Chapter 14 Disruption , Succession and Stochasticity (original) (raw)

DISTURBANCE PROCESSES AND ECOSYSTEM MANAGEMENT

USDA Forest Service White Paper, 1994

"Ecosystems are not defined so much by the objects they contain as by the processes that regulate them" Christensen and others 1989 Awareness and understanding of disturbance ecology and the role disturbance plays in ecosystem dynamics, and the ability to communicate that information, is essential in understanding ecosystem potentials and the consequences of management choices. Ecosystems constantly change in ways that are only partially predictable. To have an effective ecosystem management policy, resource managers and the public must understand the nature of ecological resiliency and stability and the role of natural disturbance on sustainability. Disturbances are common and important in virtually all ecosystems. The positive effects of disturbance on biodiversity is now recognized. Integrating disturbance ecology into sustainable resource management may be as much a social challenge as it is a biological problem. Efforts to suppress disturbance, such as lightning-caused fires, floods, erosion, drought, disease, and insects, which have been perceived to be in conflict with economic interests, have resulted in reduced biodiversity and ecosystem health. The more we attempt to maintain an ecosystem in a static condition, the less likely we are to achieve what we intended. We must be willing to bear both the economic and biologic consequences of such management. Disturbance is pervasive throughout forest and grassland ecosystems. It is not a question of whether disturbance will happen, but when, where, and what kind. Forest Service managers must consider and incorporate the following information on disturbances into the Agency's forest plans: the types of disturbance that are likely within specific ecosystems and criteria for predicting where particular disturbances will occur as well as the probability of occurrence. This information together with a knowledge of the vulnerability of certain areas to particular disturbances and the management objectives for those areas can increase the accuracy of assessments of the impact of disturbance and help managers better determine appropriate alternatives. Disturbances caused by drought, disease, fire, insects, and wind are common in ecosystems managed by the Forest Service, but are most often viewed as difficult to predict or unpredictable. Because they occur with relative frequency across these ecosystems, the characterization of these disturbance regimes and an understanding of their role in ecosystem dynamics will increase the predictability of their occurrence and their socioeconomic impacts. The "tools" to facilitate this process, such as Global Positioning Systems, Geographic Information Systems, and geo-statistical technologies, are now available. Including disturbance potential in land management plans will increase our capability to respond appropriately following the occurrence of disturbances. "Nothing is permanent but change" Heraclitus 500 B.C.

Disturbances, organisms and ecosystems: a global change perspective

Ecology and evolution, 2013

The present text exposes a theory of the role of disturbances in the assemblage and evolution of species within ecosystems, based principally, but not exclusively, on terrestrial ecosystems. Two groups of organisms, doted of contrasted strategies when faced with environmental disturbances, are presented, based on the classical r-K dichotomy, but enriched with more modern concepts from community and evolutionary ecology. Both groups participate in the assembly of known animal, plant, and microbial communities, but with different requirements about environmental fluctuations. The so-called "civilized" organisms are doted with efficient anticipatory mechanisms, allowing them to optimize from an energetic point of view their performances in a predictable environment (stable or fluctuating cyclically at the scale of life expectancy), and they developed advanced specializations in the course of evolutionary time. On the opposite side, the so-called "barbarians" are wea...

Disturbance-driven changes in the variability of ecological patterns and processes

Ecology Letters, 2008

Understanding how disturbance shapes the dynamics of ecological systems is of fundamental importance in ecology. One emerging approach to revealing and appreciating disturbance effects involves examining disturbance-driven changes in the variability of ecological responses. Variability is rarely employed as a response variable to assess the influence of disturbance, but recent studies indicate that it can be an extremely sensitive metric, capturing differences obscured by averaging and conveying important ecological information about underlying causal processes. In this paper, we present a conceptual model to understand and predict the effects of disturbance on variability. The model estimates qualitative changes in variability by considering disturbance extent, frequency and intensity, as well as ecosystem recovery, and thereby captures not only the immediate effects of disturbance but also those that arise over time due to the biotic response to an event. We evaluate how well the model performs by comparing predictions with empirical results from studies examining a wide variety of disturbances and ecosystems, and discuss factors that may modify or even confound predictions. We include a concise guide to characterizing and detecting changes in variability, highlighting the most common and easily applied methods and conclude by describing several future directions for research. By considering variability as a response to disturbance, we gain another metric of fundamental system behaviour, an improved ability to identify organizing features of ecosystems and a better understanding of the predictability of disturbance-driven change -all critical aspects of assessing ecosystem response to disturbance.