Planting native forest species in northern Patagonian woodlands: response to canopy opening in contrasting sites

Abstract

Enriching forests with native trees used for their high-value timber could allow productivity and biodiversity conservation goals to be achieved together. In certain Patagonian forests (e.g. low forests composed by resprouting species), this requires an analysis of the degree of canopy opening that guarantees planting success. We evaluated the influence of canopy opening intensity (OI) on the survival and height growth of a plantation of native tree species in three contrasting sites (south slope: SS, north slope: NS, and valley bottom: VB). At each site, we established an OI gradient of 0, 30, 50, and 70 % of initial biomass extraction, and planted Austrocedrus chilensis, Nothofagus dombeyi, N. pumilio, N. antarctica, N. alpina and N. obliqua (monitored for nine years). The optimal OI for average seedling survival was site-dependent; in SS the optimal survival was at intermediate OI (62 - 78 %), while in NS no differences were observed up to 50 % OI (32 %), and in VB plant survival was less than 3 %. N. obliqua and A. chilensis had the highest survival rate (60 % and 97 %, respectively). Annual plant growth varied among sites, with 27 ± 6 cm/year in SS, 10 ± 3 cm yr^-1 in NS, and 5 ± 2 cm yr^-1 in VB. N. obliqua reached the highest average plant height, with 4.2 ± 2 m in SS and 1.8 ± 1 m in NS. In SS most of the species grew from 18 to 60 % annually. Our results showed that management schemes should be species and site specific. We recommend planting on wetter slopes and initially removing up to 50 % woodland biomass.