Why a gall former can be a good biocontrol agent: the gall wasp Trichilogaster acaciaelongifoliae and the weed Acacia longifolia

ABSTRACT.

• 1 The pteromalid Trichilogaster acaciaelongifoliae (Froggatt) causes galls to develop in the place of inflorescences during the reproductive phase of its host Acacia longifolia (Andr.) Willd. (Fabaceae). After being introduced to South Africa during 1982 and 1983, this wasp reduced the reproductive potential of A. longifolia by >89% when only 50% of the branches on a tree were galled. In addition, vegetative growth of galled branches was reduced by 53% when the vacated galls had desiccated.
• 2 The wasp is able to manipulate its host so effectively because: (a) the dry mass of developing galls was significantly greater than that of the corresponding reproductive organs, peaking in spring (September) when galls were 25 times the mass of unfertilized inflorescences. (b) The large biomass diverted to gall production is accounted for by a high proportion (66–73%) of multiple-chambered galls. The dry mass of multiple-chambered galls was significantly greater than that of both single-chambered galls and pods. (c) The extent of biomass diversion to gall production was relatively greater during the earlier part of the reproductive season, enhancing stress on the host. (d) The wasp sometimes forced the plant to produce up to 200% more galls per branch than the normal quota of inflorescences. This phenomenon, called forced commitment, further increases stress on the host plant. (e) Galls constituted up to 21% and 40% of the dry and wet biomass of above-ground parts of infested trees, respectively. This caused breakage and mortality of large branches and stems. (f) Reproduction in A. longifolia has been shown elsewhere to be so energy consuming that vegetative growth is strongly inversely related to pod production. Because the stress from galling by T. acaciaelongifoliae coincides with and replaces reproduction with a greater stress, successful reduction of both reproduction and vegetative growth are achieved.
• 3 This biological control programme is the first in which a gall-forming hymenopteran has been used to control a weed. Since the effects of gall-formers are indirect compared with those of insects attacking vegetative plant parts, their potential as biocontrol agents has been underrated. This research provides ecologically based guidelines for the future selection of such agents.

     

Seasonal Changes in Total Free Sugar Content of Field Cocoa Plants

As part of a study of factors affecting the vegetative and reproductive characteristics of cocoa, Theobroma cacao L., (viz. leaf flushing, flowering, cherelle wilt, pod setting and pod growth), seasonal changes in total free sugar levels of the bark and wood of field cocoa trees growing under medium shade provided by Gliricidia sepium Steud. trees were studied over a period of 13 months. On dry weight basis, sugar content of the bark (13 to 63 mg/g) was higher than that of the wood (9 to 40 mg/g). Free sugar content was significantly correlated with sunshine hours for the whole period, except October-November 1975, and March 1976 when pod load, and flowering and leaf flushing respectively, caused considerable reduction in free sugar levels. The peaks of flowering and flushing coincided with those of sunshine hours and free sugar levels. The results, analysed in terms of the prevailing microclimatic conditions, suggest that light is a limiting factor for photsynthesis of shaded cocoa and that the reported stimulation of flowering and leaf flushing, which accompany shade removal, may be attributed to increased sugar status of the trees due to increased photosynthetic activity.     

