Phenological Processes Research Articles

Environmental drivers of drought deciduous phenology in the Community Land Model

Abstract. Seasonal changes in plant leaf area have a substantial impact on global climate. The presence of leaves and the time when they appear affect surface roughness and albedo, and the gas exchange occurring between leaves and the atmosphere affects carbon dioxide concentrations and the global water system. Thus, correct predictions of plant phenological processes are important for understanding the present and future states of the Earth system. Here we compare plant phenology as estimated in the Community Land Model (CLM) to that derived from satellites in drought deciduous regions of the world. We reveal a subtle but important issue in the CLM: anomalous green-up during the dry season in many semi-arid parts of the world owing to rapid upwards water movement from wet to dry soil layers. We develop and implement a solution for this problem by introducing an additional criterion of minimum cumulative rainfall to the leaf-out trigger in the drought deciduous algorithm. We discuss some of the broader ecological impacts of this change and highlight some of the further steps that need to be taken to fully incorporate this change into the CLM framework.

Interactive Vegetation Phenology, Soil Moisture, and Monthly Temperature Forecasts

AbstractThe time scales that characterize the variations of vegetation phenology are generally much longer than those that characterize atmospheric processes. The explicit modeling of phenological processes in an atmospheric forecast system thus has the potential to provide skill to subseasonal or seasonal forecasts. We examine this possibility here using a forecast system fitted with a dynamic vegetation phenology model. We perform three experiments, each consisting of 128 independent warm-season monthly forecasts: 1) an experiment in which both soil moisture states and carbon states (e.g., those determining leaf area index) are initialized realistically, 2) an experiment in which the carbon states are prescribed to climatology throughout the forecasts, and 3) an experiment in which both the carbon and soil moisture states are prescribed to climatology throughout the forecasts. Evaluating the monthly forecasts of air temperature in each ensemble against observations—as well as quantifying the inherent predictability of temperature within each ensemble—shows that dynamic phenology can indeed contribute positively to subseasonal forecasts, though only to a small extent, with an impact dwarfed by that of soil moisture.

Global change at the landscape level: relating regional and landscape‐scale drivers of historical climate trends in the Southern Appalachians

ABSTRACTOrganisms in montane environments are sensitive to fine‐scale climatic variation associated with highly dissected topography, yet few studies have examined the sensitivity of different landscape positions to climate change. We downscaled biologically significant temperature variables to below‐canopy 30 m resolution and assessed temporal trends from 1980 to 2011 across elevation and topographic gradients in Great Smoky Mountains National Park (GSMNP; Tennessee and North Carolina, USA) using a previously developed empirical model derived from a 120‐sensor temperature network. Additionally, we assessed GSMNP climate trends from 1900 using six historical climate records from the region and an additional eight records from 1980, spanning the Park's elevation gradient. Regional temperatures increased through the 1980s and 1990s, but currently remain at or below those recorded in the early to mid‐20th century and are strongly associated with different phases of the North Atlantic Oscillation. In contrast, annual and growing season precipitation steadily rose during the past century. Landscape‐scale analysis showed that rates of change for maximum seasonal temperatures, frost‐free days (FFD), and growing degree days were strongly mediated by topographic position, with high‐elevation ridges having greater rates of maximum temperature increases, whereas high‐elevation near‐stream positions showed the least amount of increase in FFD and growing degree days. Most importantly, we show how modelled differences in rates of climatic change based on landscape position could have significant ecological effects in this biologically significant region, depending on how organisms respond to particular climate factors. Organisms that depend on growing season length may experience the largest climate effects at the lowest elevations, while those that depend on warm days in spring and autumn for particular phenological processes will experience the largest shifts at high‐elevation ridges.

