Such dead or dying trees provide a growth medium for fungi and epiphytes, as well as food and shelter for insects and the birds.
[citation needed] Variable retention harvesting retains more than 15% of the original stand in both rolling and permanent pockets of untouched trees and refugia patches.
Some timber companies have restricted the use of variable retention silviculture to only poorly stocked stands of rare but valuable tree species.
[citation needed] Ecologists regard the variable retention method of harvesting as being far less detrimental to the forest ecosystem than clearcutting.
A review of studies in British Columbia and in similar forest types indicates that while both aggregated and dispersed retention can contribute to biodiversity conservation there may be some negative consequences for timber production such as wind damage to retained trees and reduced growth rates of tree regeneration compared to clearcuts, concluding in favour of an adaptive management approach for balancing competing objectives of production of wood and biodiversity conservation.
[7] Forestry organizations, such as the Forest Stewardship Council (FSC), approve of variable retention and are now declaring timber obtained through such a harvesting method as certified wood for green building.