Stand dynamics in an advenced regeneration phase of Nothofagus pumilio 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

In south Patagonia there are important forest areas of lenga (Nothofagus pumilio) that have been harvested over the last 50 years, and where natural regeneration has established. The silvicultural regime is a typical uniform shelterwood system with a 100-year rotation and a 40-year regeneration period (early and advanced). In general, the regeneration phase is characterised by a great number of trees per hectare, high competition rates (mainly for light), and a high mortality rate. Circular long-term plots of 100 m² were installed (1996) in homogeneous stands of advanced regeneration of lenga in Santa Cruz province (54º 32´S, 67º 03´W), Argentina. The objective of the study was to evaluate stand dynamics and tree growth of the advanced regeneration of lenga. Mortality, DBH, volume, crown classes, and tree form were recorded annually for each tree. The initial stand stocking, aged 30-38 years, was 19,350 stems/ha growing at a site index of 9.8 m at base age 60 years. The competition-induced mortality is occurring at a rate of 250 trees/ha/year. Mortality is confined to first diameter classes (1-3 cm and 3-5 cm), and intermediate and suppressed crown classes. The unimodal diameter-class frequency distribution suggests an even-aged population, with a mean DBH of 5.8 cm (36% of stems were in the 3-5 cm class, and 27% in the 5-7 cm class). The growth rate showed different responses, according to the crown classes. The mean annual DBH rate measured was 0.22, 0.10, 0.03 and 0.02 cm/year for dominants, codominants, intermediates and suppressed trees, respectively. The total mean volume increment averaged 10.5 m3/ha/year, where 71% of this was provided by the dominant crown class. A similar tend was observed for basal area increment where the mean values were 1.16, 0.43, 0.13 and 0.05 m2/ha/year for dominant, codominant, intermediate and suppressed crown classes, respectively.  Also, a transposing of crown classes categories occurred over time due to the competition. While the proportion of dominant and codominat trees decreased from 23 and 25% in 1996 to 18 and 22% in 1999, respectively, the proportion of suppressed trees increased 7% for the same period of time. These long-term plots will provide essential data to develop a future computer-based model for forest management planning in Patagonia.