Impact of warming climate and cultivar change on maize phenology in the last three decades in North China Plain

As climate change could significantly influence crop phenology and subsequent crop yield, adaptation is a critical mitigation process of the vulnerability of crop growth and production to climate change. Thus, to ensure crop production and food security, there is the need for research on the natural (shifts in crop growth periods) and artificial (shifts in crop cultivars) modes of crop adaptation to climate change. In this study, field observations in 18 stations in North China Plain (NCP) are used in combination with Agricultural Production Systems Simulator (APSIM)-Maize model to analyze the trends in summer maize phenology in relation to climate change and cultivar shift in 1981–2008. Apparent warming in most of the investigated stations causes early flowering and maturity and consequently shortens reproductive growth stage. However, APSIM-Maize model run for four representative stations suggests that cultivar shift delays maturity and thereby prolongs reproductive growth (flowering to maturity) stage by 2.4−3.7 day per decade (d 10a−1). The study suggests a gradual adaptation of maize production process to ongoing climate change in NCP via shifts in high thermal cultivars and phenological processes. It is concluded that cultivation of maize cultivars with longer growth periods and higher thermal requirements could mitigate the negative effects of warming climate on crop production and food security in the NCP study area and beyond.

Modeling the effects of post-anthesis heat stress on rice phenology

Heat stress significantly accelerates senescence process during reproductive phase in rice, but the effects of heat stress are not yet well simulated by most of the existing crop models. Three-year experiments under different temperature levels and temperature durations at anthesis and 12 days after anthesis were carried out in phytotron using two japonica cultivars. Significant positive correlations were observed between the shortened grain growing days from anthesis to maturity (GDAM) and heat degree-days (HDD). The impact of post-anthesis heat stress on rice phenology was quantified by adding thermal effectiveness of heat stress to the original RiceGrow model. Performance of the improved model was tested with phenological data from different cultivars under post-anthesis heat stress of phytotron environments and field conditions. Validation results showed that root mean square error (RMSE), mean bias error (MBE) and variance of the distribution of differences (Sd2) for the prediction of GDAM, decreased from 4.60d, 2.65d and 7.80 in the original model to 1.58d, −0.16d and 2.40 in the improved model, respectively, under post-anthesis heat stress conditions. The determination coefficient (R2) and index of agreement (IA) between simulated and observed GDAM, increased from 68.5% and 0.71 in the original model to 93.5% and 0.92 in the improved model under post-anthesis heat stress conditions, respectively. Overall, the improved model gave better predictions of GDAM in different rice cultivars under different post-anthesis heat stress environments. Our study highlights the necessity of accurately simulating the heat stress effects on phenological processes in rice to forecast crop production for ensuring food security under climate change reliably.

Grazing and watering alter plant phenological processes in a desert steppe community

Phenology is well recognized as one of the most sensitive indicators of environmental change. Previous studies have focused on flowering phenology with few efforts given to the phenological successes and vegetative processes. Additionally, grazing is often characterized as a driver for community evolutionary processes, while precipitation is known as the most important abiotic cue in arid regions. Given this knowledge, we installed a nested experiment in a desert steppe to explore the coupled effects of grazing and watering on plant species’ reproductive successes and phenological timing in 2012–2013. We found that grazing increased the proportion of non-flowering individuals, with a greater proportion in 2013 than that in 2012. It decreased species richness and changed the habitat preferences in both years, and watering also reduced the richness in both years. Grazing also delayed the phenological timing for some dominant species and significantly delayed the green-up timing (5.67 days) and shortened the growing season length (GSL) in both 2012 (7.74 days) and 2013 (4.71 days). The application of watering, however, delayed some dominant species’ timing—including the browning timing of five dominate species ranging from 9.57 days in 2013 to 1.93 days in 2012—but it did not delay the species’ green-up timing. This resulted in a significantly prolonged growing season in 2013 (8.58 days). The high soil water and optimal soil temperature in the spring of 2013 contributed to an earlier green-up time (6.1 days) than in 2012.

Phenological decoupling of mortality from wave forcing in kelp beds.

