Mid-term results and prospects for irregular shelterwood systems in hardwood-dominated temperate rainforests in Chile

Abstract

Background: When possible, silviculture should aim to develop mixed-species multi-aged forests that can be more productive and resilient to disturbances, provide high-quality timber and sustain greater amounts of biomass. Southern Chile is covered by temperate rainforests dominated by a mixture of tree species, such as the Evergreen forest type (EFT). The irregular shelterwood regeneration method is a novel approach aimed at developing irregular multi-aged forests following the retention of the residual forest (no final cut). Here, we report mid-term results after implementing these cuttings in two EFT forests in the Coastal Range and discuss its prospects for other temperate rainforests. Methods: Two forests were sampled and evaluated in terms of composition, structure and growth, focusing on the new cohorts developed or released after the irregular shelterwood cuts. One forest was cut in a low-productivity site at 600 m (Hueicolla) in 1983, and the other in a medium-productivity site at 350 m (Llancahue) in 2009. In Hueicolla, 63% of the basal area was harvested from an old-growth forest where the main residual tree species were Eucryphia cordifolia, Laureliopsis philippiana and Saxegothaea conspicua. In Llancahue, 40% of the total basal area was harvested in a mature secondary forest dominated by Nothofagus dombeyi. Results: The understorey developed in Hueicolla had 3,600 trees per ha and a quadratic stand diameter of 15 cm. It was dominated by the mid-tolerant species Eucryphia cordifolia, Gevuina avellana and Lomatia ferruginea, plus the shade-tolerant Amomyrtus luma. In Llancahue, a dense lower canopy was dominated by Podocarpus salignus and Drimys winteri, both mid-tolerant species, which included 81,000 seedlings and saplings < 5 cm per hectare and 560 ingrowth 5-10 cm trees per hectare. Conclusions: The irregular shelterwood cuts allowed the development of dense understorey tree layers below the residual trees. However, the tree composition of the new cohorts largely differed from that of the residual trees and was dominated by mid-tolerant species, including some short-lived species. The irregular shelterwood method proves appropriate for the EFT and may likely be successful in other forest types with valuable mid-tolerant species.