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Low temperature as it affects the selection of woody ornamentals in British Columbia Rhodes, Hubert Lloyd Joseph 1950

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LOW TEMPERATURE AS IT AFFECTS THE SELECTION OF WOODY ORNAMENTALS IN BRITISH COLUMBIA by Hubert Lloyd Joseph Rhodes A Thesis Submitted i n P a r t i a l Fulfilment of The Requirements for the Degree of MASTER OF SCIENCE IN AGRICULTURE In the Department of HORTICULTURE The University of B r i t i s h Columbia May, 1950. ABSTRACT LOW TEMPERATURE AS IT AFFECTS THE SELECTION OF WOODY ORNAMENTALS IN BRITISH COLUMBIA; by Hubert L. J. Rhodes Low winter temperature was taken as the most important factor influencing the selection of ornamental trees and shrubs for d i f f e r e n t areas of B r i t i s h Columbia. The l o c a l i t y around a meteorological station was made the unit of investigation, with the meteorological s t a t i o n as a reference point. Average extreme lowest temperature of the year for each B r i t i s h Columbia meteorological station was calculated from figures compiled f o r the ten year period 1940-49. # - Certain methods were used to interpret low temperature information i n an o r i g i n a l way: the use of the winter rather than the calendar year as the unit i n considering low temperature, the application of s t a t i s t i c a l analysis to express v a r i a t i o n i n low temperature between winters, and the conversion of s t a t i s t i c a l estimates to temperatures corresponding to a convenient p r o b a b i l i t y r a t i o e a s i l y understood by p r a c t i c a l workers. Average extreme lowest temperature of the winter based on the ten-winter period from 1940-41 to 1949-50, standard deviation, and the ninety percent point were calculated for selected B. C. meteorological stations. ABSTRACT - Cont The ninety percent point i s that temperature above which the extreme lowest temperature of a sta t i o n w i l l f a l l i n approximately nine out of ten winters, and below which the extreme lowest temperature w i l l f a l l i n approximately one out of ten winters, according to mathematical expectancy based on s t a t i s t i c a l analysis of temperatures observed over a period of winters. This concept combines the information to be obtained from the average extreme lowest temperature and the standard deviation. The ninety percent point i s found by sub- t r a c t i n g the standard deviation multiplied by 1 .3 from the average extreme lowest temperature of the winter. A survey was conducted to obtain an estimate of the in j u r y to ornamental trees and shrubs i n B r i t i s h Columbia following two severe winters. The information was used to test the usefulness of low temperature data as a guide i n selecting woody ornamentals for hardiness in a l o c a l i t y , and to get accurate low temperature l i m i t s i n the P a c i f i c coastal region for a number of ornamental species. Low temperature information was found useful within l i m i t a t i o n s as an in d i c a t i o n of the amount of winter i n j u r y to woody ornamentals to be expected i n a l o c a l i t y of B r i t i s h Columbia aft e r a severe winter. ACKNOWLEDGMENTS The d i r e c t i o n of the following pro- fessors i s acknowledged: Professor J . W. N e i l l , Department of Horticulture, f o r the suggestion of the topic and major d i r e c t i o n of the invest i g a t i o n . Dr. V. C. Brink, Department of Agronomy, Dr. T. M. C. Taylor, Department of Biology and Botany, and Professor J . D. Chapman and Dr. J. R. Mackay, Department of Geology and Geography, for d i r e c t i o n i n c o l l e c t i n g , analyzing, and presenting temperature information. Acknowledgment i s due to Dr. A. F. Barss, Head of the Department of Horticulture, fo r general d i r e c t i o n of the Master's work. Mr. A. R. McCauley, D i s t r i c t Meteorologist, Vancouver, gave assistance by providing l o c a l weather information. Mr. W. G. H. F i r t h , Chief Geographer, B. C. Department of Lands and Forests, provided base maps of B r i t i s h Columbia. Mr. W. H. Robertson, Pr o v i n c i a l H o r t i c u l t u r i s t , the D i s t r i c t H o r t i c u l t u r i s t s , and a number of nurserymen and gardeners throughout the province gave assistance with the winter injury survey. TABLE OF CONTENTS Page I N T R O D U C T I O N 1 R E V I E W OF L I T E R A T U R E . . . . . . . . . 5 A N A L Y S I S OF T H E S U B J E C T . . . . . . . 13 Development of the Method . . . . . 13 Extreme Lowest Temperature . . . . . 16 Extreme lowest temperature of the year • 16 Extreme lowest temperature of the winter . . . . . . . . 22 Analysis of extreme lowest temperature v a r i a t i o n . 23 The ninety percent point . . . . . 27 The Winter Injury Survey 32 Purpose of the survey . . . . . . 32 Description of methods 33 Results 34 Conclusion . . . . . . . . . . . . 37 DISCUSSION . . . 39 , SUMMARY . . . . . . . . . 43 LITERATURE CITED . 45 TABLES: Table I Ten Year Averages of Extreme Lowest Temperature of the Year 19 Table I I Analysis of Low Temperature Data . 30 TABLE OF CONTENTS - Cont. P a f i e ILLUSTRATIONS (following page) Fi g . 1 - Variation i n extreme lowest temperature of the winter during the ten- winter period from 1940-41 to 1949-50 at four B r i t i s h Columbia meteorological stations . . . . . . . . . . . . . . . . 24 F i g . 2 - S t a t i s t i c a l expression of ex- treme lowest temperature of the winter at ten B r i t i s h Columbia meteorological stations . . . . . . . . . . . . . . . •'. 26 F i g . 3 - Normal frequency d i s t r i b u t i o n curve showing approximate proportions divided by ninety percent point. . . . . 28 F i g . 4 - Approximate low temperature zones i n the set t l e d coastal region. . » 38 Map - Average extreme lowest temperature for the ten year period 1940-49 . . . • Appendix APPENDIX Appendix I - Extreme Lowest Temperature of the Winter at Selected B. C. Meteorological Stations for the Ten-Winter Period from 1940-41 to 1949-50. ... . . . . . . . . . Appendix II - Species of Trees and Shrubs Included i n the Winter Injury Survey, 1950. LOW TEMPERATURE AS IT AFFECTS THE SELECTION OF • WOODY ORNAMENTALS IN BRITISH COLUMBIA INTRODUCTION One of the important steps i n the development of horticulture i n any region i s the obtaining of i n f o r mation on suitable ornamental plants f o r d i f f e r e n t parts of the country. The accumulation of such i n f o r - mation i s usually the resu l t of considerable experience Involving a large amount of t r i a l and error with a range of plant materials. In the older parts of the world the behaviour of ornamental plants and t h e i r s u i t a b i l i t y f o r di f f e r e n t areas i s well known. As l i t t l e known or newly discovered plants are introduced to gardens t h e i r s u i t a b i l i t y f or p a r t i c u l a r d i s t r i c t s i s deter- mined with the help of information about plants which have been long i n c u l t i v a t i o n i n these d i s t r i c t s . Great B r i t a i n i s an example of a country which has a well developed h o r t i c u l t u r e i n connection with i t s long period of c i v i l i z a t i o n . Detailed information on suitable ornamentals i s generally available for a l l the d i f f e r e n t l o c a l i t i e s from the southwestern coast to the northern i s l a n d s . In the settlement of the new world immigrants customarily brought with them the plants with which they had been f a m i l i a r i n t h e i r old surroundings. They soon found which of these would survive i n the new land where they happened to s e t t l e . People have tended to r e l y on those introduced trees and shrubs which have proved successful, rather than explore the possi- b i l i t i e s of native species or other plants which they had not known i n t h e i r old surroundings. Nurseries have made a practice of growing only the plants f o r which there i s considerable demand. Consequently there has been a conservative trend i n the planting of ornamentals. There are usually a few species of good ornamental plants which are p a r t i c u l a r l y well suited to the climate of an area. These species may be overlooked unless a well organized scheme of t r i a l s i s conducted. Before our surroundings can be s a t i s - f a c t o r i l y landscaped, a thorough knowledge of the best existing plant materials must be attained. In B r i t i s h Columbia there i s a d e f i n i t e need for better organized and more r e a d i l y available information as to which plants may be grown i n d i f f e r e n t l o c a l i t i e s . Even i n the well se t t l e d d i s t r i c t s around Vancouver there are few gardens where p o s s i b i l i t i e s i n plant materials are exploited. Most gardeners have to make a choice of plants with- out any r e a l knowledge of the wide array of good ornamentals which might be used* Some plants which are p a r t i c u l a r l y adapted to l o c a l conditions are not re a d i l y available at the l o c a l nurseries, and con- sequently they are not widely grown. Others which are available have been avoided because they have been thought to be not hardy enough* Many of these plants could be grown successfully i f given a suitable l o c a t i o n and adequate care. Better p r a c t i c a l h o r t i c u l t u r e i n B r i t i s h Columbia must depend primarily on the ap p l i c a t i o n of the best s c i e n t i f i c methods of obtaining information that are at our disposal. In t h i s in v e s t i g a t i o n every attempt has been made to use the tools of sciences related to horticulture i n attacking a h o r t i c u l t u r a l problem. Climatological methods, e s p e c i a l l y the s t a t i s - t i c