January 2000: Policy direction for biodiversity is now represented by the Landscape Unit Planning Guide. This Extension Note should be regarded as technical background only.
Various plants and animals rely on different forest ecosystem "stages" to meet their habitat needs. Grizzly bears, for example, can range over hundreds of square kilometres in search of the food resources available in open and young forests before hibernating deep in mature forests. Some plant species can only develop on open, treeless, freshly disturbed sites, while certain canopy-dwelling insects spend their entire lifetime on the broad lichen- and moss-covered limbs of a single ancient spruce. During spring and summer, deer may sample tender herbs in clearcut areas, but, in severe winters, retreat several kilometres to protective old-growth stands.
Landscapes and the ecosystems that compose them "age" through time. The process of forest aging called "succession" transforms the composition of forested ecosystems as biotic communities respond to and modify their environment. Succession is an important topic in landscape ecology because of its significant effects on landscape diversity and the subsequent biological diversity and viability of various plant and animal populations.
The Forest Practices Code acknowledges the importance of landscape ecology concepts by enabling district managers to designate planning areas called landscape units, each with specific landscape unit objectives. The Biodiversity Guidebook (B.C. Ministry of Forests and B.C. Ministry of Environment, Lands and Parks 1995), a component of the Code, recommends procedures to maintain biodiversity at both the landscape and the stand level. This approach, which uses principles of ecosystem management tempered by social considerations, recognizes that the habitat needs of most forest and range organisms are met if a broad range of forest stand ages ("seral stages") are maintained across landscapes.
This extension note is the seventh in a series designed to raise awareness of landscape ecology concepts and to provide background for the ecologically based forest management approach recommended in the Biodiversity Guidebook. The focus here is on seral stages. We first define succession and seral stages. We then discuss the evolving views of ecosystem dynamics and succession theory, the role of disturbances in the current general model of forest development, and the influence of different seral stages on biodiversity. We conclude by suggesting how these concepts can be applied in landscape-level planning for biodiversity.
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Updated April 17, 2007