Geophytoelectrical current in trees of a subtropical rainforest in Mexico

The geophytoelectrical current of three evergreen tropical tree species is studied as an indirect measure of their relative water content. Two intermediate shade-tolerant species (Aphananthe monoica and Pleuranthodendron lindenii), distributed in the middle and upper canopy strata, and an understory shade-tolerant species (Psychotria costivenia) were examined. The annual rhythm of geophytoelectrical currents per cm of diameter (DBH) is seasonal, with the highest occurrence in the winter and summer. There is a significant association between maximum temperature, moisture in the environment, and geophytoelectrical current per cm of DBH in the three species, as shown by multiple regression analysis. This finding suggests the existence of various geophytoelectrical current patterns which differs from that reported for temperate species.     

Importance of topography and soil texture in the spatial distribution of two sympatric dipterocarp trees in a Bornean rainforest

Relationships between spatial distributions and site conditions, namely topography and soil texture, were analyzed for two congeneric emergent trees, Dryobalanops aromatica and Dryobalanops lanceolata (Dipterocarpaceae), in a tropical rainforest in Sarawak, East Malaysia. A 52-ha permanent plot was divided into 1300 quadrats measuring 20m×20m; for each Dryobalanops species, the number and total basal area of trees 1cm in d.b.h. were compared among groups of quadrats with different site conditions. Because spatial distributions of both Dryobalanops and site-condition variables were aggregated, Monte-Carlo permutation tests were applied to analyze the relationships. Both single and multifactor statistical tests showed that the density and basal area distributions of the two species were significantly non-random in relation to soil texture and topographic variables. D.aromatica was significantly more abundant at higher elevations, in sandy soils, and on convex and steep slopes. In contrast, D.lanceolata preferred lower elevations and less sandy soils. In the study plot, there were very few sites (3 of 1150 quadrats tested) where the models of Hayashis method predicted the co-occurrence of the two species. These results suggest that between-species differences in habitat preferences are so large that they alone explain the spatially segregated distributions of these two species within the 52-ha study plot.     

Intra‐specific relatedness,spatial clustering and reduced demographic performance in tropical rainforest trees

Intra‐specific negative density dependence promotes species coexistence by regulating population sizes. Patterns consistent with such density dependence are frequently reported in diverse tropical tree communities. Empirical evidence demonstrating whether intra‐specific variation is related to these patterns, however, is lacking. The present study addresses this important knowledge gap by genotyping all individuals of a tropical tree in a long‐term forest dynamics plot in tropical China. We show that related individuals are often spatially clustered, but having closely related neighbours reduces the growth performance of focal trees. We infer from the evidence that dispersal limitation and negative density dependence are operating simultaneously to impact the spatial distributions of genotypes in a natural population. Furthermore, dispersal limitation decreases local intra‐specific genetic diversity and increases negative density dependence thereby promoting niche differences and species coexistence as predicted by theory.     

Stem growth rhythms in trees of a tropical rainforest in Southern Brazil

Key message

We demonstrate that tropical trees growing in wet climates can have a marked seasonality in cambium activity and stem growth associated with high temperature and day length of summer.

Abstract

Monitoring the rhythm of tree growth associated with the growth rings can contribute substantially to understanding forest dynamics and the management of tropical forests. In this study, we monitored the girth increment rhythm and described the wood characteristics (anatomy of growth rings, wood specific gravity) in 10 tropical tree species (103 individuals) naturally occurring in a wet and weakly seasonal region of Atlantic Forest in southern Brazil. We aimed to verify whether tree growth dynamics are associated with climate and woody anatomy in tropical trees with contrasting ecological characteristics. We installed permanent dendrometer bands and monthly assessed the girth increment for 22 months. We collected wood samples (non-destructive method), measured wood specific gravity and prepared permanent slides to characterize the growth ring markers. We found growth rings in all species (distinct in six species); deciduous species produced more distinguishable tree rings compared with semi-deciduous and evergreen tree species. Species varied in their accumulated girth growth (in average, from 1.83 to 62.64 mm), growth rates (1–15 %), and annual radial increment (0.16–5.44 mm). Girth increment was positively related to temperature and day length in five out of ten tree species, indicating the possible effects of these climatic variables in triggering cambial activity in these species. The growth pattern varied among species and was marginally associated to the tree deciduousness. We concluded that even in wet and less seasonal climates, there can be an association in the cambium activity and stem growth with the hotter and longer days of summer months.

