Hawaii as a Natural Laboratory for Research on Climate and Plant Response1
E. J. BRITTEN 2
THE INTERPLAY of genetic and environmental phasis has been placed on agricultural meteorol forces has resulted in the process of evolution. ogy in an attempt to refine studies on this phase The distribution of indigenous plants is a prod of the plant's environment. Sprague (1959) and uct of the genetic make-up of the successful in others have shown the importance of micro vaders of a particular area and the total physical climate in understanding the plant's develop and biological environment of that area. Native ment. plants have achieved a point in which their Experimental work on the relationship of the genetic constitution is in a certain degree of genotype to its environment points up the mag harmony with their environment. Plants in ex nitude of the problem. Probably more such treme latitudes, for example, have a genetic con studies have not been made because of the dif stitution which few, if any, tropical plants pos ficulty of obtaining adequate comparative data. sess and so are able to withstand the low tem The interest in methods of obtaining controlled peratures. The successful cultivation of eco environment for research on plant growth and nomic plants is in even greater measure depend reproduction attests to the need for this type of ent upon the harmonious interaCtion of the information. plant's genes and its environment. One of the Two general methods may be used to obtain most important components of the plant's en data on this problem. First, plants may be grown vironment is climate. in the field, and, second, they may be grown Adaptability studies of plants have been of under controlled environment conditions. Field major concern to research workers from the studies usually provide greater size and number standpoint of both genetics and physiology. of plants in a test and require small capital out Clausen, Keck, and Hiesey (1940) and Clausen lay. In a controlled environment greater preci and Hiesey (1958) have emphasized the role of sion of climatic regulations may be obtained interaction of environment with particular geno plus a greater number of treatments. A combi types; Went (1957) has demonstrated the prac nation of both methods gives the most useful ticability of greenhouses with close environ information, since field studies may then be mental control. confirmed by laboratory methods but few loca Research workers concerned with crop pro tions provide sufficiently different conditions in .duction have been studying adaptability in an the field for studies of this kind. Also, installa attempt to find the best phenotype for a par tions on the scale of the Phytotron at the Cali ticular environment. Plant breeders try to create fornia Institute of Technology are beyond the highly adapted phenotypes. Recently much em- resources of most institutions. This study demonstrates that the Hawaiian 'Published with the approval of the Director of Islands by virtue of their diverse climatic zones the Hawaii Agricultural Experiment Station as Miscel present a natural laboratory for studying effects laneous Paper 132. Manuscript received May 6, 1961. of environment on plant growth and reproduc Acknowledgment is made to Mr. Saul Price and other personnel of the US. Weather Bureau, to Mr. James tion. The data reported, for the most part, are Lindsey and other personnel of the Haleakala National concerned with the physical environment, tem Park, and to personnel of the Haleakala Branch Sta perature, and rainfall. Concurrent studies were tion. The work was supported by Western Regional made of growth and reproduction of Trifolium Technical Committee W-58. Experimental sites were repens. These findings will be reported in other kindly made available by Haleakala Ranch Company. 2 Associate Agronomist, Hawaii Agricultural Exper papers for which this paper will serve as a ref iment Station. erence for the data on physical phenomena.
