Showing papers in "Journal of Tropical Ecology in 2000"
TL;DR: Results have shown that their important contribution to total basal area and biomass can continue as the forest matures, even as the numbers of established lianas declines.
Abstract: The abundance and diversity of lianas were examined along a tropical forest chronosequence at the Barro Colorado Nature Monument, Panama. Lianas M 0.5 cm diameter were sampled along transects in two replicated stands in second- ary (20, 40, 70 and 100 y after abandonment) and old-growth (>500 y) forests. Ordination of stands based on relative abundance, but not presence-absence, showed a significant separation of stands by age. Lianas were significantly more abundant and diverse (Fisher's α) in younger forests (20 and 40 y) than in older forests (70 and 100 y, and old-growth). The decline in liana abundance with stand age was offset by increased mean basal area per individual, resulting in a relatively constant total basal area and estimated biomass across stand age. The proportions of tendril climbers decreased and stem twiners increased over stand age. Decline in liana abundance and changes in liana composition may be related to changes in support and light availability. Although lianas are recognized as playing an important role in the early secondary succession of many tropical forests, these results have shown that their important contribution to total basal area and biomass can continue as the forest matures, even as the number of established lianas declines.
360 citations
TL;DR: A large number of newly published and unpublished hectare plots in Amazonia and the Guiana Shield area allow an analysis of family composition and testing of hypotheses concerning alpha-diversity in the south American rain forest as mentioned in this paper.
Abstract: A large number of newly published and unpublished hectare plots in Amazonia and the Guiana Shield area allow an analysis of family composition and testing of hypotheses concerning alpha-diversity in the south American rain forest. Using data from 94 plots the family-level floristic patterns in wet tropical South America are described. To test diversity patterns, 268 plots are used in this large area. Contrary to a widely held belief, western Amazonian plots are not necessarily the most diverse. Several central Amazonian plots have equal or even higher tree diversity. Annual rainfall is not a good estimator for tree diversity in the Amazonia area and Guiana shield. Plots in the Guiana Shield area (and eastern Amazonia) usually have lower diversity than those in central or western Amazonia. It is argued that this is not because of low rainfall or low nutrient status of the soil but because of the small area of the relatively isolated rain forest area in eastern Amazonia and the Guiana Shield. The low diversity on nutrient-poor white sand soils in the
343 citations
TL;DR: Both the species composition and structure are totally affected by such an episodic drought even in a per-humid tropical forest, indicating a change in the size-class structure of the forest.
Abstract: The impact of the unusually severe drought associated with the 1997-1998 El Nino on tropical forest dynamics in Sarawak, Malaysia was examined. Mortality during the non-drought period (1993-1997) in a core plot (1.38 ha) was 0.89 % y -1 , while that during the drought period (1997-1998) in the same plot and a peripheral plot was 6.37 and 4.35 % y -1 , respectively. The basal area lost in the drought interval was 3.4 times that of the annual incremental basal area in 1993-1997. Drought mortality was higher for the smaller trees, though it was less size dependent than the non-drought mortality. Dipterocarpaceae, which is the dominant family in the study plot, had a mortality 12-30 times higher in the drought than the non-drought period. There were no significant differences in mortality among the topographic types. From the results of a log-linear model (multi-factored contingency table), the death of trees was correlated with size class, indicating a change in the size-class structure of the forest. Thus, both the species composition and structure are totally affected by such an episodic drought even in a per-humid tropical forest.
246 citations
TL;DR: An allometric regression biomass equation was developed to estimate the aboveground biomass of live lianas and trees to the total biomass of forest patches in four stature classes: gap, gap phase, low stature, medium stature, and high stature.
Abstract: This study provides an estimate of aboveground live biomass for an intact eastern Amazonian forest. An allometric regression biomass equation was developed to estimate the aboveground biomass of live lianas. This equation, together with a previously published equation for trees, was then used to estimate the contributions of lianas and trees to the total biomass of forest patches in four stature classes: gap (openings in the canopy of at least 25 m2 with the dominant vegetation 25 m canopy height). Total stand-level biomass was estimated as the weighted average of the stature classes. In 130 ha of surveyed forest, forest stature classes were found in the following proportions: gap phase 8%; low stature 31%; medium stature 44%; and high stature 17%. Total aboveground biomass was found to be three times higher in high stature forest than in low. Liana biomass, however, showed the opposite result, being three times higher in low stature forest. Stand-level aboveground live biomass was estimated at 314 t ha−1 of which 43 t ha−1 (14%) was lianas. Liana leaf area index (LAI) ranged from 1.3 m m−2 in high stature forest to 5.3 m m−2 in low stature. Abundant lianas are generally interpreted as a sign of past forest disturbance. As forests throughout the Amazon basin are increasingly disturbed through human activities, it is likely that their biomass will be underestimated if the contribution of lianas is ignored.
199 citations
TL;DR: The importance 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 net basal area losses recorded over the 53-y observation period.
