Dominance of primary rain forests by the ectomycorrhizal, leguminous canopy tree Dicymbe corymbosa (Caesalpiniaceae) was investigated in the Pakaraima Mountains of western Guyana. In five 1-ha forest inventory plots in the Upper Ireng and Upper Potaro River drainages basal areas of D. corymbosa ranged from 38.4-52.8 m2 ha-1 (63-85% of total) among all trees ≥10 cm diameter at breast height (dbh), values in the upper range for tropical moist forests worldwide. The high basal areas for D. corymbosa were due to the prevalence of large (>150 cm dbh), multi-stemmed individuals. Stem densities in Dicymbe plots ranged from 276-433 ha-1, with D. corymbosa contributing 24.6-59.8%. In three 1-ha mixed forest plots adjacent to the Dicymbe plots, D. corymbosa was absent. In the mixed forests, stem densities were higher (480-585 ha-1), basal areas were lower (36.7-39.8 m2 ha-1), species diversity was higher, and canopy tree species were more equitably distributed than in the Dicymbe plots. Tree community composition was not qualitatively different between Dicymbe and mixed forests. In the Dicymbe plots, mean sapling and seedling densities of D. corymbosa were significantly higher than most other canopy species, indicating persistent monodominance. Edaphic variation did not account for variation in forest composition. Life history traits are discussed which may contribute to clumping in D. corymbosa, including coppicing and mast-fruiting, and the potential role of litter-trapping physiognomy and ectomycorrhiza-mediated nutrient dynamics in promoting monodominance is noted.

Senna spectabilis is a tree native to South and Central America. Thirty-five years ago it invaded the Mahale Mountains National Park in western Tanzania where it presently covers c. 225 ha. We quantified its occurrence relative to that of sympatric species of native trees, and compared girdling and felling as methods for its control in three 0.25 ha plots. Within invaded areas of forest this exotic species was both the most abundant and dominant of the 26 species of tree recorded. During 4 years of monitoring the experimental plots the abundance of S. spectabilis declined markedly in the plots where control methods were practised, but increased slightly in the unmanipulated plot. In contrast, the abundance of native tree species increased markedly in the plots where S. spectabilis had been removed or killed, with higher densities in the girdled rather than the felled plot. S. spectabilis appears to suppress the recruitment of native trees in the Park, and its removal can encourage regeneration of the degraded forest without the need for artificial seeding.

Three ectomycorrhizal legume trees, Microberlinia bisulcata, Tetraberlinia bifoliolata and T. moreliana, form discrete groves in the southern part of Korup National Park, in southwest Cameroon and contribute c. 45–70% of stand basal area locally in a matrix of otherwise species-rich arbuscular mycorrhizal forest. A transplant experiment was performed to assess the importance of ectomycorrhizal infection associated with proximity to parents in seedling establishment of the grove-forming species. Nonectomycorrhizal seedlings of the three species were transplanted into plots of two forest types, one of high (HEM, within-grove) and one of very low (LEM, outside the grove) abundance of all three species as adult trees. For two species (T. moreliana and M. bisulcata) there was no difference in survival over 16 months, but for the third (T. bifoliolata) survival was best in HEM forest, and correlated with the basal area of adult trees of ectomycorrhizal species. Only one species (T. moreliana) increased in biomass over the experimental period; the others declined. There was no effect of forest type on overall growth of any species, but the survivors of two (T. moreliana and M. bisulcata) had heavier stems in the HEM forest. Differences in survival and growth of transplants between the three species were in accord with the ecology of the species as inferred from the frequency distributions of adult tree size in the forest. Seedlings became infected with ectomycorrhizas in both forest types; where there was a difference in extent of infection (T. moreliana) this was not related to survival or growth; and where there was a difference in survival (T. bifoliolata) this was not related to extent of infection. These results confirm that mycorrhizal inoculum associated with conspecific adults is neither a prerequisite nor a guarantee of seedling establishment, but indicates that in some circumstances there might be benefits of being close to parents. Further research is required to unravel the complexities of ectomycorrhizal community structure in this spatially and temporally heterogeneous forest, and to clarify the extent to which the various hosts share ectomycorrhizal partners.

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.