Climate and microhabitat shape the prevalence of endozoochory in the seed rain of tropical montane forests

Endozoochory, the dispersal of seeds by animal ingestion, is the most dominant mode of seed dispersal in tropical forests and is a key process shaping current and future forest dynamics. However, it remains largely unknown how endozoochory is associated with environmental conditions at regional and local scales. Here, we investigated the effects of elevation, climate, and microhabitat conditions on the proportion of endozoochorous plant species in the seed rain of the tropical Andes of southern Ecuador. Over 1 year, we measured seed rain in 162 seed traps on nine 1-ha forest plots located at 1000, 2000, and 3000 m a.s.l. We recorded climatic conditions (mean annual temperature and rainfall) in each plot and microhabitat conditions (leaf area index and soil moisture) adjacent to each seed trap. In total, we recorded 331,838 seeds belonging to 323 morphospecies. Overall, the proportion of endozoochorous species in the seed rain decreased with elevation. The relative biomass of endozoochorous species decreased with increasing rainfall, whereas the relative seed richness of endozoochorous species increased with increasing temperature and leaf area index. These findings suggest an interplay between climate factors and microhabitat conditions in shaping the importance of endozoochorous plant species in the seed rain of tropical montane forests. We conclude that changing climatic and microhabitat conditions are likely to cause changes in the dominant dispersal modes of plant communities which may trigger changes in the current and future dynamics of tropical forests.     

How much have we learned about seasonality in tropical insect abundance since Wolda (1988)?

Seasonal patterns in climatic conditions affect the life cycles and temporal patterns in the abundance of most temperate insect species. In tropical regions where there is no winter season, the situation may be different. For a better understanding of the evolution of seasonal life cycles, and the dynamics affecting temporal patterns in abundance of tropical insect populations and assemblages, it is important to study the life cycles of tropical insects and the presence or absence of seasonality in relation to climatic conditions. By reviewing studies on temporal patterns of abundance, this article examines the patterns of seasonality in adult tropical forest insects and discusses the variation in such patterns in various forest types. Seasonal and aseasonal patterns were found to be common in tropical dry and wet regions, respectively. In wet regions, which lack a distinctive dry season, there exists a wide variety of temporal patterns in addition to aseasonal patterns: distinctively seasonal and supra‐annual fluctuations in some insect species. Some of the problems of hidden ecological mechanisms underlying seasonal patterns in abundance are discussed, and the definition of seasonality in temporal patterns of insect abundance at a particular stage in the life cycle is considered. Methodological problems are also discussed.     

Seed Ecology of Woody Species in a Caribbean Dry Forest

Peak flowering activity among woody species in the tropical dry forests of St. John, U.S. Virgin Islands, coincided with the brief spring rainy season but continued at moderate levels for six months, abating with the autumn rains. Fruit maturation showed a major peak in the long winter dry season and a minor crest during the summer dry season. Seeds of wind-dispersed species disseminated mainly during the winter dry season, while animal dispersal of seeds (74% of all woody species) followed the bimodal pattern (for wet and dry seasons) described for the community as a whole. Under shadehouse conditions, most dry forest tree species germinated well (> 80%) and emerged promptly (within four weeks of planting) and synchronously (90% emergence within a four-week interval). Nine of 29 species tested in the shadehouse manifested dormancy of at least six weeks. Seed germinability varied among tree species, and the viability of most species began to decline following six months of dry storage. Few species retained high germinability after nine months of dry storage. The species composition of soil seed banks did not correspond closely with above-ground communities on three forested sites of varying stand age. In the youngest stand (35 years old), dominated by the weedy, arborescent legume Leucaena leucocephala, the soil seed bank was also dominated by this species, but no seeds of any other tree species were found in the soil samples. Seeds of native trees were scarcely encountered (only one indigenous species) in soil seed bank samples of three forest sites. Local seed rain from less disturbed forest may not be sufficient for prompt recovery of the dry forest community on degraded sites.     

