Restoration potential of de-watered riparian ecosystems: Role of soil seed banks

Desert rivers have highly variable flow regimes, with intense floods and short-lived resource pulses. Their floras thus are dominated by species with short life cycle but long-lived seeds. We summarize three studies designed to address the role of soil seed banks in restoration projects involving the return of stream flows to dewatered rivers. The first study showed that despite decades of diversion, a riparian zone downstream of a dam had viable soil seed banks, with composition and diversity similar to a reference river (but with shifts toward upland species). The second study, along a dewatered urban river, showed that small pockets of riparian vegetation developed at storm drain outflows, with diversity and composition (of seed banks and vegetation) similar to above-dam control sites. A third study suggested that landscape position can influence seed banks, with some dry sites in close proximity to wet sites having greater densities of wetland seeds than those located farther away from resource-rich areas. Implications for restoration and future research are: 1) viable seed banks in dry reaches may obviate the need for seed augmentation (for particular functional groups) in conjunction with flow restoration; 2) restoration efforts should pay attention to landscape context and connectivity, as they influence processes such as seed migration;  3) studies are needed to determine the decay rate of seed viability in dewatered reaches, as this will set the length of the 'revegetation potential' window.