Lowland Tropical Forest Trees Research Articles

Agricultural Foam as a Propagation Substrate for Lowland Tropical Forest Tree Species

Agricultural Foam as a Propagation Substrate for Lowland Tropical Forest Tree Species

Heterospecific and conspecific associations of trees in lowland tropical forest of New Guinea

Abstract. Murdjoko A, Jitmau MM, Djitmau DA, Siburian RHS, Ungirwalu A, Wanma AO, Mardiyadi Z, Rumatora A, Mofu WY, Sineri AS, Fatem SM, Worabai D, May NL, Tokede MJ, Warmetan H, Wanggai CB, Wanma JF, Sirami EV, Paembonan JB, Unenor E, Kuswandi R, Lekitoo K, Khayati L, Benu NMH, Tambing J, Saragih ASB. 2020. Heterospecific and conspecific associations of trees in lowland tropical forest of New Guinea. Biodiversitas 21: 4405-4418. The vegetation in the tropical rainforest of New Guinea consists of a large number of species that interact with each other within and among species. While several studies have attempted to reveal the diversity of flora of New Guinea, little is known about plant communities that develop associations. This study aimed to investigate the associations of tree species in lowland tropical forest in New Guinea. The associations depicted in this study were in the form of conspecific associations (among small and large individuals within same species) and heterospecific (among individuals of different species and divided into under and upper story). We established 48 rectangular plots created in Murkim and Teiraplu as part of Pegunungan Bintang Regency, Papua Province. Canonical correspondence analysis (CCA) was used to analyze heterospecific and conspecific associations. The results showed that the understory and upper story vegetation had different patterns of heterospecific association. The understory configured three heterospecific associations, consisting of 5, 13, and 90 species, while the upper story formed four heterospecific associations with 4, 8, 11, and 63 species. The analysis of conspecific associations showed of 149 tree species recorded in the study sites, only 66 species that had both small and large individuals, displaying the pattern of conspecific association. Among them, 41 species had positive associations while 25 species had negative associations. Our findings enrich the knowledge in theoretical ecology of tropical forests, especially in New Guinea.

Leaf litter inputs reinforce islands of nitrogen fertility in a lowland tropical forest

The role of lowland tropical forest tree communities in shaping soil nutrient cycling has been challenging to elucidate in the face of high species diversity. Previously, we showed that differences in tree species composition and canopy foliar nitrogen (N) concentrations correlated with differences in soil N availability in a mature Costa Rican rainforest. Here, we investigate potential mechanisms explaining this correlation. We used imaging spectroscopy to identify study plots containing 10–20 canopy trees with either high or low mean canopy N relative to the landscape mean. Plots were restricted to an uplifted terrace with relatively uniform parent material and climate. In order to assess whether canopy and soil N could be linked by litterfall inputs, we tracked litter production in the plots and measured rates of litter decay and the carbon and N content of leaf litter and leaf litter leachate. We also compared the abundance of putative N fixing trees and rates of free-living N fixation as well as soil pH, texture, cation exchange capacity, and topographic curvature to assess whether biological N fixation and/or soil properties could account for differences in soil N that were, in turn, imprinted on the canopy. We found no evidence of differences in legume communities, free-living N fixation, or abiotic properties. However, soils beneath high canopy N assemblages received ~ 60% more N via leaf litterfall due to variability in litter N content between plot types. The correlation of N in canopy leaves, leaf litter, and soil suggests that, under similar abiotic conditions, litterfall-mediated feedbacks can help maintain soil N differences among tropical tree assemblages in this diverse tropical forest.

Rainforest trees respond to drought by modifying their hydraulic architecture.

