Leaf flushing phenology and herbivory in a tropical dry deciduous forest,southern India

Patterns of leaf-flushing phenology of trees in relation to insect herbivore damage were studied at two sites in a seasonal tropical dry forest in Mudumalai, southern India, from April 1988 to August 1990. At both sites the trees began to flush leaves during the dry season, reaching a peak leaf-flushing phase before the onset of rains. Herbivorous insects emerged with the rains and attained a peak biomass during the wet months. Trees that flushed leaves later in the season suffered significantly higher damage by insects compared to those that flushed early or in synchrony during the peak flushing phase. Species whose leaves were endowed with physical defenses such as waxes suffered less damage than those not possessing such defenses. There was a positive association between the abundance of a species and leaf damage levels. These observations indicate that herbivory may have played a major role in moulding leaf flushing phenology in trees of the seasonal tropics.     

Phenology of tree species of tropical moist forest of Uttara Kannada district,Karnataka, India

Phenological observations on tree species in tropical moist forest of Uttara Kannada district (13ℴ55′ to 15ℴ31′ N lat; 74ℴ9′ to 75ℴ10′ E long) during the years 1983–1985 revealed that there exists a strong seasonality for leaf flush, leaf drop and reproduction. Young leaves were produced in the pre-monsoon dry period with a peak in February, followed by the expansion of leaves which was completed in March. Abscission of leaves occurred in the post-monsoon winter period with a peak in December. There were two peaks for flowering (December and March), while fruit ripening had a single peak in May–June, preceding the monsoon rainfall. The duration of maturation of leaves was the shortest, while that of full ripening of fruits was the longest. Mature flowers of evergreen species lasted longer than those of deciduous species; in contrast the phenophase of ripe fruits of deciduous species was longer than that of evergreen species.     

Climate-growth relations of congeneric tree species vary across a tropical vegetation gradient in Brazil

Seasonally dry tropical forests are an important global climatic regulator, a main driver of the global carbon sink dynamics and are predicted to suffer future reductions in their productivity due to climate change. Yet, little is known about how interannual climate variability affects tree growth and how climate-growth responses vary across rainfall gradients in these forests. Here we evaluate changes in climate sensitivity of tree growth along an environmental gradient of seasonally dry tropical vegetation types (evergreen forest – savannah – dry forest) in Northeastern Brazil, using congeneric species of two common neotropical genera: Aspidosperma and Handroanthus. We built tree-ring width chronologies for each species × forest type combinations and explored how growth variability correlated with local (precipitation, temperature) and global (the El Niño Southern Oscillation - ENSO) climatic factors. We also assessed how growth sensitivity to climate and the presence of growth deviations varied along the gradient. Precipitation stimulates tree growth and was the main growth-influencing factor across vegetation types. Trees in the dry forest site showed highest growth sensitivity to interannual variation in precipitation. Temperature and ENSO phenomena correlated negatively with growth and sensitivity to both climatic factors were similar across sites. Negative growth deviations were present and found mostly in the dry-forest species. Our results reveal a dominant effect of precipitation on tree growth in seasonally dry tropical forests and suggest that along the gradient, dry forests are the most sensitivity to drought. These forests may therefore be the most vulnerable to the deleterious effects of future climatic changes. These results highlight the importance of understanding the climatic sensitivity of different tropical forests. This understanding is key to predict the carbon dynamics in tropical regions, and sensitivity differences should be considered when prioritizing conservation measures of seasonally dry topical forests.     

Inter-species variation of photosynthetic and xylem hydraulic traits in the deciduous and evergreen Euphorbiaceae tree species from a seasonally tropical forest in south-western China

The objective of the present study was to examine the functional coordination among hydraulic traits, xylem characteristics and gas exchange rates across three deciduous Euphorbiaceae tree species (Hevea brasiliensis, Macaranga denticulata and Bischofia javanica) and three evergreen Euphorbiaceae tree species (Drypetes indica, Aleurites moluccana and Codiaeum variegatum) from a seasonally tropical forest in south-western China. The deciduous tree species were more vulnerable to water stress-induced embolism than the evergreen tree species. However, the deciduous tree species generally had higher maximal rates of sapwood and leaf-specific hydraulic conductivity (K _S and K _L), respectively. Compared with the evergreen tree species, the deciduous tree species, however, possessed a lower density of sapwood and a wider diameter of xylem vessels. Regardless of leaf phenology, the hydraulic vulnerability and conductivity were significantly correlated with sapwood density and mean vessel diameter. Furthermore, the hydraulic vulnerability was positively correlated with water transport efficiency. In addition, the deciduous tree species exhibited higher maximal photosynthetic rates (A _max) and stomatal conductance (g _max), but lower water use efficiency (WUE). Interestingly, the A _max, g _max and WUE were strongly correlated with K _S and K _L across the deciduous and evergreen tree species. These results suggest that xylem structure, rather than leaf phenology, accounts for the difference in hydraulic traits between the deciduous tree species and the evergreen tree species. Meanwhile, our results show that there is a significant trade-off between hydraulic efficiency and safety, and a strong functional correlation between the hydraulic capacity and gas exchange rates across the deciduous and evergreen tree species.     

