ECOSYSTEMS OF THE EAST SLOPE OF THE FRONT RANGE IN COLORADO* BY JOHN W. MARR ASSOCIATE PROFESSOR OF BIOLOGY AND DIRECTOR OF THE INSTITUTE OF ARCTIC AND ALPINE RESEARCH UNIVERSITY OF COLORADO UNIVERSITY OF COLORADO STUDIES Series in Biology No. 8 UNIVERSITY OF COLORADO PRESS BOULDER, COLORADO, NOVEMBER, 1961 Price $2.50 * Contribution from the Institute of Arctic and Alpine Research UNIVERSITY OF COLORADO STUDIES Editor: KARL K. HULLEY Editorial Board: FLOYD K. BASKETTE, ROBERT E. GSEGG, CLAY P. MALICE, PAUL V. THOMPSON, HAROLD F. WALTON Numbers of the UNIVERSITY OF COLORADO STUDIES are issued from time to time as suitable contributions are received from members of the Faculty, preference being given to articles which may be (1) too long for publication in the usual journals, (2) not quite suited to any other journal, or (3) concerned especially with Colorado. Established as an outlet for such materials as are mentioned above, the Studies was first published in January, 1902. Since that time, two changes have been made for the purpose of unifying the content of the several issues, the first having been effected in the academic year 1938-1939, when the Studies was divided into four series, three of which were limited to articles in some broad field of knowledge — humanities, social studies, and physical and biological sciences. The second change was made in the aca- demic year 1947-1948, when the series were revised so as to limit each one to a particular field, as indicated in the list on the fourth page of the cover of this number. It is requested that all exchanges be addressed to Serials Division, University of Colorado Libraries, Boulder, Colorado — not to the Editor. Educational institutions, libraries, and societies desiring to be placed on the exchange list should make request to the Editor of University Oj Colorado Studies, Boulder, Colorado. Business communications also shoulo be sent to the Editor. CONTENTS I. INTRODUCTION 1 II. THE UNIT OF STUDY AND ITS CHARACTERISTICS 6 III. THE PROGRAM OF INTENSIVE FIELD STUDIES 12 A. Selection of Stands 12 B. Environment Measurements 12 1. Status of Knowledge of Mountain Environment 12 2. Factors to be Measured 14 3. Instrumentation 14 4. Methods and Procedures 15 5. Preparation of Summaries 16 C. Study of Vegetation 17 IV. REGIONAL FEATURES OF THE FRONT RANGE 19 A. Geography and Geology 19 B. Climate and Weather 20 C. Vegetation 21 D. Regional Ecosystems 23 V. THE CLIMAX REGIONS AND STANDS 25 A. The Lower Montane Forest Climax Region 25 1. Regional Characteristics 25 2. The Major Stand-Types 28 a. Ponderosa Pine Stand Complex 28 b. Douglasfir-Ponderosa Pine Stand Complex 35 c. Douglasfir Stand-Type 37 d. Grassland Complex 37 e. Valley Floor Stand-Types 37 B. The Upper Montane Forest Climax Region 39 1. Regional Characteristics 39 2. The Major Stand-Types 41 a. Douglasfir-Ponderosa Pine Complex 41 b. Ponderosa Pine-Douglasfir Stand-Type 47 c. Douglasfir Stand-Type 48 d. Ponderosa Pine Stand Complex 50 e. Limber Pine Stand-Type 50 f. Aspen Stand Complex 50 g. Lodgepole Pine Stand-Type 51 h. Valley-Floor Stand-Types 51 i ii UNIVERSITY OF COLORADO STUDIES C. The Subalpine Forest Climax Region 53 1. Regional Characteristics 53 2. The Major Stand-Types 56 a. Spruce-Fir Stand-Type 56 b. Lodgepole Pine Stand-Type 58 c. Aspen Stand-Type 65 d. Limber Pine Stand-Type 69 e. Willow-Birch Stand-Type 74 f. Wet Sedge-Grass Meadow Complex 74 g. Dry Subalpine Meadow Stand-Type 75 D. The Alpine Tundra Climax Region 75 1. Regional Characteristics 75 2. The Major Stand-Types 81 a. Kobresia Meadow Stand-Type 83 b. Hair grass Stand-Type 86 c. Parry's Clover Meadow Stand-Type 88 d. Adoneus Buttercup Stand-Type 90 e. Snowbank Complex 92 f. Cushion Plant Stand-Type 92 g. Dryas Stand-Type 92 h. Sedge-Grass Wet Meadow Stand-Type 93 i. Willow-Sedge Hummock Stand-Type 94 j. Tundra Valley Stands 95 VI. SUMMARY 101 LITERATURE CITED 104 APPENDIX I. LIST OF PLANT SPECIES 110 APPENDIX II. SUMMARIES OF ENVIRONMENT DATA 119 LIST OF PHOTOGRAPHS FRONTISPIECE. Aerial View of the East Slope of the Front Range vi PLATE 1. A. Environment-Measurement Station 96 B. Montane Landscape 96 PLATE 2. A. Ponderosa Pine Stand 97 B. Douglasfir-Ponderosa Pine Stand 97 PLATE 3. A. Aspen Stand 98 B. Spruce-Fir Stand 98 PLATE 4. Patterned Ground in Alpine Tundra on Niwot Ridge 99 PLATE 5. A. Kobresia Meadow Stand in Early Fall 100 B. Kobresia Meadow Stand in Winter 100 iii LIST OF TABLES 1. Regional Ecosystems on the East Slope of the Front Range 24 2. Lower Montane Soils Data 26 3. A-l Ponderosa Pine Stand Vegetation Data 30 4. A-3 Ponderosa Pine Stand Vegetation Data 32 5. Comparison of Four Stands in the Lower Montane Climax Region.. 