An alternative to measuring additional trees as part of the
external buffer method is conditional simulation outside the monitoring
plot. This method involves a structural analysis of the spatial
pattern inside the plot and a simulation of this pattern outside the
plot based on the results of the structural analysis. ‘‘Conditional’’ in
this context means that the simulation does not modify the spatial
pattern within the monitoring plot but only generates new patterns
outside, which are statistically similar to those inside and
have statistically correct ties to inner trees (see Biber, 1999; Illian
et al., 2008).
The internal buffer or guard method is a minus-sampling method.
Like all minus-sampling methods the fixed-buffer method only
uses a subset of the trees in the monitoring plot. Again the choice
of the buffer width is difficult (see Diggle, 2003, p. 5) and refined
versions have been developed which create a flexible buffer by
addressing each tree’s potential relation to off-plot neighbours
individually. These methods are known as nearest-neighbour edge
mitigation methods and have been proposed and investigated as
NN1 and NN2 methods in Pommerening and Stoyan (2006), where
a detailed description can be found. The NN1 method was identified
as a very reliable and robust option.