160 Climate and Plant Response-BRIlTEN 161
There are many stations in Hawaii reporting RESULTS AND DISCUSSION to the U. S. Weather Bureau (USWB) most of Temperature which report only rainfall. Temperature stations are, for the most part, in the low elevations. The seven major islands in the Hawaiian Relatively little data are available at the inter group represent the eroded peaks of volcanoes mediate and higher elevations. All Hawaiian which extend from great ocean depths. Two of temperature data reported herein are from origi them, Maui and Hawaii, have peaks over 10,000 nal data except those at the 10,000-ft elevation ft above sea level. Differences in time since ces on Maui. Air temperature data at sea level, sation of volcanic activity and in amounts of 2,000, and 7,030 ft have been extended by data rainfall on different islands have caused great from the USWB in order to increase the length topographical differences. The islands range of time of observations. All soil temperature from land areas with relatively smooth contours, data are original. Air temperatures at 3,500 and in one case still actively growing from vulcan 5,000 ft on Maui are reported for the first time. ism, to highly dissected mountain masses with The importance of islands in the study of deep canyons and shore cliffs several thousand biological phenomena has been emphasized by feet high. Darwin (1839) and his contemporary, Wallace Geographically, the islands are just within the (1881). In Hawaii Ripperton and Hosaka northern belt of the tropics, ranging from ap (1942) have reported the effects of climate on proximately 19° to 22° 15' N. They are sepa vegetation zones. A bibliography on Hawaiian rated from the nearest continent, North Amer ica, by 2,400 miles-thus are probably as little rainfall was published by Taliaferro in 1959. A under the direct effect of other land masses as summary of the climate of Hawaii was pub any other land area of the world. lished by the U. S. Department of Agriculture The location within the Tropical Zone plus in 1941. the insular condition give the islands tempera MATERIALS AND METHODS tures which at sea level are warm throughout the year. Excessively high temperatures are not Air temperatures were obtained at the experi encountered because of the maritime conditions. mental plots from USWB maximum and mini The highest recorded temperature at Honolulu, mum thermometers read daily or, at remote sta which is just above sea level, is 90 F. Increase in tions, from thermograph tracings. The thermo elevation tends to be accompanied by a decrease graphs were checked periodically against a in temperature of approximately 3 F for each thermometer and at most stations a maximum 1,000 ft. From the mean annual temperature of and minimum thermometer was read weekly for 75 F at Honolulu to that of a station at 11,000 further check. A series of temperature readings ft on Mauna Loa on Hawaii, the temperature range corresponds to that from the southern was made by exposing a thermometer at 500-ft tip of Florida to a point midway in Maine intervals of elevation while driving to the ex (0. S. Dept. Agr., 1941). perimental plots. Corrections for diurnal varia Mean annual temperatures do not present a tions which occurred during the time of travel complete picture of temperature relationships were made by examination of thermograph as far as plant growth is concerned, as they fail tracings at three stations along the route, and to show diurnal and seasonal fluctuations. Mean by adjusting the temperature to 10:00 AM. monthly temperatures at different altitudes are Elevations were obtained by an airplane alti given in Figure 1. Mean temperatures rather meter. Alti~eter readings were checked against than mean maxima and minima are shown so locations of known elevation. that all may be placed on one graph for com Soil temperatures were read from soil thermo parison. It is possible to select the approximate graphs (either Friez or Dickson "minicorder") temperature desired by selecting the altitude. with the sensing bulb 3 inches below the sur Mean monthly maxima and minima are given face of an adapted grass cover. Instruments were for a number of locations in Figures 2-8. Figure housed in standard USWB shelters. 2 compares the mean maximum and minimum 162 PACIFIC SCIENCE, Vol. XVI, April 1962