Leaf flushing during the dry season: the paradox of Asian monsoon forests

Aim Most deciduous species of dry monsoon forests in Thailand and India form new leaves 1–2 months before the first monsoon rains, during the hottest and driest part of the year around the spring equinox. Here we identify the proximate causes of this characteristic and counterintuitive ‘spring‐flushing’ of monsoon forest trees. Location Trees of 20 species were observed in semi‐deciduous dry monsoon forests of northern Thailand with a 5–6‐month‐long severe dry season and annual rainfall of 800–1500 mm. They were growing on dry ridges (dipterocarp–oak forest) or in moist gullies (mixed deciduous–evergreen forest) at 680–750 m altitude near Chiang Mai and in a dry lowland stand of Shorea siamensis in Uthai Thani province. Methods Two novel methods were developed to analyse temporal and spatial variation in vegetative dry‐season phenology indicative of differences in root access to subsoil water reserves. Results Evergreen and leaf exchanging species at cool, moist sites leafed soon after partial leaf shedding in January–February. Drought‐resistant dipterocarp species were evergreen at moist sites, deciduous at dry sites, and trees leafed soon after leaf shedding whenever subsoil water was available. Synchronous spring flushing of deciduous species around the spring equinox, as induced by increasing daylength, was common in Thailand's dipterocarp–oak forest and appears to be prevalent in Indian dry monsoon forests of the Deccan peninsula with its deep, water‐storing soils. Main conclusions In all observed species leafing during the dry season relied on subsoil water reserves, which buffer trees against prolonged climatic drought. Implicitly, rainfall periodicity, i.e. climate, is not the principal determinant of vegetative tree phenology. The establishment of new foliage before the summer rains is likely to optimize photosynthetic gain in dry monsoon forests with a relatively short, wet growing season.     

Vegetative and reproductive phenology of the mangrove Kandelia obovata

Mangroves in the subtropical area of Japan are growing to their northern limits, yet little is known of their phenology. The aim of the present study was to understand both vegetative and reproductive phenology patterns, such as leaf emergence, leaf fall, bud setting, flowering, fruiting and propagule setting, in the mangrove Kandelia obovata. The phenology of this species was assessed using litter‐fall data for 5 years. Leaf and stipule litter‐falls continued with a clear monthly pattern throughout the years. New leaf production and leaf fall peaked in summer, immediately after the propagules fell. Leaf and stipule litter‐falls were linked to monthly sunshine hour, and monthly mean air temperature and monthly mean air relative humidity, respectively. Kandelia obovata had a distinct flowering period, with the flowering phenophase starting in spring and continuing into summer. Fruit initiation started at the end of summer and continued into autumn, whereas propagule production occurred during winter and spring. Flowering of K. obovata was influenced by monthly sunshine hour and monthly mean air temperature, whereas fruit and propagule litter‐falls were not linked to any climatic factors. The present results showed that a small portion (4.4%) of flowers developed into propagules. The average development period from flower buds to mature propagules was approximately 11 months. Kendall's consistency coefficient suggested that the monthly trends in vegetative and reproductive litter‐fall components, except for branches, did not change significantly among years.     

Proximate weather patterns and spring green‐up phenology effect Eurasian beaver (Castor fiber) body mass and reproductive success: the implications of climate change and topography

Low spring temperatures have been found to benefit mobile herbivores by reducing the rate of spring‐flush, whereas high rainfall increases forage availability. Cold winters prove detrimental, by increasing herbivore thermoregulatory burdens. Here we examine the effects of temperature and rainfall variability on a temperate sedentary herbivore, the Eurasian beaver, Castor fiber, in terms of inter‐annual variation in mean body weight and per territory offspring production. Data pertain to 198 individuals, over 11 years, using capture‐mark‐recapture. We use plant growth (tree cores) and fAPAR (a satellite‐derived plant productivity index) to examine potential mechanisms through which weather conditions affect the availability and the seasonal phenology of beaver forage. Juvenile body weights were lighter after colder winters, whereas warmer spring temperatures were associated with lighter adult body weights, mediated by enhanced green‐up phenology rates. Counter‐intuitively, we observed a negative association between rainfall and body weight in juveniles and adults, and also with reproductive success. Alder, Alnus incana, (n = 68) growth rings (principal beaver food in the study area) exhibited a positive relationship with rainfall for trees growing at elevations >2 m above water level, but a negative relationship for trees growing <0.5 m. We deduce that temperature influences beavers at the landscape scale via effects on spring green‐up phenology and winter thermoregulation. Rainfall influences beavers at finer spatial scales through topographical interactions with plant growth, where trees near water level, prone to water logging, producing poorer forage in wetter years. Unlike most other herbivores, beavers are an obligate aquatic species that utilize a restricted ‘central‐place’ foraging range, limiting their ability to take advantage of better forage growth further from water during wetter years. With respect to anthropogenic climate change, interactions between weather variables, plant phenology and topography on forage growth are instructive, and consequently warrant examination when developing conservation management strategies for populations of medium to large herbivores.     

