Overall techniques and specific techniques
Silviculture is the science and craft of growing forests. It has two levels.
Overall techniques are the big plan. You choose:
- Natural regeneration: the forest grows again from seeds and sprouts that fall on their own.
- Artificial regeneration: people plant seedlings or sow seeds.
- Even-aged forest: all trees about the same age. Uneven-aged forest: trees of many ages and sizes.
Specific techniques are the single jobs done on the ground: site preparation, planting, weeding, cleaning, thinning, pruning, and final felling. The time from planting to final felling is the rotation, for example 40 to 50 years for a fast conifer.
Silviculture of production forests
A production forest is grown mainly to give timber, so the aim is straight, thick, knot-free trunks at a fair cost. The jobs in order:
- Site preparation: clear the land and loosen the soil.
- Planting: seedlings in rows, often 2 m apart, so about 2,500 trees on 1 hectare.
- Weeding in the first years, so seedlings are not shaded out.
- Cleaning: cut climbers and unwanted young trees.
- Thinning: remove weak or crooked trees. The best ones, called crop trees, get more light and grow thicker.
- Pruning: cut low branches so the log has few knots.
- Final felling at the end of the rotation, then replant.
Cutting all trees of a patch at once (clear-cutting) is cheap and gives same-age forest. Cutting only some (selection or shelterwood) keeps more cover but costs more.
Management of environmental forests
An environmental forest is kept for public benefits: clean water, firm soil on slopes, wildlife, clean air, and a place to walk and learn. Timber is not the main goal.
- Keep a mixed forest with many tree kinds and a multi-layer look: tall trees, shrubs and ground plants.
- Prefer natural regeneration and long rotations, so big old trees remain.
- Cut lightly and in small patches. Avoid bare ground on steep slopes.
- Leave some dead wood: insects, fungi and birds live in it.
- Keep a belt of trees along streams.
- Watch for problems such as pests, fire and too many grazing deer, and act early.
Choosing the right technique
Ask three questions. What is this forest for? (timber, water, wildlife). What does the site allow? (steep or flat, wet or dry). How long can we wait? Then pick the plan. Many forests mix both: rows on the flat low land for timber, natural forest on the steep slope and near the spring.
Key formulas and definitions
- Trees per hectare = 10,000 m² / (row gap × tree gap)
- Trees left after thinning = trees before × (1 − share removed)
- Rotation = years from planting to final felling
- Key jobs in order: prepare, plant, weed, clean, thin, prune, fell
Worked examples
1. Seedlings are planted 2 m apart in rows 2 m apart. How many trees fit on 1 hectare?
1 hectare = 10,000 m². Each tree needs 2 × 2 = 4 m². Trees = 10,000 / 4 = 2,500.
2. A stand has 2,500 trees. A first thinning removes 30%. How many are left?
Removed = 0.30 × 2,500 = 750. Left = 2,500 − 750 = 1,750 trees.
3. A hill above a village keeps losing soil in the rains. Which forest type and technique suit it?
An environmental forest. Keep a mixed, multi-layer forest, use natural regeneration, avoid clear-cutting on the steep slope, and keep a tree belt along the stream.
4. Trees on 1 ha are planted 2.5 m × 2 m. How many trees? What spacing gives about 1,600 trees?
Each tree needs 5 m², so 10,000 / 5 = 2,000 trees. For 1,600 trees each needs 10,000 / 1,600 = 6.25 m², for example 2.5 m × 2.5 m.
Common mistakes
- Thinking thinning wastes trees. It gives the best trees room to grow thicker.
- Mixing up weeding (small plants, early years) with thinning (cutting trees that are already big).
- Believing an environmental forest is never cut. It is cut lightly and with care, not for maximum timber.
- Forgetting to convert area: 1 hectare is 10,000 m², not 100 m².