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J. Northeast For. Univ. Vol. 1, No. 1, November 1990
AN E C O L O G I C A L A P P R O A C H TO FOREST H A R V E S T I N G
Shi Jiyan
Northeast Forestry University, Harbin, 150040, China
ABSTRACT This paper deals with the relationships between forest harvesting and forest ecology. It
proposes basing annual cuts and forest operation plans on ecological principles. Harvestable forest re-
sources are decreasing and regeneration is slow. The combination of forest harvesting with ecology
can be viewed as a solution to the forest harvesting dilemma in China.This paper als0 makes some
technical recommendations for forest operations based on ecological principles.
Key words: tlarvesting, Forest ecology, Forest operations, Logging technique, Post harvest regenera-
tion
Forcs t harves t ing com bi ned with ecology
is a controvers ia l topic at present. At a sym-
posium o f the society o f Chinese Fores t En-
gineering in June 1986, mos t attcn~lants
agreed that logging opera t ions in China
should be based on ecological principles, so
as to ensure the cont inuing utility of forest re-
s o u r c e s .
Fores t harvest ing and ecology are con-
t radictory to some extcnt .A key p rob lem is,
the reduct ion of negative logging effects on
ecological systems, and the direct improve-
mcnt of ecological env i ronments in some as-
pects. Therefore , the following should be
cons idered seriously.
C O N T R O L A N N U A l , C U T B A S E D ON
E C O L O G I C A L P R I N C I P L E S
Accord ing to ecological principles, the
annual cut o f all fo rms o f harves t (converted
into growing stock), plus var ious consump-
t ions each year, mus t not exceed annual
growth. The forest resources in China would
be perpetual ly avai lable if we acted in this
way. However , m a n y logging bureaus in
China have been overcut t ing for a long time,
so the forest resources that can be harvcsted
are gradual ly being exhausted. Therefore , the
Manuscript received lune 12, 1990
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allowable cut of each logging bureau must be
checked and adjusted to a standardized vol-
ume. Since the late 1970s when we began to
do this,we gained corresponding benefits,but
the speed of adjustment is slow.
I N T E G R A T I O N OF I IARVESTING
M E T I I O D S WITH ECOLOGICAL
PRINCIPLES
When we sclect a harvesting method,the
particular forest conditions must be consid-
ered, but we pay little attention to them.
Since 1949, the harvesting methods in China
have changed a lot(Anon, 1988). For
cxample, in Iteilongjiang province, the per-
ccntage of harvesting done by selection cut-
ting was 98% in area from 1950 to 1955; clear
cutting was widespread from 1956 to 1964,
and in 1962, it comprised 97% of all cutting
systems. From 1965 to 1978, the harvesting
method was redirected again from clear cut-
ting to selection catting, and was stablized at
about 80-90% of all cutting. After that, the
percentage of clear cutting went up to about
35%-45%. At present, the percentage of
clear cutting is about 50%.
After 1949, we determined that the in-
tensity of selection cutting should be more
than 60n/o of prcfelling growing stock(stem
volume ) in China. Since 1987, the intensity
of selection cutting in China has been ad-
justed to 40% . Most experts agree that this
seems to be a more reasonable level.
PLAN FOREST OPERATIONS AC-
CORDING TO ECOLOGY
Size o f Clear Cuts. The choice ofclearcut
size is related to the regeneration method
used after cutting. If artificial regeneration is
to be used within 2 years after cutting, and we
are careful about the selection of seedlings,
cultivation technology a n d management,
young trees wouid grow well and no soil ero-
sion would be observed (FSLP, 1982).
I f natural regeneration is used, the size of
cutting areas would seem to be important.
The broader the cutting area, the more seri-
ous the soil erosion. According to data from
the Soviet Union(Deng, 1985), when the min-
imum dimension of clcarcutting was changed
from 50 to 200 metres, the degree of soil ero-
sion increased one to two fold; with a clearcut
width of 400 metres, the degree incrc'ascd
three to four times. If the clcarcut width was
less than 50 metres, especially on sandy soil,
sandy loam and good drainage soils, water
and soil conservation in stands was the same
as that in the selection cut and shelter wood
cut areas.Also, the wider the clear cut is, the
lower the sapling density. The ctTccts of dif-
ferent cut sizes on larch 3years after cutting at
a logging unit in Daxinganling are reported in
Tablel (FSLP, 1982).
When the width o f the cutting area was
large, the qualitative results showed that
herbs grew profusely 3 years after harvesting,
the environmental conditions deteriorated
and natural regeneration was not ensured. In
general, when the width of the cutting area is
less than 100m, the natural regeneration in
the area is good (FSLP, 1982). Therefore, the
size of clearcutting area for natural regenera-
tion should be 50-100m across.
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Table 1. The effect of clearcut width on sapling density.
Width of
clcarcut(m) Before cutting 20 3000 50 12000
100 5900 250 4000 500 1900
Sapling density ( per hectare )
After cutting 3500 1000 1600 2000
310
Width of Stripcuts The width o f str ipcuts
is the same as the distance between the skid
roads, which can affect the sapling survival
rate. According to Soviet Union research
(Mo, 1983), when the width of a str ipcut
equals the tree height , the sapling survival rate
is 80% -90% ; w h e n the width o f t h e s t r i p c u t
is two times the trcc height, the sapling sur-
vival rate is 70% -74% . According to t heex -
pcricnccs from the Daxinganl ing forest area,
when the crowns fell on the skid road, the
sapling survival rate was higher, so the meth-
od of three skid roads within 100m is pro-
posed, with the width o f cut t ing strip being
33-34m. This nar row stripcut should be used.
