The effects of Cyclone Waka on the structure of lowland tropical rain forest in Vava'u, Tonga

Abstract

On 31 December 2001, Tropical Cyclone Waka passed directly over the Vava'u island group, Kingdom of Tonga, with sustained and maximum wind speeds of 185 km h⁻¹ and 230 km h⁻¹ respectively. During a prior study of forest secondary succession, 44 forest plots on 13 islands had been surveyed in 1995 and their locations marked. Nineteen of the plots were resurveyed and two additional transects established in May–June 2002, 6 mo following the cyclone. Cyclone-related tree mortality averaged 6%, varied from 0–7% for lowland late-successional species, and tended to be higher for early successional plots (8–16%) and species (4–19%). Severe damage (uprooting, snapped stems) affected 25% of the 2030 stems measured. The proportion of snapped stems was disproportionately high in the 10–15-cm stem diameter class. Uprooting was more prevalent than expected by chance among larger trees (>20 cm diameter). The greatest mortality and severe damage (combined,>35% of stems) occurred in plots that were early successional. Over the 6 y prior to the storm, background recruitment and mortality averaged 1.4% and 3.3% respectively. Mortality was greater than recruitment, while basal area was increasing, in most plots that had not experienced additional anthropogenic disturbance.