Spring Budburst Research Articles

Late frost damage risk for viticulture under future climate conditions: a case study for the Luxembourgish winegrowing region

Background and Aims Late frosts are a significant risk to grape production in frost-prone viticultural regions. Increasing air temperature because of climate change is likely to advance grape budburst and last frost events in spring. So far, it is unclear whether one trend will be more pronounced than the other, and hence, whether the risk of late frost damage will increase or decrease. The aim of this work was to investigate the future frost risk in the Luxembourgish winegrowing region by assessing the effect of simulated future climate conditions on the timing of budburst and last frost date. Methods and Results Late frost risk was assessed by combining: (i) a phenological model for budburst of the grapevine (DORMPHOT); and (ii) ensemble-based projections of future air temperature. Analyses indicated that increasing spring temperature will advance the timing of budburst and the date of the last frost. This advancement, however, will be more pronounced for last frost events than for budburst. Conclusions Modelled projections showed that the frequency of spring frost damage in the Luxembourgish winegrowing region will decrease, without completely excluding them for the near (2021–2050) or the far future (2069–2098). Significance of the Study The application of a combination of a phenological model for grape budburst and ensemble-based projections of future air temperature enables the assessment of the future late frost risk in a frost-prone viticulture region.

Susceptibility of grapevine tissues to Neofusicoccum luteum conidial infection

This study investigated the ability of Neofusicoccum luteum to infect wounded shoots, trunks, pruned cane ends, leaf surfaces, buds, berries and roots, and its further progression into stem tissues. All tissue types were susceptible to infection except roots, with highest incidences in trunks (100%), cane ends (100%), shoots (92%) and buds (88%), indicating that in New Zealand, N. luteum is primarily a trunk and shoot pathogen. In trunks, there were no external symptoms, although N. luteum could be reisolated from 60 to 70 cm acropetally from the inoculation site after 4 months, by which time the pathogen had progressed into side shoots which became necrotic. Wounded and non‐wounded buds became infected; most were killed, with basipetal progression of the pathogen into the supporting shoots. Berries wounded and inoculated at the pre‐bunch closure stage were susceptible to N. luteum infection, with isolation incidence increasing over the season and peaking at harvest, when infected berries became mummified and produced pycnidia with many conidia. The pathogen was also able to progress from berries into bunch stems and supporting canes. Results from this research have indicated that N. luteum infection can occur in all aerial grapevine tissues and progress to young stem tissues where it causes wood necrosis. Growers should remove mummified berries from vineyard trash to ensure that pruning and trimming times do not coincide with rainy periods when conidia are released and dispersed. Furthermore, the susceptibility of buds to N. luteum infection indicates the need for fungicide sprays before budburst in spring.

Impacts of multiple extreme winter warming events on sub‐Arctic heathland: phenology, reproduction, growth, and CO2flux responses

AbstractExtreme weather events can have strong negative impacts on species survival and community structure when surpassing lethal thresholds. Extreme, short‐lived, winter warming events in the Arctic rapidly melt snow and expose ecosystems to unseasonably warm air (for instance, 2–10 °C for 2–14 days) but upon return to normal winter climate exposes the ecosystem to much colder temperatures due to the loss of insulating snow. Single events have been shown to reduce plant reproduction and increase shoot mortality, but impacts of multiple events are little understood as are the broader impacts on community structure, growth, carbon balance, and nutrient cycling. To address these issues, we simulated week‐long extreme winter warming events – using infrared heating lamps and soil warming cables – for 3 consecutive years in a sub‐Arctic heathland dominated by the dwarf shrubsEmpetrum hermaphroditum, Vaccinium vitis‐idaea(both evergreen) andVaccinium myrtillus(deciduous). During the growing seasons after the second and third winter event, spring bud burst was delayed by up to a week forE. hermaphroditumandV. myrtillus, and berry production reduced by 11–75% and 52–95% forE. hermaphroditumandV. myrtillus, respectively. Greater shoot mortality occurred inE. hermaphroditum(up to 52%),V. vitis‐idaea(51%), andV. myrtillus(80%). Root growth was reduced by more than 25% but soil nutrient availability remained unaffected. Gross primary productivity was reduced by more than 50% in the summer following the third simulation. Overall, the extent of damage was considerable, and critically plant responses were opposite in direction to the increased growth seen in long‐term summer warming simulations and the ‘greening’ seen for some arctic regions. Given the Arctic is warming more in winter than summer, and extreme events are predicted to become more frequent, this generates large uncertainty in our current understanding of arctic ecosystem responses to climate change.

