Use of a new thinning method to reduce risk of windthrow in lenga forests of Patagonia, Argentina.

PERI P; MARTINEZ PASTUR G; VUKASOVIC R; DIAZ B; LENCINAS MV; CELLINI M

Valdivia (Chile), 5-7 Abril

Jornada; Reunión Internacional: Modelos y Métodos Estadísticos Aplicados a Bosques Naturales.; 2000

Universidad Austral de Chile

A new thinning method to reduce the risk of windthrow in a high site quality (SI60= 23.22 m) of Lenga (Nothofagus pumilio) forests is proposed and analysed. Sixty seven-year-old even-aged stands were thinned in 1996 (age at DBH). The method involves thinning from above to maintain the stand stability. This method proposes a slight reduction of crown density facilitating a gradual growth of the remnants selected trees (target trees). The system is carried out by five successive interventions, which incorporate the technique of girdling the follower trees. Two thinning levels were defined: at 800 stems/ha (alternative 1) and 489 stems/ha (alternative 2), with 1 hectare receiving each treatment. Within these 1 ha areas, 6 long-term plots were located. Also, four permanent plots were located where not thinned (control). DBH, basal area and volume growth were recorded for all treatments, and mortality rate and crown class dynamics were measured for the control. Wood volume yield data were collected from trees felled in the first thinning intervention. Three year-results from this study indicated that this new thinning method could achieve maximum growth for a high quality site, and avoid large gaps between the crowns of neighbouring trees that may create problems such as windthrow.