Table

References on the Concept of Organisms as Ecosystem Engineers

Species

Action

Reference

Beaver (Castor canadensis)

Dam building and hydrologie modification

Pollock et al., 1995; Johnston, 1994

Earthworms

Modification of soils

Lavelle, 1997; Lawton, 1994

Moss (Sphagnum fuscum)

Growth and nutrient accumulation

Svensson, 1995

Fish (Prochilodus mariae)

Sediment processing

Flecker, 1996

Mussel (Mytilus edulis) and tube-worm (Lanice conchilega)

Modification of current flows

Hild and Gunter, 1999

Midges (Chironomidae)

Improving the porosity of filter beds

Wotton and Hirabayashi, 1999

Deposit feeding invertebrates

Sediment processing (bioturbation)

Levinton, 1995

Termite (Macrotermes michaelseni)

Nutrient accumulation and improvement of soil physical properties

Dangerfield et al., 1998

cutting riparian forests and by altering stream hydrology and geomorphology, beavers have significant influences on biogeochemistry and biodiversity of the landscapes they inhabit. Also, because they abandon their complexes after the preferred food tree species have been depleted, they initiate succession sequences of vegetation that last on the order of tens to hundreds of years. From the human perspective, the positive roles of beavers have been long recognized. Historically, beavers were harvested for their fur almost to the point of extinction through the 1800s, but this use is now insignificant. Starting in the early 1900s the indirect positive roles of beavers due to their dam building behavior were acknowledged in terms of soil and water conservation. For example, Finley (1937) described benefits from beavers, especially in the western U.S., in conserving water and controlling erosion with the ponds created by their dams. In terms of erosion control, the ponds reduce the velocity of stream flow, causing sedimentation according to the Hjulstrom relationship. This role was particularly relevant during the human dam building era of the mid-1900s for storing sediments that otherwise would have accumulated in the man-made reservoirs of the western U.S. These reservoirs provide several water resource benefits, which become impaired as sedimentation reduces their water storage capacity. Techniques were even described (representing an early form of ecological engi-

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