Seasonal fluctuation of organic and inorganic components in xylem sap of Populus nigra

Deciduous trees show annual periodicity in shoot growth and development, but such periodicity is not well investigated in roots. To clarify the seasonal fluctuation in root functions, xylem sap from Populus nigra branches was analyzed for 2 years. Various xylem sap components including calcium, potassium, glucose, and proteins showed seasonal fluctuations with peaks from winter to spring. Abscisic acid (ABA) was the most abundant hormone in the xylem sap throughout all seasons and showed two peaks from late autumn to spring. We hypothesize that low temperature in winter promotes metal loading into the xylem sap and the synthesis of proteins and sugars in roots as an adaptation to the winter environment and to prepare for spring bud burst. acetic acid; IA-Ala, indole-3-acetyl- L-alanine; IA-Ile, indole-3-acetyl-L-isoleucine; IA-Leu, indole-3-acetyl- L-leucine; IA-Asp, indole-3-acetyl-L-aspartic acid; IA-Trp, indole-3-acetyl-L-tryptophan; IA-Phe, indole- 3-acetyl-L-phenylalanine; GA, gibberellic acid; ABA, abscisic acid

APPLE PRODUCTION UNDER CONDITIONS OF SUB-OPTIMAL WINTER CHILLING IN SOUTH AFRICA

Apples are widely accepted to need ca. 1000-1200 Utah model chill units to break dormancy, yet in South Africa apples are often produced successfully with 500 chill units. Numerous chilling models are used locally to quantify winter chilling. These models are discussed in light of their shortcomings under low chill conditions. Branching in spring on year-old shoots is acrotonic (from the most distal buds). Dominance of these distal buds develops slowly during winter and is clearly defined before budburst in spring. It is the lack of an extended dormant period associated with the mild local winters that impedes the development of acrotony. This is due to an inherent low growth rate of the buds (increased endodormancy), and less synchronization among buds at the time of spring budburst, resulting in both a delayed and more erratic budburst. Furthermore, a considerably increased paradormant inhibition by the distal shoot parts is observed. Paradormancy accounts largely for the inhibition of budburst of the upper lateral buds under conditions of sub-optimal chilling. The causes of delayed foliation may reside more in the shoot piece than in the buds themselves. Cytokinins are known to release buds from dormancy, especially when applied in late winter. Also, under normal winter conditions, a flush of endogenous cytokinins is observed shortly before budburst. This cytokinin flush is triggered by the application of rest-breaking agents. The predominant system currently used is a tree with a single central leader and fruiting branches directly situated on the leader. The tree is similar to the French Solaxe, but is unique in the sense that its evolution is the result of an improved understanding of the reaction of the apple tree to a lack of winter chilling, hot growing conditions and poor soils. Finally, other practical manipulations of branching on both young and mature trees are discussed.