Seasonal rhythms of seed rain and seedling emergence in two tropical rain forests in southern Brazil

Seasonal tropical forests show rhythms in reproductive activities due to water stress during dry seasons. If both seed dispersal and seed germination occur in the best environmental conditions, mortality will be minimised and forest regeneration will occur. To evaluate whether non-seasonal forests also show rhythms, for 2 years we studied the seed rain and seedling emergence in two sandy coastal forests (flooded and unflooded) in southern Brazil. In each forest, one 100 x 30-m grid was marked and inside it 30 stations comprising two seed traps (0.5 x 0.5 m each) and one plot (2 x 2 m) were established for monthly monitoring of seed rain and a seedling emergence study, respectively. Despite differences in soil moisture and incident light on the understorey, flooded and unflooded forests had similar dispersal and germination patterns. Seed rain was seasonal and bimodal (peaks at the end of the wetter season and in the less wet season) and seedling emergence was seasonal and unimodal (peaking in the wetter season). Approximately 57% of the total species number had seedling emergence 4 or more months after dispersal. Therefore, both seed dormancy and the timing of seed dispersal drive the rhythm of seedling emergence in these forests. The peak in germination occurs in the wetter season, when soil fertility is higher and other phenological events also occur. The strong seasonality in these plant communities, even in this weakly seasonal climate, suggests that factors such as daylength, plant sensitivity to small changes in the environment (e.g. water and nutrient availability) or phylogenetic constraints cause seasonal rhythms in the plants.     

Climatic seasonality, resource bottlenecks, and abundance of rainforest birds: implications for global climate change

We demonstrate that within-year climatic variability, particularly rainfall seasonality, is the most significant variable explaining spatial patterns of bird abundance in Australian tropical rainforest. The likely mechanism causing this pattern is a resource bottleneck (insects, nectar, and fruit) during the dry season that limits the population size of many species. The patterns support both the diversity–climatic–stability hypothesis and the species–energy hypothesis but clearly show that seasonality in energy availability may be a more significant factor than annual totals or means. An index of dry season severity is proposed that quantifies the combined effect of the degree of dryness and the duration of the dry season. We suggest that the predicted increases in seasonality due to global climate change could produce significant declines in bird abundance, further exacerbating the impacts of decreased range size, increased fragmentation, and decreased population size likely to occur as a result of increasing temperature. We suggest that increasing climatic seasonality due to global climate change has the potential to have significant negative impacts on tropical biodiversity.     

Diversity and community composition of euglossine bee assemblages (Hymenoptera: Apidae) in western Amazonia

Tropical forests are known for their diverse insect fauna. We aimed to determine the effect and relative importance of latitude, elevation and climatic factors affecting species richness and turnover in euglossine bee assemblages along a gradient of 18° latitude from tropical rainforests to subtropical, deciduous dry forests in Peru and Bolivia. Sixteen forest sites were sampled during the dry season. Variance partitioning techniques were applied to assess the relative effects of the spatial and environmental variables on species richness and composition. Furthermore, we conducted a Species Indicator Analysis to find characteristic species for the biogeographic zones. There was a significant decrease in species richness towards the subtropical area. The best predictors of species richness were precipitation and its consequences on soil properties as well as temperature seasonality. The abundance of euglossines was most closely related to precipitation and soil-pH, but the causal links of abundance to these factors is unclear since soil-pH itself is correlated to a drastic turnover of vegetation structure. Based on the analysis of assemblage composition we propose three different assemblages with a transitional zone at the southern tropical area. The biogeographical distribution of euglossine bees along our study transect appears to be primarily related to climatic conditions and does not reflect the common subdividion of Amazonia into drainage systems.     

