Disturbance (ecology)

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A forest fire is a disorder that can be natural or human

In the biological discipline of ecology, a disturbance is an event that results in a change in the biomass or other measurable parameters of an ecosystem . Both a relative and an absolute definition were discussed; the latter has prevailed. While disorders and their effects were described early on in the biological sciences, a separate subject did not develop until the 1970s. The disturbance ecology deals with the influence of disturbances on ecosystems and their reaction.

Disturbances are of particular concern because they occur in a wide variety of biocenoses and occur at all levels of ecological organization. They are an essential factor in the dynamics of ecosystems and counteract succession . Disturbances as environmental factors are of particular importance for the justification of process protection as a strategy in nature conservation .

Definitions

An event is considered a disruption in the relative sense if it triggers a deviation from the expected processes of the ecosystem. According to a relative definition, a wild fire in a grassland would not be a disturbance, since the grassland ecosystem is set up for fire and even needs fire as a regular influence in order not to overgrowth . The long-term absence of fire would then be regarded as a disturbance. Even a falling old tree in a closed forest and the processes up to the renewed crown closure would not be a disturbance. This definition has been criticized because the underlying assumption of a known, defined development of an ecosystem, which is referred to as normal, is in the vast majority of cases not sufficiently scientifically proven. In addition, the normality of a development depends on assumptions and assessments of temporal and spatial limits.

In contrast, the absolute definition relies on measurable quantities. According to White and Pickett 1985, a disturbance is “a single, time-definable event that intervenes in an ecosystem, the biocenosis or population structure and changes the resources, availability of substrate or the abiotic environment . A disturbance in this sense changes the state of structural and physical variables of the ecosystem, even if these changes in turn change functions and processes of the ecosystem ”.

Within the absolute definition, a distinction is made between 1st and 2nd order disturbances: A 1st order disturbance takes place within the dynamics of an ecosystem, such as the regeneration of a grassland after a fire or the growth of trees up to the top after the collapse of a tree in a closed forest . Second order disturbances are those that restart the succession, like a landslide, after which open ground has to be repopulated. In most cases, 1st and 2nd order disturbances lead to developments that restore the previous state. The extent of the disruption is then below the resilience of the ecosystem. However, as a result of disturbances of the 2nd order, completely different ecosystems can arise. An example would be a rise in sea level that turns dry land into a tidal zone or sea ​​floor . If the system cannot recover on its own, it can be artificially supported with methods of renaturation ecology .

Further aspects of the definition are the distinction between endogenous disturbances that are created in the ecosystem itself and exogenous disturbances that have an external effect on the ecosystem, whereby the latter can be of natural or human origin. Local events are also treated as disturbances for the ecosystems affected, as are regional events or events that go far beyond this, such as volcanic eruptions . Disturbances must always be recorded in the spatial and temporal context of the ecosystem under consideration. As an example, the influence that a brief vortex has on microorganisms that colonize a stream pebble is used. This event does not represent a disturbance for the forest ecosystem on the banks of the brook. However, when examining an ecosystem on different temporal and spatial scales, characteristics of self-similarity emerge .

As a result, disturbances are defined as events that “have an abrupt impact of more than just a small extent on measurable parameters of the ecosystem in a short, definable period of time. Processes that do not abruptly intervene in the ecosystem are not disruptions, but stressors . "

Development of discipline

In the context of the concept of ecological equilibrium, disturbances were initially examined as those influences that bring an ecosystem out of its assumed equilibrium. With the turning away from the assumption of such a balance and the increasing awareness of the dynamics of all ecological systems, the foundations had to be re-established. Systematic approaches began in the 1970s in the Anglo-Saxon area in marine biology and vegetation . Towards the end of the decade, the concept was able to establish itself in ecology. The mosaic cycle concept replaced the idea of ​​a climax society as the end point of succession; it was closely linked to the model of perturbation ecology.

In Germany from 2004 to 2009 there was a joint working group “Disturbance Ecology and Vegetation Dynamics” with a junior professorship at the Helmholtz Center for Environmental Research - UFZ in Leipzig and the University of Bayreuth . Since 2011, Bayreuth has had the first professorship for disturbance ecology.

literature

Web links

Individual evidence

  1. ^ White, Pickett 1985, p. 383
  2. ↑ Jax 1999, p. 248 f.
  3. ↑ Unless otherwise stated, this chapter is based on: White, Jentsch 2001, pp. 404–414
  4. ^ White, Pickett 1985, p. 7
  5. ↑ White, Jentsch 2001, p. 412
  6. ↑ White, Jentsch 2001, p. 409
  7. ↑ Jax 1999, p. 242 f.
  8. ^ Center for Environmental Research: Working Group: Disturbance Ecology and Vegetation Dynamics
  9. ↑ University of Bayreuth: First Professorship for Disturbance Ecology (PDF; 95 kB) Press release from February 15, 2011