General Flowering Research Articles

No evidence of carbon storage usage for seed production in 18 dipterocarp masting species in a tropical rain forest.

Most canopy species in lowland tropical rain forests in Southeast Asia, represented by Dipterocarpaceae, undergo mast reproduction synchronously at community level during a general flowering event. Such events occur at irregular intervals of 2-10years. Some species do not necessarily participate in every synchronous mast reproduction, however. This may be due to a lack of carbohydrate resources in the trees for masting. We tested the hypothesis that interspecific differences in the time required to store assimilates in trees for seed production are due to the frequency of masting and/or seed size in each species. We examined the relationship between reproductive frequency and the carbon accumulation period necessary for seed production, and between the seed size and the period, using radiocarbon analysis in 18 dipterocarp canopy species. The mean carbon accumulation period was 0.84years before seed maturation in all species studied. The carbon accumulation period did not have any significant correlation with reproductive frequency or seed size, both of which varied widely across the species studied. Our results show that for seed production, dipterocarp masting species do not use carbon assimilates stored for a period between the masting years, but instead use recent photosynthates produced primarily in a masting year, regardless of the masting interval or seed size of each species. These findings suggest that storage of carbohydrate resources is not a limiting factor in the masting of dipterocarps, and that accumulation and allocation of other resources is important as a precondition for participation in general flowering.

An ecological transcriptome approach to capture the molecular and physiological mechanisms of mass flowering in Shorea curtisii.

Climatic factors have commonly been attributed as the trigger of general flowering, a unique community-level mass flowering phenomenon involving most dipterocarp species that forms the foundation of Southeast Asian tropical rainforests. This intriguing flowering event is often succeeded by mast fruiting, which provides a temporary yet substantial burst of food resources for animals, particularly frugivores. However, the physiological mechanism that triggers general flowering, particularly in dipterocarp species, is not well understood largely due to its irregular and unpredictable occurrences in the tall and dense forests. To shed light on this mechanism, we employed ecological transcriptomic analyses on an RNA-seq dataset of a general flowering species, Shorea curtisii (Dipterocarpaceae), sequenced from leaves and buds collected at multiple vegetative and flowering phenological stages. We assembled 64,219 unigenes from the transcriptome of which 1,730 and 3,559 were differentially expressed in the leaf and the bud, respectively. Differentially expressed unigene clusters were found to be enriched with homologs of Arabidopsis thaliana genes associated with response to biotic and abiotic stresses, nutrient level, and hormonal treatments. When combined with rainfall data, our transcriptome data reveals that the trees were responding to a brief period of drought prior to the elevated expression of key floral promoters and followed by differential expression of unigenes that indicates physiological changes associated with the transition from vegetative to reproductive stages. Our study is timely for a representative general flowering dipterocarp species that occurs in forests that are under the constant threat of deforestation and climate change as it pinpoints important climate sensitive and flowering-related homologs and offers a glimpse into the cascade of gene expression before and after the onset of floral initiation.

Characterization of Leaf Transcriptome in a Tropical Tree Species, <i>Shorea curtisii</i>, over a Flowering Season

General flowering (GF) is a synchronous flowering phenomenon in the Southeast Asian tropical rainforests that occurs at irregular intervals of multiple years. While in this study, the leaf transcriptome of a GF species, Shorea curtisii obtained from three-time points – before and after floral initiation, and post-flowering stage – was sequenced, the unpredictable intervals of GF raise conservation concerns for these under-researched forests with rich economically and ecologically important species. We assembled 243,759,478 sequencing reads into 39,943 non-redundant unigenes including 677 putative homologs of Arabidopsis thaliana flowering-related genes. Differential expression analysis conducted on pairwise comparisons of the time points identified 930 differentially expressed unigenes, which includes 17 flowering-related homologs. The differential expression of unigenes with significant enrichments of functions related to drought corroborated the involvement of drought as an environmental cue for GF, with the outcomes of this study offering an insight into the conservation of floral regulatory genes and pathways in Shorea and possibly being used as a model to better understand the floral initiation cues and regulation of GF trees.

