The effect of natural canopy gaps on the performance of naturally occurring tree seedling populations was studied in a tropical rain forest in French Guiana. This was done at two levels of scale. Firstly, on a 20 m × 250 m forest transect intersecting four canopy gaps, it was investigated how patterns of recruitment, growth and survival of seedlings of Cecropia obtusa, Dicorynia guianensis and Pourouma bicolor differed between canopy gaps and closed forest. Secondly, for one large natural canopy gap, performance of seedling cohorts established before (‘pre-gap’ cohorts) and after (‘post-gap’ cohorts) gap formation was studied in relation to environmental heterogeneity. The direct site factor (DSF) was used as an indicator of light availability in the gap zone. Cecropia specialised in large gaps, and also in specific sites within the large gap: seedling performance was increased by light, and by dead wood. Pourouma mainly germinated under closed forest conditions, where it can survive for a long period until a canopy gap is formed nearby. Pourouma seedlings adjusted well to the new gap environment but they did not specialise in specific places within the gap. Seedling location of Pourouma seedlings was mainly determined by accidental positioning before gap formation. Dicorynia was able to germinate both in gaps and under closed forest conditions. Although the number of gaps studied in this study was low, the results show that seedling establishment, early growth and survival of the three tree species were affected by canopy gaps and by the environmental heterogeneity within a large gap.

This study examined whether postdispersal fruit and seed removal by terrestrial mammals of common plant species was affected by the type of item, item density (low, medium, high), and habitat (gap, mid-succession, mature). Fruits of Brosimum alicastrum and Ficus yoponensi (Moraceae), Astrocaryum mexicanum (Palmae), and Nectandra ambigens (Lauraceae), and seeds of Omphalea oleifera (Euphorbiaceae) and Cymbopetalum baillonii (Annonaceae) were tested at the Los Tuxtlas rainforest in Mexico. Item removal from 108 experimental patches (N = 2340 fruits or seeds for each plant species tested) after 5 d was lower for F. yoponensis (6.6%) than for N. ambigens (68.8%), B. alicastrum (67.8%), C. baillonii (64.0%) and A. mexicanum (60.0%). No seeds of O. oleifera were removed. A higher fruit or seed removal was observed from high density than low density food patches in A. mexicanum, C. baillonii and N. ambigens, but not in B. alicastrum and F. yoponensis. A higher fruit or seed removal was observed from food patches in mature forest than in gaps in all plant species tested. Similar removal values between open (open to all terrestrial mammals) and caged (open to small rodents) fruit and seed patches, abundant rodent live-trapping, and a scarcity of large terrestrial mammals, indicated that forest-dwelling small rodents were the main postdispersal removal agents. Differences in plant species seedling recruitment resulting from small rodent food choices can partially determine long-term forest floristic composition at the Los Tuxtlas rainforest.

Petioles are not usually thought of as a habitat for wood-boring insects. The large, woody leaf petioles of Neotropical Cecropia trees, however, have a diverse coleopterous fauna: 36 beetle species in three subfamilies of Cerambycidae and Curculionidae were recorded from Cecropia leafstalks in Costa Rica. A high percentage of the petioles were colonized by beetles in many patches, though fewer were colonized in sun-exposed sites. Community composition was dependent on forest type, petiole moisture and geographical location, but not on the species of Cecropia. Species of Scolytinae were most abundant though species of Zygopinae and Lamiinae were found regularly. The host-specific scolytine genus Scolytodes dominated in most localities, although species of Hypothenemus, Coccotrypes and Xylosandrus morigerus occurred frequently. Sympatric species of Scolytodes clearly used different parts of the petioles. Brood sizes of scolytine beetles were extremely low, ranging from two to ten offspring on average. However, mortality due to parasitoid wasps or predators was low, and since fresh leaves fall close to the previously fallen ones, mortality due to dispersal may also be low. Thus, large beetle populations can exist despite extremely low brood sizes.

