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Timberlands And Sustainable Management Of Native Forests
- Part 2
Dorothy - 19/3/99
If you haven't already, you may wish to read
part 1 in this series.
Beech harvesting - the preliminary trials
Visits to Waituna and Slaty Creek
Rob explained some of the processes involved in beech harvesting and
to let
us see the results of the trials took us to sites at Waipuna and Slaty
Creek.
What we saw
Waipuna
Rob took us to a site at Waipuna on a fertile river flat where the
forest
was mainly red and silver beech with some kahikatea. It had been
clear-felled some eighty years ago which meant that the trees were of
a
fairly uniform size.
Regeneration of sites such as this is profuse with up to 20,000 beech
seedlings per hectare common. Competition is fierce and probably only
about
2% of the seedlings will reach the pole stage (Canopy height 25+
metres,
20-60cms diameter). Even at this stage, competition-induced stress is
often
severe enough that the weakened forest often becomes susceptible to
drought
and insect attack. Such attack can result in total collapse of the
forest
structure.
Trees under stress give off chemicals which attract the male beetles.
They
give off pheromone which attracts the females which lay eggs that
mature in
two to three years. The beetles carry fungi and the holes they create
give
the fungi access to the trees. They in turn block the vessels in the
tree
clogging the movement of fluid, and ultimately killing the tree.
Thinning by old style harvesting methods
One possible answer to collapse of the forest is to reduce competition
and
create more space by thinning or removing some of the trees. However,
when
this was tried with horses, tractors, and skidders the problems of
access
led led to a high level of damage to the retained trees, poor hygiene
leading to pinhole attack and destabilisation through induced
windthrow.
This meant that the trees that were retained would frequently collapse
after the thinning.
Helicopter thinning
A much more effective option is to use a small helicopter for
selective
thinning to give space. This involves very low use of roading, has
insignificant on-ground effects, and ensures that remaining seedlings
and
poles are untouched. In this method trees that are removed are felled
so
that they fall into natural gaps, and the logs are removed vertically.
Branches and trimmings that are over 15 centimetres in diameter are
cut
into small lengths so that they will dry or decay more quickly and not
offer sites for the pinhole beetle.
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Waipuna Trial - Interior view of forest following thinning
Photo source TWC
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Eighteen hectares were thinned in a trial area in November 1995.
Before
thinning began the forest was measured intensively. 12% of the total
volume of poles of saleable dimension was taken. Even though there
has
been no indication of negative effects, Timberlands has opted for a
conservative maximum removal of 10% of volume in its sustainable
management
plans for such 'recovery' forests. The abundant remaining poles are
growing
well, given more light by the thinning process.
The largest trees were retained as to remove these with their large
spreading crowns would damage surrounding trees during felling. These
trees
will also be retained to form the 'old age' component of the
developing
forest. Thinning results in the forest once again being made up of
trees
of different ages with younger trees having the chance to grow.
Had the removal of the trees not been pointed out we would not have
noticed
it.
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Stump treated to deter the pinhole beetle
Photo source Peter Hunt
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We looked at a stump where the pinhole beetles were at the larval
stage.
The method of controlling them was to make a plunge cut in the stump
and
apply urea. Water collecting in the cut raises the wood moisture
content,
and this with the urea encourages fungi to invade and grow within the
stump. This makes conditions unlivable for the pinhole larvae and they
ultimately die. Finally litter from the forest floor was spread on
top of
the stump.
Regeneration occurs around the stumps. Some seedlings grow on coarse
woody
debris (CWD) left after logging. The raised site is often beneficial
for
regeneration as it lifts the seedlings above the competing fern. The
CWD
also helps maintain the forest floor micro-climate, thereby
maintaining a
healthy environment for native plants and invertebrates.
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Waipuna Trial - Regeneration of red beech on a raised site, a tree stump
Photo source TWC
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The survival of the Prince of Wales fern, which is very susceptible to
desiccation, is a good indicator that forest floor temperature and
humidity
has been effectively unchanged. It was abundant at the site we were
viewing.
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Prince of Wales fern
Photo source Peter Hunt
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Slaty Creek
This is the site of the first trial for the new method of beech group
selection harvesting. An average of three or four trees is taken from
each
site.
There are all ages of trees here as unlike the forest that was logged
eighty years ago this is unmodified forest. The logging here was done
two
years ago, and with this method poles, saplings and seedlings are all
coming on. Prince of Wales fern is abundant and healthy. We would
have
had difficulty identifying it as a logging site as the stumps were
mossed
and the beech seedlings and undergrowth were abundant - a total
contrast
from the sites we were accustomed to seeing after harvesting by the
old
method.
The harvesting process
A model is developed determining how many of what species and of what
size
can be taken.
The forester then knows how many he can take, picks the site, selects
the
trees from the list, and puts a tag on them.
The Global Positioning System is used and the feller has a map to
enable
him to find the tagged tree. It is his final decision as to whether
the
tree can be felled safely and without damage to surrounding trees. He
may
refuse. Once the tree is felled the tag is nailed back on the stump.
The stump is treated as described above as beetles are quick to bore
into
freshly felled timber.
The tree is recorded in the register for auditing.
The tree is cut into logs which are the right weight for the
helicopter,
and organised to give the biggest load possible. The helicopter uses a
scissor-type grapple which tightens on the logs as it lifts them. A
square of white plastic is attached to the log to indicate the grapple
point. Two squares indicate that two logs are tied together: three
indicate three logs.
The helicopter transports the logs to the landing where they are
trimmed,
cut to the appropriate length, graded, put on a truck and transported
to
the mill.
Beech utilisation
Beech wood has traditionally been regarded by the saw milling industry
as
inferior to rimu. This was not due to the inherent properties of beech
wood, but because the timber is more difficult to saw and dry, and
because
it has higher levels of internal defects such as knots, pinhole, rots,
and
staining.
Research done by Timberlands has shown that the timber is at least as
high
a quality as rimu provided care is taken during drying. Often it is
air
dried for six months and then finished in a kiln. The drying process
varies with the species of beech.
Millers see a problem in the long return on the cash outlay and the
fact
that there is less clear wood from the trees. Earlier millers
preferred
rimu because it was easier to work with. There is a strong demand
world
wide for high quality hardwood timbers such as beech, and Timberlands
is
working on the challenge of developing suitable markets both here and
abroad.
Beech timber is harder than rimu and stronger. There is an excellent
range
of colours and it makes superb flooring panelling, joinery and
furniture.
Comparison between roading for aerial logging and uphill to ridge
tops
where roads are highly visible
Conventional systems involve cable logging uphill. Where these
hauling
systems involved up to twenty eight lineal metres of road per hectare,
helicopter logging involves around three to four lineal metres per
hectare.
Helicopter logging is also almost exclusively downhill, which means
that
the low impact roads are located in valley bottoms where they are
generally
visible only from an elevated position.
Facilities provided for tourists
These roads are a recreational asset opening up the forests to
visitors.
Bark covered helicopter pads and sites for parking are provided,
making the
forests attractive to tourists, trampers, mountain bikers and
hunters.
My questions about future plans for beech production
Are beech plantations to be established?
There are no plans for the establishment of beech plantations which
will be
thinned and pruned as under sustainable management such intervention
will
not be tolerated.
Are beech logs to be chipped for the chipboard market?
Beech is regarded as a specialty timber to be used for its beauty and
its
strength, not for the chip market.
Read Part 3 of the articles on Timberlands next week to see how the
SOE
is undertaking research into the ecology of the forests under its
management.
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