Fig. 51. Permanent chart quadrat, Andosacile, Carex-Campanulacoryphium.
Fig. 52. Chart of the quadrat shown in figure 51. Legend: a, Androsace chamaejasme; c, Carex rupestris; t, Tetraneuris lanata; p, Potentilla rubricaulis; as, Arenaria sajanensis; ar, Artemisia scopulorum; ag, Agropyrum scribneri; sa, Silene acaulis; st, Sieversia turbinata; d, Dasyphora fruticosa; al, Allium reticulatum; o, Oreoxis alpina.
209. Mapping is invariably begun at the upper left-hand corner of the chart, and is carried across the strip marked off by the plotting tape, decimeter by decimeter. As soon as this strip is completed, a second one is formed by moving the top tape to a position one decimeter below the plotting tape, which then becomes the upper one. This is repeated until the last strip is reached. Little difficulty is experienced in locating each plant exactly, as the decimeter interval is small, and the centimeter square which corresponds is divided into twenty-five tiny squares. Each plant is put in whenever possible, but mats, turfs, and mosses are merely outlined in mass if the individuals are not distinguishable. This holds true of all large rosettes and mats, even when they are single plants. Symbols were formerly used for indicating the various species. They have the advantage of requiring little space on the chart, and the disadvantage of necessitating constant reference to the legend. They are at present replaced by initials. By this plan, the decapitalized first letter of the generic name is used if no other genus found in the quadrat begins with the same letter. If, however, two or more genera begin with a, for example Agropyrum, Anemone, and Allium, the most abundant one is indicated by a, and the others by the first two letters, as an, al. In case two species of the same genus are present, the species initial is used in connection with that for the genus, as ac and ar for Agropyrum caninum and Agropyrum richardsonii respectively. It is rarely necessary to exceed two letters for any species. Plants which regularly have several stems from the same root are indicated by the initial and an exponent as a3. Seedlings are represented by a line drawn through the letter. Usually the chart sheet affords sufficient space below the chart for the legend. When the list of species is long, the back of the sheet is used.
210. Factors and photographs. Each chart is numbered, and the formation, station, and date indicated. The constant factors, altitude, slope, and exposure are ascertained and recorded on the sheet. The variable factors are read in each quadrat whenever possible, and in addition to being preserved in the record book, are noted on the chart sheet along with the base reading in the formation for the same time. This facilitates the interpretation of the differences found when two or more charts are compared. Chart quadrats are regularly photographed. For this purpose a long focus 4 × 5 camera with a telephoto lens is used. At the proper distance this will make a view of the same size as the chart, thus making possible an exact comparison of the two. The chart and photograph serve as mutual checks, as well as complements, since the former shows number, position, and arrangement, and the latter, height, form, position, and arrangement. The view is usually made by placing the camera directly in front of the middle of the lower tape, at such a distance that the side tapes fall just within the limits of the ground glass. The swing is always used in order that the focus may be uniformly sharp. Surface views of the quadrat can be taken by means of a device which permits the camera to hang downward from the tripod, or by means of a tripod with a swinging platform. Such views are especially valuable for the study of competition, since they give a clear idea of the spread and density of the various plants. They are difficult to make unless the vegetation is low and nearly uniform in height. The usual photograph is much more serviceable in regular quadrat work.
The Permanent Quadrat
211. Description and uses. As stated heretofore, either list or chart quadrats may be rendered permanent in order that they may be followed from season to season or from year to year. As a matter of fact, however, an area which is to be studied repeatedly really demands charting, and in practice chart quadrats alone are made permanent. This is done simply by driving a labeled stake at one corner of the quadrat, and locating the latter definitely in relation to a conspicuous landmark. When one is in residence for several years, practically all chart quadrats are converted into permanent ones, since the work already done in the chart quadrat is so much accomplished towards the permanent one. This is not necessary when one wishes merely to compare different areas of stable formations. As a rule, however, some change is constantly being wrought by invasion or competition, and the amount and direction of this can only be revealed by the permanent quadrat. The latter has a fundamental value for all kinds of invasion, but it is absolutely indispensable in studying complete invasion or succession, and in discovering and recording the gradual effects of competition. It is in the detailed investigation of these dynamic phenomena that the paramount importance of the quadrat is most evident. If the experience of several years be taken as conclusive, no other method is capable of revealing the minute changes as they are occurring.
Fig. 53. Permanent quadrat, Polygonile (Polygonum bistortoides) Ruxton Park; mapped and photographed July 22, denuded September 8, 1903.