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THE EFFECTS OF SELECTIVE LOGGING ON FOREST STRUCTURE
Aim:
To
assess whether the selective logging of trees in a forest has an effect on the
overall structure of the forest, which in turn may have implications for the
integrity of the forest as a whole.
Objectives:
Introduction:
There
is evidence of selective logging of certain valuable first class trees within
the Kakenauwe Nature Reserve on the island of Buton, South-East Sulawesi.
This area of forest is within close proximity to several small villages
that rely heavily on first class timbers for house building.
These first class trees may be species that are typical of a climax
community. Within the reserve there
is evidence of many felled and cut trees within the forest, these trees having
straight cut trunks that are not found under natural treefall conditions. Also within the forest are many naturally fallen trees, which
include many less valuable second-class tree species. The selective logging of large individual trees within the
forest may have implications for the future integrity of the selected species,
and also harvesting the forest and removing many individuals of the same species
may suppress seral succession and reduce the abundance of these first class
trees if they are typical of a climax community.
The
Lambusango Nature Reserve, also on the island of Buton in South-East Sulawesi,
has not been selectively logged in the past.
This forest therefore can be used in comparison with the previously
logged forest in the Kakenauwe Nature Reserve to assess whether selective
logging has any affect on forest structure.
Methods:
Fallen
tree data:
Within
both the Kakenauwe and Lambusango nature reserves there is a hectare grid cut in
the forest. Within each of these
grids are 20 transect lines, each at approximately 100m apart.
Sampling of fallen trees was carried out along as many of these grid
lines as possible, to create a map of fallen trees across the grid.
Tree species, tree height, diameter at breast height (DBH) (as if tree
was still standing) and direction of fall were all measured using tape measures
for the height and DBH and a compass for the direction of fall.
Presence of epiphytes, mosses and fungi were noted and a qualitative
scale of decomposition made, to try and assess how long the tree has fallen.
These data also indicated at what rate certain species decomposed.
The nature of the treefall was also noted, whether it was felled, felled
and cut, naturally fallen or naturally fallen and cut.
Canopy
cover and indicator species data:
Within
each grid, 100m transects were created to assess canopy cover and presence or
absence of disturbance indicator species. Every
10m along the 100m transect, amount of sky cover and any evidence of disturbance
was noted. Within the first, middle and last 10m a detailed study of indicator
species and canopy cover was made.
The
presence of the photophilic fern Selagenella sp. was noted along with
pioneers such as ginger and grasses. Presence of shade tolerant plants such as mosses, bole
climbers and epiphylls was also noted. By
measuring the percentage cover of the different layers of less than 1m, 1-5m,
5-20m and greater than 20m canopy disturbance could be assessed.
The collection of this data allowed the assessment of how the forest
structure altered along the transect.
Initial
results:
The fallen
tree data from within the Kakenauwe grid indicated that more selective logging
occurred in close proximity to the 3 paths that run through the grid, namely
Jalan Tarsius, Jalan Batas and Jalan Gajar.
This may have implications for forest structure, as most of the first
class species have been removed from certain sections of the forest.
There is no evidence of recent logging. Also initial results suggest that average DBH of trees fallen
on the slopes is less than those trees found on the plateaus, and direction of
fall are more similar for those trees that have fallen on the slopes.
DBH of fallen trees may be related to soil depth, which in turn may be a
result of aspect or drainage on these slopes.
Direction of fall may also be linked to aspect.
Contrary
to previous opinion, fallen tree data from the Lambusanga study grid indicates
that, although not logged to the same extent as the Kakenauwe grid, this area is
also experiencing selective logging. Only
one month before data collection began, two large first class trees, one with a
DBH of 140cm were felled within the study grid.
It is illegal to fell trees within this reserve, with heavy fines
imposed. These felled trees raise
important questions for the current methods of policing this reserve.
A
comprehensive data set of canopy cover and disturbance indicators is still being
compiled for the Kakenauwe grid, therefore no initial results are known.
The presence of the photophilc fern Selagenella sp. within the
Lambusanga grid is widespread within the transects, despite this forest being,
up until about 1 month ago, undisturbed. Natural
differences between the forest within the Kakenauwe
and Lambusanga grids may question the usefulness of such species when doing
inter-forest comparisons, however intra-forest comparisons using these indicator
species may still be possible.
A dissertation entitled The
effects of selective logging on forest structure will be produced by Matthew
Loveday, University of Leeds by
June 2003.