Flowering Phenology Research Articles

Flower phenology as a disruptor of the fruiting dynamics in temperate oak species

Many perennial plants display masting, that is, fruiting with strong interannual variations, irregular and synchronized between trees within the population. Here, we tested the hypothesis that the early flower phenology in temperate oak species promotes stochasticity into their fruiting dynamics, which could play a major role in tree reproductive success. From a large field monitoring network, we compared the pollen phenology between temperate and Mediterranean oak species. Then, focusing on temperate oak species, we explored the influence of the weather around the time of budburst and flowering on seed production, and simulated with a mechanistic model the consequences that an evolutionary shifting of flower phenology would have on fruiting dynamics. Temperate oak species release pollen earlier in the season than do Mediterranean oak species. Such early flowering in temperate oak species results in pollen often being released during unfavorable weather conditions and frequently results in reproductive failure. If pollen release were delayed as a result of natural selection, fruiting dynamics would exhibit much reduced stochastic variation. We propose that early flower phenology might be adaptive by making mast-seeding years rare and unpredictable, which would greatly help in controlling the dynamics of seed consumers.

Climate change shifts natural selection and the adaptive potential of the perennial forb Boechera stricta in the Rocky Mountains.

Heritable genetic variation is necessary for populations to evolve in response to anthropogenic climate change. However, antagonistic genetic correlations among traits may constrain the rate of adaptation, even if substantial genetic variation exists. We examine potential genetic responses to selection by comparing multivariate genetic variance-covariances of traits and fitness (multivariate Robertson-Price identities) across different environments in a reciprocal transplant experiment of the forb Boechera stricta in the Rocky Mountains. By transplanting populations into four common gardens arrayed along an elevational gradient, and exposing populations to control and snow removal treatments, we simulated future and current climates and snowmelt regimes. Genetic variation in flowering and germination phenology declined in plants moved downslope to warmer, drier sites, suggesting that these traits may have a limited ability to evolve under future climates. Simulated climate change via snow removal altered the strength of selection on flowering traits, but we found little evidence that genetic correlations among traits are likely to affect the rate of adaptation to climate change. Overall, our results suggest that climate change may alter the evolutionary potential of B. stricta, but reduced expression of genetic variation may be a larger impediment to adaptation than constraints imposed by antagonistic genetic correlations.

Phenology, flowering and fruit-set patterns of baobabs, Adansonia digitata, in southern Africa

Baobabs (Adansonia digitata) are iconic and highly valued trees that characterise many semi-arid environments across Africa. The aim of this study was to describe leaf, flowering and fruit phenology, flower production and fruit-set patterns of southern African baobabs. This was done on a sample of 106 trees across five land-use types at monthly intervals over two-years. Rainfall in the first year (2006/7, Year 1) was only 275 mm, but doubled in the second year (516 mm; 2007/8, Year 2), being below and above the long term mean of 461 mm, respectively. Leaf flush preceded the onset of rains (October) in 88% of trees in Year 1, but after the onset of rains (August) in all trees in Year 2. Leaves flushed in November and were retained until April and in October and retained until March, respectively. Leaf fall occurred one month later in Year 1 (May) than in Year 2 (April). Flowering followed a steady-state pattern, lasting for 1–5 months with peak flowering in November in both years. For adult trees, flower number/tree (Year 1: 711 ± 72 (S.E.) and Year 2: 287 ± 33), but not fruit-set (mean of 20 ± 4%) varied significantly between years. Flower number showed a logarithmic relationship with tree size (stem diameter) (R2 = 0.3830, P < 0.0001), while fruit-set was unrelated to tree size (R2 = 0.0045, P = 0.5081). Flower number and fruit-set did not vary between five land-use types, but length of flowering did, with village trees flowering for the longest period. Baobabs are hermaphrodite plants with both male and female reproductive structures in the same flower. Yet, across Africa many people refer to individual trees as being ‘male’ (fruiting is absent or minimal) or ‘female’ (substantial fruiting). Producer ‘female’ and poor-producer ‘male’ trees, did not differ in flowering phenology (number, timing and length of flowering), but fruit-set over two sequential years differed greatly between producer (33.5 ± 5.2%) and poor producer (0.2 ± 0.1%) trees. Leaf flush was responsive to early rains and hence baobabs appear to be facultative early greeners. However flowering and fruit-set patterns were not significantly different between these two years, despite the large rainfall difference. Although flower production was not different between producer and poor-producer trees in either year, fruit set was three orders of magnitude higher in producer than poor-producer trees. These quantitative results suggest that baobabs may be functionally dioecious and thus a complete characterization of the reproductive biology is required. Mechanisms underlying this pattern are discussed in terms of tree age, environment, pollination, genetics and evolutionary biology.