Abstract: Species composition and turnover that have occurred in a series of permanent sample plots established during the 1930s and 1940s in Budongo, a semi-deciduous Ugandan forest, are reported. The plots were established as part of a sequence first used to describe forest succession, five of which have been 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 established in wooded grassland at the forest edge and is now closed high forest. Evaluation of the remaining three plots is complicated by silvicultural interventions 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 forest tree flora, and including two exotics) has now been recorded from within the plots. The pattern of shade- tolerance in the original plot series conforms to patterns expected for succession with an increasing proportion of shade-tolerant species with development, and large stems appearing to 'lag behind' smaller stems in this respect. The time series data are less consistent, and while plot 7 increased in the proportion of shade-tolerant stems through time, the proportion of shade-tolerant species actu- ally declines. Stem-turnover (the mean of mortality and recruitment) slowed with implied successional stage. Most species have a higher recruitment than mortality rate and stem numbers have thus increased in all plots. This is most pronounced in the putatively 'early successional' plot. Stem size structure has changed within the plots, with an increased proportion of smaller stems. Species show different rates of turnover and these vary from plot to plot and period to period. In plot 7, the overall mortality rate decreased with initial 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 importance 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 net basal area losses recorded over the 53-y observation
184 citations
TL;DR: The concept of keystone plant resources is reviewed using potential candidates proposed in the literature for neotropical forest sites and those producing reliable, low-redundancy resources that are consumed by a large proportion of the bird and mammal assemblage with which they coexist are defined.
Abstract: Keystone plants that produce seasonally critical trophic resources comprise one of the main classes of keystone species, yet no studies have attempted to examine the ecological attributes that might help us recognize them and evaluate their importance in species-rich plant assemblages. In this paper the concept of keystone plant resources is reviewed using potential candidates pro- posed in the literature for neotropical forest sites. A poorly known example of a potential keystone resource—the gums produced by mature pods of two emergent tree species (Parkia nitida and P. pendula, Leguminosae: Mimosoideae)—is described for primates and other arboreal vertebrates in Amazonian forests. In particular, the fruiting phenology, tree density, patterns of vertebrate consump- tion, and nutritional quality of Parkia gums in Amazonian terra firme forests are considered. Putative neotropical keystone resources are then divided into four intersecting ecological attributes defining their community-wide importance to vertebrate frugivores: (1) temporal redundancy, (2) degree of consumer specificity, (3) reliability, and (4) abundance. From a vertebrate perspective, keystone plants are here defined as those producing reliable, low-redundancy resources that are consumed by a large proportion of the bird and mammal assemblage with which they coexist. Plant populations proposed to date as keystone species range widely across two of these four variables, which may disqualify most putative taxa (including Parkia spp.) from a more formal definition of keystone resources. Other importance attributes, the context-dependent role, the taxonomic refinement, and removal effects of the keystone plant resource concept as applied to tropical forests are also discussed.
182 citations
TL;DR: Bird species richness attending flocks was significantly correlated with the availability of understorey arthropods, but not with that of either understoreY and canopy fruits, which appears to affect profoundly the reproductive schedules of the understoreys avifauna, which in turn influences the seasonal variation of flock size and composition.
Abstract: Multi-species bird flocks in tropical forests are maintained throughout the annual cycle despite seasonal differences in resource availability, and the reproductive schedules and ecological requirements of individual species. This study examines the relationship between seasonal variation in flock structure and the availability of fruits and arthropods over a 12-mo period at a coastal Atlantic forest within the Jureia-Itatins Ecological Station, Sao Paulo, Brazil. Fruit abundance was estimated by a phenological survey of both canopy and understorey trees, whereas arthropod abundance was quantified monthly on the basis of a nocturnal visual census technique. The seasonal variation in flock structure and composition was affected by both the breeding seasons of different core and attendant species, and the availability of food resources. The number of bird species attending flocks was greater during the dry season, declining thereafter during the breeding season. Understorey fruit availability exhibited a marked seasonal fluctuation with the lowest levels between the late dry and early wet season. Seasonal variation in canopy fruit availability, on the other hand, was far less demarcated than that of understorey plants. Arthropod abundance was greatest during the wettest months of the year, which apparently determined the timing of the main breeding season. Bird species richness attending flocks was, therefore, significantly correlated with the availability of understorey arthropods, but not with that of either understorey and canopy fruits. Arthropod abundance thus appears to affect profoundly the reproductive schedules of the understorey avifauna, which in turn influences the seasonal variation of flock size and composition.
154 citations
TL;DR: Long-term data on flower and fruit production of the forest community in two lowland tropical rain forests in north-western Sumatra suggest that additional factors to ENSO play a role in determining forest-level mast fruiting, and it is hypothesized that frugivorous animals have the opportunity to trackmast fruiting.
