restricted access IV.1 Landscape Dynamics
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IV.1 Landscape Dynamics David J. Tongway and John A. Ludwig OUTLINE 1. A view of landscapes as functioning systems 2. Spatial heterogeneity as an organizing principle in landscape dynamics 3. Function and dysfunction in landscape dynamics 4. The role of feedback loops 5. Assessing landscape dynamics: Thresholds and climate change 6. Concluding remarks A terrestrial landscape can be viewed as a system of biological elements (organisms, populations, communities) forming a pattern across a topographic geomorphic unit. The dynamics of these landscape systems are driven by topography and climate and by interacting geochemical and biophysical processes. Although we recognize that important conceptual advances in landscape dynamics have been developed, such as how landscapes behave as complex adaptive and self-organizing systems, in this chapter we particularly focus on the development of the notion of landscape function, that is, how a landscape works as a geochemical–biophysical system to regulate vital resources over space and time. In highly functional landscapes, a major rainfall event will trigger runoff, but, overall, little loss of water, topsoil, and organic matter occurs from the system because these resources are dynamically captured by patterned structures within the landscape such as vegetation patches, which function as reserves or resource ‘‘banks.’’ Vegetation patches then utilize retained resources (water, nutrients) in growth pulses to produce biomass such as seeds, most of which are cycled back into the system (soil seed banks). Biomass can also function to maintain the retentive capacity (structure) of the patch and can provide shelter and food for fauna or for consumption by livestock, which when harvested represent offtake from the system. Damaged landscapes become dysfunctional by losing their capacity to effectively regulate resources. GLOSSARY landscape dynamics. How a landscape, as a system of interacting components, structures, and processes, varies in space and time landscape function. How a landscape works as a tightly coupled geochemical–biophysical system to regulate the spatial availability and dynamics of resources landscape heterogeneity. The mix of different components , structures, and processes occurring in a landscape ,suchashowdifferentorganismsdisperseamong different vegetation patches landscape restoration/rehabilitation. The actions and processes taken to help damaged landscapes recover toward a specified goal (landform, land use) landscapes as self-organizing systems. How components , structures, and processes in a landscape dynamically organize to form complex, adaptive, and stable systems landscape system threshold. A point in the dynamics of a landscape where the system changes to a different state, as, for example, a damaged landscape becomes dysfunctional to the point where available resources no longer support a species 1. A VIEW OF LANDSCAPES AS FUNCTIONING SYSTEMS We view landscapes and marvel at the patterning of their interconnected ecosystems and wonder about what dynamic processes have caused these patterns. What have we learned about the dynamics of landscape patterns and processes in recent times? In this chapter we explore new developments in landscape dynamics by building on the work of Turner, Gardner, and O’Neill (2001) and others and by adding our Australian perspective . Disturbance-induced effects on landscapes are described in later chapters in part IV. The importance of spatial heterogeneity and selforganization for explaining landscape dynamics has become increasingly recognized over the last 25 years as seen in the writings of Kolosa and Pickett (1991) and Rietkerk and others (2002). This recognition has led to studies on landscape function, that is, how a landscape works as a tightly coupled geochemical–biophysical system that regulates the sources and dynamics of energy , water, and nutrient resources (Tongway and Ludwig, 1997). Landscape function and its dynamics in space and time can be resolved into the availability of vital resources, which strongly affect the responses of biota, especially if stressed or disturbed. Initially, distinctions were made between measured system complexity and functional heterogeneity, which described how ecological entities such as species perceived , related to, and responded to each other. In the last 25 years, fine-scaled ecological processes have been increasingly integrated with broad-scale geographic–geomorphologic studies to better understand overall landscape function. The underlying processes that determine how landscapes function, the need for understanding heterogeneity, and how function is affected by stress and disturbancehavebeenstudiedinmoredetailbyintegrating disciplines (Lovett et al., 2005); this has benefited both the science and the management of landscapes. A metaphor for how landscapes function as an integration of processes is a gear train (Lavelle et al., 2006). A landscape may be visualized as system of intermeshing gears, with each gear being a distinct ecosystem with its unique structures (composition) and processes (size, speed) but tightly interconnected (meshed...