Past selection shaped phenological differentiation among populations at contrasting elevations in a Mediterranean alpine plant

Flowering phenology is an important life-history trait strongly influenced by the environment that directly affects plant fitness. Climate change is bringing about shifts in flowering time caused by adaptive evolution and phenotypic plasticity, but their relative contributions and effects are poorly understood. This is especially critical in Mediterranean alpine species, which experience steep environmental gradients at short distances characteristic of alpine environments and an intense summer drought period derived from the Mediterranean climate. Moreover, tracking climate change through migration to higher elevations is not always possible for alpine species since many already find their optimal niche at mountain summits. In this study, we aimed to determine if flowering phenology is genetically differentiated among populations inhabiting contrasting environmental conditions and ascertain if it has been subjected to past selection. This knowledge is crucial to understanding adaptation of alpine plants to current environmental gradients and to provide insight about what adaptations may be necessary to cope with future and ongoing climate warming. We used a common garden experiment to analyze genetic differentiation in phenological traits of nine populations of Silene ciliata Pourret (Caryophyllaceae) distributed at two environmentally differentiated areas (optimal and marginal habitat suitability) in three mountain ranges of Central Spain. Environmentally optimal areas for this species are close to the mountain tops, whereas marginal areas are found at the lower distribution edge. We also studied the relation between neutral genetic differentiation (FST) and quantitative trait differentiation (PST) to infer past selection on characters under contrasting environmental conditions. We found genetic differentiation for the onset, peak and end of flowering between populations in optimal and marginal areas in the presence of substantial gene flow. This finding highlights the strong diverging selection pressures between the different Mediterranean alpine environments. We also found evidence of past diversifying selection for flowering peak and end of flowering. This evidence of past adaptation in addition to adaptive phenotypic plasticity to advance flowering dates under warmer temperatures suggest that adaptation of flowering phenology to current and future warming should be feasible, especially for populations inhabiting optimal areas.

The changing flowering phenology of Crinum lilies in arid and semi-arid regions: implications for phenological responses to climate change

Herbarium data have availed the much-needed long-term data that have constrained long-term and real-time phenological studies. Using herbarium specimens from the National Herbarium of Namibia, species, region, rainfall, latitude and longitude were regressed against the day of flowering to determine the effect of each variable on the day of flowering. This study used parameter estimates and the odds ratios from ordinal regression analysis to interpret the influence of the explanatory variables on the day of flowering. The results revealed that flowering dates of C. lugardiae have advanced by six days/decade during the period 1950 to 2010. Average summer rainfall decreased by approximately 3 mm per year from 1960 to 2015 in Namibia. Consequently, significant rainfall effects were recorded on the day of flowering for C. buphanoides, C. stuhlmannii subsp. delagoense and C. paludosum which have advanced by approximately 1 day/decade/mm, 1 day/decade/mm and 2 day/decade/mm during the period studied, respectively. Increase in latitude delayed day of flowering whilst an advancement of the day of flowering with an increase in longitude was observed. Substantial interaction effects among the explanatory variables were demonstrated. Combined effects of rainfall and latitude had a negative effect on the day of flowering whereas interaction effects of average summer rainfall and longitude had a positive combined effect on day of flowering. Our results, therefore, reveal the complex effects of rainfall and geographical location on flowering phenology of different Crinum species. The potential impacts of the phenological responses of different Crinum species on other organisms are discussed.

