Leaf and twig anatomy of Eriope, a xeromorphic genus of Labiatae

The leaf and twig anatomy of 25 species of the genus Eriope were studied. The twig anatomy is very uniform apart from the level of formation of early layers of cork. Leaf anatomy shows considerable variation between the species, and this is correlated to some extent with the extreme habit range from trees to woody herbs. Characters of the lamina that show variation are: trichome type and frequency, cuticular markings, leaf dorsiventral or isobilateral, presence of adaxial stomata, presence of a hypodermis, number of layers of adaxial palisade mesophyll cells, occurrence of large bundles of phloem fibres at main veins, type of areolation and marginal venation. Petiole vasculature is simple and generally with either four distinct vascular bundles or two vascular arcs. The most xeromorphic species are usually woody herbs or sub-shrubs, and tend to have thick, isobilateral leaves with large bundles of phloem fibres and few hairs, or strongly dorsiventral leaves with a hypodermis and stomata in deep abaxial hair-lined depressions. The correlation of xeromorphic characters with environmental conditions is discussed. Leaf anatomy is of limited value in elucidating relationships within the genus.     

Leaf anatomy of the subtribe Hyptidinae (Labiatae)

The leaf anatomy of the subtribe Hyptidinae (Labiatae), which consists of four small genera and the largr genus Hyplis , is dercribed. The leaves may be dorsiventral or isobilateral. Variable characters of the lainina include: frequency and forms of trichomes, cuticular markings, presence of adaxial stoinata, thickness of leaf, thickness of adaxial epidermis, presence of a hypodermis, occurrence of sclcrified tissues (especially sclerified bundle sheath extensions, phloem and xylem fibres), mesophyll structure and venation pattern. Petiole vasculature varies from simple to complex, sometimes with medullary traces present. Most of the variable characters are related to xeromorphy and are tax-onomically useful within the framework of the present classification.     

西双版纳热带山地雨林生物量研究

观测了西双版纳山地气候,建立了山地雨林生物量回归方程,调查了海拔1 100~1 820 m范围5块样地(面积0.16~0.25 hm2)的热带山地雨林生物量。结果表明,海拔1 105和1 610 m的年平均温度分别为20.1和16.6℃,年降雨量分别为1 659和2 011 mm,旱季(11~4月)降雨量分别为295和283mm,年平均相对湿度分别为81%和84%;5块样地生物量变化为256.4~368.6 t.hm-2,平均为312.6t.hm-2,其中乔木占97.1%、木质藤本占1.2%、幼树和灌木占1.3%、草本和幼苗占0.4%;采用热带季节雨林生物量回归方程估计山地雨林生物量,会使得总生物量以及树干和树根生物量高估38.3%~61.5%,树枝生物量低估7.6%~30.8%。可见,西双版纳山地海拔增加导致雨季降雨量增加,山地雨林生物量较热带季节雨林降低32.6%,季节雨林生物量方程不适用于山地雨林。     

Leaf anatomy plasticity of Alchornea triplinervia (Euphorbiaceae) under distinct light regimes in a Brazilian montane Atlantic rain forest

 Alchornea triplinervia trees occur in a montane Atlantic rainforest at the Macaé de Cima State Ecological Reserve (Nova Friburgo, RJ, Brazil). They are found in two adjacent secondary forests at distinct successional stages: a late-secondary (shaded and humid) and an early-secondary forest (drier, higher light intensities reaching the understory). Leaf samples collected in these environments were compared in regard to various anatomic parameters. Histochemical tests, anatomic measurements and counting indicated no significant variation for the basic leaf anatomy. Nevertheless, as compared to the late-secondary forest, the leaves of the early-secondary forest individuals showed an increased bulk of sclerenchyma at the main nervation and petiole, gelatinous fibers with hygroscopic walls all along the central vascular system, thicker cuticle, a higher abaxial stomatal density, abundance of tannin in the mesophyll, a significantly thicker palisade and spongy parenchyma, and compactation of the spongy parenchyma. This anatomical variation indicates an increased xeromorphism of leaves under the drier conditions of the early-secondary forest. Leaf anatomy plasticity may contribute to the high ecological plasticity of this widespread neotropical species. Received: 11 November 1996 / Accepted: 5 February 1997     

