This region, however, does not support a continued and un- 
broken mature forest. In the lower iands, early logging operations, 
together with sanguine but often abortive attempts at homesteading 
have modified the stand to some extent. Tne most profound and active 
agent of destruction both in the lowlands and within the mountainous 
interior has been fire, often the result of severe electrical storms. 
With the destruction of the forest canopy through successive fires 
and the reduction of the thick duff to ashes, it is obvious that the 
ecological conditions are greatly modified. Ignoring the burned areas 
and considering only those in which young or mature stands are thrifty 
and well developed, the forest has been classified into five principal 
types. In some places these may be readily discerned, in others they 
merge and anastomose in a confusing way. Almost nowhere can the climax 
be thought of as being complete, but only approximating the ideal and 
shadowing the associations which would prevail generally if the exter- 
nal factors producing them were more uniforn. 
YELLOW PINE TYPE 
The yellow vine tyve ranges along the eastern border of the grassland, 
competing with it, from the Clark Fork Valley west of Lake Pend Oreille, 
southward to Moscow, and eastward to Orofino, descending into the Clear- 
water canyon and tne canyons tributary to it. This strip is continuous 
with the forests of the Spokane plains. From east to west it varies in 
width from a few hundred yards to several miles, penetrating deeply in- 
