Search

We inferred climate drivers of 20th-century years with regionally synchronous forest fires in the U.S. northern Rockies. We derived annual fire extent from an existing fire atlas that includes 5038 fire polygons recorded from 12,070,086 ha, or 71% of the forested land in Idaho and Montana west of the Continental Divide. The 11 regional-fire years, those exceeding the 90th percentile in annual fire extent from 1900 to 2003 (102,314 ha or approximately 1% of the fire atlas recording area), were concentrated early and late in the century (six from 1900 to 1934 and five from 1988 to 2003). During both periods, regional-fire years were ones when warm springs were followed by warm, dry summers and also when the Pacific Decadal Oscillation (PDO) was positive. Spring snowpack was likely reduced during warm springs and when PDO was positive, resulting in longer fire seasons. Regional-fire years did not vary with El Niño-Southern Oscillation (ENSO) or with climate in antecedent years. The long mid-20th century period lacking regional-fire years (1935-1987) had generally cool springs, generally negative PDO, and a lack of extremely dry summers; also, this was a period of active fire suppression. The climate drivers of regionally synchronous fire that we inferred are congruent with those of previous centuries in this region, suggesting a strong influence of spring and summer climate on fire activity throughout the 20th century despite major land-use change and fire suppression efforts. The relatively cool, moist climate during the mid-century gap in regional-fire years likely contributed to the success of fire suppression during that period. In every regional-fire year, fires burned across a range of vegetation types. Given our results and the projections for warmer springs and continued warm, dry summers, forests of the U.S. northern Rockies are likely to experience synchronous, large fires in the future.

A phytosociological study of the "pinyon-j uniper association" in the eastern foothills of the Rocky Mountains was initiated in September, 1951 and ended in August, 1953. Two field trips totalling over 16,000 miles in four states were undertaken for the collection of data by the firstnamed author, one during the summer of 1952 and the other during the spring of 1953. Twenty-four representative stations were analyzed for comparing the community characteristics of pinyonj uniper stands throughout the eastern range of this type except in the extreme northern portion. One of the primary objectives was the development of a sampling method sufficiently rapid for a broad reconnaissance study of a large region without sacrificing accuracy. This called for the statistical determination of adequacy of sampling. Another point considered important was obtaining reliable data on cover especially, because of its relation to erosion. These needs were met by combining into one sampling unit the line-interception principle plus a very long narrow quadrat. This unit is termed the "line-strip." The main area studied extends from the Davis Mountains in Texas to the Colorado-Wyoming boundary and is bounded on the west by the continental divide. The latter forms a rather natural boundary for delimiting the scope of the problem to an area of manageable size. The area is mapped in Fig. 1, which also compares the boundary of this type as recognized by Shantz and Zon (1924) and the U. S. Forest Service (1949). Farther north, a single station was sampled in the Big Horn Mountains, Wyoming. Economically, the woodland is important mainly as grazing land; the timber has some importance as mine props, fuel

The matter presented in this paper is the result of study of over five hundred vials of material collected by the authors during the summers of I913, 'I4, '15 and '2I, along the valley of South Boulder Creek in Gilpin and Boulder Counties, Colorado, from the Continental Divide eastward and downward to the western edge of the Great Plains. The work is supplemented by observations made by the senior author during several other summers spent in the region collecting entomostraca and making observations on climatic and physiographic conditions. The present paper is an outgrowth of, and should be studied in connection with, similar work upon the entomostraca of the region (Dodds, '17 and '20). Recognition should also be given to field work done by W. L. Brosius, who assisted with the collecting in I9I3. The area covered by these collections is of especial interest because it includes a cross section through five life zones: Upper Austral, Transition, Canadian, Hudsonian, and Arctic-Alpine. The Upper Austral is represented by an area of the plains, extending about four miles from the base of the foothills, with an elevation of about 5,300 feet above sea level. The other zones include portions of the mountain region along the creek for a distance of about 20 miles, up to its headwaters at elevations of about II,250 feet. The topography and climate of this region are described in earlier papers.