Abstract: Long-term data on flower and fruit production of the forest commun- ity in two lowland tropical rain forests in north-western Sumatra are presented. The proportion of years with mast fruiting was found to be similar to that found elsewhere in Malesia. However, masting at the two sites, 70 km apart, did not coincide, and showed no correlation with the El Nifio-Southern Oscillation phe- nomenon (ENSO). Comparisons with other sites in Malesia suggest a general waning of ENSO's impact toward western Malesia. Spatial variation at various scales in the timing of masting events was noted in Sumatra and elsewhere. This suggests that additional factors to ENSO play a role in determining forest-level mast fruiting, and we hypothesize that frugivorous animals have the opportunity to track mast fruiting. It is hypothesized that asynchrony between nearby areas in masting increases toward the western edge of Malesia.
154 citations
TL;DR: As the last of the Pleistocene megafauna of the region, tapirs may have particular importance as dispersers of large seeds and generators of unique seed dispersion patterns.
Abstract: Tapirs (Tapiridae) are the last representatives of the Pleistocene megafauna of South and Central America. How they affect the ecology of plants was examined by studying the diversity, abundance, and condition of seeds defec- atedd by the lowland tapir (Tapirus terrestris) in Amazonian Brazil. Additionally, the spatio-temporal pattern of the seed-rain and seed-shadows generated by tapirs was recorded. Three hundred and fifty-six tapir faeces were examined. Eleven per cent were found in water (n = 41), while 88% were located on dry land (n = 315). Of those found on dry land, 84% were located at sites that flood seasonally, while 14% of the total were encountered at forest sites that do not flood. In 127 faeces checked in the laboratory over 12 906 seeds of at least 39 species were found. Seed viability ranged from 65% for Maximiliana maripa to 98% for Enterolobium schomburgkii. Of nine seed species planted in the laboratory, seven germinated within 4 wk, with one species achieving an 89% germination rate. For many species recruitment to the seedling stage was also high under natural conditions, with 13 plant species occurring as seedlings in older faeces. Tapir generated seed-rain occurred throughout the year, with seeds defecated in all months. Two temporal patterns in species seed rain occurred: (1) contiguous monthly occurrence with peaks in abundance, and (2) discontinuous occurrence (time clumped) with small (a few months) to large (many months to more than a year) temporal gaps. The highest diversity of seeds appeared in April, at the end of the dry season. As the last of the Pleistocene megafauna of the region, tapirs may have particular import- ance as dispersers of large seeds and generators of unique seed dispersion patterns.
151 citations
TL;DR: The unimodal pattern of species richness was not correlated with nutrient concentrations, and relationships among faunal abundance, species richness, nutrient inputs and environment are too complex to warrant simple generalizations about nutrient resources and diversity, even in apparently simple microhabitats.
Abstract: Nutrient inputs into tank bromeliads were studied in relation to growth and productivity, and the abundance, diversity and biomass of their animal inhabitants, in three forest types along an elevational gradient. Concentrations of phosphorus, potassium and calcium in canopy-derived debris, and nitrogen and phosphorus in phytotelm water, declined with increasing elevation. Dwarf forest bromeliads contained the smallest amounts of debris/plant and lowest concentrations of nutrients in plant tissue. Their leaf turnover rate and productivity were highest and, because of high plant density, they comprised 12.8% of forest net primary productivity (0.47 t ha−1 y−1), and contained 3.3 t ha−1 of water. Annual nutrient budgets indicated that these microcosms were nutrient-abundant and accumulated < 5% of most nutrients passing through them. Exceptions were K and P in the dwarf forest, where accumulation was c. 25% of inputs. Animal and bromeliad biomass/plant peaked in the intermediate elevation forest, and were positively correlated with the debris content/bromeliad across all forest types. Animal species richness showed a significant mid-elevational peak, whereas abundance was independent of species richness and debris quantities, and declined with elevation as forest net primary productivity declined. The unimodal pattern of species richness was not correlated with nutrient concentrations, and relationships among faunal abundance, species richness, nutrient inputs and environment are too complex to warrant simple generalizations about nutrient resources and diversity, even in apparently simple microhabitats.
127 citations
TL;DR: The results show that the initial growth of the woody species which take part in the initial phases of succession may be more dependent on the AM fungi, in soils poor in minerals, while those that make up the final succession phases may be less dependent.