Increased drought is forecasted for tropical regions, with severe implications for the health and function of forest ecosystems. How mature forest trees will respond to water deficit is poorly known. We investigated wood anatomy and leaf traits in lowland tropical forest trees after 24 months of experimental rainfall exclusion. Sampling sun‐exposed young canopy branches from target species, we found species‐specific systematic variation in hydraulic‐related wood anatomy and leaf traits in response to drought stress. Relative to controls, drought‐affected individuals of different tree species variously exhibited trait measures consistent with increasing hydraulic safety. These included narrower or less vessels, reduced vessel groupings, lower theoretical water conductivities, less water storage tissue and more abundant fiber in their wood, and more occluded vessels. Drought‐affected individuals also had thinner leaves, and more negative pre‐dawn or mid‐day leaf water potentials. Future studies examining both wood and leaf hydraulic traits should improve the representation of plant hydraulics within terrestrial ecosystem and biosphere models, and help fine‐tune predictions of how future climate changes will affect tropical forests globally.

Comparison of forest regeneration in two sites with different primate abundances in Northwestern Ecuador

There is increasing evidence that large-bodied primates play important roles as seed dispersers and in the maintenance of tree diversity in forest ecosystems. In this study we compared forest regeneration at two sites with differing primate abundances in the Ecuadorian Chocoan rainforest. We predicted: (1) significant differences in primate abundance between the two sites; (2) higher understory tree species richness and density at the site with greater primate abundance; (3) the site with lower primate abundance characterized by tree species dispersed by non-primate biotic agents and/or abiotic factors. We compared two sites, Tesoro Escondido (TE) a campesino cooperative, and the El Pambilar (EP) wildlife refuge that both maintain populations of mantled howler monkey (Alouatta palliata), the brown-headed spider monkey (Ateles fusciceps fusciceps) and the capuchin monkey (Cebus capucinus). We characterized canopy structure by point-quadrant sampling, determined primate abundance and sampled seedlings/saplings in 1 m2 plots, classifying tree species based on three dispersal syndromes: adapted for primate dispersal, dispersed by other biological agents, and abiotic dispersal. We compared sites in terms of primate abundance (groups and individuals observed per day) and regeneration characteristics (overall density, species richness, and dispersal syndrome). We carried out within site comparisons and constructed understory tree species accumulation curves. Overall the forests were structurally similar - with significantly higher densities of A. f. fusciceps at TE. Encounter rates for the other two primate species were similar at both sites. Understory tree density and species richness was significantly higher in TE with no stabilization of tree species accumulation curves. The species accumulation curve for understory trees at EP stabilized. Higher densities and species richness of primate dispersed tree species were observed at TE, with non-primate biotically dispersed tree species the dominant dispersal syndrome at both sites. Our observations are consistent with those from other studies investigating the role of large-bodied frugivorous primates in forest regeneration, and point to a general pattern: future lowland tropical forest tree diversity depends on maintaining robust populations of large primate species in these systems. It is highly probable that the maintenance of high levels of tree diversity in Chocoan rainforests is dependent on the conservation of its largest resident primate, the critically endangered brown-headed spider monkey (A. f. fusciceps).

Effects of seed traits on the success of direct seeding for restoring southern Thailand’s lowland evergreen forest ecosystem

The success of direct seeding, as a low-cost approach to forest restoration, varies with tree species and seed characteristics. A system to predict which tree species are likely to be suitable for direct seeding would therefore be useful for improving forest restoration projects. Therefore, this study aimed to determine the effects of seed traits on the success of direct seeding to restore tropical forest in southern Thailand. Seeds of 19 indigenous lowland tropical forest tree species were collected, from both the east and west sides of the Thailand peninsular and the following parameters measured: seed size, shape, coat thickness and moisture content. Field trials were established to determine seed germination rates and to calculate a “direct seeding suitability score” for each species, which combined seedling establishment and growth rates. Seed size, shape and moisture content were associated with germination percentage. Species with higher seedling survival tended to have large or intermediate-sized seeds, round or oval seeds and seeds with low or medium moisture content. Only seed coat thickness was significantly correlated with the suitability score (r = 0.65, p 0.4 mm coincided with higher rank suitability score. These conditions successfully predicted the success or failure of direct seeding for 15 out of 19 species tested. Eight tree species are recommended as suitable for restoring lowland evergreen forest ecosystems in southern Thailand, by direct seeding.

