and lowering the water table, ultimately resulting in conditions that support a climax
forest.

 Little evidence exists to support the supposition that a wetland will become an
upland because of the influence of vegetation on hydrology, but succession within a
forested wetland may be directional. Clements acknowledges that stochastic events or
other environmental factors can block the pathway of succession and can result in the
maintenance of a subclimax community. Van der Valk (1981) considered that allogenic
processes dominate in wetlands. Through interactions with the life history characteristics
of wetland vegetation allogenic processes can predict successional change in wetlands.
His qualitative model of wetland succession predicted either progression toward a
climax-forested wetland or maintenance of a subclimax community based on relatively
few parameters including vegetation life history (species life-span, propagule longevity,
establishment requirements) and wetland environment condition (flooded or drawdown).
This model assumes that interactions among species, such as competition and allelopathy,
and would not result in the loss of any species from the wetland.


Soil Succession

 Studies of successional processes in soil formation support the concept of
directional change in many soil parameters. If these changes are dependable, repeatable
and measurable within a reasonable time frame, they may lend themselves to the
development of predictive trajectories for soil succession.

 Jenny (1941) identified five soil-forming factors including climate, organisms,
parent material, relief and time. Vegetation strongly influences initial soil development
(Salisbury 1925; Jenny and others 1969; Olsen 1958; Dickson and Crocker 1953; Crocker
and Major 1955). Yaalon (1975) emphasized the importance of parent material in
determining the properties and genesis of young soils. Organic carbon, total nitrogen, pH
and bulk density changed rapidly during initial soil development and were influenced
strongly by vegetation (Dickson and Crocker 1953).

 Sithe and others (1971) studied soil genesis in iron-mine spoils in West Virginia.
Spoils had deeper rooting, higher cation exchange capacity, and higher exchangeable
nutrients than natural soils. Natural soils had lower bulk density, higher porosity, greater
soil structure, and higher nitrogen and organic carbon contents. Wali and Freeman
(1973) studied species composition and soil characteristics of North Dakota mine spoils
compared to adjacent undisturbed areas. Spoils had higher pH, electrical conductivity,
exchangeable magnesium, exchangeable sodium, total phosphorus, sulfur and silt and
clay content. Unmined sites had greater organic carbon; exchangeable potassium, species
diversity, species abundance, and species density. Caspall (1975) found that organic
matter content increases rapidly with time in the top few centimeters of Illinois' mine
soils. Organic matter increases more slowly below about 5 cm. After only 14 years,
organic matter in the upper 12 cm of mine soils was about 60 percent of equilibrium.