STUDY APPROACHES ON THE CHESTNUT GALL WASP, DRYOCOSMUS KURIPHILUS YASUMATSU IN CHINA

Approaches of studies on the chestnut gall wasp, Dryocosmus kuriphilus Yasumatsu in China were documented in this paper. The pest distributes over 16 provinces covering all the chestnut productive area in the country with yield damage 15-30% every year. It was observed only 1 generation each year and seems to reproduce by parthenogenesis. Over wintering as young larvae within the host buds, it feeds acting with the budburst in spring, and its cabin forms with the leaf growth and spread. The adult eclosion is at end of male flower blooming. There have been 28 parasitical wasps reported as the nature enemies of the pest up today. Among them, Torymus sineresis Y. is the most predominant one. Pollarding in winter, releasing natural enemy during April to June, using black light trap from June to September, and utilizing resistant cultivars are the main methods of IPM.

Growth, phenology, and cold hardiness of 32 Douglas-fir full-sib families

Thirty-two full-sib families of coastal Douglas-fir ( Pseudotsuga menziesii (Mirb.) Franco var. menziesii) with a range of predicted breeding values were monitored for growth rate, phenology, and cold hardiness over 2 years on two sites to investigate if other traits are being selected when family selection is based on height. Significant differences among families existed in most phenological, growth, and cold-hardiness traits. On average, taller families burst bud later but did not have significantly different growth rates or length of growing period than other families. We found no significant correlations between family date of bud burst and cold hardiness in late spring or between duration of shoot growth or height and autumn freezing damage. Family differences in freezing tolerance were greatest in September and October. In these months, family current-year leaf nitrogen was positively correlated with cold hardiness. Families that were most hardy in the autumn were not the most hardy families in spring. We conclude that, for the studied breeding series, selection based on height does not have a significant impact on cold hardiness. We found no consistent relationships between phenological, growth, or cold-hardiness parameters and final height that could explain family ranking by height. Relationships between grandparent elevation and dates of bud burst and cold hardiness were observed.

Dehydrins expression related to timing of bud burst in Norway spruce

Cold deacclimation and preparation to flushing likely requires rehydration of meristems. Therefore, water stress related genes, such as dehydrins (DHN), might play an important role in providing protection during winter dormancy, deacclimation and bud burst timing processes. Here we report the sequence analysis of several Norway spruce DHN identified in late and early flushing suppressive subtraction hybridization cDNA libraries and in our Norway spruce EST database. We obtained 15 cDNAs, representing eight genes from three distinct types of DHN, and studied differential expression of these genes before and during bud burst in spring, using qRT-PCR. We found the visible reduction in transcript level of most DHN towards the bud burst, supported by a significant down-regulation of the DHN in needles during experimental induction of bud burst applied at three time points during autumn in Norway spruce grafts. For most of the DHN transcripts, their expression levels in late-flushing spruces were significantly higher than in the early flushing ones at the same calendar dates but were remarkably similar at the same bud developmental stage. From our results we may conclude that the difference between the early and the late families is in timing of the molecular processes leading to bud burst due to differences in their response to the increasing temperature in the spring. They are induced much earlier in the early flushing families.

Dinâmica da dormência e brotação de gemas de vimeiro no Planalto Sul Catarinense

O objetivo deste trabalho foi avaliar a dinâmica e a heterogeneidade de dormência de gemas, e avaliar o efeito de diferentes épocas de colheita de ramos na brotação do vimeiro, no Planalto Sul Catarinense. Ramos de ano foram colhidos nos meses de abril a agosto de 2005, nos municípios catarinenses de Lages, Bocaina do Sul e Urupema. A dormência de gemas foi avaliada em estacas retiradas da base (0 a 12 cm), centro (12 a 24 cm) e ápice (24 a 36 cm) de ramos com comprimento superior a 150 cm. Foram utilizadas estacas com e sem redução para uma única gema. As brotações das plantas em campo também foram avaliadas. A dormência mais intensa de gemas de ramos de ano ocorreu em maio, quando a intensidade de dormência e a freqüência de gemas dormentes decresceram do ápice para a base do segmento basal dos ramos. A colheita do vime em abril induziu a brotação antes do inverno e prejudicou a brotação primaveril.