Host-plant mediated geographic variation in the life history of Platycotis vittata (Homoptera: Membracidae)

Abstract.

• 1 The oak treehopper Platycotis vittata (Fabricius) is bivoltine throughout its range with discrete generations in the early spring and autumn. Females of both generations diapause.
• 2 Latitudinal variation in the timing of life history exists among four populations of P. vittata along the eastern coastal plain of the United States.
• 3 We disrupted synchronization between P.vittata life history and host-plant phenology in the springs of 1984 and 1985 by placing southern populations on northern trees with a different phenology. This caused some females to oviposit abnormally in late spring, without entering diapause. The offspring of these females had reduced reproductive success.
• 4 Winter diapause can be broken by providing females with a newly flushing tree with high levels of amino nitrogen in the sap. Females terminated winter diapause on trees breaking winter dormancy while females on trees still in winter dormancy did not, under identical photoperiod and temperature regimes.
• 5 The role of host-plant mediated life history variation as a process promoting intraspecific geographic differentiation in the arboreal sap-feeding guild is discussed.

     

Phenological patterns of <Emphasis Type="Italic">Ficus citrifolia</Emphasis> (Moraceae) in a seasonal humid-subtropical region in Southern Brazil

Year-round flowering is widely reported in fig trees and is necessary for the survival of their short-living, specialized Agaonid pollinators. However, seasonality in both fig and leaf production has been noted in almost all published phenological studies. We have addressed the following questions in the present study: (1) Are reproductive and vegetative phenologies seasonal and, consequently, related to climate? (2) Does Ficus citrifolia produce ripe figs year round? (3) Is the fig development related to climate? And, (4) Are reproductive and vegetative phenologies independent? By investigating these questions with a F. citrifolia population over a two-year period, at the southern edge of the tropical region in Brazil, we detected phenological seasonality that was significantly correlated with climate. Our findings can be summarized as follows: (1) Trees became deciduous during the cold and dry months; (2) The flowering onset was asynchronous among individuals, but with moderate concentration during the hot and rainy months; (3) There was a correlation between the onset of flowering and vegetative phenology, with significantly higher crop initiations in individuals with full-leaf canopy; (4) Fig developmental time was longer in cold months; and (5) Ripe fig production occurred year-round and was not correlated with climate. Our results suggest that there are strong selection pressures that maintain the year-round flowering phenology in figs, for we have observed little seasonality in the phenology of such species despite the strong seasonality in the environment.     

Oviposition pattern and within-season spatial and temporal variation of pre-dispersal seed predation in a population of Mimosa bimucronata trees

Spatial and temporal variation of pre-dispersal seed predation was investigated in a population of Mimosa bimucronata trees located in the south-east region of Brazil. Three main hypotheses were addressed: (1) that the life stages of the seed predator Acanthoscelides schrankiae are synchronised with the reproductive stages of its host plant; (2) that seed predation levels vary spatially as a result of differences in fruiting phenology synchrony and fruit production among trees; and (3) that predation levels should be affected by the proximity of trees, showing a spatial structure. Also investigated was the oviposition pattern of A. schrankiae among seeds and fruits. Twenty spatially referenced trees were monitored throughout a year to examine tree phenology and egg laying and adult emergence. The bruchine’s life stages were synchronised with the reproductive stages of M. bimucronata trees. Egg distribution among seeds and fruits was aggregated. Infestation rates of adult bruchines were not spatially related to fruiting phenology and there is evidence that seed predation is a spatially density-independent process, because the relationship between infestation rates and fruit production was not significant. Finally, it was observed that the distribution of adult bruchines was spatially structured, because similar levels of infestation were found among nearby trees.     