a l analysis of temperature data, have been found most u s e f u l . Of the numerous factors which determine the s u i t a b i l i t y of ornamental trees and shrubs for par- t i c u l a r l o c a l i t i e s , low winter temperature i s undoubtedly very important. This i s es p e c i a l l y true i f , as i n t h i s investigation, the area under study i s characterized by marked climatic d i v e r s i t y . In B r i t i s h Columbia there i s a wide range i n the severity of winter tempera- - k - ture i n di f f e r e n t l o c a l i t i e s . Around V i c t o r i a on the southern t i p of Vancouver Island the winters are generally mild enough to permit the outdoor culture of nearly any woody plant from the temperate zones of the world. At Prince George, toward the other extreme, only a few notably cold resistant trees and shrubs w i l l survive. The purpose of t h i s investigation i s to provide a foundation f o r a sound appraisal of l o c a l i t i e s of B r i t i s h Columbia as to s u i t a b i l i t y for the growth of d i f f e r e n t species of ornamental trees and shrubs* Although the problem has a number of important aspects, investigation i s confined here to the study of low winter temperature as i t af f e c t s the selection of woody ornamentals. REVIEW OF LITERATURE One would expect that an appreciable amount of i n - vestigation on trees and shrubs suitable for B r i t i s h Columbia would be under way, considering the youth of the province as a settled area. Unfortunately there has been l i t t l e detailed work for s p e c i f i c purposes. The Dominion Experimental Farms Service have taken the lead i n t r y i n g out ornamental plants for d i f f e r e n t climatic regions i n Canada. Their work has been quite valuable f o r Canada as a whole, e s p e c i a l l y the cold regions which occupy the majority of the country* Such work applies to the cold i n t e r i o r of B r i t i s h Columbia, but not to the warm coastal region of the province, where the population i s concentrated. Some detailed l o c a l work has been done at branch farms and stations, but l i t t l e of t h i s i s published* From Ottawa have come b u l l e t i n s on hedges (Macoun, 1931), trees (Ol i v e r , 1945), shrubs and climbers (Oliver, 1944) , and perennials (Preston, 1946) . Oliver's b u l l e t i n s give tables showing hardiness of the trees and shrubs which have been t r i e d at d i f f e r e n t branch farms and stations* In the H o r t i c u l t u r a l Branch of the P r o v i n c i a l Department of Agriculture the major attention has been directed toward f r u i t crops rather than ornamentals* Interest i n the s u i t a b i l i t y of ornamentals has been eon- fined c h i e f l y to answering queries from the public. D i s t r i c t H o r t i c u l t u r i s t s undoubtedly have accumulated some good i n - formation r e l a t i n g to i n d i v i d u a l d i s t r i c t s . This i n f o r - mation would be more useful i f i t were compiled and published f o r the use of people who are not f a m i l i a r with the province. There has been some attempt at The University of B r i t i s h Columbia to recommend plants suitable for the province. The l i s t of ornamental trees and shrubs com- p i l e d by F. E. Buck (1946) has been useful, but i t makes no d i s t i n c t i o n between d i f f e r e n t areas of the province. Brink and Farstad (1949) i n an approach to the problem of recommending suitable crop plants, have summarized the physiography of the a g r i c u l t u r a l areas of B r i t i s h Columbia, and Brink (1950) has organized some cli m a t o l o g i c a l i n f o r - mation for the use of a g r i c u l t u r a l investigators i n the f i r s t of a series of four publications. Muirhead (unpub.) has done some o r i g i n a l work i n his investigation of s u i t - able street trees for Vancouver. There i s promise of an increased i n t e r e s t i n l o c a l problems of t h i s nature. In the American States south of B r i t i s h Columbia the exploration of l o c a l p o s s i b i l i t i e s has progressed more rapidly. Grant and Grant (1943) have given a good summary of the newer ideas i n a book on trees and shrubs f o r the P a c i f i c Northwest. Snyder's (no date) l i s t of shrubs for Washington i s applicable to parts of B.C., but i t does not give any d e t a i l s of climatic s u i t a b i l i t y . Graham and McMinn (1941) have considered shrubs and vines f o r the P a c i f i c coast* McMinn and Maino (1935) include ornamentals i n t h e i r account of trees of the P a c i f i c coast. Numerous a r t i c l e s i n semi-popular gardening magazines contain valuable but scattered fragments of i n - formation on the culture of trees and shrubs i n the P a c i f i c Northwest. Grant (1944), f o r example, has written on rhododendron culture i n the area. The study of climate i n r e l a t i o n to the growth of plants has attracted wide attention i n the l a s t twenty- f i v e years, owing to the stimulus of the new science of plant ecology. The f i r s t comprehensive quantitative c l a s s i f i c a t i o n of climate by Thornthwaite (1931) i s well known. The application of Thornthwaite 1s system to a p a r t i c u l a r problem such as the selection of trees and shrubs should be preceded by careful consideration of the factors involved. Any one factor such as temperature i s dealt with very generally i n such a complex c l a s s i f i c a t i o n ; one temperature category includes almost a l l the B r i t i s h Columbia stations. Since differences i n winter temperature are very important i n the se l e c t i o n of trees and shrubs, Thornthwaite 1s c l a s s i f i c a t i o n has a l i m i t e d use i n t h i s kind of work. A new c l a s s i f i c a t i o n by Thornthwaite (1948) has appeared, and t h i s has been applied to a c l a s s i f i c a t i o n of the climates of Canada by Sanderson (1948). Another development i n the science of climatology i s the s t a t i s t i c a l approach* Although s t a t i s t i c a l methods have not been used as extensively as they might i n clima- t o l o g i c a l work, there has been an increased attempt to apply such methods to climatic studies i n the l a s t decade, p a r t i c u l a r l y for m i l i t a r y purposes. An authoritative text covering fundamentals and recent applications of s t a t i s t i c a l climatology by Conrad (1944) has stimulated a wider use of these methods, e s p e c i a l l y i n r e l a t i o n to a g r i c u l t u r e . Foster (1948) has demonstrated the possi- b i l i t i e s of the s t a t i s t i c a l approach i n his book on hydrology. Brink (1950) emphasizes the value of a thorough appraisal of the climate of B r i t i s h Columbia for improving the e f f i c i e n c y of a g r i c u l t u r a l production. Quoting Land8berg (1946) he shows that climate i s i n essence an inexhaustible natural resource which, since i t i s f a i r l y constant over a period of years, can be treated as a calculable r i s k . Writings with s p e c i f i c reference to the B. C. climate have been rather numerous. Connor dealt with temperature and p r e c i p i t a t i o n i n an early publication (1915), and more recently (1949) has discussed the f r o s t - free period. A summary of the B. C. Climate by Denison (1925) i s found i n the Monthly Weather Review. Koeppe (1931) included some detailed remarks about the climates of d i s t r i c t s of B r i t i s h Columbia i n his book on the Canadian climate. The work of Brink (1950) i s mentioned above. Characteristics of mountain climates of Western North America have been discussed by F. S. Baker (1944). The behaviour of temperature i n mountains has been treated f u l l y by Peattie (1936). The history of the development of methods of c l a s s i f y i n g plants according to climatic requirements and of c l a s s i f y i n g climates according to t h e i r s u i t a b i l i t y to plants i s a long one dating into antiquity and associated with the o r i g i n and development of botanical gardens. Yet only during the twentieth century have attempts been made to put these climatic studies on a quantitative basis. The development of a plant growth region map by F. L. Mulford of the United States Department of Agriculture was an early attempt to c l a s s i f y the United States for plants. O r i g i n a l l y intended as a basis for recommending roses and street trees, Mulford 1s system was modified and refined with the aid of many s p e c i a l i s t s i n the U.S.D.A. The o r i g i n a l thirteen regions were increased to thirty-two (Mulford, 1926). Van Dersal (1938) gives a detailed account of Mulford's system, with characterizations of the diff e r e n t regions under (a) climate according to Thorn- thwaite 's C l a s s i f i c a t i o n , (b) length of growing season; and (c) average annual snow cover. These descriptions reveal the complexity of Mulford's system and the d i f f i c u l t i e s - 10 - that would be involved i n applying t h i s system to B r i t i s h Columbia. The climates of the regions occupying mountainous areas are very diverse, sometimes defying de s c r i p t i o n . Mulford*s system undoubtedly has p r a c t i c a l value for areas of regular climate, but i t i s too complex to be useful i n distinguishing growth regions i n B r i t i s h Columbia. Van Dersal (1938, 1942) has applied Mulford's growth regions to his work with American woody plants, l i s t i n g the regions fo r which each plant i s recommended. Another quantitative approach to the c l a s s i f i c a t i o n of plants for climate was the development of a system of winter hardiness zones for cultivated trees and shrubs by Alfr e d Rehder of the Arnold Arboretum. Information about the hardiness of