112 C. O. ROSENDAHL AND F. K. BUTTERS 



The subsequent disappearance of most of the pine from south- 

 eastern Minnesota and northeastern Iowa can be ascribed to a 

 combination of causes. The gradual warming up of the cHmate 

 brought about conditions more favorable for the development of 

 deciduous forests and in the competition that ensued the pine 

 gradually lost out. Such competition would be less sharp, and 

 the dangers to the pines from the excessive shade of the decidu- 

 ous trees less imminent on the ledges and steep slopes where the 

 pines are now found. A factor which undoubtedly played an 

 important part in the elimination of the pine was the repeated 

 entrance of fires from the neighboring prairie country. Even 

 within the wooded region of southeastern Minnesota there are 

 numerous small prairie tracts, especially along the high ridges, 

 and the south-facing hills of the east and west trending river and 

 stream valleys. It is a well known fact that pine trees are much 

 more easily injured and destroyed by running fires than decidu- 

 ous trees, and the only place where they would have a chance to 

 survive would be on some of the favorable rocky ledges and river 

 bluffs where the fires could not reach them — just the places 

 where the pine now occurs in this region. That fires, such as are 

 known to have been habitually started by the Sioux Indians, 

 had much to do in determining the extent of even the deciduous 

 forests of southeastern Minnesota, is shown by the fact that 

 numerous exposed ridges in Houston and Fillmore Counties are 

 now timbered, which were devoid of trees at the time the country 

 was settled some sixty-five years ago. Since the country became 

 settled and the fire danger thereby was eliminated, numerous 

 artificial groves of white pine have been established through- 

 out the region. Some of the best examples of these groves 

 are located as far west as Austin in Mower County, well out 

 in what is classed as prairie country. 



Even though the Jack pine is represented in southeastern Min- 

 nesota by but a single known natural grove, our assumption is 

 that it occurred synchronously with the white pine and balsam fir^ 



' For a similar isolated occurrence of the latter tree in the adjacent part of 

 northeastern Iowa, see Sargent, C. S., American Sylva, 12, 109. This locality is 

 believed to be now extinct. According to M. P. Somes the balsam fir occurs also 

 several miles south of Hesper, Iowa. 



