Long-term permanent plot observations of vegetation dynamics in Budongo, aUgandan rain forest

Species composition and turnover that have occurred in a series of permanen t sample plots established during the 1930s and 1940s in Budongo, a semi-de ciduous Ugandan forest, are reported. The plots were established as part of a sequence first used to describe forest succession, five of which have be en maintained and which were last measured in 1992-1993. One plot (plot 7) provides 53 y of data from old-growth pristine forest. Plot 15 was establis hed in wooded grassland at the forest edge and is now closed high forest. E valuation of the remaining three plots is complicated by silvicultural inte rventions carried out in the 1950s. Forty species have been added since the first evaluations and a total of 188 tree species (over 80% of Budongo's f orest tree flora, and including two exotics) has now been recorded from wit hin the plots. The pattern of shade-tolerance in the original plot series c onforms to patterns expected for succession with an increasing proportion o f shade-tolerant species with development, and large stems appearing to 'la g behind' smaller stems in this respect. The time series data are less cons istent, and while plot 7 increased in the proportion of shade-tolerant stem s through time, the proportion of shade-tolerant species actually declines. Stem-turnover (the mean of mortality and recruitment) slowed with implied successional stage. Most species have a higher recruitment than mortality r ate and stem numbers have thus increased in all plots. This is most pronoun ced in the putatively 'early successional' plot. Stem size structure has ch anged within the plots, with an increased proportion of smaller stems. Spec ies show different rates of turnover and these vary from plot to plot and p eriod to period. In plot 7, the overall mortality rate decreased with initi al stem size. Estimates imply that some tree species may easily live longer than 500 y after reaching 10 cm DBH, and that 1000 y is possible. The impo rtance of large trees in determining forest dynamics is illustrated by the finding that death of only seven stems in plot 7 contributed over 60% of ne t basal area losses recorded over the 53-y observation period. Many of the observed patterns were not predicted and could only have been found by long -term studies.