d i f f e r e n t species had been s t e a d i l y accumulating as a result of the introduction and tes t i n g of plants from the East through the botanical gardens of Europe and America. Rehder (1927) made t h i s information available i n his manual on cultivated trees and shrubs. He divided North America into eight climatic zones based on the "lowest mean temperature of the coldest month". The numeral for the corresponding zone (I-VIII) was given with the description of each species i n the manual. A plant of Zone III would be hardy i n Zones III to VIII, but not i n Zones I to I I . In the second edition of his manual (1940) Rehder explained the basis of his c l a s s i f i c a t i o n somewhat d i f f e r e n t l y . The number of zones was reduced to seven, and - 11 - these zones were based on the "annual minimum temperature". The average annual minimum temperature l i s t e d f o r the d i f f e r e n t zones i s as follows: Zone I: exceeding -50°P II: -50° to -35° I I I : -35° to -20° IV: -20° to -10° V: -10° to -5° VI: -5° to • 5° VII: •5° to flO° A map showing the approximate lo c a t i o n of these zones i n North America i s included with the manual. This map i s adapted from a map of average annual minimum tem- perature i n the Atlas of American Agriculture (0. E. Baker, 1936). The usefulness of Rehder 1s map for determining the zone of a place i s limited by the small scale and the lack of d e t a i l i n out l i n i n g the zones. It i s clear from Rehder 1s explanation of his system that he believes many other factors besides winter temperature have an important bearing on the hardiness of plants. The general recognition of Rehder*e taxonomic work on cultivated trees and shrubs has been accompanied by a wide acceptance of his winter hardiness zones as a basis for c l a s s i f y i n g woody plants according to climate, Wyman (1938) referred to Rehder 1s winter hardiness zones as standard f o r the United States. He assigned somewhat - 12 - modified ratings based on Render's system to each species i n his l i s t of hedge plants. Grant and Grant (1943) have extended his zones from seven to ten to include the mild coastal areas of the P a c i f i c Northwest, and they assigned hardiness ratings to each species i n t h e i r l i s t of plants for t h i s area. The quantitative basis for the extended zones i s not given i n t h e i r explanation of th e i r modification. Writings describing investigations of the nature of winter injury and the factors influencing winter hardiness have been very extensive (Imperial Bureau of Plant Breeding and Genetics. 1939; L e v i t t . 1941). Some discussions of the problem of winter hardi- ness i n r e l a t i o n to ornamental plants are those of Bowers (1947), Crane (1947), Skinner (1944), and Teuscher (1941). The assessment of winter injury to ornamental plants af t e r p a r t i c u l a r l y extreme winters has been given some attention i n recent years by the Royal H o r t i - c u l t u r a l Society. Reports were published a f t e r the winters of 1939-40 (R.H.S., 1941), 1940-41 (Balfour, 1 9 k l \ and 1946-47 (Harrow, 1948; R.H.S., 1948). The Frost Damage Survey conducted a f t e r the 1946-47 winter was used as a guide for the survey conducted i n connection with t h i s i n v e s t i g a t i o n . * 13 - ANALYSIS OF THE SUBJECT Development of the Method The interacting factors which determine the re l a t i o n of a plant to i t s environment are known to be extremely complex* Even the study of climatic effects involves many factors, none of which acts by i t s e l f . Never- theless, these d i f f e r e n t factors must be separated f o r purposes of invest i g a t i o n . A general approach to a com- pli c a t e d problem i s u n l i k e l y to bring about material progress i n any f i e l d of science* A s p e c i f i c approach allows the selection of the most v i t a l factor f o r i n v e s t i - gation, and consequently leads to a thorough knowledge of one important phase of the problem. The environmental factors influencing the growth of cultivated plants may be grouped under two main headings: edaphic factors and climatic f a c t o r s . While s o i l s can be modified greatly when plants are grown under close c u l t i - vation, the climatic factors are much more d i f f i c u l t to control . The groups of climatic factors a f f e c t i n g cultivated plants include moisture, l i g h t , temperature, and the movement of a i r . Moisture i n the s o i l i s r e l a t i v e l y easy to regulate, e s p e c i a l l y when i t i s naturally i n short supply during the growing season. At- mospheric humidity usually i s not important i f the amount m 1 4 *• of s o i l moisture i s properly adjusted. The effects of wind can be reduced by sheltering arrangements, although adequate shelter often involves the growing of wind resistant plants where they w i l l protect the more sus- ceptible ones. Light can be increased only with some d i f f i c u l t y , but i t i s e a s i l y reduced by shading measures. Temperature i s d i f f i c u l t to modify unless plants are grown i n some type of structure. Light i s not usually a l i m i t i n g factor i n the growth of ornamental woody plants, except i n special circumstances. Temperature remains the most c r i t i c a l and the least e a s i l y modified environmental factor a f f e c t i n g the growth of woody ornamentals. Within the temperate zones differences i n winter temperature between areas have a great influence on the kinds of woody plants which can be grown successfully. Although the extent of winter i n j u r y i s often determined by many complex fac t o r s , extremely cold temperatures i n severe winters are primarily responsible for the serious economic losses which l i m i t the number of species of ornamental woody plants i t i s p r a c t i c a l to grow i n a spe c i f i e d l o c a l i t y . A climatic study of an area such as B r i t i s h Columbia where the topography i s extremely varied and irreg u l a r involves certain problems which do not assume importance i n a study of a more gradually changing and - 15 - f a i r l y uniform area l i k e the continental p l a i n s . Meteoro- l o g i c a l stations are not representative of areas between them when they are separated by extensive ranges of mountains. For t h i s reason, broad zones i n respect to a meteorological element such as temperature are d i f f i c u l t to determine i n mountain regions. However, since the meteorological stations usually are located at lower elevations i n the general v i c i n i t y of a g r i c u l t u r a l lands and urban settlements, they may be quite valuable i n the climatic assessment of li m i t e d areas around them. Brink (1950) discusses the l i t e r a t u r e dealing with mountain climates and the caution which i s necessary i n using data r e l a t i n g to mountainous areas. In view of the problems discussed above, the following approach was adopted i n t h i s i nvestigation: Low winter temperature was taken as the most important factor influencing the selection of ornamental trees and shrubs for a l o c a l i t y , and a recognized ex- pression of t h i s climatic element was determined for most meteorological stations of the province. The l o c a l i t y surrounding one or more meteorological stations was taken as the unit for investigation, and the meteorological station was used as a reference point. L i t t l e attempt was made to indicate relationships broader than between d i f f e r e n t l o c a l i t i e s . . - 16 - Certain methods were used to interpret the i n - formation on low winter temperatures i n an o r i g i n a l way. These methods are the use of the winter rather than the calendar year as the unit i n considering low temperature, the application of s t a t i s t i c a l analysis to express the amount of v a r i a t i o n i n low temperature from one winter to another, and the conversion of s t a t i s t i c a l estimates from mathematical values to convenient p r o b a b i l i t y r a t i o s e a s i l y understood by p r a c t i c a l workers without s c i e n t i f i c t r a i n i n g * A survey was conducted to obtain an estimate of the i njury to ornamental trees and shrubs following two severe winters. The information obtained was used to tes t the usefulness of low temperature data as a guide i n selecting woody ornamentals f o r hardiness i n a l o c a l i t y , and to get accurate low temperature l i m i t s i n the P a c i f i c coastal region for a number of ornamental species* Extreme Lowest Temperature Extreme lowest temperature of the year The lowest recorded temperature during a calendar year at a p a r t i c u l a r meteorological s t a t i o n i s c a l l e d the annual minimum temperature by Baker (1936). Rehder (1940), using Baker's map of average annual minimum temperature of the United States as a basis f o r his winter hardiness zone map, follows the nomenclature used by - 17 - Baker* "Average annual minimum temperature" corresponds to what i s c a l l e d "annual averages of extreme lowest temperature" by the Canadian Meteorological Service (1946). For the sake of c l a r i t y the expression "extreme lowest temperature of the year" i s used here instead of the ex- pression "annual minimum temperature". Rehder*s well-known winter hardiness zones were to be determined for B r i t i s h Columbia l o c a l i t i e s , and i f i t should prove f e a s i b l e , a map showing the d i s t r i b u t i o n of these zones was to be constructed. Excepting some long-term averages for the more important stations, the basic data, averages of extreme lowest temperature of the year, was not avai l a b l e . To get averages for a l l stations i t was necessary to search through