Winter Chilling Requirement Research Articles

Climate change is leading to rapid shifts in seasonality in the himalaya.

Climate change has significantly impacted vegetation phenology across the globe with vegetation experiencing an advance in the spring green-up phases and a delay in fall senescence. However, some studies from high latitudes and high elevations have instead shown delayed spring phenology, owing to a lack of chilling fulfillment and altered snow cover and photoperiods. Here we use the MODIS satellite-derived view-angle corrected surface reflectance data (MCD43A4) to document the four phenological phases in the high elevations of the Sikkim Himalaya and compared the phenological trends between below-treeline zones and above-treeline zones. This analysis of remotely sensed data for the study period (2001-2017) reveals considerable shifts in the phenology of the Sikkim Himalaya. Advances in the spring start of the season phase (SOS) were more pronounced than delays in the dates for maturity (MAT), senescence (EOS), and advanced dormancy (DOR). The SOS significantly advanced by 21.3 days while the MAT and EOS were delayed by 15.7 days and 6.5 days respectively over the 17-year study period. The DOR showed an advance of 8.2 days over the study period. The region below the treeline showed more pronounced shifts in phenology with respect to an advanced SOS and a delayed EOS and DOR that above treeline. The MAT, however, showed a greater delay in the zone above the treeline than below. Lastly, unlike other studies from high elevations, there is no indication that winter chilling requirements are driving the spring phenology in this region. We discuss four possible explanations for why vegetation phenology in the high elevations of the Eastern Himalaya may exhibit trends independent of chilling requirements and soil moisture due to mediation by snow cover.

Surprising roles of climate in regulating flowering phenology in a subtropical ecosystem

Climate‐driven changes in phenology have widespread effects on ecological interactions and species' abundances. Most predictions of changes in phenology and the consequences for ecology and conservation are based on research in temperate systems. Climate‐driven changes in phenology are largely undocumented in subtropical regions, which host much of the world's biodiversity. Factors important to regulating phenology in temperate systems (e.g. winter chilling requirements) are likely weak or absent in subtropical ecosystems; plant phenology in these regions could respond to climate differently than in the temperate zone. Here we examine flowering phenology data for 105 plant species based on herbarium specimens and photographs from 1911 to 2015 in the southern subtropical Nanling region in south China. Temperatures in this region warmed 0.3°C over the 105‐year study period, and most plant species flowered earlier over time, although species varied substantially in the magnitude of phenological response to warming temperatures. Spring flowering times advanced in response to warming temperatures in late summer and early autumn and in early spring, with late summer and early autumn temperatures having almost twice as strong an effect on spring flowering times as early spring temperatures (−4.7 versus −2.5 days °C−1). This strong effect of late summer and early autumn temperatures is very different from temperate systems and has substantial implications for anticipating future changes in phenology. The temperatures in late summer and early autumn may affect spring phenology by accelerating bud formation or initial growth. Warming January temperature delayed summer flowering and advanced winter flowering. Increases in precipitation during April to June also tended to delay summer flowering. Autumn flowering species showed inconsistent responses to warming. These results highlight important differences between climate‐driven changes in phenology in temperate and subtropical areas. Understanding these differences will be important in understanding the effects of climate change on vegetation phenology and ecosystem processes.

Shifts in the thermal niche of fruit trees under climate change: The case of peach cultivation in France

Climate influences plant phenological traits, thus playing a key role in defining the geographical range of crops. Foreseeing the impact of climate change on fruit trees is essential to inform policy decisions to guide the adaptation to new climatic conditions. To this end, we propose and use a phenological process-based model to assess the impacts of climate change upon the phenology, the suitability and the distribution of economically important cultivars of peach (Prunus persica), across the entire continental France. The model combines temperature dependent sub-models of dormancy, blooming, fruit survival and ripening, using chilling units, forcing units, frost occurrence and growing degree days, respectively. We find that climate change could have divergent impacts on peach production. On the one hand, blooming would occur earlier, warmer temperatures would decrease spring frost occurrence and fruit ripening would be easily achieved before the start of fall. On the other hand, milder winters would impede the plant buds from breaking endodormancy, with consequent abnormal patterns of fruit development or even blooming failure. This latter impact would dramatically shift the geographic range of sites where peach production will be profitable. This shift would mainly be from the south of France (Languedoc-Roussillon, Rhône-Alpes and Provence-Alpes-Côte d'Azur), to northwestern areas where the winter chilling requirement would still be fulfilled. Our study provides novel insights for understanding and forecasting climate change impacts on peach phenology and it is the first framework that maps the ecological thermal niche of peach at a national level.

