fouiul in tlic tlood, hut the size of the population per 

 unit area, determined by live-trapping immediately 

 after the flood, was tiie same as it was immediately 

 before the flood, and a number of tagged individuals 

 were found surviving. This species readily climbs 

 trees and may well have passed the danger period 

 arboreally. Tagged box turtles were found on the 

 identical home ranges they had occupied before the 

 flooil. This flood lasted only a few days. Severe 

 flooding persisting for long periods is known to have 

 virtually exterminated species of small mammals from 

 wooded floodplains in grassland areas (HIair 19v^9). 

 [--arger mammals, such as rabbits, opossums, and 

 foxes, quickly leave flooded areas and may be tem- 

 (xjrarily concentrated around their margins. Squirrels 

 and raccoons easily obtain refuge in the trees, but 

 if the flood persists for some time, they may have 

 trouble finding food. W'oodchucks normally spend 

 considerable time in underground burrows and may 

 be trapped there by flood waters (Yeager and Ander- 

 son 1944). 



Invertebrates in the soil are also affected by flood- 

 ing. A gradually rising water-table may eventually 

 displace all the air from a soil, and the arthropods 

 are killed. Many earthworms leave their tunnels 

 when these are inundated and are killed. Some spe- 

 cies that regularly exist in areas subjected to frequent 

 flooding, however, are not injured. Crane fly larvae 

 are flood-resisting. In normal flooding, bubbles of 

 air trapped in the soil provide suflScient oxygen for 

 at least the smaller arthropods (Kevan 1956). The 

 eggs of some floodplain mosquitoes are laid just above 

 the water level of pools during late summer or 

 autumn and must be flooded the following spring be- 

 fore they will hatch. 



SUBSERES 



Abandoned fields 



When farmland is abandoned, succession back 

 to natural vegetation and ultimately to the climax is 

 rapid, since the soil is already relatively fertile and 

 does not need a great deal of conditioning. On the 

 Great Plains the subsere proceeds rapidly through 

 stages of annual herbs, several of which may be ex- 

 otics naturalized from other continents ; mixed annual 

 and perennial herbs ; a short-lived perennial grass ; 

 dense stands of triple-awned grass ; finally, the climax 

 of short grasses. This last stage may be attained in 

 10 to 20 years. 



Small mammals and grazing domestic aninrals 

 retard the succession by feeding on grasses while 

 avoiding the herbs. Sheep have the opposite effect, 

 preferring the herbs. Harvester ants denude the veg- 

 etation in a circle around their mounds and consume 



a considerable amount of the available seed supply. 

 Ant coactions may be of very great importance when 

 we consider that the population of a mound may aver- 

 age 10,000 individuals and the inimber of mounds 

 per hectare range from to 10 (0 to 4/acre) in the 

 annuals stage, 7 to 28 (3 to 11 /acre) in the mixed 

 annual and perennial herbs, 12 to 52 (5 to 21 /acre) 

 in the first grass stage. 40 to 142 (16 to 57/acre) 

 in the triple-awned grass, and to 32 (0 to 13/ 

 acre) in the final stage (Costello 1944). 



Six plant stages are recognized in the sere that 

 develops in the mixed prairie region of Oklahoma : 

 an initial stage of mixed herbs; three intermediate 

 stages involving different proportions of triple-awned 

 grass ; a subclimax ; and the climax of Andropogon 

 and Bouteloiia grasses. The insect population con- 

 sists of 293 species representing the following orders, 

 ranked in decreasing abundance : Coleoptera, Hemip- 

 tera. Homoptera. Diptera, and Orthoptera. There 

 was a greater variety of species and a greater abun- 

 dance of individuals in the intermediate stages than in 

 either the early or the climax stages, probably be- 

 cause of the greater variety of plant species present 

 in the intermediate stages. Of the 144 species of in- 

 sects in the climax, 58 per cent entered the sere in its 

 initial stage, 15 per cent in the second stage, 12 in the 

 third, 5 in the fourth, 2 in the fifth, and only 8 per 

 cent were limited to the climax itself. The ecesis of 

 the mature animal community was therefore a grad- 

 ual and progressive one. On the other hand, many 

 species that were present in the early stages did not 

 persist into the climax community (Smith 1940). 



Succession in abandoned fields of the southern 

 .Atlantic and Gulf states is of special interest. During 

 the first year, crabgrass and horse-weed, annuals, pre- 

 dominate. During the second year an aster and a rag- 

 weed, and in the third year the perennial broomsedge 

 grass, become dominant. The grass is invaded quickly 

 by loblolly and shortleaf pines which form closed 

 stands in some areas in as little as 10 to 15 years. 

 These pines do not reproduce in their own shade. 

 They mature in 70 to 80 years, and are replaced by 

 tlie climax oaks, hickories, beech, and sugar maple 

 which take complete dominance by the time the area 

 is 150 to 200 years old (Oosting 1942). 



The bird succession (Table 8-6) shows a change 

 from grassland to forest-edge to forest species with 

 an increase of both species and number of pairs as 

 the sere progresses. A great diversity of species in- 

 iiabits the pine forest since several forest-edge spe- 

 cies persist, while pine warbler, brown-headed nut- 

 liatch, solitary vireo, and yellow-throated warbler 

 are particularly characteristic of it. Pine-mice and 

 meadow voles are common in the grassy stages and 

 pine-mice, cotton-mice and golden mice in the for- 

 ested stages. 



In Michigan, the sere in abandoned fields passes 

 through the following stages: annuals-biennials; 



Rock, sand, and clay 1 15 