Abstract: Seedlings from 43 native woody species belonging to different successional groups from the Tibagi River Basin, Parana State, South Brazil were studied to obtain information on the importance of colonization by native arbuscular mycorrhizal (AM) fungi. The experiment was carried out in a greenhouse for 15 to 45 wk, with soil-mix treatments and four successional groups. The mycorrhizal dependency was 90, 48, 12 and 14% of the pioneer, early secondary, late secondary and climax species, respectively. The content of P, Ca and K was 20, 17 and 23 times greater, respectively, in the leaves of the pioneer species than in the other successional groups. The colonization by AM fungi in field was studied in seedlings of 36 native woody species collected in the interior of the forest of the Mata dos Godoy State Park, and in open area at the beginning of arboreal succession. The mycorrhizal colonization in the field was 55.5, 26.9, 6.1 and 2.2% for the pioneer, early secondary, late secondary and climax species, respectively. To assess the mycorrhizal inoculum potential, rhizosphere soil was collected in the interior of the forest and a gap in the same forest and in a cleared area abandoned for natural regeneration. The inoculum potentials and the spore number in the area at the beginning of succession were 5.6 and 53.4 times greater than in the interior of the forest. The results show that the initial growth of the woody species which take part in the initial phases of succession may be more dependent on the AM fungi, in soils poor in minerals, while those that make up the final succession phases may be less dependent. The potential of the AM fungi inoculum decreases throughout the successional process and there is a relation between the inoculum potential found in the field and the occurrence for the different habitats of the species of adult plants belonging to different successional groups.
TL;DR: A high growth during the wet season provided gap plants with a decisive size advantage over understorey plants during the dry season, which led to a shorter deciduous period for Cedrela plants, although it did not lead to a higher plant growth.
Abstract: In tropical moist forests, length of the dry period may have a pro- found influence on leaf dynamics, plant growth and survival. To evaluate the role of light and water availability on seedling performance, a 1-y experiment was car- ried out in a tropical moist forest in the Bolivian Amazon in which seedlings of three tree species (Brosimum lactescens, Cedrela odorata and Schizolobium amazonicum) were planted in gaps and the understorey. Variation in length of the dry period was simulated by subjecting part of the seedlings to a water treatment at the end of the dry period. Gaps and understorey had a similar soil moisture content, which varied between 39% in the wet season and 16% in the dry season. Height and leaf growth rates were higher in gap compared to understorey plants, and in the wet compared to the dry season. A high growth during the wet season provided gap plants with a decisive size advantage over understorey plants during the dry season. Their larger root system allowed gap plants to explore a larger surface area and deeper soil layers for water. Consequently, gap plants of Cedrela experi- enced a shorter deciduous period (22 d) compared to understorey plants (61 d). Watering at the end of the dry season cued the flushing of new leaves by Cedrela, although it did not lead to a higher plant growth.
TL;DR: Structural measurements were made in a series of secondary forest stands, from 4–30 y old, in Brazil and Bolivia, and biomass accumulation was significantly slower, around 5.0 Mg ha−1 y−1, for reg growth following continuous pasture than for regrowth following 1 y of cultivation.
Abstract: A study was conducted on the effect of extended land-use on secondary forest biomass accumulation in the Amazon. Structural measurements were made in a series of secondary forest stands, from 4-30 y old, in Brazil and Bolivia. Half of the stands were forest regrowth following clearance and only 1 y of cultivation; the other half were regrowth following 4 y or more of continuous pasture in Brazil and three or more rotations of medium-fallow agriculture in Bolivia. Above-ground live biomass was estimated using published allometric equations. Total biomass ranged from 17 to 207 Mg ha -1 . Biomass of pioneer trees was poorly related to stand age, while that of later-successional trees increased linearly with age. Total biomass accumulation in Bolivia averaged 5.4 Mg ha -1 y -1 over the entire age sequence. Biomass accumulation for regrowth following short-term use was not greater than that for regrowth following medium-fallow agriculture. In Brazil, biomass accumulation averaged 9.1 Mg ha -1 y -1 over the first 12 y of regrowth and 5.9 Mg ha -1 y -1 over the entire age sequence. Biomass accumulation was significantly slower, around 5.0 Mg ha -1 y -1 , for regrowth following continuous pasture than for regrowth following 1 y of cultivation.
TL;DR: Changes in floristic composition and structure in a cerrado sensu stricto area were studied over a 9-y period and suggested a highly resilient community.
Abstract: Changes in floristic composition and structure in a cerrado sensu stricto area were studied over a 9-y period. A sample of 19 (20-m × 50-m) permanent plots was assessed at 3-y intervals from 1985 to 1994, when all stems ≥ 5 cm at 0.30 m above the ground level were measured. There was little change in species composition over the period. Changes in density and basal area of the whole community were in the range of 5% over the 9 y. These parameters fluctuated over the years with the greatest differences found in the comparisons of 1991, 2 y after an accidental fire reached the site, with other years. The changes in density and basal area were greater than in several tropical forests, probably due to disturbances such as fire occurring at 3 to 5-y intervals. The nearly constant density and basal area suggested a highly resilient community.
TL;DR: In this paper, a new aggregation of tree species of the dipterocarp rain forests in Sabah (Borneo), Malaysia, is developed based on the two criteria successional status and potential maximum height.
