Emergent Tree Species Research Articles

Height-diameter allometric equations of an emergent tree species from the Congo Basin

Reliable tree height-diameter (H-D) allometric equations are a key tool for the estimation of forest productivity and Above Ground Biomass (AGB). Most existing H-D allometric equations developed for the tropical region are based on large-scale multi-species datasets, and their use to derive information on productivity and AGB at the species level is prone to uncertainties. The single-species H-D allometric equations available are mainly focused on monocultures or stands with simple tree species mixtures and did not account for the site effects. Here we measured the height and diameter of 2,288 trees of the emergent tree species Pericopsis elata (Harms) Meeuwen in the Democratic Republic of the Congo (DRC) and in Cameroon. We first examined how accurate multispecies H-D allometric equations are in predicting the total height of P. elata. We then tested whether single-species H-D allometric equations vary between sites. We developed the first H-D allometric equation of P. elata and tested whether and how stand-level and environmental variables induce changes in H-D allometric relationship of P. elata at the regional level. We additionally evaluated whether tree-level variables are important at the local level where climate and stand development stage are expected to be less variable. We found that pantropical, regional and local H-D allometric equations significantly underestimate the total height of P. elata. The local multi-species H-D allometric equation developed for Yangambi showed the highest underestimation in all the studied sites. This result supports the need for an H-D allometric equation specific for P. elata. The species-level H-D allometric equation developed showed significant underestimations for trees from the disturbed and undisturbed forests in DRC, while overestimations were observed for similar sites in Cameroon. Using a mixed-effect H-D allometric equation, we showed that even within a single species, a substantial variation exists between sites. This variation showed to be driven by the differences in the maximum asymptotic height (Hmax) between sites. We found that P. elata trees are taller and attain higher Hmax in DRC than in Cameroon. The basal area showed to be a significant covariate accounting for the site effects at the regional-scale where climate variables showed minor effects. However, at the local-scale, none of climate or stand variables showed to be significant. Local-scale variation showed to be associated with differences in light availability, highlighting the potential of management options that shape the local environment in driving species productivity.

Intensification of açaí palm management largely impoverishes tree assemblages in the Amazon estuarine forest

The exploitation of non-timber forest products has been encouraged in order to reconcile economic uses, biodiversity conservation and the provision of ecosystem services. In this paper we investigate how increments on the açaí palm density (Euterpe oleracea) via forest management change tree assemblages across 47 plots in the Amazon estuarine forest (Brazil). Assemblage attributes were confronted to açai clump density, soil fertility, canopy openness and elevation. Both tree species density and richness were negatively affected by acai, but species richness was also affected by tree abundance. Species-accumulation curves also indicated higher alpha and beta diversity across low-intensity forest patches with high-intensity patches lacking half of the tree species. A small set of species dominated forest patches, but açaí density did not correlate with the abundance of valuable species. Explanatory variables, including açai density, explained a small fraction of the variation on the functional profile of tree assemblages, but functional richness was reduced by a half across forest stands exceeding 600 açaí clumps per ha. Our results suggest that açaí intensification alters the structure of woody plant assemblages in estuarine forest. Tree abundance and species richness consistently declines as açaí clump density increases, with some forest stands being dominated by açaí and almost lacking any tree species. Accordingly, landscapes dominated by high-intensity forest stands are largely impoverished in terms of understory, canopy and emergent tree species. These findings question the current legal regulations and thresholds adopted for açai management, while alert for potential disasters caused by poorly-regulated extractions of NTFPs.

