Marking a first thinning in an unthinned teak plantation
A 120 hectare teak plantation in Nandurbar district was raised in 2003 at 2 m x 2 m, giving 2,500 stems per hectare at planting. It is Site Quality III, top height about 15 m, mean DBH 17 cm and basal area 27 square metres per hectare. No thinning has ever been done. The canopy is fully closed, leaf litter is thin, there is almost no regeneration and the occasional suppressed tree is dying. About 250 cattle from two hamlets graze inside the plantation, and ground fire enters every summer. The working plan prescribes a first thinning at 20 years, subsequent thinnings at 10 year intervals, and a rotation of 70 years. The Range Forest Officer must mark the thinning, decide what to do about grazing and regeneration, and respond to a local sawmill that has offered to lift all thinnings at the gate.
1. Prescribe the thinning: type, intensity, stems to be removed and marking rules. Show the arithmetic behind your prescription.
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Present stocking is 27 square metres per hectare with trees of mean DBH 17 cm. The basal area of one such tree is 0.7854 x 0.17 x 0.17, about 0.0227 square metres, so the stand carries roughly 27 / 0.0227, that is about 1,190 stems per hectare. That is dense and heavily suppressed at DBH 17 cm on Site Quality III.
Type: a low thinning, thinning from below (Grade B, tending towards C). Remove suppressed and dying stems, overtopped trees, forks, cankers, epicormic-heavy trees and wolf trees. Do not touch the dominant and good co-dominant trees that will form the final crop.
Intensity: remove about 340 stems per hectare, roughly 28 percent of stems and about 8 square metres of basal area, leaving around 850 stems and 19 square metres per hectare. This is heavier than a light first thinning because the stand is already overdue, but light enough to avoid windthrow and epicormic shoots that follow sudden exposure of teak stems.
Marking rules: first select 200-250 permanent crop trees per hectare, well spaced at 6-7 m, straight and clean; mark them with a distinct paint band; then mark competitors touching their crowns and everything suppressed. Do not remove more than one neighbour of any crop tree in a single operation.
Timing: November to February, when bark peels less and wounds heal, and sale can be completed before the monsoon.
2. How would you handle grazing, fire and the failure of natural regeneration in the same operation?
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These three problems reinforce each other and should not be addressed plantation-wide at once.
Grazing: 250 cattle over 120 hectares is light in absolute terms but concentrated, and the hamlets depend on it. Do not impose a straight ban across the whole area, which is unenforceable. Divide the plantation into four blocks and graze three, resting one for two years in rotation, with no grazing at all in the marked regeneration blocks; supply grass from the rested block to the hamlets so that the ban is compensated.
Fire: cut 5 m fire lines before February, clear the boundary strip, and engage the hamlets as fire watchers, since they are the ones who benefit. Village fire watchers are cheaper and more effective than departmental patrols over 120 hectares.
Regeneration: teak needs a seed source, mineral soil and light. The thinning supplies the light. Retain 25-40 well-formed seed bearers per hectare, scarify the soil under their crowns before seed fall, and protect those patches. For the poorest 10 hectares, use strip clear felling in 0.5-1 hectare coupes with a two-year taungya crop, which removes competition, provides weeding and gives the hamlets a stake in success. Teak coppice is vigorous but of poor form, so treat coppice as a nurse rather than as the future crop.
Accept the sawmill offer only for material above the small-timber size class, and reserve poles and firewood for village rights first.
3. Why is clear felling and replanting at 20 years the wrong decision here, even though the stand is dense and stagnant?
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Clear felling at 20 years against a 70-year rotation throws away most of the stand's productive potential, because mean annual increment on Site Quality III is still rising steeply at this age. The tress are barely a third of rotation age and have not yet converted years of suppressed growth into merchantable volume.
There are practical risks as well. Removing the canopy in a single operation over 120 hectares exposes soil on a site where litter is already thin, so erosion and nutrient loss follow. Teak is a light demander only after establishment; the exposed site is quickly colonised by Lantana and other weeds that cost more to clear than the thinning itself. Regeneration from felling would be uneven, and young teak seedlings suffer browsing from the same 250 cattle.
A clear felling also removes the seed source at the very moment it is needed. Retention of seed bearers only works if there are trees to retain, which there would not be.
The stagnation is real, but its cause is overstocking and the absence of tending, not old age. Thinning removes the cause; clear felling removes the crop. Reserve clear felling for the small regeneration coupes proposed for the poorest patches, and revisit the whole question at about 40 years, when a second thinning has produced a merchantable stand.