Seasonal control over allocation to reproduction in a tussock-forming and a rhizomatous species of Eriophorum in central Alaska

Summary The evergreen tussock-forming Eriophorum vaginatum revealed consistently earlier (c. 1 moth) phenology and greater biomass per tiller than the summergreen rhizomatous E. scheuchzeri in all four components measured (vegetative and reproductive shoots and stems) under the same climatic regime in central Alaska over one growing season. Greatest allocation to vegetative shoot growth occurred in mid-summer in both species. The tussock growth form of E. vaginatum raised shoot meristems 25–30 cm above the soil surface, where temperatures were warmer, permitting shoot growth to begin earlier in spring and continue longer in autumn than in E. scheuchzeri. Consequently, E. vaginatum was able to allocate reserves to reproductive tillers primarily in autumn and early spring, times when minimal reserves were required for vegetative growth. By contrast, the rhizomatous E. scheuchzeri had a more constrained growing season, and allocation to reproduction coincided with allocation to vegetative growth. For this reason, reserves were drawn down more fully in mid-summer in E. scheuchzeri than in E. vaginatum. The more conservative use of nutrient stores in E. vaginatum may relate to its great longevity, reduced allocation to reproduction (including low seedling recruitment), and relatively stable habitats. The mid-seasonal pulse of allocation to reproduction in E. scheuchzeri appears viable only in relatively fertile disturbed sites, where the soil nutrient supply is sufficient to support simultaneous allocation to vegetative growth and reproduction.     

Effect of methabenzthiazuron on growth and nitrogenase activity in Vicia faba

The effects of the herbicide methabenzthiazuron (175 and 220 g ha^-1) on vegetative and reproductive growth, nodulation and nitrogenase activity of Vicia faba were studied in the field under Mediterranean conditions. Nitrogenase activity of excised nodules was estimated using the acetylene reduction assay four times during the developmental period. Leaf area index, dry weight and nitrogen content of the different parts of the plants were measured. Methabenzthiazuron-treated plants showed an increase in nodulation, nitrogenase activity and vegetative growth at early pod fill. Methabenzthiazuron also caused an increase in leaf N content and fruits. These were transient effects found during early and mid pot fill. Nevertheless, plants treated with these sublethal doses of herbicide improved seed production and nitrogen content of seeds at harvest time. The stimulatory effect of methabenzthiazuron on N₂ fixation and vegetative growth seems not be related with the transient stimulatory effect on photosynthetic capacity, also caused by the herbicide, since the stimulatory effect on N₂ fixation was apparent during pod fill, when photosynthetic capacity declined and was not modified by methabenzthiazuron.     

小叶桦花序生长物候及其生态适应意义

小叶桦(Betula microphylla)是一种典型的荒漠和山地乔木植物,在中国仅分布于新疆。为了明确小叶桦花序生长物候规律及发育特征,该研究对小叶桦进行了花序物候观测,分析其生长规律及果实结籽情况。结果显示:小叶桦雄花序为越年生殖器官,物候周期为345d,其中营养生长期154d、休眠期158d、开花生长期33d;雌花序与果序为当年生殖器官,物候期为105d,其中雌花序生长期24d、果序生长期90d。虽然雄花序比雌花序的生长周期明显较长,但开花授粉均在4月中下旬,雄花序散粉期和雌花序可授粉期之间具有较高的同步性和协调性,表现出集中开花授粉模式,同时这种开花模式在自然条件下,果序的结籽数和结籽率分别为220和76.7%,种子库中具有活力的种子约每平米4万粒,表明小叶桦在荒漠极端环境中能顺利完成有性生殖过程。     

Plant phenology and seed predation: interactions between gorses and weevils in Brittany (France)

