Tropical Seasonal Forest Research Articles

Camera trapping reveals multispecies use of water‐filled tree holes by birds and mammals in a neotropical forest

AbstractUsing camera traps, we documented that 21 bird and 9 mammal species use water‐filled tree holes (dendrotelmata) in the seasonal tropical forest of the Calakmul Biosphere Reserve, in southern Mexico. These species visited dendrotelmata primarily for foraging and drinking. The overall use of dendrotelmata was equally frequent between dry and rainy seasons but drinking behavior increased among birds during the dry season.Abstract in Spanish is available with online material.

Cool-dry season depression in gas exchange of canopy leaves and water flux of tropical trees at the northern limit of Asian tropics

Trees on the northern boundary of Asian tropics experience hot-humid and cool-dry seasons, but little is known about their seasonal dynamics in canopy physiology. We used a canopy crane to reach the canopy of nine tropical tree species and measured canopy leaf gas exchange, water status, and trunk sap flux during the hot-humid and cool-dry seasons in Xishuangbanna, China. We found that most tree species exhibited significant reductions in maximum photosynthetic rate (Amax), stomatal conductance (gsmax), predawn and midday leaf water potentials, and maximum sap flux density in the cool-dry season. Compared to the hot-humid season, Amax declined by 19–60%, and maximum water flux declined by −14% (an increase) to 42%. The cool-dry season decline in Amax of four species can be partly explained by an increased stomatal limitation (decreased gsmax and intercellular CO2 concentrations). Therefore, a predicted increase in drought in this region may decrease the carbon sequestration and productivity of these forests. We did not find a tradeoff between performance (Amax in the hot-humid season) and persistence through the cool-dry season; species with higher Amax in the hot-humid season did not show higher percent seasonal declines in the cool-dry season. Amax was significantly and positively associated with the trunk sap flux for both seasons, but the association was weaker in the cool-dry season. Thus, our results suggest that some tradeoffs and trait associations are environment dependent. Our results are important for understanding carbon and water fluxes of seasonal tropical forests and their responses to environmental changes.

Build it and they will come, but not all of them in fragmented Atlantic Forest landscapes

Ecological restoration interventions, in most cases, aim to restore habitat structure and plant community composition, thus re‐establishing ecosystem functioning as similar as possible to that of the pre‐existing natural ecosystem. However, given the difficulty of cultivating many species, that goal seems unattainable, unless “if you build it, they will come.” Here we addressed the Field of Dreams hypothesis in the context of trees and shrubs of the seasonal tropical forest in southeastern Brazil. We aimed to verify if the species from the regional pool have been able to colonize the restoration forests and if functional patterns exist behind successful and unsuccessful colonization. We categorized each species by dispersal syndrome, seed traits, growth rate, shade tolerance, and rarity in the communities. Most, but not all, species from the regional pool are colonizing forest patches undergoing restoration. Successful colonizers are mostly zoochorous, dispersed by birds or bats, shade tolerant, of moderate or fast growth. By partially confirming the Field of Dreams hypothesis, our study implies that it is not necessary to reintroduce a large proportion of the regional pool in tropical forest restoration projects, given that many species will later spontaneously arrive, even in fragmented landscapes. However, the existence of a particular functional profile (slow‐growing species, dispersed by gravity or large mammals) that will rarely colonize the restoration forests should not be disregarded. Even though these are a minority, such species will likely be confined to the remaining natural fragments if they are not included in the restoration projects.

Similarity in seed removal patterns of four tree species in active and passive restoration treatments of the tropical seasonal forest after 23 years