Endogenous cytokinin levels of table grape vines during spring budburst as influenced by hydrogen cyanamide application and pruning

Abstract Cytokinins play an important role in budburst, flowering and fruit set in table grapes. Rest-breaking treatments with hydrogen cyanamide and pruning practices modify budburst and reproductive development in table grapes, especially in regions with low and often inadequate winter chilling. The effect of these treatments on the xylem sap and bud Zeatin riboside (ZR) content was determined during late winter and budburst in ‘Sultanina’, ‘Sunred Seedless’, and ‘Alphonse Lavallee’ canes in a total of nine trials conducted between 1997 and 2001. Bud ZR levels of hydrogen cyanamide treated ‘Sultanina’ canes showed an earlier and increased cytokinin peak, in particular in the distal buds. Large ZR peaks before budburst and noticeable differences between distal and proximal buds were absent on non-sprayed canes. The xylary ZR content of long pruned ‘Sultanina’, ‘Sunred Seedless’, and ‘Alphonse Lavalee’ canes showed a significantly higher and earlier cytokinin peak than in short pruned spurs. By contrast, the bud ZR content tended to be higher in spurs than canes. Pruning and rest-breaking treatments enhanced budburst and increased endogenous cytokinins in these experiments. Long pruning in ‘Sultanina’ and ‘Sunred Seedless’ (both parthenocarpic) is necessary for acceptable fruit set and yields. Possibly, in longer canes more cytokinin is available for reproductive development. ‘Alphonse Lavalee’ (seeded) is sufficiently fruitful and produces adequate yields following spur pruning.

Dryocosmus kuriphilus

<i>Dryocosmus kuriphilus</i>

High autumn temperature delays spring bud burst in boreal trees, counterbalancing the effect of climatic warming.

The effect of temperature during short-day (SD) dormancy induction was examined in three boreal tree species in a controlled environment. Saplings of Betula pendula Roth, B. pubescens Ehrh. and Alnus glutinosa (L.) Moench. were exposed to 5 weeks of 10-h SD induction at 9, 15 and 21 degrees C followed by chilling at 5 degrees C for 40, 70, 100 and 130 days and subsequent forcing at 15 degrees C in a 24-h photoperiod for 60 days. In all species and with all chilling periods, high temperature during SD dormancy induction significantly delayed bud burst during subsequent flushing at 15 degrees C. In A. glutinosa, high temperature during SD dormancy induction also significantly increased the chilling requirement for dormancy release. Field experiments at 60 degrees N with a range of latitudinal birch populations revealed a highly significant correlation between autumn temperature and days to bud burst in the subsequent spring. September temperature alone explained 20% of the variation between years in time of bud burst. In birch populations from 69 and 71 degrees N, which ceased growing and shed their leaves in August when the mean temperature was 15 degrees C, bud burst occurred later than expected compared with lower latitude populations (56 degrees N) in which dormancy induction took place more than 2 months later at a mean temperature of about 6 degrees C. It is concluded that this autumn temperature response may be important for counterbalancing the potentially adverse effects of higher winter temperatures on dormancy stability of boreal trees during climate warming.

Physiology-based phenology models for forest tree species in Germany.

Models of phenology are needed for the projection of effects of a changing climate on, for example, forest production, species competition, vegetation-atmosphere feedback and public health. A new phenology model for deciduous tree bud burst is developed and parameters are determined for a wide geographical range (Germany) and several forest tree species. The new model is based on considerations of simple interactions between inhibitory and promotory agents that are assumed to control the developmental status of a plant. Several alternative model structures were formulated emphasizing different hypothetical physiological processes. The new models fitted the observations better than classical models. The bias of the classical models, i.e. overestimation of early observations and underestimation of late observations, could be reduced but not completely removed. Differences in the best-fitting model equations for each species indicated that, for the late spring phases (bud burst of Fagus sylvatica and Quercus robur), the photoperiod played a more dominant role than for early spring phases (bud burst of Betula pendula and Aesculus hippocastanum). Chilling only plays a subordinate role for spring bud burst compared to temperatures preceding this event in our data. The presented modeling approach allowed for a species-specific weighting of the dominant processes. The model results are in accordance with experimental findings that indicate an important role of day length in late spring BB. Potentials for model improvement are discussed.

