Development and maintenance of soil properties

While light has been demonstrated to be extremely important to plant establishment in closed-canopy tropical forests, soil properties are also likely to affect the growth and species composition of colonists on deforested land. Many dramatic changes in soil properties occur after deforestation and the burning that often accompanies it . One of the most significant impacts is the loss of soil structure, as evidenced by increases in bulk density and decreases in soil porosity. A variety of chemical changes also occur after land conversion, but it is more difficult to generalize about the directionality of these processes. The loss of soil organic matter (SOM) can be particularly detrimental because SOM stabilizes soil aggregates, increases the water-holding capacity of soils, and serves as an energy source for soil decomposers; SOM also influences soil fertility by (1) holding onto organic forms of nutrients and (2) its high cation exchange capacity (CEC). A high CEC facilitates nutrient uptake by allowing cations adsorbed to the soil or SOM to be easily replaced by other cations in solution. Thus, in the long-term, deforestation can increase soil acidity and reduce soil fertility.

Additionally, the role of nitrogen in secondary succession deserves special attention because of its potential for loss in tropical ecosystems (. During land clearing, N is lost mainly through biomass removal, volatilization during burning, denitrification, and leaching (Robertson, 1984; Keller et al., 1993). However, N levels in the soil can be increased after deforestation. For example, after felling and burning Costa Rican pre-montane wet forest, NO3 and NH4 levels increased and persisted for 6 months at levels much higher than adjacent secondary forest.