Koelera-Andropogon-psilium
April 25, 1901. Clear. South wind.
April 25, 1901. Clear. South wind.
April 25, 1901. Clear. South wind.
TEMPERATURELIGHTHUMIDITYWATER-CONTENTWINDTIME P.M.3:203:243:303:353:403:453:55%2:403:05STATION1½ m.Surf.510151½ m.Surf.1½ m.Surf.510151½ m.Surf.1.27.829.617.815.810.9575917.714.617.47402802.26.531.318.316.612.8595917.912.214.311005103.26.928.518.214.213.5585916.516.9199805204.26.23016.813.211.6636624.421.324.89204605.2832.418.614.614.2596010.71717.210804906.2840.823.81615515158.310.310104107.26.430.816131168702724.321.468052
April 20, 1901. Clear. Southeast wind.
April 20, 1901. Clear. Southeast wind.
April 20, 1901. Clear. Southeast wind.
TEMPERATURELIGHTHUMIDITYWATER-CONTENTWINDTIME A.M.10:4010:4610:5010:5511:0012:0012:0511:1011:20%11:3011:45STATION1½ m.Surf.510151½ m.Surf.1½ m.Surf.510151½ m.Surf.1.16259.68.47.8.08.06738124.219.219.529802.16.230.58.58.47.8.11.0973862222.519.437523.16.217.87.67.88.08.06739522.120.421.664064.15.626.210.68.48.2.06.03819525.423.122.4275125.17.625.47.67.47.2.03.02909527.219.818.817826.16.220.28.476.2.02.01829027.620.818.811547.15.817.26.46.46.1.05.04829023.81919.3600
136.A battery of recording instruments consists of a selagraph, a psychrograph, and a thermograph, to which an anemograph is added when possible. As stated before, the determination of water-content by the geotome method is more satisfactory than by any automatic instrument yet devised. When the base station is located where the sunlight is unobstructed, which should be the case whenever possible, it is unnecessary to include a selagraph in those batteries placed in similarly exposed stations, since the light values will be the same. As a rule, batteries are established within different zones or different habitats, except where a highly diversified habitat is made the subject of special inquiry. Such a restriction arises from the fact that expense, care of operation, etc., place a limit upon the number of batteries,and, in such case, the task of primary importance is to establish the physical character of representative habitats. For these reasons, the first series of thermographs established in 1903 was located with respect to altitude, the instruments being placed at Manitou 2,000 m., Minnehaha, 2,600 m., and Mount Garfield 3,800 m. In 1904, the stations established for the record of temperature and humidity were situated with respect to habitats representing the four formations: gravel slide, half gravel slide, spruce forest, and brook bank.
The batteries are located and set up according to the directions already given. A 2–meter quadrat with the battery as the middle is staked and mapped. Within this, all readings of water-content, soil temperature, and physiographic factors are made. Altitude, slope, exposure, and cover are recorded when each battery is located, and a soil sample is taken for mechanical analysis. When the position of the batteries permits it, water-content readings should be made frequently, once or twice a week at least. In addition, a complete series of samples should be taken daily for a period sufficient to indicate the ordinary extremes of water-content.
The ecograph battery of each habitat constitutes a standard to which the results obtained by simple instruments may be referred with accuracy. It not only does this, but it also serves as a basis for interpreting the readings of simple instruments in distant habitats of the same character. In this way a few batteries judiciously placed make possible the exact physical investigation of a large number of habitats, covering a considerable area. The only limit, indeed, upon this method is that placed by time. The proportionate use of batteries and of simple instruments must be largely determined by the conditions which confront the investigator. It is obvious that, where expense is not a decisive factor, the gain in time and in completeness of results is enormously in favor of the battery. There is an additional value in the automatic and continuous record which can not be overlooked. When the use of instruments in the study of habitat and formation becomes universal, the importance of the ecograph will be immeasurably enhanced. It will be possible to secure duplicate records of batteries located in the most remote and diverse regions, from the equator to the poles, and comparative phytogeography upon a scientific basis will for the first time be possible. This opens an alluring vista of the future when ecologists the world over will cooperate in such a way that the results obtained by ecograph batteries anywhere on the globe will permit of exact comparison.
THE EXPRESSION OF PHYSICAL FACTOR RESULTS
137. The form of results.It is almost inevitable that the general adoption of precise methods of measuring the habitat will result in a common form for expressing the physical character of the latter. An actual diagnosis of each habitat is not a difficult matter, after the factors are carefully measured, and will unquestionably lead to very desirable definiteness and precision. The accurate investigation of the physical factors of a number of habitats for one growing season furnishes the necessary material for a diagnosis based upon the mean for the growing season. Similar results for two or three seasons will yield a diagnosis as accurate and as final as that of a formation, or, indeed, as that of many species. The author’s investigations have not yet gone far enough to warrant proposing a final form for this, but the following diagnosis is offered as a suggestion:
Elymus-Muhlenbergia-chalicium.Habitat: holard 9 per cent, chresard 8 per cent, relative humidity 40 per cent, light 0.6, soil colluvial gravel (gravel 70 per cent, sand 27 per cent, silt 3 per cent), air temperature 65°, surface 82°, soil 59°, wind 10 miles, rainfall 8 inches, altitude 2,800 m., slope 23°, exposure south, surface even, cover open, no active biotic agencies.