An enhanced bloom index for quantifying floral phenology using multi-scale remote sensing observations

Floral phenology, the timing and intensity of flowering, is intimately tied to the reproduction of terrestrial ecosystem and highly sensitive to climate change. However, observational records of flowering are very sparse, limiting our understanding of spatiotemporal dynamics of floral phenology from local to regional scales. Satellite remote sensing provides unique opportunities to monitor flowers through space and time in a cost-effective way. Here we developed an enhanced bloom index (EBI), based on the multispectral remotely sensed data, to quantify flowering status over almond (Prunus dulcis) orchards in Central Valley of California. Our test studies with unmanned aerial vehicle (UAV) multispectral imagery at 2.6–5.2 cm demonstrated that the EBI enhanced the signals of flowers and reduced the background noise from soil and green vegetation, and agreed well with the bloom coverage derived from supervised classification, with a R2 of 0.72. Experimental tests with multi-scale remote sensing observations from CERES aerial (0.2 m), PlanetScope (3 m), Sentinel-2 (10 m), and Landsat (30 m) satellite imagery further showed the robustness of the EBI in capturing the flower information. We found that the relatively dense time series of PlanetScope and Sentinel-2 imagery were able to capture the bloom dynamics of almond orchards. Satellite derived EBI is expected to track the bloom information and thus improve our understanding and prediction of flower and pollination response to weather and ultimately the yield.

Hyperspectral remote sensing to quantify the flowering phenology of winter wheat

Flowering phenology, as a sensitive bio-indicator to climate change, has been attracting increasing concern. However, less information is available so far for quantifying flowering phenological stages by use of hyperspectral remote sensing in winter wheat. The establishment of a vegetation index, which is sensitive to the changes of flowering rate, is important to allow the monitoring of flowering phenology through hyperspectral remote sensing. A field experiment was conducted at the Agro-meteorological Station, Nanjing University of Information Science and Technology, Jiangsu Province, China, with two nighttime warming levels, i.e., nighttime warming and ambient temperature (control), and two sowing levels, i.e., normal sowing and late sowing. The field canopy reflectance spectrum was synchronously determined with the flowering rate within 0.25 m2 area at the flowering stage of winter wheat. This study developed a new index for estimating the flowering rate that was compared with the published indices for estimating canopy structure parameter. The newly developed two bands-index (R446 − R472)/(R446 + R472), generated coefficients of determination, root mean square error, and residual prediction deviation values between the measured and predicted values of 0.75, 18.69%, and 1.66, respectively. The study suggests that hyperspectral remote sensing can be used to quantify flowering phenology in winter wheat.

Advancing Leaf-Out and Flowering Phenology is Not Matched by Migratory Bird Arrivals Recorded in Hunting Guide's Journal in Aroostook County, Maine

Historical records have the potential to temporally and spatially expand ecological studies to places and periods that garnered the attention of earlier naturalists. Few historical or contemporary scientific studies have examined the local-to-regional ecological effects of climate change in northern Maine. Recently uncovered journals of L.S. Quackenbush, a hunting guide in mid-20th century Aroostook County, ME, provide an opportunity to incorporate new historical ecological data into climate change research.The leaf-out and flowering phenology observations in the Quackenbush journals are closely tied to spring temperatures and match the direction, though not the magnitude, of changes found in southern New England. Comparisons of Quackenbush's bird records to contemporary observations are less straightforward, but help fill an important gap in regional migratory bird phenology studies. Quackenbush's routine observations, recorded daily in a rural outpost in northern Maine, provide an important contribution to climate change research in a data-poor region and highlight a type of record that may be available in other rural areas.

Perilaku Kunjungan dan Efisiensi Penyerbukan Heterotrigona itama (Cockerell) dan Tetragonula laeviceps (Smith) (Hymenoptera: Apidae) pada Labu Siam

Main insect pollinator of chayote in the neotropics is the stingless bees. In Indonesia, there is no information available on chayote pollination. Research was conducted with the objective to study the flowering phenology of chayote and the role of two specieses of stingless bees Heterotrigona itama (Cockerell) and Tetragonula laeviceps (Smith) (Hymenoptera: Apidae) on chayote pollination. Measurements included the number of staminate and pistillate flowers, volume of nectar and sugar concentration, floral handling time and visitation rate, and fruit set. Chayote plants produced more staminate flowers than pistillate flowers, with the ratio of 18:1. There was no difference in nectar volume and sugar concentration between staminate and pistillate flowers. H. itama and T. laeviceps visited both type of flowers, with the peak of daily visitation were occurred at 08:30-10:30 am local times. There were significant differences in the floral handling time and foraging rate of H. itama and T. laeviceps. Pollen load was significantly higher in H. itama (2137.50±184.49 grains) than those in T. laeviceps (1675.00±110.47 grains). H. itama seemed to deposite more pollen (14.1±4.1 grains) on stigma than T. laeviceps (9.8±3.1 grains). Flowers prevented from insect visits resulted in zero fruit set. Single flower visit by H. itama and T. laeviceps resulted in 60 and 40% fruit set, respectively. Higher percent of fruit set (80-85%) was noticed in open-pollination, suggesting that multiple visits by insect pollinators might increase the chances of successful pollination.