Utility of commercial high‐resolution satellite imagery for monitoring general flowering in Sarawak, Borneo

AbstractGeneral flowering (GF), irregular synchronous mass flowering of multiple tree species across multiple families, is a unique biological phenomenon of the mixed lowland dipterocarp forest in Southeast Asia. Characterizing the spatial extent and temporal dynamics of GF is essential for an improved understanding of climate–vegetation interactions and the potential climate change impact on this species‐rich rainforest. We investigated the utility of newly available high‐temporal (daily) and high‐spatial (3–4 m) resolution remote sensing by the PlanetScope commercial satellite constellation for detecting flowering trees in a dipterocarp rainforest at Lambir Hills National Park, Sarawak, Malaysia. Our study was focused on the latest GF event known to have occurred in the region in the year 2019. PlanetScope successfully acquired 13 clear‐sky or minimally cloud‐contaminated scenes over the park during a study period of January 1, 2019 to August 31, 2019 encompassing the 2019 GF event. In situ phenology observations verified that the PlanetScope images detected the flowering crowns of tree species that turned into white or orange. This multitemporal image dataset also captured the flowering peak and species differences. The correlation coefficients between the multitemporal image signatures and in situ phenology observations were moderate to very strong (0.52–0.85). The results indicated that the 2019 GF event was a whole‐park phenomenon with the flowering peak in May. This study reports the first successful satellite‐based observations of a GF event and suggests the possibility of regional‐scale characterization of species‐level phenology in the dipterocarp forest, key information for biodiversity conservation in Southeast Asia.

Modeling the Impact of Climate Change on General Flowering in Bukit Barisan Selatan National Park, Sumatera

In Southeast Asian dipterocarp forests, a general flowering (GF) occurs at the multiannual interval. At this phenomenon, at least 40% of the trees in the stands flower in synchrony, dominated by the flowering of the Dipterocarpaceae family that hypothesized to be caused by changes in climate factors, especially ENSO. This study aimed to determine the pattern of flowering trees in Bukit Barisan Selatan National Park (BBSNP) and to determine a model for predicting flowering patterns associated with climatic factors in 2021-2050. Flowers and fruits were observed every month from February 1998 to September 2020 at Way Canguk Research Station, BBSNP. The climatic factors used were temperature, rainfall, humidity, wind speed, and the ENSO index. We used a generalized linear model to link climatic factors and flowering and model future flowering. The results showed no GF in BBSNP because the highest flower synchronization only reached 37.8%. The climatic factor with the highest coefficient was ENSO, but flowering was mostly influenced by fluctuations in climate factors, not its absolute value. The model estimated that the flowering in 2021 - 2050 will peak to 34.4% in December 2044 and further ensure good forest regeneration. Thus, BBSNP can still be suitable for conservation purposes.

Testing the environmental prediction hypothesis for community‐wide mass flowering in South‐East Asia

AbstractGeneral flowering, in which hundreds of species synchronize their flowering at multi‐year intervals, is a puzzle to ecologists. It is hypothesized that species taking part in general flowering time their reproduction to meet favorable environmental conditions for seedling establishment. We tested this environmental prediction hypothesis using 14‐year weekly flower records of five Shorea species (Dipterocarpaceae) and daily meteorological data in a lowland rain forest in Malaysia. We first investigated causal inference between three potential flowering triggers (cooling, drought, and the synergistic signal of cooling and drought) and flowering. We then explored the causality between flowering triggers and moisture condition during seedling establishment. Our results demonstrated that the synergistic signal of cooling and drought causally influences flowering phenology with the highest predictability for the timing of flowering. Both drought and the synergistic signal of cooling and drought are causally linked to favorable wet conditions during seedling establishment, but the predictability of future rainfall by the synergistic signal was higher than the drought alone. These results support the environmental prediction hypothesis and raise the question as to whether climate change allows the prediction to hold for plant regeneration in the future.

