Wetland Seedbanks
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definition functions losses alterations Restoration Decisions: (and theory) designtype site reference sites HGM vs. IBI hydrology vegetation soil landscape success criteria floristic quality Abby Rokosch Jessen Book Siobhan Fennessy |
Seed banks have the potential to contribute to the establishment of diverse vegetation communities in wetland restoration projects (see mini-case study). Examining wetland seed banks can determine what species are present in the wetland but are currently not growing (Galatowitsh and van der Valk, 1997). The usefulness of wetland seed banks to establish native vegetation depends on the condition and composition of the seed bank. The value of the seed bank for wetland restoration depends on the type and length of disturbance that the wetland was subjected to (Middleton, 1999). Long-term drainage of wetlands can deplete the seed bank of viable seeds (Weinhold and van der Valk, 1989; Brown, 1995; Galatowitsch and van der Valk, 1996 in Brown and Bedford, 1997). Short episodes of farming can deplete the seed bank of all its useful seeds (Middleton, 1999). The loss of viable seeds may slow down the recovery or establishment of vegetation following the restoration of wetland hydrology (Brown and Bedford, 1997). Recently, transplanting remnant wetland seed banks has been studied to increase the probability of vegetation establishment (Brown and Bedford, 1997). Wetland restorationists have conflicting views about the effectiveness of using remnant wetland seed banks as methods to establish vegetation in restoration sites (Middleton,1999). Those who believe in the "self-design" approach of wetland restoration would argue that the time and effort spend on transplanting seed banks is a waste of time and that through the physical processes of nature will determine the establishment of wetland vegetation. Though they would advocate that wetland seed banks can contain rare species and have the potential to assist wetland recovery, knowledge of seed bank composition and the ways in which certain species germinate and disperse can be invaluable to wetland restoration projects (Middleton, 1999). Wetland seed banks have been extensively studied in prairie potholes (Galatowitsch and van der Valk, 1996; Middleton, 1999. Weinhold and van der Valk (1989) found that farmed prairie potholes have the potential to retain approximately 60% of their wetland plant species for up to 20 years or more (Middleton, 1999). However, not all vascular plant species can return to drained and farmed prairie potholes after hydrology is established (Zedler, 2000) In a paper by Galatowitsch and van der Valk (1996), the "efficient community hypothesis" was studied which refers to the idea that the vegetation of restored prairie pothole wetlands will develop rapidly after their hydrology has been restored. They tested the hypothesis that according to the efficient-community hypothesis, all plant species that can become established and survive under environmental conditions found at a site will eventually be found growing there and/or in its seed bank. If this hypothesis proved to be true, it would support the "self-design" theory that all restored wetlands will establish plant communities regardless of efforts to plant or seed. However, if the hypothesis proved to be false, then restoration recovery would be affected by location of propagule source and introduction of propagules by planting or seeding. These results would support the "design" theory of wetland restoration. WHAT DID THEY CONCLUDE?
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