Donor Wetland Soil Promotes Revegetation in Wetland Trials

Abstract

vegetation. T single most important goal of any wetland restoration or creation project is the establishment of a hydrological regime suitable for wetland organisms, both plant and animal. Yet, once the appropriate hydrology has been established, the development of vegetation in created or restored wetlands can be said to depend on three factors: the survival growth and reproduction of planted nursery stock; the migration of propagules into the wetland by way of wind, water or animal activity; and the recruitment of new individuals from dormant propagules present in a soil seed-bank. When donor wetland soil is used as the final topsoil covering, recruitment from the seed bank may provide the new wetland with a substantial number of individuals. A recent study on a reclaimed phosphate mine in Florida showed that the development of vegetation on areas mulched with seedand propagule-rich organic matter harvested from nearby wetlands, was superior to development on areas with unmulched overburden (Erwin, 1990). Such results support earlier reports documenting the value of wetland soil in the development of diverse vegetation on created or restored wetlands (van der Valk, 1989). The great value of donor wetland-soil for restoration purposes, lies primarily in the astonishing number of viable seeds such soils typically contain--a consequence of the conservative reproductive strategies of many wetland species. Typical wetland soil may contain between 2,000 and 50,000 seeds per square meter, and some wetland soils may contain hundreds of thousands. Most seeds are found in the upper five centimeters of soil, and large numbers of species are commonly represented (Leck, 1989). Schneider and Sharitz, for example, found 59 species of plants in a riverine wetland in South Carolina (Schneider and Sharitz, 1986). Donor soil may also increase water-retention capability and introduce microorganisms and fungi to a created wetland (Clewell and Lea, 1990). Yet, while the use of donor wetland-soil as a way of ameliorating conditions and introducing native plants into restored or created wetlands is not a new idea, there is good reason to believe that it is an under-used method, and that restorationists often rely on the outplanting of nursery stock in situations where donor soil might be both more effective and less expensive. Transplanting of nursery stock is often cited as the most effective, though expensive, method of vegetating a created wetland ( Shisler, 1990 ). The reported advantages of transplanting nursery stock include control over the species composition of the community (Levine and Willard, 1990); the ability to place species in appropriate zones or patterns (Erwin, 1990); the quick establishment of suitable cover over what would otherwise be bare substrate, and the rapid development of a functioning wetland system (Kruczynski, 1990). At the same time, there are numerous examples of the failure of transplanted nursery stock. There are also examples of forested-wetland creation projects being overrun by volunteer trees that perform better than the transplanted stock (Clewell and Lea, 1990). Many recommendations for planting nursery stock contain a