Nutrients limit photosynthesis in seedlings of a lowland tropical forest tree species

We investigated how photosynthesis by understory seedlings of the lowland tropical tree species Alseis blackiana responded to 10 years of soil nutrient fertilization with N, P and K. We ask whether nutrients are limiting to light and CO(2) acquisition in a low light understory environment. We measured foliar nutrient concentrations of N, P and K, isotopic composition of carbon (δ(13)C) and nitrogen (δ(15)N), and light response curves of photosynthesis and chlorophyll fluorescence. Canopy openness was measured above each study seedling and included in statistical analyses to account for variation in light availability. Foliar N concentration increased by 20% with N addition. Foliar P concentration increased by 78% with P addition and decreased by 14% with N addition. Foliar K increased by 8% with K addition. Foliar δ(13)C showed no significant responses, and foliar δ(15)N decreased strongly with N addition, matching the low δ(15)N values of applied fertilizer. Canopy openness ranged from 0.01 to 6.71% with a mean of 1.76 ± 0.14 (± 1SE). Maximum photosynthetic CO(2) assimilation rate increased by 9% with N addition. Stomatal conductance increased with P addition and with P and K in combination. Chlorophyll fluorescence measurements revealed that quantum yield of photosystem II increased with K addition, maximum electron transport rate trended 9% greater with N addition (p = 0.07), and saturating photosynthetically active radiation increased with N addition. The results demonstrate that nutrient addition can enhance photosynthetic processes, even under low light availability.

Coordination of leaf and stem water transport properties in tropical forest trees

Stomatal regulation of transpiration constrains leaf water potential (Psi(L)) within species-specific ranges that presumably avoid excessive tension and embolism in the stem xylem upstream. However, the hydraulic resistance of leaves can be highly variable over short time scales, uncoupling tension in the xylem of leaves from that in the stems to which they are attached. We evaluated a suite of leaf and stem functional traits governing water relations in individuals of 11 lowland tropical forest tree species to determine the manner in which the traits were coordinated with stem xylem vulnerability to embolism. Stomatal regulation of Psi(L) was associated with minimum values of water potential in branches (Psi(br)) whose functional significance was similar across species. Minimum values of Psi(br) coincided with the bulk sapwood tissue osmotic potential at zero turgor derived from pressure-volume curves and with the transition from a linear to exponential increase in xylem embolism with increasing sapwood water deficits. Branch xylem pressure corresponding to 50% loss of hydraulic conductivity (P (50)) declined linearly with daily minimum Psi(br) in a manner that caused the difference between Psi(br) and P (50) to increase from 0.4 MPa in the species with the least negative Psi(br) to 1.2 MPa in the species with the most negative Psi(br). Both branch P (50) and minimum Psi(br) increased linearly with sapwood capacitance (C) such that the difference between Psi(br) and P (50), an estimate of the safety margin for avoiding runaway embolism, decreased with increasing sapwood C. The results implied a trade-off between maximizing water transport and minimizing the risk of xylem embolism, suggesting a prominent role for the buffering effect of C in preserving the integrity of xylem water transport. At the whole-tree level, discharge and recharge of internal C appeared to generate variations in apparent leaf-specific conductance to which stomata respond dynamically.

Ecology of the arboreal tropidurid lizard Tropidurus (=Plica) umbra in the Amazon region

The tropidurid lizard Tropidurus umbra lives on medium-sized trees in lowland tropical forest of the Amazon region. Individuals may be active on tree trunks in sun or shade, with most activity occurring from 11:00 to 13:00. Body temperatures average 29.1 °C. The diet consists nearly exclusively of ants and there is no relationship between prey size and lizard size. Females reach sexual maturity at 79 mm snout–vent length (SVL) and males at 78 mm SVL. Although there appears to be no sexual dimorphism in SVL, males have relatively larger heads than females. Clutch size is usually two eggs and females appear to produce more than one clutch per season. Comparisons with other studied tropidurid lizards suggest that dietary specialization on ants, reduced sexual dimorphism, and reduced clutch size are derived characters.

