Frost Hardiness of Nothofagus procera and Nothofagus obliqua in Britain

The frost hardiness of four seedlots of Nothofagus proccra andsix seedlots of Nothofagus obliqua was measured experimentallyduring three winters. Shoots were taken from saplings growingat the Bush Estate in Scotland. All seedlots set buds in lateSeptember, hardened very slowly in the autumn, were damagedto some extent by temperatures below –14°C in mid-winter,and dehardened during frosty weather in February/March priorto budburst in mid to late April. The range of mid-winter temperaturesgiving 0%, 50% and 100% kill (LT₀, LT₅₀ and LT₁₀₀) were 8–14°C,13%20°C and 14–22°C, respectively. By contrast,British Fagus sylvatica hardened off rapidly in September, wasundamaged by frosts well below –20°C in mid-winter,and did not deharden until late April, prior to budburst atthe end of May. Nothofagus seedlots from Nuble in Chile (the most Equatorialsource) were the most frost susceptible: unfortunately, seedof this origin was supplied to many British nurseries between1976 and 1W9. Seedlots from Neuquen in Argentina, and from maturetrees of Malleco (Chile) origin growing in Britain, were themost host hardy. N. procera tended to be hardier than N. obliqua,and the trees became hardier with age. Past temperature records for Britain suggested that all theNothofagus seedlots had a high risk of suffering severe frostdamage at least once during a timkr rotation in all but mildcoastal regions. Spring and autumn frosts may be more damagingthan winter frosts. However, if it were possible to select individualswithin populations that were 3–6°C more frost hardythan the population means, such trees would be sufficientlyhardy to avoid frost damage in most lowland regions.     

Seasonal Changes in the Frost Hardiness of Provenances of Picea sitchensis in Scotland

Changes in the natural level of frost hardiness of shoots offour provenances of Picea sitchensis were monitored over twogrowing seasons by detaching shoots from 7 to 10-year-old treesgrowing in a nursery in Scotland, and subjecting them to freezingtemperatures under conditions which simulated night frosts. Six seasonal phases of frost hardiness were identified (Fig.3).

1. During each autumn, killing temperatures (the level of hardiness)decreased from –5°C to below –20°C, beginningseveral weeks after shoot elongation ceased. Alaskan provenanceshardened in September, apparently in response to shorteningday lengths alone, whereas an Oregon provenance did not hardenuntil November, after repeated frosts. Queen Charlotte Islandsprovenances were intermediate.
2. From November to March allprovenances were hardy to below –20°C,which is adequateto prevent direct freezing injury at mostplantation sites.
3. In March-April, several weeks before bud-burst, old shootsdehardenedto killing temperatures of about –10°Cin responseto warm temperatures, and southerly provenancesdid so beforenortherly ones.
4. During bud-burst the newly-emergingshoots were hardy to only–3°C to –5°C untilthey were about 3.5 cmlong. All provenances burst bud at thesame time and were equallyfrost susceptible at this time.
5. DuringMay-July the elongating shoots fluctuated in hardinessbetween–5°C and –10°C apparently in responsetofluctuating ambient temperatures.
6. In August 1980 there wasa period of late summer dehardeningto killing temperaturesof about –3°C.

Seasonal changes in hardiness are discussed in relation to changesin shoot growth and environmental factors. The main opportunitiesfor selecting frost hardy genotypes seem to be in the rate ofautumn hardening, the time of pre-bud burst dehardening, andthe time of bud-burst.     

Frost Hardiness of Red Alder (Alnus rubra) Provenances in Britain

The phenology and frost hardiness of shoots of 15 provenancesof Alnus rubra growing in Scotland were measured over one autumn,winter and spring. Dates of budset (in September) and the onsetof rapid frost hardening (in October-November) occurred about2 days earlier for each degree latitude of origin northwards,except for an Idaho provenance. However, all provenances dehardenedat about the same time in March and burst their buds between8 and 14 April. Assuming that rapid frost hardening in the autumnwas triggered primarily by shortening daylengths, Alaskan provenancesof A. rubra seemed better adapted to British conditions thansouthern British Columbian provenances, which have been mostcommonly planted. However, even Alaskan provenances are proneto spring frost damage. Scottish A. glutinosa and Alaskan A.sinuata set buds and frost hardened 1–2 weeks before eventhe Alaskan A. rubra, and burst their buds 2–3 weeks laterin April-May. All three species were hardy to below –30°Cfrom December to mid-March.     

