Studies of Plants in the Black Hills of South Dakota

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Abstract
Collections made at 50 stations during 2 summers include 765 species representing 341 genera and 91 families. The dominant flora consists of trees belonging to 9 families Pinaceae, Fagaceae, Ulmaceae, Oleaceae, Aceraceae, Pomaceae, Drupaceae, Salicaceae, and Betulaceae. The outstanding species are Pinus scopulorum, P. Murrayana, Picea albertiana, and Quercus macrocarpa. The 8 families including over 1/2 of the total number of species are: Compositae 124, Gramineae 85, Leguminosae 56, Cyperaceae 36, Rosaceae 31, Ranunculaceae 26, Cruciferae 25, and Scrophulariaceae 20. The geographic relationships of the flora based on the ranges of 750 plants are: Great Plains 26%, western 25%, eastern 9%, northern 6%, southern 5%, North American 17%, northern hemisphere 4.5%, cosmopolitan 0.5%, and ruderal or old world species 6%. The floristic studies resulted in the addition of 116 species to the known flora of the Hills. During glacial time, spruce was the dominant tree. Invasion of the more xerophytic yellow pine followed as the climate became drier and warmer; and the spruce continued to exist only at higher elevations. Continued and probably increasing aridity favored further advance of the prairie flora northward resulting in the isolation of the Black Hills from the montane forest of the Rocky Mts. At this time some of the southern species established themselves in the Hills. A gradual change from xerothermic conditions of early Postglacial time to a more humid climate halted invasion of the prairie, and an extension of the deciduous forest west and northwest followed, resulting in establishment of oak, elm, ash, and other deciduous trees. The present isolation of these trees is due to another variation in the climate toward a drier phase in the cycle. This again favored extension of the prairie and restricted tree forms to the more mesophytic river bottoms. Repeated burning of the prairie by the Indian and deforestation by the pioneer probably hastened the diminution of the deciduous forest. Three major climaxes are generally recognized: grassland, scrub, and forest. The outstanding climax associations are: mixed prairie, chaparral, deciduous forest, and montane forest. The mixed prairie is an association in which tall grasses of the true prairie and short bunch grasses of the plains intermix. The dominant genera are Koeleria, Stipa, Agropyron, Bulbilis, Boutcloua, and Carex. The chaparral is of 3 types: the basin sagebrush dominated by Artemisia tridentata; the Petran chaparral characterized by Cercocarpus and Rhus, occupying the intermediate zone between the grassland and the forest along the western foothills; and the Quercus-Rhus association, holding the same intermediate position along the eastern hills. The deciduous forest is a remnant of a once more extensive oak-hickory association of which but a few species remain, Quercus macrocarpa being the sole dominant, with Ulmus americana, Fraxinus pennsylvanica, and Acer Negundo, as sub-dominants. The montane forest is dominated by Pinus scopulorum in almost pure stands with Picea albertiana as a sub-dominant in the Harney region and on moister slopes in the northern valleys. This association is the most important in the Hills and occupies the major portion of the central area.