Machine Learning predictive model of grapevine yield based on agroclimatic patterns

Grapevine yield prediction during phenostage and particularly, before harvest is highly significant as advanced forecasting could be a great value for superior grapevine management. The main contribution of the current study is to develop predictive model for each phenology that predicts yield during growing stages of grapevine and to identify highly relevant predictive variables. Current study uses climatic conditions, grapevine yield, phenological dates, fertilizer information, soil analysis and maturation index data to construct the relational dataset. After words, we use several approaches to pre-process the data to put it into tabular format. For instance, generalization of climatic variables using phenological dates. Random Forest, LASSO and Elasticnet in generalized linear models, and Spikeslab are feature selection embedded methods which are used to overcome dataset dimensionality issue. We used 10-fold cross validation to evaluate predictive model by partitioning the dataset into training set to train the model and test set to evaluate it by calculating Root Mean Squared Error (RMSE) and Relative Root Mean Squared Error (RRMSE). Results of the study show that rf_PF, rf_PC and rf_MH are optimal models for flowering (PF), colouring (PC) and harvest (MH) phenology respectively which estimate 1484.5, 1504.2 and 1459.4 (Kg/ha) low RMSE and 24.6%, 24.9% and 24.2% RRMSE, respectively as compared to other models. These models also identify some derived climatic variables as major variables for grapevine yield prediction. The reliability and early-indication ability of these forecast models justify their use by institutions and economists in decision making, adoption of technical improvements, and fraud detection.

Nectar and pollen production in ornamental cultivars of Prunus serrulata (Rosaceae)

Abstract Planting ornamental species can help to create pollinator-friendly habitats. In the present study the flowering phenology and floral reward (nectar and pollen) in two cultivars of Prunus serrulata (‘Kanzan’ and ‘Amanogawa’) were evaluated in 2014-2015 in the city of Lublin (south-east Poland). On average, the onset of flowering of P. serrulata occurred in the first ten days of April (‘Kanzan’) or at the end of April (‘Amanogawa’), and lasted 8-17 days. In each year of the study, P. serrulata ‘Kanzan’ started flowering 11-18 days earlier than P. serrulata ‘Amanogawa’. The double flowers of P. serrulata ‘Kanzan’ offered only tiny amounts of nectar and pollen. The total mass of sugars was 0.59 mg per flower and that of pollen 0.08 mg per flower. The semi-double flowers of P. serrulata ‘Amanogawa’ produced 4.5 mg of sugars per flower and 0.17 mg of pollen per flower. The frequency of pollinator visits to flowers was low in P. serrulata ‘Amanogawa’ and very low in P. serrulata ‘Kanzan’. Therefore, if pollinator-friendly arrangements are made in urban areas, these cultivars should not be planted.

Phenology, flowering and fruit-set performance of six recent pear cultivars of Nordic origin

ABSTRACT Flowering performance and phenology of six new pear cultivars of Nordic origin were examined during a 12 year period. The seasonal timing of shoot growth and flower initiation were monitored in three years. The morphological floral stages of the flower bud formation process were examined for the cultivar ‘Celina’. Seven floral stages were identified and described. The date of full bloom varied between years as a function of the currently accumulated heat sum in early spring. Still, the earliness ranking of the cultivars was consistent across years for both flower initiation and blooming. The cultivars ‘Anna’ and ‘Ingeborg’ consistently initiated floral primordia 2–3 weeks earlier than ‘Celina’, ‘Clara Frijs’, ‘Fritjof’ and ‘Kristina’, and this was accompanied with 4–5 days earlier blooming in the following spring. The early flower initiation cultivars ‘Anna’ and ‘Ingeborg’ also had richer flowering than the late-blooming cultivars. ‘Fritjof’ was identified as a suitable pollinator for ‘Celina’ in the Nordic climate. Comparison of the flowering phenology of pear and apple cultivars showed that while the pears, on average, flowered a week ahead of the apples, they initiated flower primordia almost two weeks later, thus rendering the intervening period approximately three weeks longer in pear than in apple.

