Wind Damage as an Ecological Process in Mountain Beech Forests of Canterbury, New Zealand

Sites in four areas of Canterbury, New Zealand were examined to determine the principal factors influencing wind damage, and study sites at two areas were used to investigate forest age-class structure and stand dynamics. At all sites large-scale topographic features funnelled storm winds to produce recurrent damage, and smaller-scale topographic features determined precise points affected by winthrow. Lee slopes provide shelter to susceptible sites during normal weather conditions and therefore permit better stand growth, but stand damage increases in storms. Stands on exposed windward slopes form a wind-shaped canopy which is constrained by stem breakage during minor storms. Damage occurs in stands over a critical height of about 18 m and where stem diameter is large. Winddamaged forests have restricted age-distribution compared with those of partially damaged and vulnerable forests. Wind damage is little cause for concern as it must be viewed in a framework of short-term forest stability. Periodic mortality in mountain beech forests can be seen as a regeneration strategy of a lightdemanding species, since it produces ideal conditions for forest perpetuation. Forest collapse, followed by rapid massed regeneration is thus an effective competitive mechanism against a more shade-tolerant canopy species.