TABLE 8-5 Distribution of annelid worm spe 

 Original nomenclature revised by W. J. Harma 



the Sangamon River floodplain forest of central Illinois (Goff 1952). 



and boxelder follow; then a mixed forest that in- 

 cludes black walnut, butternut, black maple, Ohio 

 buckeye, red mulberry, American basswood, tuliptree, 

 and hackberry ; next an oak-hickory stage ; and finally 

 the beech-sugar maple climax. The herb and shrub 

 strata are usually well developed in mature floodplain 

 forests. Telescoping or skipping of stages is not un- 

 common in this sere, since variation in ground level 

 or in height of terraces is considerable and the tran- 

 sition between heights is often abrupt. The later 

 stages occur only on the very oldest terraces and may 

 be hard to find at all. 



Animal life 



In the bare areas, in the herbs, and among the 

 invading trees occur such beetles as Heterocerus 

 pallidus and Bembidion laevigatum that feed on the 

 algae and detritus present on the shore. They make 

 their burrows in sand. Fly larvae, a cocklebur weevil, 

 a cocklebur mirid, and a cocklebur fly also occur. 

 The tiger beetles Cicindela hirticollis, C. cuprascens, 

 and on slightly higher ground C. puncUdata, prey on 

 the ground species and may even dig them out of 

 their burrows. Spiders, ground beetles, and rove 

 beetles invade from higher stages. In the herb 

 stratum and in the shrubby growth of willows, adult 

 midge flies and other flies are sometimes very abun- 

 dant. Tarnished plant bugs, 12-spotted cucumber 

 beetles, and other insects of open area habitats are 

 present, and there is invasion of various species from 

 the forest itself (Hefley 1937, Shelford 1954b). 



The animal life of the floodplain forest is much 

 the same as that of the deciduous forest in general 

 (Chapter 9) and does not need to be discussed here 

 except for its unique features. Annelid worms make 

 their appearance in the ruderal stage, become very 

 abundant in the moist soils of the elm-ash and mixed 

 floodplain forests, then decrease in numbers in the 

 drier soils of the late serai stages. They occur mostly 



in the first 5 to 10 cms below the surface in moist 

 soil, but up to 30 cms or more in dry soil. During 

 the winter they keep below the frostline, and in very 

 dry weather they roll up in small knots and aestivate. 

 Ten species occur in the floodplain of the Sangamon 

 River in central Illinois, and each species has its par- 

 ticular range of moisture requirements between the 

 river's edge and the upland forest (Table 8.5). 



Snails and slugs are moisture-loving animals and 

 occur in large numbers and great variety in flood- 

 plain forests; it is not hard to find 15 to 20 species 

 with a little searching. Mesodon thyroidns is a com- 

 mon snail, and on a floodplain in central Illinois an 

 average population of 6.3 individuals per m^ was 

 found during the autumn (Foster 1937). This 

 amounts to a biomass of living flesh (shell excluded) 

 of 15.8 g/m^ (141 lbs/acre). Siiccinea ovalis on 

 another old Illinois floodplain (Strandine 1941) aver- 

 aged 6.5 individuals per m^ in September with a 

 biomass of only 0.878 g/nr (7.84 lbs/acre). Snail 

 flesh is an important source of food for such small 

 mammals as the short-tailed shrew. 



Effects of flooding 



Animals living on floodplains must usually tol- 

 erate flooding of their habitats almost yearly, and in 

 years with heavy precipitation, often several times 

 annually. All land except the surrounding bluffs may 

 be flooded. Leaves are swept up from the forest floor 

 and piled with other debris against shrubs and the 

 bases of trees. Herbs and shrubs may be damaged, 

 sometimes killed. 



Observations during time of flood (Stickel 1948) 

 showed that emergent brush, the bases of trees, and 

 debris rafts supported masses of insects, spiders, 

 millipedes, snails, and amphibians. Debris rafts were 

 refuges for box turtles and pine-mice as well. Snakes, 

 turtles, and amphibians were also seen swimming or 

 floating in the water. No white-footed mice were 



114 Habitats, communities, succession 



