Báo cáo khoa học: "Predicted global warming and Douglas-fir chilling requirements"

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Original article global warming Predicted Douglas-fir chilling requirements and Lavender RK Hermann 2 2 DP 1 McCreary DD College of Forestry, Oregon State University, Corvallis, Oregon 97331-5704, USA; 1 Faculty of Forestry, University of British Columbia, MacMillan Buildmg, 193-2357 Main 2 Mall, Vancouver, BC, Canada V6T 1W5 February 1990) 26 accepted 22 November 1988; (Received from warm Summary - Potted Douglas-fir [Pseudotsuga menziesii (Mirb) Franco] seedlings coastal and cool mountainous Oregon seed sources, grown under natural conditions, were chilled at constant temperatures of 5, 7, or 9° C for periods of 9, 11, 13 or 15 wk beginning bud break in mid-October. After a growth period of 9 wk following chilling, the degree of treatment and the weight of new shoot growth were recorded. The longest and coldest chilling with the greatest growth response for all seed sources. Results are discussed produced to predicted global warming. reference / bud burst / reforestation global warming / chilling / Douglas-fir Résumé - Réchauffement du Globe et besoin en froid du douglas. Des semis de 2 ans de sapins de Douglas [Pseudotsuga menziesii (Mirb) Franco] ont été transférés en conteneurs, Ils provenaient de puis placés en conditions naturelles pendant une saison de végétation. ils ont été sites côtiers chauds ou montagneux frais de l’Orégon. A partir de mi-octobre 13 soumis à une température constante de 5, 7 ou 9 °C pendant des durées de 9, 11, ou de lever leur dormance. Ensuite, après une mise en végétation à 15°C 15 semaines, en vue le degré de débourrement des plants et pendant 9 semaines, on a individuellement noté déterminé le poids sec des nouvelles pousses formées. Quelle que soit l’origine des graines, de dormance la réponse à la croissance est d’autant meilleure que la phase d’élimination dans la est plus longue (tableau I) et plus froide (tableau II). Les résultats sont discutés des effets d’un réchauffement du Globe. perspective / débourrement / / conditionnement par le froid / réchauffement du globe douglas reboisement Management Resource Correspondence and reprints. Present address: Department of Forestry and * University of California, PO Box 249 Browns Valley, CA 95918, USA
INTRODUCTION the relative chilling requirements of - seedlings grown from seeds collected in areas with different winter climates. The role of low temperatures in the Although previous studies have ex- breaking of dormancy was first dis- amined Douglas-fir chilling require- covered in 1801 (Doorenbos, 1953). Al- ments (Wommack, 1964; Van den though delayed foliation of peach trees Driessche, 1975; Wells, 1979), they reported in Georgia in 1890 was have either used seedlings that were (Weinberger, 1967), low temperatures not transplanted at least 1 growing sea- generally not related to the break- were prior to the study, have grown them son ing of dormancy of woody plants until under artificial conditions, or have ex- 1908 - when it was recognized that posed seedlings to daily photoperiods peaches differed in their rest period than longer 12 h after chilling. (Chandler, 1957) - and the subsequent Lavender and Stafford (1985) strongly decade, when Colville (1920) reported suggest that if data are to be truly rel- his studies on chilling. evant for natural populations, the use Today, "chilling requirement" refers of undisturbed plants grown under nat- to the temperature (commonly around ural conditions is essential; and daily 5 °C) and duration of exposure nec- photoperiods greater than 12 h have essary to prepare the apical mer- been shown to compensate for the lack istems of temperate perennial plants of chilling in Douglas-fir (Lavender et for resumption of growth when al, 1970). temperatures rise in the spring. This requirement is confined largely to plants that are exposed to freezing METHODS winter temperatures, and has evolved to prevent active shoot growth during Douglas-fir seeds were collected from ele- brief, warm winter spells because vations below 150 m near the central Oregon such growth could be damaged by coast (Western Forest Tree Seed Council subsequent low temperatures. seed zones 071-0.5 and 072-0.5) and from A number of papers offer evidence the Oregon Cascade Range east of Eugene that mean global warming of 3-4 °C at elevations of about 1000 m (Western Fo- rest Tree Seed Council seed zones 451-2.5 could occur within the next century, and 491-4.5). Winters in the coastal area are particularly during the winter months relatively warm, ie the average temperature (Seidel and Keyes, 1983; Cooper, 1984; between 1 December and 1 March is ca McBeath et al, 1984; Rind and Lebed- 7°C, whereas the winters in the mountainous eff, 1984; Slocum, 1985; Smith, 1985). area are cooler with average temperatures This could profoundly affect the amount for the same period of about 3° C. However, the coastal area experiences about 3 000 h of chilling that Douglas-fir [Pseudot- annually of temperatures between 0°C and suga menziesii (Mirb) Franco] receives. 7°C, whereas the mountainous area has so- The present study was undertaken mewhat fewer, ca 2500 h. Seeds were sown to determine: in spring, 1982 in the Oregon State Board the effect of the chilling period upon of Forestry Nursery near Elkton, Oregon. The - resultant seedlings were maintained under subsequent growth of Douglas-fir seed- standard nursery conditions until late Fe- lings; bruary, 1984, at which time they were lifted, the efficiency of slightly higher chil- - stored for 6 wks, and planted in pressed fi- ling temperatures in preparing seed- ber pots (8 seedlings per pot) containing lings for growth resumption; 12 I of forest soil each. Prior to planting, the
lowed to permit computation of the date of were sorted by size within each seedlings bud break both for the individual chil- seed source and the populations for each mean ling temperatures and periods and for the pot made up from this distribution to assure levels within seedling crowns. These data a relatively uniform seedling size. The see- are not presented, however, as they follow dlings from the coastal seed sources were the same pattern as that for numbers of ac- generally larger than those from the interior tive buds, ie seedlings maintained at 5°C in- at the beginning of the 1984 growing sea- itiated bud activity more rapidly than, those son. The potted seedlings were kept outside at 9°C; plants chilled for 15 wk, more rapidly with frequent irrigation until mid-summer, than those chilled for 9. In addition there was and most of them grew vigorously during this no observed effect of position in the seedling period. From mid-summer until early fall, the crown upon rate of bud break. seedlings were subjected to moderate mois- Each set of seedlings was harvested after ture stress, which induced well-formed buds 9 wk in the above environment, and the num- by mid-August (Duryea, 1984). ber of active buds and oven-dry weight of chosen for initiation of Mid-October was new foliage were recorded. Because care chilling because it was late enough to satisfy was taken during planting to prepare pots seedling requirements for short, mild days with equivalent seedling populations, it is as- prior to chilling (Lavender and Stafford, 1985) sumed that these data reflect seedling vigor and early enough to avoid natural chilling of rather than seedling size and bud number. seedlings. Previous studies (Lavender et al, The data were analyzed in a factorial 3- 1970) have shown that Douglas-fir seedlings way analysis of variance (Snedecor and cultured under natural conditions are in the Cochran, 1967) whose main effects were mid-rest period of their annual growth cycle chilling temperature, chilling period, and at this time and, hence, have a maximum re- seed source. Because only 1 growth room for exposure to temperatures ca quirement to prepare them for resumption of active was used for each chilling temperature, 5°C there was no true statistical replication of this growth in the following spring. Sixteen pots 1 factor. Therefore, we only considered from each seed source (64 pots in all) were differences significant at P ≤ 0.01. We also placed in each of 3 growth rooms. These developed multiple linear regression models rooms were maintained at constant tempera- with either number of active buds or foliage tures of 5, 7, and 9°C with 8 h daily photo- dry weight as dependent variables and chil- periods (125 μmol of light flux from a 5:1 ling temperature and period as independent mixture of fluorescent and incandescent lights). Pots were irrigated fortnightly to main- variables. tain soil moisture near field capacity. After 9 wks of chilling, and every 2 wks thereafter, 