Moderate chilling requirement controls budburst for subtropical species in China

It is well known that spring phenology has advanced in temperate regions over the last few decades in response to climate change. However, we understand much less about climate-driven changes in phenology within subtropical and tropical regions, where the timing of events is less predictable and has not been well-studied. It is not known whether subtropical plants have a similar winter chilling requirement to what has been well-documented in temperate species. To explore this possibility, we established a climate chamber experiment to test the effects of photoperiod and chilling on the timing of budburst within 37 subtropical woody species. We found that both moderate and strong chilling treatments advanced budburst and reduced forcing requirements, relative to plants subjected to a low chilling treatment. Longer photoperiod enhanced budburst rate for only two species, suggesting that chilling is more important for regulating budburst for most species. With respect to future climate change, the spring phenology of subtropical species is expected to be delayed further because species could lack the ability to meet their fundamental chilling requirement. These results have important implications for the conservation and management of tropical and subtropical plant populations under future climate change scenarios.

Chilling requirements of Mediterranean fruit crops in a changing climate

Fruit production in Europe may be hampered by climate change in terms of warmer winters resulting in insufficient chilling. This contribution provides a brief survey of winter chilling requirement of fruit crops. Therein, cherry and apple were identified as the fruit crops with the highest chilling requirement. Three chilling models are presented and the different ways of calculation explained. In the simplest model, Weinberger (1950) counts every hour between 0 and 7.2°C as one chilling hour (CH). The Utah model (1974) expands the temperature range to 1.4-12.4°C to calculate the chill units (CU). In this model, temperatures are weighted, namely, temperatures in excess of 16°C nullify previously accumulated CU. For the Dynamic model (1987), chill portions (CP) are calculated based on assumptions of metabolic processes at a temperature range of -2 and 12°C with an optimal chilling effective range from 6 to 8°C. First results applying the three chilling models are presented to calculate winter chilling in a cherry orchard at Klein-Altendorf (Bonn, Germany), and in an adjacent unheated greenhouse (average temperature increase by ca. 2°C to simulate global warming). When chilling was computed for the trees in the unheated greenhouse to simulate climate change, the available chilling at 50°N increased by 12% (CU), 15% (CP) and 20% (CH), respectively. In climate change predictions for other locations, the warmer winter temperatures, especially in the Mediterranean area, often induce insufficient chilling. Options and limitations of countermeasures in terms of cultivation methods such as microclimate manipulation, rest breaking agents, change of orchard location to a higher altitude and breeding are suggested and briefly discussed.

Spring predictability explains different leaf-out strategies in the woody floras of North America, Europe and East Asia.

Intuitively, interannual spring temperature variability (STV) should influence the leaf-out strategies of temperate zone woody species, with high winter chilling requirements in species from regions where spring warming varies greatly among years. We tested this hypothesis using experiments in 215 species and leaf-out monitoring in 1585 species from East Asia (EA), Europe (EU) and North America (NA). The results reveal that species from regions with high STV indeed have higher winter chilling requirements, and, when grown under the same conditions, leaf out later than related species from regions with lower STV. Since 1900, STV has been consistently higher in NA than in EU and EA, and under experimentally short winter conditions NA species required 84% more spring warming for bud break, EU ones 49% and EA ones only 1%. These previously unknown continental-scale differences in phenological strategies underscore the need for considering regional climate histories in global change models.

A crop and cultivar-specific approach to assess future winter chill risk for fruit and nut trees

Anthropogenic climate change will influence winter chill accumulation, with future declines likely in temperate locations. However, these declines only translate as impacts when cultivar winter chilling requirements are not satisfied. This study presents a methodology to evaluate future impacts of declining winter chill through a cultivarspecific approach which is useful for growers, industry and policy-makers to develop adaptation strategies. A risk based system was applied to represent the likelihood of meeting cultivar chilling requirements using low, medium, medium-high and high risk ratings based on percentiles. This was combined with climate projection uncertainty graphically at 16 Australian growing districts historically (1981–2010) and for 2030, 2050 and 2090. The results demonstrated that impacts and likely adaptation options differed between cultivars, some recording limited risk at all sites out to 2090 ('Nonpareil' almond) whilst others recorded greater risk both historically and into the future ('Chandler' walnut). Notably, risk differed across sites and with the future time period. These results highlight which cultivars are susceptible to low winter chill conditions, where this risk does and does not manifest and the different time horizons at which the risk will materialise across Australia's main growing districts. Using this approach, changes in winter chill conditions are presented in a useable form which allows for appropriate climate adaptation strategies to be developed, securing the industries into the future.