White‐tailed deer as the last megafauna dispersing seeds in Neotropical dry forests: the role of fruit and seed traits

Endozoochory is a prominent form of seed dispersal in tropical dry forests. Most extant megafauna that perform such seed dispersal are ungulates, which can also be seed predators. White‐tailed deer (Odocoileus virginianus) is one of the last extant megafauna of Neotropical dry forests, but whether it serves as a legitimate seed disperser is poorly understood. We studied seed dispersal patterns and germination after white‐tailed deer gut passage in a tropical dry forest in southwest Ecuador. Over 23 mo, we recorded ca 2000 seeds of 11 species in 385 fecal samples. Most seeds belonged to four species of Fabaceae: Chloroleucon mangense, Senna mollissima, Piptadenia flava, and Caesalpinia glabrata. Seeds from eight of the 11 species dispersed by white‐tailed deer germinated under controlled conditions. Ingestion did not affect germination of C. mangense and S. mollissima, whereas C. glabrata showed reduced germination. Nevertheless, the removal of fruit pulp resulting from ingestion by white‐tailed deer could have a deinhibition effect on germination due to seed release. Thus, white‐tailed deer play an important role as legitimate seed dispersers of woody species formerly considered autochorous. Our results suggest that more research is needed to fully understand the ecological and evolutionary effects of the remaining extant megafauna on plant regeneration dynamics in the dry Neotropics.     

Patterns of plant phenology in Amazonian seasonally flooded and unflooded forests

Few studies have successfully monitored community‐wide phenological patterns in seasonally flooded Amazonian várzea forests, where a prolonged annual flood pulse arguably generates the greatest degree of seasonality of any low‐latitude ecosystem on Earth. We monitored the vegetative and reproductive plant phenology of várzea (VZ) floodplain and adjacent terra firme (TF) forests within two contiguous protected areas in western Brazilian Amazonia, using three complementary methods: monthly canopy observations of 1056 individuals (TF: 556, VZ: 500), twice monthly collections from 0.5‐m² litterfall traps within two 100‐ha plots (1 TF, 1 VZ; 96 traps per plot), and monthly ground surveys of residual fruit‐fall along transect‐grids within each 100‐ha plot (12 km per plot). Surveys encompassed the entire annual flood cycle and employed a floating trap design to cope with fluctuating water levels. Phenology patterns were generally similar in both forest types. Leaffall peaked during the aquatic phase in várzea forest and the dry season in terra firme. Flowering typically followed leaffall and leaf flush, extending into the onset of the terrestrial phase and rainy season in várzea and terra firme, respectively. Abiotic seed dispersal modes were relatively more prevalent in várzea than terra firme; the main contrast in fruiting seasonality was more likely a result of differences in community composition and relative abundance of seed dispersal modes than differences within individual genera. We emphasize the difficulty in distinguishing the role of the flood pulse from other seasonal environmental variables without multiannual data or spatially replicated studies across the spectrum of Amazonian forest types.     

Fruiting phenology in a tropical dry evergreen forest on the Coromandel coast of India in relation to plant life-forms,physiognomic groups,dispersal modes,and climatic constraints

The fruiting phenology of 22 woody plant species belonging to 19 families was studied with respect to life-forms, physiognomic groups and dispersal modes, for 1 year at monthly intervals, in a tropical dry evergreen forest at Oorani (12°11′N, 79°57′E) on the Coromandel coast of India. At the community level, bimodal fruiting pattern prevailed, with a major peak in the dry season and a minor one in the early rainy season. An annual fruiting pattern was observed in many species and among the studied species fruiting lasted for 2–9 months. There was no significant difference in the frequency of species at three fruiting stages across the life-form categories and many species of upper and lower canopy trees and lianas were in the ripe fruiting phase during the late dry season. Plant physiognomic groups displayed distinct seasonality in fruiting pattern. The fruit maturation period was much longer for the wet season fruiting brevi-deciduous species than evergreen and deciduous species that fruited during the dry season. The variation in timing of fruiting behaviour among zoochorous species demonstrated less seasonality and zoochorous fruits were available throughout the year. Fruiting in anemochorous species peaked during the driest months and dryness favoured the dissemination of seeds. The fruiting patterns observed in the studied tropical dry evergreen forest across various plant traits were comparable with patterns recorded in other tropical seasonal forests.     

