Global climate change impacts can already be tracked in many physical and biological systems; in particular, terrestrial ecosystems provide a consistent picture of observed changes. One of the preferred indicators is phenology, the science of natural recurring events, as their recorded dates provide a high-temporal resolution of ongoing changes. Thus, numerous analyses have demonstrated an earlier onset of spring events for mid and higher latitudes and a lengthening of the growing season. However, published single-site or single-species studies are particularly open to suspicion of being biased towards predominantly reporting climate change-induced impacts. No comprehensive study or meta-analysis has so far examined the possible lack of evidence for changes or shifts at sites where no temperature change is observed. We used an enormous systematic phenological network data set of more than 125 000 observational series of 542 plant and 19 animal species in 21 European countries . Our results showed that 78% of all leafing, flowering and fruiting records advanced (30% significantly) and only 3% were significantly delayed, whereas the signal of leaf colouring/fall is ambiguous. We conclude that previously published results of phenological changes were not biased by reporting or publication predisposition: the average advance of spring/summer was 2.5 days decade À1 in Europe. Our analysis of 254 mean national time series undoubtedly demonstrates that species' phenology is responsive to temperature of the preceding

The substantial stocks of carbon sequestered in temperate grassland ecosystems are located largely below ground in roots and soil. Organic C in the soil is located in discrete pools, but the characteristics of these pools are still uncertain. Carbon sequestration can be determined directly by measuring changes in C pools, indirectly by using 13 C as a tracer, or by simulation modelling. All these methods have their limitations, but long-term estimates rely almost exclusively on modelling. Measured and modelled rates of C sequestration range from 0 to > 8 Mg C ha − 1 yr − 1 . Management practices, climate and elevated CO 2 strongly influence C sequestration rates and their influence on future C stocks in grassland soils is considered. Currently there is significant potential to increase C sequestration in temperate grassland systems by changes in management, but climate change and increasing CO 2 concentrations in future will also have significant impacts. Global warming may negate any storage stimulated by changed management and elevated CO 2 , although there is increasing evidence that the reverse could be the case.

The process of adaptation is the result of stabilising selection caused by two opposite forces: protection against an unfavourable season (survival adaptation), and effective use of growing resources (capacity adaptation). As plant species have evolved different life strategies based on different trade offs between survival and capacity adaptations, different phenological responses are also expected among species. The aim of this study was to compare budburst responses of two opportunistic species (Betula pubescens, and Salix x smithiana) with that of two long-lived, late successional species (Fagus sylvatica and Tilia cordata) and consider their ecological significance. Thus, we performed a series of experiments whereby temperature and photoperiod were manipulated during dormancy. T. cordata and F. sylvatica showed low rates of budburst, high chilling requirements and responsiveness to light intensity, while B. pubescens and S. x smithiana had high rates of budburst, low chilling requirements and were not affected by light intensity. In addition, budburst in B. pubescens and S. x smithiana was more responsive to high forcing temperatures than in T. cordata and F. sylvatica. These results suggest that the timing of growth onset in B. pubescens and S. x smithiana (opportunistic) is regulated through a less conservative mechanism than in T. cordata and F. sylvatica (long-lived, late successional), and that these species trade a higher risk of frost damage for the opportunity of vigorous growth at the beginning of spring, before canopy closure. This information should be considered when assessing the impacts of climate change on vegetation or developing phenological models.

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Mismatches in phenology between mutually dependent species, resulting from climate change, can have far-reaching consequences throughout an ecosystem at both higher and lower trophic levels. Rising temperatures, due to climate warming, have resulted in advances in development and changes in behaviour of many organisms around the world. However, not all species or phenophases are responding to this increase in temperature at the same rate, thus creating a disruption to previously synchronised interdependent key life-cycle stages. Mismatches have been reported between plants and pollinators, predators and prey, and pests and hosts. Here, we review mismatches between interdependent phenophases at different trophic levels resulting from climate change. We categorized the studies into (1) terrestrial (natural and agricultural) ecosystems, and (2) aquatic (freshwater and marine) ecosystems. As expected, we found reports of 'winners' and 'losers' in each system, such as earlier emergence of prey enabling partial avoidance of predators, potential reductions in crop yield if herbivore pests emerge before their predators and possible declines in marine biodiversity due to disruption in plankton-fish phenologies. Furthermore, in the marine environment rising temperatures have resulted in synchrony in a previously mismatched prey and predator system, resulting in an abrupt population decline in the prey species. The examples reviewed suggest that more research into the complex interactions between species in terrestrial and aquatic ecosystems is necessary to make conclusive predictions of how climate warming may impact the fragile balances within ecosystems in future.

