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In forestry, windthrow refers to trees uprooted or broken by wind. Breakage of the tree bole instead of uprooting is sometimes called windsnap.
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Ecological Effects
Windthrow disturbance generates a variety of unique ecological resources on which certain forest processes are highly dependent. Thus windthrow can act as a rejuvenating process whereby regeneration is made possible with new resource availability.
Severe uprooting opens bare patches of mineral soil that can act as seed sinks. These patches have been shown, in the Pacific Northwest of the United States, to have higher biodiversity than the surrounding forest floor. Additionally, the gap created in the forest canopy when windthrow occurs yields an increase in light, moisture, and nutrient availability in near proximity to the disturbance.
Causes
Windthrow is common in all forested parts of the world that experience storms or high wind speeds. The risk of windthrow to a tree is related to the tree's size (height and diameter), the 'sail area' presented by its crown, the anchorage provided by its roots, its exposure to the wind, and the local wind climate. A common way of quantifying the risk of windthrow to a forest area is to calculate the 'return time' of a wind speed that would damage those trees at that location. Tree senescence can also be a factor, where multiple factors contributing to the declining health of a tree, reduce its anchorage and therefore increase its susceptibility to windthrow. The resulting damage can be a significant factor in the development of a forest.
Windthrow can also increase following logging, especially in young forests managed specifically for timber. The removal of trees at a forest's edge increases the exposure of the remaining trees to the wind.
Trees that grow adjacent to lakes or other natural forest edges, or in exposed situations such as hill sides, develop greater rooting strength through growth feedback with wind movement, i.e. 'adaptive' or 'acclimative growth'. If a tree does not experience much wind movement during the stem exclusion phase of stand succession, it is not likely to develop a resistance to wind. Thus, when a fully or partially developed stand is bisected by a clearcut, the seed trees and forest edges adjacent to the clearcut may not be capable of withstanding forces in which they didn't develop.
Trees with heavy growths of ivy, wisteria, or kudzu are already stressed and may be more susceptible to windthrow, the additional foliage acts as a sail to the wind.
Popular Culture
The terms blowdown and windblow are slang terms used by hikers, hunters, mountaineers, rangers, and other outdoors people to describe a tree knocked over by the wind. The term is often used where the fallen tree (or trees) has become an obstruction to travel.
External links
References
- Alabama Hiking Trail Society Cited Dec. 2007
- USFS "Trail Information— State Route 410 Mather Memorial Parkway / Clearwater" Online bulletin board. Cited Dec. 15, 2007
Wikipedia content modification information:
- This page was last modified on 26 September 2008, at 12:17.
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