meteorological p u b l i - cations for extreme lowest temperatures f o r a ten-year period (1940-1949), and to average these readings. Infor- mation for the year 1940 was extracted from d a i l y minimum temperatures i n the Monthly Record of Meteorological Observations (1940); for the years 1941-1948 from monthly minimum temperatures i n the Climate of B r i t i s h Columbia (1941-1948); and f o r 1949 from monthly minimum temperatures i n the Monthly Weather Map of the Dominion Meteorological Service (1949). The information c o l l e c t e d and the averages calculated from these figures have been compiled into a table, which i s on f i l e at the Department of Horticulture, The University of B r i t i s h Columbia. Figures for the lowest - 18 « temperatures recorded during the record cold s p e l l of January, 1950, have been included with the table for purposes of comparison* Average readings for the d i f f e r e n t stations, with the number of years for which figures were available during the period, are given i n Table 1. These averages are also shown on a map of B r i t i s h Columbia included with the Appendix* Figures f o r those stations for which information was hot available for ten consecutive years are c i r c l e d on the map, since averages for shorter periods would not be r e l i a b l e i n making comparisons between averages of neighbouring stations. Averages covering short periods were included with the tables i n order to give a rough estimate for stations from which no information could otherwise be included. Long-term averages for some stations were found i n the Canadian Meteorological Service Summary (1946), are given i n Table 1 as figures i n brackets after the name of the s t a t i o n . The long-term averages are generally somewhat lower than the averages f o r the ten- year period 1940-1949. A d e f i n i t e pattern i s evident i n the extreme low- est temperature of lowland stations i n the coastal region. Stations close to the open P a c i f i c on Vancouver Island and the Queen Charlottes have the highest averages, over 20°F. On eastern Vancouver Island averages range from over 20° i n the south around V i c t o r i a to less than 15° i n the middle part 19 - TABLE 1 Ten Year Averages of Extreme Lowest Temperatures of the Year at B r i t i s h Columbia Meteorological Stations for the Period 1940-1949. Long Term Averages are given i n brackets aft e r names of Stations for which they are av a i l a b l e , (Degrees Fahrenheit), STATION YRS. AV. STATION YRS. AV, Abbotsford 10 11 Clayoquot (21) 9 25 Agassis 10 14 Comox (A) 5 13 Alberni (Beaver Creek) 10 11 Coquitlam Lake 10 14 Alberni, Port 10 13 Cowichan Bay 10 19 A l l i f o r d Bay 4 20 Cowichan Lake 8 16 Armstrong 10 -14 Cranberry Lake 10 -35 Ashcroft 3 -18 Cranbrook (A) (-28)10 -23 A t l i n (-38) 6 -34 Crescent Valley 10 -8 Baldonnel 10 -39 Creston 10 -5 B a r k e r v i l l o (-26) 9 -28 Cultus Lake 4 12 B e l l a Coola (1) 10 1 Cumberland 9 11 Big Creek 9 -30 Departure Bay 10 21 Blue River 3 -31 Dome Creek 10 -30 Bralorne 10 -13 Dominion Obser- 18 vatory 10 21 Britannia Beach 10 Duncan 10 10 B u l l Harbour 10 22 Estevan Point 10 23 Cape St. James 3 20 -13 Fauquier 10 -2 Carmi 0 -16 Fernie 10 -21 Chinook Cove 7 Finlay Forks 3 -54 Chute Lake 4 -23 Fort St. James 10 -32 - 20 * TABLE I - Cont. STATION Yrs • Av. STATION Yrs. Av. Ft. St. John (A) (-38) 9 -42 McCulloch 10 -23 Ganges S 19 Masset (14) 10 15 Gerrard 9 -7 Merritt 10 -13 Glacier (-19) 10 -16 M i l l Bay (Nass R.) 9 4 Golden 10 -27 Mission Creek 6 -14 Grand Forks (-17) 10 -14 Mission F l a t s 8 mm () Greenwood 10 -16 Nanaimo 10 16 Haney 4 14 Nelson (-4) 10 3 Hedley 10 -6 Newgate 8 *23 Hedley (N.P.M.) 10 -17 New Hazelton (-29) 10 -24 Hope ( L i t t l e Mt.) 9 7 New Westminster 10 14 Hope (A) 10 11 Ocean F a l l s 10 15 Invermere 7 -25 Okanagan Centre 10 3 James Island 10 22 Oliver 10 -3 Jordan River 5 21 Osprey Lake 10 -22 Kamloops (-13) 10 -8 Pachena Point 9 22 Kaslo. 10 0 P a t r i c i a Bay 7 17 Kelowna 10 -1 Pemberton Meadows 10 -8 Keremeos 10 -2 Penticton (-2) 10 -3 Kimberley 5 -21 Port Hardy (A) 5 19 Kleena Kleene 7 -34 Powell River 10 23 Langara 7 20 Premier 9 -2 Lytton 10 -2 Princeton (A)(-26) 10 -17 McBride 8 -27 Prince George (-40) 5 -25 - 21 - TABLE I - Cont STATION Yrs. Av. Prince George (A) 7 *36 Prince Rupert (11) 10 13 Quatsino 10 20 Quesnel 10 -22 Revelstoke (-14) 10 -11 Rock Creek 8 -13 Rossland 9 •2 Salmon Arm 10 -5 Shawnigan Lake 10 14 Sidney 10 21 S i n c l a i r Pass 9 -19 Smithers 10 -24 Smithers (A) 6 -25 Sooke 8 19 South Slocan 9 -6 Stave F a l l s 9 14 Steveston 3 9 Stewart (-6) 10 -5 Summerland 10 2 STATION Yrs. Av. Tappen 8 -4 Tatlayoko Lake 10 -19 Telkwa 10 -20 Terrace 10 ->2 Ucluelet 3 20" Ucluelet (A) 4 22 Vananda 10 18 Vancouver (13) 5 16 Vancouver (A) 10 14" Vavenby (-30) 10 -20 Vernon 10 -4 Vernon(Cold- stream) 9 -6 V i c t o r i a (20) 10 23 Warfield (T r a i l ) 1 0 2 Westwold 9 -18 White Rock 10 15 Williams Lake 7 -18 Wistaria 10 -24 at Comox* There i s a gradual decrease on the Lower Mainland from over 15° near the Gulf of Georgia to le s s than 10° at Hope. .- . - 22 - In the i n t e r i o r of B r i t i s h Columbia the i r r e g u l a r mountainous topography causes abrupt differences i n averages of d i f f e r e n t stations* Near the Okanagan, Arrow, and Kootenay Lakes at low a l t i t u d e s , however, the averages are a l l near 0°. In central B r i t i s h Columbia the atations represented have averages below -25°F. A map showing the approximate location of low temperature zones i n the se t t l e d part of the coastal region was drawn up* The areas represented i n the four zones are roughly those areas i n which arable land i s found accord- ing to Brink and Farstad (1949)* The average extreme lowest temperature of the year for the meteorological stations within these areas was used as the chief basis f o r the zones. Each zone includes stations with averages within a 5° range; for example, 5° to 10°. This map (Figure 4) follows the account of the winter i n j u r y survey. The soundness of using a ten year period to get a representative average of a climatic element such as temperature i s not now disputed* The ten year period i s widely used i n climatological work, since a longer period usually involves an appreciable amount of climatic change. Extreme lowest temperature of the winter For p r a c t i c a l purposes the extreme lowest tem- perature taken for each calendar year provides a s a t i s - factory basis for the ca l c u l a t i o n of averages* However, thi s basis would not be s a t i s f a c t o r y f b r a study of variation - 23 - i n low temperature between d i f f e r e n t winters. The reason for the error i s that the calendar year s p l i t s the winter into two halves, so that any winter may be represented twice or not at a l l i n the data. Since a measure of the actual v a r i a t i o n from winter to winter was required i n order to get a s t a t i s t i c a l estimate of extreme lowest tem- peratures for important stations i n B r i t i s h Columbia (see below), data which would represent each winter as a unit had to be obtained. Figures f o r extreme lowest temperature of the winter at selected B. C. meteorological stations for the ten-winter-period from 1940-41 to 1949-50 were compiled. Sources of information were the same as for figures based on the calendar year. Averages were calculated for those stations from which information was available for the ten winters. A table giving t h i s compiled information i s found i n Appendix 1. Incomplete series of figures are included with the t a b l e . Since the record low temperatures of the cold s p e l l of January, 1950, are included i n the figures based on the winter, but not i n those based on the year, the averages from the former figures are s l i g h t l y lower than those from the l a t t e r f i g u r e s . Analysis of extreme lowest temperature variations The actual variations i n extreme lowest tempera- ture from winter to winter can be represented by means of - 24 - simple bar graphs, examples of which are seen i n Figure 1. The average fo r ten winters i s used as the base, and the deviation of the minimum temperatures from t h i s mean i s shown by a darkened column above or below the l i n e of the mean, the length of the column depending on the size of the deviation. Since the mean i s shown i n r e l a t i o n to the temperature scale, comparison of the graphs for d i f f e r e n t stations reveals differences i n the average as well as i n the amount of v a r i a t i o n . Although such graphs convey a clear picture of the actual v a r i a t i o n , they are of l i t t l e use i n making quantitative predictions. The only quanti- t a t i v e generalization to be made i s the greatest spread of the deviations. The spread at Vancouver during the period was 21°; at Summerland i t was 32°; at Quesnel 44°• Differences i n the amount of v a r i a t i o n are indicated by t h i s information, but a s a t i s f a c t o r y method of approxi- mating these differences i s necessary. S t a t i s t i c a l analysis provides the method which i s required. A c a l c u l a t i o n of the standard deviation, though expressing no actual differences, constitutes a r e l i a b l e s t a t i s t i c a l measure of the amount of v a r i a t i o n . The probable size of future deviations can be r e a d i l y pre- dicted from the standard deviation by the use of mathe- matical tables. Standard deviation from the average extreme lowest temperature of the winter was calculated f o r 30- 20- 10- o- °F 1̂ COWICHAN BAY M = na°f 30- 10- °r L I L B i n VANCOUVER M=IZ.8'F (AIRPORT) : -10- -20- - 3 0 - -HO~ -50- °F SuHNERLftND M^o.l'f 10- 0- -10- -20- -30- -40- -50- °F Q u E S N E L M = -24°f Figure 1. Variation i n extreme lowest temperature of the winter during the ten winter period from 1940-41 to 1949-50 at four B r i t i s h Columbia meteorological stations. (to follow page 24) selected B. C. meteorological stations from which figures were available for the ten winters. Machine calculations were made with the use of the following formula: Standard deviation V n - 1 S S = x* „ ( £ * ) 2 n where S S = the sum of the squares.. S s the sum of x = any variate and n r=. • the t o t a l number of v a r i a t e s . e.g. Abbotsford. S S s x* r2 _ Clx ) 2 n * 95 2 - 2 0 | i = 6 8 0 # 5 St. dev. = \ / 6 * % * ? 