Little is known about how climatic variability affects fragmented forests and their abrupt edges. We contrasted effects of the 1997 El Niño drought between fragmented and continuous forests in central Amazonia, using long-term data on tree mortality. For 23 permanent 1-ha plots, annualized mortality rates of trees ≥ 10 cm diameter at breast height (dbh) were compared among a ‘baseline’ interval of 5-17 y before the drought, a 12-16-month interval during the drought, and a 12-13-month interval after the drought, using repeated-measures ANOVA. We also examined the size distributions of dead trees for each interval. During the drought, average annual tree mortality rose significantly in both forest edges (from 2.44% to 2.93%) and interiors (from 1.13% to 1.91%), and the magnitude of this increase did not differ significantly between edges and interiors. After the drought, tree mortality declined in all plots, but most dramatically on edges. Mortality rates were more variable over time on edges than interiors, and there was no evidence of time lags in mortality. In forest interiors, the size distributions of trees that died did not differ significantly among the three intervals. On edges, however, relatively fewer small (10-15 cm dbh) and more medium-sized (20-30 cm dbh) trees died in the post-drought interval, compared to other intervals. Moreover, forest edges lost a significantly higher proportion of large (≥ 60 cm dbh) trees than did forest interiors. These results suggest that droughts have relatively complex effects on fragmented Amazonian forests. Drought effects in our forest fragments probably were reduced by prior floristic and structural changes near edges and by adjoining regrowth forest that partially buffered edge vegetation from desiccating conditions.

Multiple species of primate disperse seeds and differentially contribute to the seed rain in tropical forests. The goal of this study was to examine seed dispersal by a primate community of five monkey and two ape species in the Dja Reserve, Cameroon. The density of primates in the reserve was calculated to be 77 individuals km-2. Analysis of 5789 faecal clumps demonstrated that 40% of monkey and 74% of ape faecal clumps possessed whole seeds. Six of the seven focal species acted as seed dispersers; faecal clumps passed by the black-and-white colobus (Colobus guereza) did not contain any whole seeds during the study. Seed passage trials on four captive monkey species showed monkeys to have an average seed passage time of 22 hours and defecation rate of five times per day. From the above results, the primate community was estimated to defecate 1129 seeds km-2 d-1. Seeds passed by the primate community came from 125 species of trees, lianas and shrubs, equivalent to at least 34% of the known tree flora. Rarefaction curves indicated that additional collection effort would identify more seed species passed by primates. Germination studies demonstrated that primate-passed seeds are viable. The number of seeds and plant species dispersed suggests that the primate community plays an important role in the maintenance of forest structure.

In an area of savanna-forest (S-F) mosaic of Cameroon, at Kandara near Bertoua, an enclosed savanna bordered by young semi-deciduous forests was selected for detailed studies of vegetation and soil carbon isotope compositions with a view to estimating the rate of forest advance into savannas. Forest floristic composition and structure were analysed in small plots along two S-F transects and within two large stands. Tree species counts and basal area (BA) measurements gave convergent results defining (1) an edge forest with low BA values that forms an irregular strip parallel to the S-F border, (2) a large colonization zone zone composed of pioneer species (Albizia species, with individuals of very large diameter) and (3) a mature forest composed of abundant Rinorea individuals and large individuals of Triplochiton scleroxylon and Piptadeniastrum africanum. Carbon stable isotopes were deter mined from organic matter of soil profiles sampled at various depths in savanna, colonization-zone and mature forest. In the deep soil horizons (40-50 cm) of the colonization-zone profiles, δ13C values similar to those of the present savanna reveal the past existence of a large-tree savanna. In subsurface horizons (15-20 cm), δ13C values intermediate between those of savanna and mature forest prove the encroachment of the forest ecosystem on savanna. Using 14C measurements, the mean residence time (MRT) of soil organic matter of these last horizons was determined with precision owing to the atmospheric 14C pulse from nuclear bomb tests prior to 1964. By assuming an exponential age distribution of organic compounds and by taking account of MRT and remaining carbon from the savanna, the coloniza tion zone was found to be 60-80 y old. The age of the colonization zone being the same near the present savanna and near the mature forest, it seems that the forest advance was probably not a linear process but would result from the coalescence of Albizia thickets born in savanna.

An altitudinal survey of correspondences between fruiting phenologies of fleshy-fruited tree species and seasonal dynamics of frugivorous birds on Mt. Kinabalu in Borneo was carried out for 50 weeks across four vegetation types: a hill forest (800 m asl), a lower montane forest (1700 m), an upper montane forest (2000-3000 m) and a subalpine forest (3000-3500 m). In the hill forest, a large fruiting peak following the general flowering phenomenon was observed during October-November in 1996 and a fruitless period was observed during February-April in 1997. During the fruitless period, the number of resident frugivorous birds decreased. A bimodal fruiting pattern was observed in the lower montane forest. A large number of frugivorous temperate migrants were observed when the fruiting peak occurred. The number of resident frugivorous birds increased and several lowland bird species were observed, when the number of resident birds decreased in the hill forest. In the upper montane forest and the subalpine forest, more continuous and irregular fruiting patterns without outstanding peaks were observed and the number of resident frugivorous birds was more stable throughout the year. These suggested (1) there was a strong relationship between fruiting seasonality and seasonal dynamics of temperate migrants in the lower montane forest; (2) seasonal altitudinal movements of lowland bird species to montane vegetation might occur during the fruitless period in the lowland forest; and (3) the continuous fruiting pattern in the higher vegetation zones might be related to the scarcity of available frugivorous birds. The hypothesis that the influx of temperate migrants into the montane vegetation of Mt. Kinabalu is affected by density and habits of resident frugivorous birds is supported. Montane vegetation in Borneo plays an important role as temporal refugia for temperate and altitudinal migrants by supplying fruit resources.

