Ecological constraints to re-establishing native trees on severely-degraded floodplains
Riparian zones in Mediterranean and other semi-arid regions are important ecosystems that are sustained by flooding regimes and other physical factors that affect water availability to organisms. In many dry regions, riparian ecosystems have been negatively affected by dam construction, water diversions, and floodplain development. In cases where impacts are severe, restoring natural processes such as flow regimes may not achieve restoration goals quickly, or ever, and habitat must be created by direct intervention (e.g., re-grading floodplains, constructing wetlands, planting trees). Dredger spoils from floodplain surface gold mining are particularly difficult to revegetate in arid regions because of the near-total loss of fine sediment and moisture-holding soils. Tree establishment is often constrained by both abiotic factors (e.g., drought, soil salinity) and biotic interactions (e.g., competition, herbivory), and the relative strength of these limiting factors can shift within the first few years following restoration. I am using survival time analysis to determine the shift in factors limiting survival of native riparian trees planted within a dredged floodplain on the Merced River in California’s Central Valley. Initial results indicate that temporal shifts in mortality drivers (e.g., from initial planting size to groundwater depth) interact strongly with plant traits and may play a strong role in community assembly following restoration of highly disturbed sites.
Downs, P.W., M.S. Singer, B.K. Orr, Z.E. Diggory, T.C. Church, and J.C. Stella. 2011. Restoring ecological integrity in highly regulated rivers: The role of baseline data and analytical references. Environmental Management 48:847–864. DOI: 10.1007/s00267-011-9736-y
Stillwater Sciences. 2006. Merced River Ranch revegetation experiment. Prepared by Stillwater Sciences, Berkeley, California, for CALFED, Sacramento, California. [pdf report]