Environmental Engineering Reference
In-Depth Information
alternate successional theory is applied, that abused land may not recover to its
former when released from inappropriate management, then a much more cautious
form of management is needed.
Introduction
Ecological succession and the dynamic change of communities is one of the pillars
of modern ecology and it has considerable influence on sustainability science. The
processes that drive succession and the regularly of patterns of succession have been
the topic of considerable debate over the past century - due in no small part to the
importance of the concept to basic and applied ecology. Succession is at its simplest
level the pattern of change in ecological communities and these changes can be read
on the landscape if one knows regional history or conversely can be used to interpret
a landscape's history. In the former case, the historical pattern of land abandonment
in the piedmont of the southeastern United States presents land elements abandoned
and never reclaimed since the US Civil war in 1860, land left fallow in the First
World War; farms left to ruin in the crushing economic Great Depression of the
1930s; more land left when the sons of farmers left for the Second World War; still
other farm land taken out of production in agricultural programs reduce farm acreage
in the 1950s. The landscape as one drives and automobile through Georgia or the
Carolinas, is a kaleidoscopic montage with similar parcels of land cover types
replicated on locations with similar history. In the latter case, a small patch of pine
(
Pinus
sp.) trees on a slope bears witness to recovery from a past wildfire or a Beech
(
Fagus
) forest of great stature indicates an area that has not burned, perhaps for
centuries. The dependence of pine species on fire for regeneration or the sensitivity
of the thin-barked beech to fire is written into the landscape response.
At the turn of the twentieth century, an American plant ecologist, F.E. Clements,
framed many of the definitions and concepts in ecological succession and produced
a theoretical system of concepts that explained the nature and function of ecological
communities changing over time. Clements' definitions and approaches to under-
standing the dynamics of landscapes were used to develop regional systems of land
management policies based on expectations, succession, and successional recovery.
Clements also developed a niche-based concept of using what he called “indicator
species” to evaluate the history and condition of land units [
2
]. For example, an
overabundance of bitter or poisonous herbs might be indicators of overgrazing in
a prairie systems; the occurrence of other species might indicate unusual soil
chemistry and thus the presence of valuable minerals in the bedrock. The details
of Clements' ideas were debated strongly by his contemporaries and other
ecologists in the 1920s and 1930s found differences with parts of his successional
concepts. For example, H.A. Gleason [
7
,
8
] argued that the highly coordinated
interactions in Clements concepts had at their basis the unique attributes of the
individual plant species. These will be discussed below. Perhaps the most sharply
pointed criticism was from the British ecologist, A.G. Tansley, who argued that the