Performance and Frost Hardiness of Picea sitchensis x Picea glauca Hybrids in Scotland

The growth of seven Picea sitchensis x Picea glauca hybridswas compared with the growth of two P. sitchensis provenancesand Picea glauca var.albertiana at two sites in northern Scotland.The sites were at Aultmore (an exposed, dry site with a mineralsoil) and Shin (a frosty, wet site with deep peat). They wereof the type considered more suited to Pinus contorta than P.sitchensis. At age 10, in 1984, most of the hybrids, at both sites, wereabout 10 and 20 per cent taller than P. sitchensis of Masset(Q.C.I.) and Ketchikan (Alaska) provenance, respectively. P.glauca var. albertiana grew very poorly, especially at Aultmore. At Aultmore, the frost hardiness of three of the tallest hybrids,the two P. sitchensis provenances, and P. glauca var.albertiana,was tested at about 3-weekly intervals throughout 1982 and 1983.Detached shoots were subjected to artificial frosts in a programmablechamber. P. glauca var. albertiana was frost susceptible atbudburst, but at all other times it was relatively very frosthardy (eg. to^–10°C in mid-August). Also, the hybridswere consistently more hardy than P. sitchensis of even Ketchikan(Alaska) provenance from July onwards. However, the hybridswere less frost hardy than P. sitchensis of Masset (Q.C.I.)provenance in early spring (they dehardened a week earlier inMarch-April) and their buds were equally as frost susceptibleat the time of budburst. In 1983, trees of P. glauca var. albertianaburst their buds about a week sooner than P. sitchensis. It was concluded that P. sitchensis x P. glauca hybrids canperform better than P. sitchensis at sites considered ‘marginal’for P. sitchensis, and that their good performance may be partlyattributed to, or associated with, their greater summer andautumn frost hardiness. A programme of inter-specific hybridizationis being pursued.     

Frost Hardiness of Subalpine Eucalypts in Britain

Laboratory freezing tests were used to determine seasonal changesin the frost hardiness of detached shoots of young trees ofEucalyptus gunnii (from central Tasmania), and E. niphophilaand E. debeuzevillei (‘snow gums’ from the SnowyMountains, Australian Capital Territory). The trees were growingat the Bush Estate. No difference was found between the speciesor between seedlots, all of which were from high altitudes nearthe tree line. In midwinter (February) the shoots tolerated –16°Cwithout suffering damage, and many shoots survived temperaturesas low as –18°C to –22°C. This result agreedwith Evans' (1986) observation that some trees within theseseedlots survived temperatures in the range –19°Cto –23°C in field planting during the winter 1981/82.In their native habitats the trees rarely experience temperaturesbelow –20°C. The shoots did not harden appreciably before they experiencedfrosts (in late October/early November) and so may be proneto autumn frost damage. By contrast, they were slow to dehardenin late winter and spring and did not seem prone to spring frostdamage. There were no killing air frosts during the period of this study(winter 1985/6), but many trees died, possibly as a result ofground freezing, producing root injury and/or shoot desiccation.In subalpine regions of Tasmania and the Snowy Mountains theground is covered by snow throughout the winter. Variation in frost hardiness within these hardy seedlots couldbe exploited.     

经济植物的抗寒性研究进展

综述了植物抗寒研究的新进展。植物在低温下的抗寒生长过程中，其形态结构及其超显微结构发生变化．膜脂的成分及蛋白质数量和种类也发生改变；植物的抗寒生理生化的变化是通过低温改变基因表达而引发的，在抗寒中起作用的基因已经识别出来，并且已经了解这些基因的作用方式．ABA和PP333等外源激素和钙离子能诱导植物体内的ABA水平提高，从而增强植物的抗寒能力。但诱导机理仍待研究。     

国外木本植物抗寒性测定方法综述

文中对目前国外采用的不同抗寒性测定方法的测定原理、测定程序以及优缺点等作了较为详细的介绍。这些测定方法有全株冰冻测试法（组织褐变法）、电解质渗出率法、叶绿素荧光法、热分析法（主要用差热分析法）、电阻抗图谱法以及核磁共振显微镜图谱法和可视＋近红外线光谱法等。并简介了这些测定方法的适用性和抗寒性测定方法的研究展望。     

