Growth responses after a future crop tree thinning and a thinning from below in a second-growth Nothofagus pumilio forest in Tierra del Fuego, Chile

Abstract

Nothofagus pumilio (lenga) is the most important native species for timber production in southern Patagonia both in Chile and Argentina. Thinning application to second-growth N. pumilio forests has been limited in Patagonia, probably because of the long time necessary for the investment to be recovered. In addition, experimental trials have focused mostly on thinnings from below, leaving a high residual stand density, which has led to a modest growth response. Using measurements (1995–2014) obtained from a thinning trial carried out in a second-growth N. pumilio forest located in Tierra del Fuego (Chile), the objective of this case study was to analyze whether selective thinnings with future crop trees (in the sense of Z-Baumen thinning) promote greater growth responses than those from a thinning from below. In addition, we explored the associations between climatic factors and age on N. pumilio tree growth. Trial treatments comprised a control, a thinning from below and a future crop tree thinning. The growth response after a future crop tree thinning was greater and lasted for a longer period (10 yrs) than did the thinning from below (4 yrs). The tree basal area and diameter at breast height (dbh) growth increased with dbh and annual absolute minimum temperature and decreased with age for the unthinned treatment during the period from 1977–2014 (~70–110 yrs old). Our results suggest that the future crop thinning might be a better alternative than the thinning from below for secondary N. pumilio forests in Patagonia due to the greater growth response while being a less intensive silvicultural method.