The detailed comparison of habitats is made most readily by the graphic method of curves, which constitute the most desirable form of expression in connection with the original record upon which they are based. Factor means are particularly desirable for diagnostic purposes, and they furnish valuable curves also. Factor sums are impracticable at present, and it seems doubtful that they will ever be of much value. It is by no means impossible, however, that a more detailed and exact knowledge of the physiology of adaptation, coupled with methods of precision in the habitat, will render them necessary.
138.Experience has shown that the practice of making hasty and often formless records in the field is unwise and is apt to be inaccurate as well. The time saved in the field is more than counterbalanced by that consumed in copying the results into the permanent form. The danger of error in field notes rapidly taken is very grave, and the chance of confusion and the waste of time in deciphering them are great. Moreover, the task of checking a copy with the original, which is absolutely necessary for accuracy, involves a further expenditure of time and energy. For these reasons the field record should be made in permanent form. Definite record sheets are used, and the invariable rule is made that all readings are to be noted in ink at the time and spot where they are taken. On a long journey, or in the face ofmany observations, the tendency to take notes or to record observations rapidly is very great, but this will correct itself after a few attempts to use such notes. The record forms for various factors have been indicated in the proper place, as well as the one for simultaneous readings. Ecograph sheets are carefully filed, and constitute permanent records. With a little practice they may be read almost as easily as tables, and any attempt to put them into tabular form is a mere waste of time. For purposes of study and of publication, it often becomes necessary to bring together all the results obtained for a particular habitat, both by simple instruments and by ecographs. The form of record used for this is essentially that already indicated for simultaneous readings on page92, since general features and constant factors can not well be included in the table. Record sheets of this type have been printed at a cost of $5 per thousand, and the various factor records can be obtained at about the same rate. The size of sheet used is 9½ × 7¾ inches. The record book is the usual notebook cover, which has been found neither too large nor too small. It is protected from dirt and rain by a covering of oilcloth which overlaps the edges. Record books should be carefully labeled, and each one should contain a single year’s records.
139. Plotting.The paper employed is divided into centimeter squares which are subdivided into 2–millimeter units. For ordinary curves the size of sheet is 9½ × 7¾ inches, which makes it possible for curve sheets to be filed in the record book. Tablets containing 60 of these sheets can be obtained for 20 cents each from the Central School Supply House, Chicago. For curves longer than 9 inches special sizes of sheets must be used. On account of their inconvenience large sheets are avoided whenever possible. This can usually be accomplished by increasing the numerical value of the intervals. The inks employed in plotting are the waterproof inks of Chas. Higgins & Co., Brooklyn, New York. These are made in ten or more colors, black, violet, indigo, blue, green, yellow, orange, brown, brick red, carmine, and scarlet, and cost 25 cents per bottle. In addition to being waterproof, they make it possible to combine curves in all conceivable ways without destroying their identity. Furthermore, it is a great advantage to use the same color invariably for the same kind of curve: thus, it has been the practice to indicate the 3–foot, surface, 5, 10, and 15–inch temperature curves by violet, green, yellow, blue, and carmine respectively. A fine-pointed pen, such as the Spencerian No. 1, is most satisfactory for inking; drawing pens, such as Gillott’s Crowquill, are too finely pointed for ordinary use.
In plotting a curve, it is first necessary to determine the value of the interval, and the extreme range of the curve or combination. For example, in the case of temperature, it is most convenient to assign a value of 1° Centigrade to each centimeter, since the thermometers used read to one-fifth of a degree, which corresponds exactly to the 2–millimeter units of each square. The length of the sheet permits a range of 22 degrees Centigrade, and the actual limits must be determined for the particular results to be employed. For the same region, it is very desirable that the unit interval and the range be the same, in order that all curve sheets may admit of direct comparison. Indeed, it is greatly to be hoped that in the future ecologists will agree to a uniform system of curve-plotting, cartography, etc., as the geographers are beginning to do in the construction of maps. The major intervals are written, or, better, typewritten, at both sides of the sheet, and the time or space intervals are indicated at the top. Each curve sheet is properly labeled, and essential data indicated. The readings are taken from the field record, and their proper positions indicated by a dot. These are connected first by a pencil line, the curves being made abrupt rather than flowing; and the line, after having been carefully checked, is traced in ink.
