Hill: Penobscot Vegetation 379 



size the shrubs are gradually killed out. Figure 25 shows 

 an old pasture which has been nearly overgrown by red 

 spruce, fir, and larch, with a little juniper fringing the open 

 places. The first of the shrubs to disappear is the sweet 

 fern, then the juniper and finally the blueberries which, 

 however, are sometimes able to persist until there is almost 

 a complete forest covering. The birches are able to sur- 

 vive and grow to maturity with the other trees, eventually 

 forming a part of the resulting woodland, though much out- 

 numbered by the conifers. Ultimately the area is covered 

 with a spruce-fir forest similar to that already described 

 for ordinal*} 7 uplands. 



In some localities where the soil is sandy and there are 

 seed trees present in the vicinity, the white pine is the chief 

 colonizer of these old fields. This species comes in very 

 rapidly even during the grass stage and usually results in 

 even-aged stands of the sort shown in Figure 26, which con- 

 sist almost entirely of pine, with perhaps a little birch in 

 mixture. Such areas were probably much more frequent in 

 former times when the pine was more abundant. 



b. Association-types due to fire 

 The nature of the existing vegetation in the Penobscot 

 Bay region has been more profoundly altered by fire than 

 by any other single agency. Not only have changes been 

 brought about in the species present, but in some cases the 

 soil itself has been so altered that the whole character of the 

 plant covering has been changed. The severity of a fire, 

 and its consequent effect on plant life, depends on its nature. 

 A light surface fire, running through the leaf litter, is not 

 as disastrous as a crown fire which sweeps through the 

 whole forest and destroys all growth. Future development 

 in an area after a fire depends partly on the kind of stand, 

 but more especially on the condition of the humus. A de- 

 ciduous forest is not as easily burned as a coniferous one, 

 and usuallv not as severely, since the leaf litter is less in- 



