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(i). Sampling technique.
A method of stratified sampling was used based on: undisturbed forest, lightly disturbed forest, heavily disturbed forest and completely disturbed forest. A grid of 25 km2 was superimposed on Bwindi Impenetrable map, and the forest divided into 4 sq. km units. The sites to be sampled were then selected with the aid of random digits. Four line transects each of length 1000m, marked with stakes and flagging tape, were established in each of the sites selected. Horizontal distances were measured in a series of steps to correct for the slope a procedure called “stepping”. A point approximating the center of each site was selected with the aid of topographic maps from where the transects were established. To establish the transects, a narrow path was cleared. The transects were aligned in north, east, south and west directions. Rectangular quadrats of size 25 x 30m were established (by carefully clearing a narrow path around them) at 225m intervals alternating right or left of the transect line. These were also marked with stakes and flagging tape. A total of 16 quadrats of area 750m2 each, were sampled in each site giving a sampling intensity of 1.2 ha per site.
(ii). Vegetation sampling.
The enumeration of trees was based on diameter size classes in nested quadrats of different sizes using sub-sampling techniques. Nesting implied that sub-plots measured to smaller limits were contained within the plots measured to higher limits. The following plot dimensions were used:
2 x 5m----------------------------------------------Seedlings.
5 x 10m --------------------------------------------Saplings
10 x 15m--------------------------------------------Poles.
15 x 20m--------------------------------------------Smaller trees.
25 x 30m---------------------------------------------Larger trees.
Although quadrat and
sub-plot boundaries
were clearly marked,
care was taken not
to cut any trees
which represented
the part of the
population being
measured.
Diameter
measurements for the
saplings, poles,
smaller trees and
larger trees were
carried out at
breast height
(1.3m). The
diameters of the
seedlings were
measured immediately
above the root
collar. All canopy
tree species found
within the plots
were enumerated for
different diameter
size classes. The
trees were
identified using
vegetative field
characteristics with
reference to
scientific
identification keys
of Hamilton (1981).
Where identification
was not possible in
the field, the
unidentified
specimen was
preserved for
herbarium
identification.
The trees were
inspected and their
conditions recorded
in addition to any
apparent causes of
damage or death.
Stumps were also
enumerated and their
cause recorded,
where evident.
Sprouts from various
forms of vegetative
growth (from roots,
fallen stems and
stumps) were also
enumerated. Where
possible they were
identified to
species in the field
and the diameters of
leading shoots
measured. The amount
of ground vegetation
cover (GVC)in the
plots was estimated
visually and scored
arbitrarily in the
following
categories;
(0 - 25%)- Ground
almost bare.
(25 - 50%)- Sparse
GVC.
(50 - 75%)- Fairly
dense GVC.
(75 - 100%)- Very
dense GVC.
The plots were
thoroughly searched
for fruits and seeds
to study the
importance of the
existing larger
trees as seed
sources. Altitude,
slope position and
aspect were
recorded. Altitude
was determined from
altimeter readings
corrected for
temperature and
regular daily
fluctuations of
pressure. The slope
positions were
recorded as upper,
mid- or lower
slopes. Aspect was
recorded as north,
east, south, west
facing slopes or not
applicable (where
there was no slope).
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