Variability of herbaceous productivity along Nothofagus pumilio forest-open grassland boundaries in northern Chilean Patagonia

In order to develop a general model of aboveground net primary production (ANPP) of herbaceous communities in grazing systems that combine forested and open grasslands in temperate areas, biomass production and a set of biotic and abiotic variables were measured at four adjacent forest and grassland sites in Chile’s northern Patagonia for two consecutive growing seasons. At each site, one transect of 80 m long (40 m in open grassland and 40 m in forest) × 10 m wide was established. ANPP was significantly higher in open grasslands but no gradual change in biomass production was observed from inside the forest towards the open grassland. In open grasslands ANPP was spatially uniform but highly variable between years of contrasting weather conditions, whereas in forests it was more spatially heterogeneous and less variable over time. ANPP was highly correlated with cattle consumption. Structural equation models developed for the whole system confirm that ANPP was driven mainly by photosynthetically active radiation (PAR) and available nitrogen. However, we found important differences between forests and the adjacent open grasslands. In forests ANPP was enhanced by positive feedbacks between the amount of transmitted PAR through the canopy and soil nutrient input via cattle dung deposition. In open grasslands nitrogen availability appeared to be the main limiting factor but also influenced by weather conditions (dryer or wetter years). The coexistence of forests and grasslands patches, with different susceptibility of ANPP to meteorological and soil nutrient availability, highlights the importance of implementing an integrated silvopastoral system with lenga (Nothofagus pumilio [Poepp. & Endl.] Krasser) in northern Patagonia.     

新疆野苹果天然群体抗寒性的电阻抗图谱分析

以新疆巩留县和新源县2个居群下的7个新疆野苹果群体当年生枝条为材料,应用EIS法对各群体抗寒性进行测定,并与电导率法进行对比分析。结果表明:巩留和新源2个居群内群体间的半致死温度差异不显著,2个居群间的差异显著,巩留居群的半致死温度显著低于新源居群,证明巩留居群的抗寒性高于新源居群。电阻抗图谱法单-DCE模型中6个参数(τ,ψ,r,r1,re,ri)中,r1,re,τ3个参数可以得出供试样品的半致死温度,其中r1,re所得的半致死温度与电导率法相关系数达到极显著水平,说明参数r1,re适用于新疆野苹果的抗寒性测定。电阻抗图谱法(EIS)与电导率法的抗寒性测定结果基本一致,但省时、不需温育,具有更大优越性。     

Overwinter Storability of Conifer Planting Stock: Operational Testing of Fall Frost Hardiness

Operational stock-testing facilities that estimate overwinter storability of seedlings (ability to survive and grow after storage) need a reliable method that provides fast results to forest nurseries. We compared three methods using container-grown seedlings of Douglas-fir, interior spruce, lodgepole pine, and western larch from forest nurseries in British Columbia. On three to nine dates in autumn, frost hardiness at −18°C was estimated using visible injury of foliage or stems (VI), electrolyte leakage from needles or stems (EL), and chlorophyll fluorescence of shoots (CF). Seedlings were placed into overwinter cold storage (−2°C). In the spring, stored seedlings were planted in nursery beds; survival and growth were assessed after one growing season. There were close correlations (r ≥ 0.93) between the assessment methods. Seedlings lifted after they reached thresholds of 69% or higher for CF and 25% or lower for EL and VI had over 90% survival at harvest and doubled shoot dry weight compared with seedlings lifted earlier. Measuring CF was the fastest and most easily replicated method to estimate successful storability, and reduced testing time by 6 days relative to VI tests.     

Late Autumn Frost Resistance of Twelve North European Provenances of Quercus Species

Twelve north European oak provenances [11 Quercus robur L. and one Quercus petraea (Matt.) Liebl] were tested for late autumn frost hardiness using visual methods and measurements of relative conductivity. Tissue from buds and twigs from 2-yr-old seedlings was used. The test was carried out in November and December. Temperatures between ?20 and ?32°C were necessary to cause serious damage to tissue, even when tissues were tested only a few weeks after leaf fall. Visual methods proved to be fast and could be applied in practical test applications. Estimation of twig viability was found to be a more reliable variable than bud assessment, which appears to be sensitive and not necessarily related to plant mortality. Relative conductivity is a more labour-intensive method and requires some technical equipment, but it provided the most consistent statistical results. Strong correlation between the visual methods and relative conductivity was demonstrated. Provenances originating from locations close to the Atlantic ocean (The Netherlands, the UK, Denmark and Norway) tended to be less frost resistant than more continental provenances (from Norway, Sweden, Finland and Poland). Frost tolerance was correlated with budset, but not with growth of the provenances. The results confirm the existence of specific ecotypes and suggest a high potential for adaptation in Q. robur.     

