Average precipitation for ten years 21.70 inches.
Rain or snow fell on 76 days; 91 days were cloudy; 49 days were partially cloudy; and the sky was clear on 149 days.
The above figures show that the climate is an extreme one, the winter season being cold and severe and lasting five months, while in summer a high temperature is often reached.
The western larch grows usually mixed with other conifers; and the number of accompanying species and the proportions of the admixture are very variable, being dependent on the climate and altitude, and on the quantity of moisture in the soil. Douglas fir is the most common companion of the larch, and Pinus ponderosa steps in where the soil is dry. Engelmann's spruce and Abies lasiocarpa descend into the larch forests, but never constitute any large element of it. Pinus monticola, Tsuga albertiana, and Abies grandis are often met with in small quantity at low altitudes in the larch forests of Montana; farther west, in the Priest River Forest Reserve, Pinus monticola is more abundant than the larch itself between 2400 and 4800 feet. Thuya plicata, in regions with a moist climate, forms a notable part of certain larch stands, often to the exclusion of the other species which usually accompany the larch.
The following notes on a few of the larch forests visited by me will illustrate some different types in Montana.
Near Missoula, in Pattie Cañon, which is a very dry valley at 3500 feet elevation in a rather arid climate, the larch only grows on the cool northern aspect, and is mixed with Douglas fir and Pinus ponderosa. An acre contained, of trees over a foot in diameter, twenty larches, four firs, and three pines. An average good larch tree measured 143 feet by 9 feet 7 inches; and a tree which we cut down, 14 inches in diameter, showed 211 annual rings, the sapwood being 1¼ inch in thickness and containing thirty-one rings.
On the southern end of Lake Macdonald, at 3500 feet altitude in a humid climate, I saw a fine stand composed almost exclusively of larch and Thuya plicata. The soil was glacial clay, very deep, and covered with a thick layer of humus. The