140. Kinds of curves.Curves are named both with reference to the factor concerned and the position or sequence of the readings. The factors which lend themselves most readily to this method of representation are the variable ones, water-content, humidity, light, temperature, and wind, and corresponding curves are distinguished. Altitude and slope may likewise be shown by means of curves, but the use of cross section or contour lines serves the same purpose and is more natural. With regard to time and position, curves are distinguished as level, station, and point curves. A level curve is one based upon readings made at the same level through a series of stations or of habitats, e. g., the level curve of surface temperature. The station curve represents the various levels or points at which readings are made in a single station. The point curve has for a basis the hourly or daily variation of a factor at a particular point or level in a station. All of these may be simple curves, when established upon a single reading for a series, or mean curves when they are based upon the mean of a number of readings. Curves which show the extremes of a factor, i. e., the maximum and minimum, are also extremely valuable, though a combination of the two for comparison is preferable.
141. Combinations of curvesare invaluable for bringing similar curves together, and permitting ready comparison of them. For this, and also because they save space, they are regularly employed to the almost completeexclusion of single curves. Combinations are made simply by tracing the curves to be compared upon the same sheet, it being understood that dissimilar curves, e. g., level and station, can not be combined. Colored inks are an absolute necessity in combining; the primary principle underlying their use is that curves that approach closely or cross each other must be traced in inks that contrast sharply. As elsewhere stated, it has been made the invariable rule to use the same color for the same level or point. This applies especially to temperature, but holds also for humidity, light, wind, and water-content, so that the color always indicates the level. For the same reason, it is applied to a combination of point curves for one station, though it is inapplicable to a series of point curves when these lie in the same level. Light readings above 6 feet and water-content readings below 15 inches necessitate the use of additional colors.
Combinations may be made of the curves of a single factor for purposes of comparison, or they may consist of curves of different factors in order to aid in interpreting or indicating their relation to each other. Curves of the same factor may be combined to form various series. The level series consists of all the level curves for the stations under observation, e. g., the six levels for temperature, three levels for wind, etc. Similarly, the station series is a combination of all the station curves, and a corresponding arrangement may be made for point curves with reference either to station or to level. An extremely valuable combination of curves is that of the holard and chresard for a series of stations. The most important combinations of the curves of different factors are naturally those based upon factors intimately related to each other or to the plant. The grouping of water-content and humidity curves is of great value, especially when the transpiration curve is added. Light and temperature curves make an interesting combination, while a humidity, temperature, and wind series is of much aid in tracing the connection between these factors. Finally, it is altogether feasible to arrange the curves of water-content, humidity, light, temperature, and wind upon the same sheet in such fashion as to give a graphic representation of the whole physical nature of a single habitat or a series. In all combinations of curves representing different factors, it must be borne in mind that the position of a curve does not represent a definite value with reference to the others, since some are based upon per cents, others upon degrees, etc. The comparison must be based upon the character of the curves, but even then it is an important aid. An instructive grouping has been employed where series of readings on the same day, or on two successive days in forest and in prairie have yielded the usual level series of curves. The series for the two habitats are arranged on the same page, one at the right and the other at the left, and permit directcomparison of corresponding level or factor curves, both with respect to position and character.
142. The amplitude of all the curvesdescribed above is determined by the unit values of the factors concerned, while the length is dependent upon the number of stations, points, or times. The value assigned the latter upon the plotting paper is purely arbitrary, but it is most convenient to fix this at the centimeter square. The unit value for temperature is 1° Centigrade per square, each subdivision of the latter representing 0.2, and the range being 22 degrees. For water-content curves, each square represents a value of 2 per cent, the smaller square being 0.4 per cent, and the range 2–48 per cent. The unit value for humidity is taken as 5 per cent, making each small square 1 per cent, and giving room on the sheet for the entire range from 1–100 per cent. Owing to the anemometer used, curves of wind velocity have been based upon the number of feet per minute. One hundred feet is taken as the unit value, and the range is from 0–2200 feet. The unit value for the curve of light intensity is .005. Each small square is .001, which permits a range from .001 to .01 on one sheet. Consequently, when it is desired to plot the curve of a series of habitats with a range in intensity greater than this it is necessary to use a double sheet. This is the usual device when the range of curves is too great, except where the excess is slight. In this case the curve is left open at the top, and the value which the crest attains is indicated. All curves in combination are labeled at the beginning or left to indicate the level, station, or point, and at the end or right to show the time, or day, if this is not the basis of the curve or series.
The discussion that precedes deals exclusively with curves representing factors determined in the field. It applies with equal force to results obtained by instruments in control houses. In these, however, all factors except those directly experimented with, usually water-content and light, are practically equalized, and the curves based upon them are used chiefly to show how nearly equal they have become. The important curves are those of the water-content series, both holard and chresard, and of the shade tents. Where several houses are differentiated with respect to temperature or humidity, curve series of both these factors are necessary.
143.It has been shown elsewhere that the daily mean of temperature can be closely approximated from the maximum and minimum of both day and night. Maximum-minimum instruments for the other factors are lacking, however, and for light, humidity, and wind these values can only be obtainedfrom the ecograph which makes it possible to get the exact mean from the sum of all the hour readings. When it comes to the seasonal mean, the ecograph is even more necessary, exception being made for water-content, in which case a number of readings on various days through the season will suffice. The value of factor means for diagnosis and for curves has already been sufficiently commented upon, and the feasibility of factor sums already indicated.