The intra-crop variation in the concentrations of major nutrients in the embryo-cum-endosperm (EE) fraction of seeds of 12 tree species of SE Asian lowland rain forest was investigated. Increased seed size was associated with a significant decrease in the EE concentration of N in 10 species, P and K in seven, Mg in six, and Ca in four. In contrast, the EE nutrient content increased with seed size, typically by about 1.6-fold where seed mass was 2-fold greater. In three species the allocation to protective tissues decreased with increased seed size. The results are potentially relevant to competition among young seedlings, optimal foraging by predators, allocation to defence by plants, and understanding the controls on filling of seeds.

The effect of the change in vegetation structure from closed rain forest to tall open forest on the small mammal assemblage was studied by live trapping at three sites where the ecotone was very narrow (> 20 m) near the southern end of the Wet Tropics World Heritage Area of Australia. Habitat heterogeneity was significantly higher in the mixed open forest/ecotone area than in the adjacent rain forest. There was a large change in the struture of the small mammal assemblage coincident with the vegetation discontinuity. Although the species richness of small mammals was relatively constant across the gradient, the evenness and diversity of the assemblage declined across the transition from open forest into rain forest and biomass increased, largely due to the high abundance of Rattus fuscipes in the rain forest. The results suggest that the species richness of the small mammal assemblage was not determined by the spatial heterogeneity of the vegetation struture. The species composition of the rain forest is probably related to the historical biogeography of the area whereas the species richness of the wet sclerophyll forest is probably due to a mass-area effect from the adjcant large areas of rain forest and dry sclerophyll forest. However, the evenness, and therefore the diversity of the assemblage, was strongly affected by habitat heterogeneity.

Dispersal of seeds away from the parent plant may facilitate escape from density-dependent seed mortality. However, many post-dispersal events can have a profound influence on the survival of dispersed seeds. By incorporating seeds in the dung that dung beetles process for consumption and oviposition, dung beetles could enhance seed survival if they remove seeds from areas of high predation risk and place them in locations that avoid subsequent predation and that are suitable for germination. The role of dung beetles in seed survival was investigated over 15 mo in Kibale National Park, Uganda. Depths of seeds buried by beetles, levels of predation on buried and unburied seeds, and germination success of seeds buried to different depths were examined. Results suggest that by burying seeds dung beetles increase the probability that seeds will escape predation and germinate. Of seeds placed in dungpiles, 69% remained at the surface, while 25% were buried from 1–3 cm in depth. Larger seeds were buried more shallowly than smaller seeds. Buried seeds were less likely to be removed by predators than seeds at the surface. Germination of seeds buried at 1- and 3-cm depths was significantly higher than seeds buried at 10 cm. For the species tested, many seeds were buried by dung beetles between 1 and 3 cm and at this depth there was a high probability of escaping predators and germinating. This demonstrates the potential ecological importance of dung beetles in facilitating seed survival and provides data to consider the role of dung beetles in the evolution of seed attributes.

The nutrient contents and accessions in litterfall over a period of 3 y are reported for undisturbed areas and at two sites disturbed by selective harvesting in tropical rain forest in North Queensland, Australia. Mean concentrations (mg g&supminus1; dry weight) of nutrients in litterfall ranged from 10 to 12 for nitrogen; 0.33 to 0.43 for phosphorus; 3.6 to 4.3 for potassium; 6.0 to 10.5 for calcium; and 1.7 to 2.6 for magnesium. These concentrations are in the middle to lower part of the spectrum of values recorded for tropical forests. Accessions of nutrients in litterfall (kg ha&supminus1; y&supminus1;) ranged from 59 to 64 N; 1.9 to 2.4 P; 20 to 24 K; 34 to 63 Ca; and 9 to 16 Mg. These rates, particularly for N and P, are among the lowest recorded for tropical forests. There were no consistent between-site differences in total nutrient accessions in small litterfall. In terms of the contribution of litterfall to the accessions of nutrients to the forest floor, this suggests that the logged sites have recovered from the effects of selective harvesting within 25 y. Nutrient accessions at each site were distinctly seasonal, with maximum accessions occurring in the late dry season to late in the wet season. Leaf-fall accounted for the largest proportion of nutrient accessions over the study period, although at certain times accessions in both reproductive material and wood were significant. A cyclone which crossed the coast near the study sites resulted in large nutrient accessions over a short period but had little effect on the total annual accession. A comparison with previous studies of litterfall in Australian tropical rainforests indicates that nutrient return in litterfall is directly related to soil fertility.

