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- The vegetation rnatrix is not easy to burn.
- Mechanical land clearing is uneconomic.
- Erowsing animals should be few or absent altoqether.
- Weed regrowth in cleared areas is generally more vigorous than on average in less
disturbed areas.
- Overhead shade from big trees must be removed early.
In the region Lhe langest areas of line planting are in Fiji, the Solomons and Western
Samoa.
All aneas exhibit. a range from failure to $Jccess. Mosl species growing successful in
line planting do not occun as monoeultures in nature in the tropics. Where monocultures do
occur in tropical forest the site is often specialized as with Terminalia bras"il swamps,
Casuarina groves on ullramafic rocks, Aqathis on basalt riaqes, and mFngrove areas.
Elsewhere monocultures are genenally a limiLed seral stage, Widespread observations indicate
that retention of a reasonably complex vegetative mix contributes to success. Where there is
little damage to the relict natural vegetation, especially of former understorey components,
line planting is often zuccessful.
In the Solomons, measurements on mature trees over a range of sizes on 20 to 25 years
rotations indicated that crown diameters of final erop trees were of the order of l0 netres.
Until recently most line planting has been carried out at about this spacing. When a strip
about two metres wide is cleared, 80% of the relict vegetation need not be disturbed. Where
the canopy has been destroyed by logging, weed regrowth, particularly by Merremia and
Mikania species, has been rampant.
This causes severe losses to planted trees. Heavily logged areas seldom exceed 20% to
25% of the total; so that special techniques involvinq closer planting will have to be evolved
to combat lhe problem of rampant climbing weeds. Final crops of around 100 sLems per ha
are anticipated for trees with 50 Lo 50 cm average diameter. Anticipated average
merchantable bole length varies from about 5 m to 12 m for hardwoods on 15 to 25 year
rotalions. Few line planted areas have yet reache{maturity and conservative estimates would
put yields of sawlogs in the range of 75 to 2OO m-/he, with a small end diameter limit of l0
cm. Total wqpd yield based trr an interpolation from Table 2 is likely to be of the range of
f50 to 500 m'/ha. Additional sawlog volunEs could be harvested if the merchantable small
end diameter limit were reduced to about 20 cm. ln all cases a considerable proportion of the
total yield could be used m pulpwood or for energy.
The wisdom of continuing line planting has been questioned because of two recent
events. The first was the discovery of Ambrosia beetle at.tack and associated problems with
the fungi Armellaria and Fomes on 5ffiT6- macrophylla plantations in Fiji in 1971.
Secondly, inventories of the line planting in the Solomons in 1980 revealed much lower
stockings of potential final crop trees in all ages than was anticipated. In both cases the
authorities curteiled their replanting programmes and lnstituted a radicel change of emphaais
in their replanting work. In Fiji a wider range of speciea were introduced that had not then
been proven s'l a wide scele in line planting. ln the Solomons the line planting technique was
changed by reducing the specing between lines to 5 m. In Fiji the ereas ubsequently
replanted to mixed hardwoode were extremely variable and no large area of fully stocked
plantations has yet been ruccessfully established. In the Solomons the reduction of spacing
between lines h8s lead not mly to removal of the relict understorey between lines, but aleo
to the increased incidence of rempant climbers, early and heavy branching on speciee like
Campnogoerma, attack by insecta like Ambleypelta m Cempnoeperma, and potential danger of
atteck by Hypsipylle on Swietenia which had virtuelly been absent in wider spaeed line
planting. Had there not been arch a radical reection to the probbms, it ought to heve been
poesible to have maintained the rnomentum of the planting programmes. Field rnanagement and
financing in Fiji and the Solomons then loat rrpmentum.
Reaearch hes strowed that the redical corrective techniquee had their own srious
probbms. Closer control end edrytetion of forrner procedures also had a sribstantial place in
retaining cost effectivenegs.