Despite experimental evidence of the individual and interactive effects of photoperiod and temperature on bud growth, photoperiod has not yet been effectively accounted for in models of budburst. However, in some tree species, such as Betula pubescens (birch), photoperiod has an important role in phenological control, and its inclusion in process-based models of budburst might affect phenological projections under climate change scenarios. The aim of the present study was to integrate photoperiod into a process-based phenological model (Chuine 2000; J Theor Biol 207: 337-347; Unified model), using experimental findings in which photoperiod was found to significantly affect budburst in B. pubescens (Caffarra et al. 2011; Clim Res 46:147-157, this issue). The effect of photoperiod was integrated into the model at 2 levels. Firstly, photoperiod, in interaction with temperature, affects the course of dormancy induction. Secondly, photoperiod modifies the response to temperature during the phase of forcing. The resulting model (DORMPHOT) for the simulation of birch budburst was fitted to a large phenological dataset, including data from different latitudes, and validated with 7 datasets from 4 different European countries. Besides giving more biological realism to the model, the newly introduced mechanisms improved its predictive performance. The DORMPHOT model outperformed the Unified model, the linear regression model (budburst date vs. spring average temperature), and the UniForc model. It also proved to be more accurate at predicting budburst in extremely warm years, which suggests it might be more reliable than previous models when using future climate change scenarios. KEY WORDS: Betula pubescens · Budburst · Calibration · Phenological models · Photoperiod · ValidationResale or republication not permitted without written consent of the publisher Clim Res 46: 159-170, 2011 temperature changes as dormancy progresses, and its responses are, in some cases, proportional to the amount of time of exposure to a particular environmental condition. These findings have resulted in the elaboration of models that describe budburst timing as the end point of 2 consecutive phases: endodormancy, which is released upon the cumulative effect of chilling temperatures (cool, autumn-winter temperatures), and ecodormancy, during which the cumulative effect of forcing temperatures (warm, spring temperatures) promotes cell growth (Hänninen 1990, Battey 2000. These models account for the effects of temperature in terms of developmental units, and different functions relate temperature to the rate of growth or the rate of dormancy release of the buds.Among these models, the simplest consider only the effects of forcing temperatures for the prediction of budburst timing. In the Spring Warming model (Cannell & Smith 1983, Chuine et al. 1998, Pop et al. 2000, also called the Thermal Time model (Hunter & Lechowicz 1992), and in the UniForc model (Chuine 2000), temperature is linearly or sigmoidally related to the rate of growth...

The main factors triggering and releasing bud dormancy are photoperiod and temperature. Their individual and combined effects are complex and change along a transition from a dormant to a non-dormant state. Despite the number of studies reporting the effects of temperature and photoperiod on dormancy release and budburst, information on the parameters defining these relationships is scarce. The aim of the present study was to investigate the effects and interaction of temperature and photoperiod on the rates of dormancy induction and release in Betula pubescens (Ehrh.) in order to develop a conceptual model of budburst for this species. We performed a series of controlled environment experiments in which temperature and photoperiod were varied during different phases of dormancy in B. pubescens clones. Endodormancy was induced by short days and low temperatures, and released by exposure to a minimal period of chilling temperatures. Photoperiod during exposure to chilling temperatures did not affect budburst. Longer exposure to chilling increased growth capability (growth rate at a given forcing temperature) and decreased the time to budburst. During the forcing phase, budburst was promoted by photoperiods above a critical threshold, which was not constant, but decreased upon longer chilling exposures. These relationships between photoperiod and temperature have, as yet, not been integrated into the commonly used processbased phenological models. We suggest models should account for these relationships to increase the accuracy of their predictions under future climate conditions. KEY WORDS: Betula pubescens · Controlled environment experiments · Phenology · Photoperiod · Temperature · Dormancy · Budburst Resale or republication not permitted without written consent of the publisherClim Res 46: [147][148][149][150][151][152][153][154][155][156][157] 2011 1995, Thomas & Vince Prue 1997). The action of these environmental drivers is complex and changes along the transition from a dormant to a non-dormant state. In addition, it has been shown that photoperiod and temperature interact at various stages during dormancy induction, release and quiescence (Håbjørg 1972, Junttila 1980, Heide 1993, 2003, Myking & Heide 1995, Partanen et al. 2001.Photoperiod affects the time at which buds enter a phase of winter rest. Short days (ShDs) signal the onset of winter, which, in turn, triggers decreasing 'growth competence' (growth capability). Once the plant has been exposed to a certain number of dormancyinductive days (dormancy induction requirement), the phase of endodormancy is reached, a period during which buds do not grow even under favourable environmental conditions (Downs & Borthwick 1956, Håb-jørg 1972, Howe et al. 1996, Thomas & Vince Prue 1997, Welling et al. 1997.Chilling temperatures are the main trigger for endodormancy release (Perry 1971, Sarvas 1974, Cannell & Smith 1983, Battey 2000. The concept of 'chilling temperature' is not clearly defined, and a consistent response to chilling has not been ...