Soil‐based habitat partitioning in understorey palms in lower montane tropical forests

Aim Dispersal assembly and niche assembly are two competing theories proposed to explain the maintenance of species diversity in tropical forests. Dispersal theory emphasizes the role of chance colonization events and distance‐limited seed dispersal in explaining species abundance and distribution, whereas niche theory emphasizes differences among species in requirements for potentially limiting resources. Species distribution patterns in tropical forests often correlate with geology and topography, but tests of the relative importance of dispersal and niche partitioning have been hampered by an inadequate characterization of resource availability. The aim of this study was to explore how soil chemical and physical properties, climate, and geographic distance affect understorey palm communities in lower montane forests. Location Fortuna Forest Reserve, Chiriqui Province, and Palo Seco Forest Reserve, Bocas del Toro Province, in western Panama. Methods Understorey palms and soil nutrient concentrations were surveyed within 10 sites on different soil types across a 13‐km transect. Variation in palm community composition was examined in relation to spatial and environmental variables. Results The 25 understorey palm species recorded in the study were non‐randomly distributed among forests differing in soil nutrient availability. In support of dispersal theory, floristic similarity decreased predictably with increasing geographic distance. However, environmental and soil variables were also correlated with geographic distance. Floristic similarity was also highly associated with a subset of environmental variables. Variation in palm community similarity was most strongly correlated with inorganic nitrogen availability and cation concentration. A subset of soil variables had a stronger relationship with floristic similarity when geographic distance was controlled for than did geographic distance when differences in soils were controlled for. Main conclusions Both dispersal and niche processes affect palm species distribution patterns. Although spatially limited dispersal may influence species distribution patterns, soil‐based habitat associations, particularly with respect to soil nitrogen, cation availability and aluminium concentrations, remain important factors influencing palm community composition at the mesoscale level in this tropical montane forest.     

Annual Rainfall and Seasonality Predict Pan-tropical Patterns of Liana Density and Basal Area

We test the hypotheses proposed by Gentry and Schnitzer that liana density and basal area in tropical forests vary negatively with mean annual precipitation (MAP) and positively with seasonality. Previous studies correlating liana abundance with these climatic variables have produced conflicting results, warranting a new analysis of drivers of liana abundance based on a different dataset. We compiled a pan-tropical dataset containing 28,953 lianas (≥2.5 cm diam.) from studies conducted at 13 Neotropical and 11 Paleotropical dry to wet lowland tropical forests. The ranges in MAP and dry season length (DSL) (number of months with mean rainfall <100 mm) represented by these datasets were 860–7250 mm/yr and 0–7 mo, respectively. Pan-tropically, liana density and basal area decreased significantly with increasing annual rainfall and increased with increasing DSL, supporting the hypotheses of Gentry and Schnitzer. Our results suggest that much of the variation in liana density and basal area in the tropics can be accounted for by the relatively simple metrics of MAP and DSL.     

Rainfall seasonality predicts the germination behavior of a tropical dry‐forest vine

Seed dormancy is considered to be an adaptive strategy in seasonal and/or unpredictable environments because it prevents germination during climatically favorable periods that are too short for seedling establishment. Tropical dry forests are seasonal environments where seed dormancy may play an important role in plant resilience and resistance to changing precipitation patterns. We studied the germination behavior of seeds from six populations of the Neotropical vine Dalechampia scandens (Euphorbiaceae) originating from environments of contrasting rainfall seasonality. Seeds produced by second greenhouse‐generation plants were measured and exposed to a favorable wet environment at different time intervals after capsule dehiscence and seed dispersal. We recorded the success and the timing of germination. All populations produced at least some dormant seeds, but seeds of populations originating from more seasonal environments required longer periods of after‐ripening before germinating. Within populations, larger seeds tended to require longer after‐ripening periods than did smaller seeds. These results indicate among‐population genetic differences in germination behavior and suggest that these populations are adapted to local environmental conditions. They also suggest that seed size may influence germination timing within populations. Ongoing changes in seasonality patterns in tropical dry forests may impose strong selection on these traits.     