90 during the summer but lower in the winter. The air minima are consistently less than those of the soil. Air temperatures at 3,500 ft (Fig. 5) are 80 cooler than at 2,000 ft, but the range is similar. HONOLULU No soil thermometer was available for this loca lJ..: o 70 tion. The range of temperatures at the 5,000-ft w ,.0--0--0---0--0...,.. station (Fig. 6) is about the same as at 2,000 a:: 2000 .-0--....0--,..-0-'-0- 1"""0-1"""'000.., "0 => .:.0--0---<1"" .....,...'.....,....0.·0. " and 3,500 ft, but again the temperatures are ~ 60 3,eoo .....,...' o' o. '", a:: 1"'-0-1-0-\ o' ...0-... 0 •• 0 lower. Air minima are consistently lower than w eooo 0" .....,....--0-. .. Q. .! Q •• o·.-tT"" "o.....~.""O-... 0 those of the soil. The lower air temperatures ~ 7,030 ./' .-0''''0 may be explained by the cooling of the air to a ~ 50 '~.~ ..-o"'--o"'~'.'" ,,0.., '0"'-0... greater extent than that of the soil because of . ]0,000 /," "0 """"0 ..• --1)"- faster radiation. The condition might be inten 40 sified by drainage of air from higher elevations, thus lowering the air temperature but having relatively little effect on the soil. 3 2 ...~F:--M..L--A'-""M:--..LJ-J'-""A-~S~O~""N:-::'D J The pattern of air and soil temperatures at MONTHS 7,030 ft (Fig. 7) is marked by the greater range FIG. 1. Mean monthly air temperature of six loca between maxima and minima of both air and tions varying in elevation from Honolulu at sea level soil and the higher temperature of the soil than to summit of Haleakala at 10,000 ft. Incteasing ele of the air. The soil maximum is actually greater vations bring progressively lower tempetatutes. Selec than that of soil at 5,000 ft probably because tion of temperature desired may be made by choice of elevation. Note relatively uniform tempetatures at the 5,000 ft elevation station is within the cloud each station throughout year. zone and so may not receive as much direct sun as at the higher station, at the upper edge of the cloud zone. temperatures of a station at 2,000 ft and one at 7,030 ft. There is some overlapping of tempera m 2,000 FT. ture bands. If a comparison is made between m 7,030 FT. Honolulu near sea level and the station at 7,030 80 ft (Fig. 3) there is no overlapping when means u.: are compared, but there would be overlapping o of extremes. Range between maximum and w minimum increases with altitude. a: => The temperature of the air is usually meas I (II] HONO~U~U Island temperatures fluctuate less than those I;S:'l 7,030 FT. in continental areas. The mean diurnal change 80 in Honolulu is 9.3 F (USWB, 1960a). The mean maximum of Sep, the warmest month, is 82.9 F lL and for both Jan and Feb, the coldest months, o 70 is 76.4 F. The difference between maximum of w a: the coldest and the warmest months is then only :::> I- 6.5 F, which is less than the diurnal change. o--AIR 80 0-__ AIR MEAN 80 ---- SOIL --- SOIL MEAN lJ..: 0 70 lJ..: w • 70 a:: w ::l a:: ti ::l a:: 60 w ",.,CJI"*_O_-o...... o__ a::ti 60 Q. 0_-°'" 0__0 w ~ ...... Q. w 50 _0__0 --° ~ t- ~·50 4 __0 --0 --°_ " -0-_0-....; 0--0/ 40 L---'------L_..L--L---'_-'---'-_'----'------L---J JFMAMJJA SON D ..... _- "" 40 J FMAMJJASON D MONTHS MONTHS FIG. 5. Air temperatures, maximum, minimum, and mean ar 3,500-ft station. Temperatures are lower than FIG. 7. Air and soil temperatures at 7,030-ft on at 2,000 ft. No soil thermograph was available. Period Haleakala. Soil temperatures exceed air temperatures of record, 2Yz years. and range between maxima and minima is greater than at lower elevations. Period of record, 2Yz years. Because of relatively small horizontal distances The most frequently encountered inversion was in Hawaii, it is possible to plot temperatures between 5,000 and 5,500 ft. In twO instances against altitude within a reasonable time. Air inversions occurred between 1,500 and 2,000 ft. temperatures are shown for twO different dates The records confirmed previous reports that for in Figures 9 and 10. To compensate for diurnal each 1,000 ft increase in altitude, a drop of changes in temperature which occurred during approximately 3 F occurred. This figure repre the drive, thermograph tracings for