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Fragmentation

Ecosystem fragmentation, along with many other global trends, is causing the natural world to undergo profound changes, at all spatial scales from the micro-habitat to the continental. The widespread and unprecedented human impact upon nature has adversely affected ecosystem health and resilience, biodiversity, and the provision of ecological goods and services that all species depend on (e.g. clean air, fresh water and healthy soils). The Society for Ecological Restoration (SER) International maintains that even with the tremendous pressures that humans presently exert upon our ecosystems, fragmentation is neither inevitable nor irreversible.

Whether it is through the creation of buffer zones, wildlife corridors/habitat, and stepping stone islands of biodiversity, the innovative approaches within a bioregional planning framework, and/or the formulation of grand continental-scale management strategies, reversing ecosystem fragmentation and reinstating connectivity is fundamentally about transforming our approach to land management from one of maximizing short-term resource use to one of optimizing long-term resilience and health, while providing socio-economic and cultural survival benefits.

Ecosystem fragmentation occurs when habitats, landscapes, and ecosystems are disconnected by human or non-human determinants, including the short-term, non-sustainable exploitation of renewable or non-renewable natural capital. As a result, contiguous natural areas are broken up into smaller pieces or patches that lead to shrinkage, attrition, and isolation — all of which can be summarized under the term fragmentation. This creates discontinuities in ecological processes (e.g. nutrient flows, energy transfers and genetic exchanges) that impede or alter the flow of goods and services to the detriment of ecosystem health and human well-being (Aronson et al. 2007). In this statement, restoration planning recognizes a distinction between landscape level ecological processes or services and the role of fragments in their habitat suitability for particular species. In this sense, species-specific functions of habitats are not necessarily the functional equivalent of ecosystems or landscapes.

Fragmentation can best be understood as a continuum with intact or pristine ecosystems at one end, variegated or fragmented habitats in the middle, and relictual landscapes at the other (McIntyre & Hobbs 1999, Lindenmayer & Fischer 2006). Intact ecosystems are precious not only due to their structure as forests or wetlands but also because of their functionality — that is their ability to sustain the healthy and resilient species populations that coevolved within as well as the health and resilience of human communities that depend on them for survival. Perhaps the most important feature of an intact ecosystem is connectivity at multiple spatial scales that encourages the dynamic ecological processes that all biota rely on.

Variegated landscapes are typically characterized by both gradual and abrupt boundaries between native and non-native vegetation, and often times the dissection and utilization of only one or two components, such as a forest that is managed for timber production, grasslands transformed for livestock grazing, or arid lands that are stripped for metals and minerals. In general, some degree of connectivity survives and these modified ecosystems can continue to exist without the full disruption or complete loss of structure, function, and biodiversity.  Fragmented landscapes are characterized by more abrupt boundaries between native and non-native vegetation and are typically found in areas developed for agriculture or production forestry, where remnants of native vegetation abut land which is usually cleared and cultivated, or planted with non-native tree species.

Relictual ecosystems occur most often when humans replace complex intact ecosystems with simplified linear ones, as is the case with industrial agricultural production systems where forests are clear-cut, grasslands tilled, and wetlands drained. The transformation of a healthy forest into a monoculture for timber or the delineation of grasslands for livestock grazing often leaves only isolated historical remnants of native vegetation. Relictual landscapes also result from urban/suburban development and the ecologically degrading practices of extractive industries, like strip-mining and the harvesting of oil sands. With little or no connectivity among the small patches scattered across the landscape, these ecosystems are no longer able to provide the goods and services necessary to support prior levels of biodiversity.

Even seemingly innocuous linear barriers to connectivity (e.g. fences and power lines, roads and canals) can sometimes significantly impact biota and even reduce biodiversity by disrupting essential ecological processes. As a result, they can have cascading effects, such as secondary extinctions and facilitating the spread of invasive non-native species, which affect the developmental trajectory of ecosystems. For example, the loss of dispersal and migration opportunities in some species can result in a weaker gene pool and thereby a less healthy and resilient population through ruptures in metapopulation dynamics. On the other hand, badly planned or implemented corridor restoration can also facilitate the spread of invasives, disease and fire (e.g. the provision of nutrient rich soils in roadside vegetation schemes can facilitate the spread of invasive plant species). Connectivity does not equal “corridors” but relates to the overall characteristics of the landscape which facilitate or hinder movement of oranisms across the landscape. Hence, the goal is to provide the opportunity for native biota to move as necessary but limit the potential for negative effects from invasives, diseases, etc.

The effects of ecosystem fragmentation often linger and expand, much like a ripple in a pond. One way this can happen is when ecosystem fragmentation introduces edge effects that occur along the margins of natural areas. These edge effects include the seepage of deleterious transformations in ecological structure and function from the boundary deep into the interior of remnant patches causing a further erosion in biodiversity which affects different species at different depths of penetration. Finally, fragmentation can result in regime shifts when the loss of dominant or keystone species fundamentally alters ecosystem structure, function, and composition as has been in the case with wide-ranging predators and migrating herds.

Read the October 2008 SER Policy Position Statement on Ecosystem Fragmentation


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