Precipitation and Tree Growth in the Harney Basin, Oregon

Abstract

PROBLEMS connected with water supply and its utilization commonly require more data on the general variations and trends of precipitation than is covered by the usual short-time climatological record. The use of tree-ring records in extending the short-time precipitation records is well known.1 An example in the form of a composite diagram was given in the January number of the Geographical Review in reference to the general problem of climatic trends in the submarginal lands of the western United States. A specific instance, obtained in the course of water-supply investigations in the Harney Basin, Oregon, is given herewith. One interesting feature of this analysis is the use made of the juniper, commonly regarded as offering difficulties to the investigator of tree-ring records.2 In this case the juniper was selected because the tree grows on the foothills close to the valley floor and at an altitude not far above that of the Harney Branch Experiment Station (4139 feet), where meteorological observations are made. The species of juniper growing in the Harney Basin tend to branch near the ground and the trunks of the mature trees to become lobate in cross section, so that they have flutings. In many trees the several lobes grow at somewhat different rates, so that the width of a particular annul ring may not be constant. Also, the older trees generally have extensive decayed sections, particularly at the heart or core. For these reasons a considerable number of trees were examined, but sections of only four were found satisfactory for study. These were full sections taken from isolated trees growing well above the bottom of any draw or depression and located as follows: