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.