Dynamic and synergistic influences of air temperature and rainfall on general flowering in a Bornean lowland tropical forest

AbstractSupra‐annually synchronized flowering events occurring in tropical forests in Southeast Asia, known as general flowering (GF), are “spectacular and mysterious” forest events. Recently, studies that combined novel molecular techniques and model‐based theoretical approaches suggested that cool temperature and drought synergistically drove GF. Although these advanced our understanding of GF, it is still difficult to know whether the individual‐based molecular measurements and model‐based mathematical representations reasonably well capture the complex and dynamic GF processes at the community level. In the present study, we collected a 17‐year set of community‐wide phenology data from Lambir Hills National Park in Borneo, Malaysia, and analyzed it using a model‐free approach, empirical dynamic modeling (EDM), which does not rely on specific assumptions about the underlying mechanisms, to overcome and complement the previous limitations. We found that GF in the region is driven synergistically, not independently, by cool air temperature and drought, which is consistent with the previous studies. More importantly, our model‐free approach showed for the first time that effects of cumulative meteorological variables on GF changed over time. The time‐varying influences of meteorological variables on GF imply that the relationship between GF and meteorological variables might be influenced by other factors such as plant/soil nutrient resource dynamics. Our study provides a novel insight about the mechanism underlying the spectacular tropical forest event GF, and future studies integrating advanced mathematical/statistical frameworks, long‐term and large spatial scale ecosystem monitoring and molecular phenology data are promising for achieving better understanding and forecasting of GF events in Southeast Asia.

Drought and cool temperature cue general flowering synergistically in the aseasonal tropical forests of Southeast Asia

AbstractThe family Dipterocarpaceae, along with species from many other families, flower synchronously at irregular intervals of several years in the extensive humid forests of Southeast Asia. The intermittent mast seeding in these forests satiates seed predators whose populations remain low due to starvation in non masting periods, effectively increasing seed survival and seedling recruitment. A previous study demonstrated that a synergistic interaction between drought and cool temperatures, instead of either climate factor alone, best explains the occurrence of general flowering events observed over 14 years at the Pasoh Research Forest, Malaysia. However, several measures of drought were proposed and which drought measure should be used to explain general flowering remains untested. Here we examined the relationship between flowering of five Shorea species and three drought indices, the difference between the mean daily accumulation of precipitation and a threshold level of precipitation, water deficit and antecedent precipitation index. Our analyses confirmed that for most of Shorea species we studied the synergistic model that considers both cool temperature and drought performs the best regardless of the choice of drought index. In addition, a simplest drought measure using cumulative precipitation is sufficient to explain flowering activities in Shorea species.

Data paper: Long‐term litter production in a lowland dipterocarp forest, Peninsular Malaysia from 1992 to 2017

Tropical rainforests in Southeast Asia dominated by Dipterocarpaceae show a unique reproductive event, general flowering. This paper records long‐term seed production of a tropical rainforest in Pasoh Forest Reserve, Peninsular Malaysia. Study site is a lowland dipterocarp forest dominated by Dipterocarpaceae and Fabaceae. Seed and other litter production data are essential for analyzing general flowering and evaluating net primary production (NPP) of rainforest ecosystems under climate change. Unfortunately, there is a lack of long‐term litter production data in Dipterocarp forests. This paper presents such a long‐term litter data from 1992 to 2017. We collected litter samples every month from May 1992 to December 2017 in Pasoh F.R., Peninsular Malaysia (2°59′N, 102°18′E, 120–152 m a.s.l.). Litter was collected using 100 litter traps spaced evenly within a 2‐ha core area of the 6‐ha study plot. Each litter trap was made of 1 mm mesh with a circular area of 0.5 m2 from May 8, 1992 to December 22, 1998. Then litter trap was changed to a square type with 4 mm mesh until now. Litter samples were collected and separated to leaf, flower, seed and others (debris). After sorting litter samples were dried at 85°C for 48 hr and weighed. Seeds and flowers were separated according to tentative morphological types and identified. This data paper contains two data sets. Litter data set contains weight of each litter fractions. Seed data set contains number and weight of morphological seed types and identified scientific name.