Differences in climate-growth relationships between two tree species that co-occur in a seasonally dry tropical forest in Northeastern Brazil

Seasonally dry tropical forests are an important global climate regulator and represent one of main drivers of carbon sink dynamics. However, projections of climate change suggest future productivity losses and negative impacts on forest functioning. Understanding the interaction between climate variability and tree growth responses between species with different growth strategies represents a crucial challenge to forecast ecosystem functioning in the future. Here we used tree ring chronology to evaluate changes in growth and climate sensitivity of two tropical tree species that co-occur in a seasonally dry tropical forest in Brazil: Cedrela odorata and Ceiba glaziovii. Using Pearson correlations and linear regressions we explored how growth variability is correlated with local (precipitation, temperature) and global (ocean temperature and El Niño Southern Oscillation - ENSO) climatic factors. Tree growth was closely related with precipitation in C. odorata (r = 0.59) and C. glaziovii (0.24). Differences were found at monthly level, which C. odorata showing greater sensitivity in the beginning of rainy season. The South Atlantic Temperature was positively correlated with C. odorata, while ENSO was negatively correlated. Our results showed a dominant effect of precipitation on tree growth and suggest that are different growth strategies among species, which C. odorata being the most sensitive to drought and C. glaziovii more adapted with parenchyma in trunk. Therefore, C. odorata is probably more vulnerable to the deleterious effects of future climate change than C. glaziovii. Our findings highlight the importance of understanding the climate sensitivity of different seasonally dry tropical forest species, which is critical to predicting carbon dynamics in tropical regions. These also reveal that differences in sensitivity must be considered when prioritizing conservation measures for seasonally dry tropical forests.     

Phenology of trees in a sub-tropical humid forest in north-eastern India

Phenological observations were made on 122 tree species in a subtropical humid seasonal forest in north-eastern India. The forest had a high proportion of evergreen compared to deciduous species. Leaf-fall of most of the tree species coincided with the dry season. Flushing started towards the end of the dry season for a majority of the tree species, the degree and period of leaflessness varying with the species. Leaf production in the overstorey species extended over a longer period compared to the understorey species. For most of the species, flowering coincided with leaflessness. Proportionately more overstorey species flowered during the dry season and wet season flowering was more characteristic of understorey species. A majority of the species produced fleshy fruits during the wet season. Fruits, produced during the dry season, were mostly dry.Nomenclature follows. Holdridge, L. R., 1967. Life zone Ecology. Tropical Science Center, San Jose, Costa Rica.This work was supported by a research grant from the Department of Science and Technology, Government of India. The authors are thankful to K. Haridasan, Taxonomy laboratory, Department of Botany, NEHU for the help in species identification.     

Albedo model for a tropical dry deciduous forest in western Mexico

A simple albedo model is presented for a tropical dry deciduous forest. The model is based on point observations of the solar radiation, leaf cover of the vegetation, precipitation and air temperature from 1981 to 1988 in western Mexico. Four main periods were noted: leafing, leafed, leaf-fall and leafless. During the leafed period the albedo was almost constant (0.16) but increased slowly in the leaf-fall period, at a rate of 0.0008/day, until its maximal values in the leafless period (0.24). During the leafing and leafed periods, the albedo decrease was a hyperbolic function of precipitation at a rate of 7.9 albedo percentage/mm. Albedo showed a linear regression on leaf cover and decreased at a rate of 0.119 albedo percentage per leaf cover percentage.     