Genetic threats to the Forest Giants of the Amazon: Habitat degradation effects on the socio‐economically important Brazil nut tree (Bertholletia excelsa)

Societal Impact StatementThe Brazil nut is a highly valuable non‐timber forest product from a wild, hyperdominant, emergent tree species that is increasingly vulnerable and exposed to habitat degradation. We provide evidence for how Brazil nut genetic resources are negatively affected by forest degradation and discuss the consequences of this for reproductive success. To avoid negative effects of genetic erosion and inbreeding, we discuss the need to cease large‐scale forest conversion and to promote landscape connectivity. This could support gene flow, maintain genetic diversity across individuals reproducing in clustered patterns and contribute to securing the long‐termed reproductive viability and resilience of this high socio‐economically and ecologically valuable species.Summary Ecosystem degradation in the Amazon drives this biodiverse rainforest toward an ecological tipping point. Sustainable management and restoration of degraded rainforest therein are central to counteract this crisis. One hyperdominant, keystone species of high ecological and socio‐economic value, the Brazil nut tree, offers additional benefits as a major carbon sink and a nutritional source of the most prominent globally traded non‐timber forest product. Despite Brazil nut trees being protected by conservation regulation, forest degradation threatens sufficient gene‐flow among Brazil nut tree populations. This has impacts on the reproductive success, genetic diversity, and consequently on the resilience of this species to environmental change. We used 13 microsatellite loci to explore the consequences of forest degradation on the reduction in genetic diversity of Brazil nut populations. We examined the clustering of genetically related individuals as fine‐scale genetic structure (FSGS) and the variation in genetic diversity and inbreeding across adult trees and seedlings along a categorized forest‐degradation gradient ranging from conserved to degraded areas. In addition, we applied direct and indirect approaches to estimate contemporary pollen‐mediated gene flow. We found significant levels of FSGS, comparable to other similar tropical tree species. Brazil nut seedlings had consistently lower genetic diversity and higher inbreeding than adults, significantly associated with the degree of forest degradation of their origin. We observed limited pollen dispersal, differential patterns in pollen heterogeneity, and disproportionate paternal‐assignment rates from few individuals shaping the effective population size in our dataset. We discuss how this evidence for reproduction vulnerability may affect the genetic resources and undermine the resilience of this ecological and socio‐economic system in Peru.

Harpy Eagle (Harpia harpyja) nest tree selection: Selective logging in Amazon forest threatens Earth's largest eagle

Characterizing wildlife conservation problems is essential to properly inform conservation planning, and requires detailed knowledge on critical life stages, such as reproduction. Large tropical raptors often require large emergent trees to build their huge nests. However, large emergents are also in heavy demand by the timber industry. Here, we review the literature to characterize nesting structures used by Earth's largest eagle, Harpy Eagles (Harpia harpyja) and examine to what extent nest-tree selectivity is targeted by selective logging. We show that Harpy Eagles selected specific forest canopy structures as nesting platforms. Nests were large (mean size 152 × 99 cm) and typically located on the main fork of 28 emergent tree species, 92.8% of which are commercially targeted by the timber industry. AIC-based stepwise regression indicated that, compared with non-nesting emergent trees, nest trees were 19.6% taller at the first bifurcation; had crowns 26.6% wider; had 33.3% fewer branches <45°, which were on average 35% lower-angled. Tree size varied widely across the range of nesting tree species, but peaked near the Equator, and were high-statured in unflooded forest compared with flooded forests. Our results show that commercial loggers target the same set of species and individuals on which Harpy Eagles nest, questioning whether large tracts of selectively logged Amazonian primary forests still provide suitable nesting habitat for this mega-raptor. We conclude that suitable Harpy Eagle nesting trees have been rapidly lost over the species last stronghold, and this information may prove useful to the upcoming species evaluation by IUCN.

The contribution of leaching to nutrient release from leaf litter of two emergent tree species in a Malaysian tropical peat swamp forest

