Fragmentation

Definitions

According to the dictionary, the term fragmentation means “the breaking apart or up into pieces.” It follows, then, that habitat fragmentation means the breaking apart of habitat into pieces. Unfortunately, this definition doesn't apply perfectly to habitat fragmentation in the real world. Using an analogy, when a porcelain vase is “fragmented,” the amount of porcelain remains constant. Yet habitat fragmentation generally occurs through a process of habitat removal, because the total area under consideration remains constant, while the total area of habitat is reduced. Therefore, habitat loss and fragmentation per se are inextricably linked in real-world landscapes. The simple dictionary definition of fragmentation fails to address the following considerations.

First, habitat fragmentation is a process of landscape change. It is not a state or condition of the landscape at any snapshot in time, even though it is often meaningful to substitute space for time and compare the relative fragmentation of habitats among landscapes. Strictly speaking, however, habitat loss and [Page 150]fragmentation involve the progressive reduction and subdivision of habitat over time, which results in the alteration of landscape structure and function. This transformation process involves a number of physical changes in landscape structure and can proceed in different patterns and at different rates, depending on the causal agent and the ecological characteristics of the landscape.

Second, habitat fragmentation is a landscape-level process, not a patch-level process. Fragmentation alters the spatial configuration of habitat patches within a broader habitat mosaic or landscape, not merely the characteristics of a single patch. Thus, although individual patches are affected by fragmentation (mainly through isolation from other patches), the entire landscape mosaic is transformed by the fragmentation process.

Third, habitat fragmentation is a species-specific process, because habitat is a species-specific concept. Habitat is defined differently, for example, depending on whether the target species is a forest generalist or forest specialist. Attention to habitat specificity is crucial because the fragmentation trajectory within the same landscape can differ markedly depending on how broadly or narrowly habitat is defined. In addition, since organisms perceive and respond to habitats differently, not all organisms will be affected in similar ways by the same landscape changes. As one focal habitat undergoes fragmentation, some organisms will be adversely affected and some may actually benefit, whereas others will be unaffected.

Fourth, habitat fragmentation is a scale-dependent process, both in terms of how we (humans) perceive and measure fragmentation and in how organisms perceive and respond to fragmentation. The landscape extent in particular can have an important influence on the measured fragmentation level; a highly fragmented habitat at one scale may be comparatively unfragmented at another scale (e.g., when fragmented woodlots occur within a forested region). In addition, for habitat fragmentation to be consequential, it must occur at a scale that is functionally relevant to the organism under consideration.

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