From observations to experiments in phenology research: investigating climate change impacts on trees and shrubs using dormant twigs.

Climate change is advancing the leaf-out times of many plant species and mostly extending the growing season in temperate ecosystems. Laboratory experiments using twig cuttings from woody plant species present an affordable, easily replicated approach to investigate the relative importance of factors such as winter chilling, photoperiod, spring warming and frost tolerance on the leafing-out times of plant communities. This Viewpoint article demonstrates how the results of these experiments deepen our understanding beyond what is possible via analyses of remote sensing and field observation data, and can be used to improve climate change forecasts of shifts in phenology, ecosystem processes and ecological interactions. The twig method involves cutting dormant twigs from trees, shrubs and vines on a single date or at intervals over the course of the winter and early spring, placing them in containers of water in controlled environments, and regularly recording leaf-out, flowering or other phenomena. Prior to or following leaf-out or flowering, twigs may be assigned to treatment groups for experiments involving temperature, photoperiod, frost, humidity and more. Recent studies using these methods have shown that winter chilling requirements and spring warming strongly affect leaf-out and flowering times of temperate trees and shrubs, whereas photoperiod requirements are less important than previously thought for most species. Invasive plant species have weaker winter chilling requirements than native species in temperate ecosystems, and species that leaf-out early in the season have greater frost tolerance than later leafing species. This methodology could be extended to investigate additional drivers of leaf-out phenology, leaf senescence in the autumn, and other phenomena, and could be a useful tool for education and outreach. Additional ecosystems, such as boreal, southern hemisphere and sub-tropical forests, could also be investigated using dormant twigs to determine the drivers of leaf-out times and how these ecosystems will be affected by climate change.

Cultivo do mirtilo: atualizações e desempenho inicial de variedades de baixa exigência em frio no Estado de Säo Paulo

A produção comercial de mirtilos na América do Sul tem passado por mudanças importantes nos últimos anos, em função do aumento da oferta de frutos frescos dos principais países produtores, causando forte queda de preços em plena safra, entre os meses de dezembro e fevereiro. Uma alternativa para esta situação é a produção de mirtileiros de maturação precoce ou muito tardia, fora da época de meia-estação, caracterizada pelos menores preços da fruta. Em 2010, foram introduzidas no Brasil novas variedades de mirtileiros de baixa exigência em frio desenvolvidas pela Universidade da Flórida, que podem ser cultivadas em regiões quentes e apresentam uma frutificação mais precoce, quando comparadas com as variedades tradicionalmente cultivadas no Brasil. Essas novas variedades apresentam grande potencial para a produção precoce de mirtilos no País em regiões sem frio hibernal, aumentando significativamente a rentabilidade da cultura. Para viabilizar esta produção, é necessário validar estratégias de manejo para estas variedades, devido à falta de informação técnica sobre seu cultivo nas condições edafoclimáticas brasileiras. Atualmente, estäo sendo conduzidas as primeiras pesquisas fitotécnicas no Estado de Säo Paulo para avaliar o crescimento e a produção destas variedades na ausência total de frio, situação de ocorrência particular em poucos países produtores do mundo.

Drivers of leaf‐out phenology and their implications for species invasions: insights from Thoreau's Concord

To elucidate climate-driven changes in leaf-out phenology and their implications for species invasions, we observed and experimentally manipulated leaf out of invasive and native woody plants in Concord, MA, USA. Using observations collected by Henry David Thoreau (1852-1860) and our own observations (2009-2013), we analyzed changes in leaf-out timing and sensitivity to temperature for 43 woody plant species. We experimentally tested winter chilling requirements of 50 species by exposing cut branches to warm indoor temperatures (22°C) during the winter and spring of 2013. Woody species are now leafing out an average of 18d earlier than they did in the 1850s, and are advancing at a rate of 5±1d°C(-1) . Functional groups differ significantly in the duration of chilling they require to leaf out: invasive shrubs generally have weaker chilling requirements than native shrubs and leaf out faster in the laboratory and earlier in the field; native trees have the strongest chilling requirements. Our results suggest that invasive shrub species will continue to have a competitive advantage as the climate warms, because native plants are slower to respond to warming spring temperatures and, in the future, may not meet their chilling requirements.