Kelps often live in a harsh hydrodynamic environment where wave-driven dislodgement of individuals can alter the biodiversity and functioning of reef systems, and increase production in coastal ecosystems adjacent to reefs. The current paradigm is that winter storms tear kelps from reefs once hydrodynamic forces exceed attachment or tissue strength--a threshold response that implies a pulsed relationship between wave forces and dislodgement. Here, we challenge this understanding by showing how kelp phenology can decouple susceptibility to dislodgement from seasonal patterns in wave forces. We measured kelp dislodgement rates and hydrodynamic forces at nine subtidal reefs over two years (n = 4320 kelps tagged and monitored). Contrary to expectation, we found relatively low and constant dislodgement rates for all reefs (13% +/- 6% [mean per season +/- SD]) in spite of a strong temporal pattern in wave action and extreme water velocities (winter peaks up to 3-4 m/s). A biomechanical model, based on the balance between kelp attachment strength and hydrodynamic drag, demonstrated that severe reduction in individual kelp size toward winter (>50% decrease in biomass for all sites) minimized drag and made the kelps less susceptible to high water velocities, allowing individuals to survive storm velocities over 3-4 m/s. We conclude that the timing of reduced susceptibility to disturbance, through the seasonal reduction of individual kelp biomass that coincides with times of highest water velocities is critical to the dynamics of kelp dislodgement and survival. We propose that phenological processes maintain many kelp beds in a higher degree of population stability and equilibrium with hydrodynamic forces than previously believed.

Investigation of North American vegetation variability under recent climate: A study using the SSiB4/TRIFFID biophysical/dynamic vegetation model

AbstractRecent studies have shown that current dynamic vegetation models have serious weaknesses in reproducing the observed vegetation dynamics and contribute to bias in climate simulations. This study intends to identify the major factors that underlie the connections between vegetation dynamics and climate variability and investigates vegetation spatial distribution and temporal variability at seasonal to decadal scales over North America (NA) to assess a 2‐D biophysical model/dynamic vegetation model's (Simplified Simple Biosphere Model version 4, coupled with the Top‐down Representation of Interactive Foliage and Flora Including Dynamics Model (SSiB4/TRIFFID)) ability to simulate these characteristics for the past 60 years (1948 through 2008). Satellite data are employed as constraints for the study and to compare the relationships between vegetation and climate from the observational and the simulation data sets. Trends in NA vegetation over this period are examined. The optimum temperature for photosynthesis, leaf drop threshold temperatures, and competition coefficients in the Lotka‐Volterra equation, which describes the population dynamics of species competing for some common resource, have been identified as having major impacts on vegetation spatial distribution and obtaining proper initial vegetation conditions in SSiB4/TRIFFID. The finding that vegetation competition coefficients significantly affect vegetation distribution suggests the importance of including biotic effects in dynamical vegetation modeling. The improved SSiB4/TRIFFID can reproduce the main features of the NA distributions of dominant vegetation types, the vegetation fraction, and leaf area index (LAI), including its seasonal, interannual, and decadal variabilities. The simulated NA LAI also shows a general increasing trend after the 1970s in responding to warming. Both simulation and satellite observations reveal that LAI increased substantially in the southeastern U.S. starting from the 1980s. The effects of the severe drought during 1987–1992 and the last decade in the southwestern U.S. on vegetation are also evident from decreases in the simulated and satellite‐derived LAIs. Both simulated and satellite‐derived LAIs have the strongest correlations with air temperature at northern middle to high latitudes in spring reflecting the effect of these climatic variables on photosynthesis and phenological processes. Meanwhile, in southwestern dry lands, negative correlations appear due to the heat and moisture stress there during the summer. Furthermore, there are also positive correlations between soil wetness and LAI, which increases from spring to summer. The present study shows both the current improvements and remaining weaknesses in dynamical vegetation models. It also highlights large continental‐scale variations that have occurred in NA vegetation over the past six decades and their potential relations to climate. With more observational data availability, more studies with different models and focusing on different regions will be possible and are necessary to achieve comprehensive understanding of the vegetation dynamics and climate interactions.

