Skógræktarritið - 15.05.2001, Side 102

than just the young trees, which
are not necessarily related to the
trees, such as disturbance, other
vegetation types present, expo-
sure and social behaviour.
Sheep, being domestic, are more
controllable, but without active
shepherding their use of different
areas is also highly variable for
the same reasons.
How can we predict and, more
importantly, test, how these
other factors affect herbivore
range use? Traditionally, radio-
tracking was one of the main
methods used to describe the
positions of herbivores, but it is
time-consuming and often very
difficult to locate animals in
large mountainous areas. This
approach is therefore of relative-
ly limited value in this kind of
terrain. However, recent devel-
opments in Global Positioning
Technology have opened new,
exciting opportunities in this
area of work (as well as in many
others) (Pastor & Naiman 1992;
Pastor, Moen & Cohen 1997).
To give a Scottish example,
research at the Macaulay Land
Use Research Institute has used
Global Positioning Systems to
track red deer movements to an
accuracy of <10m (Sibbald in
press). Each animal has a collar
fitted with a GPS and data
recorder, which records the loca-
tion of animal as frequently as
required, and data is down-
loaded remotely via a radio link
onto a computer every few
months. Over the course of a
year, two distinct scales of varia-
tion can be identified from such
work: the first is a clear seasonal
Figure 2. Four-yearold pine saplings
subjected to simulated browsing dam-
age (50% of shoots) in the previous
year (Hester, unpublished data).
difference in large scale range
use; the second is much smaller
scale variability in location on
different days or times of day. At
this level of resolution one can
match location to vegetation,
weather, visitor numbers (distur-
bance), and so on, to elucidate
the main causes of the variation
recorded. This type of technolo-
gy thus represents a real break-
through in a currently poorly
understood area of research, as
it will facilitate more widespread
collection of data to aid in the
development and testing of
hypotheses about the relative
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SKÓGRÆKTARRITIÐ 2001 l.tbl.