Leaf Gas Exchange in Canopy Species of a Venezuelan Cloud Forest

Tropical cloud forests are considered humid ecosystems with frequent cloud cover down to the ground surface. However, seasonal variation in precipitation may induce short-term water stress. For canopy leaves, this water stress may also be a consequence of large atmospheric vapor pressure deficits. The objective of this work was to study five canopy cloud forest species to determine if there are restrictions to leaf gas exchange as a consequence of seasonality in precipitation and to daily water deficit due to air evaporative demand mainly during maximum incoming radiation hours. Seasonal daily courses of microclimatic variables (air temperature, relative humidity, photosynthetic photon flux density) and plant responses (leaf water potential, stomatal conductance, CO₂ assimilation rates, leaf nitrogen concentration) were measured at 2400 m asl in Monterrey, an intermontane valley of the Venezuelan Andes. A gradient in terms of responses to water stress conditions was observed between the species, with Clusia multiflora (a 46% reduction in stomatal conductance between seasons) as the most affected and Miconia resimoides (increased stomatal conductance) responding more favorably to slight water stress conditions. If we consider the limitations of water stress and/or light conditions on CO₂ assimilation we may arrange the species into those in which water stress conditions have a greater impact on leaf carbon gain, those where light conditions are determinant and one in which both water stress and light conditions may affect leaf carbon assimilation.     

海南五指山热带山地雨林植物物种多样性研究

王指山热带山地雨林的物种种类十分丰富,在１ｈｍ＾２样地中共出现５４个科,１００个属的乔木树种１７７种,１３３７个个体。区系地理分析表明属的分布区类型以热带分布型成分占优,为８９．０％,充分体现了五指山山地雨林的热带性质。多样性指数分析结果为：样地１Ｍａｒｇａｌｅｆ指数１７．８２２,Ｓｈａｎｎｏｎ－Ｗｉｅｎｅｒ指数５．６２１,均匀度０．８２３,Ｓｉｍｐｓｏｎ指数０．０５０,均匀度６．７７５,表明五指     

BRIEF COMMUNICATION Geographic parthenogenesis in a tropical forest tree

As evidenced by embryological studies, certain tropical tree species can reproduce asexually via seed; however, it has generally been assumed that such apomictic reproduction is facultative. Here I report the existence of a population of the lowland Malaysian rain forest tree Garcinia scortechinii King that consists entirely of pistillate individuals (40 female trees and no male trees recorded within a 25-ha area). This constitutes the first documented observation of a geographically segregated, obligately asexual population among wild tropical trees. Six additional Garcinia species showed a trend toward female bias relative to other dioecious tree species studied, an observation that is consistent with facultative apomixis. The more surprising result for G. scortechinii runs counter to the generalization that obligate apomicts occur only in environments in which the absence of competitors might enable persistence of taxa that lack genetic recombination through mixis.     

Hydraulic architecture and water use of selected species from a lower montane forest in Panama

 Plant water relations of nine woody species were studied in a lower montane rain forest in Panama. These data provide a partial test of the hypothesis that hydraulic architecture of lower montane species might limit transpiration and thus leaf size or nutrient transport (as suggested by J. Cavelier and E. G. Leigh, respectively). Diurnal variation in leaf transpiration was closely correlated with changes in net radiation. Peak transpiration rates (7 × 10^–5 kg s^–1 m^–2) were as high as peak transpiration rates from tropical lowland forests but mean daily water use [0.39 ± 0.08 (SEM) kg m^–2 day^–1] were mostly lower than comparable data from tropical lowland forests. Thus transpiration rates are sufficiently high for sufficiently long periods to make it unlikely that nutrient transport is limited by transpiration. Another objective of this study was a comparison of two different methods to measure hydraulic conductance (K_h = flow rate per unit pressure gradient) and leaf specific conductance of stem segments (K_L = K_h/leaf area distal to the segment). The results obtained with the traditional conductivity apparatus and the high pressure flow meter method, yielded similar results in six out of seven cases. Received: 20 March / Accepted: 21 October 1997     

Changes in diversity along a successional gradient in a Costa Rican upper montane Quercus forest

