192 



standpoint of natural vegetation, are the heterogeneous deposits 

 of gravel, sand, and clay known as till. On such soils succession 

 progresses so rapidly that, except where conditions have been 

 modified by human interference, pioneer associations are seldom 

 encountered. It should also be mentioned at this point that 

 frequently, due to the influence of soil structure or ground water 

 relations, swamps may be developed on uplands. But from an 

 ecological standpoint these are better considered in connection 

 with lowlands. 



Several allusions have been made to the effect on vegetation 

 of human interference. Unfortunately for the ecologist this is a 

 factor which too often must be reckoned with. There is one type 

 of succession resulting from man's activities which is deserving 

 of special mention because of its widespread occurrence, viz., 

 ruderal succession.* Whenever a plowed field is allowed to lie 

 fallow for a year, a ruderal association arises. At first the plant 

 population of such an area is composed largely of weeds, many 

 of which are annuals. Of these. Ambrosia artemisifolia is almost 

 omnipresent, but it is hardly worth while to attempt a represen- 

 tative list of the others. It may be noted in passing, however, 

 that among the mosses some forms like Funaria hygrometrica and 

 Physcomitrium turhinatum should be classed as weeds. If a 

 field is permanently abandoned perennial herbaceous plants 

 soon form a sod, so that annual species are largely excluded, and 

 woody plants begin to assert themselves. In this way there may 

 originate the type of vegetation known to the forester as the 

 "old field type." This type is a common one in abandoned 

 pastures, constituting one of the most familiar features of a 

 Connecticut landscape. The characteristic trees are usually gray 

 birch and red cedar, with which are associated low juniper and 

 many other pioneer shrubs (fig. 9). If left to themselves such 

 areas, in the course of time, may become clothed with meso- 

 phytic forests. 



Taken as a whole, the observations recorded in the preceding 

 paragraphs are applicable to upland vegetation in any part of 

 Connecticut, but there are a few noteworthy discrepancies. The 

 earlier stages in the succession are essentially alike everywhere, 



* See Clements, F. E. Research methods in ecology, p. 253. Lincoln. 1905. 