4 pots per seed source were RESULTS moved from each chilling room to a 4th that was maintained at a constant temperature of 15°C and a 12-h daily photoperiod Chilling temperature, chilling period (250 μmol of light flux from fluorescent light- and seed source all had significant ef- ing). The foregoing photoperiod was chosen fects on the measured growth parame- because, unlike the 16-h photoperiod which ters. For example, the "F" values for the has been employed in other studies of dorm- ancy of Douglas-fir, this daily photoperiod total weight of new foliage shown in does not compensate in part for the chilling tableI are 44.249 for chilling tempera- requirement and hence does not stimulate ture, 404.182 for duration of chilling bud growth on seedlings which have re- and 15.304 for seed source, respec- ceived little chilling. Moisture in these pots tively. Bud activity and foliage dry was maintained near field capacity, and seed- lings were examined weekly. Buds that had weight, for each seed source and aver- broken (ie whose needles had emerged all seed sources, were aged over through the bud scales) during the preced- in the longest and coldest chil- greatest ing week were marked at the base with a ling treatments (table I). Although this small dot of colored paint (1 color for each trend was true for all seed sources, examination date). This procedure was fol-
grown from seed collected in seedlings linear regression models, adjusted for with warmer winters generally differences in seed source, explained areas 75% of the variability (R 2 0.75) in the produced the greatest number of buds = and the most foliage (table II). Multiple number of active buds and 86% of the
Most Oregon, Washington, variability (R 2 0.86) in foliage dry success. = and British Columbia nurseries that now The relative importance of the weight. receive only Douglas-fir seedlings experimental variables is reflected by grow natural chilling hours each slightly more the "F" value above. year than the seedlings require. Be- cause methods of harvest, shipping, DISCUSSION and planting definitely affect seedlings’ respond to chilling (Lavender to ability Although coastal North American winters 1985), we may expect and Stafford, are now sufficiently cold and long to poorly conditioned nursery stock to be satisfy the chilling requirements of in- increasingly at risk in the coming years digenous Douglas-fir, a small tempera- if global temperatures do rise. How- ture rise in the warmer portions of its nurseries, ever, bareroot and container range might have profound effects. Long- subjected to cold whose stock is term weather records from the Oregon satisfy seedling chil- storage in order to Coast and Cascade Ranges indicate ling requirements, might not be directly December, January, and February mean in- temperature affected by mean temperatures of 5-8 °C for the that area creases. includes seed zones 071-0.5 and 072-0.5 Cannell and Smith (1984), studying of the present study (Simonson, 1963); if Sitka spruce planted in Great Britain, mean winter temperatures of these areas suggested that another effect of warming were to increase by the predicted 3- climates is increased seedling suscepti- 4 °C, the average winter climate would bility to damage from late frosts. Al- probably be too warm for adequate chil- though a similar situation may be ling of Douglas-fir. This hypothesis is obtained for Douglas-fir, we know of no supported not only by the differential data which substantiate this hypothesis. ability of the tested temperatures to and there- long-lived is Douglas-fir satisfy the chilling requirements, but also a whose bud- fore slow-evolving species by the effect of duration of chilling. The burst is under strong genetic control data we have used to characterize the (White et al, 1979), and it is thus un- natural climate is based on the average likely that its chilling requirements temperature for the coldest 3 months. As would be substantially modified within the climate warms, the duration of low the 100-year period over which global temperatures will shorten so that Dou- warming has been predicted. Because glas-fir will be affected by both higher our results suggest that chilling require- minimum temperatures and briefer dura- ments of this species are not greatly in- tion of same. Copes (1983) reported that fluenced by the winter climate of the grafted Douglas-fir coastal