To understand the role of abiotic leaching in nutrient release within the nutrient-deficit tropical peat swamp forest (TPSF), an experiment was conducted over 30 days using leaf litter from two common emergent TPSF trees, Koompassia malaccensis and Shorea uliginosa. The main objectives were to determine leaf litter nutrient leaching dynamics, and the effect of water pH and potential microbial influence on nutrient release. Leaf litter (single species and combined) was subjected to 3 treatments: peat water (natural acidic conditions), poisoned peat water (NaN3 as microbial poison) and deionized water (control). Despite loss of nutrients from the leaves, this was not associated with the loss of mass or carbon (C) from the leaves because they are resistant to decomposition. Nutrient loss occurred in the order of phosphorus (P) > nitrogen (N) > C whereby litter P content was quickly exhausted. Microbial activity only affected the bioavailable P (PO4 −) whereby initial litter P release stimulated microbial growth, which resulted in the subsequent immobilization of P. Lastly, the effect of pH was not profound in this study. In conclusion, abiotic leaching from leaf litter releases considerable amounts of nutrients (notably PO4 3−) and functions as an important autochthonous nutrient source for the TPSF.

Ecological distribution of leaf stomata and trichomes among tree species in a Malaysian lowland tropical rain forest.

The vertical structure of a tropical rain forest is complex and multilayered, with strong variation of micro-environment with height up to the canopy. We investigated the relation between morphological traits of leaf surfaces and tree ecological characteristics in a Malaysian tropical rain forest. The shapes and densities of stomata and trichomes on the abaxial leaf surfaces and their relation with leaf characteristics such as leaf area and leaf mass per area (LMA) were studied in 136 tree species in 35 families with different growth forms in the tropical moist forest. Leaf physiological properties were also measured in 50 canopy and emergent species. Most tree species had flat type (40.4%) or mound type (39.7%) stomata. In addition, 84 species (61.76%) in 22 families had trichomes, including those with glandular (17.65%) and non-glandular trichomes (44.11%). Most leaf characteristics significantly varied among the growth form types: species in canopy and emergent layers and canopy gap conditions had higher stomatal density, stomatal pore index (SPI), trichome density and LMA than species in understory and subcanopy layers, though the relation of phylogenetically independent contrasts to each characteristic was not statistically significant, except for leaf stomatal density, SPI and LMA. Intrinsic water use efficiency in canopy and emergent tree species with higher trichome densities was greater than in species with lower trichome densities. These results suggest that tree species in tropical rain forests adapt to a spatial difference in their growth forms, which are considerably affected by phylogenetic context, by having different stomatal and trichome shapes and/or densities.

Litterfall production and chemistry of Koompassia malaccensis and Shorea uliginosa in a tropical peat swamp forest: plant nutrient regulation and climate relationships

This study shows that two emergent tree species growing in a nutrient-limited tropical peat swamp forest use different mechanisms for nutrient regulation. The main aim of this study is to understand the contribution of litterfall to nutrient supply and regulation of two emergent tree species in a tropical peat swamp forest (TPSF) in Peninsular Malaysia. The questions posed by this study include: (1) Do coexisting tree species in TPSF differ in terms of litter production, physico-chemical traits and litterfall patterns? (2) How do these relate to possible nutrient regulation mechanisms of the tree species and do the strategies involved differ between a nitrogen (N) fixing legume (Koompassia malaccensis, Family Fabaceae) and a dipterocarp (Shorea uliginosa, Family Dipterocarpaceae)? (3) Is litterfall timing of the selected tree species driven by climatic variables? Litterfall was collected from litter traps placed under the selected trees in the Sungai Karang TPSF. Green leaves of the selected tree species were also collected. Both leaf litter and green leaves were assessed for their physico-chemical properties (toughness, total phenols, total tannins, proximate fibre–cellulose–lignin and a range of nutrients) and compared. Results obtained indicate that K. malaccensis relies on a combination of high litter quality (higher N coupled with lower amount of tannins, fibre and cellulose) and low annual litterfall mass (388.17 g m−2) for nutrient regulation while the opposite strategy is used by S. uliginosa, which was found to produce an annual litterfall mass of 918.14 g m−2. Due to the aseasonal environment, no significant relationships were observed between climatic variables and litterfall. Therefore, litterfall characteristics in aseasonal tropical regions may depend more on species-specific physico-chemical properties than on climatic variables.

