An ecological approach to forest harvesting

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  • J. Northeast For. Univ. Vol. 1, No. 1, November 1990

    AN ECOLOGICAL APPROACH TO FOREST HARVESTING

    Shi J iyan

    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

    Forcst harvesting combined with ecology

    is a controversial topic at present. At a sym-

    posium of the society of Chinese Forest En-

    gineering in June 1986, most attcn~lants

    agreed that logging operations in China

    should be based on ecological principles, so

    as to ensure the continuing utility of forest re-

    sources .

    Forest harvesting and ecology are con-

    tradictory to some extcnt.A key problem is,

    the reduction of negative logging effects on

    ecological systems, and the direct improve-

    mcnt of ecological environments in some as-

    pects. Therefore, the following should be

    considered seriously.

    CONTROL ANNUAl , CUT BASED ON

    ECOLOGICAL PR INCIPLES

    According to ecological principles, the

    annual cut of all forms of harvest (converted

    into growing stock), plus various consump-

    tions each year, must not exceed annual

    growth. The forest resources in China would

    be perpetually available if we acted in this

    way. However, many logging bureaus in

    China have been overcutting for a long time,

    so the forest resources that can be harvcsted

    are gradually being exhausted. Therefore,the

    Manuscript received lune 12, 1990

    9 99 9

  • 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.

    INTEGRATION OF I IARVESTING

    METI IODS 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 of 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 and management,

    young trees wouid grow well and no soil ero-

    sion would be observed (FSLP, 1982).

    If 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 of 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.

    9 100 9

  • 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 of stripcuts

    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 stripcut

    equals the tree height,the sapling survival rate

    is 80% -90% ;when the width of thestr ipcut

    is two times the trcc height, the sapling sur-

    vival rate is 70% -74% . According to theex-

    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 of cutting strip being

    33-34m. This narrow stripcut should be used.

    Operating Sea~m and Road Cons-

    truction. Tractor skidding in summer greatly

    damages the soil surface, especially when ruts

    are formed on the main skid roads after skid-

    ding. Thcrcl'orc, The use of tractor skidding

    in summcr should bc evaluated carefully.

    Moreover, wooden skid roads are required

    for summer skidding whcn timber consump-

    tion is high. According to investigations

    (Wang, 1988), i[" main skid roads are covered

    with polcwoodsizc logs, 0.71m3of timber is

    rcquircd per meter of skid road.This repre-

    sents 20% of the volume skidded. I f skid

    roads are built with brushwood, 0.1m3of

    brushwood will also be consumed per meter

    of road, the use representing 10%-12% of

    the volume skidded.

    Harvesting SystemsTr immed log and

    tree- length logging operations are used in

    China. Tree length harvesting has generally

    made up 90% of the harvest in northeast for-

    est areas of China . Dur ing the 1980s, the

    percentage decreased to about 75%-80%.

    However, the regeneration was heavily dam-

    aged by tree- length skidding. ThcrcI'ore,

    tr immed log skidding should be used in areas

    with many saplings.

    ESKIDDING SYSTEMS ACCORD-

    ING TO PR INCIPLES OF ECOLOGY

    There are currently thrcc skidding meth-

    ods used in China:animal skidding, cable

    yarding and tractor skidding. For the protec-

    tion of trees, saplings and the soil surface, an-

    imal skidding and cable yarding arc better

    than tractor skidding. However, caterpil lar

    tractor skidding is still the main skidding sys-

    tem in northeast China, representing some

    86% of all skidding by volume. Research oll

    the relationship between tractor 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

  • Daxinganling forcst area, the natural regen-

    eration is not affected by tractor skidding and

    may ever be better.

    Tree injuries caused by tractor 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 LP -157 feller-

    forwarders were operating, the permeability

    o fso i l in skidding roads decreased 99% .The

    operation rcsuhcd in loss of water properties

    and poor soil conservation in cutting areas.

    Japanese rcscarch(Jia, 1987)showed that the

    soil compaction o[" skid roads doubled after

    skidding, and soil porosity 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 tractor runs on skid roads,

    the soil density increased only 2% .

    RESUI ,TS OF ECOLOGY-BASED

    I IARVEST ING TECI IN IQUES

    In our studies of directional tree felling,

    wc concentrated on fclling the trees toward

    the skid roads, and paid less attention 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, Heilongjiang

    province. In seven sample areas at

    Shuangzihc logging bureau, the rate was

    about 80%. In Xinlin logging bureau in the

    Daxinganling forest area, the survival rate o["

    young tree regeneration before cutting in-

    creased from 20% to 60%, because sup-

    porting poles were used to control tree-fal l

    directions.

    Treelength tractor 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 tractor should pull the trees

    one at a time and not leave the skid roads.

    RESEARCI I ING I ,ABOUR ORGANI-

    ZAT ION BASED ON ECOI ,OGY

    Forest harvesting and. forest regenera-

    tion are different but closely related subjects,

    and should bc considered together in labour

    organization. The logging work unit is the

    main organization of forest operations in

    China, but currently this organization is only

    responsible for harvcst production tasks

    without considering post-harvest 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 arrangement

    emerged again . Since 1973, the co-ord ina-

    tion of harvesting, regeneration and utiliza-

    9 102 .

  • tion by the same workers has been tried in

    some logging units in Daxinganl ing forest

    areas. Under this labour arrangement, the

    work unit must harvest the forest rationally,

    protect the young trees and seed trccs, and

    regenerate in time. This kind of lab~,,lr organ-

    ization is good, but needs further refinement.

    9 103 9

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