A silvicultural system in which the over wood is removed gradually in two or more successive fellings depending on the progress of regeneration. The primary intent of this system is to protect and shelter the developing regeneration.

The trees which are growing vigorously are retained to provide shelter, Seed, rapid diameter increment and value increment and protection of site against deterioration.

Criteria for leave-trees in shelter wood systems are: larger, dominant trees, wind firm trees, desirable species and desirable physical characteristics .

Advantages

• Marking and felling of trees of the over wood are simpler than selection system
• Soil is not completely denuded so there is little risk of soil deterioration and erosion.
• As the regeneration operations are carried out under the shelter of older crop, there is little danger of invasion of the area by weeds and grasses
• The young crop is protected against adverse climatic factors such as cold, frost, etc.
• As the regeneration is obtained from seeds obtained from best selected trees, the new crop is superior.
• Suitable system for the regeneration of both light demander and shade bearer spps.
• It makes supervision and control of various operations easy.
• From aesthetic point of view, the system is superior to clear felling system.

Disadvantages

• As the over wood is removed in more than one operation, there is much damage to the young crop.
• The isolated seed bearers are susceptible to wind damage.
• After seeding felling, invasion by weeds and regeneration may be affected.
• Weeding and cleaning have to be done for longer period and the natural regeneration becomes costly.

Pattern of Felling

1. Preparatory Felling: A felling made under a high forest system, usually towards the end of the rotation, with the object of creating conditions favorable to seed production and natural regeneration.
   • Create gaps in the canopy
   • Create favorable conditions on the forest floor
2. Regeneration felling: A felling made with a view to inviting or assisting regeneration under a shelter wood system. It includes seeding felling, secondary felling and final felling.
   • Seeding felling: Opening the canopy of a mature stand to provide conditions for securing regeneration from the seed of trees retained for that purpose. It is the first stage of regeneration felling.
   • Secondary felling: A regeneration felling carried out between the seeding felling and the final felling under a shelter wood system in order to gradually remove the shelter and admit increasing light to the regenerated crop. Removal of trees in secondary felling depends on progress of regeneration and its light requirement. It also helps in the manipulation of mixture of crop.
   • Final felling: The removal of the last seed or shelter trees after regeneration has been affected under a shelter wood system. It is the final stage in regeneration felling when the area is completely stocked with established regeneration

Periodic Block

It is necessary to divide the rotation period in to as many parts as the number by which the rotation is divisible by the time taken to regenerate an area.

Example:

If the rotation is 120 years and it takes 30 years to regenerate the area naturally. The rotation will be divided into periods. As each of this part is felled and regenerated in a particular period, it is called a periodic block.

120/30 = 4 periodic blocks

Kinds of Shelterwood Systems

1. Uniform shelter wood system (Uniform System):The canopy is uniformly opened up over the whole area of a compartment to obtain uniform regeneration under the shelter of remaining old crop.
2. Strip shelter wood system: Regeneration felling is done in the form of strips successively from one side of the compartment, progressing against the direction of wind. The width of the strip varies according to local conditions.

3. Group system: Smallest circle for final felling, medium circle or secondary felling, and largest circle for seeding felling

   Group shelter wood system: A silviculture system in which regeneration fellings, instead of being done uniformly all over the compartment, are carried out in scattered groups in which the foci of regeneration can be enlarged centrifugally to merge with each other ultimately. Advance growth is the main source of regeneration. It was tried in Deodar, Kail and Sal forests in India but it was not successful.

4. One cut shelter wood system: In this system, regeneration felling is done in one operation. It is applied only when advance regeneration is well.
5. Indian Irregular shelter wood System: Silvicultural System is which mature crop with recalcitrant regeneration having large quantities of advance growth of various ages and sizes including immature poles and trees upto 40 cm dbh, which are retained as part of the future crop to complete regeneration work . The crop to be regenerated is opened up irregularly and the resultant crop is uneven aged. This system is applied to Sal, Deodar, Fir, Spruce and other evergreen forests in India.
6. Irregular shelter wood system: Regeneration felling is on the pattern of group system but as the regeneration period is long, the crop produced is uneven aged or irregular. This is a compromise between shelter wood group system and selection system.