Performance of seedlings of seven rain forest, canopy dominant Shorea species was studied in a transplant experiment in forest sites at three different elevations (low, mid and high) within the humid zone of southwest Sri Lanka. Five species generally inhabit low- to mid-elevations, one at mid- and lower montane elevations, and one exclusively at lower montane elevations. Temperature, rainfall and cloudiness varied with elevation. For each site seedlings were grown in pots under partial shade conditions using similar soils and evermoist conditions. All growth measures showed differences among elevation sites, among species and in the interaction between species and elevation sites. Performances of species collectively showed (i) decline in height and leaf number with increase in elevation, (ii) higher dry mass at low- and mid-elevation sites compared to that at high-elevation and (iii) a higher mass of single leaves at the mid-elevation site than at the high-elevation site. Rank order of species changed across elevations for both height and dry mass. Dry mass declined with elevation in four of the seven species studied. S. gardneri, the only exclusively lower montane species, increased dry mass with elevation. Height declined with elevation for six of the species with only S. gardneri showing no change. Changes with elevation in the rank order of species for total leaf number and mass of single leaves were small. However, total leaf number and masses of single leaves differed among species and among elevations. S. megistophylla and S. disticha had a few leaves with high individual masses, while S. gardneri, S. affinis and S. trapezifolia had many leaves with less mass per individual leaf. One group of species showed relatively little change in leaf number per seedling and large changes in mass of single leaves. The other group varied more in leaf number but mass of individual leaves remained constant. Growth allocation to leaf production versus individual leaf size appears related to the successional division of Shorea section Doona. Also all species grew better at the low-elevation site irrespective of their natural ranges except S. gardneri, whose natural range is restricted to high elevations, and exhibits markedly lower growth responsiveness than the other wide ranging species.

For sustainable logging to be achieved in tropical forests, there must be successful gap-phase regeneration to restock the logged-over area. This study examined three aspects of gap-phase regeneration in selectively logged lowland swamp forest of northeast Costa Rica. First, logging gaps were censused immediately after extraction to determine the density of advanced regeneration. Stem density and basal area of residual trees ≥ 10 cm dbh in logging gaps was >85% lower than undisturbed forest, and all trees in gaps had sustained structural damage. The common canopy species Pentaclethra macroloba (Fabaceae) was the most abundant species in gaps whereas the timber tree Carapa nicaraguensis (Meliaceae) was absent from all censused gaps. This suggests that canopy replacement, particularly by Carapa, will depend on trees <10 cm dbh or by seed input into logging gaps. Second, the diversity of the understorey was compared with 6-y old single-tree and multiple-tree logging gaps. Multiple-tree logging gaps were the most diverse, but dominated by two ruderal species; however many shade-tolerant species were present in those gaps. This indicates that controlled selective logging can result in a localized shift in species composition, but that logging gaps should return to pre-logging composition with time under a carefully implemented, controlled harvesting regime. Finally, this study found a significant effect of a fringing Carapa tree on logging gap seedling density. Thus, seed arrival into gaps is a barrier to logging gap regeneration, particularly for a large-seeded tree species. Gap-phase regeneration by a large-seeded tree species in managed forest would benefit from seed broadcasting into gaps.