stations on sents the total drop including the inversion the route were examined. Appropriate correc layer. The location of the inversion layer may tions were then made to the original readings often be identified by clouds (Fig. 11). to adjust all temperatures to 10:00 AM. In the Comparisons of temperatures in Hawaii with twO instances given, temperature inversion oc those of certain continental locations are in curred between 4,000 and 4,500 ft in one case structive. The headquarters of the Haleakala and between 6,000 and 6,500 ft in the other. National Park at 7,030 ft and 20° 46' latitude 80 70 O--AIR 0-__ AIR MEAN lJ..: -SOIL 0 --- SOIL MEAN w 60 a:: ::l ti a:: 50 w Q. ~ w t- 40 40 L-...... l_...... L___''---'---L.--L_~....l_...... L___'-..J 30 L-...... l---'-_L-...... l---I-_L..-....l---I-_L..-....L---' JFM A MJJA SON D JFMAMJJASOND MONTHS MONTHS FIG. 6. Air and soil temperatures at 5,000-ft on FIG. 8. Air temperatures near summit of Haleakala Haleakala. Temperatures of both air and soil are very at approximately 10,000 ft. Temperatures are lower similar except that air minima are consistently less than at lower elevations. Period of record, 3 years. than minima of soil. Period of record, 2 years. Data courtesy USWB. Climate and Plant Response-BRITTEN 165 has the same annual mean temperature (54 F) sides adapted perennials there is a profusion of as Beltsville, Maryland, at 120 ft and 39° 40' annuals. The Hawaiian mountain flora, on the latitude (USWB, 1957, 1960b). Graphs show other hand, is predominantly perennial. ing mean montHly maxima and minima for the two locations are in Figure 12. The Beltsville RAINFALL station has colder winters and warmer summers The rainfall pattern in Hawaii is extremely than its Hawaiian thermal counterpart. The complex. Rainfall in different localities ranges cooler summer of the Hawaii station indicates from less than 10 to 456 inches on a mean an that it is more favorable to plants adapted to nual basis. Rainfall is determined by exposure cool conditions than is Beltsville, nearly twice to the prevailing wind, elevation, and local top the distance from the equator. Experiments ography. During the major part of the year, the with white clover (Trifolium repens) have northeast trades are the main factor governing shown that at 7,000 ft in Hawaii growth is vir precipitation in most parts of the islands. Areas tually stopped for about 2 months in the winter exposed to the trades, if backed by high moun but except for some damage to the edge of the tains (10,000 ft or more), receive heavy rain leaves, the clover remains green and flowers fall. Conversely the lee sides of such mountains continuously. Summer growth is excellent. Frost (and any other smaller island to the leeward) is frequent in the winter but snow never falls. may be very arid. From 9,000 ft to the summit at 10,025 ft snow may sometimes cover the ground but does not 10,000 10,000 persist. On Hawaii, with two peaks over 13,000 ft snow frequently occurs and may last for days. Because of relative inaccessibility, low rainfall, 9,000 9,000 and lack of soil, the higher elevations have not been used for plant research. 8,000 8,000 The 7,030 ft Hawaiian location and a con tinentallocation at about the same elevation are I- W compared in Figure 13. Marshall, Wyoming, has w 7,000 7,000 I.L an elevation of 7,010 ft and latitude of 39° 03'. Z The mean annual temperatures differ markedly, 6,000 being 54 and 38 F (USWB, 1955, 1960b) for z 6,000 2 the Hawaiian and Wyoming locations, respec I- ~ tively. Despite the higher mean annual tem w 5,000 5,000 ..J perature of the Hawaiian station, the summer W maximum in Wyoming is actually higher than the maximum in Hawaii at the same elevation. 4,000 4,000 This indicates that even though Hawaii is in the Torrid Zone, at the higher elevations low 3,000 3,000 temperatures may be more limiting for growth than are places within the Temperate Zone. These differences between the two locations 2,000 2,000 are reflected in the plant life of the two areas. 1,5001---JL...