75.6 =8.7 The mean and standard deviation of each station i s given i n Table I I . The standard deviation for coastal stations was found to be appreciably smaller than that of i n t e r i o r stations which are not affected by the moderating influence of bodies of water. It i s evident that areas where the winters are more severe generally have a greater amount of v a r i a t i o n i n the extreme lowest temperature of - 26 - the winter than areas where the winters are more mild* The gradual increase i n the standard deviation as the average extreme lowest temperature decreases i s shown i n Figure 2, which i l l u s t r a t e s graphically the mean and standard deviation for ten selected 8* C. stations* On t h e o r e t i c a l grounds a c a l c u l a t i o n of the standard deviation i s considered r e l i a b l e i f based on a random sample of s u f f i c i e n t numbers from a population or group which i s normally dis t r i b u t e d * The ten winter series here taken at random, though small i n numbers, i s s i m i l a r to the ten year periods from which s t a t i s t i c estimates of various elements are made i n climatology (Conrad, 1948). There i s , however, some evidence that the d i s t r i b u t i o n of extreme lowest temperatures i s not completely normal. In regions with a climate s i m i l a r to that of Western Europe there i s some skewing to the l e f t , caused by occasional extremely cold periods which are the re s u l t of a p a r t i c u l a r combination of weather conditions. These conditions are a r c t i c a i r penetrations associated with clear skies and an e f f e c t i v e snow cover* Clear skies and a snow cover inten- s i f y the cold periods i n i t i a t e d by a r c t i c a i r penetrations, causing phenomenally low temperatures well out of the normal range to occur* These conditions prevailed at Vancouver during the cold s p e l l i n January, 1950* Despite the f a c t that the d i s t r i b u t i o n of extreme lowest temperatures over a period of winters i s not quite Figure 2. S t a t i s t i c a l expression of extreme lowest temperature of the winter at ten B r i t i s h Columbia meteorological stations. The bar represents two standard deviations, one above, and one below the mean. ( t o f o l l o w page 26) normal, calculations r e l a t i n g to the central parts of the curve are expected to be r e l i a b l e enough for p r a c t i c a l purposes. The ninety percent point Application of s t a t i s t i c a l methods i n analysis of temperature data permits an approximation of the r e l a t i o n of the mean (or average) to the range of deviations on which i t i s based. The standard deviation of the extreme lowest temperature of the winter i s a r e l i a b l e index of the amount of v a r i a t i o n from the mean to be expected. Consequently, i f the mean and standard deviation are known, the p r o b a b i l i t y of any p a r t i c u l a r low temperature occurring at a station can be found by using s t a t i s t i c a l tables. However, t h i s technical approach would confuse the nurseryman or p r a c t i c a l gardener who i s not f a m i l i a r with s t a t i s t i c a l concepts. In addition, there i s a d i s - advantage i n finding the p r o b a b i l i t y of a given temperature rather than selecting a p r o b a b i l i t y and ca l c u l a t i n g the temperature corresponding to i t ; i f a selected p r o b a b i l i t y i s employed, comparable temperature information can be calculated for a l l the stations being studied. A proba- b i l i t y which i s convenient f o r studying the problem of selecting woody ornamentals would be the one chosen. A simple method of expressing the s t a t i s t i c a l information as a p r o b a b i l i t y appropriate for the a p p l i c a t i o n was desired. For these reasons a concept known as the ninety -28 - percent point was formulated. The ninety percent point i s that temperature above which the extreme lowest temperature w i l l f a l l i n approximately nine out of ten winters, and below which the extreme lowest temperature w i l l f a l l i n approximately one out of ten winters, according to mathematical expectancy based on s t a t i s t i c a l analysis of temperatures observed over a period of winters. A one to nine r a t i o was chosen because s a t i s - factory survival i n nine out of ten winters i s a reasonable l e v e l of success for woody ornamental plants. Many of the most beautiful shrubs are on the borderline of hardiness for most B r i t i s h Columbia l o c a l i t i e s ; an enthusiastic gardener would be s a t i s f i e d with a one to nine r i s k i n any pa r t i c u l a r winter. Species which are not injured at the ninety percent point for a l o c a l i t y are expected to remain unharmed i n nine out of ten winters when planted with due regard for h o r t i c u l t u r a l requirements. When f u l l y hardy trees or shrubs are desired, species with low temperature l i m i t s well above the ninety percent point should be selected. The ninety percent point i s offered as a p r a c t i c a l and convenient method of providing a r e l i a b l e expression of the low temperatures to be expected at a p a r t i c u l a r place. Whenever the approximate low temperature l i m i t of a plant species i s known, a knowledge of the ninety percent point of the l o c a l i t y w i l l be useful i n estimating the Figure 3» Normal frequency d i s t r i b u t i o n curve showing approximate proportions divided by the ninety percent point. (to f o l l o w page 28) - 29 - r i s k involved i n growing the plant* A method of converting information i n terms of standard deviation to information i n terms of the ninety percent point was developed* The ninety percent point i s found by subtracting the standard deviation mul t i p l i e d by 1*3 from the average extreme lowest temperature of the winter* The factor 1*3 i s based on a c a l c u l a t i o n of the deviation which divides a series so that greater deviations w i l l represent twenty percent of the t o t a l number of observations ( i . e . ten percent i n each of the t a i l s ) * According to a table given by Simpson and Eoe (1939), a deviation of approximately 1.3 times the standard deviation divides a normally d i s t r i b u t e d series i n the above proportion. Part of t h i s table i s given below i n rearranged form: Areas of the normal curve % area outside % area inside deviation s t . dev. 23 17 1.10 19 81 1.30 For p r a c t i c a l purposes the factor 1.3 i s s u f f i c i e n t l y accurate to correspond to the value where twenty percent of the area i f outside the l i m i t s . The d i v i s i o n of the normal curve at the ninety percent point i s shown by a diagram i n Figure 3« The following example indicates how the ninety - 30 - percent point i s calculated: Abbotsford, B. C. Mean = 9.5°F. St. dev. = 8.7 90$ point = Mean - (1.3 x St. dev.) = 9.5° - (1.3 x 8.7) = 9.5 - 11.3 = - 0.8° F. The ninety percent point for extreme lowest temperature of the winter was calculated for selected B. C. meteorological stations. The mean, standard deviation, and ninety percent point f o r each station i s found i n Table I I . TABLE I I . Analysis of Low Temperature Data. Average extreme lowest temperature of the winter for the ten- winter period from 1940-41 to 1949-50, standard deviation, and ninety percent point for selected B. C. Meteorological Stations. Station Mean St. Dev. 90$ Point Abbotsford 9.5 8.7 -1.8 Agassiz 13.2 10.5 -0.4 Alberni (Beaver Greek) 8.0 10.4 -5.5 Alberni, Port 10.5 8.3 -0.3 Armstrong -17.9 14.2 -36.4 Bella Coola 0.3 10.4 -10.5 Coquitlam Lake 12.4 10.0 -0.6 Cowichan Bay 17.8 6.3 9.6 Cranbrook (A) -24.0 14.9 -43.4 31 - TABLE II - Cont. Station Mean St. Dev. 9 0 % Point Creston -6.2 9.0 -17.8 Duncan 10.2 7.5 f 0.4 Fernie -22.2 10.2 -35.5 Golden -28.3 10.5 -42.0 Grand Forks -16.0 10.0 -29.0 Hope 6.8 10.7 - 7.1 James Island 21.1 8.0 .•10.7 Kamloops -11.0 14.2 -29.5 Kelowna - 1.6 12.8 -18.2 Lytton - 4.3 10.3 -17.7 McBride -25.4 12.6 -41.8 Masset 14.9 7.9 . f 4.6 Merritt -17.7 14.6 -36.7 Nanaimo 14*8 6.7 6.1 New Westminster 12.0 8.1 1.5 Ocean F a l l s 16.3 9.7 3.7 Okanagan Centre f 0.5 12.1 -15.2 Oliver - 5.0 11.8 -20.3 Penticton 0.4 9.3 -11.7 Princeton (A) -19.3 11.7 -34.5 Prince Rupert 13.4 9.8 • 0.7 Quesnel -24.8 15.1 -44.4 - 3 2 - TABLE II - Cont. Station Mean St. Dev. 9 0 $ Point Revelstoke - 1 1 . 8 1 0 . 3 - 2 5 . 2 Salmon Arm - 7 . 6 1 2 . 9 - 2 4 . 4 Sidney 2 0 . 0 7 . 2 1 0 . 6 Summerland 0 . 1 1 1 . 0 -14 . 2 Terrace - 3 . 9 1 0 . 4 - 1 7 . 4 Vancouver (A) 1 2 . 8 7 . 9 f 2 . 5 Vernon - 6 . 7 1 2 . 5 - 2 3 . 0 V i c t o r i a 2 1 . 2 8 . 8 9 . 8 White Rock 13 . 9 7 . 8 3 . 