内蒙古地带性针茅植物对CO2和气候变化的适应性研究进展

内蒙古地带性针茅植物对CO₂和气候变化的适应性研究进展

PLANT WATER RELATIONS AND PHENOLOGICAL SHIFTS IN RESPONSE TO DROUGHT IN CASTANOPSIS INDICA AT PHULCHOWKI HILL, KATHMANDU, NEPAL

In the central Himalaya, plants are subjected to a prolonged dry period , thus developing moisture stress. Phenomorphological variations such as leaf expansion and flowering are affected by the interaction between water availability, stem water storage, wood moisture percentage, wood density and wood water. Sensitivity to wate r stress and phenological processes such as leaf emergence, senescence, flowering, fruiting and their relationship with wood water properties, starch percentage content, specific leaf mass (SLM), nitrogen content in leaves was studied in one Himalayan ever green tree species, Castanopsis indica . Wood moisture, reserved starch percentage and SLM had a strong effect on phenological activities. They increased during the vegetative bud break and leaf emergence and decreased during senescence. Similarly leaf nitr ogen in the studied species was at the crest of concentration during leaf initiation then declined, one in expanded leaves as the concentration became diluted by increasing cell wall material, and the other at the time of senescence by resorption.

ROLE OF WOOD WATER PROPERTIES AND LEAF DYNAMICS IN PHENOLOGY AND RESPONSE TO DROUGHT IN EVERGREEN HIMALAYAN TREE SPECIES

Five evergreen Himalayan trees namely Castanopsis indica, Schima wallichii, Rhododendron arboreum, Quercus lanata and Q. semecarpifolia were studied for their phenological responses to drought. Wood water properties (wood moisture percentage, wood density and water in wood per volume), starch percentage content, specific leaf mass, nitrogen content in leaves and phenological processes such as leaf emergence, senescence, flowering and fruiting were measured. Measurements were taken 28 times from December 1998 to April 2001 except for the monsoon months. There was significant variation in starch percentage in zero and one year old twigs. Mean starch percentage content ranged from 23% and 17.1% (S. wallichii) to 64% and 61.7% (C. indica) in zero year and one year old twig, respectively. Wood water properties were highest in R. arboreum and lowest in C. indica. SLM showed significant variation with sampled species and mean SLM was highest in R arboreum (1.6 × 10-2 g cm-2) and lowest in S. wallichii (0.64 × 10-2 g cm-2). Mean N ranged from 1.13% (R arboreum) to 1.98% (C. indica). Reserved starch percentage and SLM had a strong effect on phenological activities. They increased during the vegetative bud break and leaf emergence and decreased during senescence. Similarly, leaf nitrogen in the studied species was at the crest of concentration during leaf initiation then declined, one in expanded leaves as the concentration became diluted by increasing cell wall material, and the other at the time of senescence by resorption. DOI: http://dx.doi.org/10.3126/eco.v19i0.9857Ecoprint An International Journal of Ecology Vol. 19, 2012 Page: 71-84 Uploaded date: 2/14/2014