Seed removal has been considered an important ecological filter in plant community assembly during the first years of restoration. However, little is known about the influence of the restored ecosystems attributes on seed consumption patterns by predators and, consequently, on the composition and structure of the regenerating community. We tested whether seed removal differs between natural and restored ecosystems and whether it depends on the seed consuming agent (insects, rodents and birds). We evaluated seed removal in three forest restoration treatments (two active and one passive) established over 20 years ago. We used a fragment of old-growth native seasonal semideciduous tropical forest close to the experimental area, as a reference ecosystem. We installed exclusion stations for different consumer groups (insects, rodents and birds) of seeds belonging to four tree species from different successional groups and dispersal syndromes (Tabernaemontana hystrix Steud, Schinus terebinthifolius Raddi, Pterogyne nitens Tul and Anadenanthera colubrina var. cebil (Griseb.) Altschul. Insects were the main agent removing seeds from the species tested as a whole, regardless of the restoration treatment. Seed removal proportions were generally low and differed between active and passive restoration treatments, depending on the tree species. However, they were similar to the native forest, regardless of the restoration treatment. We found an effect of the interaction of restoration treatments and consuming agents only for one of the zoochoric species tested (Tabernaemontana hystrix). Seed removal no longer seems to represent a biotic filter limiting plant recruitment for T. hystrix, S. terebinthifolius, P. nitens and A. colubrina recruitment in the restoration treatments, regardless of the restoration technique.

Tree species consistent co-occurrence in seasonal tropical forests: an approach through association rules analysis

Aim of study: Aassessing the existence of consistent co-occurrence between tree species that characterize seasonal tropical forests, using the association rules analysis (ARA), that is a novel data mining methodology; and evaluate evaluating the taxonomic and functional similarities between associated species.Area of study: forty-four seasonal forest sites with permanent plots (40.2 ha of total sample) located in Southeast Brazil, from which we obtained species occurrences.Material and methods: we applied association rules analysis (ARA) to the dataset of species occurrence in sites considering the criteria of support equal to or greater than 0.63 and confidence equal to or greater than 0.8 to obtain the first set of associations rules between pairs of species. This set was then submitted to Fisher’s criteria exact p-value less than 0.05, lift equal to or greater than 1.1 and coverage equal to or greater than 0.63. We considered these criteria to be able to select non-random and consistent occurring associations.Main results: We obtained a final result of 238 rules for semideciduous forest and 11 rules for deciduous forests, composed of species characteristic of vegetation types. Co-occurrences are formed mainly by non-confamilial species, which have similar functional characteristics (potential size and wood density). There is a difference in the importance of co-occurrence between forest types, which tends to be less in deciduous forests.Research highlights: The results point to out the feasibility of applying ARA to ecological datasets as a tool for detecting ecological patterns of coexistence between species and the ecosystems functioning.Keywords: data mining; coexistence; semideciduous forests; deciduous forests; biotic interaction.

Temporal organization among pollination systems in a tropical seasonal forest.

Temporal constancy of pollination systems is essential for the maintenance of pollinators through time. Community-level assessment of flowering phenology allows understanding variations across seasons and years and the risks of decoupling flowering and pollinators' activity. We evaluated flowering patterns and temporal diversity of pollination systems in a tropical seasonal forest. We asked whether the temporal organization of flowering times differs among pollination systems; if there is a constancy of pollination systems through the year, since climate and phylogenies constraint flowering time; if there is a prevalent flowering pattern by pollination system, and if the temporal organization of pollination systems by modularity analyses is coherent with grouping by pre-defined seasons. We characterized 10 pollination systems, examined flowering strategies, climate cues and phylogenetic constraints. Pollination by large-to-medium bees dominated (49.2%), followed by diverse insects (22.1%) and flies (14.7%). The remaining systems represented 14% of species. Flowering occurred year-round for most pollination systems, predominating the seasonal flowering strategy. Flowering patterns ranged from aggregated to nested, and random. Climate affected the flowering of most pollination systems, but there was no phylogeny constraint. Modularity grouped pollination systems differently than rainfall seasonality. Contrasting the expectations of reduced temporal constancy, most systems were present year-round, facilitating the exploitation of floral resources by pollinators. Diversity of pollination systems remained constant despite climate seasonality, indicating that several factors influence the optimum flowering time for pollination in seasonally dry vegetations. Global warming may disrupt phenological patterns and the temporal organization of plant communities, a matter for future studies.