Chemical composition of floral scents from three Plumeria rubra L. (Apocynaceae) forms linked to petal color proprieties

The floral scents of three forms of cultivated Plumeria rubra L. were evaluated through mass flowering phenology using the dynamic headspace adsorption method and were identified with coupled gas chromatography and mass spectrometry. The forms P. rubra f. acutifolia and P. rubra f. lutea had white and yellow flower petals, respectively, and the flower petals of P. rubra f. rubra were red. Although 68 components of the flower scents of the three forms were recorded in different proportions, only 14 chemical compounds were identified with statistically significance. The main volatile compounds in the red form of P. rubra L. were fatty acid derivatives (56.75%). The main compounds in the white and yellow forms of P. rubra L. were benzenoid and terpene, with proportions of 48.38% and 33.33% in P. rubra f. acutifolia and proportions of 42.30% and 47.43% in P. rubra f. lutea, respectively. These differences in the flower scents might be one result of the minor genetic differences between these forms, similar to the role of genetic differences in the flower color combinations of the three forms. We conclude that petal color traits can, to some extent, reflect differences in floral scent compositions and that minor genetic differences of different plant forms exert impacts not only on flower color but also on the phytochemistry of floral scents.

Phenology of farmland floral resources reveals seasonal gaps in nectar availability for bumblebees

Abstract Floral resources are known to be important in regulating wild pollinator populations and are therefore an important component of agri‐environment and restoration schemes which aim to support pollinators and their associated services. However, the phenology of floral resources is often overlooked in these schemes — a factor which may be limiting their success. Our study characterizes and quantifies the phenology of nectar resources at the whole‐farm scale on replicate farms in Southwestern UK throughout the flowering season. We quantify the corresponding nectar demands of a subset of common wild pollinators (bumblebees) to compare nectar supply and pollinator demand throughout the year, thereby identifying periods of supply‐demand deficit. We record strong seasonal fluctuations in farmland nectar supplies, with two main peaks of nectar production (May and July) and a considerable “June Gap” in between. March and August/September are also periods of low nectar availability. Comparing the phenology of nectar supply with the phenology of bumblebee nectar demand reveals “hunger gaps” during March and much of August/September when supply is unlikely to meet demand. Permanent pasture and woodland produced the greatest share of farmland nectar because of their large area; however, linear features such as hedgerows and field margins provided the greatest nectar per unit area. Fifty percent of total nectar was supplied by just three species (Allium ursinum, Cirsium arvense and Trifolium repens), but some less productive species (e.g. Hedera helix and Taraxacum agg.) were important in ensuring phenological continuity of nectar supply. Synthesis and applications. By comparing the phenology of farmland nectar supply with the phenology of pollinator demand, we demonstrate that the timing of nectar supply may be as important as total nectar production in limiting farmland pollinator populations. Considering phenology in the design of agri‐environment or restoration schemes is therefore likely to improve their suitability for pollinators. Plant species which flower during periods of resource deficit (early spring and late summer) should be prioritized in schemes which aim to conserve or restore pollinator populations. Maintaining a range of semi‐natural habitats with complementary flowering phenologies (e.g. woodland, hedgerows and field margins) will ensure a more continuous supply of nectar on farmland, thereby supporting pollinators for their entire flight season.

Influence of Regional Water Temperature Variability on the Flowering Phenology and Sexual Reproduction of the Seagrass Zostera marina in Korean Coastal Waters