Seasonality of weather and tree phenology in a tropical evergreen mountain rain forest

Flowering and fruiting as phenological events of 12 tree species in an evergreen tropical mountain rain forest in southern Ecuador were examined over a period of 3–4 years. Leaf shedding of two species was observed for 12 months. Parallel to the phenological recordings, meteorological parameters were monitored in detail and related to the flowering and fruiting activity of the trees. In spite of the perhumid climate of that area, a high degree of intra- and inter-specific synchronisation of phenological traits was apparent. With the exception of one species that flowered more or less continuously, two groups of trees could be observed, one of which flowered during the less humid months (September to October) while the second group started to initiate flowers towards the end of that phase and flowered during the heavy rains (April to July). As reflected by correlation coefficients, the all-time series of meteorological parameters showed a distinct seasonality of 8–12 months, apparently following the quasi-periodic oscillation of precipitation and related cloudiness. As revealed by power spectrum analysis and Markov persistence, rainfall and minimum temperature appear to be the only parameters with a periodicity free of long-term variations. The phenological events of most of the plant species showed a similar periodicity of 8–12 months, which followed the annual oscillation of relatively less and more humid periods and thus was in phase or in counter-phase with the oscillations of the meteorological parameters. Periods of unusual cold or dryness, presumably resulting from underlying longer-term trends or oscillations (such as ENSO), affected the homogeneity of quasi-12-month flowering events, fruit maturation and also the production of germinable seeds. Some species show underlying quasi-2-year-oscillations, for example that synchronise with the development of air temperature; others reveal an underlying decrease or increase in flowering activity over the observation period, influenced for instance by solar irradiance. As Ecuador suffers the highest rate of deforestation in South America, there is an urgent need for indigenous plant material for reforestation. A detailed knowledge of the biology of reproduction in relation to governing external factors (mainly climate) is thus required.     

Influence of mineral nutrient availability on growth of tree seedlings from the tropical deciduous forest

The effects of different nutrient availabilities on growth and biomass partitioning in seedlings from the tropical deciduous forest in Mexico were compared. The tree species studied were Heliocarpus pallidus, a species associated with disturbed parts of the forest, and Caesalpinia eriotachys, Jacquinia pungens and Recchia mexicana, species from mature, undisturbed habitats. The tropical deciduous tree seedlings were grown in pure silica sand for 50 days inside growth chambers under four nutrient regimes; 5, 20, 100 and 200% Long Ashton nutrient solutions. Data showed contrasting responses among species to different nutrient availabilities. Except Jacquinia pungens, all species had increased growth and productivity as nutrient level increased from 5 to 100%; however, no significant differences in these parameters were detected between 100 and 200% in all species. Compared with mature forest species, pioneer species showed higher variations in biomass production, relative growth rate and net assimilation rate. In contrast to mature forest species, root/ shoot ratios in Heliocarpus pallidus were greater and thus showed higher biomass allocation to roots when nutrient supply was limited. This response suggests higher phenotypic plasticity in pioneer species. Species from mature parts of the forest (Caesalpinia eriostachys, Recchia mexicana) showed less dependency on nutrient supply than pioneer species. These responses appear to support observations from studies with temperate plants investigating growth responses to soil fertility.     

Variation in seed and seedling traits in Pithecellobium pedicellare,a tropical rain forest tree

Summary Pithecellobium pedicellare, a mimosoid legume, is a large canopy tree in the tropical rain forests of Costa Rica. We examined the pattern of variation in seed weight, germination date, hypocotyl length (stem), and rachis length (the first leaf) of the seedlings in this species. Seeds collected from widely dispersed individual trees at the La Selva Biological Station, Costa Rica, were randomly planted in blocks, and grown under controlled, indoor conditions for about 2 weeks. There-fore, we were able to quantify the effects of maternal family on mean seed weight and the effects of maternal family and microenvironment on the remaining traits examined. A significant effect of maternal family was detected for all traits. In particular, the maternal effects on germination date and seedling size traits which were consistently significant even after controlling the initial seed weight may indicate that the maternal effects reflect, at least to some extent, maternal genetic control over these traits. Despite overall strong maternal effects, the performance of maternal siblings, such as the rachis length, differed among blocks. The sensitivity of maternal siblings to the local environments may contribute to the maintenance of genetic variability in this highly outcrossing tropical species.     

Phenology of tree layer species from the timber line around Kumaun in Central Himalaya,India

Phenology of tree layer species from the timber line of Kumaun in Central Himalaya was carried out during the years 1988-1989. The study indicates the prevalence (66%) of deciduous tree species at timber line vegetation. Growth initiation started in early summer with the rise of temperature. Different phenophases succeeded one another, culminating in leaf drop with the advent of winter. The various phenophases of the tree species at timber line have been discussed and compared with the lower Himalayan forests of Kumaun in India. The present study also supports the idea that the intense fluctuations in environmental conditions determine the onset of different growth activities within the short growing season.Financial support from the Department of Environment, New Delhi and Council of Scientific and Industrial Research, New Delhi is gratefully acknowledged.     

