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Gradsect
A gradsect or gradient-directed transect is a low-input, high-return sampling method where the aim is to maximise information about the distribution of biota in any area of study. Most living things are rarely distributed at random, their placement being largely determined by a hierarchy of environmental factors. For this reason, standard statistical designs based on purely random sampling or systematic (e.g. grid-based) systems tend to be less efficient in recovering information about the distribution of taxa than sample designs that are purposively directed instead along deterministic environmental gradients.
Ecologists have long been aware of the significance of environmental gradient based approaches to better understand community dynamics and this is reflected especially in the work of Robert Whittaker (1967)〔Whittaker R. H. (1967). Gradient analysis of vegetation. ''Biological Reviews'' 42: 207–264.〕 and others. Although in practice, life-scientists intuitively sample gradients, until the early 1980s there was little formal theoretical or empirical support for such an approach, sample design being driven largely by traditional statistical methods based on probability theory incorporating random sampling.
== Origins ==
Intensively sampled landscape-based surveys in Australia provided a reference platform for developing and testing a less logistically demanding and yet statistically acceptable gradient-based survey design that avoided the need for random or purely grid-based sampling. These initial studies 〔Gillison, A.N. (1984). Gradient oriented sampling for resource surveys – the gradsect method. In: K.R. Myers, C.R. Margules and I. Musto (eds.) ''Survey Methods for Nature Conservation'' pp. 349–74. Proc. Workshop held at Adelaide Univ. 31 Aug. to 31 Sept. 1983. (CSIRO (Aust.) Division of Water and Land Resources, Canberra)〕 and subsequently developed statistical support for purposive, gradient-based survey〔Gillison, A.N. and Brewer, K.R.W. (1985) The use of gradient directed transects or gradsects in natural resource surveys. ''Journal of Environmental Management'' 20; 103–127.〕 provided a formalized, practical alternative to more logistically demanding traditional designs. It was here the term ''gradsect'' was coined that coupled purposive, transect sampling with a hierarchical framework of environmental gradients considered to be key determinants of species distribution.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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