A commented checklist of woody plants in the Northern Republic of Congo

Aim – This paper aims to provide the first exhaustive list of woody species present in the northern part of the Republic of Congo, describing the vegetation types, characterizing the ligneous forest stands and explaining the distribution range of characteristic species. Location – The 1.23 million ha of the logging concession of ‘Congolaise Industrielle des Bois’, situated in the North of the Republic of Congo (1.41°N 16.32°E), were prospected during six years. The study area is bordered by the Sangha River to the west and by the Likwala-aux-Herbes swamps to the east. Methods – The checklist, given as an electronic appendix, documents 702 woody species. Each species is annotated with the following headings when the information is known: scientific, pilot and local names, lifeform, preferential habitat, distribution, seed dispersal type, human use, abundance and foliage phenology. Field observations have been augmented with existing bibliography. Results – A total of 392 genera and 79 families are presented. Ficus is the largest genus with seventeen species. 73% of taxa are endemic to the Guineo-Congolian Region centre. The sarcochorous functional diaspore type represents 71%. Eleven percent of the species are anemochorous and are mostly emergent trees. Forty-four species newly recorded for the Republic of Congo are especially commented. Main conclusions – Terra firma forests are characterized by deciduous, light-demanding and winddispersed emergent tree species. Evergreen stands are mainly found at the confluence of the Sangha River and Likwala-aux-Herbes swamps. This forest could be regarded as equivalent to the other interfluvial forest blocks of the Major Fluvial Refuge in the Congo basin.

The periodic wetting of leaves enhances water relations and growth of the long‐lived conifer Araucaria angustifolia

The importance of foliar absorption of water and atmospheric solutes in conifers was recognised in the 1970s, and the importance of fog as a water source in forest environments has been recently demonstrated. Araucaria angustifolia (Araucariaceae) is an emergent tree species that grows in montane forests of southern Brazil, where rainfall and fog are frequent events, leading to frequent wetting of the leaves. Despite anatomical evidence in favour of leaf water absorption, there is no information on the existence and physiological significance of a such process. In this study, we test the hypothesis that the use of atmospheric water by leaves takes place and is physiologically relevant for the species, by comparing growth, water relations and nutritional status between plants grown under two conditions of soil water (well-watered and water-stressed plants) and three types of leaf spraying (none, water and nutrient solution spray). Leaf spraying had a greater effect in improving plant water relations when plants were under water stress. Plant growth was more responsive to water available to the leaves than to the roots, and was equally increased by both types of leaf spraying, with no interaction with soil water status. Spraying leaves with nutrient solution increased shoot ramification and raised the concentrations of N, P, K, Zn, Cu and Fe in the roots. Our results provide strong indications that water and nutrients are indeed absorbed by leaves of A.angustifolia, and that this process might be as important as water uptake by its roots.

The Impact of Annual and Seasonal Rainfall Patterns on Growth and Phenology of Emergent Tree Species in Southeastern Amazonia, Brazil

AbstractUnderstanding tree growth in response to rainfall distribution is critical to predicting forest and species population responses to climate change. We investigated inter‐annual and seasonal variation in stem diameter by three emergent tree species in a seasonally dry tropical forest in southeast Pará, Brazil. Annual diameter growth rates bySwietenia macrophyllademonstrated strong positive correlation with annual rainfall totals during 1997–2009;Hymenaea courbarilgrowth rates demonstrated weak positive correlation, whereasParkia pendulaexhibited weak negative correlation. For bothSwieteniaandHymenaea, annual diameter growth rates correlated positively and significantly with rainfall totals during the first 6 mo of the growing year (July to December). Vernier dendrometer bands monitored at 4‐wk intervals during 3–5 yr confirmed strong seasonal effects on stem diameter expansion. Individuals of all three species expanded in unison during wet season months and were static or even contracted during dry season months. Stems of the deciduousSwieteniacontracted as crowns were shed during the early dry season, expanded slightly as new crowns were flushed, and then contracted further during 3–5 wk flowering periods in the late dry season by newly mature crowns. The three species’ physiographic distribution patterns at the study site may partially underlie observed differences in annual and seasonal growth. With most global circulation models predicting conditions becoming gradually drier in southeast Amazonia over the coming decades, species such asSwieteniathat perform best on the ‘wet end’ of current conditions may experience reduced growth rates. However, population viability will not necessarily be threatened if life history and ecophysiological responses to changing conditions are compensatory.