5 The Winter injury Survey Purpose of the survey Low temperature In? severe winters had been selected as the chief factor l i m i t i n g the number of species of ornamental woody plants which may be grown i n a l o c a l i t y , and the degree of low temperature i n d i f f e r e n t l o c a l i t i e s had been ascertained by certain methods. In order to test the value of t h i s climatic data as a guide i n the selection of plants for d i f f e r e n t l o c a l i t i e s , information on injury to ornamentals following severe winters was needed. This information could also be used to get accurate low temperature l i m i t s i n the P a c i f i c coastal - 33 - region for a number of important species of ornamental trees and shrubs* The l a s t two winters were well suited to a survey of Winter i n j u r y . The Winter of 1948-49 was the coldest i n s i x years i n most parts of the Province, and the Winter of 1949-50 was the coldest on record i n Western Canada. Consequently, there was a good opportunity to check the hardiness of those trees and shrubs which were expected to be badly injured or k i l l e d i n severe winters, as well as those which are only s l i g h t l y tender i n some areas. Description of methods The formal winter i n j u r y survey was preceded by preliminary l e t t e r s to D i s t r i c t H o r t i c u l t u r i s t s and the p r i n c i p a l nurseries of the province. Replies to these l e t t e r s indicated s u f f i c i e n t interest i n the subject of winter injury to ornamental plants to j u s t i f y compiling a form which would f a c i l i t a t e r e p l i e s and the subsequent analysis of information received. A l i s t of one hundred and four species was compiled by choosing from Rehder's Manual (1940) the more common species of ornamental trees and shrubs l i k e l y to be injured during severe winters i n the sett l e d areas of B r i t i s h Columbia. Almost a l l of these species are i n Zone V, VI or VII according to Rehder's winter hardiness c l a s s i f i c a t i o n . The zone number, s c i e n t i f i c name and common name were given i n the l i s t . Columns were provided f o r information on the number of years planted, damage a f t e r the winter of 1948- 49 and af t e r the winter of 1949-50, and other remarks. The system of symbols used by the Royal H o r t i c u l t u r a l Society (1948) was used to indicate the amount of i n j u r y . A form l e t t e r explaining the reason for the survey was enclosed with each l i s t sent out. A l i s t of the species included on the survey i s found i n Appendix I I . Survey forms were sent to s i x t y - f i v e addresses i n B r i t i s h Columbia, including the Dominion Experimental Farms and Stations, the D i s t r i c t H o r t i c u l t u r i s t s , and most of the nurseries. In order to cover s e t t l e d l o c a l i t i e s which were not represented by the above addresses, a number of forms were sent to f l o r i s t s , growers, and amateur gardeners; or i f no information as to a suitable recipient was available, the form was addressed to the l o c a l post- master. The information received i n reply was transferred to a master form. The master form l i s t e d the l o c a l i t i e s i n geographical order and the species i n the order they appear on the l i s t . This method of compiling the data allowed comparisons of the behaviour of any species i n dif f e r e n t l o c a l i t i e s to be made at a glance. Result s Twenty-five winter i n j u r y survey forms were re- turned with the requested information f i l l e d i n . A few forms were returned with no information. The response - 35 - varied c h i e f l y according to the part of the province from which the reply came. Replies from the i n t e r i o r d i s t r i c t s were less complete than those from coastal d i s t r i c t s , since the majority of the species on the l i s t are not usually grown i n the i n t e r i o r . The thoroughness of the reply also depended on how close to the subject of study the interests and t r a i n i n g of the recipient were. Keen amateurs gave the most adequate information on l e s s common ornamentals. Experimental Farms were able to give accurate planting dates of mature specimens. Nurserymen provided information on comparative damage to a number of species grown under sim i l a r conditions i n the same l o c a t i o n . Details of injury a f t e r the winter of 1 9 4 8 - 4 9 were i n - cluded i n some of the r e p l i e s . A comprehensive report on the information accumulated by means of the winter injury survey i s beyond the scope of t h i s i nvestigation. The findings of the survey are ex- pected to be valuable for future reference, since the i n - formation constitutes the beginning of a permanent record of the behaviour of ornamental species i n severe winters i n B r i t i s h Columbia. The l e t t e r s of reply, returned survey forms, and the master form have been f i l e d at the Department of Horticulture, The University of B r i t i s h Columbia. Examples of the reports which were used as the basis of the conclusions are presented below. The extent of injury to woody ornamental plants - 36 - i n d i f f e r e n t l o c a l i t i e s of B r i t i s h Columbia a f t e r the winter of 1949-50 was related more or less c l o s e l y to the lowest temperatures recorded during the winter at the nearest meteorological stations. Injury to some species corresponded c l o s e l y with the low temperatures to which the plants had been subjected. Injury to other species did not appear to be correlated with low temperature except over a wide range. For example, Cedrus a t l a n t i c a was reported un- injured at Sidney (S°F.), s l i g h t l y injured at New Westminster (-1°), and k i l l e d at Nelson (-16°)j Wistaria sinensis was reported uninjured at Hope (-11°), s l i g h t l y injured at Keremeos (-23°) and badly injured at Vernon (-31°). On the other hand. Cryptomeria .laponica was reported uninjured at Port Alberni (-7°), s l i g h t l y injured at V i c t o r i a (6°), and s l i g h t l y to badly injured at Vancouver (0°); Mahonia aquifolium was reported s l i g h t l y injured at V i c t o r i a (6°), uninjured at Hope (-11°), and s l i g h t l y injured at Keremeos (-23°)• The above temperatures are the lowest recorded during the winter of 1949-50. The amount of i n j u r y to low-growing shrubs depended on the depth of snow around the plants during the cold weather. At Vancouver the leaves of Cotoneaster microphylla were burned where they were exposed, but completely un- > touched where the snow covered them. Most injury to broad- leaved evergreens was d i r e c t l y related to the amount of - 37 - exposure to the bright sun during the cold weather* At the coast^ Prunus Laurocerasus. Prunus l u s i t a n i c a . Camellia japonica and many other species often showed severe scorching on the sunny side of the plant, but no damage on the shaded parts* Injury to conifers, on the other hand, was widely d i s t r i b u t e d over the plant, or concentrated on the side exposed to wind* Injury related to exposure to wind was evident i n large specimens of Cryptomeria .japonica and Sequoiadendron giganteum at Vancouver. Conclusions The general extent of injury i n cert a i n l o c a l i t i e s was greater -than the extreme lowest temperature of the winter, compared with that of other l o c a l i t i e s , would indicate. V i c t o r i a with 6° F., Vancouver with 0°, and Port Alberni with -7° a l l received approximately the same amount of damage* Along the east coast of Vancouver Island, although temperatures lower than at V i c t o r i a were recorded, l i t t l e general injury was noticeable. Modifying factors such as exposure to wind, amount of sunshine during the cold weather, and depth of the snow cover are judged responsible. In the i n t e r i o r of B r i t i s h Columbia somewhat lower temperatures than those at the coast were required i n producing s i m i l a r injury for the same species. An approximate estimate of the low temperature l i m i t s was made for f i f t y - s i x species of ornamental trees 38 and shrubs i n the P a c i f i c coastal area* Even though numerous discrepancies are evident i n the information provided by t h i s survey, a general conclusion as to the approximate temperature at which a plant i s reasonably safe from damage can be made. This was done by comparing reports of injury to each species with the lowest tem- peratures recorded at the corresponding stations. The low temperature l i m i t s determined are given with the l i s t of species i n Appendix I I . Figure 4. Approximate low temperature zones i n the s e t t l e d coastal region, based on average extreme lowest temperature (ten-year period 1940-49); areas zoned are arable lands as defined by Brink and Farstad. - 39 - DISCUSSION Discussions of the d i f f e r e n t methods which were employed have been given with the explanations of the methods* For thi s section there remains a general discussion of conclusions* Certain modifications should be made i n Rehder's system of winter hardiness zones when t h i s system i s applied i n B r i t i s h Columbia. According to the figures calculated here, averages of extreme lowest temperature of the year f o r stations i n the coastal area of B. C. (see Figure 4) are above the range given for Zone VII by Rehder. Yet information from the winter i n j u r y survey and general observations indicate that most species l i s t e d as Zone VI or VII by Rehder are not f u l l y hardy i n t h i s area. One way of overcoming the d i f f i c u l t y would be to al t e r the scale used by Rehder; l o c a l i t i e s with extreme o lowest temperature averages above 20 F. would be included i n Zone VII and those with averages between 10° and 20° in Zone VI. Another method would be to use the ninety percent point of a station, instead of averages, to correspond with averages given i n the scale used by Rehder. In addition to modifications i n the scale for the zones, however, modifications are necessary i n many of the hardiness zone ratings assigned to species by Rehder. The necessary modifications could be made by checking the zones assigned by Rehder with the