Phenology of a dipterocarp forest with seasonal drought: Insights into the origin of general flowering

Abstract Our understanding of the factors that shape reproductive phenology in Southeast Asian tropical forests comes almost exclusively from studies of everwet, general flowering (GF) forests. Therefore, we examined the phenology of an evergreen dipterocarp forest in a climate exhibiting seasonal drought in Southeast Asia, with the aim of evaluating what evidence it brings to bear on the hypothesis that reproductive phenology in contemporary dipterocarp forests is the product of evolutionarily conserved responses to seasonal drought. We hypothesized that (1) dipterocarp forests that experience seasonal drought would exhibit annual reproduction and seasonality similar to that of forests with similar climates in other parts of the world, (2) within species, flowering frequency would be climate‐dependent, not a fixed trait, and (3) climatic events that cue flowering in everwet forests would also cue flowering in seasonally dry forests. From 2001 to 2009, we monitored flowering and fruiting monthly for 1,344 trees (>300 spp.) in a forest in Khao Chong (KC), Thailand that experiences an annual 2–4 month dry season, assessing frequency, duration, seasonality and synchrony of reproduction. We also examined phenological records for trees in three dipterocarp‐dominated forests in everwet climates. Reproductive phenology of the KC forest was more similar to tropical forests with similar rainfall seasonality in other parts of the world than it was to dipterocarp‐dominated forests in everwet regions of Southeast Asia. The forest exhibited annual reproduction, with peak flowering occurring at the end of the dry season and peak fruiting occurring early in the wet season. Approximately half of all species and individuals reproduced annually, including several species that are known to exhibit “general flowering” in everwet climates. Short dry spells appeared to cue flowering for early flowering species, while later flowering species may have responded to either low precipitation or temperature, consistent with data from everwet forests. GF behaviour also showed significant phylogenetic signal. Synthesis. Our results support the hypothesis that the phenological behaviour of both seasonal and everwet dipterocarp forests may have initially evolved in response to seasonal drought and that the general flowering phenomenon is a product of evolutionary conservatism.

Species‐specific flowering cues among general flowering Shorea species at the Pasoh Research Forest, Malaysia

Abstract In a unique phenomenon restricted to the ever wet forests of Southeast Asia, hundreds of species from dozens of plant families reproduce synchronously at irregular, multi‐year intervals. The proximate environmental cues that synchronize these general flowering events have not been evaluated systematically because there have been no long‐term, high temporal resolution, species‐level records from the region. We present 13 years of weekly flowering records for five Shorea species as well as daily temperature and rainfall records from the Pasoh Forest Reserve, Peninsular Malaysia. We constructed models to evaluate hypothesized relationships between flowering and cool temperature, drought, and additive and synergistic effects of cool temperature and drought for each species. Model parameters include periods of time for floral cue accumulation and flower development and temperature and/or rainfall thresholds required for floral initiation. Parameters estimated using flowering observations from 2001 to 2011 were used to forecast flowering for 2011–2014. We show that drought and cool temperatures acting synergistically best explain the timing of flowering events for all Shorea species in the section Mutica and forecast the largest general flowering event accurately. Periods estimated for signal accumulation ranged from 54 to 90 days among species. Periods estimated for flowers to develop ranged between 43 and 96 days and closely followed the interspecific sequence of flowering in the Shorea species. Drought and temperature thresholds also varied among species, with Shorea maxwelliana requiring the most severe drought and Shorea leprosula the lowest temperatures. Synthesis. Our results indicate that cool temperatures and low rainfall occurring on seasonal time‐scales of about 2–3 months rather than brief cold snaps or brief droughts best explain general flowering in Shorea species at the Pasoh Forest Reserve. Low rainfall is equally likely in winter (December–February) and summer (July–August) and cool temperatures are most likely in winter at Pasoh, which explains why general flowering events are restricted to spring and fall, with more frequent and stronger flowering in spring. In addition, species‐specific sensitivity to environmental cues suggests that future climate change will have differential impacts on the frequency of reproduction, with potential consequences for regeneration of these dominant species of lowland tropical forests.