Changes in terrestrial vascular plant diversity along a successional gradient were studied in a Costa Rican upper montane Quercus forest. In 1991 and 1992 species presence and cover were recorded in 12 successional 0.1 ha forest plots. A total of 176 species in 122 genera and 75 families were found. Asteraceae was the most speciose family. With the help of TWINSPAN three successional phases were classified: (i) Early Secondary Forest (ESF, 145 spp.), (ii) Late Secondary Forest (LSF, 130 spp.) and (iii) Primary Forest (PF, 96 spp.). Detrended Correspondence Analysis (DCA) species ordination using DECORANA illustrates that different ecological species groups can be distinguished along the time sequence. Alpha diversity (Shannon-Wiener index, among others) in ESF and LSF was significantly greater than in PF. This is probably explained by downslope migration of numerous sub(alpine) species to cleared and recently abandoned montane sites. Beta diversity applying Sørensen's similarity coefficients declined during succession. Using linear regression, the minimum time required for floristic recovery following disturbance and abandonment was calculated at 65.9 years. A comparison with other studies shows that secondary forests in upper montane Costa Rica can be as diverse as in neotropical lowlands.     

Microclimatic factors associated with elevational changes in army ant density in tropical montane forest

Abstract.  1. The density (rate of encountering foraging raids) and species richness of army ants (Formicidae: Ecitoninae, and behaviourally convergent Ponerinae) was measured in montane tropical forest. Above-ground and subterranean army ant raids were sampled using standard protocols at four sites across an elevational gradient (1200–1650 m above mean sea level) in and near cloud forest in the area of Monteverde, Costa Rica.
2. Mean ambient temperature differed among sites, and decreased with elevation. For the above-ground foraging army ant species, raid rates also declined with elevation. Surface army ant raid rates, however, were not affected by day to day weather variation within sites (temperature, cloud cover, or precipitation).
3. For the underground foraging army ant species, raid rates did not vary directionally with elevation, and subterranean raid rates were not affected by day to day weather variation within sites.
4. Army ant species richness was not directionally related to elevation, and species sharing among sites was generally high.
5. Army ant community structure changes with elevation in Neotropical montane forest, and the results suggest that the strongest effects are of temperature regimes on the density of raids. These findings provide a baseline against which to detect changes in army ant communities that may accompany directional climate change in tropical cloud forests.     

Photosynthesis and successional status of Costa Rican rain forest trees

Seven tree species from three different light environments in the wet lowland forests of Costa Rica were grown under controlled environment conditions to assess light related photosynthetic potentials. Light saturated photosynthesis rates were clearly related to light levels of the field environments. Mean saturated, net photosynthetic rates ranged from 6.8 to 11.3 to 27.7 mol m^–2 sec^–1 for plants from heavy shade, canopy light gaps and man-made clearings respectively. Light saturation of plants from clearings occurred at photosynthetic photon flux densities greater than 1000 mol m^–2 sec^–1 whereas plants from heavy shade environments became light saturated near 500 mol m^–2 sec^–1. Plants that normally occur in intermediate light environments were intermediate in light saturation levels. Mean maximum stomatal conductances ranged from 1.0 to 7.3 mm sec^–1 and followed a pattern similar to photosynthetic rates.     

Wind creates crown shyness,asymmetry, and orientation in a tropical montane oak forest

In a cloud forest dominated by Quercus costaricensis, the gap size between the crowns was consistent and crowns were asymmetrical, being elongated perpendicular to the prevailing wind direction. A wind storm of 20 m/s removed 1.5% of the leaves, consistent with the idea that wind abrasion shapes tree crowns.     

Hydrological properties of the epiphyte mass of a montane tropical rain forest,Colombia

The effect of a well-developed epiphytic vegetation on the interception of rainfall was investigated in an upper montane rain forest at an altitude of 3370 m in the Cordillera Central of the Colombian Andes. Total epiphyte mass was estimated at 12 tonnes dry weight per hectare, most of it being bryophytes and dead organic matter. The hydrological properties of the epiphyte mass were studied using detached branches. Water gain (during rainfall) and water loss (after experimental saturation) were determined gravimetrically in the field.Rain falling on epiphyte-covered branches was efficiently captured. Drainage of water (held temporarily in excess of the retention capacity) was very gradual. Water loss through evaporation was slow. The observations are in accordance with previously reported data for rainfall interception in the forest studied. The potentially large influence of the exceptionally high canopy storage capacity is restricted due to the clumped distribution of epiphytes and associated low turnover rates of water in the epiphyte mass.     

