be modified to accommodate logistic tradeoffs. The selection discipline requires that the fullest possible range of each hierarchical level is sampled. This commonly results in a set of progressively nested clusters of sample sites contained within the overarching primary gradient that may not reflect a linear distribution. At relatively local landscape scale, a primary gradients may be represented by salinity levels or water depth as in tidal wetlands or micro-topographic relief as in forest margins or a riparian zone. For most practical purposes, transects are commonly laid out along contours perpendicular to the main direction of the gradient. Iterative spatial analysis of environmental layers over a digital elevation model can then be used to identify areas requiring additional sampling thereby improving environmental representativeness. Advantages and limitations Initial studies in gradsect development revealed considerable logistic and other advantages over more traditional non-gradient-based survey designs concerned primarily with random sampling. This finding is now widely supported especially in biodiversity and other areas of environmental surveying and conservation design (see Applications next). Apart from improved logistic efficiency, the gradsect method seeks to maximise environmental representativeness which has the dual advantage of potentially improving location of rarities and enhancing spatial modelling of species distribution. Because the underlying statistical model is not based on probability theory, gradsect sampling cannot be used to estimate numbers of species or other biological attributes per unit area. For that purpose some measure of random sampling needs to be built into the sample design. Applications Since the publication of gradsect theory in 1984, subsequent vegetational and landscape studies in regional Australia (Austin and Heyligers 1989); Ludwig and Tongway (1995) were followed by a successful evaluation of the method in faunal surveys in South Africa (Wessels et al.). Since then applications involving gradsects have ranged from habitat suitability studies of fungi (Shearer and Crane 2011 ), termites (Gillison et al. 2003) other macro invertebrates (Lawes et al. 2005 ); birds (Damalas 2005) small and large mammals (Laurance 1994; Ramono et al. 2009). Vegetation studies using gradsects have been widely applied in many countries ranging from tidal wetlands (Parker et al. 2011) and agricultural cropping systems and forested landscape mosaics (Gillison et al. 2004) to infectious diseases (Boone et al. 2000 ). At broader geographic and national scales (Grossman et al., 1998, 2007; USA/NPS 2012) gradsects have been applied to guide field sampling and forest mapping in mountainous terrain (Sandman and Lertzmann