Stomatal and environmental control of transpiration in a lowland tropical forest tree

ABSTRACTStomatal control of crown transpiration was studied in Anacardium excelsum, a large‐leaved, emergent canopy species common in the moist forests of Central and northern South America. A construction crane equipped with a gondola was used to gain access to the uppermost level in the crown of a 35‐m‐tall individual. Stomatal conductance at the single leaf scale, and transpiration and total vapour phase conductance (stomatal and boundary layer) at the branch scale were measured simultaneously using the independent techniques of porometry and stem heat balance, respectively. This permitted the sensitivity of transpiration to a marginal change in stomatal conductance to be evaluated using a dimensionless coupling coefficient (1‐ω) ranging from zero to 1, with 1 representing maximal stomatal control of transpiration. Average stomatal conductance varied from 0.09 mol m−2 s−1 during the dry season to 0.3 mol m−2 s−1 during the wet season. Since boundary layer conductance was relatively low (0.4 mol m−2 s−1), 1‐ω ranged from 0.46 during the dry season to only 0.25 during the wet season. A pronounced stomatal response to humidity was observed, which strongly limited transpiration as evaporative demand increased. The stomatal response to humidity was apparent only when the leaf surface was used as the reference point for measurement of external vapour pressure. Average transpiration was predicted to be nearly the same during the dry and wet seasons despite a 1 kPa difference in the prevailing leaf‐to‐air vapour pressure difference. The patterns of stomatal behaviour and transpiration observed were consistent with recent proposals that stomatal responses to humidity are based on sensing the transpiration rate itself.

A Structural Approach to the Function of Buttresses of Quararibea Asterolepis

Buttresses of lowland tropical forest trees have long been thought to serve as structural supports. This morphometrical study of the buttresses and other characteristics of Quararibea asterolepis demonstrates and describes the nature of the support role played by buttresses. Buttresses tend to grow on the side of the tree that faces the prevailing winds, thereby functioning as tension members that help prevent the tree from being blown over. The buttresses become proportionately larger as the tree grows, providing the tree with greater support as its crown becomes exposed to the stronger winds of the upper forest canopy. In particular, buttress height increases much faster than tree height. This disproportionate increase reduces by °15% the potential vulnerability of the trunk to snapping or twisting under stress due to winds. On the other hand, no specific relationship independent of tree size can be demonstrated between the length of a buttress and the radius of the crown above or opposite that buttress. There is thus no evidence that buttresses counteract stresses due to crown asymmetries of a particular trees.