34 6. A-2 Douglasfir-Ponderosa Pine Stand Vegetation Data 36 7. Upper Montane Soils Data 40 8. B-l Douglasfir-Ponderosa Pine Stand Vegetation Data 43 9. Comparison of Four Climax Regions 45 10. B-2 Douglasfir-Ponderosa Pine Stand Vegetation Data 46 11. Comparison of Four Stands in the Upper Montane Climax Region.. 47 12. B-3 Ponderosa Pine-Douglasfir Stand Vegetation Data 49 13. Subalpine Soils Data 54 14. Silver Lake Spruce-Fir Stand Vegetation Data 58 15. C-1C Lodgepole Pine Stand Vegetation Data 60 16. C-3A Lodgepole Pine Stand Vegetation Data 62 17. Comparison of Stands in the Subalpine Climax Region 63 18. C-2A Lodgepole Pine Stand Vegetation Data 64 19. C-1D Aspen Stand Vegetation Data 68 20. C-3B Aspen Stand Vegetation Data 70 21. C-2B Aspen Stand Vegetation Data 71 22. C-lA Limber Pine Stand Vegetation Data 72 23. C-1B Limber Pine Stand Vegetation Data 73 24. Alpine Soils Data 78 25. D-lA Kobresia Meadow Stand Vegetation Data 85 26. D-2A Kobresia Meadow Stand Vegetation Data 87 27. Comparison of Four Stands in the Alpine Climax Region 88 28. D-1B Parry's Clover Stand Vegetation Data 90 29. D-3A Adoneus Buttercup Stand Vegetation Data 91 30. D-1C Cushion Plant Stand Vegetation Data 93 LIST OF FIGURES 1. East Slope of the Front Range in Boulder County, Colorado 2 iv Pholoyrayh by Floyd Walters Aerial view of the east slope of the Front Range and the University of Colorado campus in Boulder. Natural vegetation of campus is grassland. Snow-covered landscape is mostly above upper treelimit. ECOSYSTEMS OF THE EAST SLOPE OF THE FRONT RANGE IN COLORADO I. INTRODUCTION A distant summer view of the East Slope of the Front Range in northern Colorado shows a dark band of coniferous forest limited by lighter-colored landscapes of grassland below and tundraland above (Fig. 1 and Frontispiece). Each of the three contrasting areas appears to be homogeneous, and the borders between them appear sharp. A closer view, however, reveals great diversity within each area and borders that are poorly defined. Herbaceous communities and stands of deciduous aspen trees occur scattered through the prevailing evergreen forest, and the species of dominant evergreen changes from one site to another; fingers of forest and isolated stands of trees pene- trate the tundra and grass landscapes for varying distances and become pro- gressively less common until they disappear entirely. This landscape, then, actually is broken up into a myriad of small units, most of which are repeated from place to place in an intricate, changing pattern, and the major areas gradually merge into one another. Description and explanation of this land- scape pattern, processes which require identification, characterization and classification of the units which make it up, present a challenge to ecologists. Partial explanation for the diversity of this landscape is evident after only brief acquaintance. It is general knowledge that mountain slopes rising a mile in altitude intersect different types of climate. Along one contour at any given altitude many features cause diversity: changes in topography produce differences in exposure to sun and wind; variations in soil parent material and topographic situation result in differences in texture, depth, and water content of soils; fires have burned small and large areas, sometimes repeatedly; miners, lumbermen, even farmers, along with sheep and cattle, have left few square feet unmodified by their activities. Adding details and quantitative features to this general picture of mountain ecology is a much more tedious process, and progress has been slow. Meas- urements of environment factors in the high mountains were made as early as 1874 by the U. S. Army Signal Corps on the top of Pike's Peak. In the early part of this century, while ecology was just taking form in America, many of the young ecologists were attracted to the Front Range. C. S. Cran- dall published an analysis of lodgepole pine succession in 1897; William S. Cooper began his pioneer work on alpine ecology in 1904; Robert T. Young measured temperature and humidity for brief intervals at Boulder and at timberline on Arapahoe Peak in 1905; F. E. Clements applied his dynamic 1 to Climax Regions Subalpine Montane Lower Montane a < < w fd CO J Boulder HH H «! O a o e o >S) !Neder!and> o o CO H a t-eH s - LEGEND- CO Contour Interval 500 Feet Science Lodge SL Scale In miles Road I Location of ridge top and slope stands — • Location of valley stands X map by r.e.f. FIG. 1. East Slope of the Front Range in Boulder County, Colorado ECOSYSTEMS 3 concepts to study of lodgepole pine succession after fires in 1910; Francis Ramaley published landscape classifications, measured environment factors (as early as 1910), studied a variety of community types, and stimulated and supervised many graduate students in field ecology; A.