Abstract: For analysing field data as well as for modelling purposes it is useful to classify tree species into a few functional types. In this paper a new aggregation of tree species of the dipterocarp rain forests in Sabah (Borneo), Malaysia, is developed. The aggregation is based on the two criteria successional status and potential maximum height. Three classes of successional status (early, mid and late successional species) and five classes of potential maximum heights ( 36 m) lead to a combination of 15 functional types. The criteria of the developed classification are chosen to suit for applications with process-based models, such as FORMIx3 and FORMIND, which are based on photo- synthesis production as the main process determining tree growth. The concept is universal and can easily be applied to other areas. With this new method of group- ing a more realistic parametrization of process-based rain forest growth models seems to be possible.
TL;DR: At sites with short periods of flooding in igapó forests, on high levels in the flooding gradient, the need for rapid height growth may have selected for species with larger seeds which enable seedlings to be less dependent on soil nutrients.
Abstract: In the Central Amazonian floodplains, several hundred tree species grow in areas that are periodically flooded by nutrient-rich white-water rivers (varzea) and by nutrient poor black-water rivers (igapo). Seed masses of 31 species from varzea and 27 species from igapo were compared taking into consideration their taxonomic relatedness. Overall average seed mass was higher (mean = 7.08 g) in nutrient-poor igapo than in nutrient-rich varzea (mean = 1.16 g). In igapo, the species growing at high elevations on the flooding gradient had significantly higher seed masses than the species growing at low elevations. In varzea, no difference was found between species growing at high and low elevations. Four large-seeded species from igapo occurring at high elevations on the flooding gradient were responsible for most of the difference in average seed mass between forest types. These data suggest that at low positions in the flooding gradient in igapo, selection pressure on seed size is probably the same as in varzea. At sites with short periods of flooding in igapo forests, on high levels in the flooding gradient, the need for rapid height growth may have selected for species with larger seeds which enable seedlings to be less dependent on soil nutrients.
TL;DR: It is discussed, that the high bryophytic biomass in montane compared to lowland forests is a major reason for differences in humus biomass between these forest types.
Abstract: Epiphyte diversity as well as distribution and composition of epiphytic biomass was investigated in two lowland and two montane rain forests in Ecuador. Species numbers of epiphytes per tree were slightly higher in the montane (22–41 in Los Cedros, 33–54 in Otonga) than in the lowland forests (9–43 in Yasuni, 19–32 in Tiputini), however differences were not significant. In contrast, some epiphyte families did show significant altitudinal differences. The total epiphytic biomass per branch surface decreased from the centre of the crown to the periphery, and was generally higher in the montane (6.0 kg m−2 on central branches in Los Cedros, 1.8 kg m−2 in Otonga) than in the lowland forests (1.3 kg m−2 in Yasuni and 1.8 kg m−2 in Tiputini). Especially, dry weight of bryophytes and dead organic matter was higher in the mountains. In contrast, the biomass of green parts of vascular epiphytes on central branches was about the same in all four forests (0.4–0.6 kg m−2). A comparison with literature data from other study sites of tropical moist forests supports the observation that biomass of vascular epiphytes does not significantly change with altitude. It is discussed, that the high bryophytic biomass in montane compared to lowland forests is a major reason for differences in humus biomass between these forest types.
TL;DR: The dietary relationships found in this study support the idea that these birds forage opportunistically, and that some differences found among their diets may be the result of random seed sampling from the heterogeneous seed pool available.
Abstract: A total of 537 crops from four coexisting granivorous doves (Columbina minuta, C. passerina, C. talpacoti and Scardafella squammata), collected on seven sam- pling dates in a Venezuelan savanna, were examined to assess food partitioning. These closely related doves are resident birds, and overlap broadly both in daily activity patterns and habitat use; in circumstances like this, segregation in the use of food resources often occurs. It was found that: (a) differences in body dimen- sions did not account for variations in seed size taken by doves; they all ate seeds in the same size range and they showed high similarity in seed size preferred; (b) the importance of different seed sizes in the diets changed seasonally with similar tendencies for all four species, (c) there were differences up to 4-fold in mean seed size consumed by individuals of the same species on the same date; (d) seeds of 63 plant species were consumed by the four dove species and constituted from 98 to 99.5% of the diets; (e) high dietary overlap both in prey size and prey type was found throughout the year. The dietary relationships found in this study support the idea that these birds forage opportunistically, and that some differences found among their diets may be the result of random seed sampling from the heteroge- neous seed pool available.
TL;DR: Monitoring of leaf water and osmotic potentials and gas exchange during a prolonged El Niño drought in 1998 for saplings of seven species in a Bornean heath forest found deep roots and strong stomatal control favour trees in tropical heath forests where water deficits probably occur regularly.
