Thinning on growth of Nothofagus pumilio regeneration phase in south Patagonia, Argentina.

PERI P.L.; MARTINEZ PASTUR G.; MONELOS L.; DIAZ, B.

Lincoln, Canterbury, New Zealand

Congreso; III Southern Connection Congress; 2000

Lincoln University

Lenga (Nothofagus pumilio) is the most important timber native species in southern Patagonia, Argentina. The shelterwood silvicultural system is the most frequently used for this species. This system mimics the natural forest dynamics through the opening of large canopy gaps, offering better ecological conditions for regeneration. For sawlog production, planned thinning in young stands may reduce the time required to yield products of a desired quality, concentrate growth on selected trees and increase production by utilizing trees that would die in the absence of thinning. Long-term thinning plots were located in 1996 in an even-aged advanced regeneration phase of lenga (18,500 stems/ha, age 35-40 years, SI60= 9.8 m) in Santa Cruz province (54º 32´S, 67º 03´W), Argentina. The aim of this study was to quantify the growth response (DBH and volume) of lenga to different thinning regimes. Over the total stocking, 1,111 crop trees (dominants, straight stems and good health) were selected. The thinning trial consists of four treatments: elimination of one, two and all effective competitors (T1, T2, and Tt, respectively) and a control (Tc). The effective competitor was defined as any tree which has a contact crown point with the selected tree),. Each treatment was replicated ten times in a split plot design (plots are 1440 m2 in area), where the main plots were three different levels of canopy cover of the remaining seed trees (0, 12 and 33%) and subplots were the thinning treatments. At the present, there are no interactions between canopy cover and thinning treatments. Three-year results from this study indicated that there was not a significant difference in growth response among treatments. Because the growth rate of lenga is slow, the reaction to thinning could occur later. However, the maximum mean diameter and volume growth was for the treatment Tt at 12% canopy cover (2.1 mm/year DBH; 1.9 m3/ha/year) and the minimum mean growth was at 33% canopy cover for Tc (1.5 mm/year DBH; 1.3 m3/ha/year). The diameter growth for Tt was 17% higher than the treatment control (1.8 mm/year). Total volume growth was greater at 12% canopy cover (1.7 m3/ha/year) than the treatment without any dominant trees in the superior strata (1.3 m3/ha/year). Furthermore, this thinning system proposed for lenga reduce the probability of windthrow and enhances the form of the selected trees, because it only removes the effective competitors and maintains a high stocking which offers mutual protection for the trees. These results are preliminary and the trial need to be monitored to evaluate if significant differences emerge between treatments.