-J-.'J^ Proceedings Portland Society Natural History 



t\*|H', is the culminating type of vegetation on ordinary up- 

 lands where the various physiographic factors are favorable. 

 Elsewhere, owing to the effect of factors which preclude the 

 development of the regional type, the succession of vegeta- 

 tion may he halted lower down in the successional series and 

 physiographic climaces result. 



The suecession on igneous rocks passes through a rock 

 surface, crevice, and heath mat stage to a spruce-fir forest 

 which constitutes a physiographic climax. This is very 

 frequent on the islands and the outer shores of the main- 

 land. On glacial drift such a forest may be followed by 

 one of the regional climax type. On sedimentary rocks the 

 succession is quite similar save for the introduction of a pine 

 forest following the heath mat. Where this consists of 

 pitch pine it represents a physiographic climax, but if white 

 or red pines are present these latter trees are usually suc- 

 ceeded by a spruce-fir forest. 



Succession on uplands along the coast varies depending 

 on whether the locality is on an eroding or a depositing 

 shore. Sea bluffs are frequent and often have a character- 

 istic growth of prostrate shrubs at their crest, though the 

 coniferous forest may extend to the very edge of the cliffs. 

 If the exposure is extreme, barren headlands may occur with 

 a carpet of grasses, or low shrubs, and rarely of stunted 

 trees. Beaches are either of the shingle or gravel type, the 

 former often occurring as barrier beaches, and their vegeta- 

 tion displays no unusual features. 



Secondary successions on uplands resulting from cultiva- 

 tion, fire or lumbering are extremely common and have 

 greatly altered the nature of the vegetation. Old fields and 

 pastures are eventually reclaimed by a forest of spruce and 

 fir or in sandy places by white pine. After a fire the fire- 

 weeds, which spring up the first year, are followed by a 

 birch-poplar wood which may persist for some time but 

 is later succeeded by a coniferous wood. A fire which de- 

 stroys the humus reduces the area to the rock surface stage 