Abstract: . Leaf water and osmotic potentials and gas exchange were monitoredduring a prolonged El Nin˜o drought in 1998 for saplings of seven species in aBornean heath forest and compared with measurements taken during a sub-sequent wet period. The four dipterocarp species maintained reasonably goodwater status throughout the drought, especially Dipterocarpus borneensis which hadthick and deep tap roots. In contrast, two of three non-dipterocarp species, Cleis-tanthus baramicus and Tristaniopsis obovata displayed predawn leaf water potentialsapproaching their turgor-loss points. During the drought, all species except D.borneensis displayed strongly reduced stomatal conductance after a brief exposureto sun, and all displayed lower maximum rates of stomatal conductance and netphotosynthesis than during the wet period. Only Cotylelobium burckii displayed signi-ficant osmotic acclimation to the drought. T. obovata possessing a superficial rootsystem suffered a high mortality due to the drought, but recovered faster after thefirst rains than the other species all of which had tap roots. Deep roots and strongstomatal control favour trees in tropical heath forests where water deficits prob-ably occur regularly.KEY WORDS: dipterocarps, drought tolerance, El Nin˜o drought, haze, leaf waterpotential, osmotic potential, photosynthesis, root architecture, stomatal conduct-ance, tropical heath forest
TL;DR: Investigation on recently isolated land-bridge islands in Lago Guri, Venezuela suggests that reduced predation is a potentially important factor underlying observed variation in Atta density patterns in the Guri islands.
Abstract: The potential role of predation as a factor underlying variation in leaf-cutter ant (Atta sp.) densities was investigated on recently isolated land-bridge islands in Lago Guri, Venezuela. A survey of mature Atta colonies revealed a sharp increase in densities on small and medium islands (5.6 and 2.3 colonies ha-' respectively) compared to large islands (0.72 colonies ha-') and the mainland (0 nests in 5.5 ha). Incipient colonies showed the reverse trend with higher densities on larger landmasses. Cage experiments were conducted to test the impacts of predation on the survival of incipient and young Atta colonies. Protection by wire- mesh cages increased the survival of both incipient and young colonies at all sites. The survival of unprotected incipient and young colonies was significantly reduced on larger landmasses relative to small islands. These results are consistent with burrow survey data that provided indirect evidence of higher armadillo densities on larger landmasses. Findings suggest that reduced predation is a potentially important factor underlying observed variation in Atta density patterns in the Guri islands.
TL;DR: In this paper, a long-term (2.5-11 y) weekly record of stream water chemistry on eight forested watersheds (catchment basins) in the Luquillo Moun- tains of Puerto Rico was presented.
Abstract: Stream water chemistry responds substantially to watershed disturb- ances, but hurricane effects have not been extensively investigated in tropical regions. This study presents a long-term (2.5-11 y) weekly record of stream water chemistry on eight forested watersheds (catchment basins) in the Luquillo Moun- tains of Puerto Rico. This includes a period before and at least 2 y after the disturbance caused by the 1989 Hurricane Hugo. Nitrate, potassium and ammo- nium concentrations increased after the hurricane and remained elevated for up to 2 y. Sulphate, chloride, sodium, magnesium and calcium showed smaller relative significant changes. Average stream water exports of potassium, nitrate and ammonium increased by 13.1, 3.6 and 0.54 kg ha -1 y -1 in the first post-hurricane year across all watersheds. These represent increases of 119, 182 and 102% respectively, compared to the other years of record. The increased stream outputs of potassium and nitrogen in the first 2 y post-hurricane are equivalent to 3% (potassium) and 1% (nitrogen) of the hurricane-derived plant litter. Effects of hurricanes on tropical stream water potassium and nitrogen can be greater than those caused by canopy gaps or limited forest cutting, but less than those following large-scale deforestation or fire.
TL;DR: The feeding behaviour of free-ranging black-handed tamarins, Saguinus midas niger, was monitored over 6 mo in a forest fragment in eastern Amazonia, indicating that S. m.
Abstract: The feeding behaviour of free-ranging black-handed tamarins, Saguinus midas niger , was monitored over 6 mo in a forest fragment in eastern Amazonia. The tamarins' diet included arthropods and plant exudates, but was predominantly frugivorous (87.5% of feeding records, 18 plant species) in all months. The seeds of at least six species were ingested whole and defecated intact. Ingested seeds were relatively large, but those with diameter > 1 cm or length > 2 cm were discarded. Seeds took 2–4 h to pass through the digestive tract, and more than half (50.6%) were dispersed to a habitat different from that in which they were ingested. A fifth (19.3%) of all seeds were dispersed from primary to secondary forest, indicating that S. m. niger may play an important role in forest regeneration, a role that will become increasingly important in the fragmented landscape of eastern Amazonia.
TL;DR: Intermittent transfers by females between groups suggest that the defence of diurnal roosts by males represents a more profitable mating strategy than the direct defence of compositionally labile female groups.
