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Landscape Connectivity of Geographically Isolated Wetlands

Landscape Connectivity of Geographically Isolated Wetlands. Scott G. Leibowitz U.S. Environmental Protection Agency National Health and Environmental Effects Research Laboratory Western Ecology Division June 20, 2006. Outline of Talk. Significance of isolated wetlands

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Landscape Connectivity of Geographically Isolated Wetlands

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  1. Landscape Connectivity of Geographically Isolated Wetlands Scott G. Leibowitz U.S. Environmental Protection Agency National Health and Environmental Effects Research Laboratory Western Ecology Division June 20, 2006

  2. Outline of Talk • Significance of isolated wetlands • Isolation vs. connectivity • Hydrological connectivity • Biological connectivity

  3. Significance of Isolated Wetlands Why do we care? Under the Clean Water Act, “Waters of the U.S.” include intrastate lakes, rivers, streams, wetlands the use, degradation or destruction of which could affect interstate commerce [“(a)(3)” regs]

  4. Significance of Isolated Wetlands Why do we care? The “Migratory Bird Rule” included habitat by migratory birds as an example of such a commerce link

  5. 2001 SWANCC Ruling Held: Title 33 CFR §328.3(a)(3), as clarified and applied to petitioner’s site pursuant to the Migratory Bird Rule, exceeds the authority granted to respondents under §404(a) of the CWA.

  6. Regulatory Implications • CWA intended some “connection” to navigability • Isolated waters need “significant nexus” to navigable waters to be jurisdictional

  7. Outline of Talk • Significance of isolated wetlands • Isolation vs. connectivity • Hydrological connectivity • Biological connectivity

  8. What is an Isolated Wetland? Hydrological and biological definitions are difficult to apply and require detailed information

  9. What is an Isolated Wetland? Geographically isolated wetlands • Wetlands completely surrounded by upland (Tiner 2003b) • Practical, can use GIS and/or three parameter approach

  10. Major Conclusion Isolation is not a discrete, generic property, but should be viewed as a spatial and temporal continuum

  11. Outline of Talk • Significance of isolated wetlands • Isolation vs. connectivity • Hydrological connectivity • Biological connectivity

  12. Water table Confining layer Hydrological Connectivity GW discharge GW recharge Local flow system Intermediate flow system Regional flow system Adapted from Sando 1996

  13. YEARS HYDRAULIC CONDUCTIVITY (m/s x 10-4) Ground Water Travel Time Source: Winter and LaBaugh 2003

  14. D100 D25 Water table Confining layer Dt = v t c = K (dh/dl) ne-1 t c GW discharge GW recharge Local flow system Intermediate flow system Regional flow system Adapted from Sando 1996

  15. Surface Water Connectivity

  16. Intermittent SW Connectivity Source: Wigington et al. 2005

  17. Intermittent SW Connectivity Source: Leibowitz and Vining 2003

  18. Intermittent SW Connectivity Source: Leibowitz and Vining 2003

  19. Intermittent SW Connectivity

  20. Source: Wolock et al. 2004

  21. Outline of Talk • Significance of isolated wetlands • Isolation vs. connectivity • Hydrological connectivity • Biological connectivity

  22. Community Function • Prior to 1980s, ecological communities considered a function of on-site habitat • Regional biodiversity results from sum of individual parts + +

  23. Landscape Perspective “…flows and transfers between spatial components assume special importance, and the process of redistribution of organisms, materials and/or energy among landscape components is thus an essential feature of landscape ecology” Risser, P.G., J.R. Karr, and R.T.T. Forman. 1984. Landscape Ecology: Directions and Approaches. Illinois Natural History Survey Special Publication Number 2, Champaign, IL.

  24. Landscape Perspective Regional biodiversity dependent on complex interactions between components

  25. Landscape Perspective Because isolated wetlands often occur as complexes within the landscape, they should serve as examples of how community function is dependent on the landscape

  26. Metapopulation Theory Levins 1970 • Species regarded as a population of local populations • Extinction of species equivalent to extinction of constituent local populations

  27. Metapopulation Theory Levins 1970 • Metapopulation dynamics are function of extinction and recolonization dynamics dN/dt = mg(N) – ēN N = Proportion of sites supporting populations • Metapopulation can persist if ē < m

  28. BIOGEOGRAPHIC PATTERN MENDELIAN SELECTION POPULATION SIZE SPECIES DURATION IN TIME DRIFT GROUP SELECTION Metapopulation Theory Levins 1970 BEHAVIOR Number of migrants Maximum travel distance (tmax) SPATIAL PATTERN OF ENVIRONMENT Distance between sites (d ) MIGRATION RATE MIGRANT SELECTION METAPOPULATION EQUILIBRIUM LOCAL POPULATION DYNAMICS GENETIC CHANGE COMMUNITY STRUCTURE EXTINCTION RATE

  29. Isolated vs. Connected tmax << dmin: completely isolated >> dmax: completely connected >> dmin >>> dmin > dmin

  30. Are Isolated Wetlands Isolated? • Mean nearest neighbor distance 0.3-0.4 km (low d) • Many species with high tmax(e.g., wind- dispersed seeds, waterfowl) • tmax >> d

  31. Are Isolated Wetlands Isolated? “[Prairie potholes] are not isolated habitats. Most wetland plants and animals found in the region have the mobility or dispersability needed to spread rapidly from pothole to pothole, with fish being a significant exception.” van der Valk and Pederson 2003

  32. Are Isolated Wetlands Isolated? tmax = 100 km tmax = 200 km tmax = 500 km Source: Roshier et al. 2001

  33. Are Isolated Wetlands Isolated? Source: Tiner 2003b

  34. What About Aquatic Species? “[Prairie potholes] are not isolated habitats. Most wetland plants and animals found in the region have the mobility or dispersability needed to spread rapidly from pothole to pothole, with fish being a significant exception.” van der Valk and Pederson 2003

  35. What About Aquatic Species? ?? tmax = 0

  36. Intermittent SW Connectivity

  37. Intermittent SW Connectivity Reinterpreting travel distance • For non-aquatic species, tmax is function of physiology and behavior • For aquatic species, travel distance depends on storm frequency, AMC, soil imperviousness, and relief

  38. Multiple Habitat Requirements • Amphibians require wetland and core upland habitat during different life stages (Gibbons 2003) • Requires more complex analysis that considers spatial and temporal arrangement of core habitat types and timing of life history needs

  39. Effects of Isolated Wetland Loss 1000 Density = Connections = 3836 100 250 500 32 936 217

  40. Conclusions • Isolation is not a discrete, generic property, but should be viewed as a spatial and temporal continuum • Metapopulation persistence depends, in part, on the species ability to disperse and the spatial arrangement of sites

  41. Conclusions • Any impacts that increase the extinction rate or decrease the migration rate will alter community composition • A landscape perspective that considers connectivity and supplemental habitat is necessary to conserve the rich biota associated with isolated wetlands

  42. Questions? leibowitz.scott@epa.gov

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