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A treefall gap is a distinguishable hole in a forest with vertical sides extending through all levels down to an average height of two meters above ground.〔Brokaw, N. (1982). The Definition of Treefall Gap and Its Effect on Measures of Forest Dynamics. Biotropica, 14(2), 158-160.〕 These holes occur as result of a falling tree or large limb. The ecologist who developed this definition used two meters because believed that "a regrowth height of 2 m was sufficient" for a gap to be considered closed, but not all scientists agreed.〔 For example, Runkle believed that regrowth should be 10–20 meters above the ground.〔 Alternatively, a treefall gap as "the smallest gap (must ) be readily distinguishable amid the complexity of forest structure."〔 There is no upper limit in gap size. However, it must be caused by a tree or a large limb.〔 For example, a field would not be considered a treefall gap.〔Jansen, D. H. 1990. An abandoned field is not a tree fall gap. Vida Silvestre Neotropical 2:64–67.〕 Tree falls are commonly caused by old age, natural disasters, or parasites (i.e. epiphytes). == Measurement == Scientists have not been able to come to a conclusion on one absolute method for measuring a treefall gap. However, there are two types of measurements that are commonly used: ;Two-dimensional This method does not necessarily take into account irregularity in gap shapes.〔Schliemann, S., & Bockheim, J. (2011). Methods For Studying Treefall Gaps: A Review. Forest Ecology and Management,2011,1143-1151.〕 Most gaps do not conform to one particular shape or another, so assumptions must be made.〔 Gaps that are uniformly shaped (e.g. ellipse, triangle, etc.) can be quantified by measuring the length and width of each gap.〔 Commonly, however, the gap is irregularly (i.e. not uniform) shaped and must be divided into smaller sections to be measured individually in order to obtain higher accuracy.〔 ;Three-dimensional This method provides a more accurate measurement as it takes into account differences in structure of the gap descending from the canopy to the forest floor.〔 One of the most recent strategies, pioneered by K. and S.I. Yamamoto, "utilized two photographs of the canopy gap, taken at different heights, and a series of geometric calculations to calculate the gap area." 〔 By doing this, the scientists were able to obtain a more accurate measurement as they are now accounting for differences in structure around the periphery of the gap. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「treefall gap」の詳細全文を読む スポンサード リンク
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