Species composition and turnover that have occurred in a series of permanentsample plots established during the 1930s and 1940s in Budongo, asemi-deciduous Ugandan forest, are reported. The plots were establishedas part of a sequence first used to describe forest succession, five ofwhich have been maintained and which were last measured in 1992-1993. Oneplot (plot 7) provides 53 y of data from old-growth pristine forest. Plot15 was established in wooded grassland at the forest edge and is now closedhigh forest. Evaluation of the remaining three plots is complicated bysilvicultural interventions carried out in the 1950s. Forty species havebeen added since the first evaluations and a total of 188 tree species (over80% of Budongo's forest tree flora, and including two exotics) has nowbeen recorded from within the plots. The pattern of shade-tolerance in theoriginal plot series conforms to patterns expected for succession with anincreasing proportion of shade-tolerant species with development, and largestems appearing to ‘lag behind’ smaller stems in this respect. The timeseries data are less consistent, and while plot 7 increased in theproportion of shade-tolerant stems through time, the proportion ofshade-tolerant species actually declines. Stem-turnover (the mean ofmortality and recruitment) slowed with implied successional stage. Mostspecies have a higher recruitment than mortality rate and stem numbers havethus increased in all plots. This is most pronounced in the putatively‘early successional’ plot. Stem size structure has changedwithin the plots, with an increased proportion of smaller stems. Speciesshow different rates of turnover and these vary from plot to plot and periodto period. In plot 7, the overall mortality rate decreased with initial stemsize. Estimates imply that some tree species may easily live longer than 500y after reaching 10 cm DBH, and that 1000 y is possible. The importance oflarge trees in determining forest dynamics is illustrated by the findingthat death of only seven stems in plot 7 contributed over 60% of net basalarea losses recorded over the 53-y observation period. Many of the observedpatterns were not predicted and could only have been found by long-termstudies.

Maracá is a riverine island located in the Rio Uraricoera in Roraima State (Brazil) and has an area of about 100,000ha. A forest type dominated by Peltogyne gracilipes Ducke (Caesalpiniaceae) occurs on Maracá Island on a range of soil types. This study compares the structure, floristic composition and soils of the Peltogyne forest with the most widespread lowland forest type on Maracá. Three 0.25ha plots were set up in each of three forest types: Peltogyne-rich forest (PRF), Peltogyne-pooi forest (PPF) and forest without Peltogyne (FWP). Within each plot all trees (≤ 10cm dbh) were recorded. Seedlings and saplings were sampled in subplots of 2m × 1m (seedlings) and 4m × 4m (saplings). In the PPF and FWP, Sapotaceae were the most important family with the highest relative dominance and relative density values. Caesalpiniaceae showed high values in the PRF and PPF. Licania kunthiana, Pradosia surinamensis and Simarouba amara occurred in the canopy layer in all the forest types. Peltogyne dominated the canopy in the PRF and comprised 20% of stems and 53% of the total basal area of all trees ≥ 10cm dbh, and 91% of the stems and 97% of the total basal area of individuals ≥ 50cm dbh. In PPF, Lecythis corrugata and Tetragastris panamensis were the most abundant species, followed by Peltogyne. In the FWP the most abundant trees (≥ 10cm dbh) were Licania kunthiana and Pradosia surinamensis. In all forest types, the soils were sandy and acid with low concentrations of extractable phosphorus and exchangeable cations, but the soils under PRF were notably richer in magnesium.