Leaf display and photosynthesis of tree seedlings in a cool-temperate deciduous broadleaf forest understorey

To examine a possible convergence in leaf photosynthetic characteristics and leaf display responses to light environment in seedlings of three canopy and two shrub tree species in understorey of cool-temperate deciduous broadleaf forest, relationships between light environment, leaf orientation and leaf light-photosynthetic response were measured. Light capture of the seedlings (17-24 individuals with 2-12 leaves for each species) was assessed with a three dimensional geometric modeling program Y-plant. Leaf photosynthetic characteristics of the five species were found to have acclimated to the understorey light environment, i.e., low light compensation point and high apparent quantum yield. In addition, light-saturated photosynthetic rates were higher in seedlings inhabiting microsites with higher light availability. Efficiencies of light capture and carbon gain of the leaf display were evaluated by simulating the directionalities of light capture and daily photosynthesis for each seedling using hemispherical canopy photography. The results showed that most of the seedlings orientated their leaves in a way to increase the daily photosynthesis during the direct light periods (sunflecks) rather than maximize daily photosynthesis by diffuse light. Simulations also showed that daily photosynthesis would increase only 10% of that on actual leaf display when the leaves orientated to maximize the diffuse light interception. Simulations in which leaf orientations were varied showed that when the leaf display fully maximized direct light interception, the time that leaves were exposed to excessive photon flux density of >800 mumol photons m(-2) s(-1) were doubled. The understorey seedlings studied responded to the given light environments in a way to maximize the efficiency of acquisition and use of light during their short (approximately 3 month) seasonal growth period.     

Variation in bark thickness in a tropical forest community of Western Ghats in India

1. We examined the relation between bark thickness and girth in a large sample of trees from evergreen and semi-evergreen rain forest.
2. There is a significant tendency for bark thickness to increase with tree girth. Removing this tendency, we find a significant trend for species from more disturbed habitats to possess thicker bark.
3. Species from more disturbed habitats also have a greater propensity for secreting gums and resins.
4. Nine of the 29 species occurring in more than one habitat type and with a sample size of at least 11 individuals show a tendency for possession of a thicker bark by individuals in the more disturbed habitats.
5. We conclude that bark thickness and occurrence of gums and resins are physiognomic–structural attributes of value in characterizing tree communities created by different levels of disturbance.     

Growth responses of tropical deciduous tree seedlings to contrasting light conditions

Summary The growth responses of seedlings of Amphipterygium adstringens, Caesalpinia eriostachys, and C. platyloba, species associated with undisturbed parts of the tropical deciduous forest in México, and Apoplanesia paniculata and Heliocarpus pallidus, two gap-requiring pioneer species, were determined under contrasting light conditions in a growth chamber experiment. The high (400 mol m^–2 s^–1) and low (80 mol m^–2 s^–1) light treatments correspond to the light available in a medium size gap and underneath the vegetation canopy in the deciduous forest during the rainy season, respectively. Following four destructive harvests the biomass production, relative growth rate, root/shoot ratio, specific leaf area, net assimilation rate, leaf area ratio and light dependency were determined for all species. In the high light treatment all species achieved higher relative growth rates and net assimilation rates than when growing at low light intensity. However, the two pioneer species showed the highest light dependency and were the species more affected by the low light treatment in biomass production. The two Caesalpinia species showed similar growth responses, but C. platyloba was the most shade tolerant species. Plastic adjustments in terms of the specific leaf area were more evident in the two pioneer species.     

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 CO₂ acquisition in a low light understory environment. We measured foliar nutrient concentrations of N, P and K, isotopic composition of carbon (δ¹³C) and nitrogen (δ¹⁵N), 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 δ¹³C showed no significant responses, and foliar δ¹⁵N decreased strongly with N addition, matching the low δ¹⁵N values of applied fertilizer. Canopy openness ranged from 0.01 to 6.71% with a mean of 1.76 ± 0.14 (±1SE). Maximum photosynthetic CO₂ 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.     

