Thinning schedules to reduce risk of windthrow in Nothofagus pumilio forests of Patagonia, Argentina

PERI, P.L.; MARTINEZ PASTUR G.; VUKASOVIC R.; DIAZ B.; LENCINAS M.V.; CELLINI J.M.

BOSQUE (VALDIVIA)

UNIV AUSTRAL CHILE

Año: 2002 vol. 23 p. 19 - 28

0304-8799

A thinning method to reduce windthrow risk in a high quality site (SI60= 23.2 m) of lenga (Nothofagus pumilio) forests is proposed. Sixty seven-year-old (base age at 1.3 m) even-aged stands were thinned in 1996. The method involved thinning from above to maintain the stand stability. This method proposed a  gradual reduction of crown density  increasing the growth of selected trees (target trees). The system  was carried out by five successive operations  that incorporated the technique of girdling follower trees. Two thinning levels were defined: at 872 stems/ha ( light thinning treatment) and 489 stems/ha (heavy thinning treatment).  Each treatment had an area of 1 hectare with 6 long-term plots. Four permanent plots were established as control (not thinned). Diameter, basal area and volume growth were recorded for all treatments, and mortality rate and crown class dynamics were measured in the control. Total stem volume over bark and merchantable volume by log type  were collected from trees felled in the first thinning intervention. Six year results from this study indicated that the proposed thinning method could achieve maximum growth and simultaneously avoid large gaps between tree crowns that may induce  windthrow.