Exapion ulicis (Forster) and Exapion lemovicinum (Hoffmann) (Coleoptera: Curculionoidea: Apionidae) are seed predators of the three gorse species occurring in Brittany (France): Ulex europaeus L., Ulex gallii Planch., and Ulex minor Roth.(Fabaceae). Host‐plant phenology plays a major role in the relationship between apionid weevils and their gorse species, because larvae develop within gorse pods and adults have to wait for pod dehiscence to be released. We monitored flowering and fruiting phenology of gorse species, weevil reproductive behaviour, and egg‐laying patterns in six natural populations in the native area of these gorse species. At each site, U. europaeus, which flowers mainly in spring, was sympatric with one of two autumn flowering gorse species, U. gallii and U. minor. We noticed that E. ulicis laid eggs in spring and was restricted to U. europaeus whereas E. lemovicinum laid eggs in autumn and was restricted to the two autumn‐flowering species U. gallii and U. minor. Therefore, host specificity depended on gorse phenology, and not on geographic proximity. In addition, the infested pod content showed that E. ulicis laid several eggs per pod and suggested that females chose pods with the highest numbers of seeds. In contrast, E. lemovicinum laid a single egg per pod and showed no preference for pods with many seeds. Finally, the impact of seed predation by E. ulicis was higher than that of E. lemovicinum.     

Individual resource allocation to vegetative growth and reproduction in subgenus <Emphasis Type="Italic">Cyclobalanopsis</Emphasis> (<Emphasis Type="Italic">Quercus</Emphasis>, Fagaceae) trees

The resource allocation for vegetative growth and female reproduction in three tree species of subgenus Cyclobalanopsis (Quercus, Fagaceae), i.e., Q. salicina, Q. sessilifolia, and Q. acuta, were examined on a per-individual basis in two consecutive reproductive seasons, in order to test whether these trees fit the predictions of the masting hypotheses about resource matching versus resource switching. Since the three Quercus species have a biennial fruiting habit, it takes 3 years for the observation of two reproductive events. Female flower and acorn production per tree were investigated by using a seed-trap method and a numerical analysis of seed dispersal. The net production of each individual was estimated as the sum of the annual increase in the dry mass of vegetative organs and reproductive investment per tree. In the data analyses, the three species were pooled, since all 12 sample trees of the subgenus apparently showed masting in the same year, with no exceptions. Female flower and acorn production per individual tree changed considerably between years. The net production per tree increased with tree size, but did not differ between years. Therefore, the reproductive allocation (proportion of a plant’s annual assimilated resources which are used for reproduction) differed dramatically between years. On the other hand, within a year, the reproductive allocation increased with increasing net production per tree. These results suggest that the switching of resource allocation between years within an individual are occurring in subgenus Cyclobalanopsis species, and the intensity of the switching increases with increasing tree size.     

Alpine grassland plants grow earlier and faster but biomass remains unchanged over 35 years of climate change

Satellite data indicate significant advancement in alpine spring phenology over decades of climate warming, but corresponding field evidence is scarce. It is also unknown whether this advancement results from an earlier shift of phenological events, or enhancement of plant growth under unchanged phenological pattern. By analyzing a 35‐year dataset of seasonal biomass dynamics of a Tibetan alpine grassland, we show that climate change promoted both earlier phenology and faster growth, without changing annual biomass production. Biomass production increased in spring due to a warming‐induced earlier onset of plant growth, but decreased in autumn due mainly to increased water stress. Plants grew faster but the fast‐growing period shortened during the mid‐growing season. These findings provide the first in situ evidence of long‐term changes in growth patterns in alpine grassland plant communities, and suggest that earlier phenology and faster growth will jointly contribute to plant growth in a warming climate.     