Allometry of emergent tree species from saplings to above-canopy adults in a Costa Rican rain forest

Abstract:Relations between crown width and tree height and trunk diameter and tree height were measured for trees of all sizes of six large emergent species (Balizia elegans, Dipteryx panamensis, Hieronyma alchorneoides, Hymenolobium mesoamericanum, Lecythis ampla and Terminalia oblonga) in the lowland tropical wet forest at La Selva, Costa Rica. Thirty to 45 individuals were chosen per species to provide a relatively even height distribution from 1 m up to the maximum encountered height. Among small juveniles, the crown widths of the two species with the smallest leaves and horizontally spreading branches were greater than those of the four large-leaved species. On reaching and exceeding the canopy, all but one species showed pronounced increases in crown width with increasing height. These patterns are linked to leaf size and first branching height in small juveniles and low densities of emergent trees at La Selva and other tropical forests, where crown expansion in all directions enhances light interception under the equatorial sun in trees that are not crowded by neighbours of similar height.

Carbon Storage in a Fragmented Landscape of Atlantic Forest: The Role Played by Edge-Affected Habitats and Emergent Trees

Patterns of carbon retention and distribution across human-modified landscapes have been poorly investigated. In this paper carbon distribution across three forest habitats of a fragmented Atlantic forest landscape in northeast Brazil is examined. Data on tree assemblages (DBH ≥10 cm) inhabiting forest interior stands, forest edges and fragments (2.05–365 ha) were obtained via information from 59 0.1-ha plots (a total of 4,845 stems and 198 tree species), and it was further incorporated in four allometric equations for estimation of above-ground biomass and carbon. Stocks of carbon were highly variable within habitats of Serra Grande, but forest interior plots retained almost three times more carbon (202.8 ± 23.7 TonC/ha) than edge and fragment plots, while these edge-affected habitats exhibited similar scores. Moreover, emergent tree species accounted for the majority of the carbon retained (59.13%) in interior plots with understorey species playing a minor role. However, carbon retained by emergent species decreased by a half across forest edges and forest fragment since large stems (&gt; 70 cm DBH) and very tall trees (&gt; 31 m height) were very rare in these habitats. Finally, a forest cover mapping revealed the occurrence of 213.19 km2 of forest interior habitat in the whole Atlantic forest of northeast Brazil. This figure means that only 8% of total remaining forest habitat has a full potential for carbon storage, with the other 92% (edge-affected habitats) storing just a half of that. Our results suggest that habitat fragmentation and the consequent establishment of edge-affected habitats (forest edges and fragments) drastically limit forest capacity for carbon storage across human-modified landscapes since the loss of carbon due to reduced abundance of large trees is not compensated by either canopy or understorey species.

Outcrossing rate of Couratari multiflora (J.Smith) Eyma (Lecythidaceae), a low-density tropical tree species from a central Amazonian rainforest

A multilocus mixed-mating model was used to evaluate the mating system of a population of Couratari multiflora, an emergent tree species found in low densities (1 individual/10 ha) in lowland forests of central Amazonia. We surveyed and observed phenologically 41 trees in an area of 400 ha. From these, only four mother trees were analyzed here because few of them set fruits, which also suffered high predation. No difference was observed between the population multilocus outcrossing rate (t mp = 0.953 ± 0.040) and the average single locus rate (t sp = 0.968 ± 0.132). The four mother trees were highly outcrossed (t m ~ 1). Two out of five loci showed departures from the Hardy-Weinberg Equilibrium (HWE) expectations, and the same results occurred with the mixed-mating model. Besides the low number of trees analyzed, the proportion of loci in HWE suggests random mating in the population. However, the pollen pool was heterogeneous among families, probably due to both the small sample number and the flowering of trees at different times of the flowering season. Reproductive phenology of the population and the results presented here suggest, at least for part of the population, a long-distance pollen movement, around 1,000 m.