clones from seed source (in a subsequent experi- Oregon either died or demonstrated very ment we observed similar chilling re- weak shoot growth after being trans- quirements for seedlings raised from planted to the Monterey coast in Cal- seed collected in the State of Washing- ifornia, and suggested that the reason ton), it may prove difficult to reduce was average monthly winter tempera- those requirements through forest-tree satisfy tures (9.3-12.2 °C) are too high to breeding techniques. The prospect of the trees’ chilling requirements. global warming thus presents the immediate concern Perhaps of more possibility of a loss in the adaptive syn- predicted to foresters is the effect of the chrony between growth initiation and reforestation global warming trend on
seasonal temperature. Further, the pre- requirement, bud activity, and foliage new production. Can J For Res 15, 309-312 sent climate of the Douglas-fir region is McBeath JH, Juday GP, Weller G (1984) The characterized by wet winters and dry potential effects of carbon-dioxide-in- summers - over 85% of the annual pre- duced climatic changes in Alaska. School cipitation commonly falls between Oc- of Agriculture and Land Resources Man- tober and May. If then, the less efficient agement, University of Alaska-Fairbanks, chilling of Douglas-fir occasioned by Fairbanks. Misc Publ 83-1, 208 p the predicted increased mean tempera- Rind D, Lebedeff S (1984) Potential climatic impacts of increasing atmospheric CO 2 ture results in a delay of growth initia- with emphasis on water availability and hy- tion in the spring, such delay could drology in the United States. Environmental result in growth severely restricted by Protection Agency, NASA Goddard Space late spring and summer drought. Flight Center, NY, 96 p Seidel S, Keyes D (1983) Can we delay a greenhouse warming? Environmental Pro- REFERENCES tection Agency, US Government Printing Office, Washington, 215 p Cannell MGR, Smith RI (1984) Spring frost Simonson GH (1963) Temperature and the damage on young Picea sitchensis 2. water balance for Oregon weather sta- Predicted dates of budburst and prob- tions, Spec Rep 150. Oregon Agric Exp ability of frost damage. Forestry 57(2), Stn 127 p 177-197 Slocum RW (1985) Major climate changes Chandler WH (1957) Deciduous Orchards. likely, say scientists. J For 83, 325-327 Lea and Febiger, Philadelphia, PA. 492 p Smith WH (1985) Forest quality and air quality. Colville FV (1920) The influence of cold in J For 83, 82-92 stimulating the growth of plants. J Agric Snedecor GW, Cochran WG (1967) Statisti- Res 20, 151-160 cal Methods. Sixth edition. Iowa State Cooper AW (1984) Ecological and en- University Press, Ames, IA. 593 p vironmental threats to forests of the fu- Van den Driessche R (1975) Flushing re- ture: a global appraisal. Proc Soc Am For sponse of Douglas-fir buds to chilling and Bethesda, Maryland, 84-90 to different air temperatures after chilling. Copes DL (1983) Failure of grafted Douglas- British Columbia Forest Service Research fir planted at Monterey, California. Tree Division, Victoria, BC. Res Note 71, 22 p Planters’ Notes 34(3), 9-10 Weinberger JH (1967) Some temperature re- Doorenbos J (1953) Review of the literature lations in natural breaking of rest of on dormancy in buds of woody plants. peach flower buds in the San Joaquin Meded Landbouwhogesch Wageningen Valley, California. Proc Am Soc Hortic Sci 53, 1-24 91, 84-89 Duryea ML (1984) Nursery cultural practices: Wells SP (1979) Chilling requirements for op- impacts on seedling quality. In: Forest timal growth of Rocky Mountain Douglas- Nursery Manual, Production of Bareroot fir seedlings. USDA Forest Service, Seedlings (Duryea ML, Landis TD, eds) Intermountain Forest and Range Experi- Martinus Nijhoff/Dr W Junk, The Hague, ment Station, Res Note INT-254, 9 p The Netherlands, 143-164 White TL, Ching KK, Walters J (1979) Effects Lavender DP, Hermann RK, Zaerr JB (1970) of provenance, years and planting loca- Growth potential of Douglas-fir seedlings tion on bud burst of Douglas-fir. For Sci during dormancy. In Physiology of Tree 25(1), 161-167 Crops (Luckwill LC, Vutting CV, eds) Aca- Wommack DE (1964) Temperature effects on demic Press, London, 209-221 the growth of Douglas-fir seedlings. PhD Lavender DP, Stafford SG (1985) Douglas-fir dissertation, Oregon State University, seedlings: some factors affecting chilling Corvallis, 176 p