Yield loss at the different growth stages in soybean due to insect pests in Ghana

Insecticide protection at the vegetative, reproductive or both vegetative and reproductive (complete) crop growth stages and untreated control was used to assess yield loss due to insect pests at the different growth stages of soybean in Ghana from 2007–2009. The objectives were to determine the economic importance of the two major insect pest guilds in soybean, viz. defoliators and pod feeders, and when to apply control measures for maximum benefit. The defoliators recorded were Podagrica spp., Ootheca mutabilis (Shalberg), Zonocerus variegatus L., Sylepta derogata F., Spodoptera littoralis Boisduval, Amsacta spp. and Helicoverpa armigera Hübner. The pod feeders recorded were the pod-sucking bugs (PSBs) Riptortus dentipes F., Thyanta sp. Aspavia armigera F., Nezara viridula L. and Dysdercus völkeri Schmidt. Generally, insect densities, pod and seed damage were lower while seed yields were significantly greater and similar in plots that were protected at the reproductive stage against PSBs and those protected at both vegetative and reproductive stages. Yield loss ranged between 25.8 and 42.8% in untreated plots, 11.1 and 34.3% in plots that were protected at the vegetative stage, and 5.2 and 11.3% in plots that were protected at the reproductive stage. There was a consistent negative correlation between yield and numbers of PSBs as well as pod and seed damage. These results showed that PSBs that attack soybean at the reproductive stage were the most important insect pests limiting soybean yield in Ghana.     

Flowering phenology of <Emphasis Type="Italic">Ulex europaeus</Emphasis>: ecological consequences of variation within and among populations

Reproductive phenology of gorse (Ulex europaeus L., Genisteae, Fabaceae) is unusual in that the onset and duration of flowering vary greatly among individuals within populations: some plants initiate flowering in autumn or winter and continue flowering through spring, others initiate flowering in early spring. To understand the origin of this diversity and its ecological consequences, we investigated flowering phenology of randomly sampled individuals from five different natural populations in Brittany (France). Reproductive success was evaluated for individuals with contrasting flowering patterns, from 16 natural populations. Flower production, pod production, seed production and seed predation were estimated. Plants initiating flowering in spring produced larger numbers of flowers and pods over a shorter period than plants flowering from winter to spring, which produced few flowers and pods at a time but over a longer period. Pod production of long-flowering plants did not differ significantly between winter and spring, but their pods were more intensively attacked by seed predators in spring than in winter. We discuss our results in relation to biotic and abiotic parameters. We postulate that long-flowering can be interpreted as a bet-hedging strategy, spreading the risk of pod failure (rotting or freezing) in winter and of seed predation in spring.     

How is the invasive gorse <Emphasis Type="Italic">Ulex europaeus</Emphasis> pollinated during winter? A lesson from its native range

Many examples of plant-insect interactions have shown that selection from herbivores can act on flowering and fruiting phenology. In Ulex europaeus (Fabaceae), escaping seed predation resulted in extended, but variable flowering periods, with some plants flowering from autumn until spring and others flowering only in spring. The present study aims at understanding how gorses can have a high reproductive success during winter despite harsh climatic conditions and low number of pollinators. We measured pollen production, flower size and seed production in spring and winter, and compared the different seasons. The pollination success of flowers was high in both seasons. The flowers produced as much pollen, and were of comparable size in spring and winter, but they stayed open twice as long in winter than in spring. The high pollination rate we observed was thus due to the longer opening period of flowers and the high attractiveness of flowers during winter. However, pod abortion was higher in winter, with 43% of the flowers in winter and 75% in spring producing ripe pods. Antagonistic selective pressures exerted by biotic and abiotic interactions may, therefore, have lead to the observed flowering polymorphism, and allow U. europaeus to thrive in various climates, thus, increasing its invasiveness in different countries.     

Vegetative and reproductive responses,oil yield and composition from olive trees (Olea europaea) under contrasting water availability during the dry winter‐spring period in central Argentina

