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Mark Anderson: Landscape Resilience = Options and Alternatives

Mark Anderson 11/15/2012

Sandhill ecologist Aldo Leopold captured the concept of ecological resilience in one elegant 1949 statement: “Health is the capacity of the land for self-renewal. Conservation is our effort to understand and preserve this capacity” (Leopold 1949).
More than 50 years later, Lance Gunderson defined resilience as nature’s “capacity for renewal in a dynamic environment” (Gunderson 2000). Intentionally or not, Gunderson linked his definition to Leopold’s while updating it to incorporate the reality of change — a recognition fundamental to today’s practice of conservation.   
Many ecologists, most notably C.S. Holling (1973), have tried to pin down the concept of resilience and identify the mechanisms that create it; but its elusive character is familiar to anyone who follows politics or watches sports. In these arenas, resilience is characterized by surprises and unexpected twists — the crushed candidate who rebounds in a wholly unexpected way, or the team that rises when their star goes down and a bunch of previously overlooked players suddenly catch fire. In these cases, the expected results didn’t occur because somewhere in the mix there were options and alternatives. Such options and alternatives build resilience in the ecological realm as well.
In our work on the resilience of eastern landscapes of the United States to climate change (Anderson, Clark and Sheldon 2012, Anderson and Ferree 2010), we have focused on identifying the factors that create options and alternatives for species and processes within places. The distinction is important: the attributes of resilience differ depending on whether you are focused on species and ecosystems, or on enduring physical landscapes. The question we have grappled with is: which factors allow a landscape — defined as geophysical setting — to sustain ecological function and maintain a diverse array of species places even as the climate changes? It’s a great conservation question, because those places with inherent properties that build resilience will likely also be natural strongholds for species and nature into the future.
Are there identifiable factors that create options for species and processes within places? At least two characteristics have emerged in the literature based in on-the-ground evidence, and they are related to how complex and permeable a particular landscape is.
Complexity refers to the way topographic and elevation diversity parse the regional climate into an array of microclimates that in turn provide climate options for the extant species. Consider a landscape with hot southern slope faces, moist cool coves, and depressed basins that accumulate moisture; the temperature extremes within these local climates can be greater than the regional mean and variance. Stuart Weiss’s work in the California foothills (Weiss et al. 1998) and Patrick McMillan’s in the South Carolina mountains suggests that these topo-climates are a key to the persistence of plants and animals within these settings — McMillan recorded temperatures as high as 105 degrees F. on a south slope, but only 73 degrees F. on the connected shady north slopes at the same time (McMillan pers. com). Of course, hikers in the New England forests have long known they can store their beer in talus-formed ice caves on a hot August day and return to find it cold and ready for consumption, sharing space with spruce and snowberry more typical of farther north. Species persist in a changing climate by taking advantage of this array of microclimate options when available within their local landscape. The concept has now been coined as “microclimatic buffering” (Willis and Bhagwat 2009). And as climate scientists fit topographic diversity into their models, this buffering is being found to slow down the velocity of climate change’s effects on a variety of species (Luoto and Heikkinen 2008, Loarie et al. 2009).
How permeable a landscape is with respect to its natural processes and ecological flows is a second factor in creating options. By definition, resilient landscapes are dynamic and will rearrange their components to take advantage of microclimates and species turnover. In highly fragmented landscapes, contrasting uses such as development, roads or high-intensity agriculture create resistance that disrupts, restricts and channels natural movements. The ultimate effect is reduced options. However, the permeability of a landscape can be increased depending on how the matrix lands are managed, how farming is practiced, how development is zoned, how roads are planned. The interplay of resistance and permeability is a ripe area for conservation action and research. 
Resilience and Change
Finally, increasing resilience by increasing options for species and processes is not the same as knowing what is going to happen. In our work for the eastern United States, we defined resilience as the ability of a place to sustain ecological function and maintain a diverse array of species. But how the communities actually change — which species will thrive and which ones won’t — is dependent on a myriad of interactions, disturbances, starting conditions and arbitrary events. If the outcome is completely predictable, then there must be very few options or alternative paths available to the inhabitants…which is a good definition of a vulnerable, non-resilient site. Still, I hope even the vulnerable site will have some surprises in it. Sixty-three years after Leopold made his statement, I think we still have a long way to go to understanding and conserving the capacity of the land for self-renewal.

Anderson, M.G., M. Clark, and A.O. Sheldon. 2012. Resilient sites for terrestrial conservation in the Northeast and Mid-Atlantic region. The Nature Conservancy. See: http://conserveonline.org/workspaces/ecs/documents/resilient-sites-for-terrestrial-conservation-1
Anderson M.G., and C. Ferree. 2010. Conserving the stage: Climate change and the geophysical underpinnings of species diversity. PLoS ONE 5(7):E11554.doi:10.1371/journal.pone.0011554
Beier, P and B. Brost. 2010. Use of land facets to plan for climate change: Conserving the arenas, not the actors. Conservation Biology 24:701-710.
Gunderson, L.H., 2000. Ecological resilience — in theory and application. Annual Review of Ecology and Systematics 31:425-439.
Heller, N.E., and Zavaleta E.S. 2009. Biodiversity management in the face of climate change: A review of 22 years of recommendations. Biological Conservation 142:14-32.
Holling, C.S. 1973. Resilience and stability of ecological systems. Annual Review of Ecology and Systematics 4:1-23.
Krosby, M., Tewksbury, J., Haddad, N.M., Hoekstra, J. 2010. Ecological connectivity for a changing climate. Conservation Biology 24(6):1686–1689.
Leopold, A. 1949. A Sand County Almanac. Random House: New York.
Loarie, S. R., P.B. Duffy, H. Hamilton, G.P. Asner, C.B. Field, and D.D. Ackerly. 2009. The velocity of climate change. Nature 462:1052-1055
Luoto, M. and R.K. Heikkinen. 2008. Disregarding topographical heterogeneity biases species turnover assessments based on bioclimatic models. Global Change Biology 14(3):483–494.
Randin, C.F., R. Engler, S. Normand, M. Zappa, N. Zimmermann, P.B. Pearman, P. Vittoz, W. Thuiller and A. Guisani. 2008. Climate change and plant distribution: Local models predict high-elevation persistence. Global Change Biology 15(6):1557-1569.
Weiss, S. B., D. D. Murphy, and R. R. White. 1988. Sun, slope, and butterflies: Topographic determinants of habitat quality for Euphydryas editha bayensis. Ecology 69:1386.
Willis, K.J. and Bhagwat, S.A. 2009. Biodiversity and climate change. Science 326:807.

Mark Anderson is the Director of Conservation Science for the Eastern North America Division of The Nature Conservancy.