Increasing sea surface temperature due to global climate change is a major threat to the growth and survival of many temperate seagrasses, while cold-water upwelling can potentially ameliorate high-temperature stress on temperate seagrass meadows during growing seasons. Seagrasses in the coasts of Korea are increasingly influenced by rising water temperatures and water temperature anomalies in recent decades due to climate change, but the impacts of such events on reproductive phenology of seagrasses remain poorly understood. We investigated the reproductive phenology and sexual reproduction of Zostera marina in four seagrass meadows along the coasts of Korea. Two study sites were located on the south coast where water temperature shows significant warming trends, while two other study sites were located on the east coast where coastal cold-water upwelling is prevalent. Water temperature exhibited stronger seasonality with cooler winter and warmer summer in the south coast sites than in the east coast sites. Cold-water upwelling events occurred frequently along the east coast of Korea, leading to anomalously cool water temperatures during the growing season. Z. marina flowering was prolonged and/or precocious at the east coast sites relative to the south coast sites. The mean flowering period was 5–7.5 months at the east coast sites and 3.5 months at the south coast sites. Moreover, reproductive shoot density and biomass, as well as the corresponding flowering frequency and reproductive efforts were much higher (2–3 times) at the east coast sites than at the south coast sites. Consequently, the potential seed production was higher in the east coast sites than in the south coast sites. Overall, high summer water temperature appeared to reduce sexual reproduction of Z. marina in the south coast sites, while regional cold-water upwelling on the east coast changed seasonal temperature patterns and decreased summer temperature highs, consequently provided a relatively long period of optimal water temperature for production of reproductive shoots. Regional water temperature variability has an important role in shifting the flowering responses of seagrass, which could affect the long-term stability and maintenance of seagrass meadows via the regulation of the sexual-asexual reproductive trade-off.

Growth controls over flowering phenology response to climate change in three temperate steppes along a precipitation gradient

Our understanding of how simultaneous climate warming and changing precipitation influence plant phenology in grasslands is still limited. As part of a field transplant experiment, this study was conducted to explore the flowering phenology of the dominant species in three temperate steppes (i.e. a desert, typical, and meadow steppe) along a precipitation gradient in response to simulated night warming and precipitation manipulation (i.e. decreased, ambient, and increased precipitation). Of all monitored species and across three growing seasons (2015–2017), night warming advanced flowering date in the desert and typical steppes, but delayed it in the meadow steppe. Decreased precipitation postponed flowering date but increased precipitation advanced it in all the three steppes. Plant growth largely determined the changes in flowering date under night warming and changing precipitation across and in each of the three steppes. The dominant role of plant growth in modulating reproductive phenology provides mechanistic understanding in interpreting phenological response and facilitate the projections of response of temperate grasslands under future climate change scenarios.

Multispectral Approach for Identifying Invasive Plant Species Based on Flowering Phenology Characteristics

Invasive plant species (IPS) are the second biggest threat to biodiversity after habitat loss. Since the spatial extent of IPS is essential for managing the invaded ecosystem, the current study aims at identifying and mapping the aggressive IPS of Acacia salicina and Acacia saligna, to understand better the key factors influencing their distribution in the coastal plain of Israel. This goal was achieved by integrating airborne-derived hyperspectral imaging and multispectral earth observation for creating species distribution maps. Hyperspectral data, in conjunction with high spatial resolution species distribution maps, were used to train the multispectral images at the species level. We incorporated a series of statistical models to classify the IPS location and to recognize their distribution and density. We took advantage of the phenological flowering stages of Acacia trees, as obtained by the multispectral images, for the support vector machine classification procedure. The classification yielded an overall Kappa coefficient accuracy of 0.89. We studied the effect of various environmental and human factors on IPS density by using a random forest machine learning model, to understand the mechanisms underlying successful invasions, and to assess where IPS have a higher likelihood of occurring. This algorithm revealed that the high density of Acacia most closely related to elevation, temperature pattern, and distances from rivers, settlements, and roads. Our results demonstrate how the integration of remote-sensing data with different data sources can assist in determining IPS proliferation and provide detailed geographic information for conservation and management efforts to prevent their future spread.

Heterodichogamy, Pollen Viability, and Seed Set in a Population of Polyploidy Cyclocarya Paliurus (Batal) Iljinskaja (Juglandaceae)