When the grass wasn't greener: Megafaunal ecology and paleodroughts

A 42,000-year record of coprophilous fungal (Sporormiella, Podospora, Cercophora), fossil pollen and charcoal data assessed megafaunal use of woodland versus grassland settings in Central American landscapes by Pleistocene megafauna. The sedimentary record from Lake Petén-Itzá showed that vegetation growing around the lake shifted between scrub grasslands, Pinus-dominated woodlands, Quercus-dominated woodlands, and tropical seasonal forest. A series of regression analyses and probabilistic models revealed that vegetation assemblages and temperature influenced the abundance of coprophilous fungus, a proxy for megafaunal abundance. We found that megafaunal populations were almost continuously present around Petén-Itzá during the Pleistocene, and that the peak abundances appear to have been associated with cool, moist Quercus-rich parklands. In contrast, the lowest inputs of coprophilous fungi occurred during cold, dry events when scrub grasslands expanded. The dry grasslands may have been nutrient-limited, offering poor quality grazing for megafauna. The decline of the Pleistocene megafauna at Petén-Itzá was a multi-stage event, with a series of population collapses prior to an inferred local extirpation c. 13,600 years ago.

FATORES AMBIENTAIS AFETAM A ABUNDÂNCIA DE BROMÉLIAS EPÍFITAS EM FLORESTA TROPICAL SAZONAL SECA

Epiphytes can have both your richness and abundance altered by environmental conditions. In this study, we tested whether host plant characteristics (phorophyte) and other environmental factors contribute to the increased abundance of vascular epiphytes. Seventy-five fixed 20 × 20 m plots were sampled, distributed among three fragments of Dry Seasonal Tropical Forest (Caatinga) in three municipalities of Sergipe, Brazil: Poco Redondo (area 1), Porto da Folha (area 2) and Poco Verde (area 3). The hypotheses tested were: I. the greater the structural complexity of the phorophyte, greater the abundance of epiphytes in response to a greater diversity of fixing sites; II. Epiphyte abundance will be positively related to environmental factors that favor photosynthetic activity and nutrient absorption. Thus, a positive relationship between abundance and light, air relative humidity and altitude is expected, as well as a negative relationship between abundance, air temperature (possible water stress) and canopy cover (greater shading). 2,728 epiphytes were observed belonging to six species of Bromeliaceae, registered in 514 phorophytes of 29 species and 15 families. The abundance of epiphytes responded to some characteristics of the phorophytes and some of the abiotic factors. Thus, trunks with larger diameter and number of branches, smooth rhytidome and higher temperatures positively influenced the abundance of epiphytes, while increases in altitude and humidity affected the abundance negatively. It is concluded that the abundance of epiphytes in Caatinga fragments is directly associated with factors such as phorophyte structure and microclimatic conditions. Keywords: Caatinga, Interaction epiphyte-phorophyte, Microclimate.

Tropical Rainforest Successional Processes can Facilitate Successfully Recovery of Extremely Degraded Tropical Forest Ecosystems Following Intensive Mining Operations

Reforestation is an effective way to alleviate deforestation and its negative impacts on ecosystem services. In tropical rainforest ecosystem, however, frequent typhoons and heavy rainfall can result in landslides and uprooting of many seedlings, making reforestation efforts very difficult, especially within extremely degraded sites where soil conditions cannot support any plant life. Here, we described a reforestation protocol which is based on tropical rainforest successional processes to not only prevent landslides and tree uprooting due to frequent typhoon and heavy rain, but also accelerate tropical forest succession. This protocol first used the slope and soil layer of the undisturbed old-growth tropical rainforest as a reference to reconstruct slope and soil layers. Then multiple tropical tree species with high growth and survival rate were separately monocultured in the reconstructed soil layers. In the year of 2015 and 2016, we tested the effectiveness of this protocol to recover a 0.2 km2 extremely degraded tropical rainforest which consists of bare rock and thus does not support any plant life, in Sanya city, China. Our results showed that, both typhoons and heavy rains did not result in landslide or any tree damages in the area this reforestation protocol was used. Moreover, our separately monocultured eight fast-growing tree species have much higher fast-growing related functional traits than those for tree species in the adjacent undisturbed tropical seasonal forest, which in turn resulted in large soil water and nutrient loss within 3 years. This seemed to simulate a quick transition from primary succession (consist of bare rock and cannot support any plant life) to mid-stage of secondary tropical rainforest succession (many fast-growing pioneer tree species induced high soil water and nutrient loss). Thus, mixing the late-successional tropical tree species with each of the separately monocultured eight fast-growing tree species can accelerate recovery to the undisturbed tropical rainforest as soon as possible. Overall, based on tropical rainforest successional processes, our research provides an effective protocol for quickly and effectively restoring an extremely degraded tropical rainforest ecosystem. We expect that this work will be important for the future recovery of other extremely degraded tropical rainforest ecosystems.