Noah Multi Physics 모델과 CERES-Rice 모델의 작물 생육 및 증발산 모의 비교

대기와 지표면을 구성하고 있는 토양 및 식생은 생물리학적/생지화학적인 과정을 통해 서로 상호작용을 한다. 이러한 과정을 모의하기 위해 지표모델과 작물 생육모델이 사용되고 있다. 지표모델인 Noah MP 모델과 작물생육모델인 CERES-Rice 모델을 비교하기 위해 해남 플럭스 관측소 인근 지역에서 작물의 생육과 증발산량을 모의하였다. 플럭스 관측자료가 수집된 2003년부터 2012년까지 해남 플럭스 관측소의 주요 식생인 벼를 대상으로 생육과 증발산량을 모의되었다. Noah MP 모델은 단순한 식생 모의 과정으로 인해 개화기를 전후로 하는 벼의 LAI 변화양상을 정확하게 반영하지 못하였다. 벼의 생체중 예측에 있어서도 실제 관측될 수 있는 생체중보다 대략 10분의 1 수준에 해당하는 생체중이 모의되었다. 증발산량 모의의 경우에도, CERES-Rice 모델의 모의값보다 약 21%에 해당하는 증발산량을 모의하였다. 반면, CERES-Rice 모델의 경우 LAI의 변화와 생체중 모의 값은 실제의 벼 생육 양상과 유사할 것으로 추정되었다. 또한, 증발산량의 경우에도 해남 플럭스 관측소에서 측정된 값과 비교하였을 때 Noah-MP모델의 모의값이 CERES-Rice 모델의 모의값에 비해 RMSE 값이 1.8배 높았다. Noah MP 모델이 보이는 높은 오차값들은 Noah MP모델이 논의 지표상태를 적절히 반영하지 못하였기 때문으로 사료되었고, 특히 과소추정된 생체중을 보정하여 증발산량을 예측할 경우 오차를 30%까지 줄일 수 있을 것으로 보인다. 따라서, Noah MP 모델에 논에서의 지표 특성을 반영할 수 있다면 보다 정확한 물질순환과 에너지 교환을 예측할 수 있을 것으로 사료된다. Biophysical and biochemical processes through which crops interact with the atmosphere have been simulated using land surface models and crop growth models. The Noah Multi Physics (MP) model and the CERES-Rice model, which are a land surface model, and a crop growth model, respectively, were used to simulate and compare rice growth and evapotranspiration (ET) in the areas near Haenam flux tower in Korea. Simulations using these models were performed from 2003 to 2012 during which flux measurements were obtained at the Haenam site. The Noah MP model failed to simulate the pattern of temporal change in leaf area index (LAI) after heading. The simulated aboveground biomass with the Noah MP model was underestimated by about 10% of the actual biomass. The ET simulated with the Noah MP model was as low as 21% of those with the CERES-Rice model. In comparison with actual ET measured at Haenam flux site, the root mean square error (RMSE) of the Noah MP model was 1.8 times larger than that of the CERES-Rice model. The Noah MP model seems to show less reliable simulation of crop growth and ET due to simplified phenology processes and assimilates partitioning compared with the CERES-Rice model. When ET was adjusted by the ratio between leaf biomass simulated using CERES-Rice model and Noah MP model, however, the RMSE of ET was reduced by 30%. This suggests that an improvement of the Noah MP model in representing rice growth in paddy fields would allow more reliable simulation of matter and energy fluxes.

Microsporogenesis of Apricot Cultivars in Hungary

Like all phenological processes, microsporogenesis is mainly determined genetically, but its phenotypical expression is greatly influenced by environmental factors, particularly the temperature. During the 3-year experimental period, the process of microsporogenesis was examined in eight apricot cultivars originated in North America and in Romania. The Hungarian cultivar ‘Gönci magyar kajszi’ was used as the control. Based on the results it was possible to rank the cultivars in terms of their microsporogenesis schedule. The same order was found in all three years. This order also indicates the yield reliability of the cultivars. Endodormancy ended between January 10th and 25th in the buds of the earliest cultivar ‘Pinkcot’, but not until February 5-10th in the latest cultivar ‘Harlayne’. Three of the cultivars had faster flower bud development than the control, in the order ‘Pinkcot’, ‘Orange Red’ and ‘Harcot’. Growing these cultivars thus involves greater risk than for ‘Gönci magyar kajszi’ in Hungary, due to their rapid winter flower bud development. Some cultivars found to have slower flower bud development than ‘Gönci magyar kajszi’; ‘Litoral’, ‘Harogem’, ‘Comandor’, ‘Sirena’ and ‘Harlayne’ – thus these cultivars can be grown more reliably.

Spatiotemporal variability of winter wheat phenology in response to weather and climate variability in China

Weather and climate variability are predicted to impact food security by altering crop growth, phenology, and yield processes. Adaptation measures are critical for reducing future vulnerability of crop production to warming weather and climate variability. It is therefore vital to investigate the shifts in crop phenological processes in response to weather/climate variability. This study analyzes the trends in the dates of winter wheat (Triticum aestivum L.) phenology in relation to average temperature of different growth stage and the adaptation of the crop to weather/climate variability in China. The results suggest that the phenological phases of winter wheat have specific regional patterns in China. There are also significant shifts in the dates of winter wheat phenology and the duration of the growth stages in the investigated 30-year period of 1980–2009. While the date of sowing winter wheat delays, the dates of post-winter phenological phases (e.g., heading and maturity dates) advances in most areas of China. Detailed analysis shows that the changes in the phenological phases of winter wheat are strongly related to temperature trends. Temporal trends in phenological phases of winter wheat are similar in characteristics to corresponding trends in temperature. Although warming weather and climate variability is the main driver of the changes in winter wheat phenology, temperature is lower than before in most of the investigated stations during the period from heading to maturity—mainly the grain-filling stage. This is mainly due to the early heading and maturity dates, which in turn not only prolong growth stages but also enhance productivity of winter wheat. This could be a vital adaptation strategy of winter wheat to warming weather with beneficial effects in terms of productivity.