Responses of pre‐dispersal seed predators to sequential flowering of Dipterocarps in Malaysia

AbstractMany species of Dipterocarpaceae and other plant families reproduce synchronously at irregular, multi‐year intervals in Southeast Asian forests. These community‐wide general flowering events are thought to facilitate seed survival through satiation of generalist seed predators. During a general flowering event, closely related Shorea species (Dipterocarpaceae) stagger their flowering times by several weeks, which may minimize cross pollination and interspecific competition for pollinators. Generalist, pre‐dispersal seed predators might also track flowering hosts and influence predator satiation. We addressed the question of whether pre‐dispersal seed predation differed between early and late flowering Shorea species by monitoring flowering, fruiting and seed predation intensity over two general flowering events at the Pasoh Research Forest, Malaysia. Pre‐dispersal insect seed predators killed up to 63 percent of developing seeds, with Nanophyes shoreae, a weevil that feeds on immature seeds being the most important predator for all Shorea species. This weevil caused significantly greater pre‐dispersal seed predation in earlier flowering species. Long larval development time precluded oviposition by adults that emerged from the earliest flowering Shorea on the final flowering Shorea. In contrast, larvae of weevils that feed on mature seeds before seed dispersal (Alcidodes spp.), appeared in seeds of all Shorea species almost simultaneously. We conclude that general flowering events have the potential to satiate post‐dispersal seed predators and pre‐dispersal seed predators of mature fruit, but are less effective at satiating pre‐dispersal predators of immature fruit attacking early flowering species.

Satellite-based characterization of climatic conditions before large-scale general flowering events in Peninsular Malaysia

General flowering (GF) is a unique phenomenon wherein, at irregular intervals, taxonomically diverse trees in Southeast Asian dipterocarp forests synchronize their reproduction at the community level. Triggers of GF, including drought and low minimum temperatures a few months previously has been limitedly observed across large regional scales due to lack of meteorological stations. Here, we aim to identify the climatic conditions that trigger large-scale GF in Peninsular Malaysia using satellite sensors, Tropical Rainfall Measuring Mission (TRMM) and Moderate Resolution Imaging Spectroradiometer (MODIS), to evaluate the climatic conditions of focal forests. We observed antecedent drought, low temperature and high photosynthetic radiation conditions before large-scale GF events, suggesting that large-scale GF events could be triggered by these factors. In contrast, we found higher-magnitude GF in forests where lower precipitation preceded large-scale GF events. GF magnitude was also negatively influenced by land surface temperature (LST) for a large-scale GF event. Therefore, we suggest that spatial extent of drought may be related to that of GF forests, and that the spatial pattern of LST may be related to that of GF occurrence. With significant new findings and other results that were consistent with previous research we clarified complicated environmental correlates with the GF phenomenon.

Marine influence controls plant phenological dynamics in Mediterranean Mexico

Aims To assess the role of moisture in phenological timing in the mediterranean coastal flora of Baja California, and specifically to assess the role of coastal fog and ocean-derived moisture in plant phenology. Moisture seems to be the primary driver of flowering times and durations at the arid end of the mediterranean-climate region, where rainfall is often sporadic (temperature and day length can be expected to play a much lesser role as they are not growth limiting). We aimed to understand: What factors drive climatic variation between sites? Are there general flowering patterns allowing us to identify phenological categories? Do flowering patterns vary in relation to site-specific weather? and most importantly, does maritime influence on weather affect flowering dynamics in coastal mediterranean ecosystems? Methods The southernmost extent of the California Floristic Province (in Baja California, Mexico) is a biological diversity hotspot of high endemism and conservation value, with two steep moisture gradients: rainfall (N–S) and coastal fogs (W–E), providing an ideal study system. We installed five weather stations across the moisture gradients, recording data hourly. We monitored flowering phenology in the square kilometer surrounding each weather station from 2010 to 2013. About 86 plant taxa were monitored across the five sites, every 6–8 weeks. Averaged climatic data is presented with general trends in flowering, and specific flowering syndromes were observed. Data for flowering intensity across the sites was analyzed using a principal components analysis. Important Findings Data analysis demonstrates a general seasonal pattern in flowering times, but distinct differences in local weather and phenology between the five study sites. Three flowering syndromes are revealed in the flora: (i) water responders or spring bloomers, (ii) day-length responders or fall-blooming taxa and (iii) aseasonal bloomers with no seasonal affinity. The two moisture gradients are the strongest drivers of flowering times. Inland sites showed higher phenological variation than coastal sites where seasonality is dampened by ocean-derived moisture, which extends and buffers perennial plant phenology and is a probable driver of local endemism. Phenological controls vary globally with climate and geography; moisture is the primary driver of phenology in mediterranean climates and fog is an important climatic variable in coastal Mexico.