Abstract: Patterns of dispersion and site fidelity were investigated in a tent- roosting population of the short-nosed fruit bat, Cynopterus sphinx (Megachiroptera), in southern India. A local population of C. sphinx occupied diurnal roosts in a variable subset of 45 stem tents constructed within the dense foliage of mast trees (Polyalthia longifolia). Individually marked tent-roosting bats were visually censused over the course of a 38-d interval spanning the postpartum oestrus period. On any given day, 33.3-85.7% (mean = 60.8%, SD = 14.2) of adult males roosted singly, with the remainder holding harems of 1-10 breeding females (mean = 3.01, SD = 0.79). Average harem sex ratio was 2.8-fold higher than the adult sex ratio of the total tent-roosting population within the study area, indicat- ing the potential for a high variance in male mating success within a single breed- ing season. Bats of both sexes typically occupied one primary tent, interspersed with shorter periods of residency in alternate tents. Males exhibited a significantly higher degree of roost fidelity than females. Some females roosted sequentially with different males and with different combinations of females, whereas others remained continuously associated with a single male and/or particular female roostmates over the duration of the census period. There were no statistically significant relationships between physical characteristics of tents and rates of occupancy by males or females. Intermittent transfers by females between groups suggest that the defence of diurnal roosts by males represents a more profi- table mating strategy than the direct defence of compositionally labile female groups.
TL;DR: Aggressive invasion and monospecific stands of P. aduncum are explained by its dominance in the seed bank, fast growth, and high rates of biomass accumulation.
Abstract: Secondary fallow vegetation in parts of the Papua New Guinea low- lands is dominated by the shrub Piper aduncum L. that originates from South Amer- ica. Here we report on its seed bank, growth rate and biomass accumulation. P. aduncum accounted for 69 % (408 m -2 ) of the seed bank in the forest and 53 % (1559 m -2 ) of the seed bank under fallow. About 90 % of the tree seed bank at the fallow site was dominated by P. aduncum whereas this was 78 % in the forest soil. Two-year-old P. aduncum had grown to 4.5 m height and had accumulated 48 Mg dry matter (DM) per ha of above ground biomass. The rate of biomass accumula- tion increased from 10 Mg DM ha -1 y -1 in the first year to 40 Mg DM ha -1 y -1 in the second year when 76 % of the biomass consisted of mainstems. The highest growth rate of 134 kg DM ha -1 d -1 occurred when P. aduncum was 17-mo-old. Aggressive invasion and monospecific stands of P. aduncum are explained by its dominance in the seed bank, fast growth, and high rates of biomass accumulation. P. aduncum is a major competitor to indigenous tree species and presents a threat to Papua New Guinea's rich biodiversity.
TL;DR: In this article, the authors measured litterfall along transects 10, 50, 100 and 250m from the forest edge in the Amazonian lowland rain forest in the dry season of 1990.
Abstract: Forest edges bordering on pasture were created by cutting and burn- ing the surrounding Amazonian lowland rain forest in the dry season (June) of 1990. Litterfall was measured for 3.5 y along transects 10, 50, 100 and 250-m into the forest from the forest edge. Litterfall along the 10-m transects increased by up to 2.5 times that on spatial controls (250-m transects) in the dry season in which the edge was created. In the second dry season after edge creation litterfall at 10-m was lower than on controls, after which it returned to control rates in the second wet season, 1.5 y after edge creation. Litterfall 50-m into the forest was less affected; there was a smaller rise in the dry season in which the edge was cut, and no significant effects after that. At 100-m there was no effect of edge creation on litterfall. Phosphorus concentrations in litterfall were elevated along 10-m transects, 10-12 wk after edge creation, possibly because of reduced retransloca- tion prior to abscission. The changes in litterfall described here are inextricably linked to the biomass collapse, which occurs near forest-fragment edges in the same area.
TL;DR: Evidence supporting the hypothesis that plant populations are collapsing without elephants is conspicuously absent in these datasets, although Balanites wilsoniana is likely to suffer dramatically on a centennial scale in the absence of forest elephants.
Abstract: Elephant populations have declined greatly in the rain forests of Upper Guinea (Africa, west of the Dahomey Gap). Elephants have a number of well-known influences on vegetation, both detrimental and beneficial to trees. They are dispersers of a large number of woody forest species, giving rise to concerns that without elephants the plant diversity of Upper Guinean forest plant communities will not be maintained. This prospect was examined with respect to four sources of inventory and research data from Ghana, covering nearly all (more than 2000) species of forest plant. Evidence supporting the hypothesis that plant populations are collapsing without elephants is conspicuously absent in these datasets, although Balanites wilsoniana is likely to suffer dramatically on a centennial scale in the absence of forest elephants. A few other species are likely to decline, although at an even slower rate. In the context of other processes current in these forests, loss of elephants is an insignificant concern for plant biodiversity. Elephant damage of forests can be very significant in Africa, but loss of this influence is more than compensated for by human disturbance. Elephants have played a significant part in the shaping of West African rain forest vegetation. However, it is the conservation of elephants that should be of primary concern. Tree populations should be managed to promote them, rather than vice versa.
TL;DR: In this paper, the authors report on the impact of tropical cyclone 'Rona' on forest canopy openness at six lowland rain forest sites with contrasting management histories (old-growth, selectively logged and regrowth).