Phenology and pollinating wasp dynamics of Ficus microcarpa L.f.: adaptation to seasonality.

BackgroundIn the obligate plant/pollinator mutualism, pollinator abundance is conditioned by the host resource. In order to investigate the population fluctuation of pollinating wasps and the phenological processes involved, this study examined the dual dynamics of the pollinator and the syconium phenology of a seasonal fruited fig tree population, Ficus microparpa, in Taipei, Taiwan.ResultsOur results revealed three seasons in the annual phenology: spring crop, summer-fall crop and winter trough seasons. The syconium quantity was correlated most significantly with temperature based on the generalized linear model with the meteorological data transformed by a principal component analysis. The pollinator population showed an increasing trend in spring, reached the maximum abundance in summer, and then declined drastically in winter, consistent with the syconium production fluctuation. With the small amount of local pollinators from the winter syconia and potential immigrating foundresses from other populations, the pollinator population size can increase very quickly from almost zero to over 40,000 wasps for this 29-tree local population within a season.ConclusionThis syconium phenological scheme, coupled with the fast-recovery rate of pollinators, may explain the worldwide adaptation and invasion of Ficus microcarpa.Electronic supplementary materialThe online version of this article (doi:10.1186/1999-3110-54-11) contains supplementary material, which is available to authorized users.

Daily MODIS 500 m reflectance anisotropy direct broadcast (DB) products for monitoring vegetation phenology dynamics

Land surface vegetation phenology is an efficient bio-indicator for monitoring ecosystem variation in response to changes in climatic factors. The primary objective of the current article is to examine the utility of the daily MODIS 500 m reflectance anisotropy direct broadcast (DB) product for monitoring the evolution of vegetation phenological trends over selected crop, orchard, and forest regions. Although numerous model-fitted satellite data have been widely used to assess the spatio-temporal distribution of land surface phenological patterns to understand phenological process and phenomena, current efforts to investigate the details of phenological trends, especially for natural phenological variations that occur on short time scales, are less well served by remote sensing challenges and lack of anisotropy correction in satellite data sources. The daily MODIS 500 m reflectance anisotropy product is employed to retrieve daily vegetation indices (VI) of a 1 year period for an almond orchard in California and for a winter wheat field in northeast China, as well as a 2 year period for a deciduous forest region in New Hampshire, USA. Compared with the ground records from these regions, the VI trajectories derived from the cloud-free and atmospherically corrected MODIS Nadir BRDF (bidirectional reflectance distribution function) adjusted reflectance (NBAR) capture not only the detailed footprint and principal attributes of the phenological events (such as flowering and blooming) but also the substantial inter-annual variability. This study demonstrates the utility of the daily 500 m MODIS reflectance anisotropy DB product to provide daily VI for monitoring and detecting changes of the natural vegetation phenology as exemplified by study regions comprising winter wheat, almond trees, and deciduous forest.

Influence of thermal requirement in the aerobiological and phenological behavior of two grapevine varieties