Biodiversity and carbon storage are correlated along a land use intensity gradient in a tropical montane forest watershed,Mexico

Tropical montane cloud forest landscapes are changing, and forest conversion to other land uses is a major driver of biodiversity loss. Land use intensification can lead to significant losses in biodiversity and carbon storage (C); however, the impacts may vary greatly depending on land use type, management practices, and environmental context. We investigated how biodiversity and C are related along a gradient of land use intensification characterized by four dominant land uses in the upper part of Antigua River watershed, Mexico. The land uses were montane cloud forest, secondary forest, and traditional and intensive shade coffee plantations. We determined tree species composition, diversity, ecosystem structure, wood density and C content in dominant tree species to assess aboveground biomass (AGB) and C storage within eight study sites across the land use intensity gradient. A total of 83 tree species was recorded. A canonical correspondence analysis indicated that land uses are separated by particular tree species assemblages. Forests had higher basal area, density, and biomass than coffee plantations, however, the traditional shade coffee plantation had values similar to secondary forest. Calculating C using the standard estimate of 50% of AGB resulted in an overestimation of stored C by 5.8 to 4.1% compared to calculations based on actual measurements. Carbon storage in AGB and biodiversity were strongly and positively related across the land use intensity gradient, although the distinction between the two different intensities of coffee plantation management was not consistently as clear as we had expected. Carbon was highest in forest, but secondary forests and traditional shade coffee plantation had similar C, while intensive coffee had the lowest C content. These results highlight the importance of considering the potential of low intensity land uses such as traditional coffee plantations to mitigate biodiversity loss and preserve ecosystem functions as part of conservation efforts.     

西双版纳热带山地常绿阔叶林蕨类植物多样性研究

基于4个50m×50m(包含400个5m×5m)样方调查,统计了蕨类植物的α多样性指数、优势度指数、相似性指数及β多样性指数。结果表明:在调查的1hm2西双版纳热带山地常绿阔叶林里,蕨类植物的物种丰富度为32种;不同样地蕨类植物丰富度指数、多样性指数、优势度指数及均匀度指数的变化趋势一致;该森林群落蕨类植物的物种多样性虽然不高,但优势种群显著;通过3个无人为干扰与1个受人为干扰样地的对比分析研究看出,该类森林遭受一定程度的人为干扰后,蕨类植物物种丰富度、多样性、优势度及相似性等均显著下降,其中物种多样性的降低尤为显著,既使群落的外貌、结构等恢复至接近原始林状态,蕨类植物丰富度及多样性也难以恢复,故此,保护原始的森林植被是保护该森林蕨类植物多样性的有效措施之一。     

Tropical montane forest ecotones: climate gradients, natural disturbance, and vegetation zonation in the Cordillera Central, Dominican Republic

Aim We examined relationships between climate–disturbance gradients and patterns of vegetation zonation and ecotones on a subtropical mountain range. Location The study was conducted on the windward slopes of the Cordillera Central, Dominican Republic, where cloud forest appears to shift in a narrow ecotone to monodominant forest of Pinus occidentalis. Methods Climate, disturbance and vegetation data were collected over the elevation range 1100–3100 m and in 50 paired plots along the ecotone. Aerial photographs were georeferenced to a high‐resolution digital elevation model in order to enable the analysis of landscape‐scale patterns of the ecotone. Results A Shipley–Keddy test detected discrete compositional ecotones at 2200 and 2500 m; the distributions of tree species at lower elevations were continuous. The elevation of the ecotone determined with aerial photographs was fairly consistent, namely ± 164 m (SD) over its 124‐km length, but it exhibited significant landscape variation, occurring at a lower elevation in a partially leeward, western zone. The ecotone also occurred significantly lower on ridges than it did in drainage gullies. Ecotone forest structure and composition differed markedly between paired plots. In pine paired plots, the canopy height was 1.7 times higher and the basal area of non‐pine species was 6 times lower than in the cloud forest directly below. Fire evidence was ubiquitous in the pine forest but rare in the abutting cloud forest. Mesoclimate changed discontinuously around the elevation of the ecotone: humidity and cloud formation decreased markedly, and frost frequency increased exponentially. Main conclusions The discreteness of the ecotone was produced primarily by fire. The elevational consistency of the ecotone, however, resulted from the overarching influence of mesoclimate on the elevational patterns of fire occurrence. Declining temperature and precipitation combine with the trade‐wind inversion to create a narrow zone where high‐elevation fires extinguish, enabling fire‐sensitive and fire‐tolerant taxa to abut. Once established, mesotopography and contrasting vegetation physiognomy probably reinforce this boundary through feedbacks on microenvironment and fire likelihood. The prominence of the pine in this study – and of temperate and fire‐tolerant taxa in subtropical montane forests in general – highlights the importance of climate‐disturbance–biogeography interactions in ecotone formation, particularly where fire mediates a dynamic between climate and vegetation.     