Liana abundance and diversity increase with rainfall seasonality along a precipitation gradient in Panama

In tropical regions, rainfall gradients often explain the abundance and distribution of plant species. For example, many tree and liana species adapted to seasonal drought are more abundant and diverse in seasonally-dry forests, characterized by long periods of seasonal water deficit. Mean annual precipitation (MAP) is commonly used to explain plant distributions across climate gradients. However, the relationship between MAP and plant distribution is often weak, raising the question of whether other seasonal precipitation patterns better explain plant distributions in seasonally-dry forests. In this study, we examine the relationship between liana abundance and multiple metrics of seasonal and annual rainfall distribution to test the hypothesis that liana density and diversity increase with increasing seasonal drought along a rainfall gradient across the isthmus of Panama. We found that a normalized seasonality index, which combines MAP and the variability of monthly rainfall throughout the year, was a significant predictor of both liana density and species richness, whereas MAP, rainfall seasonality and the mean dry season precipitation (MDP) were far weaker predictors. The strong response of lianas to the normalized seasonality index indicates that, in addition to the total annual amount of rainfall, how rainfall is distributed throughout the year is an important determinant of the hydrological conditions that favor liana proliferation. Our findings imply that changes in annual rainfall and rainfall seasonality will determine the future distribution and abundance of lianas. Models that aim to predict future plant diversity, distribution, and abundance may need to move beyond MAP to a more detailed understanding of rainfall variability at sub-annual timescales.     

Species-Specific Growth Responses to Climate Variations in Understory Trees of a Central African Rain Forest

Basic knowledge of the relationships between tree growth and environmental variables is crucial for understanding forest dynamics and predicting vegetation responses to climate variations. Trees growing in tropical areas with a clear seasonality in rainfall often form annual growth rings. In the understory, however, tree growth is supposed to be mainly affected by interference for access to light and other resources. In the semi-deciduous Mayombe forest of the Democratic Republic of Congo, the evergreen species Aidia ochroleuca, Corynanthe paniculata and Xylopia wilwerthii dominate the understory. We studied their wood to determine whether they form annual growth rings in response to changing climate conditions. Distinct growth rings were proved to be annual and triggered by a common external factor for the three species. Species-specific site chronologies were thus constructed from the cross-dated individual growth-ring series. Correlation analysis with climatic variables revealed that annual radial stem growth is positively related to precipitation during the rainy season but at different months. The growth was found to associate with precipitation during the early rainy season for Aidia but at the end of the rainy season for Corynanthe and Xylopia. Our results suggest that a dendrochronological approach allows the understanding of climate–growth relationships in tropical forests, not only for canopy trees but also for evergreen understory species and thus arguably for the whole tree community. Global climate change influences climatic seasonality in tropical forest areas, which is likely to result in differential responses across species with a possible effect on forest composition over time.     