Research Highlights: Cyclocarya paliurus, native to the subtropical region of China, is a monoecious species with a heterodichogamous mating system. Its flowering phenology and low seed success characteristics differ from other typical heterodichogamous Juglandaceae species. This could be caused by the existence of polyploidy in the population. Background and Objectives: C. paliurus has been attracting more attention as a result of its medicinal value. To meet the needs for leaf harvest, cultivation expansion is required, but this is limited by a shortage of seeds. This study aims to profile the flowering phenology and the efficacy of pollen dispersal as well as elucidate on the mechanism of low seed success in the population. Materials and Methods: The flowering phenology pattern of C. paliurus was observed in a juvenile plantation containing 835 individuals of 53 families from 8 provenances at the individual (protandry, PA and protogyny, PG) and population levels for 5 consecutive years (2014–2018). Slides with a culture medium of 10% sucrose and 0.01% boric acid were used to estimate pollen density and viability in the population, and seeds were collected from 20 randomly selected PA and PG individuals to assess seed success during 2017–2018. Results: Four flowering phenotypes and strongly skewed ratios of PA/PG and male/female occurred in the juvenile population. Sexual type and ratio changed significantly with the growth of the population over the years, showing an increasing monoecious group (11.1% to 57.2%) and a decreasing unisexual group (33.6% to 16.3%), as well as a tendency for the sexual ratio to move towards equilibrium (5.42:1 to 1.39:1 for PG:PA). Two flowering phases and bimodality in gender were displayed, as in other heterodichogamous species. However, the high overlap of inter-phases and within individuals was quite different from many previous reports. Owing to the low pollen viability of C. paliurus (~30%), low seed success was monitored in the plantation, as well as in the investigated natural populations. Conclusions: Female-bias (PG and F) and a skewed ratio of mating types corresponded to nutrient accumulation in the juvenile population. Heterodichogamy in C. paliurus was verified, but was shown to be different from other documented species in Juglandaceae. The latest finding of major tetraploidy in a natural population could explain the characteristics of the flowering phenology and seed set of C. paliurus and also give rise to more questions to be answered.

Seasonality and Prevalence of Pollen Collected from Hawaiian Nectarivorous Birds1

Hawaiian nectarivorous forest birds play a vital ecological role as pollinators in Hawaiian ecosystems. However, little is known about what nectar resources are utilized by Hawai‘i's nectarivorous birds, how seasonality influences nectar availability, and how nectar preference differs by bird species. We sampled pollen from the heads of ‘i‘iwi (Drepanis coccinea), ‘apapane (Himatione sanguinea), Hawai‘i ‘amakihi (Chlorodrepanis virens), and the non-native Japanese white-eye (Zosterops japonicas) captured at Hakalau Forest National Wildlife Refuge on Hawai‘i Island. ‘Ōhi‘a (Metrosideros polymorpha) was the most prevalent pollen species, observed throughout the sampling period while other pollen species were more seasonal in occurrence. Consistent with the peak flowering phenology of the plant species, pollen from koa (Acacia koa), māmane (Sophora chrysophylla), and gorse (Ulex europaeus) plant speciesweremore commonly sampled frombirds in the winter months, while ‘ōhelo (Vaccinium reticulatum), ‘ākala (Rubus hawaiensis), and blackberry (Rubus argutus)were more prevalent during the spring months.We also found an association between bird species and pollen resources, with ‘i‘iwi and Hawai‘i ‘amakihi having a higher diversity of pollen than ‘apapane and Japanese white-eye, which primarily had just ‘ōhi‘a. These results demonstrate that ‘ōhi‘a is likely the most important nectar resource for Hawai‘i's nectar feeding birds, but seasonally abundant nectar may be important for some species.

Phenology and floral synchrony of Rhizophora mangle along a natural salinity gradient

AbstractRhizophora mangle is the most common species of mangrove within its range and a major component of coastal ecosystems in the tropics and subtropics. Its phenology is affected by seasonal variations in temperature, salinity, and precipitation, all of which may be altered by impending climate change. In this work, the monthly leaf, flower, and fruit phenology of R. mangle was assessed at three sites, along a natural salinity gradient for 12 months. We assessed phenological states using litter traps installed in mangrove stands, and by direct observation of leaf production at two sites, and flower, and fruit production at a single site. Phenological events were compared with seasonal climatic variations (in wind, rain, and temperature) to explore potential abiotic controls on the phenology of this species. Leaf shedding was lowest at the low salinity site. Leaf and stipule production showed a seasonal trend, decreasing during the cool and dry winter months. Flowering was highly seasonal and synchronous and peaked during the rainy season. Flowering was correlated with average temperature (r = 0.82; p &lt; 0.05) at all three study sites, but was not correlated with precipitation. At the high‐salinity site, flowering was restricted to the rainy season. Fruit abortion was associated with wind speed (r = 0.79; p &lt; 0.05). Flowering of R. mangle is induced by increasing temperatures and the onset of rains. Rising temperatures, drier summers, and more frequent and intense storms, due to climate change, may influence mangrove productivity, population dynamics, and floral synchrony.