Plotless Sampling - Introduction to Ecological Sampling - page 75

6
Plotless Sam pling
Jorge Navarro
6.1 Introduction
Sampling methods have been developed for studying different properties
(e.g., density, spatial pattern) of sets of points or items (e.g., trees, nests, etc.)
distributed within an area of space. In many instances, sampling is the only
solution as it is not possible to map or census all the points in the area; con-
sequently, the field ecologist is constrained to select points from subregions
within the total area. Diggle (2003) calls the sampling methods involved in
this last case sparse sampling methods to distinguish them from those con-
cerning mapped populations within an area. In general, sparse sampling
methods can be divided into two different classes, depending on the way
points within a subregion are selected. One method is quadrat or plot sam-
pling, and the other method is plotless sampling. Although quadrat sam-
pling has always been a popular field technique in forestry and plant ecology,
plotless sampling techniques have also been applied by foresters and plant
ecologists when rapid estimates of the density of plants in a large region are
needed. In fact, plotless sampling is often considerably more efficient than
quadrat sampling because searching for all the items in a quadrat might be
time consuming.
Traditional plotless sampling methods are based on the measurement of
distances from random points to the nearest item and distances from the
nearest item to its nearest (or k th-nearest) neighbor (Kleinn and Vilčko, 2006),
which is why these procedures are also known by the name of distance sam-
pling. However, the term plotless is preferred here because distance sampling
may also refer to line or point transect sampling methods (Buckland et al .,
2001), like those described in Chapter 4.
Plotless sampling methods are useful if the interest is only in the density
of certain distinct items (e.g., trees above a certain size), it is relatively easy
in the field to lay out a large grid of systematic points that are separated by
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