MODELS FOR QUANTIFYING EFFECTIVE WINTER CHILL ON APPLE ENDODORMANCY

Under southern Uruguayan conditions (34°37'SL;56°11'O, 40 m) winter chilling requirements are not always satisfied for the main commercial apple (Malus domestica Borkh) cultivars. The use of chemical rest breaking agents (mineral oils and hydrogen Cyanamid) to compensate these requirements is widely used. Therefore winter chill quantification should be a relevant issue to adjust this technique. To do so, adequate models to represent the advances in the endodormancy process as a function of climatic conditions are necessary. The UTAH and CH models are usually applied, regardless of which species or cultivar is considered. Although these models have the advantage to be widely spread and incorporated to commercial production, there are evidences of the lack of adjustment to the phenologyc behaviour of the main cultivars. This work's goal was to quantify the occurrence of winter chill during the endodormancy period with six models, in four apple cultivars ('Red Chief', 'Granny Smith', 'Royal Gala' and 'Fuji') during 2005 and 2006. The models used were CH, UTAH, UTAH+, Dynamic Model, North Carolina Model and Model for Subtropical Conditions. The beginning of endodormancy release was determined when 50% of leaf fall was reached and the process finished when 50% of one-year-old shoot buds sprouted in a forcing chamber. All model quantifications were based on hourly temperature data, obtained from sensors located in the tree and at the nearest weather station. The greatest temperature amplitude registered at field conditions, compared to weather station conditions, modified up to 2.5 times, the quantifications performed by the same model, being the UTAH model, the most affected by this phenomenon. These results show differences among models and years, consequently, in order to determine the viability of them in southern Uruguayan conditions, a longer evaluating period is needed.

REST COMPLETION AND GROWTH OF 'THOMPSON SEEDLESS' GRAPES AS A FUNCTION OF TEMPERATURES

Research was carried out over four seasons, from 2000 to 2003, in order to establish the effect of temperature on phenological development of 'Thompson Seedless' grapevine in the Aconcagua Valley, Chile (32°45S, 600 m a.s.l.). Winter chilling requirement to break dormancy was determined by different models, which were compared according to Ashcroft et al. methodology (1977). Grapevine development since dormancy breaking was characterized based on growing degree-hours (GDH) and degree-days (DD). It was concluded that the Utah model was the least variable model for rest estimation, with 430 chilling units up to dormancy break, which would have occurred between June 6 and June 17 for the years between 2000 and 2003. Heat requirement from rest completion up to full bloom were 9,451 GDH, 252 DD and 145 days, and 16,101 GDH, 713 DD or 77 days were required from 4 mm berry up to harvest. In order to validate heat requirements for berry growth, phenological stages were estimated for the season 2003-2004, the most accurate estimation was obtained when GDH were used.

Modeling the effects of winter environment on dormancy release of Douglas-fir

Most temperate woody plants have a winter chilling requirement to prevent budburst during mid-winter periods of warm weather. The date of spring budburst is dependent on both chilling and forcing; modeling this date is an important part of predicting potential effects of global warming on trees. There is no clear evidence from the literature that the curves of chilling or forcing effectiveness differ by species so we combined our data and published information to develop new curves on the effectiveness of temperature for chilling and forcing. The new curves predict effectiveness over a wide range of temperatures and we suggest both functions may be operating at the same time. We present experimental data from 13 winter environments for 5 genotypes of Douglas-fir ( Pseudotsuga menziesii var. menziesii) and use them to test various assumptions of starting and stopping dates for accumulating chilling and forcing units and the relationship between budburst and the accumulation of chilling and forcing units. Chilling started too early to be effective in one treatment but the other 12 environments resulted in budburst from many combinations of chilling and forcing. Previous reports have suggested benefits or cancellations of effects from alternating day/night or periodic temperatures. Our simple models do not include these effects but nevertheless were effective in predicting relationships between chilling and forcing for treatments with a wide range of conditions. Overall, the date of budburst changed only slightly (+1 to −11 days) across a wide range of treatments in our colder test environment (Olympia, WA, USA) but was substantially later (+29 days) in the warmest treatment in our warmer environment (Corvallis, OR, USA). An analysis of historical climate data for both environments predicted a wide range in date to budburst could result from the same mean temperature due to the relative weightings of specific temperatures in the chilling and forcing functions. In the absence of improved understanding of the basic physiological mechanisms involved in dormancy induction and release, we suggest that simple, universal functions be considered for modeling the effectiveness of temperature for chilling and forcing. Future research should be designed to determine the exact shape of the curves; data are particularly lacking at the temperature extremes. We discuss the implications of our data and proposed functions for predicting effects of climate change. Both suggest that the trend toward earlier budburst will be reversed if winter temperatures rise substantially.