THERMAL TIME REQUIREMENT AND HARVEST TIME FORECAST FOR PEACH CULTIVARS WITH DIFFERENT FRUIT DEVELOPMENT PERIODS

Non-linear models using growing degree hours (GDH), based on the choice of base, critical and optimum temperatures, have been successfully applied to calculate thermal time required for spring bud burst in deciduous fruit trees. The flexibility of the model can fit the wide range of temperatures that occur during the peach fruit development period (FDP), which takes place from early spring to late summer. In this experiment, fruit growth was studied in relation to thermal time accumulated from bloom to fruit harvest for peach and nectarine cultivars whose fruit development period range from 70 to 150 days. Thermal time was calculated in terms of degree days (DD) (base temperature 7 °C, and critical temperature 35 °C) and GDH (base temperature 7.5 °C, optimum temperature 26 °C and critical temperature 38.5 °C). Climatic and phenological data (bloom and harvest dates) were available for a minimum of three to a maximum of nine years. GDH showed a lower coefficient of variation and a higher predictive capacity, in terms of days, than degree days for all of the cultivars tested. Taking into account the whole FDP, the accuracy of the GDH model in predicting harvest time ranged from 1 day, in the early ripening peach cultivar ‘Maycrest,’ to 4 days in late ripening peach cultivar ‘O’Henry.’ An accurate early forecast of fruit harvest time was obtained using the GDH accumulated during the first 25-52 days of FDP, depending on the cultivar. INTRODUCTION The development period of peach fruits is genetically controlled (Vileila-Morales et al., 1981) but ranges greatly with season (Blake, 1930) and environment (Weinberger, 1948; Topp and Sherman, 1989; Caruso et al., 1993). Time of ripening depends on bloom time and on the length of the fruit development period (FDP), which is regulated chiefly by the temperature range from bloom to ripening and by the cultivar response to temperature (Boonprakob et al., 1992); as a matter of fact, temperature has been used for building models to predict harvest time (Munoz et al., 1986; Boonprakob et al., 1992; Caruso et al., 1993; Motisi et al., 1992; Motisi et al., 1998). FDP has been associated to the average daily mean temperature (Munoz et al., 1986) or to mean monthly temperature (Topp and Sherman, 1989). Anyhow, prevailing temperatures during the first 2 months after full bloom vary the most and are the best correlated to the FDP, serving as the best predictor for harvest time (Lilleland, 1965; Boonprakob et al., 1992; Caruso et al., 1993). Motisi et al. (in press), re-examining FDP data by Munoz et al. (1986), showed that the coefficient of variation (c.v.) of thermal time accumulated from bloom to harvest, for five early ripening peach cultivars grown in four different environments, is much lower than the c.v. relative to the same period and expressed in term of days. As a matter of fact, thermal time requirement, during fruit growth, is cultivar dependent and its c.v. between years or environments, should be close to zero. Based on this hypothesis the Proc. 5 IS on Peach Eds. R.S. Johnson & C.H. Chrisosto Acta Hort. 592, ISHS 2002

Climatic control of the high-latitude vegetation greening trend and Pinatubo effect.

A biogeochemical model of vegetation using observed climate data predicts the high northern latitude greening trend over the past two decades observed by satellites and a marked setback in this trend after the Mount Pinatubo volcano eruption in 1991. The observed trend toward earlier spring budburst and increased maximum leaf area is produced by the model as a consequence of biogeochemical vegetation responses mainly to changes in temperature. The post-Pinatubo decline in vegetation in 1992-1993 is apparent as the effect of temporary cooling caused by the eruption. High-latitude CO(2) uptake during these years is predicted as a consequence of the differential response of heterotrophic respiration and net primary production.

