may be completely unrepresentative of the surrounding area. The use of a sward
stick overcomes this problem by providing a measure of the height of the bulk of
the vegetation within a defined area. Sward sticks often consist of a circular disc of
thin wood or plastic with a hole in the center, which slides up and down a vertical
rod. The rod is placed vertically with its end on the soil surface and the disc is
allowed to rest on the vegetation. The height of the disc is then read off from
graduations marked on the rod (easiest if graduations allow for disc thickness).
The weight and diameter of the disc are chosen to suit the aims of the study and
we recommend the use of standard discs. We suggest a 20-cm diameter disc
weighing 144 g (to give 4.6 kg m^2 ) for grass swards. A heavier disc could be
used for denser and more rigid vegetation. The bulk of the vegetation should be
compressed but not flattened.
The concealment provided by ground vegetation or its density can be assessed
using a vertical board with a chequerboard or square grid pattern. The researcher
looks horizontally at the board from the height of its center at a distance of 1 m and
records the number of grid intersections that are visible through the vegetation. This
gives measures of vegetation density and can be carried out at different heights, such
as ground level and 1.5 m. Some use the chequerboard in different ways, such as the
number of squares without any cover. These are, however, difficult to standardize.
The heights of trees and bushes can be estimated using a clinometer to measure
the sighting angle to the top of the tree, when the researcher is at a measured dis-
tance from its trunk. Measurements of the diameter or of the stem at a 1.3-m
height (diameter at breast height), is the standard measure of tree size, which is
usually determined by measuring circumference. If the tree has a buttress then the
diameter is taken just above the buttress. If the tree has multiple stems then each
stem should be counted and measured.
A thin rod marked with 10-cm graduations can be pushed through bushes or
hedges to measure their horizontal extent. It can also be held vertically and the
number of contacts with vegetation in each 10-cm band counted (Weins 1973).
The quantity of foliage at different heights in a tree can be assessed by lying under
the tree at a sample of points and looking upwards into the canopy through
binoculars on which the focusing wheel has been calibrated so that the distance
between the observer and the object can be estimated. By focusing the binoculars
on foliage or branches at different levels an assessment of the amount of vegetation
at different heights can be made.
Canopy cover can be estimated using a sighting tube made simply by adding a
cross wire to any tube or using commercially available sighting tubes with mirror
and levels to ensure it is vertical. It is used to look upwards at points placed on a
regular grid or along a transect and record whether the cross piece is covered by
Vegetation| 259