An accessory system is a silvicultural system, which originates from other even-aged systems by modification of techniques, resulting in an irregular or uneven age stand.
Types of accessory system
- Two storied high forest system
- High forest with reserve
- Improvement felling
Two storied high forest system
In this silvicultural system, a two-storeyed forest is formed in which the canopy can be differentiated into two strata, in each stratum the dominant species is usually different. It is a form of forest produced by introducing a young crop under an existing immature one.
- The upper story consists of strong light demanded species that are of seedling origin.
- The lower story includes shade-demander species that may be obtained by natural regeneration. but also can be planted under the following circumstances;
- For the protection of soil
- Improve the proportion of valuable species inside the forest.
- To propagate certain species which cannot be raised in open
The upper story is grown, thinned heavily when it is approaching or has reached the middle stage, and shade-bearing species are introduced artificially as an understory.
Applicability
- Two major species grown in the irrigated plantation at present are Shisham and Mulberry.
- In Germany mixed plantations of Scots pine and beech
- In UK Oak and Larch
- In India Chir pine and Oak
High forest with the reserve system
It is a silvicultural system in which, selected trees of the crop being regenerated are retained for part or whole of the second rotation in order to produce large-sized timber. It is a form of forest produced by retaining certain trees of the old crop after regeneration is completed.
Reserve or standard may be retained, scattered singly or in small groups for whole or part of the second rotation. Regeneration may be carried out either naturally from seed or artificially by sowing or planting.
The recent trend of reserving some trees of the old crop in the clear-felling system is an example of this system.
Improvement felling
This method essentially includes the removal of inferior growing stock in the interest of better growth and more valuable individuals, basically applied to the mixed uneven-aged forest. But, it is not truly a silvicultural system as it neither aims at regenerating the crop, nor producing a crop of distinctive characteristics.
It involves the felling of the dead, dying, diseased trees, unsound over mature trees removal, removal of undesirable undergrowth or inferior trees, climber cuttings, etc.
Advantages
- Increase in productivity by growing two crops on the same land.
- Propagation of shade-bearing species in the lower story. Example; Taxus baccata, Acer saccharum, Sugar Maple.
- Effective soil protection as cover crops like Musea , switenia, evodia, bamboo, etc are used.
- To furnish early returns on the investments in the form of thinning in the over wood.
- The stand volume and yield from thinning in the over wood increases gradually.
- Removal of inferior growing stock (dead, dying, diseased).
- Control of weeds.
Disadvantages
- Considerable damage to the understory crops, when thinning or felling are carried out in the over storey crops.
- Requires very high levels of skills, very difficult in operation, and labor incentive.
- Under storey crops may affect the growth of upper-storey crops.
- Under planting operations are difficult and unless done carefully, are likely to fail.
- Requires a high degree of knowledge for plantation of crops for better production.