Adaptation of a generalist moth, Operophtera brumata, to variable budburst phenology of host plants

AbstractThe adaptation of three allopatric populations of a generalist moth, Operophtera brumata (L.), on two tree species, Prunus padus (L.) and Quercus robur (L.) which represent the extremes of the timing of budburst in spring, was studied in Finland and Sweden. The synchrony of the hatching and budbursting was monitored, and its importance to dispersal and growth of larvae was assessed by rearing cohorts of larvae, whose hatching dates were manipulated, on both hosts. In addition, the realised heritability of the hatching time was estimated.Experimental populations hatched in approximate synchrony with the budburst of their original host species. As a result of the manipulation of the hatching dates of larvae, the growth rates of larvae decreased and the dispersal rates increased on both hosts in relation to the ageing of foliage. The realised heritability of hatching times was rather high (0.63). There were fewer differences in the host use efficiency and behaviour of the experimental populations than in the hatching phenology. The synchrony of hatching with the budburst of the local dominant host plant is probably a result of stabilising selection.

Interspecific defoliation responses of trees depend on sites of winter nitrogen storage

Summary To determine if the response of trees to herbivory is related to their ability to store nitrogen, saplings of Pinus sylvestris L., Betula pendula Roth. and Sorbus aucuparia L. were clipped, either when dormant or at spring bud burst, to remove half the previous year’s shoot growth. The impact of clipping on N remobilization and uptake was quantified in relation to their growth responses. Pinus sylvestris stored N during the winter in needles grown the previous summer, whereas B. pendula and S. aucuparia used their woody roots and older stems. Therefore, N remobilization was unaffected by clipping the deciduous species, but was reduced by half in the evergreen. For both P. sylvestris and B. pendula, root uptake contributed N for leaf growth immediately after bud burst, concurrently with remobilization. Sorbus aucuparia had remobilized half the N from storage before any N was taken up by the roots. Pinus sylvestris, which has a fixed pattern of growth, produced a lower total needle mass when clipped, but individual needles were heavier. Nitrogen uptake during summer was reduced by 26 and 44% for winter‐ and spring‐clipped saplings, respectively. Both deciduous species showed compensatory leaf growth such that, by the end of the summer, leaf mass (and B. pendula leaf area) were unaffected by clipping. Nitrogen uptake by both deciduous species was unaffected by clipping. We conclude that the site of N storage during winter is a crucial factor in determining the response of a sapling to herbivory, as interactions with the growth patterns of the three species can lead to different responses to damage. We suggest that for evergreen trees, the production of antiherbivory compounds serves primarily to protect N stored in their foliage, rather than the leaves themselves.

Endogenous cytokinin distribution patterns at budburst in Granny Smith and Braeburn apple shoots in relation to bud growth

The possible relationship of branching habit to cytokinin content of apple shoots ( Malus× domestica Borkh.) was investigated. One-year old apple shoots are acrotonic (distal branching), more strongly so in Granny Smith than in Braeburn. In the first trial, long, 1-year old Granny Smith and Braeburn apple shoots were sprayed on 29 August 1995 to break rest with dinitro- o-cresol (DNOC) oil (5%). The cytokinin contents of the xylem sap, the combined bark and buds, and the wood were determined in distal and proximal shoot halves over the next 6 weeks. Budburst (terminal and lateral buds) was first visible (green tip) in both cultivars on 20 September 1995. A greater increase in cytokinin content of distal xylem sap, coupled with elevated cytokinin in the distal wood, reflect the overall acrotony of both cultivars. The strong acrotony of Granny Smith is reflected in the higher cytokinin concentration in distal portion 1 week before the proximal portion of the shoot. The differential distribution of cytokinin reflects the pattern of budburst and may be correlated with growth habit. In a subsequent trial, Granny Smith shoots chilled and forced in the absence of roots showed an increase in cytokinin content of the bark and buds, and the wood as growth resumed. This was roughly comparable in magnitude to the increase observed under field conditions. The cytokinin increase in rootless shoots and differential distribution of cytokinin prior to sprouting, support the hypothesis that shoot-derived, rather than root-derived, cytokinins act to trigger spring budburst.

