THE PROBABLE ORIGIN OF THE FORESTS OF THE 

 BLACK HILLS OF SOUTH DAKOTA. 



By p. L. Buttrick. 



In 1896, the U. S. Department of Agriculture published a list 

 of plants from the Black Hills Section of South Dakota.* It 

 was compiled by Dr. P. A. Rydberg, mainly from his own col- 

 lections. In the introduction he speaks briefly of the probable 

 manner in which the various species reached the region. 



Perhaps- an amplification of the subject as it applies to forest 

 trees may be of sufficient interest to foresters to warrant publi- 

 cation. Most of the conclusions expressed here were reached 

 by the writer before seeing Dr. Rydberg's Bulletin. 



The Black Hills in southwest South Dakota and eastern Wyo- 

 ming rise to a height of nearly 5,000 feet above the surrounding 

 plains', and cover an area about the size of the State of Connecti- 

 cut. They present conditions in every way different from the 

 treeless plains and Badland surrounding them. In contrast the 

 Hills are (or were) heavily timbered. 



They form what is essentially an island — an island in the 

 midst of the land. Like other islands they have received their 

 fauna and flora from neighboring but larger lands, and, after 

 receiving it, have modified it to suit their own peculiar insular 

 conditions. 



Islands receive such plants and animals as are, in some man- 

 ner able to cross the barriers to them. Wind, water, birds and 

 insects are among the agents supplying islands with plant life. 



Doubtless these have done their part in the colonization of the 

 Black Hills. However, migrations along well defined lines are 

 responsible for the presence of most, possibly all the tree species 

 of the Hills. 



Western Yellow pine (Pinus ponderosa) is the most important 

 tree, constituting at least 90 per cent, of the forest. The other 

 pines, Lodgepole (Pinus murrayana) and Limber pine (Pinus 



*Contributions from U. S. National Herbarium, Vol. Ill, No. 8, 1896. 

 Division of Botany, U. S. Department of Agriculture. 