Temporal variation of tree diversity of main forest vegetation in Xishuangbanna

In order to evaluate the temporal changes in tree diversity of forest vegetation in Xishuangbanna, Yunnan Province, the study collected tree diversity data from four main forest vegetation in the region through a quadrat survey including tropical rainforest (TRF), tropical coniferous forest (COF), tropical lower mountain evergreen broad-leaved forest (TEBF), tropical seasonal moist forest (TSMF). We extracted the distribution of four forest vegetation in the region in four periods of 1992, 2000, 2009, and 2016 in combination with remote sensing images, using simp son Shannon Wiener and scaling species diversity indexes compare to the differences of tree evenness of four forest vegetation and use the scaling ecological diversity index and grey correlation evaluation model to evaluate the temporal changes of forest tree diversity in the region in four periods. The results show that: (1) The proportion of forest area has a trend of decreasing first and then increasing, which is shown by the reduction from 65.5% in 1992 to 53.42% in 2000, to 52.49% in 2009, and then to 54.73% in 2016. However, the tropical rainforest shows a continuous decreasing trend. (2) There are obvious differences in the contributions of the four kinds of forest vegetation to tree diversity. The order of evenness is tropical rainforest > tropical mountain (low mountain) evergreen broad-leaved forest > warm coniferous forest > tropical seasonal humid forest, and the order of richness is tropical rainforest > tropical mountain (low mountain) evergreen broad-leaved forest > tropical seasonal humid forest > warm coniferous forest, The order of contribution to tree diversity in tropical rainforest > tropical mountain (low mountain) evergreen broad-leaved forest > tropical seasonal humid forest > warm tropical coniferous forest. (3) The tree diversity of tropical rainforests and tropical seasonal humid forests showed a continuous decreasing trend. The tree diversity of forest vegetation in Xishuangbanna in four periods was 1992 > 2009 > 2016 > 2000. The above results show that economic activities are an important factor affecting the biodivesity of Xishuangbanna, and the protection of tropical rainforest is of great significance to maintain the biodiversity of the region.

Disentangling the Effects of Vapor Pressure Deficit and Soil Water Availability on Canopy Conductance in a Seasonal Tropical Forest During the 2015 El Niño Drought

AbstractWater deficit in the atmosphere and soil are two key interactive factors that constrain transpiration and vegetation productivity. It is not clear which of these two factors is more important for the water and carbon flux response to drought stress in ecosystems. In this study, field data and numerical modeling were used to isolate their impact on evapotranspiration (ET) and gross primary productivity (GPP) at a tropical forest site in Barro Colorado Island (BCI), Panama, focusing on their response to the drought induced by the El Niño event of 2015–2016. Numerical simulations were performed using a plant hydrodynamic scheme (HYDRO) and a heuristic approach that ignores stomatal sensitivity to leaf water potential in the Energy Exascale Earth System Model (E3SM) Land Model (ELM). The sensitivity of canopy conductance (Gs) to vapor pressure deficit (VPD) obtained from eddy‐covariance fluxes and measured sap flux shows that, at both ecosystem and plant scale, soil water stress is more important in limiting Gs than VPD at BCI during the El Niño event. The model simulations confirmed the importance of water stress limitation on Gs, but overestimated the VPD impact on Gs compared to that estimated from the observations. We also found that the predicted soil moisture is less sensitive to the diversity of plant hydraulic traits than ET and GPP. During the dry season at BCI, seasonal ET, especially soil evaporation at VPD > 0.42 kPa, simulated using HYDRO and ELM, were too strong and will require alternative parameterizations.