-J'-lI---J 1,5 00 ~""""'L...LJ---J The temperate zone station is characterized by 50 70 90 50 70 90 extremely cold winters and relatively warm TEMP. 0 F TEMP. OF summers. Perennial plants in such an area must FIGS. 9, 10. Air temperatures at 500-ft intervals, possess genes for cold resistance. Perennials in Haleakala, Maui. Temperatures adjusted to 10:00 AM. Hawaii do not need the genes to withstand a Fig. 9 (left) data obtained on Sep. 24, 1959. A tem rigorous winter. But there is not the same heat perature inversion was encountered between 6,000 energy in the Hawaiian high-altitude summer 7,000 ft. Fig. 10 (right) data were obtained on Jan. 29, 1959. A temperature inversion was found above which proves so favorable for annuals in the 4,000 ft. An average 3 F drop in temperature occurs mountains of the Temperate Zone, where, be- for each 1,000 ft increase in elevation. 166 PACIFIC SCIENCE, Vol. XVI, April 1962 FIG. 11. Few locations afford an opportunity to observe a mountain stretching from sea level to 13,796 ft elevation, as in this photograph of Mauna Kea on Hawaii. The inversion layer is marked by the line of clouds. Where the mountains are not as high (i.e., come visibly greener block by block as one goes less than 5,000 ft), the rainfall on the windward up the valley. side is not as heavy at the base as on the high The rainfall pattern on Haleakala, Maui (Pine mountains. Rain increases toward the crest, and apple Res. Inst., 1955), a 10,025 ft mountain, is swept over the summit and down the lee side. is simpler. Topographical and rainfall contours Lee slopes therefore receive heavy precipitation (isohyets) are given in Figure 14. The seacoast which falls off rapidly with distance from the area, being in the direct path of the trade winds, peak. Honolulu is on the lee side of a low records precipitation of about 125 inches. Rain mountain range. Rainfall on the windward side fall at this location increases rapidly with ele at sea level is 40 inches; at the crest it is over vation until maximum amounts of 400 inches 200 inches. Rainfall at the head of the lee val are received at about 3,000 ft. From this point, leys is over 100 inches. At the head of the val rainfall falls off rapidly so that at the summit ley in which the University of Hawaii is located it is less than 30 inches. Here rainfall increases it is 150 inches; at the lee shore, about 5 miles then decreases with altitude. However, the iso from the mountain ridge, it is about 25 inches. hyets describe ever enlarging ellipses as they The vegetation on the adjoining ridge parallel approach that part of the mountain which is to the valley changes from the arid type of somewhat sheltered from the prevailing winds prickly pear cactus and associated plants to rain but not yet in its lee. The rainfall tends to be forest within a distance of 2 miles. Lawns be- constant from sea level to near the summit. Climate and Plant Response-BRITIEN 167 Therefore, in this region, indicated by the ar 80 rows (Fig. 14), rainfall tends to be constant while temperature tends to decrease with alti tude. This situation is of interest since one 70 variable is changed at a time. The foregoing discussion refers to annual ~60 means. It is apparent that at anyone time there w may be a departure from the mean which mayor a:: may not be significant. There are also seasonal ~ 50 ~ differences. In parts of the islands sheltered a:: from the trades, winters tend to be wetter than w ~40 summers. w Important in studying plants in relationship I- to their environment is accessibility. On Maui 30 paved roads extend to the summit (10,025 ft). On Hawaii automobiles may be driven to 9,000 ft and 4-wheel-drive vehicles to the summit of 20 Mauna Loa (13,680 ft). 10 90 0 J F M A M JJ A S 0 N D 80 MONTHS FIG. 13. Air temperatures at 7,030 ft, Haleakala, 70 Hawaii (broken line) compared with a location of similar elevation (7,010 ft) in Marshall, Wyoming (solid line). Winter temperatures in Temperate Zone ~ 0 60 station are extremely low compared with Hawaii. W Even though both stations are at same elevation and ll:: ~ Hawaiian station is within Tropical Zone, summer t 50 maxima are greater for Temperate Zone station than ll:: for Hawaiian location. Period of Marshall record, 20 W Q. years. :::?; w 40 to- Experiments utilizing the unique conditions 30 of the Hawaiian Islands have been described by Britten (1960, 1%1) who has investigated the HAWAII 7030 