     

Thirteen years of change in trees and lianas in a Gabonese rainforest

Inventories of trees and lianas were performed at a 13-year interval (1979–1992) in an evergreen forest in north-east Gabon. The number of trees decreased while their basal area and species richness increased. In contrast, both the richness and density of lianas decreased. Lianas with active climbing mechanisms were the main types to disappear.     

Utilization of fruiting trees by monkeys as analyzed from feeding traces under fruiting trees in the tropical rain forest of Cameroon

Individual trees of the food species of monkeys were identified by placing plastic tapes with an identification number on them in the tropical rain forest of Cameroon, West Africa. In order to determine the use of the feeding trees by monkeys, the ground under each of the trees was checked at least once a week to see if there were any fallen fruits or traces of feeding on fruits. Some fruit species were not fed on by either monkeys or large arboreal squirrels. Among the food species common to both the monkeys and large squirrels, a larger proportion in terms of quantity in each species was mainly eaten by the monkeys except in the case of super-abundantly fruit producing species. The monkeys and large arboreal squirrels were well segregated in their diets. Larger proportions (more than 85% for most of the monkeys' major foods) of fruits of larger sizes were made to fall on the ground by the monkeys and squirrels. The monkeys displayed a tendency to visit fruiting trees rather evenly (even rate of visit = even frequency of visit/duration of fruiting) not ignoring any area of the home range, although a small difference in this tendency was observed between the two study periods, one an abundant season and the other a poor fruiting season. On average, one associated polyspecific group of monkeys encountered only 14 fruiting trees per day. On the other hand, fruits were available all around the year, as the fruiting periods of different tree species were widely distributed around the year, or the fruiting periods of some species were very long. Although the monkeys are able to depend heavily on fruits, the quantity of fruits is not so great. The population size of monkeys is well balanced with the available food supply in the tropical rain forest of West Africa.     

Blind population genetics survey of tropical rainforest trees

Rainforest tree species can be difficult to identify outside of their period of reproduction. Vascular tissues from Carapa spp. individuals were collected during a short field trip in French Guiana and analysed in the laboratory with nuclear and chloroplast markers. Using a Bayesian approach, > 90% of the samples could be assigned to one of two distinct clusters corresponding to previously described species, making it possible to estimate the genetic structure of each species and to identify cases of introgression. We argue that this blind procedure represents a first-choice rather than a fallback option whenever related taxa are investigated.     

Spatial dispersion patterns of trees in a tropical rainforest in Xishuangbanna,southwest China

Ecological Research - Spatial dispersion patterns of trees at different life stages are an important aspect to investigate in understanding the mechanisms that facilitate species co-existence. In...     

Do wild dogs exclude foxes? Evidence for competition from dietary and spatial overlaps

Abstract The management of wild canids (wild dogs/dingoes and foxes) presents a conservation dilemma for land managers across Australia. These canids are predators of wildlife and domestic stock but dingoes are considered native and anecdotal reports suggest that they may suppress foxes such that dingo/dog conservation may have a net benefit to wildlife. This study examines dietary and spatial interactions between wild dogs and foxes in the Greater Blue Mountains region of NSW to address the possibility of suppression through competitive exclusion by dogs on foxes. Predator diets were compared using faecal analysis as well as an analysis of 19 dietary studies from similar forest habitats in eastern Australia. Spatial relationships were examined using data from an extensive canid control programme. Diets of wild dogs and foxes showed a high degree of overlap in species taken, indicating potential for competition. But there was also evidence of resource partitioning with the size and arboreality of mammalian prey differing between the two predators. Wild dogs and foxes responded to different landscape‐scale variation in the physical environment, but there was no clear evidence of large‐scale differences in their distribution. At the fine scale there was a negative association between these predators that indicated possible temporal avoidance or localized habitat shifts. Therefore, there is evidence for dietary competition and fine‐scale exclusion, but no support for landscape‐scale exclusion of foxes by wild dogs in the Blue Mountains.     

Evidence for widespread pollen limitation of fruiting success in Cape wildflowers

We used spot checks of stigmatic pollen deposition and hand-pollination experiments to test whether fruit production in Cape wildflower populations is limited by pollen availability. Natural levels of stigmatic pollen deposition were very low (median = 30.0% of flowers) in populations of 33 orchid species. We found similarly low levels of fruit set (median = 32% of flowers per plant) in six Orchidaceae and four Amaryllidaceae species. Experimental hand pollination at the whole plant level caused significant increases in fruit production in 11 of the 12 study populations. These results indicate that pollen limitation of fruit set may occur frequently among some plant families in the Cape flora. Received: 15 April 1996 / Accepted: 10 November 1996