Operating Sea~m and Road Cons -
truction. Trac to r skidding in s um m er greatly
damages the soil surface, especially when ruts
are formed on the main skid roads after skid-
ding. Thcrcl 'orc, The use of t ractor skidding
in s u m m c r should bc evaluated carefully.
Moreover , wooden skid roads are required
for summer skidding whcn t imber consump-
tion is high. According to investigations
(Wang, 1988), i[" main skid roads are covered
with polcwoodsizc logs, 0.71m3of t imber is
rcquircd per meter o f skid road.This repre-
sents 20% of the volume skidded. I f skid
roads are built with b rushwood , 0.1m3of
b rushwood will also be consumed per meter
o f road, the use represent ing 1 0 % - 1 2 % of
the vo lume skidded.
Harvesting S y s t e m s T r i m m e d log and
t r ee - l eng th logging opera t ions are used in
China. Tree length harves t ing has generally
made up 90% of the harvest in nor theas t for-
est areas o f China . Dur ing the 1980s, the
percentage decreased to a b o u t 7 5 % - 8 0 % .
However , the regenerat ion was heavily dam-
aged by t r ee - l eng th skidding. ThcrcI 'ore,
t r immed log skidding should be used in areas
with m a n y saplings.
E S K I D D I N G S Y S T E M S A C C O R D -
I N G T O P R I N C I P L E S O F E C O L O G Y
There are current ly thrcc skidding meth-
ods used in China :an imal skidding, cable
yard ing and t rac tor skidding. F o r the protec-
tion of trees, saplings and the soil surface, an-
imal skidding and cable yard ing arc bet ter
than t rac tor skidding. However , caterpi l lar
t rac tor skidding is still the main skidding sys-
tem in nor theas t China, represent ing some
86% of all skidding by volume. Research oll
the relat ionship between t rac tor skidding and
ecological systems is necessary.
The following conclusions can bc drawn
from research results both in China and
abroad .
According to the experiences in the
�9 101 �9
Daxinganl ing forcst area, the natural regen-
eration is not affected by t rac tor skidding and
may ever be better.
Tree injuries caused by t ractor skidding
are inevitable, and the rate of injury is high.
In Wu Yiling logging bureau, Heilongjiang
province, the rate of injury was 32%, reaching
40% including the loss to skid roads. In
Daxinganling forest areas, it was estimated
that the survival rate of young trees and sap-
lings was only about 40%.
According to Soviet Union research (Jia,
1987), in areas where L P - 1 5 7 feller-
forwarders were operating, the permeabil i ty
o f s o i l i n skidding roads decreased 99% . T h e
operat ion rcsuhcd in loss of water properties
and poor soil conservat ion in cutt ing areas.
Japanese rcscarch(Jia, 1987)showed that the
soil compact ion o[" skid roads doubled after
skidding, and soil porosi ty decreased
12"/0-13%. As is commonly known, the best
solution to this problem is to widen the cat-
crpillar tread or to use wide,low pressure
tires. In Canadian tests (Jia, 1987), when such
tires (100cm to 127cm in width, 83kpa of
pressure) were uscd, there was no significant
ditl'crcnce in soil density before and after
skidding. After 20 t ractor runs on skid roads,
the soil density increased only 2% .
R E S U I , T S OF E C O L O G Y - B A S E D
I I A R V E S T I N G T E C I I N I Q U E S
In our studies of directional tree felling,
wc concentra ted on fclling the trees toward
the skid roads, and paid less at tention to the
damage to young trees when felling. Because
of incorrect felling directions, the rates of
damage to young trees by falling trees were
52% and 53% in two sample areas at
Shangganling logging bureau, Hei longj iang
province. In seven sample areas at
Shuangzihc logging bureau, the rate was
abou t 80%. In Xinlin logging bureau in the
Daxinganl ing forest area, the survival rate o["
young tree regenerat ion before cutt ing in-
creased from 20% to 60%, because sup-
port ing poles were used to cont ro l t ree-fa l l
directions.
Treelength t ractor skidding with one
rope has been the main skidding system for a
long time in China. This means that several
tree lengths are pulled at a time, so many
young trees are greatly damaged by the trees.
Therefore , in order to meet the ecological re-
quirements , the t ractor should pull the trees
one at a time and not leave the skid roads.
R E S E A R C I I I N G I ,ABOUR O RG A N I-
Z A T I O N BASED ON E C O I , O G Y
Forest harvesting a n d . f o r e s t regenera-
tion are different but closely related subjects,
and should bc considered together in labour
organizat ion. The logging work unit is the
main organizat ion of forest operat ions in
China, but current ly this organizat ion is only
responsible for harvcst product ion tasks
without consider ing pos t -ha rves t regenera-
tion. Therefore , harvesting and regeneration
are separate. Under tree farm leaders, forest
harvesting and regeneration are carried out
by two work units (crews). At Donglcng log-
ging bureau in 1969, it was proposed to com-
bine harvesting and regeneration labour ac-
tivities.In the early 1980's, this a r rangement
emerged again . Since 1973, the co -o rd in a -
tion of harvesting, regeneration and utiliza-
�9 1 0 2 .
tion by the same workers has b e e n tried in
some logging units in Daxinganl ing forest
areas. U n d e r this labour a r r angement , the
work unit mus t harvest the forest rat ional ly,
pro tec t the young t rees and seed trccs, and
regenerate in time. This kind o f lab~,,lr organ-
ization is good , but needs fur ther ref inement.
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