This is the first of a proposed series of papers growing out of studies carried on during several summers in the Colorado Rockies, with headquarters at the Summer Mountain Laboratory of the University of Colorado, at Tolland, Gilpin County, Colorado. The authors are much indebted to Francis Ramaley, Director of the laboratory, for materials and equipment, as well as for a stimulating interest in the work. Our studies in that region have dealt with various phases of the ecological relations of the nymphs of stoneflies and mayflies and the larvae of caddisflies, giving special attention to the means by which these insects have met the difficult conditions of life in the swift streams of the region. The Laboratory is located in the valley of South Boulder Creek, at 9,ooo feet, on the east slope of the Front Range of the Rockies, within four miles of the Continental Divide on the west, and about I5 miles from the plains on the east. It has within easy reach a wide range of topographic, climatic and biotic conditions. The creeks and numerous small lakes of the region are of great interest, and are fully described, together with the important topographic and climatic features, in former papers by one of the authors (Dodds, 'I7, '20). The most abundant and striking part of the fauna of the lakes and streams is the insect life, including the immature stages of mayflies, stoneflies, and caddisflies, which here are found in an abundance wholly unknown in ordinary lowland portions of the United States, except in the northern tier of states. We have made special study of the swift streams. It should be clearly recognized that the swift streams of this region are far more than the " babbling brook " or the riffles of streams in level or moderately hilly country, but are in reality often torrential, especially during high water. These streams frequently make a descent of a thousand feet within a distance of a mile, and

The area surveyed in this study is in the southwest part of Glacier National Park and lies only 5-7 mi. west of the Continental Divide. McDonald Valley is one of the larger and better known valleys on the west slope of the Park. Lake McDonald, the largest body of water in the Park, is approximately 10 mi. long and between 1.5 and 2 mi. wide. It owes its existence to a Pleistocene valley glacier which deposited sediments at the lower end of the valley to form a moraine which dammed up the basis and produced the lake. The glacier is calculated to have been at least 1400 ft thick, for the lake attains a depth in some places of 400 ft and there are evidences of moving ice oln the ridges paralleling the lake 1000 ft or more above the present water level. The term, Lake McDonald Forest, is the author's own coinage and refers to that part of McDonald Valley near the lake and below 4200 ft elevation (Fig. 1). It is felt that this constitutes a rather natural area since the slopes above 4200 ft or 4300 ft typically become more precipitous and the aspect of the forest exhibits gradual but marked changes. To the south and west of Lake McDonald lies the extensive Flathead Valley with an average elevation of approximately 3000 ft.

Sphagnumi bogs are not comm-inon in the northern Rocky Mountain region of the United States, and many that do exist are more or less inaccessible with a reasonable amount of time and effort. The writer was fortunate to locate two bogs in Glacier National Park whose sections reveal excellent pollen profiles from which the postglacial forest succession has been reconstructed and the climatic sequence interpreted. These organic sediments have accumulated in Johns and Fish Lakes, both. of which lie about one mile east of the north end of McDonald Lake near the southwest boundary of the Park. Johns Lake lies at an elevation of about 3300 feet. and Fish Lake has an altitude of about 4100 feet and is located about two and one-half miles due south of the former. Both are less than five miles west of the Continental Divide which rises to an elevation of about 8000 feet in this area. The sites of both lakes were overriden by the McDonald Valley glacier which probably was of Late Wisconsin age. McDonald Lake drains into the Middle Fork of the Flathead River which coalesces with the North and South Forks to form the Flathead River which empties into Flathead Lake south of the Park. Johns Lake covers about 5 acres and is bordered by a sphagnum-sedge mat from 10 to 25 feet wide. Typical plants growing on the mat are Drosera xrotmiidifolia L., Potentilla palustris L., Dulichium arundinaceumn (L.) Pritt., Kainia poli