Disturbances Maintain Habitat

dark brown and black mountains with white snow next to water and clouds

Biological Strategy

Scandinavian subalpine and alpine habitats

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Manage Disturbance in a Community

When environmental conditions change, they can disrupt an ecosystem’s equilibrium. Excessive rain can cause flooding and drought can cause forest fires. An ecosystem must be resilient to such disturbances. Disturbances are unpredictable in location, size, and intensity, so ecosystems must be able to regrow and must have a variety of duplicate forms, processes, or systems that are dispersed in location. For example, a forest ecosystem can recover from fire because diverse organisms play different roles in different ways and in different locations. Many organisms can resprout or grow from seeds triggered by fire, and their dispersed distribution ensures that an entire population isn’t decimated. Though the recovered ecosystem may look totally different from the pre-fire one, the ecosystem as a whole remains healthy.

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Biological Control of Populations, Pests, Diseases

An ecosystem must prevent overpopulation of any given species within it, as well as the spread of pests and diseases, to allow organisms to survive without threatening extermination of other organisms or ecosystems. To control pests and diseases, living systems use such strategies as developing antibodies and killing or repelling pests or disease-causing organisms. Ecosystems have checks and balances to maintain populations, pests, and diseases. For example, in a lake, a balance of predators, prey, and nutrients is crucial for proper functioning of the ecosystem. Predatory fish keep down the numbers of smaller prey fish, which in turn keep populations of algae-eating zooplankton in check. When the levels of any of these organisms change, the change can disrupt the health of the entire ecosystem.

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Maintain Biodiversity

The greater the amount of genetic and species variation in an ecosystem, the more resilient that ecosystem is to disturbances. Variation in ecosystems across the Earth also contributes to the Earth’s resilience to unpredictable changes. This variation is called biodiversity. Because living systems compete with each other for scarce resources, maintaining biodiversity involves creating conditions for a large variety of species to successfully co-occur and reproduce. For example, within a wetland, there are different vegetation types. This diversity results in a complex mosaic of microenvironments as the vegetation types alter air flows, light regimes, and water temperatures and chemistry. Because organisms vary in their ideal environmental conditions, these micro-environments increase the diversity of plants in the wetland. In turn, having a wetland in an otherwise dry area increases biodiversity at an even larger scale.

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a mountain with snow is in the background of a landscape with trees and shrubbery

Ecosystems

Eco- ("household"), system ("organized whole")

An ecosystem consists of all the biological and nonbiological elements that make up a defined area. That definition might seem vague, but that means it’s flexible: We can apply the word across different scales and times. Ecosystems can be small, like a single tide pool, or large, like coastal wetlands. Ecosystems can include plants, animals, bacteria, fungi, rocks, temperature, light, soil, and climate—all linked through the flow of energy and cycle of nutrients. Each part of an ecosystem interacts with, and is influenced by, other members of the system. These interactions are dynamic, leading to changes to any ecosystem over time.

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Scandinavian subalpine and alpine habitats are maintained when they continue to experience pulsed disturbances.

“We term this network of species, their dynamic interactions between each other and the environment, and the combination of structures that make reorganization after disturbance possible; the ‘ecological memory’ of the system (21, 22)…The ecological memory is a key component of ecological resilience, i.e. the capacity of the system to absorb disturbances, reorganize, and maintain adaptive capacity (25)…Among the major disturbances [in Scandinavian alpine and subalpine regions, dominated by heaths and mountain bird forests] are grazing by rodents, reindeer and moth caterpillars (Epirrita autumnata) (87–90). These occur as pulses with different frequencies and spatial scales (Table 3). Rodents are usually cyclic (87) and play a role in the maintenance and dynamics of dwarf shrubs and mosses (88). Reindeer, controlling the abundance of lichens, traditionally grazed in a pulsed manner both between years on single sites and regionally on a longer time scale, as reindeer populations waxed and waned on a 30–50 year cycle (89). Fire occurs irregularly, and affects dwarf shrub composition, favoring Vaccinium at the expense of Empetrum (91)…However, if we recognize the dynamic nature of the mountain ecosystems and the rights of the Sami and other local residents to use these areas for their subsistence, another approach is more likely to be successful. This includes the removal of fences that hinder the natural migration routes, and a dynamic reserve or set-aside system aimed at restoring the seminatural dynamics of mountain ecosystems, with their pulsed disturbances.” (Bengtsson et al. 2003:389, 393, 394)

Last Updated August 18, 2016

References

Journal article

Reserves, Resilience and Dynamic Landscapes

AMBIO: A Journal of the Human Environment | 11/03/2009 | Janne Bengtsson, Per Angelstam, Thomas Elmqvist, Urban Emanuelsson, Carl Folke, Margareta Ihse, Fredrik Moberg, Magnus Nyström

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