Knowledge about the timing of the aerobiological and phenological processes in plants with economic interest results of great agronomical importance, mainly for the establishment of the adaptive capacity of different varieties to various environmental conditions and the optimization of cultural practices. An agrometeorological study in two authorized varieties (Treixadura and Godello) of the Designation of Origin Ribeiro (North-western Spain) was conducted during the years 2008–2011. As consequence of the studied area bioclimatic conditions, the grapevine cycle exceed than 190 days and the varieties cultivated are considered as “late varieties.” The presence of Vitis pollen grains in the vineyard atmosphere was mainly registered during the stages 5 (inflorescence emerge) and 6 (flowering) which benefit a successful fertilization process. The variations in airborne pollen concentrations are related to temperature and humidity. Phenological models proposed in this paper offer a high accuracy as the standard deviation of error between estimated and observed values was low. The prediction variability ranges around 2 phenological scales in 2008 and 1 phenological scale in 2009, 2010 and 2011. These results indicate that the models developed to predict the phenology, in terms of degree days accumulated (GDD) using as a threshold temperature 10 °C, can be a useful tool to forecast the successive phenological events in the Designation of Origin Ribeiro area. During the stage 8 (ripening of berries), the GDD and the Brix Index were particularly correlated, so far as the differences between plants of the same variety are minimal.

Modelling dry season deciduousness in Mexican Yucatán forest using MODIS EVI data (2000–2011)

This study maps interannual variation in the spatial extent of deciduousness in the dry tropical forests of the southern Yucatán (Mexico) from 2000 to 2011 using seasonal variability thresholds based on Moderate Resolution Imaging Spectroradiometer (MODIS) Enhanced Vegetation Index (EVI) data and relates deciduousness to precipitation- and temperature-derived climate variables using linear regressions. The annual occurrence of deciduousness is most frequently observed in forests located in a regional rain shadow at moderate elevations. Regression results suggest that deciduousness is more strongly associated with atypically hot conditions (–2°C; R 2 = 0.44) than with atypically dry conditions (R 2 = 0.19), in contrast to other phenological processes (e.g. leaf growth, peak productivity) driven primarily by precipitation.

Habitat Change Effects on the Flowering Behavior ofBergebnia crassifolia(L.) Fritsch.

Bergebnia crassifolia (L.)Fritsch.(Saxifragaceae) is evergreen perennial herb with flowering period from May to August. It is a local wild plant with high ornamental value. Altay Forestry Science Research Institute, Xinjiang planted them in 2003. In order to discuss the artificial cultivation and environment effects on flowering behavior, we observed the flowering phenological process of B. crassifolia in different growing conditions: the introduction at the low altitudes and the wild at the high altitude. The results showed that: At individual or colony levels, first-flowering dates of the introduction was earlier than the wild. Flowering was 20d in the introduction, while 40d in the wild. The differences were significant between introduction and wild (P<0.05); The flowering process of the introduction and the wild is the same; Environmental change has no effect on the pollen vigor and stigma receptivity of B. crassifolia; Introduction and wild flowering rates and abortive rates were observed. It was found that flowering rate was significantly different (P<0.05), and the abortive rate had highly significant differences (P<0.01). The differences between introduction and wild showed that there was a close relationship between phenological characteristics of B. crassifolia and some meteorological factors like altitude, temperature and so on.

Phenological patterns in a natural population of a tropical timber tree species, Milicia excelsa (Moraceae): Evidence of isolation by time and its interaction with feeding strategies of dispersers

Population genetic structuring over limited timescales is commonly viewed as a consequence of spatial constraints. Indirect approaches have recently revealed reproductive isolation resulting from flowering time (so-called isolation by time, IBT). Since phenological processes can be subject to selection, the persistence of flowering asynchrony may be due to opposing selective pressures during mating, dispersal, and regeneration phases. Our study aimed to investigate phenology, fruit handling by animals, and their interaction in a timber tree species, Milicia excelsa. We analyzed phenological data collected over 6 years on 69 genotyped trees in a Cameroonian natural rainforest complemented by data from germination trials and field observations of dispersers. Initiation of flowering was correlated with variation in temperature and relative humidity, but was also affected by genetic factors: pairwise differences in flowering time between nearby individuals correlated with kinship coefficient, and earliness of flowering remained stable over time. A decrease in mean seed production per fruit with increasing flowering time suggests selection against late bloomers. However, germination rate was not affected by seed collection date, and the main seed disperser, the bat Eidolon helvum, seemed to increase in abundance at the end of the reproductive season and preferred trees in open habitats where early and late bloomers are expected. The pairwise approach performs well in detecting IBT. The persistence of different mating pools in such a case may result from a trade off between selective forces during the mating and seed dispersal processes.