370 MINNESOTA BOTANICAL STUDIES 



1. Flood succession 



2. Burn or clearing succession 



1. FLOOD SUCCESSION 



The survey party has made no specific study of secondary suc- 

 cession resulting from flooding by lakes or streams in any of the 

 deciduous areas. The general course of development may be indi- 

 cated, however, leaving the discussion of details for a later report. 

 Flood successions occur most frequently along river valleys and are 

 due to silting up of rivers, which ponds the water above the place 

 where silting occurs or to the formation of small lakes on the flood 

 plain of a river during a period of overflow. Usually the water is 

 sufiiciently shallow so that the succession can begin with the appear- 

 ance of Typlia, Scirpus, Phragmites and often also Spartina cyno- 

 suroides. Phragmites and Spartina grow in shallower water than 

 Typlia or Scirpus so that the latter are usually most abundant in 

 shallow lakes on flood plains. These are followed by species of 

 Carex of which C. trichocarpa is probably most abundant. With it 

 are usually to be found Calamagrostis, Panicularia americana and 

 Spartina. As filling of the flooded area proceeds, species of Salix 

 and Populus are able to invade and still later Acer negundo, and 

 finally the climax dominants Uhnus, Quercns, Tilia, and Acer 

 sacchariim become established. If flooding is recurrent the succes- 

 sion may be held in the Typha-Phragmites stage, or if the depth of 

 water is less, in the Carex-Calamagrostis stage. 



2. BURN OR CLEARING SUCCESSION 

 a. Ix THE Climax Forest 



Causes : The removal of the climax forest by burning or clear- 

 ing is the fundamental cause of the initiation of secondary succes- 

 sion. Either of these causes results in a drier habitat, since the soil 

 is directly exposed to the drying action of sun and wind. Plants 

 growing in such areas are likewise exposed to drying action of sun 

 and wind, and in consequence only those which are structurally 

 adapted to prevent or check transpiration, or which are capable of 

 physiological adjustment to such conditions, are able to grow in the 

 altered environment. The changed light relation, since it affects 

 the plants by affecting transpiration and by increasing the evapora- 

 tion of water from the soil, is an important consideration. 



