193] FLORA OF COLUMBIA AND VICINITY 5 I 



fering invasion, and in which the final outcome of the struggle 

 between sylvan and open species is still uncertain; third, brush- 

 lots with the young trees in control, thus denoting the final vic- 

 tory of the sylvan elements; fourth, brush-lots apparently of a 

 stable thicket formation, with shrubby species in control; fifth, 

 brush-lots which have become swarded over with grass, the 

 brush growing thinner every year, and the open elements in 

 control. The park-like half-wild pastures stand for the final 

 victory of the open vegetation. 



The fiora of brush-lots cannot be separated into definite 

 plant-societies, till some degree of stability in the vegetation 

 has been reached. The unpastured young brush-lot has an ex- 

 ceedingly dense plant-growth consisting of an inextricable mix- 

 ture of sylvan, prairie and ruderal plants. All that it is possi- 

 ble to do is to determine the nature and extent of the invasion, 

 and to endeavor to discover the ultimately dominant element. 

 Moreover portions of the tract may be in various stages of de- 

 velopment. Thus side by side there may be going on a process 

 of reforesting, and a process of disintegration into a wild pas- 

 ture. 



A brush-lot is measurably stable only when it is dominated 

 by shrubby species. It is probable, however, that in a region 

 natural to forests a fruticetum leads ultimately to a sylva. 



1. Arbustales rhuoides. The sumac association is 

 extremely heterogeneous. The fruticose element, consisting of 

 shrubs, lianas, arborescent plants, and the young growth of 

 timber trees, has little unity. The true shrubs tend to grow in 

 dense patches. Thus on one hillside the sumacs {Rhus glabra, 

 R. copallina, R. aromatica) may form a compact growth, on 

 another Rhamnus lanceolata, Euonymus atropurpureus or Cor- 

 niis asperifolia, C. Drummondii, and C. candidissima may form 