Leaffall Phenology in a Subtropical Wet Forest in Puerto Rico: From Species to Community Patterns

Leaffall phenology is an important periodical event in forests, contributing to mobilization of organic matter from primary producers to soil. For seasonal forests, leaffall periodicity has been related to rainfall regime and dry season length. In weakly seasonal forests, where there is no marked dry season, other climatic factors could trigger leaf shed. In this study, we aimed to determine if other climatic variables (wind speed, solar radiation, photosynthetic photon flux density [PPFD], day length, temperature, and relative humidity) could be better correlated with patterns of litter and leaffall in a weakly seasonal subtropical wet forest in Puerto Rico. Leaffall patterns were correlated mainly with solar radiation, PPFD, day length, and temperature; and secondarily with rainfall. Two main peaks of leaffall were observed: April–June and August–September, coinciding with the periods of major solar radiation at this latitude. Community leaffall patterns were the result of overlapping peaks of individual species. Of the 32 species analyzed, 21 showed phenological patterns, either unimodal (16 species), bimodal (three species), or multimodal (two species). Lianas also presented leaffall seasonality, suggesting that they are subject to the same constraints and triggering factors affecting trees. In addition to solar radiation as a main determinant of leaffall timing in tropical forests, our findings highlight the importance of interannual variation and asynchrony, suggesting that leaffall is the result of a complex interaction between environmental and physiological factors.     

Habitat‐dependent occupancy and movement in a migrant songbird highlights the importance of mangroves and forested lagoons in Panama and Colombia

Climate change is predicted to impact tropical mangrove forests due to decreased rainfall, sea‐level rise, and increased seasonality of flooding. Such changes are likely to influence habitat quality for migratory songbirds occupying mangrove wetlands during the tropical dry season. Overwintering habitat quality is known to be associated with fitness in migratory songbirds, yet studies have focused primarily on territorial species. Little is known about the ecology of nonterritorial species that may display more complex movement patterns within and among habitats of differing quality. In this study, we assess within‐season survival and movement at two spatio‐temporal scales of a nonterritorial overwintering bird, the prothonotary warbler (Protonotaria citrea), that depends on mangroves and tropical lowland forests. Specifically, we (a) estimated within‐patch survival and persistence over a six‐week period using radio‐tagged birds in central Panama and (b) modeled abundance and occupancy dynamics at survey points throughout eastern Panama and northern Colombia as the dry season progressed. We found that site persistence was highest in mangroves; however, the probability of survival did not differ among habitats. The probability of warbler occupancy increased with canopy cover, and wet habitats were least likely to experience local extinction as the dry season progressed. We also found that warbler abundance is highest in forests with the tallest canopies. This study is one of the first to demonstrate habitat‐dependent occupancy and movement in a nonterritorial overwintering migrant songbird, and our findings highlight the need to conserve intact, mature mangrove, and lowland forests.     

Distribution of twelve moist forest canopy tree species in Liberia and Côte d'Ivoire: response curves to a climatic gradient

Abstract. The occurrence and abundance of 12 canopy tree species from the moist tropical forests of West Africa have been studied in relation to a climatic gradient. We focused on environmental factors related to water availability: annual amount of rainfall, the length of the dry season, and cumulative water deficit. Species occurrence and abundance data are used for 39 forest sites in Liberia and southwest Côte d'Ivoire. Species responses are modelled using a set of five increasingly complex models, ranging from a no-trend model to a skewed bell-shaped response curve. The study species show different distribution patterns. Most of them suggest a close relationship to climatic conditions. Fitting of species occurrence data to each of the three climatic factors results in most cases in simple models. In only one out of 36 cases a bell-shaped response curve is needed to describe the data. Four of the 12 species show no response to the climatic factors when only occurrence is evaluated. When abundance data are used, in 33 of the 36 cases significant response models are found. In general these are much more complex than in the cases of species occurrence data: in 10 of the 36 cases a bell-shaped response model is found to describe the data best. This is in contrast with the widespread belief that species response curves are bell-shaped: within the forest zone in the area studied this is not generally the case. The importance of the three climatic factors for the distribution of the species is evaluated: for four species mean annual rainfall is the most important variable, for four species the length of the dry period, and for one species cumulative water deficit. Consequently, the assumption that mean annual rainfall is the most important factor determining tree species distribution in West African forests is not correct. Species response models to climatic factors show where species have their geographical optima. Implications for forest management are briefly discussed.     

