Probable Origin of the Black Hills Forests. 227 



capacity to grow abundantly on upland sites as they do in their 

 old eastern homes. 



It is possible that there are other species from the three forest 

 regions which are more or less suitable for the Black Hills, but 

 which have never been able to reach them. 



It is probable that the forces of evolution will continue in the 

 future as they have in the past to produce specialized forms for 

 insular conditions and that the differentiation of the trees of the 

 Black Hills into local varieties and species will continue, chiefly 

 among the hardwoods. It is not impossible that further acces- 

 sions will be made from the eastern hardwoods as they work 

 their way further and further west. And those species now at 

 the gate-way of the Hills will climb higher and higher into them. 

 Whether these changes will be rapid enough to be perceptible to 

 us remains to be seen. 



It is unlikely that any species will of itself usurp the place of 

 the Yellow pine, which despite the ravages of fire and insects 

 holds its own so well. For the purposes of the forester and the 

 lumberman the development of the forests of the Black Hills is 

 complete. 



