An Introduction to Landscape Ecology

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the altered flooding regimes, increased suspended loads, chemical contamination, and community structure changes in virtually every temperate river in the world. The degradation of EarthÕs ecosystems is further signaled by the unprecedented decline of thousands of species, many of which have become extinct. Many of these crises are the result of cumulative impacts of land use changes occurring over broad spatial scales (i.e., landscapes). Questions of how to manage populations of native plants and animals over large areas as land use or climate changes, how to mediate the effects of habitat fragmentation or loss, how to plan for human settlement in areas that experience a particular natural disturbance regime, and how to reduce the deleterious effects of nonpoint source pollution in aquatic ecosystems all demand basic understanding and management solutions at landscape scales. 1.9  # Concepts of scale Despite early attention to the effects of sample area on measurements, such as species-area relationships, the importance of scale was not widely recognized until the 1980’s. Recognition that pattern-process relationships vary with scale demanded that ecologist give explicit consideration to scale in designing experiments and interpreting results. It became evident that different problems require different scales of study, and that most problems require multiple scales of study. The theory of scale and hierarchy emerged as a framework for dealing with scale. The emergence of scale and hierarchy theory provided a partial theoretical framework for understanding pattern-process relationships, which became the basis for the emergence of landscape ecology as a discipline. 1.10  # Dynamic ecosystem view A major paradigm shift in ecology from the ÒequilibriumÓ view of ecosystems to a ÒdynamicÓ view occurred in the 1980’s. Coupled with the view that ecosystems are dynamic, characterized more by their dynamics than by their tendency towards a stable equilibrium, is the notion that ecosystems are not isolated systems and cannot be understood without considering the flow of energy and material across ecosystem boundaries. This view of ecosystems as ÒopenÓ systems required an understanding of how mosaics of ecosystems interact to effect ecosystem processes, and this led to the emergence of landscape ecology. 1.11  # Technological advances Technological advances, in particular, rapid advances in computing power, availability of remotely sensed data such as satellite images, and development of powerful computer software packages called geographic information systems (GIS) for storing, manipulating, and displaying spatial data, provided the tools for studying spatial patterns over broad spatial scales. Indeed, because landscapes are often large in extent, the use of computers and computer models are essential to studying their behavior. Technological advances since the 1980’s has made possible the study of landscapes. The American school of landscape ecology, in particular, is heavily invested in the use of these technologies. 1.12  3. Why is landscape ecology important to resource managers? Landscape ecology (or a landscape perspective) with its focus on spatial patterns is important to resource managers because: 1) ecosystem context matters, 2) ecosystem function depends on the interplay of pattern and process, and 3) because human activities can dramatically alter landscape context and the relationship between patterns and processes, resource managers have a stewardship responsibility to understand and manage these impacts Ð more pragmatically, resource managers have a policy and legal mandate to include a landscape perspective in resource management decisions. 1.13  # Because ecosystem context matters Landscape ecology is founded on the principle that ecosystem composition, structure and function partially depend on the spatial (and temporal) context of the ecosystem (i.e., its landscape context); i.e., that what we observe ecologically at any particular location is affected by what is around that location. This shift in perspective from the site to the site embedded in a landscape context has profound implications for resource management. LetÕs consider a couple of examples: ¥ Metapopulations.ÐMetapopulations depend on the number and spatial arrangement of habitat patches Ð where the probability of a habitat patch being occupied at any time is at least partially dependent on its proximity to other habitat patches. Focusing management on the individual site, in this case, without consideration of its landscape context, can have disastrous consequences for the population. ¥ Forest succession.ÐNeighborhood effects can play an important role in determining the successional response following a disturbance. For example, edge effects that modify the distribution of energy and water and the plant species composition of the immediate neighborhood (which can influence the relative abundance of propagules) can exert a strong influence on succession in forest gaps and in larger openings, e.g., via wave-form succession. Ignoring these effects can lead to undesirable outcomes, including an unwanted shift in species composition or an inadequate recovery of vegetation altogether. 1.14  # Because ecosystem function depends on the interplay of pattern and process Landscape ecology is also founded on the principle that spatial patterns affect ecological processes, which in turn affect spatial patterns. This interplay of spatial pattern and process is in fact the overarching focus of landscape ecology. While it can be argued that ÒecologyÓ has always sought to explain the relationship between pattern and process, it is safe to assert that ÒlandscapeÓ ecology has shifted the focus to pattern-process relationships over broad spatial extents and emphasized the role of humans in creating and affecting these relationships. This shift has profound implications for resource managers. LetÕs consider a couple of examples: ¥ Habitat fragmentation.ÐDisruption of habitat connectivity is a major impact of human activities on plant and animal populations and one of the leading causes of the biodiversity crisis. Anthropogenic landscape elements (e.g., roads, developed land, dams) can function as impediments to the movement of organisms across the landscape, and the cumulative impacts of these impediments over broad spatial extents can be devastating. ¥ Alteration of disturbance regimes.ÐDisruption of natural disturbance regimes has long- lasting ecological and socio-economic impacts. For example, disruption of fuel mass and continuity by human land use practices (e.g., livestock grazing) over broad spatial extents can dramatically alter fire regimes in fire-dependent ecosystems, leading to shifts species distributions and community structure