Mycorrhizae Influence Tropical Succession

Most vascular plants depend to some extent on vesicular-arbuscular (V-A) mycorrhizae for mineral uptake, although a few species do not. Some mycotrophic plants cannot grow without mycorrhizae; others grow better without mycorrhizae in fertile soils, but benefit from mycorrhizae in poor soils. Thus, the mycorrhizal fungus content and the fertility of soil influence the occurrence of plant species. Because V-A mycorrhizal fungi depend on mycotrophic plants for carbon, and because they produce few spores which may survive only a short time in the lowland humid tropics, plant community composition in turn affects the mycorrhizal fungus content of soil. This influences the further course of plant succession by affecting which species of plants can subsequently occur in the community. Pool soils may favor alternate stable communities. If mycorrhizal fungi are present, obligately mycotrophic species are the best competitors and should dominate communities. They support an abundance of mycorrhizal fungi, ensuring the continued superiority of obligate mycotrophs. If mycorrhizal fungi are absent, non-mycorrhizal species will comprise the community. Even if mycorrhizal fungi are subsequently introduced, these plants will not support them, favoring persistence of the non-mycorrhizal species. On fertile soils, facultative mycotrophs are most common. They will support infection if mycorrhizal fungi are available when the soils age and fertility declines, paving the way for their replacement by obligate mycotrophs. If mycorrhizal fungi are unavailable, facultatively mycotrophic species will be replaced by non-mycorrhizal plants. Non-mycorrhizal plants may also derive competitive advantage where mycorrhizal fungi are present, from not needing to await infection to start growing. Thus, pioneer species are often non-mycorrhizal. Seral species tend to be facultative mycotrophs, and most lowland tropical forest trees tend to be obligately mycotrophic. Ectomycorrhizal individuals are likely to occur in abundance in nutrient-starved or disturbed habitats, although ectomycorrhizal species are rare in the lowland tropics. Ectomycorrhizal associates may influence tropical succession by lowering populations of V-A mycorrhizal fungi. THIS PAPER SUGGESTS how interactions between vascular plants and mycorrhizal fungi may influence succession. I discuss: 1) how plants depend on mycorrhizae to different degrees for mineral uptake; 2) how different dependence on mycorrhizae might affect the competitive success of plants in soils with different mycorrhizal fungus contents and mineral availabilities, and as a consequence, might influence plant community composition; 3) how plant communities, in turn, may affect mycorrhizal fungus populations; and 4) how further development of a plant community thereby might be influenced. There is evidence for the first three of these interactions; the fourth, consequent successional change, is based on inference. I focus on vesicular-arbuscular (V-A) mycorrhizal associations in the lowland tropics. Ectomycorrhizal associations, rare in the lowland tropics, are discussed as exceptions, because compared to V-A mycorrhizal fungi ectomycorrhizal fungi are more host-specific, disperse better, and some species may not be as dependent on their hosts. PLANTS DIFFER IN THEIR DEPENDENCE ON MYCORRHIZAE Most species of plants are capable of associating with fungi of a single zygomycetous family, the Endogonaceae, to form V-A mycorrhizae (Gerdemanin 1968). By improving mineral nutrition, especially if substrate mineral availability is low or imbalanced, V-A mycorrhizae can increase the growth of host plants (Mosse 1973b), can improve water uptake and resistance to temporary wilting (Safir, Boyer and Gerdemann 1972; Menge et al. 1978), and may improve seedling survival (Baylis 1959; Gerdemann 1965; Kleinschmidt and Gerdemann 1972; Janos 1975a, 1975b, 1977). Mycorrhizae seem to minimize the expense to the host of seeking-out minerals (Harley 1975) even though the hosts supply carbon to V-A mycorrhizal fungi (Ho and Trappe 1973). The external hyphae of mycorrhizae increase mineral uptake, especially uptake of phosphorus which is relatively immobile in soil, probably by providing a large, well-distributed absorbing surface (Mosse 1973b). The advantage of an extensive absorbing surface is diminished in fertile soils (Voigt 1971), however, and continued support of mycorrhizae in fertile soils may decrease host growth (Cooper

THE REPRODUCTIVE BIOLOGY OF CUPANIA GUATEMALENSIS RADLK. (SAPINDACEAE).

Intraspecific floral polymorphism is of widespread occurrence in flowering plants. Perfect, staminate, and pistillate flowers may be found on the same or different plants in diverse combinations as exemplified by monoecy, dioecy, androdioecy, gynodioecy, polygamy and the like; in addition, within perfect-flowered species, polymorphism may exist in the form of distyly and tristyly. It is generally presumed that floral polymorphisms increase the probability of outcrossing. The level of outcrossing, however, has not been measured in any zoophilous species with polymorphic flowers except for some heterostylous species (Ornduff, 1971, 1975). Floral polymorphism, by introducing spatial variation in floral rewards, also influences the foraging behavior of pollinators. The foraging behavior of pollinators, in turn, is likely to influence not only gene flow but also the evolution of floral polymorphism itself. Yet it is somewhat surprising that the effect of floral polymorphism on the foraging behavior of pollinators has not so far been examined. This paper describes the reproductive biology of a monoecious species, Cupania guatemalensis Radlk. (Sapindaceae), a small tree found in lowland tropical forests of Central America. It examines the pattern of spatial and temporal variation in the relative frequencies of staminate and pistillate flowers at the individual and population levels; differences in floral reward of staminate and pistillate flowers; differences in the foraging behavior and visitation rates of pollinators on staminate and pistillate flowers; and the effect of flowering behavior and floral polymorphism on the foraging behavior of pollinators and the degree of outcrossing. In addition, the floral phenology of some other members of the Sapindaceae is interpreted in the light of findings reported here. The investigations are part of a wider study of the breeding systems of lowland tropical forest trees (Bawa, 1974; Bawa and Opler, 1975).