Gap‐phase dynamics and coexistence of a long‐lived pioneer and shade‐tolerant tree species in the canopy of an old‐growth coastal temperate rain forest of Chiloé Island, Chile

SummaryAim A major question with regard to the ecology of temperate rain forests in south‐central Chile is how pioneer and shade‐tolerant tree species coexist in old‐growth forests. We explored the correspondence between tree regeneration dynamics and life‐history traits to explain the coexistence of these two functional types in stands apparently representing a non‐equilibrium mixture.Location This study was conducted in northern Chiloé Island, Chile (41.6° S, 73.9° W) in a temperate coastal rain forest with no evidence of stand disruption by human impact.Methods We assessed stand structure by sampling all stems within two 50 × 20 m and four 5 × 100 m plots. A 600‐m long transect, with 20 uniformly spaced sampling points, was used to quantify seedling and sapling densities, obtain increment cores, and randomly select 10 tree‐fall gaps. We used tree‐ring analysis to assess establishment periods and to relate the influences of disturbances to the regeneration dynamics of the main canopy species.Results Canopy emergent tree species were the long‐lived pioneer Eucryphia cordifolia and the shade‐tolerant Aextoxicon punctatum. Shade‐tolerant species such as Laureliopsis philippiana and several species of Myrtaceae occupied the main canopy. The stem diameter distribution for E. cordifolia was distinctly unimodal, while for A. punctatum it was multi‐modal, with all age classes represented. Myrtaceae accounted for most of the small trees. Most tree seedlings and saplings occurred beneath canopy gaps. Based on tree‐ring counts, the largest individuals of A. punctatum and E. cordifolia had minimum ages estimated to be &gt; 350 years and &gt; 286 years, respectively. Shade‐tolerant Myrtaceae species and L. philippiana had shorter life spans (&lt; 200 years). Most growth releases, regardless of tree species, were moderate and have occurred continuously since 1750.Main conclusions We suggest that this coastal forest has remained largely free of stand‐disrupting disturbances for at least 450 years, without substantial changes in canopy composition. Release patterns are consistent with this hypothesis and suggest that the disturbance regime is dominated by individual tree‐fall gaps, with sporadic multiple tree falls. Long life spans, maximum height and differences in shade tolerance provide a basis for understanding the long‐term coexistence of pioneer and shade‐tolerant tree species in this coastal, old‐growth rain forest, despite the rarity of major disturbances.

Seed rain of fleshy and dry propagules in different habitats in the temperate rainforests of Chiloe Island, Chile

In temperate rainforests on Chiloé Island in southern Chile (42°S), most canopy trees bear fleshy, avian-dispersed propagules, whereas emergent tree species have dry, wind-borne propagules. In the present study, the following hypothesis was tested: regardless of species, fleshy propagules are deposited in greater numbers in canopy gaps and in forest margins and hence have a more heterogeneous seed shadow than wind-dispersed propagules. To test this hypothesis, the seed rains of these two types of propagules were compared in the following forest habitats: (i) tree-fall gaps (edges and centre); (ii) forest margins with adjacent pastures; and (iii) under closed canopy (forest interior). Seed collectors (30-cm diameter) were placed in two (15 and 100 ha) remnant forest patches (n = 60–100 seed collectors per patch) distributed in the four habitats. Seeds were retrieved monthly from each collector during two reproductive seasons (1996, 1997). In both years, the seed rain was numerically dominated by two species with dry propagules (Laureliopsis philippiana and Nothofagus nitida) and three species with fleshy fruits (Drimys winteri, Amomyrtus luma, and Amomyrtus meli). The seed shadows of the two species with dry, wind-dispersed seeds differed markedly. Seeds of L. philippiana were deposited predominantly in canopy openings, whereas N. nitida seeds fell almost entirely in the forest interior. The fleshy-fruited species, Drimys and Amomyrtus spp., had similar seed deposition patterns in the various habitats studied, but the between-year differences in seed rain were greater in Drimys winteri than in Amomyrtus spp. Although no more than 10% of fleshy-fruited propagules reached the margins of the patch, approximately 7% of these were carried there by birds. Every year, canopy gaps (pooling data from edges and centres) concentrated approximately 60% of the total seed rain of both propagule types in both forest patches. Forest margins received less than 20% of the total seed rain, which was largely dominated by fleshy-fruited species. Seed shadows were a species-specific attribute rather than a trait associated with propagule type and dispersal mode.