Diverse responses of vegetation phenology to a warming climate

Warming climates have been widely recognized to advance spring vegetation phenology. However, the delayed responses of vegetation phenology to rising temperature and their mechanisms are poorly understood. Using satellite and climate data from 1982 to 2005, we reveal a latitude transition zone of greenup onset in vegetation communities that has diversely responded to warming temperature in North America. From 40°N northwards, a winter chilling requirement for vegetation dormancy release is far exceeded and the decrease in chilling days by warming winter temperature has little impact on thermal‐time requirements for greenup onset. Thus, warming spring temperature has constantly advanced greenup onset by 0.32 days/year. However, from 40°N southward, the shortened winter chilling days are insufficient for fulfilling vegetation chilling requirement, so that the thermal‐time requirement for greenup onset during spring increases gradually. Consequently, vegetation greenup onset changes progressively from an early trend (north region) to a later trend (south region) along the latitude transition zone from 40–31°N, where the switch occurs around 35°N. The greenup onset is delayed by 0.15 days/year below 31°N.

Will climate change have a different impact on different trophic levels? Phenological development of winter moth Operophtera brumata and its host plants

Will climate change have a different impact on different trophic levels? Phenological development of winter moth <i>Operophtera brumata</i> and its host plants

'Nickels' Almond × Peach Hybrid Clonal Rootstock

‘Nickels’ is a vegetatively propagated almond rootstock clone originating as a hybrid seedling ‘PA1-82’ from the cross of ‘UCD533’ almond to ‘Nemaguard’ peach. Vegetative progeny are uniform, vigorous, highly compatible with almond cultivars, and relatively easy to propagate. Compared with the commercially important ‘Hansen 536’ rootstock, ‘Nickels’ is better adapted to current nursery propagation and storage practices as well as to a wider range of California almond production environments, possibly related to its greater winter chilling requirement. ‘Nickels’ also has a similar range of resistance to nematode species as does the parental ‘Nemaguard’, which is a widely used rootstock for Prunus tree crops in California. The hybrid vigor of this interspecific rootstock confers greater vigor to the almond scion, making it particularly useful for replant situations where adjacent trees are typically larger and so more competitive. Origin

Use of bioclimatic indexes to characterize phenological phases of apple varieties in Northern Italy.

The research was designed to characterize the phenological behaviour of different apple varieties and to compare different bioclimatic indexes in order to evaluate their adaptability in describing the phenological phases of fruit species. A field study on the requirement for chilling units (winter chilling requirement) and the accumulation of growing degree hours of 15 native apple cultivars was carried out in a fruit-growing area in North West Italy (Cuneo Province, Piedmont). From 1991 to 1993, climatic data were collected at meteorological stations installed in an experimental orchard (Verzuolo, Cuneo). Four methods were compared to determine the winter chilling requirement: Hutchins, Weinberger-Eggert, Utah and North Carolina. The Utah method was applied to determine the time when the chilling units accumulated become effective in meeting the rest requirements. A comparison of the different methods indicated that the Weinberger-Eggert method is the best: as it showed the lowest statistical variability during the 3 years of observations. The growing degree hour requirement (GDH) was estimated by the North Carolina method with two different base temperatures: 4.4 degrees C and 6.1 degrees C. More difficulties were met when the date of rest completion and the beginning of GDH accumulation was determined. The best base temperature for the estimation of GDH is 4.4 degrees C. Phenological and climatic characterizations are two basic tools for giving farmers and agricultural advisors important information about which varieties to choose and which are the best and the most correct cultivation practices to follow.

Phenology-mediated effects of climatic change on some simulated British Columbia forests

We added certain aspects of species-specific phenology, and of local frost regimes to a standard invididual-based patch model of forest stand dynamics, which we used to explore the possible consequences of four climate-change scenarios in eight distinct forest regions in British Columbia, Canada. According to model projections, lowland temperate coastal forests will be severely stressed because forest tree species will no longer have their winter-chilling requirements met. High-elevation coastal forests may either remain stable or decrease in productivity, while interior subalpine forests may eventually resemble those now found in the coastal mountains. Southern interior forests are likely to persist relatively unchanged, while boreal and sub-boreal forests of the northern interior may become dominated by Douglas-fir and western larch, rather than by spruce and pine as at present. The rate of change in forest composition may be very high in some cases. Changes under the four climate-change scenarios generally vary in magnitude but not in direction. This exercise illustrates that different forest types might respond to a changing climate for different reasons, and at different rates.