information on low - 40 - temperature l i m i t s of species i n the P a c i f i c coastal region as given i n Appendix I I . Low temperature zones i n B r i t i s h Columbia and low temperature l i m i t s for species i n this area are not stated here i n terms of Rehder's zones because t h i s i n f o r - mation i s considered more Valuable i f expressed i n terms of temperature. Caution was found necessary since Rehder's system did not f i t into the pattern i n B r i t i s h Columbia. If temperature information for B. C. were stated i n the symbols of Rehder's system, the accuracy of some, of the information would be l o s t , owing to the imperfections of that system when applied to B.C. The u t i l i t y of the ninety percent point concept depends on how important a factor low temperature i s as a cause of winter injury, on how representative the low temperature information i s f o r a l o c a l i t y , and on how prec i s e l y low temperature l i m i t s of plant species can be determined. The results of the winter injury survey indicate that low temperature may be modified by a number of other factors i n i t s effects on plants. Nevertheless, for most woody ornamental plant species, the amount of damage following a severe winter corresponds approximately to the low temperatures which have been endured. The low temperature l i m i t s determined are stated within f i v e degrees for most species. Plants w i l l not - 41 - always survive temperatures at or above the low temperature l i m i t a , unless they are grown with due regard for h o r t i - c u l t u r a l requirements. They may survive lower temperatures i f they are given sp e c i a l protection, or i f other factors modifying temperature are i n favour of t h e i r s u r v i v a l . Thus, the low temperature l i m i t s must be considered approximate, and the method used to determine them a rough one. The s t a t i s t i c a l methods used i n the analysis of temperature data, on the other hand, are r e l a t i v e l y exact. The temperature data on which the s t a t i s t i c a l analysis i s based, however, i s taken to represent a rather extensive area (the l o c a l i t y around a meteorological s t a t i o n ) . Although there may be many s l i g h t differences within a l o c a l i t y , these differences can be accounted for by an experienced person who i s f a m i l i a r with the l o c a l topography. Minor corrections i n the ninety percent point to account for these differences could be made by adding or subtracting f i v e to ten degrees, according to the amount of the difference expected. Consequently, the main l i m i t a t i o n i n the p r a c t i c a l a p p l i c a t i o n of the ninety percent point i n selecting woody ornamentals i s the d i f f i c u l t y i n getting precise low temperature l i m i t s for the plant species concerned. The ninety percent point would be d i f f i c u l t to use with species which have i l l - d e f i n e d low temperature - 42 - l i m i t s * It must be admitted that many ornamental species do not have as well-defined l i m i t s as had been expected* Nevertheless, within i t s l i m i t a t i o n s the ninety percent point concept provides a r e l i a b l e method of estimating the chances of survival i n a p a r t i c u l a r place for most of our important ornamental trees and shrubs. Other applications of the ninety percent point are suggested by a glance at f i e l d s of study related to t h i s investigation. The idea behind the ninety percent point i s to express the mean and standard deviation of a series i n terms of the deviation which corresponds to a selected p r o b a b i l i t y . This idea should be applicable to any study of low temperature, and possible to other series of a similar nature. Within h o r t i c u l t u r e , commercial f r u i t growing involves many factors s i m i l a r to those studied here i n r e l a t i o n to the selection of woody ornamentals. The low temperature l i m i t s of woody f r u i t plants are well known* If the risks involved i n growing a certain type of tree f r u i t i n a given l o c a t i o n were calculated, the investment of large sums of money i n new plantings could be made with a f u l l e r knowledge of the changes involved. The r i s k i n regard to low winter temperature, an important factor i n orchard culture, could be estimated by comparing the low temperature corresponding to a selected p r o b a b i l i t y for t h i s l o cation with the low temperature l i m i t of the plant to be grown* 43 - SUMMARY To meet the need f o r r e l i a b l e information on the s u i t a b i l i t y of set t l e d areas of B r i t i s h Columbia for d i f f e r e n t species of ornamental trees and shrubs, a study of low winter temperature as i t aff e c t s the selection of woody ornamentals f o r l o c a l i t i e s of the province was made. Average extreme lowest temperature of the year for each B. C. Meteorological station was calculated from figures compiled for the ten-year period 1940-49* Average figures were arranged on a map of B r i t i s h Columbia for geographical comparison. A map showing approximate low temperature zones for settled parts of the coastal region was constructed. Average extreme lowest temperature of the winter for each of selected meteorological stations was c a l - culated from figures compiled for the ten-winter period from 1940-41 to 1949-50. The amount of v a r i a t i o n i n extreme lowest temperature from winter to winter was approximated s t a t i s t i c a l l y by ca l c u l a t i n g the standard deviation for each s t a t i o n . As expected, the coastal stations were found to have a generally lower standard deviation than i n t e r i o r stations. A new concept c a l l e d the ninety percent point was employed to provide a s t a t i s t i c a l expression of low m 44 temperature i n simple terms. The ninety percent point i s that temperature above which the extreme lowest temperature of a station w i l l f a l l i n approximately nine out of ten winters, and below which the extreme lowest temperature w i l l f a l l i n approximately one out of ten winters, according to mathematical expectancy based on s t a t i s t i c a l analysis of temperatures observed over a period of winters. This concept combines the information to be obtained from the average extreme lowest temperature and the standard deviation. The ninety percent point i s found by subtracting the standard deviation m u l t i p l i e d by 1 . 3 from the average extreme lowest temperature of the winter for the st a t i o n . A survey was conducted to obtain an estimate of the injury to ornamental trees and shrubs i n B r i t i s h Columbia following two severe winters. The information was used to test the usefulness of low temperature data as a guide i n selecting woody ornamentals f o r hardiness i n a l o c a l i t y , and to get accurate low temperature l i m i t s i n the P a c i f i c coastal region f o r a number of ornamental species. Low temperature information was found useful within l i m i t a t i o n s as an in d i c a t i o n of the amount of winter injury to woody ornamentals to be expected i n a l o c a l i t y i n B r i t i s h Columbia. Many species react to given temperatures i n a predictable way under most conditions. Some species behave as though factors other than low temperature are mainly responsible f o r the extent of i n j u r y . — 45 - LITERATURE CITED BAKER, F. S., 1944. Mountain climates of the Western United States, Ecolog. Monoer. 14:223-254. BAKER, 0 . E., 1936. Atlas of American A g r i c u l t u r e f Physical b a s i s f climate t Washington, U. S. Govt. P r i n t i n g Off., p. 9, f i g . 7. BALFOUR, F., 1941. Low temperatures i n January, 1941 i n S. E. Scotland and t h e i r e f f e c t on shrubs and trees, Rov. Hort. Soc. Jour. 66:230-236. BOWERS, C. G., 1947. Rhododendron notes; factors a f f e c t - ing hardiness, Nat. Hort. Mag. 26:231-237. BRINK, V. C., 1950. Climates of B r i t i s h Columbia for agrologists, part l f some general features of the climates. University of B r i t i s h Columbia, Agronomy Dept., Technical Communication. BRINK, V. C. and L. FARSTAD, 1949* The physiography of the a g r i c u l t u r a l areas of B r i t i s h Columbia,. S c i . Agric. 29:273-301. BRITISH COLUMBIA, Dept. of Agriculture, Climate of B r i t i s h Columbia. V i c t o r i a , B. G., 1941 to 1948. BUCK, F. E., 1946. A p a r t i a l l i s t of ornamental trees and shrubs recommended f o r landscape use i n the province of B r i t i s h Columbia f University of B r i t i s h Columbia, mimeographed f o l d e r , rev. ed. CANADA, Meteorological Service, 1940. Monthly record of meteorological observations T Toronto, Canada. January, 1940 to March, 1941. CANADA, Meteorological Service, 1946. Climate summaries fo r selected meteorological stations i n the Dominion of Canada. v o l . 1, Toronto, Canada, (1946) CANADA, Meteorological Service, 1949. Monthly weather mapt January, 1949 to February, 1950. CRANE, H. L., 1947. Factors influencing the hardiness of woody plants, North. Nut Growers Assn. Report. 