Gap dynamics: Difference between revisions

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[[File:Small Forest Gap.JPG|thumb| Treefall gaps in the Amazon allow sunlight to reach the forest floor.]]

'''Gap dynamics''' refers to the pattern of plant growth that occurs following the creation of a forest gap, a local area of natural disturbance that results in an opening in the canopy of a forest. Gap dynamics are a typical characteristic of both temperate and tropical forests and have a wide variety of causes and effects on forest life.

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Until recently, forest regeneration practices in North America have largely followed an agricultural model, with research concentrated on techniques for establishing and promoting early growth of planted stock after [[clearcutting]] (Cleary et al. 1978, Lavender et al. 1990, Wagner and Colombo 2001),<ref name="clea">Cleary, B.D.; Greaves, R.D.; Hermann, R.K. (Compilers and Eds.). 1978. Regenerating Oregon’s Forests. Oregon State Univ. Exten. Serv., Corvallis OR. 287 p.</ref><ref name="laven">Lavender, D.P.; Parish, R.; Johnson, C.M.; Montgomery, G.; Vyse, A.; Willis, R.A.; Winston, D. (Eds.). 1990. Regenerating British Columbia’s Forests. Univ. B.C. Press, Vancouver BC. 372 p.</ref><ref name="wag">Wagner, R.G.; Columbo, S.J. (eds.). 2001. Regenerating the Canadian forest: Principles and practice for Ontario. Fitzhenry & Whiteside, Markham, Ont.</ref> followed by studies of growth and yield emphasizing single-species growth uninfluenced by overstorey canopy. Coates (2000)<ref name="coat1">Coates, K.D. 2000. Conifer seedling response to northern temperate forest gaps. For. Ecol. Manage. 127 (1–3):249–269.</ref> questioned this approach and proposed a shift to a more ecologically and socially based approach able to accommodate greater diversity in managed stands. Predictive models of forest regeneration and growth that take account of variable levels of canopy retention will be needed as the complexity of managed forest stands increases (Coates 2000).<ref name="coat1" />

Tree regeneration occurring inside canopy gaps after disturbance has been studied widely (Bazzaz and Pickett 1980, Platt and Strong 1989).<ref name="bazz">Bazzaz, F.A.; Pickett, S.T.A. 1980. Physiological ecology of tropical succession: A comparative review. AnnAnnu. Rev. Ecol. Syst. 11:287–310.</ref><ref name="pla">Platt, W.J.; Strong, D.R. 1989. Special feature: gaps in forest ecology. Ecology 70:535–576.</ref> Studies of gap dynamics have contributed much to an understanding of the role of small-scale disturbance in forest ecosystems, but they have been little used by foresters to predict tree responses following partial cutting (Coates and Burton 1997).<ref name="coat2">Coates, K.D.; Burton, P.J. 1997. A gap-based approach for development of silvicultural systems to address ecosystem management objectives. For. Ecol. Manage. 99:337–354.</ref>

In high-latitude northern forests, position inside a gap can have a pronounced effect on resource levels (e.g., light availability) and microclimate conditions (e.g., soil temperature), especially along the north–south axis. Such variation must inevitably affect the amount and growth of regeneration; but relying solely on natural regeneration to separate the effects of gap size and position is problematic (Coates 2000).<ref name="coat1" /> Among the many factors affecting seedling establishment following canopy disturbance are parent tree proximity and abundance, seedbed substrate, presence of seed consumers and dispersers, and climatic and microclimatic variability. Planted trees can be used to avoid many of the stochastic events surrounding natural seedling establishment.