Climate and kiwifruit cv. ‘Hayward’ 2. Regions in New Zealand suited for production

Abstract Matching crops to climate is an important activity for planning production. Three important climatic factors were identified as being important determinants of kiwifruit (Actinidia deliciosa ’Hayward’ (A. Chev) C.F. Liang et A.R. Ferguson) distribution: winter chilling; growing season thermal time; and annual rainfall. Indices for each of these factors were developed to enable mapping of the most suitable areas for kiwifruit production. These were May‐July temperatures of 11°C or less as the optimal winter chilling requirement, a thermal time accumulation of 1100 degree‐days above 10°C from October to April, and an annual rainfall of 1250 mm or more. Apart from Northland, all the traditional areas of kiwifruit production have a suitable climate. However, there are substantial areas of inland Bay of Plenty to Rotorua, the Waikato, north Taranaki, and northern Hawke's Bay where the climatic requirements are also satisfied. A high frequency of extreme winds may be an additional limiting factor in some of these regions, such as Taranaki. The total area of suitability is enlarged if irrigation is available, particularly in the southern North Island and central Marlborough. Within this climatic range the estimated dates for the average end of dormancy and 50% flowering are spread over 4 weeks, and estimated budburst dates over 11 days. Although use of average climate data to describe kiwifruit distribution provides a valuable first‐order assessment, it would be desirable to incorporate analyses of climate variability in future studies of this kind.

Boreal forest futures: Modelling the controls on tree species range limits and transient responses to climate change

Range limits and broad-scale geographic variations in the productivity of boreal and northern deciduous tree species in Europe are simulated with a bioclimatic model (STASH). STASH is based on a small number of distinct mechanisms by which climate is thought to affect the survival, regeneration and growth of trees. Survival is limited by summer warmth requirements and winter cold tolerance; regeneration, additionally by winter chilling requirements; and growth rate by net assimilation, which in turn is related to photosynthetically active radiation, growing-season length, temperature (relative to species-specific optima) and soil moisture supply (relative to evaporative demand). These mechanisms are quantified either as thresholds (for survival and regeneration) or multipliers (for growth), based on bioclimatic variables computed from monthly climate normals interpolated three-dimensionally to a 10-minute grid. Growing-season and growing degree day calculations take into account the effects of chilling. The drought calculations also take into account the effects of soil-moisture storage by means of a physically based evapotranspiration calculation coupled to a one-layer soil hydrology model. STASH is used to examine changes in potential range limits under a 2×CO2 climate-change scenario. Associated transient responses at selected sites in the boreal and boreo-nemoral zones of Sweden are also simulated, using the forest gap model FORSKA2. The species-specific survival and regeneration constraints and growth responses of STASH modify the growth, establishment and mortality of trees in FORSKA2. The results obtained in this way differ sharply from the results of conventional forest gap models, where growth rates are assumed to decline to zero at minimum and maximum growing degree day limits. For example, towards the southern limit of Picea abies (Norway spruce), STASH correctly shows no decline in productivity, but rather an abrupt cut-off corresponding to a chilling requirement during regeneration that is not met further south or west. In transient warming scenarios, this mechanism has the effect that natural regeneration can be blocked due to the warm winters even as yield is increasing due to the longer and warmer summers. STASH predicts drastic changes in species distributions in response to the large climate changes (especially winter warming) expected for northern Europe. Some of the common boreal species (e.g., Picea abies; Pinus sylvestris; Alnus incana) are unlikely to survive in much of their present range, withdrawing to the far north. Other species already widespread may be able to occupy some of the few sites that are today unavailable to them (e.g., Betula spp.; Corylus avellana). Other temperate deciduous species such as Fagus sylvatica could have dramatic range expansions, potentially occupying large tracts of the present boreal zone. FORSKA2 transient simulations illustrate some of the possible routes towards different types of forest in a changed climate. Some sites in the north show little change in species composition, but sites towards the southern boundary of the boreal zone could develop a new suite of dominants. The degree of sensitivity of a particular site depends both on the climate change prediction and on the transient dynamics of the forest community. Many types of transient behaviour are shown to be possible. Coupled with uncertainties about the future role of dispersal and changes in disturbance rate, the complexity and variety of these transient responses imply a highly uncertain future for the north European boreal forests.