Vascular Epiphyte Communities in the Inner‐Crown of Hyeronima alchorneoides and Lecythis ampla at La Selva Biological Station, Costa Rica

ABSTRACTThe community composition and percent cover of vascular epiphytes were examined in relation to photosynthetic photon flux density (PFD), temperature, vapor pressure, and tree characteristics in the inner‐crown of two emergent tree species, Hyeronima alchorneoides and Lecythis ampla, at La Selva Biological Station, Costa Rica. A total of 53 species were found in a total sampled branch area of 32 m2 in eight trees—four trees per species. Community composition varied both among individuals of the same tree species and between tree species. However, percent cover patterns of vascular epiphytes were significantly different between the two tree species; Hyeronima had a significantly greater percent cover of epiphytes than Lecythis. The higher percent light transmittance as well as lower humidity in Lecythis are likely causes of its lower percent cover of epiphytes.

Inner‐crown Microenvironments of Two Emergent Tree Species in a Lowland Wet Forest1

ABSTRACTVascular epiphyte communities, comprising up to 25 percent of tropical forest flora, contribute to plant diversity and thus ecosystem‐level processes; however, one of the proximal determinants of those communities, microclimate, is little studied. Here we present the first comprehensive study of microclimates in the inner crowns of two emergent tree species, Hyeronima alchorneoides and Lecythis ampla, at La Selva Biological Station, Costa Rica. We examined photon flux density, temperature, vapor pressure, and humidity in inner‐crown branches during the wet and dry seasons and during the wet‐season leafless phase of Lecythis. In both seasons, the percentage daily PFD in foliated Lecythis crowns (9%, wet season; 11%, dry season) was significantly higher than in Hyeronima crowns (5%, both seasons), with the leafless wet‐season PFD of Lecythis reaching 23 percent of full sun. Temperature and vapor pressure varied less in Hyeronima than in Lecythis crowns during the dry season. Microenvironmental conditions for epiphytes within Hyeronima crowns were more spatially and temporally homogeneous and were more buffered from ambient conditions than within Lecythis crowns. Growing conditions within the crowns of the same trees and among different trees were measurably different and are likely to affect the structure and composition of the resident epiphyte communities.

DIURNAL CHANGES OF PHOTOSYNTHETIC CHARACTERISTICS AND CHLOROPHYLL FLUORESCENCE IN CANOPY LEAVES OF FOUR DIPTOCARP SPECIES UNDER EX_SITU CONSERVATION