FT. role of genotype and temperature in flowering 20 BELTSVILLE, MD. of Trifolit-tm repens. The combination of a nat ural field laboratory and controlled environment facilities offers an opportunity to study funda 10 J F M A M J J A S 0 N D mental and applied problems of plant growth MONTH S and reproduction. FIG. 12. Air temperatures at 7,030 ft, Haleakala, SUMMARY Hawaii, and Beltsville, Maryland. Both stations have same mean annual temperature. Wincer temperatures The Hawaiian Islands are in the northern at Beltsville are much lower than at Hawaii location fringe of the tropics. Elevations range from sea and summer temperatures correspondingly warmer. level to over 13,000 ft. Mean annual tempera Beltsville station is about twice the distance of Hawaii location from equator. Period of record: Beltsville, tures associated with differences in elevation 5 years; Haleakala, 15-18 years. compare with those ranging from southern 168 PACIFIC SCIENCE, Vol. XVI, April 1962 Florida to Maine. By selection of elevation, de REFERENCES sired temperature conditions may be secured. The unique conditions obtained by a high oceanic island can be utilized for research on BRITTEN, E. J. 1960. Genetic and environmen plant response to climate. tal control of flowering of Trifolium repens Details of air and soil temperatures are given in the tropics. Science 13: 100-101. for different locations at different elevations. --- 1961. The influence of genotype and Comparisons are made between two Temperate temperature on flowering in Trifolium repens. Zone stations with a location in the islands. Agron. Jour. 53: 11-14. Rainfall patterns are discussed and attention is drawn to a situation where rainfall remains con CLAUSEN, JENS, DAVID D. KECK, and WILLIAM stant but temperature changes with elevation M. HIESEY. 1940. Experimental Studies on from sea level to high elevation. Utilization of the Nature of Species, 1. Effects of Varied such conditions in conjunction with controlled Environments on Western North American environment cabinets makes possible integration Plants. Carnegie Inst. of Washington Publ. of field and laboratory experiments. 520.452 pp. o 5 I MILES I FIG. 14. Map of Maui. The 10,025-ft mountain, Haleakala, forms southeastern part of island. Topographi cal contours are shown as solid lines and mean annual rainfall contours (isohyets) as dotted lines. Figures for elevations are shown in thousands of feet and for rainfall in hundreds of inches. Rainfall figures for Haleakala only are given. Rainfall ranges from 10-400 inches in about 20 miles. In region denoted by arrows, rainfall is constant from sea level to approximately 6,000 ft. In this region, temperature varies with elevation while rainfall is constant. Rainfall data from Pineapple Research Institute, 1954. Climate and Plant Response-BRITTEN 169 --- and WILLIAM M. HIESEY. 1958. Ex u. S. DEPARTMENT OF AGRICULTURE. 1941. perimental Studies on the Nature of Species, 1941 Yearbook of Agriculture. Climate and IV. Genetic Structure of Ecological· Races. Man. Washington D. C. 1,248 pp. Carnegie Inst. of Washington Pub!. 615. 312 U. S. WEATHER BUREAU. 1955. Climatic Sum pp. mary of the United States. Supplement for DARWIN, CHARLES. 1839. The Voyage of the 1931 through 19'52. Wyoming. Washington . Beagle. New York. D. C. No. 42. 44 pp. PINEAPPLE RESEARCH INSTITUTE, and EXPER --- 1957. Climatic Summary of the United IMENT STATION, HAWAIIAN SUGAR States. Supplement for 1931 through 1952. PLANTERS' ASSOCIATION, in cooperation with Maryland and Delaware. Washington D. C. the U. S. Weather Bureau. 1955. Average No. 15. 33 pp. Monthly Rainfall Maps. 13 pp. --- I%Oa. Local Climatological Data with RIPPERTON, J. c., and E. Y. HOSAKA. 1942. Comparative Data 1959, Honolulu, Hawaii. Vegetation Zones of Hawaii. Hawaii Agr. Ash,eville, N. C. 4 pp. Expt. Sta. Bull. 89. 60 pp. --- 1960b. Climatological data, Hawaii. Annual Summary (1959) 55: 154-162. SPRAGUE, HOWARD B. 1959. Grasslands. Am. Ass. Advancement of Science Pub!. 53. 406 WALLACE, ALFRED RUSSEL. 1881. Island Life. pp. London. TALIAFERRO, WILLIAM J. 1959. Rainfall of WENT, FRITS W. 1957. The Experimental Con the Hawaiian Islands. [Mimeo.] Honolulu. trol of Plant Growth. Chronica Botanica 17. 394 pp. 343 pp.