1947: 30-37 CONNOR, A. J . , 1915. The temperature and p r e c i p i t a t i o n of B r i t i s h Columbia, Canadian Meteorological Service, Ottawa, Canada. CONNOR, A. J . and s t a f f , 1949. The f r o s t free season i n B r i t i s h Columbia. Canadian Meteorological Service, Toronto, Canada. CONRAD, V. A., 1944. Methods i n climatology. Harvard University Press. DAUBENMIRE, R. F., 1947. Plants and environment, New York, Wiley, Chap. 4 . DENISON, F. N., 1925. The climate of B r i t i s h Columbia, Monthly Weather Review 53-354. FOSTER, E. E., 1948. R a i n f a l l and runoff. New York, MacMillan, 1948. GRAHAM, E., and H. McMINN, 1941. Ornamental shrubs and woody vines of the P a c i f i c coast, Berkeley, Cal., G i l l i c k Press. GRANT, J . A., 1944. Rhododendrons i n the P a c i f i c Northwest/ Home Gard. 3(6): 13-14. GRANT, J . A. and C. L. GRANT, 1943. Trees and shrubs fo r P a c i f i c Northwest gardens, Seattle, McCaffrey Publishing Co. HARROW, R. L., 1948. The effect of f r o s t i n the winter of 1946-47 on vegetation, Rov. Hort. Soc. Jour. 63(1.1) :389. IMPERIAL BUREAU OF PLANT BREEDING AND GENETICS, 1939. Bibliography on cold resistance i n plants f Cambridge, England, School of Agriculture. KOEPPE, C. E., 1931. The Canadian climate, Bloomington, 111., McNight•and McNight. LANDSBERG, H., 1946. Climate as a natural resource, S c i . Month. 63(4):293-298. 1946. LEVITT, J . , 1941. Frost k i l l i n g and hardiness i n plants, Minneapolis, Burgess Publishing Co. MACOUN, W. T., 1931. Hedges and t h e i r uses, Dom. Dept. Agric. Bui. 142 (N.S.), Ottawa, Canada. MULFORD, F. L., 1920. Street trees, U. S. Dept. Agric. Bui. 6*16, Washington, U. S. Govt. P r i n t . Off. - 4 8 - MULFORD, F. L., 1926. Trees f o r roadside planting, U. S. Dept. Agric. Farm Bui. 1482, Washington, U. S. Govt. P r i n t . Off. MUIRHEAD, G. D., (unpubl.). An evaluation of the street trees i n the un i v e r s i t y area of Vancouver, B. C , University of B r i t i s h Columbia, Graduating essay, 1950. McMINN, H. E. and MAINO, E., 1935. An i l l u s t r a t e d guide to P a c i f i c Coast trees, University of C a l i f o r n i a Press. OLIVER, R. W., 1944. Ornamental shrubs and woody climbers more commonly used f o r landscape purposes throughout Canada, Dom. Dept. Agric. Publ. 713, Farmer's Bui. 100, Ottawa, Canada. OLIVER, R. W., 1945. Deciduous trees and conifers more commonly used f o r ornamental purposes throughout Canada, Dom. Dept. Agric. Farmer's Bui. 49, Ottawa, Canada. PEATTIE, R., 1936. Mountain geography: a c r i t i q u e and f i e l d study, Harvard University Press. PRESTON, I., 1946. Herbaceous perennials for Canadian gardens, Dom. Dept. Agric. Farmers' Bui., 138, Ottawa, Canada. REHDER, A., 1927. Manual of cu l t i v a t e d trees and shrubs hardv i n North America, New York, MacMillan, 1 s t ed. REHDER, A., 1940. Manual o f c u l t i v a t e d t r e e s and shrubs hardy i n N o r t h America, , New Y o r k , M a c M i l l a n , 2nd e d . ROYAL HORTICULTURAL SOCIETY, 1941. E f f e c t o f the c o l d s p e l l , 1939-40, R o v . H o r t S o c . J o u r . 66:207-209. i ROYAL HORTICULTURAL SOCIETY, 1948. F r o s t damage s u r v e y , 1946-47, Rov . H o r t . S o c . J o u r . 63:390-415, 439-448. SANDERSON, M a r i e , 1948. The c l i m a t e s o f Canada a c c o r d i n g to the new Thornthwai t e c l a s s i f i c a - t i o n , S ^ j l g r i s j . 28:501-517. SIMPSON, G . L . and ROE, A . , 1939. Q u a n t i t a t i v e z o o l o g y , New Y o r k , McGraw H i l l , 1st e d . p. 137. SKINNER, F . L . , 1944. H a r d i n e s s i n p l a n t s , N a t . H o r t . Mag. 23^236. SNYDER, John C . , no d a t e . Ornamental shrubs f o r l andscape p l a n t i n g s i n W a s h i n g t o n . U . S . D e p t . A g r i c . c o o p e r a t i n g w i t h S t a t e C o l l e g e o f Washington , P u l l m a n , W a s h i n g t o n . TEUSCHER, H . , 1934. H a r d i n e s s i n p l a n t s , J o u r . New York B o t . G a r d . 35:121-131. THORNTHWAITE, C . W . , 1931. The c l i m a t e s o f N o r t h Amer ica a c c o r d i n g t o a new c l a s s i f i c a t i o n . G e o g r . Rev . 21:633-655. - 50 - THORNTHWAITE, C. W., 1948. An approach toward a ra t i o n a l c l a s s i f i c a t i o n of climate. Geogr. Rev. 38:55-94. VAN DERSAL, W.R., 1938. Native woodv plants of the United States. U. S. Dept. Agric. Misc. Publ. 303, Washington, U. S. Govt. P r i n t . Off. VAN DERSAL, W. R., 1942. Ornamental American shrubs. Oxford University Press. WYMAN, D., 1938. Hedges, screens and windbreaks, New York, McGraw H i l l . ft A P F E H D I X APPENDIX I. Ertreme Lowest (Temperature of the Winter at Selected B. C. Meteorological Stations for the Ten-Winter Period from 1940-41 to 1949-50. Averages are given for stations from which information was available for a l l ten winters. (Degrees Fahrenheit). station 1940 41- 42- 43-44-45- 46-4V- 48- 49- Average -41 42 43 44 45 46 47 48 49 50 Abbotsford (A) 21 15 -1 22 11 9 7 8 9 -6 +9.5 Agassis 22 18 -4 25 20 19 3 19 12 -2 13.2 Alberni (Beaver Cfc) 19 9 -3 17 8 17 5 16 6 -14 +8.0 Alberni, Port 20 12 9 17 13 20 2 12 7 -7 10.5 Armstrong -8 -5 -39 -12 -5 -6 -16 -17 -27 -44 -17.9 Ashcroft -23 -26 -15 -22 -35 Barkerville -23 -23 -45 -17 -22 -20 -52 -26 Bella Coola 5 7 -5 15 9 4 ^10 4 -12 -20 +0.3 Comox 19 9 13 1 -6 Coquitlam Lake 22 14 5 24 20 19 4 18 4 -6 12.4 Cowichan Bay 24 18 11 26 21 24 13 20 15 6 17.8 Cranbrook (A} -12 -22 -41 ^12 -19 -16 -22 -20 -35 -41 -24.0 Creston 7 0 -18 4 -4 -10 -3 -13 -20 - 6.2 Cultus Lake 8 15 11 -5 Cumberland 17 13 -3 22 16 15 3 15 Dominion Obser- vatory 25 24 7 28 26 23 14 21 Duncan 15 9 9 19 13 19 7 14 2 -5 10.2 Pernio -18 -17 -30 -9 -18 -12 -20 -21 -38 -39 -22.2 Golden -15 -31 -40 -18 -26 -17 -30 -25 -36 -47 -28.3 Grand Forks -6 -7 -30 -12 -10 -8 -18 -11 -25 -33 -16.0 Haney _ 9 18 9 -5 Hope 17 13 -8 20 12 12 -3 12 4 -11 +6.8 James Island 26 25 7 29 27 27 17 25 20 8 21.1 Jordan Biver 26 17 20 19 4 Eamloops 2 0 -27 2 2 -2 -20 -10 -20 -37 -11.0 Kelowna 9 4 ^15 9 10 10 -9 2 -12 -24 -1.6 Seremeos 7 0 -17 6 2 7 -5 1 -10 -22 -3,1 Zimberley -8 -18 -18 -32 -40 Lytton 0 1 -15 6 4 6 ^11 0 -9 -25 -4.3 MeBrlde -20 -19 -43 -8 -20 -12 -35 -28 -23 -46 -25.4 Masset 20 21 5 26 22 19 4 12 14 6 14,9 Merritt -2 -6 -33 -8 -2 -11 -21 -16 -30 -46 -17.7 Hanairao 24 13 6 22 19 20 13 15 13 3 14.8 Nelson 10 1 -13 12 5 10 0 6 2 -16 +1.7 New Westminster 20 16 -1 21 17 18 7 11 12 -1 12.0 Ocean Falls 18 23 -1 25 27 22 3 22 17 5 16.3 Okanagan Centre 9 6 -16 15 11 9 -5 Z -4 -22 +0.5 Oliver 11 3 -21 3 3 0 -10 1 -17 -23 -5.0 Penticton 10 9 -10 7 11 0 -4 4 -7 -16 +0.4 Port lardy (A) 23 14 22 17 6 Powell River 27 25 11 30 28 28 13 26 APPENDIX I-Cont. Station 1940 -41 41- 42 42- 43 43-• 44-Tins 45 45- 46 46- 47 47- 48 48- 49 49- 50 Avers Princeton (A) -9 -16 -37 • - i i -11 -9 -22 -14 -22 -42 -19.3 Prince George (A) -28 -25 -52 -39 -46 -58 Prince Rupert 15 22 1 26 24 21 -3 10 12 3 13.4 Qnesnel -17 -13 —<3i> -10 -12 -10 -43 -23 -33 -52 -24.8 Revelstoke -3 -12 -30 0 -6 -1 -14 -10 -15 -27 -11.8 Salmon Arm 6 -1 -26 5 0 3 -15 -5 -13 -30 -7.6 Sidney 26 22 10 28 24 26 13 24 19 8 20.0 Smither8 -20 -21 -32 • -11 -17 Stave Falls 17 10 -3 20 18 19 12 14 Steveston 11 2 21 13 -2 16 Summerland 10 7 -13 10 9 7 -2 2 -7 -22 +0.1 Terrace 3 -3 -10 14 6 -3 -17 -6 -2 -21 -3.9 Vancouver (A) 20 15 3 21 21 16 5 18 9 0 12.8 Vernon 1 2 -25 4 4 2 -7 -4 -13 -31 -6.7 Victoria 28 25 7 31 28 25 17 26 19 6 21.2 W&rfield ((Trail) 11 3 -16 13 5 5 -2 4 -5 White Rock 21 17 2 22 19 18 8 19 12 1 13.9 Williams Lake -15 -13 -42--12 -10 -24 APPMDIX II Species of frees and Shrubs Included in the Winter Injury Surrey, 1950. Approximate low temperature limits in the Paeifie coastal region, as determined from information obtained by means of the survey, are given for certain species. (Degrees Fahrenheit). Low Temp. Limit Botanical Fame Low Temp, Limit Botanical Fame Taxus baceata -5 to 46 §• cuspldata -10 to +5 Cephalotaxus drupacea var. fastiglata Araucaria araucana 0 to +5 Abie8 plnsapo A. conoolor Cedrus atlantiea -5 to +5 C. deodara +5 to +10 Pinus radiata Sequoia sempervirens +5 to +10 Sequoiadendron giganteum +5 to +10 Cryptomeria japonica -5 to +10 Cunninghamla lan- ceolata fhujopsis dolobrata Cupres8us arizonica C. macrocarpa +10 to +15 Chamaecyparia lawsoniana 0 to +10 Juniperus app, Salix oablonica Garrya elliptica Juglans regie -5 to +5 Carya Pecan Quercus Virginians Peonia suffruticosa X Clematis jackmani Mahonia aquifolium Berber!s buxifolia X B. stenophylla -5 to +5 B. darwini +5 to +10 B. Tfcoribexgl X Magnolia Soulangeana M. grandiflora +5 to +10 M. stellata Carpentaria californlea Umbellularia ealifornica Hydrangea macrophylla var. Hortensis 0 to +10 Escallonia rubra +10 to +15 X langleyensis +15 to +20 Ootoneaster Franeheti +10 to+15 0 , miorophylla +5 to +15 Pyraeantha eoccinea P. crenato-serrata Photlnia serrulate +15 to +20 Stranvaesia Davidiana +5 to +10 Boss vars, Prmms triloba PruBUS lusitanica +10 to +15 Prunus Laurocerasus +15 to +20 Cereis Sillquastrum +10 to +15 Spartium junceum +10 to +15 Laburnum anagroldes Indlgofera spp. Wistaria sinensis +5 to +10 Ohoisya ternata +15 to +20 Skimmla japonica +5 to +10 Sarcococca spp. +5 to +10 Pachysandra terminal!s Buxus sempervirens +5 to +10 B. miorophylla Ilex aquifolium +5 to +10 1. opaea Euonymus Fortune! var. radieans 0 to +10 E. japonica +5 to +10 Pachystima myrsinites Acer palmaturn X Oeanothus Delilianus +15 to+20 C. velutinus +5 to+10 Titis vinifera -5 to +5 Hibiscus 8yriaeus +5 to +10 Camellia japonica +15 to +20 Camellia Sa sanq.ua Hypericum calyeinum +5 to +10 Tamarix anglica 0 to +5 Clstus ladanlferus +5 to +10 Opuntia spp. Daphne laureola +5 to +10 Eucalyptus Gunnii +10 to +15 Fuchsia magellaniea var. Biehartonii +10 to +15 APPMDIX II - Cont. Low Temp. Low Temp. Botanical Same Limit Botanical Name Limit Hedera helix +5 to +10 Buddlela Davldi +10 to +15 Fatsia japonica +10 to +15 Rosemarinus Aralla chinensis officinalis Aucuba japonica •10 to +15 Salvia officinalis Cornua Huttallii Lit ho speranim Rhododendron spp.(half diffusum +10 to +15 hardy spp.) Paulowala tomentosa Arbutus Kensiesli +5 to +10 Hebe spp. +10 to +20 Aret08taphylo8 Viburnum Davldi •10 to +15 tomentosa Viburnum tinus +15 to +20 Vaecinium ovatum X Abelia grandiflora +15 to +20 Forsythla spp. Olearia Haastii •10 to +15 Ligustrum lucidum Ruscus aculeatus Oamanthus i l i c l f o l i u s Jasmlnum nudlflorum +5 to +10 

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