Long-term changes in liana loads and tree dynamics in a Malaysian forest.

The importance of lianas through time and their effect on tree reproduction are evaluated for the first time in a Southeast Asian Dipterocarp forest. We quantified flower and seed production by lianas and trees for 13 years, assessed liana loads in the crowns of all trees larger than 30 cm in diameter at breast height (1.3 m) in 2002 and 2014, and assessed levels of reproduction for the same trees during a strong general flowering event in 2014 for the 50-ha forest dynamics plot at the Pasoh Forest Reserve, Malaysia. General flowering refers to synchronous reproduction by hundreds of plant species at irregular, multiyear intervals and only occurs in Southeast Asian Dipterocarp forests. Overall, lianas were present in 50% of tree crowns and comprised 31% of flower production and 46% of seed production. Lianas reduced growth, survival, and reproduction by their host trees. Lianas were less frequent in canopy- emergent trees, Dipterocarps comprised a disproportionately large proportion of canopy emergents, and, as a consequence, lianas were less frequent in Dipterocarps than in trees from other plant families. Lianas infested the crowns of significantly fewer trees in 2014 (47.9%) than in 2002 (52.3%); however, the decrease was restricted to trees with the lightest liana loads and sample sizes and statistical power were enormous. Lianas comprised a stable proportion of flower production and a highly variable proportion of seed production from 2002 through 2013. We conclude lianas have a huge impact on trees in this forest and were a stable component of the forest between 2002 and 2014. The emergent habit and associated ability to avoid lianas might contribute to the success of the Dipterocarpaceae.

Biotic and abiotic drivers of dipterocarp seedling survival following mast fruiting in Malaysian Borneo

Abstract:South-East Asian tropical rain forests experience sporadic, but profuse, seed production after general flowering, leading to the synchronous emergence of various seedlings and subsequent seedling dynamics, which play a crucial role in determining species distribution and coexistence. We examined the relative importance of both biotic (initial height, conspecific seedling density) and abiotic (canopy openness, per cent sand, soil water content) drivers using survival data for 1842 seedlings of 12 dipterocarp species for 1.5 y following mast fruiting in an old-growth Bornean tropical rain forest. More than 30% of all dipterocarp seedlings survived 1.5 y after mast fruiting. When all species were analysed together, we found that initial seedling height, canopy openness and conspecific seedling density affected dipterocarp seedling survival. Negative density dependence indicated that predators were not satiated, but dipterocarp seedlings rather suffered from host-specific natural enemies or intraspecific competition. Species-level analyses of seven dipterocarp species showed large variation in response to biotic and abiotic factors. These results suggest that interspecific differences in the relative importance of biotic and abiotic effects on seedling survival might contribute to species coexistence.