Autumn Frost Damage on Young Picea sitchensis 2. Shoot Frost Hardening, and the Probability of Frost Damage in Scotland

The natural increase in frost hardiness of detached shoots ofPicea sltchensis during August to November was measured usinga programmable freezing chamber. Oregon, Queen Charlotte Islandsand Alaskan provenances were compared, and the effects on hardeningof long days, warm temperatures and frosts were determined.A computer model was constructed to mimic the observed patternsof autumn frost hardening, as functions of air minimum temperatures,daylengths and the occurrence of frosts. The model was used(a) to describe the pattern of autumn frost hardening at differentsites in northern Britain, using past meteorological records,and hence (b) to determine when frosts occurred that might havedamaged young trees. The model accurately predicted known instancesof autumn frost damage at Kirroughtree and Carnwath. The predicted probability of autumn frost damage on young treesof P. sitchensis in upland areas of Scotland was much lowerthan that previously predicted for spring frost damage. Theestimated return time for autumn frost damage to an Oregon provenanceat Eskdalemuir was 8.3 years, and the return time for a Q.C.I.provenance was longer than 10 years. Most damaging frosts occurredin October, but frosts like those on 13–15 October 1971,which followed warm weather and caused wide spread damage inScotland, have been quite rare. Alaskan provenances would rarelybe damaged by autumn frosts, nor would trees of Q.C.I. provenancegrowing in lowland areas of Scotland, or at Masset on the QueenCharlotte Islands.     

白皮松茎和针叶的电阻抗参数与抗寒性的相关性

用电阻抗图谱法(EIS)和常规的电导法(EL)测定抗寒锻炼期间不同种源白皮松茎和针叶的抗寒性,比较2种方法的相关性,完善 EIS法测定植物抗寒性技术.抗寒锻炼期间,对北京十三陵苗圃的北京蟒山、甘肃两当和山西孝义3个种源的8年生白皮松茎和针叶的抗寒性进行电阻抗法分析和电导法分析.未经冷冻处理的白皮松茎和针叶的阻抗图谱分别用Double-DCE模型和Model-A模型表示.冷冻处理后的样本,用EIS法和EL法测定其抗寒性.未经冷冻处理样本的弛豫时间τ1,(茎)、胞内电阻率r1(茎和针叶)与抗寒性有较高的相关性(R2=0.79～0.86);冷冻处理后的茎和针叶的胞外电阻率re、针叶细胞膜时间恒量τm与抗寒性显著相关(R2=0.92～0.94);EIS法和EL法测定白皮松茎和针叶抗寒性也具有明显的线性相关,但EIS法较EL法低估抗寒性.EIS法是一种测定植物抗寒性的可行方法,尤其用于估测不经冷冻处理样本的抗寒性.     

Frost hardiness of 16 European provenances of sessile oak growing in Scotland

The frost hardiness of 16 European provenances of sessile oakQuercus petraea (Matt.)Liebl. originating from six Europeancountries was examined from autumn until budburst in springusing the method of relative conductivity. There were significant differences of frost hardiness betweenprovenances and a strong relationship between phenology andfrost hardiness. In spring, provenances that burst bud earlydehardened earlier than provenances that burst bud later. Inautumn, provenances that stopped growing early were more frosthardy than provenances that continued to grow. The interprovenance ranges of frost hardiness were greatestin spring and autumn and least in midwinter. Consequently, itwas not possible to demonstrate significant differences of frosthardiness between provenances in December and January. Overall, German, Polish and Danish provenances were more frosthardy than French, Austrian and British provenances. Frenchprovenances were least hardy at all times.     