Four common fallow tree species were tested for a response to nitrogen and phosphorus fertilization. Seedlings or cuttings of Melicope glabra (Rutaceae), Macaranga gigantea (Euphorbiaceae), Persea romosa (Laureaceae), Peronema canescens (Verbenaceae) were grown in pots of a 50:50 mix of native soil and sand under 18% full sun for 18 weeks. Every 2 weeks, plants received either added N, added P, added N+P, or no added nutrients (control). Persea, a shade-tolerant species, and Macaranga, a light-demanding pioneer, improved relative growth rate with the addition of both N and P. Neither responded to N or P alone. Peronema and Melicope demonstrated luxury consumption of both N and P but did not show enhanced growth. Two of the four species tested (Persea and Melicope) were more limited by P than N. Macaranga was equally limited by both and Peronema was more limited by N. Along with previous studies, evidence for positive growth response and luxury consumption among light-demanding species suggests that P, rather than N, should limit seedling performance and may ultimately influence tree diversity in young secondary tropical forests.

Although acacias are ecologically and economically important, their demography is poorly known. In part this is because few field experiments have been undertaken. Also, a bewildering diversity of factors have been suggested to determine their demography. These factors include disease, fire, large and small browsers and grazers, climatic variation, competition with grass, seed predation and anthropogenic impacts. This synthesis concentrates on the life-history period from seed to adult plant and indicates that important hurdles have been demonstrated for some species in some habitats. Seed and seedling limitation have not been clearly demonstrated, nor has the value of dispersal been quantified. In contrast, the impacts of herbivores and fire in affecting the escape or release of resprouts has been repeatedly demonstrated. Whether fire and herbivory merely slow down the rate of promotion through size-classes or actually prevent it, needs further work. We note that very little comparative work amongst Acacia species has taken place. Most studies have concentrated on single aspects of their life history (especially seed predation), and have not been analysed in relation to population growth. Few field experiments, especially concerning seedling biology, have been performed. We conclude with some suggestions of a framework for interpreting acacia demography.

The poor availability of suitable substrate and nutrients strongly limits the distribution and growth of vascular epiphytes in lowland rain forests (Benzing 1990, Nieder et al. 2000). In some epiphyte species nutrition may be assisted by adventitious roots that grow into animal debris in plant cavities such as domatia and bromeliad tanks (Huxley 1980). For epiphyte species lacking these modifications, animals may nevertheless play a substantial role by providing a large proportion of the limited substrate in lowland forests (Catling 1995, Longino 1986). Such associations between epiphytes and nutrient/substrate-providing animals may often be non-specific and commensalistic (Davidson & Epstein 1989, Longino 1986), while highly evolved mutualistic associations occur in the case of ant gardens which are very abundant in neotropical forests (Huxley 1980, Kleinfeldt 1986, Ule 1901). Ant gardens typically are densely inhabited by different epiphytes from various plant families whose seeds or fruits are attractive to the ants and carried into the nest (Davidson 1988). In addition, ants have been suggested to play a role in protection and nutrition of ant-garden epiphytes (Kleinfeldt 1978, 1986). Ants may benefit from epiphytes through increased nest stability (Yu 1994) or nutrition via extrafloral nectaries, fruit pulps or seed arils (Davidson 1988, Kleinfeldt 1986). In this study,we compare the nutrient quality of such ant gardens with other similar substrates rarely inhabited by epiphytes, namely nests and galleries of ants and termites.

Isolated canopy gaps involving one to several trees occur continuously and frequently in many moist and wet neotropical forests (sensu Holdridge et al.1971), shaping tree community structure through a shifting mosaic of patches of high resource availability for small and young trees (Denslow 1980). Though there are few relevant data (Jans et al. 1993), forests with significant seasonal drought are expected to have lower rates of canopy-gap formation (gaps ha-1 γ-1), smaller gap sizes, and, thus, lower rates of canopy disturbance (%γ-1, see review in Whigham et al. 1999). At the extreme, very dry tropical forests do not appear to fit the gap-phase dynamics concept (Swaine et al. 1990).

Further studies on growth and reproduction of many tree species are needed to know the regeneration patterns of tropical forests (Clark & Clark 1987, Heideman 1989). Thus, the need for studies on the c. 3% of Atlantic forest that remains in Brazil is acute, particularly in the rarely studied swamp habitats (Scarano et al. 1997). We studied the canopy tree species Calophyllum brasiliense Camb. (Clusiaceae) in flooded and unflooded habitats of a coastal lowland rain forest, in order to describe demography, sexual expression, phenology and flower and fruit production. We report the differences of such traits among three contiguous habitats found in the lowlands - unflooded forest, freshwater-flooded forest and mangrove.

Seed dispersal is the predominant mobile stage for sessile plants, and critically affects the distribution patterns of the species (Nathan & Muller-Landau 2000). Thus, seed dispersal patterns are important in understanding the population dynamics of the species.