In Argentina, the climatic pattern of the olive production areas is characterised by a marked water deficit during winter and spring months. A field experiment was carried out to evaluate the effect of water availability during the pre‐flowering–flowering period on vegetative, reproductive and yield responses of olive trees grown in central Argentina. From the end of autumn to mid‐spring, four irrigation treatments were imposed to olive trees (Olea europaea, cv. Arbequina and Manzanilla) at 0, 25, 50 and 75% estimated crop evapotranspiration (ETc). Also, a control treatment was kept at 100% ETc for the entire year. For the first crop year evaluated, water deficit applied at early June, approximately 4 months prior to bloom, reduced the vegetative shoot growth and delayed the flowering time, resulting in shortening of the fruit maturation period and, ultimately, decreased fructification. Trees irrigated with high (75% of ETc) and full (100% of ETc) winter‐spring water supply presented significantly higher values of flower density, fruit density and final fruit yield which resulted in water productivity (kg fruits mm^?1 of irrigation/ha) enhancements of about 500% (cv. Arbequina) and 330% (cv. Manzanilla) with respect to those obtained from the corresponding unirrigated treatments. Differences between treatments in oil content and composition were primarily attributed to variations in fruit maturity. Differences in fatty acid composition were stronger in cv. Arbequina where a gradual increase in oleic acid content was registered in parallel to the increase in irrigation water supply. From a practical stand point, results obtained from most of the analysed parameters were quite similar for both T75 and T100 treatments. Thus, the possible convenience of irrigation at T75% ETc should be considered since it may warrant profitable olive production while saving a considerably quantity of irrigation water in the olive production area in central Argentina.     

Continuous and Fluctuating Leaf Phenology of Adults and Seedlings of a Shade‐tolerant Emergent Tree,Dipterocarpus sublamellatus,in Malaysia

Continuous leaf phenology, with sequential production of metamers, is usually found in pioneer species, but is rare in shade‐tolerant species. Because of the nature of ‘continuous’ growth, continuous phenology has seldom been related to meteorological factors. We studied the leaf demography of seedlings and tall trees of a shade‐tolerant emergent species, Dipterocarpus sublamellatus (Dipterocarpaceae), in Malaysia. Although leaf phenology of D. sublamellatus was classified as continuous, the rates of leaf production and leaf fall were not constant and greatly fluctuated during the census period. Seasonal patterns of leaf production and fall were not synchronized across tall trees in most combinations or between seedlings and tall trees. Mean number of leaves produced per month and its seasonal fluctuation were greater in tall trees than in seedlings. Moreover, relationships between leaf phenology and meteorological factors (monthly rainfall, net radiation, maximum and minimum temperature, and minimum relative humidity) differed among trees. This suggests that endogenous rhythms, i.e., differences in allocation of resources to growth and storage among trees, are important to fluctuations in leaf phenology. These patterns are in contrast to patterns found in various pioneer species with continuous phenology, in which rates of leaf production and fall are generally constant. Different patterns might be caused by differences in allocation to growth and storage between pioneer and shade‐tolerant species, and might be related to their regeneration strategies.     

Consistent shifts in spring vegetation green‐up date across temperate biomes in China, 1982–2006

Understanding spring phenology changes in response to the rapid climate change at biome‐level is crucial for projecting regional ecosystem carbon exchange and climate–biosphere interactions. In this study, we assessed the long‐term changes and responses to changing climate of the spring phenology in six temperate biomes of China by analyzing the global inventory monitoring and modeling studies (GIMMS) NOAA/AVHRR Normalized Difference Vegetation Index (NDVI) and concurrent mean temperature and precipitation data for 1982–2006. Results show that the spring phenology trends in the six temperate biomes are not continuous throughout the 25 year period. The spring phenology in most areas of the six biomes showed obvious advancing trends (ranging from ?0.09 to ?0.65 day/yr) during the 1980s and early 1990s, but has subsequently suffered consistently delaying trends (ranging from 0.22 to 1.22 day/yr). Changes in spring (February–April) temperature are the dominating factor governing the pattern of spring vegetation phenology in the temperate biomes of China. The recently delayed spring phenology in these temperate biomes has been mainly triggered by the stalling or reversal of the warming trend in spring temperatures. Results in this study also reveal that precipitation during November–January can explain 16.1% (P < 0.05), 20.9% (P < 0.05) and 14.2% (P < 0.05) of the variations in temperate deciduous forest (TDF), temperate steppe (TS), temperate desert (TD) respectively, highlighting the important role of winter precipitation in regulating changes in the spring vegetation phenology of water–limited biomes.