Spatiotemporal Variability in the Reproductive Success of the Continually Flowering Shrub Dillenia suffruticosa in Borneo

AbstractContinually flowering plants bloom continuously throughout the year, as often seen in plants distributed along the roadsides or in the understory layers in Southeast Asia's tropical rain forests. Dillenia suffruticosa (Griff. ex Hook. f. & Thomson) Martelli (Dilleniaceae) is one such continually flowering shrub that flowers during periods of community‐wide mass flowering, general flowering (GF), and non‐GF. During irregularly occurring GF periods, when species of all forest layers flower synchronously for several months, some pollinators migrate to the canopy layer, where GF promotes the pollination success of participating plants. Continually flowering plants share the available pollinator community with GF plants, and the reproductive success of continually flowering plants may be affected during the GF period. To assess the effects of GF on the reproductive success of a diverse range of continually flowering plants, we examined the differences in pollinator density and reproductive success between GF and non‐GF periods in D. suffruticosa at four different research sites. Although the seed set differed among the four research sites, pollinator density and fruit set did not differ between GF and non‐GF periods or research sites. Our results suggest that the reproductive success of D. suffruticosa was maintained at an approximately constant level, regardless of the flowering phenology of the canopy layer or other vegetation components.

Geographical Pattern and Environmental Correlates of Regional-Scale General Flowering in Peninsular Malaysia

In South-East Asian dipterocarp forests, many trees synchronize their reproduction at the community level, but irregularly, in a phenomenon known as general flowering (GF). Several proximate cues have been proposed as triggers for the synchronization of Southeast Asian GF, but the debate continues, as many studies have not considered geographical variation in climate and flora. We hypothesized that the spatial pattern of GF forests is explained by previously proposed climatic cues if there are common cues for GF among regions. During the study, GF episodes occurred every year, but the spatial occurrence varied considerably from just a few forests to the whole of Peninsular Malaysia. In 2001, 2002 and 2005, minor and major GF occurred widely throughout Peninsular Malaysia (GF2001, GF2002, and GF2005), and the geographical patterns of GF varied between the episodes. In the three regional-scale GF episodes, most major events occurred in regions where prolonged drought (PD) had been recorded prior, and significant associations between GF scores and PD were found in GF2001 and GF2002. However, the frequency of PD was higher than that of GF throughout the peninsula. In contrast, low temperature (LT) was observed during the study period only before GF2002 and GF2005, but there was no clear spatial relationship between GF and LT in the regional-scale episodes. There was also no evidence that last GF condition influenced the magnitude of GF. Thus, our results suggest that PD would be essential to trigger regional-scale GF in the peninsula, but also that PD does not fully explain the spatial and temporal patterns of GF. The coarse relationships between GF and the proposed climatic cues may be due to the geographical variation in proximate cues for GF, and the climatic and floristic geographical variations should be considered to understand the proximate factors of GF.

Mass flowering of the tropical tree Shorea beccariana was preceded by expression changes in flowering and drought-responsive genes.

Community-level mass flowering, known as general flowering, which occurs in South-East Asia at supra-annual irregular intervals, is considered a particularly spectacular phenomenon in tropical ecology. Recent studies have proposed several proximate factors inducing general flowering, such as drought and falls in minimum temperature. However, limited empirical data on the developmental and physiological processes have been available to test the significance of such factors. To overcome this limitation and test the hypotheses that general flowering is triggered by the proposed factors, we conducted an ‘ecological transcriptome’ study of a mass flowering species, Shorea beccariana, comparing meteorological data with genome-wide expression patterns obtained using next-generation sequencing. Among the 98 flowering-related genes identified, the homologs of a floral pathway integrator, SbFT, and a floral repressor, SbSVP, showed dramatic transcriptional changes before flowering, and their flowering functions were confirmed using transgenic Arabidopsis thaliana. Expression in drought-responsive and sucrose-induced genes also changed before flowering. All these expression changes occurred when the flowering-inducing level of drought was reached, as estimated using data from the preceding 10 years. These genome-wide expression data support the hypothesis that drought is a trigger for general flowering.

Possible Negative Effect of General Flowering on Tree Growth and Aboveground Biomass Increment in a Bornean Tropical Rain Forest

AbstractWe tested the effect of general flowering (GF), community‐wide masting, and drought stress on current‐year tree diameter growth and aboveground biomass increment (ABI). General flowering but not drought had a marginally significant negative effect on tree growth and ABI at the community level. Analyses of dominant species clarified this pattern.