Short-term effects of cyclone impact and long-term recovery of tropical rain forest on Kolombangara, Solomon Islands

1 We evaluate the effects of large-scale disturbance on tropical tree communities by examining the population dynamics of all individuals > 4.9 cm in diameter at breast height (d.b.h.) of 12 tree species over 30 years (1964-94) in lowland tropical rain forest on Kolombangara, Solomon Islands.

2 During the study period Kolombangara was struck by four cyclones between 1967 and 1970. The last cyclone caused most damage to canopy structure. Mortality in the 6-month interval spanning the first cyclone was 7.0% of all trees, while mean annual mortality for all other intervals (including those spanning other cyclones) was 1.4-2.2% year(-1). Mortality varied between species but was independent of topography and geographical location.

3 Recruitment increased from very low rates (median 0.0% year(-1)) before the first cyclone to median values of 1.6-3.2% year(-1) during 1971-79, i.e. following a lag period of 3.5-8 years after the first cyclone. Recruitment rates were higher on plots showing greater mortality rates during this cyclone. Recruitment and mortality rates were still higher in 1994 than they had been before the 1967-70 cyclones.

4 Mean annual mortality rates were positively correlated with mean annual recruitment rates across species. This relationship reflects a continuum of life-history characteristics and contributes to constancy in the relative abundance of the 12 species when the same sets of plots are compared over all measurement intervals up to 30 years.

5 We conclude that cyclone impacts have only short-term effects on the relative abundance of common tree species on Kolombangara, and do not therefore prevent the establishment of an equilibrium rank abundance hierarchy or create spatial variation in tree species composition. Differences in forest composition across Kolombangara are more likely to have been caused by differential anthropogenic disturbance linked to settlement patterns.