Carnegie Institution of Washington Publication Volume 217 (Paperback)

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1915 Excerpt: ... summer and winter is quickly exerted in an elevation of the soil moisture, but at the close of these seasons it is with relative slowness that the soil falls to low percentages of moisture, particularly at the highest altitudes. The minimum moisture content of the year is usually to be detected just before the first heavy rain of the humid mid-summer, but the content in September or October may sometimes be quite as low. At low elevations in the Santa Catalinas the annual march of soil moisture may be expected to be analogous to that which has been described by the writer for Tumamoc Hill, the site of the Desert Laboratory?' Marked differences will result from a comparison of the two localities, however, owing to the difference in the character of the soil. The very fine clay of Tumamoc Hill is conservative in its changes of moisture content, both with respect to increases and decreases of moisture. while the coarse loam found at the lower elevation in the Santa Catalinas possesses a greater permeability and a lesser holding power. The soils of elevations of 7,000 feet and more are richer in organic matter than those of the Desert and Encinal regions of the mountain, and are doubtless more like the clay of Tumamoc Hill in the smoothness of their curves of change in moisture content. The few readings of soil moisture content that have been made were directed toward a determination of the soil conditions in the most arid portion of the year. It is obvious that it is these annual minima which are of the greatest importance to plants, particularly to such plants as are near the lowest limit of their vertical occurrence. Much less interest attaches to the high moisture contents which might be found in the midst of the rainy seasons. It is true that these ...