Paleoenvironmental changes in the Hiwegi Formation (lower Miocene) of Rusinga Island, Lake Victoria, Kenya

The lower Miocene of Rusinga Island (Lake Victoria, Kenya) is best known for its vertebrate fossil assemblage but the multiple stratigraphic intervals with well-preserved fossil leaves have received much less attention. The Hiwegi Formation has three fossil leaf-rich intervals, which span the entire formation from oldest to youngest: Kiahera Hill, R5, and R3. Here, we describe new fossil collections from Kiahera Hill and R3 and compared these floras to previous work from R5, as well as modern African floras. The oldest flora at Kiahera Hill was most similar to modern tropical rainforests or tropical seasonal forests and reconstructed as a warm and wet, closed forest. This was followed by a relatively dry and open environment at R5, which was reconstructed as a woodland to open tropical seasonal forest. The youngest flora at R3 was most similar to modern tropical seasonal forests and was reconstructed as a warm and wet spatially heterogenous forest. Floral composition of all three floras differed, but the Kiahera Hill and R3 floras were more similar to each other than either flora was to the R5 flora. The Kiahera Hill flora had few monocots or herbaceous taxa, was dominated by large leaves, and had higher species richness and greater evenness than the R3 flora. Our work, coupled with previous studies, suggests that the R3 landscape consisted of both closed forest areas and open areas with seasonal ponding. The absence of morphotypes from the R5 flora that were present in the Kiahera Hill and R3 floras provides evidence for local extirpation during the R5 time interval. Thus, this work indicates that the Hiwegi Formation on Rusinga Island samples multiple environments ranging from more closed tropical forests to more open woodlands in the Early Miocene and provides important context for the evolution and habitat preference of early apes.

Habitat use and feeding behavior of domestic free-ranging goats in a seasonal tropical dry forest

Traditional pastoralism based on free-ranging goats is indispensable for the rural economy of millions of people in the Brazilian Caatinga drylands. The use of landscape as rangelands for domestic herbivores benefits humans, but understanding its impacts on vegetation is crucial to sustainable strategies. Here we assessed how free-ranging domestic goats use mixed working landscapes in the largest dry forest of the Americas. We evaluated habitat use via GPS tracking and analysis of feeding preferences. Goats preferentially used open areas near human settlements and their impact on plant community may be negligible because they feed mostly on plants widely available in modified environments. Although free-ranging, the area of use was nearly constant (95.44 ha), but the size of herds varied (2–100 animals). Our study suggests that domestic goats can be considered dwellers of human-modified landscapes, foraging close to villages, on open (i.e., degraded) areas where abundant plant species thrive. Therefore, the extensive goat pastoralism in the Caatinga may have little impact on natural vegetation and could be sustainably managed under traditional management practices.

Modeling wildfire drivers in Chinese tropical forest ecosystems using global logistic regression and geographically weighted logistic regression

The tropics is an area with high incidence of wildfire all over the world in recent years, and the forest ecosystem in the tropics is extremely fragile. Thus, it is very important to identify drivers of wildfire in the tropics for developing effective fire management strategy. In this paper, global logistic regression (GLR) and geographically weighted regression (GWLR) models were employed to analyze the spatial distribution and drivers of tropical wildfires in Xishuangbanna and Leizhou Peninsula in tropical China from 2001 to 2018. The results show that the overall distribution of wildfire in Xishuangbanna and Leizhou Peninsula from 2001 to 2018 was spatially aggregated. In these tropical seasonal forest ecosystems, wildfire was mainly driven by meteorological factors, particularly by daily temperature range and precipitation. In Xishuangbanna (inland) peninsula, the impact of driving factors tended to be global, and the GLR model predicted the probability of wildfire occurrence better than the GWLR model. Drivers of wildfire in Leizhou Peninsula (coastal area) had clear spatial variation, and the GWLR model better explained the relationship. Furthermore, wildfire in Leizhou was more driven by human activities, especially management of agricultural lands. Our results demonstrate that effective forest management practice needs to adopt fire management practices with regional characteristics. The forest management strategy and traditional agriculture production system should pay more attention to changes in these driving factors and their relationship with wildfire.

Divergence of stem biomechanics and hydraulics between Bauhinia lianas and trees.