Dipterocarps dominate the canopy of tropical rainforest of Southeast Asia. They are not only the world's main source of hardwood timber, but their canopy leaves are main organs for global carbon sequestration. Due to anthropogenic activities, many species of dipterocarps are threatened. Because of this situation, ex-situ conservation efforts were employed to conserve the genetic resources of several dipterocarps. In this study, four dipterocarp species, Dipterocarpus retusus, Hopea hainanensis, Parashorea chinensis (emergent tree species in the rainforest) and Vatica xishuangbannaensis, were selected as study species that had been transplanted in 1981 to an ex-situ dipterocarp conservation forest in Xishuangbanna Tropical Botanical Garden. We measured the diurnal changes in photosynthetic rates, parameters of chlorophyll fluorescence, and morphological traits of their canopy leaves at 15-21 m height during the rainy season of 2004. The results indicated that the maximum photosynthetic rates (Pmax) per unit leaf area (7.5 to 18.1 μmol·m~-2·s~-1) and mass (89.08 to 150.82 nmol·g~-1 DW·s~-1), dark respiration rates (Rd), light saturation point (LSP), light compensation point (LCP) and leaf morphological traits differed significantly among species. Photosynthesis in the four species was depressed at midday. The results revealed that stomatal closure induced by high leaf-to-air vapor pressure deficit (LAVPD) led to photosynthetic depression at midday. Quantum yields of photosystem II (ΦPSⅡ) in four dipterocarp species decreased significantly at midday, indicating that photoinhibition occurred. However, their PSⅡ values recovered to the early morning value by sunset, indicating that photoinhibition was reversible. The nonphotochemical quenching rate (NPQ) increased significantly in D. retusus, H. hainanensis and V. xishuangbannaensis, indicating that NPQ was used mainly to dissipate excess light energy absorbed by PSⅡ. At midday, the electron transport rate (ETR) in P. chinensis was maintained at high levels, while its photosynthetic rate decreased, suggesting that a large proportion of electrons were allocated to photorespiration. Thus photorespiration was the main mechanism protecting the photosynthetic apparatuses of P. chinensis during the midday photosynthesis depression. Other parameters, such as leaf area, size and density of stomata, and total chlorophyll content, also were measured at the same time. There was a general ranking of Pmax in the following order from highest to lowest: D. retusus, P. chinensis, H. hainanensi, V. xishuangbannaensis. Based on the diurnal changes in chlorophyll fluorescence, both leaf stomatal limitations and non-stomatal effects played an important role to prevent photodamage during the midday depression of photosynthesis brought by the high irradiances, high air temperature, low humidity, and so on. The high midday leaf water potential of the four species showed that water limitations had no influence on photosynthetic rates.

Spatial structure of Aspidosperma polyneuron in two semi‐deciduous forests in Southeast Brazil

Abstract. Description of the spatial structure of vegetation is the first step in generating hypotheses regarding underlying processes. It is also important to take into account variation in spatial structure between different localities to be able to distinguish between life history traits and the influence of environment on population processes. Correlogram analysis was used to examine spatial recruitment and mortality patterns of Aspidosperma polyneuron, an emergent tree species, at Reserva Municipal de Santa Genebra (SG), a forest fragment in southeast Brazil. The spatial structure of individuals was compared with two areas with similar physiognomy, one in the same forest and another at Mata do Ribeirão Cachoeira (RC), a semi‐deciduous forest located ca. 14 km away. Seedling, sapling and adult mortality occurred in clumps, while seedling recruitment occurred mostly in one region of the area. The spatial pattern varied among the three study areas, and the differences were higher between fragments than within SG. The adults showed a negative correlation in space with saplings and seedlings in one of the SG areas, which could be a consequence of intraspecific competition, or the influence of density or distance dependent natural enemies. However, this pattern was not observed in the other areas. The results suggest that the mechanisms governing the spatial population dynamics of A. polyneuron vary among nearby and similar localities.

Spatial structure of Aspidosperma polyneuron in two semi-deciduous forests in Southeast Brazil

Abstract Description of the spatial structure of vegetation is the first step in generating hypotheses regarding underlying processes. It is also important to take into account variation in spatial structure between different localities to be able to distinguish between life history traits and the influence of environment on population processes. Correlogram analysis was used to examine spatial recruitment and mortality patterns of Aspidosperma polyneuron, an emergent tree species, at Reserva Municipal de Santa Genebra (SG), a forest fragment in southeast Brazil. The spatial structure of individuals was compared with two areas with similar physiognomy, one in the same forest and another at Mata do Ribeirao Cachoeira (RC), a semi-deciduous forest located ca. 14 km away. Seedling, sapling and adult mortality occurred in clumps, while seedling recruitment occurred mostly in one region of the area. The spatial pattern varied among the three study areas, and the differences were higher between fragments than w...