Abstract: Tropical Cyclone 'Rona' crossed the coast of the Daintree lowlands of northeastern Australia in 1999. This study reports on its impact on forest canopy openness at six lowland rain forest sites with contrasting management histories (old-growth, selectively logged and regrowth). Percentage canopy openness was calculated from individual hemispherical photographs taken from marked points below the forest canopy at nine plots per site 3-4 mo before the cyclone, and at the same points a month afterwards. Before the cyclone, when nine sites were visited, canopy openness in old-growth and logged sites was similar, but signific- antly higher in regrowth forest. After the cyclone, all six revisited sites showed an increase in canopy openness, but the increase was very patchy amongst plots and sites and varied from insignificant to severe. The most severely impacted site was an old-growth one, the least impacted a logged one. Although proneness to impact was apparently related to forest management history (old-growth being the most impacted), underlying local topography may have had an equally strong influence in this case. It was concluded that the likelihood of severe impact may be deter- mined at the landscape-scale by the interaction of anthropogenic with meteorolo- gical, physiographic and biotic factors. In the long term, such interactions may caution against pursuing forest management in cyclone-prone areas.
TL;DR: In this article, a-diversity curve (Ha) is used to identify anomalous species divers- ity behaviour of the 'ridge above the slope' subplots which may have implications on land-facet class definitions.
Abstract: Data from a hilly forest study site at Batang Ule, Sumatra, are organ- ized into 30 100-m x 10-m subplots lying perpendicular to the line of maximal topographic gradient, from the valley to the plateau/ridge. The following methodo- logical question is addressed: what species diversity measures are best used in order to reveal the ecologically distinct regions in the site. The main tool used to answer this question is the a-diversity curve (Ha). Graphical examination of tree and species densities, and a-diversity curves identifies an anomalous species divers- ity behaviour of the 'ridge above the slope' subplots which may have implications on land-facet class definitions. Factor analysis of the a-diversity curves indicates that the diversity space is two-dimensional: i.e. two diversity measures are suffi- cient to characterize the site; the species density (Ho), and the Berger-Parker index (H.,). In the two-dimensional diversity-space three distinct species diversity groups are found which relate to the topographic gradient at the Batang Ule site. The results are compared with those for a flat homogeneous site at Pasirmayang, Sumatra. The implications of the results on land-classifications in species-diversity mapping and conservation strategy are discussed.
TL;DR: In Central Amazonian floodplains, trees are subjected to periodic changes between a terrestrial and a flooding phase, which can last up to 230 d (junk et al. 1989).
Abstract: In Central Amazonian floodplains (called seasonal vairzea, Prance 1979), trees are subjected to periodic changes between a terrestrial and a flooding phase, which can last up to 230 d (junk et al. 1989). During this aquatic phase, the soil is covered by a water-table that reaches a height of 10 m. Seedlings and small trees are then completely flooded. High, adult trees, or trees standing on higher levels in the flooding gradient, suffer inundation of the roots and parts of the stems that causes a lack of oxygen in the rhizosphere (Crawford 1989). Gessner (1968) compared the growth conditions in the aquatic phase with temperate winters and introduced the term 'physiological winter'. Leaffall and reductions of growth and metabolic activity, which he observed in the aquatic phase, led him to the assumption that trees in floodplains reduce their activity as do trees of temperate forests during the period of unfavourable conditions (Gessner 1968). Annual growth rings are formed in the wood of most tree species in Central Amazonian floodplains as a consequence of regular growth reductions (Worbes 1986, 1989). Changes of root formation and function, leaf respiration, leaf metabolite and chlorophyll content, water potential and photosynthetic 02-production were observed in flooded tree seedlings in the varzea (Meyer 1991, Schluter 1989,
TL;DR: In this article, live-trapping was conducted on 175 subsequently formed islands during the flooding of primary lowland rain forest by the filling of a hydroelectric reservoir in French Guiana, and different factors affecting the trap effici- ency were analysed.
Abstract: During the flooding of primary lowland rain forest by the filling of a hydroelectric reservoir in French Guiana, live-trapping was conducted on 175 subsequently formed islands. Different factors affecting the mammal trap effici- ency were analysed. The main results show the real complexity of the sampling problem and the influence of the habitat disturbance due to the flooding. The location and/or the type of traps influenced captures of Dasypus novemcinctus, Proechi- mys spp., Metachirus nudicaudatus and Philander opossum in relation to their foraging and/or locomotion behaviour, and to their size. The conformation of the islands (height and size) had no influence on the number of captures, nor on the species richness. The number of captures increased with the number of trapnights during the first water inflow and the level stretch. The best trapping success was observed during the wet season, when the strong habitat modification and the forest frag- mentation became more significant. It resulted from the reduction of available land area and trophic resources. One year after the beginning of the water inflow, the decrease of the number of captures with the increasing number of trapnights reflected a real decrease of the number of mammals on the islands. The species richness increased with the number of trapnights in all periods, and was also the highest during the wet season.