Tansley Review No. 114

A cyclic behaviour in the intensity of maritime conditions which varies with the periodic behaviour of the North Atlantic oscillation has recently become apparent in the climatic record of northern Europe. Periodic increases in oceanicity are usually viewed as having a positive effect on plant survival, as milder winters, reduction of temperature extremes, low risk of exposure to frost, and freedom from drought reduce many aspects of environmental stress. However, warmer winters in maritime environments may also have a powerful influence in creating habitats that are unfavourable for many species. The dangers of long periods of soil saturation for overwintering plants, soaking injury to germinating seeds, premature bud burst in spring, depression of treelines by increased cloud cover and high lapse rates, as well as the constant leaching of soils, are all negative aspects of the maritime environment. Woody species in which root dormancy is delayed by mild winters are particularly vulnerable to the consequences of winter flooding. Subsequent re‐exposure to oxygen as water tables fall in spring can aggravate flooding damage through post‐anoxic injury, leading to severe dieback of anchoring roots. Soil leaching, particularly after human disturbance, can induce nutrient deficiencies and the establishment of oligotrophic communities with reduced productivity. Podzolization and iron pan formation have in the past facilitated the processes of paludification in oceanic regions. The resulting spread of bogs and acid moorlands can further reduce the potential for productivity in both agriculture and natural plant communities. Given the probability that current climatic trends may increase the degree of oceanicity in western and northern regions of Europe, the potentially negative consequences of such a climatic change need to be considered in relation to future ecological changes and their consequences for conservation and land use. contents Summary 257 I. defining and quantifying oceanicity 257 II. ecological consequences of oceanicity 261 III. ecological history of oceanicity in western europe 263 IV. positive and negative influences of oceanicity 267 V. modifying effects of oceanicity on plant distribution 269 VI. physiological impact of warm winters 271 VII. treelines and oceanicity 276 VIII. conclusions 278 Acknowledgements 279

Effects of elevated CO(2) and temperature on cold hardiness and spring bud burst and growth in Douglas-fir (Pseudotsuga menziesii).

We examined effects of elevated CO(2) and temperature on cold hardiness and bud burst of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) seedlings. Two-year-old seedlings were grown for 2.5 years in semi-closed, sunlit chambers at either ambient or elevated (ambient + ~ 4 degrees C) air temperature in the presence of an ambient or elevated (ambient + ~ 200 ppm) CO(2) concentration. The elevated temperature treatment delayed needle cold hardening in the autumn and slowed dehardening in the spring. At maximum hardiness, trees in the elevated temperature treatment were less hardy by about 7 degrees C than trees in the ambient temperature treatment. In general, trees exposed to elevated CO(2) were slightly less hardy during hardening and dehardening than trees exposed to ambient CO(2). For trees in the elevated temperature treatments, date to 30% burst of branch terminal buds was advanced by about 6 and 15 days in the presence of elevated CO(2) and ambient CO(2), respectively. After bud burst started, however, the rate of increase in % bud burst was slower in the elevated temperature treatments than in the ambient temperature treatments. Time of bud burst was more synchronous and bud burst was completed within a shorter period in trees at ambient temperature (with and without elevated CO(2)) than in trees at elevated temperature. Exposure to elevated temperature reduced final % bud burst of both leader and branch terminal buds and reduced growth of the leader shoot. We conclude that climatic warming will influence the physiological processes of dormancy and cold hardiness development in Douglas-fir growing in the relatively mild temperate region of western Oregon, reducing bud burst and shoot growth.