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The relationships between height increment of Scots pine (PINUS SYLVESTRIS L.), birch (BETULA PUBESCENS Ehrh.) and rowan (SORBUS AUCUPARIA L.) during one growing season to meteorological variables at 580 m above sea level in the northern Pennines were previously examined using orthogonalized regression analysis. The paper describes methods made to improve the efficiency of the models. Values of principal components of the meteorological variables of the current and preceding sets were associated with 76.5, 60.4 and 75.9 percentage of variability respectively, showing an improvement by allowing for lag effects in this way. Efficiency of using values of the original variables, with those of the preceding set, or with curvilinear terms, was generally less. Variation of response during the season was examined and was discussed in terms of plant behaviour.

The Black Hills occupy about 2,000,000 acres in western South Dakota and northeastern Wyoming. Geologically they consist of a sedimentary dome through which protrudes a central core of granite; northward the sandstone and limestone are pierced by several igneous cones. The sedimentary structure has eroded deeply in the eastern portion, but the western side remains fairly smooth except where cut by streams. The resulting topography changes from rolling slopes in the western limestone to a fringe of steep rugged canyons through which streams emerge at the foothills. The elevations vary from 3,500 to 7,200 feet above sea level. The climate is characterized by cold dry winters with moderate snowfall, hot summer days with cool nights, and highly variable precipitation. Of the 19-inch average annual precipitation, three-fourths occurs during the April to September growing season. Snowfall normally accumulates to a depth of two to three feet in the western limestone but tapers off toward the foothills until little accumulates except on the northern slopes. The average period between killing frosts varies from 150 days in the foothills to 90 days or less at the higher elevations. The characteristic ponderosa pine cover type is interspersed with frequent grassy parks and meadows, and broken elsewhere by temporary stands of aspen and paper birch. Farming is most common around the foothills, but within the hills there are many small dairy and stock ranches producing hay and small grains. Corn, wheat, barley, oats, and alfalfa are common crops in the foothills. Some 30,000 cattle and 25,000 sheep are grazed on the open range or in fenced pastures during the summer. Both white-tailed deer and mule deer (0. hemionus) are increasing rapidly, estimates showing 15,000 white-tailed and 5,000 mule deer. In addition there are some 500 elk (Cervus canadensis) outside of park enclosures. To stay within the limits of adequate sampling, this report covers only 500,000 acres in the northern hills of South Dakota.2 Compared to the Black 1 Game wardens, Pittman-Robertson staff members, and forest rangers of the Black Hills area assisted by collecting stomach samples. State Game Warden Dave Harris of Deadwood, South Dakota, gave wholehearted cooperation without which this study would have been impossible. 2 The timbered and brush areas east of the Wyoming-South Dakota boundary and north of the line between Townships 1 and 2 North, B. H. M., and almost wholly within the Black Hills National Forest.