Table

Comparison of Vegetation Development under Different Restoration Planting Treatments: Stem Density

Seeding Cell 1 Cell 2 Cell 3 Cell 4

Low Diversity Seeding Low Diversity Seeding Natural Colonization High Diversity

Percent of the sampled community 0.8 4.5 — 35.6

after 2 years that was originally introduced

Percent of the sampled community 99.2 95.5 100 64.4

after 2 years that colonized naturally

Percent of the sampled community 71.9 75.3 95.8 39.0

after 2 years that was made up of facultative or obligate wetland species

Note: Data are based on the number of plants that were sampled in 11 quarter meter square quadrants in each of the mitigation wetland cells.

Source: Adapted from MacLean, D. and P. Kangas. 1997. Proceedings of the 24th Annual Conference on Ecosystems Restoration and Creation. Hillsborough Community College, Plant City, FL.

Seeds Produced in Forest

Seeds Produced in Forest

Adult Plant

FIGURE 5.6 Sequential losses of individuals during the recruitment process for plants. (Adapted from Uhl, C. 1988. In E. O. Wilson (ed.). Biodiversity. National Academy of Sciences, Washington, DC.)

Adult Plant

FIGURE 5.6 Sequential losses of individuals during the recruitment process for plants. (Adapted from Uhl, C. 1988. In E. O. Wilson (ed.). Biodiversity. National Academy of Sciences, Washington, DC.)

predict the quantity or quality of biotic inputs of volunteer species, and this probably explains the continued inefficient reliance on intentional plantings in restoration projects.

Recruitment of species through natural dispersal involves several processes. This is sometimes termed supply side ecology, using an economic metaphor because it involves the rate of production of individuals (i.e., the supply) at the site (Fairweather, 1991; Roughgarden et al., 1986; Underwood and Fairweather, 1989; Young, 1987). Figure 5.6 illustrates the processes involved for a plant species, showing the sequential reduction in numbers of initially available individuals as seeds relative to the number that ultimately become established as adult plants. Of course, the seed life stage is initially critical. Seed ecology of a site involves a number of aspects including seed budgets (see, for example, Kellman, 1974) and seed banks (Leck et al., 1989; Roberts, 1981). Understanding flows of seeds in dispersal is important when considering free inputs to a restoration site (Chambers and MacMahon, 1994), but storages in seed banks are also being actively manipulated in restoration projects (Brock and Britten, 1995; Maas and Schopp-Guth, 1995; van der Valk et al., 1992). Access to naturally occurring seed sources is an important design issue in any restoration project and inputs of volunteer species can be a significant free subsidy to a project.

There are then two sources of biotic inputs in any restoration project: intentional, artificial plantings (either seeds, juveniles, or adults) and natural colonization through

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