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Summary 1We evaluate the eects 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 ®rst 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 À1 . Mortality varied between species but was independent of topography and geographical location. 3 Recruitment increased from very low rates (median 0.0% year À1 ) before the ®rst cyclone to median values of 1.6±3.2% year À1 during 1971±79, i.e. following a lag period of 3.5±8 years after the ®rst 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 re¯ects 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 eects 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. Dierences in forest composition across Kolombangara are more likely to have been caused by dierential anthropogenic disturbance linked to settlement patterns.

Study of forest dynamics commonly requires measurement of canopy gap size. Hemispherical photographs can be analysed to provide various measures whereby gaps can be ranked in order of size. For ten artificial gaps in a Bornean tropical rain forest these measures were better correlated with gap microclimate than gap area measured physically on the ground. All these measures are however relative. For detailed (e.g. ecophysiological) studies the greater detail provided by absolute measures of photosynthetically active radiation (PAR) are required. Long term PAR values can be computed from hemiphots so long as measurements in the open nearby are available. Correction for cloudy weather is essential. Computed and measured PAR are compared for the test gaps. Both have inherent limits which means that below c. 15% canopy openness, differences in PAR between gaps cannot be assessed accurately.

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. British Ecological Society is collaborating with JSTOR to digitize, preserve and extend access to Journal of Ecology. 304 Montane and lowland forest in Ecuador. II. Climate Schulz 1960), Trinidad (Pittendrigh 1948, 1950), Colombia (Bates 1944; Baynton et al. 1965) and Mexico (Goodnight & Goodnight 1956). Only Schulz (1960) published comprehensive data for extended periods; most of the other workers published only scattered data for odd days or very short periods and we cannot make very useful comparisons with their results. Records for single weeks in several situations in an Upper Montane Forest (ridges, ravines, etc.) have been published by Shreve (1914) for Jamaica. It appears that no record has been published for the forests in the Amazon basin or those on the Andes. Regarding the atmospheric conditions prevailing in montane forests, very few detailed studies have been published for any part of the tropics. Apart from Shreve (1914), only Brown (1919) has given a detailed quantitative account. It is desirable to have details of the microclimate both in the undergrowth, where all but the most light-demanding trees regenerate, and in the upper levels of the forest canopy, where the tallest species mature. We use 'canopy' to describe the sum total of the crowns of the trees of all heights and not in the sense of Richards (1952, p. 23) of a 'more or less continuous layer of tree crowns of approximately even height'. A knowledge of conditions in both situations is also needed in relation to epiphytes since these are found at all levels in the canopy at both our forest sites (Grubb et al. 1963). Ideally one should record temperature and relative humidity from a number of positions in each forest because one may expect various patterns in the distribution of their characteristics, rather as for penetration of rainfall (Hoppe 1896; Kittredge 1948; Hopkins 1965) or of radiation (Trapp 1938; Evans, Whitmore & Wong 1960). However, the amount of variation within the forests is likely to be much less than for, say, light characteristics because of air movements; Baynton et al. (1965) found a close correlation between temperatures on two 60 m towers 1100 m apart in level forest in Colombia. The variation is likely to be relatively unimportant in comparing the high forest phase of one forest with that of another.One may expect to be able to gain an indication of conditions in the upper part of the canopy from records taken in a clearing. Geiger (1961) has shown that one may expect from considerations of interception and loss of radiation a parallel between the uppermost part of the forest canopy and the soil or turf of a clearing; both are expected to be hotter by day and cooler by night tha...

In 1964 a census of all trees > 9.7 cm diameter at breast height (DBH) was conducted on 22 plots totalling 13.2 ha in lowland tropical evergreen rain forest on Kolombangara, Solomon Islands. Over the following 30 yr , populations of all individuals > 4.85 cm DBH of the 12 most common tree species and amounts of disturbance have been monitored on a declining number of these plots (in 1994, nine plots totalling 5.4 ha were still being recorded). Between November 1967 and April 1970, Kolombangara was struck by four cyclones, although only two of these caused substantial amounts of damage to the canopy structure. Multivariate analysis has identified six forest types on Kolombangara (Greig-Smith et al. 1967). The species richness and diversity of trees in the 1964 census, turnover rates of the populations monitored over [1964][1965][1966][1967][1968][1969][1970][1971][1972][1973][1974][1975], and the amount of disturbance sustained during a cyclone in 1970, were all positively correlated across five of the forest types. The sixth forest type was a consistent outlier in these analyses and is believed to have been seriously disturbed by humans about a century ago. The floristics, turnover and disturbance data support Connell's intermediate disturbance hypothesis. The most species-rich forest types contained a higher proportion of fast-growing individuals and species that are early-successional and which have low density timber. Properties of these species rendered them more susceptible to damage when struck by the 1970 cyclone. They showed higher turnover rates because disturbance-dependent species are also characterised by higher mortality and recruitment rates. Thus, periodic cyclones appear to favour the maintenance of differences in species diversity and composition between forest types.

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