Phenotypic Differences Between Natural and Selected Populations of Picea Abies. I. Frost Hardiness

The frost hardiness of non-juvenile Norway spruce [Picea abies (L.) Karst.] populations growing in northern Sweden (63°54' N) was monitored during 1996-1997. The investigated progenies originated from 12 natural populations and six seed orchards located between 58° N and 68° N in Sweden. Frost hardiness of needles was assessed by measuring chlorophyll fluorescence and electrolyte leakage after freezing. The loss of frost hardiness in 1-yr-old needles during spring occurred slightly earlier in populations originating north of 63°30' N than in those originating further south. Dehardening was slightly delayed in selected populations compared with natural populations of similar origin. The level of frost hardiness during autumn was higher in populations originating north of 63°30' N than in those originating south of this latitude, but there were no clear differences in frost hardiness between selected and natural populations of similar origin. The results are discussed in relation to climatic factors and inherent growth rhythms.     

Low temperature responses of Nothofagus dombeyi and Nothofagus nitida, two evergreen species from south central Chile

Nothofagus dombeyi (Mirb.) Blume and Nothofagus nitida (Phil.) Krasser are closely related evergreen trees native to south central Chile. Nothofagus dombeyi is a pioneer in habitats subject to high daytime irradiances and nighttime freezing temperatures and has a wider altitudinal and latitudinal distribution than N. nitida, which is restricted to more oceanic climates. We postulated that N. dombeyi has a greater cold-acclimation capacity, expressed as a greater capacity to maintain a functional photosynthetic apparatus at low temperatures, than N. nitida. Because cold-acclimation may be related to the accumulation of cryoprotective substances, we investigated relationships between ice nucleation temperature (IN), freezing temperature (FT), and the temperature causing injury to 50% of the leaf tissues (LT(50)) on the one hand, and concentrations of total soluble carbohydrates (TSC), starch and proline on the other hand. Observations were made throughout a seasonal cycle in adults and seedlings in the field and in seedlings in the laboratory under cold-acclimation inductive and non-inductive conditions. In adults, LT(50) values were lower in N. dombeyi than in N. nitida, suggesting that N. dombeyi is the more frost tolerant species. Adults of both species tolerated freezing in autumn and winter but not in spring and summer. In the fall and winter, seedlings of N. dombeyi had a much lower LT(50) than those of N. nitida. Nothofagus nitida seedlings, in autumn and winter, exhibited freezing avoidance mechanisms. Although elevated TSC and proline concentrations may contribute to freezing tolerance in adults of both species, an increase in proline concentration is unlikely to be the dominant frost tolerance response in adults because proline concentrations were higher in N. nitida than in N. dombeyi. In seedlings, however, there were large differences in proline accumulation between species that may account for the difference between them in freezing tolerance. Starch concentration in both species decreased during winter. Chlorophyll fluorescence indicated that maximal photochemical efficiency (F(v)/F(m)) remained at optimal values (~0.8) throughout the year. The effective photochemical efficiency of PSII (PhiPSII) and relative electron transport rates (ETR(r)) decreased in winter in both species. In seedlings, fluorescence parameters were more affected in winter in N. nitida than in N. dombeyi. We concluded that adults and seedlings of N. dombeyi are hardier than adults and seedlings of N. nitida, which is consistent with its wider latitudinal and altitudinal distribution.     

Frost hardening and dehardening in Abies procera and other conifers under differing temperature regimes and warm-spell treatments

Frequent bud frost damage in cultivation of Abies procera Rehderand pending climate changes are the background for this studyof cold hardiness under varying acclimation regime (in closed-topchambers) and experimental warm spells during the cold season.LT₅₀ values were established by freezing tests at differenttimes of year. Damage and deaths were assessed on leader buds,subapical lateral buds, needles and cambium. Minor parallelexperiments involved Abies nordmanniana, Picea abies and Piceasitchensis. Lower acclimation temperatures resulted in deeperfrost hardiness during late autumn but less during spring, comparedwith ambient temperature controls. Elevated temperatures resultedin less deep frost resistance. Apical buds generally developeddeeper frost hardiness than lateral buds but less deep thanthe cambium, varying with species, however. Frost damage inbuds ranged from death over partially destroyed bud contentsresulting in distorted shoots to buds seemingly remaining dormant.Responses to warm spells differed with duration, timing andspecies, ranging from dramatic decrease in frost hardiness withor without subsequent recovery to no reaction. Furthermore,the reactions did not show any clear relation to dormancy level.For A. procera, exposure to fluctuating temperatures appearedto be particularly problematic. This explains why this speciesdevelops best in coastal climates, and in sites sheltered fromtemperature extremes either by hedging, a winter snow cover,or topography. The Christmas tree production will suffer severelyon sites with harsh temperatures due to losses of lateral andterminal buds, which destroy the crown symmetry. Clipping ofgreenery is less influenced by frost damages, although the developmentof normal branch whorls is often disturbed.     