西双版纳热带森林土壤种子库的季节变化

通过萌发实验法对西双版纳地区的一类热带季节雨林 (番龙眼、千果榄仁 )和 2类次生林(白背桐林、中平树林 )的土壤种子库的季节变化进行了探讨。结果表明 :该地区的土壤种子库动态具有明显的季节性。季节雨林的土壤种子库储量相对稳定 ,土壤上层 ( 0～ 2 cm )的种子储量在雨季末期较大。2类次生林土壤种子库的变化则相反 ,土壤种子库中的种子种类在旱季末期较雨季末期多 ,土壤上层的种子储量在旱季末期较大。各样地均有一些种类只出现在旱季末期或雨季末期。种子在土壤种子库的动态与植物的繁殖物候和所处的环境紧密相关 ,不同种类植物的土壤种子库由于植物本身的生物学特性、传播方式和所处环境的影响而表现出不同的动态模式     

The Effects of Established Trees on Woody Regeneration during Secondary Succession in Tropical Dry Forests

Understanding the mechanisms controlling secondary succession in tropical dry forests is important for the conservation and restoration of this highly threatened biome. Canopy‐forming trees in tropical forests strongly influence later stages of succession through their effect on woody plant regeneration. In dry forests, this may be complex given the seasonal interplay of water and light limitations. We reviewed observational and experimental studies to assess (1) the relative importance of positive and negative effects of established trees on regeneration; (2) the mechanisms underlying these effects; and (3) to test the ‘stress gradient hypothesis’ in successional tropical dry forests. The effects of established trees on seed dispersal, seed survival, and seed germination—either through direct changes to moisture and temperature regimes or mediated by seed dispersers and predators—are mainly positive. The balance between positive and negative effects on seedling establishment is more complex and depends on the season and leaf phenology of both trees and seedlings. Seedling survival is generally enhanced by established trees mitigating dry conditions. Established trees have counteracting effects on water and light availability that influence seedling growth. The probability of a positive effect of established trees on seedling survival decreases with increased rainfall, which supports the stress gradient hypothesis. Priorities for future research are experiments to test for facilitation and competition and their underlying mechanisms, long‐term studies evaluating how these effects change with ontogeny, and studies focusing on the species‐specificity of interactions.     

Convergence in growth responses of tropical trees to climate driven by water stress

Widely documented for temperate and cold forests in both hemispheres, variations in tree growth responses to climate along environmental gradients have rarely been investigated in the tropics. Seven tree‐ring chronologies of Centrolobium microchaete (Fabaceae) in the Cerrado tropical forests of Bolivia are used to determine the growth responses to climate along a precipitation gradient. Chronologies are distributed from the humid Guarayos forests (annual precipitation > 1600 mm) in the transition to the Amazonia to the dry‐mesic Chiquitos forests (annual precipitation < 1200 mm) in the proximity to the dry Chaco. On a large spatial scale, radial growth is positively influenced by rainfall and negatively by temperature at the end of the dry season. However, this regional pattern in climate‐tree growth relationship shows differences along the precipitation gradient. Relationships with climate are highly significant and extend over longer periods of the year in sites with low rainfall and extremely severe dry seasons. At wet sites, larger water soil capacity and endogenous forest dynamics partially mask the direct influence of climate on tree growth. Stronger similarities in tree‐growth responses to climate occur between sites in the dry Central Chiquitos and in the transition to the Guarayos forests. In contrast, the relationships show fewer similarities between sites in the humid Guarayos. We conclude that growth responses to climate in the tropics are more similar between sites with limited rainfall and severe and prolonged dry seasons. Our study points to a convergence in the patterns of growth responses of tropical trees to climate, modulated by scarce rainfall and marked seasonality. The negative impact of water deficits on tree physiological processes induces not only the documented reduction in forest species richness, but also a convergence in tree‐growth responses to climate in dry tropical forests.