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Some Site Factors Affecting the Success of Reforestation and Afforestation Activities in the Willamette Valley Foothills¹

ABSTRACT

The majority of the land in the low-lying hills adjacent to the Willamette Valley is not suited for agriculture due to the nature of the soils and topography, and supports a cover of Douglas fir, mixed Douglas-fir-Oregon white oak, and oak stands. Scattered through the area are non-forested openings supporting grass or grass and oak. The soils are clay loam or clay textured derived from basalt, shales, and sandstones with some alluvial fan soils on the lower foot slopes. Summer rainfall is negligible and humidities are generally low during the growing season.

This paper reports some preliminary findings of the studies of soil moisture relations and the physical factors affecting them on several areas where reforestation or afforestation has been attempted. Soil profile descriptions are given, and results of laboratory analysis including mechanical analysis, bulk density, range of available moisture, and nutrient status are also reported. Several seasonal soil moisture curves are presented. The results of the study suggest that the narrow range of readily available moisture, i.e., water held at low tensions, in many of the soils of this area is responsible for the difficulties encountered in the attempts at reforestation and afforestation.

¹ Contribution from the Department of Soils, Oregon State College, Corvallis. Approved for publication by the Director of the Oregon State College Forest Exp. Sta. Presented before Division V-A, Soil Science Society of America, St. Paul, Minn., Nov. 11, 1954.

² Associate Forest Soils Scientist, Oregon State College. The author wishes to thank Professors G. H. Barnes and H. I. Nettleton for furnishing information and plantation survival data on the study areas, Mr. R. C. Roberts for providing soil descriptions for two of the areas, and Messrs. G. L. Lowry and C. T. Dryness for aid in portions of the laboratory work.

Received for publication October 16, 1954.