Liana abundance and biomass are increasing in neotropical and Asian tropical seasonal forests over the past decades. Stem mechanical properties and hydraulic traits influence the growth and survival of plants, yet the differences in stem mechanical and hydraulic performance between congeneric lianas and trees remain poorly understood. Here, we measured 11 stem mechanical and hydraulic traits for 10 liana species and 10 tree species from Bauhinia grown in a tropical common garden. Our results showed that Bauhinia lianas possessed lower stem mechanical strength as indicated by both modulus of elasticity and modulus of rupture, and higher stem potential hydraulic conductivity than congeneric trees. Such divergence was mainly attributed to the differentiation in liana and tree life forms. Whether the phylogenetic effect was considered or not, mechanical strength was positively correlated with wood density, vessel conduit wall reinforcement and sapwood content across species. Results of principle component analysis showed that traits related to mechanical safety and hydraulic efficiency were loaded in the opposite direction, suggesting a trade-off between biomechanics and hydraulics. Our results provide evidence for obvious differentiation in mechanical demand and hydraulic efficiency between congeneric lianas and trees.

Pure or mixed plantings equally enhance the recovery of the Atlantic forest

Planting native trees in high diversity has been widely recommended to recover tropical forests to regain ecosystems that are taxonomically and functionally similar to the native forests. However, whether planting mixed stands would provide better results than planting pure stands remains to be demonstrated. Aiming to support seasonal tropical forest restoration in the highly fragmented landscape of the Atlantic Forest, Brazil, we compared the long-term (from 24 to 53 years) outcomes of pure and mixed plantings of native tree species with a broad spectrum of reference ecosystems (degraded, secondary, and old-growth forests). We aimed to verify if pure plantings would be as successful in fostering natural regeneration as mixed plantings and if they could potentially reach the attributes of native forests in the same region. We assessed forest structure (density, biomass, basal area), richness, and taxonomic and functional diversity. We separately analyzed the upper, intermediate, and lower layers of the tree community and assessed the abundance of ferns and climbers. Functional traits included seed dispersal and pollination syndromes, growth rate, seed mass, and specific leaf area. Contrary to our expectations, pure and mixed plantings did not differ in tree density, species richness, and functional diversity. Mixed plantings had higher basal area and biomass, surpassing the reference ecosystems and higher taxonomic diversity, whereas pure plantings had more ferns, climbers, and saplings regenerating in the understory. There was no difference for most of the functional traits between the forest types, except in seed mass, which was higher in mixed plantings. Zoochorous species were dominant in all forest types and size classes. In pure plantings, fast-growing species prevailed, whereas moderate and slow-growth species predominated in the other forest types. Pure plantings did not differ from the reference ecosystems, except in taxonomic diversity and richness when compared with the old-growth forests, which takes longer to be achieved. Our results indicate that the sparse remnants of forests are still effective sources of propagules to colonize the plantings – whether using a single species or a mix – even in a highly fragmented landscape, which was the case in our study. In general, pure plantings were as effective as mixed plantings to foster the recovery of seasonal tropical forests in terms of structure and functionality in the long term. As for taxonomic diversity and richness, mixed plantings were more efficient, whereas pure plantings have not reached old-growth forests but did not differ from degraded and surpassed secondary forests in several attributes. These results highlight the relevance of planting trees, even in low diversity, for increasing biodiversity and providing ecosystem services on a landscape scale.

The carbon sink of tropical seasonal forests in southeastern Brazil can be under threat.

Tropical forests have played an important role as a carbon sink over time. However, the carbon dynamics of Brazilian non-Amazon tropical forests are still not well understood. Here, we used data from 32 tropical seasonal forest sites, monitored from 1987 to 2020 (mean site monitoring length, ~15 years) to investigate their long-term trends in carbon stocks and sinks. Our results highlight a long-term decline in the net carbon sink (0.13 Mg C ha-1 year-1) caused by decreasing carbon gains (2.6% by year) and increasing carbon losses (3.4% by year). The driest and warmest sites are experiencing the most severe carbon sink decline and have already moved from carbon sinks to carbon sources. Because of the importance of the terrestrial carbon sink for the global climate, policies are needed to mitigate the emission of greenhouse gases and to restore and protect tropical seasonal forests.

Direct seeding to restore tropical seasonal forests: effects of green manure and hydrogel amendment on tree species performances and weed infestation

Although direct tree seeding may be a potentially useful restoration practice, many biotic and abiotic barriers prevent seedling emergence and early development, reducing its success and applicability. To overcome these barriers, we undertook a field experiment to test the effects of using green manure and hydrogel alone, or in combination, on seedling performances of 14 native tree species that were planted by direct seeding in a deforested tropical seasonal forest area in southern Brazil and to examine how green manure affected the initial weed coverage in the study plots. We evaluated competing vegetation coverage and tree seedling emergence and early development for 2 years after sowing. Weed infestation was significantly higher in the experimental plots with no green manure; however, neither green manure nor hydrogel improved tree seedling emergence and early development at any time of measurement. Our results suggest that the use of green manure and hydrogel alone, or in combination, were not effective in guaranteeing direct seeding success; however, green manure can be an effective method to reduce weed infestation. Direct seeding techniques for tree species still need to be improved in order to restore tropical seasonal forests on a larger scale.

Temperature is a dominant driver of distinct annual seasonality of leaf litter production of equatorial tropical rain forests

Abstract Intra‐annual periodicity of canopy photosynthetic activity and leaf development has been documented in seasonal and weakly seasonal tropical forests in the Amazon and elsewhere. However, vegetative periodicity such as leaf flush and fall in apparently ‘aseasonal’ equatorial tropical forests has not been well documented. Moreover, causal drivers of the vegetative periodicity in those forests have not been identified largely because of the difficulty in performing manipulative experiments targeting whole forest ecosystem dynamics. Here we show a distinct annual seasonality in canopy dynamics using a Fourier analysis with a statistical significance test on the long‐term, fortnightly monitored dataset of leaf litterfall in nine evergreen tropical rain forests on Mount Kinabalu, Borneo. Statistically significant annual periodicity occurs across elevations and soil types in all years irrespective of the year‐to‐year climatic variability, suggesting that fluctuations in regional climate rather than local micro‐climatic, edaphic and/or biotic conditions cause the precise 1‐year periodicity. We examine climatic factors that have causative effects on the distinct 1‐year periodicity using the spectrum convergent cross mapping that we developed in the present study that can distinguish causal relationships from seasonality‐driven synchronization. According to the analysis, we find that mean daily air temperature is most strongly, causatively related to the 1‐year periodicity of leaf litterfall. However, knowledge on ecophysiolocial and molecular mechanisms underlying temperature‐control of tropical tree growth is limited and further studies are required to understand the detailed mechanisms. Synthesis. We suggest that intra‐annual temperature changes in association with the movement of the intertropical convergence zone cause the distinct annual vegetative periodicity. Because vegetative periodicity can be transmitted to the dynamics of higher trophic levels through a trophic cascade, interactions between vegetative periodicity and daily air temperature, not rainfall, would more strongly cause changes in the dynamics of equatorial tropical rain forests. Our results show that clear vegetative periodicity (i.e. annual seasonality) can be found in equatorial tropical rain forests under diverse local environments, and that air temperature is a more important factor than the other climate variables in the climate–forest ecosystem interactions.

Climate regime shift and forest loss amplify fire in Amazonian forests.

Frequent Amazonian fires over the last decade have raised the alarm about the fate of the Earth's most biodiverse forest. The increased fire frequency has been attributed to altered hydrological cycles. However, observations over the past few decades have demonstrated hydrological changes that may have opposing impacts on fire, including higher basin-wide precipitation and increased drought frequency and severity. Here, we use multiple satellite observations and climate reanalysis datasets to demonstrate compelling evidence of increased fire susceptibility in response to climate regime shifts across Amazonia. We show that accumulated forest loss since 2000 warmed and dried the lower atmosphere, which reduced moisture recycling and resulted in increased drought extent and severity, and subsequent fire. Extremely dry and wet events accompanied with hot days have been more frequent in Amazonia due to climate shift and forest loss. Simultaneously, intensified water vapor transport from the tropical Pacific and Atlantic increased high-altitude atmospheric humidity and heavy rainfall events, but those events did not alleviate severe and long-lasting droughts. Amazonia fire risk is most significant in the southeastern region where tropical savannas undergo long seasonally dry periods. We also find that fires have been expanding through the wet-dry transition season and northward to savanna-forest transition and tropical seasonal forest regions in response to increased forest loss at the "Arc of Deforestation." Tropical forests, which have adapted to historically moist conditions, are less resilient and easily tip into an alternative state. Our results imply forest conservation and fire protection options to reduce the stress from positive feedback between forest loss, climate change, and fire.