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

P PERI; G MARTÍNEZ PASTUR; R VUKASOVIC; B DÍAZ; MV LENCINAS; JM CELLINI

BOSQUE (VALDIVIA)

Año: 2002 p. 19 - 28

0304-8799

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