Phenology of a tropical rain forest in Malaya

During 1960-69, observations were made of flowering, fruiting and foliar activity of 61 canopy trees (representing 45 species) in a largely undisturbed tract of Hill Dipterocarp Forest. Rainfall was measured by an accumulating gauge and, at a nearby station, the number of rainy days recorded. Annually recurrent floral cycles were displayed by only ten species. In these and in 11 additional species, foliar cycles were also circannual. Gregarious flowering, apparently in response to drought, occurred in many species in 1963 and 1968. In other years, interspecific differences in periodicity maintained a minimal incidence of flowering at 44%, and fruiting at 27% of species in the sample. Despite specific variations in phenology, the community as a whole exhibited regular seasonality, with single annual peaks of flowering and fruiting and a double peak of leaf production.     

Diversity of flowering and fruiting phenology of trees in a tropical deciduous forest in India

BACKGROUND AND AIMS: In the dry tropics, vegetative phenology varies widely with tree characteristics and soil conditions. The present work aims to document the phenological diversity of flowering and fruiting with reference to leafing events in Indian dry-tropical tree species. METHODS: Nine tree species, including one leaf-exchanging and eight deciduous showing varying leafless periods, were studied. Monthly counts of leaves, flowers and fruits were made on 160 tagged twigs on ten individuals of each species for initiation, completion and duration of different phenological events through two annual cycles. KEY RESULTS: Variation in flowering relative to leaf flushing (which occurred just prior to or during a hot, dry summer) revealed five flowering types: summer flowering (on foliated shoots), rainy-season flowering (on foliated shoots following significant rains), autumn flowering (on shoots with mature leaves), winter flowering (on shoots undergoing leaf fall) and dry-season flowering (on leafless shoots). Duration of the fruiting phenophase was shortest (3-4 months) in dry-season and winter-flowering species, 6-9 months in rainy-and autumn-flowering species, and maximum (11 months) in summer-flowering species. A wide range of time lag (<1 to >8 months) between the start of vegetative (first-leaf flush) and reproductive (first-visible flower) phases was recorded in deciduous species; this time lag was correlated with the extent of the leafless period. A synthesis of available phenological information on 119 Indian tropical trees showed that summer-flowering species were most abundant (56 % of total species) amongst the five types recognized. CONCLUSIONS: The wide diversity of seasonal flowering and fruiting with linkages to leaf flush time and leafless period reflect the fact that variable reproductive and survival strategies evolved in tree species under a monsoonic bioclimate. Flowering periodicity has evolved as an adaptation to an annual leafless period and the time required for the fruit to develop. The direct relationship between leafless period (inverse of growing period) and time lag between onset of vegetative and reproductive phases reflects the partitioning of resource use for supporting these phases. Predominance of summer flowering coupled with summer leaf flushing seems to be a unique adaptation in trees to survive under a strongly seasonal tropical climate.     

Soil respiration and microbial population in a tropical deciduous forest soil of Orissa, India

An investigation was carried out to estimate soil respiration rate and its relationship with microbial population in natural tropical forest soil, deforested soil and deforested-and-cultivated soil of Orissa, India. Soil respiration measurements and microbial isolation were performed following standard procedures. Monthly variation of soil respiration was observed to be governed by soil moisture. Considering respiration as a function of microbial population a regression analysis was made. The microfungal population showed positive relationship with the rate of soil respiration. The study revealed that conversion of natural forest led to a reduction of soil microbes and rate of soil respiration. Considering the importance of the microbial component in soil, we conclude that the conversion of natural forests to different land uses leads to the loss of biological stability of the soil.     

Effects of seasonal rainfall on radial growth in two tropical tree species

 Seasonal drought may limit primary productivity in most of the tropics, but the determinants of tree growth are not well known. A 10-year study of the deciduous trees Cochlospermum vitifolium (Willd.) Spreng. (Cochlospermaceae) and Cnidoscolus spinosus Lundell (Euphorbiaceae) in southwestern México showed radial growth to be highly correlated (both r>0.85) only with precipitation during an interval of <2 months in the mid-wet season. Growth was not affected by total annual precipitation or by an early starting or late ending of the wet season, or by heavy rainfall in the dry season. Annual mean girth increments ranged from 0.03 to 3.31 cm and −0.1 to 2.01 cm, respectively. The best model for growth (r ²>0.85) was a linear combination of mid-summer precipitation (positive coefficient) and total precipitation over the previous 2 years (negative coefficient). Comparison with other species showed heterogeneous responses of wood production to climate variation, and suggests that the range of functional types of dry forest trees is still unknown. Received: 9 September 1996 / Accepted: 4 March 1997