental conditions (Whittaker 1953). Furthermore, the mechanism of species replacement is not necessarily facilitation by the replaced community (e.g., Botkin 1981, Connell and Slatyer 1977, H. Horn 1981, McIntosh 1981, Peet and Christensen 1980, Whittaker 1953,1970). Nevertheless, debate continues over the integrity of the community, the importance of autogenic factors that influence the process, and the degree of convergence toward particular community composition (Bazzaz 1990, Peet and Christensen 1980, Glenn-Lewin et al. 1992, West et al. 1981).

Oplan Termites

Oplan Termites

You Might Start Missing Your Termites After Kickin'em Out. After All, They Have Been Your Roommates For Quite A While. Enraged With How The Termites Have Eaten Up Your Antique Furniture? Can't Wait To Have Them Exterminated Completely From The Face Of The Earth? Fret Not. We Will Tell You How To Get Rid Of Them From Your House At Least. If Not From The Face The Earth.

Get My Free Ebook


Responses

  • carlo
    How is succession and biomass related?
    6 years ago

Post a comment