Leaf and photosynthetic characteristics of pioneer and forest species in tropical montane habitats

Gas exchange and chlorophyll a fluorescence measurements of expanding and adult leaves of four plant species were compared under field conditions. The pioneer species (PS) tended to have thinner leaves with lower nitrogen content and higher stomatal density compared to forest species (FS). Expanding leaves featured lower photosynthetic pigment contents and gas exchange capacity than adult leaves consistent with an immature photosynthetic apparatus. At the time of maximum irradiance, sun-exposed leaves of both PS and FS showed alteration of initial, variable, and maximum fluorescence as well as their ratios indicating photoinhibition. However, leaves recovered to some extent at predawn, suggesting the activation of photoprotective mechanisms. Sun-exposed leaves had comparable responses to high irradiance.     

Reproductive allometry in Malaysian rain forest trees: Biomechanics versus optimal allocation

Summary Quantitative predictions of reproductive allometry in iteroparous plants may be derived from two bodies of theory: biomechanics and optimal allocation theory. Biomechanical theory predicts allometric scaling exponents between reproductive (R) and vegetative (V) biomass in the range of 0.44–1.33, while very general models of life history evolution predictR–V exponents > 1 in all cases. These predictions are examined in light of allometric patterns of flower and fruit production in 32 species of Malaysian rain forest trees. Among these species the mean estimatedR–V exponents are in the range 1.8–2.0 for staminate flower, pistillate flower and fruit production. This range of exponent values provides unambiguous support for some of the general predictions of optimal allocation models, but not for biomechanical theory. Optimal allocation models also predict a positive relationship between species size andR–V slope and a positive relationship between species size andR–V intercept parameters. The latter, but not the former prediction is supported by the data.R–V allometries in sexes of dioecious species were also found to differ in intercept, though not slope, reflecting smaller sizes at reproductive onset in staminate trees. Further critical examinations of reproductive allometry are encouraged as a relatively unexplored avenue for increasing the contact of theory and data in studies of life history evolution in long-lived organisms such as tropical trees.     

云南澜沧地区热带山地雨林的群落学特征研究

在2500m2的固定样地上,共计有维管束植物100～105种,分属于45～47科、70～74属;胸径≥2cm的树种丰富度为69～74,ShannonWiener指数为3.5954～3.6267,Pielou均匀度指数为0.8426～0.8491。群落植物区系成分可分为10个类型,以热带区系成分为主,占83.17%～84.69%,其中又以泛热带和热带亚洲(印度-马来西亚)分布成分占优势,分别占33.67%～36.63%和24.75%～26.53%。群落以高位芽植物为主,其中又以中、小高位芽植物占优势,分别占50.00%～52.78%和22.12%～22.22%;在叶片生态学特征上,群落以中叶(66.67%～75%)、单叶(83.65%～85.19%)、纸质(61.11%～65.38%)、全缘(72.12%～72.22%)、非尾尖(86.11%～88.48%)为主。与西双版纳季节雨林相比,澜沧地区热带山地雨林体现出明显地向季风常绿阔叶林的过渡特征,如区系组成中的热带成分偏低而温带成分偏高,大高位芽植物以及大叶、复叶、全缘叶比例较低,而小高位芽植物以及小叶、单叶、非全缘叶比例较高。