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

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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-

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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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