Allometric above-belowground biomass equations for Nothofagus pumilio (Poepp. & Endl.) natural regeneration in the Chilean Patagonia

? In the present study, allometric biomass equations were developed for Nothofagus pumilio natural regeneration relating foliage, stem and branches (aboveground), roots (belowground), and total biomass to basal diameter and total height, based on destructive measurements of 390 naturally regenerated seedlings and saplings.

? Basal diameter was the most important independent variable in all equations and accounted for more than 88% of the variability of the different biomass components. The addition of height as a second independent variable slightly improved the predictions.

? The best-fit biomass components equations that were based on combinations of basal diameter and height as independent variables had adjusted R ² values between 0.80 and 0.95 and a mean percent standard error between 21.3% and 26.6%.

? Based on the best-fit biomass equations and the natural regeneration development in a 14-years chronosequence in forests managed under shelterwood cuts, the total biomass varied from 0.9 Mg ha^?1 (0.5 Mg ha^?1 above and 0.4 Mg ha^?1 belowground) for the primary forest, before the shelterwood cuts, to 19.5 Mg ha^?1 (13.6 Mg ha^?1 above and 5.9 Mg ha^?1 belowground) 14 years after the seed cut. In the same period, carbon storage varied, from 0.5 Mg ha^?1 to 9.8 Mg ha^?1.

     

Differential photosynthetic and survival responses to soil drought in two evergreen Nothofagus species

We asked if differences in distribution between Nothofagus nitida and N. dombeyi were associated with differences in drought tolerance. Survival, gas exchange and chlorophyll fluorescence were measured on seedlings subjected to a gradual drought. At a predawn leaf water potential (Ψ_m) of ?2.7 MPa, survival of N. nitida was 50%, compared to 100% in N. dombeyi. Under well-watered conditions, the two species displayed similar stomatal conductance (g _w ) and transpiration (E), but net photosynthesis (A) and instantaneous water-use efficiency (WUE _i ) were slightly higher in N. nitida. A, E and g _w declined in N. nitida along the gradual drought but increased in N. dombeyi at a Ψ_m between ?1.5 and ?2.5 MPa, and declined then drastically at a Ψ_m below < ?2.5 MPa. As N. dombeyi was able to maintain A at higher levels despite declining g _w , this species displayed significantly increased WUE _i at Ψ_m below ?2.5 MPa. Photochemical efficiency of PSII in the light (ΔF/Fmr) and photochemical quenching (qP) were always lower in N. nitida and along with the photochemical efficiency in the dark (Fv/Fm) they declined in both species. Non-photochemical quenching (NPQ) increased slowly in N. dombeyi along with the gradual drought, whilst it decreased in N. nitida. These results show that differences in drought tolerance are in agreement with sorting of Nothofagus species along moisture gradients in south-central Chile.     

Autumn Frost Damage on Young Picea sitchensis 1. Occurrence of Autumn Frosts in Scotland compared with Western North America

Dates of first autumn air frosts (in Stevenson screens) of –2.5°Cand 4.5°C were obtained for 42 meteorological stations innorthern Britain with runs of 18 to 116 years. Frequency distributionsof first frost dates were approximately normal. Altitude, distancefrom the sea, latitude and distance from the NWSE axis of Britaintogether accounted for 75% and 81% of the variation in datesof first –2.5°C and –4.5°C frosts, respectively,at the 42 stations. The variance in dates of first frosts decreasedfrom lowland coastal to upland inland sites. Multiple regressionswere used to produce maps of first frost dates in 20 x 20 kmgrid squares of Scotland. Dates of first 28°F (–2.2°C) and 24°F (–4.4°C)frosts were obtained for 20 sites in western North America,spanning the natural range of P. sitchensis. Mean dates wereearlier, and variances decreased, from south to north. Upland sites like Eskdalemuir and Kielder Castle experience–2.5°C and –4.5°C frosts earlier in theautumn than all coastal stations in western North America southof about latitude 58°N (between Cordova and Sitka), andabout 4 weeks earlier than at Masset on the Queen CharlotteIslands. Thus, P. sitchensis from Q.C.I. and further south mayoften experience autumn frosts in Scotland before the treeshave experienced the cool/short days that they require to inducefrost hardening.