ground and shrub strata. The herb stratum is \woT\y 

 develoiHul or absent ahogether. In the forest there 

 are tlie ground, lierb, shrub, and tree strata. Since 

 the early forest is on a floodplain, the ground is fre- 

 quently swept by floods, and the shrub stratum is 

 poorly represented. The climax forest has all strata, 

 richly developed, and possesses the greatest number 

 iif animal species. There is an increase in the abun- 

 dance of individuals per square meter with the pro- 

 gression of the sere: annuals, 268: clover, 531; 

 shrubs, 532: early forest, 748: climax, 2445 (David- 

 son 1932). 



Beetles, spiders, ants, and mites are the most 

 abundant animals in the annuals stage, and along with 

 aphids remain most abundant also in the sweet clover 

 community. Grasshoppers are fewer in number but 

 especially characteristic of the first three stages : they 

 practically disappear in the forest. Earthworms are 

 absent in the amiuals and scarce in the sweet clover, 

 as are the springtails ; as the amount of soil humus 

 increases with the development of the sere, both 

 groups become more and more numerous. Snails first 

 appear in the sweet clover stage and increase in im- 

 portance in the forest stages. 



The first two stages are not sufficiently extensive 

 to support a distinct bird fauna, but they are quickly 

 invaded by scattered shrubs and trees. A forest-edge 

 habitat is thus established and is occupied by forest- 

 edge birds (Brewer 1958). Beginning with the early 

 forest stage, these forest-edge species are replaced by 

 the forest bird community. The composition and 

 stucture of these two communities will be discussed 

 in Chapter 9. 



The first small mammal (Wetzel 1958) to invade 

 the annuals and sweet clover stages is the prairie 

 deer mouse. It attains populations as high as 22 

 per hectare (9/acre). It persits until the shrubs and 

 trees have become well established. Its place is taken 

 in advanced stages by the woodland white-footed 

 mouse. The prairie vole prefers the grassy areas 

 and is found under briars and other shrubs. Peak 

 populations are about 18 per hectare (7/acre). The 

 short-tailed shrew invades the sweet clover stage but 

 does not establish a stable population until the shrubs 

 come in ; it persists into the climax forest. Wood- 

 chucks commonly occur throughout the early stages 

 of the sere, but mostly disappear in the forest. The 

 cottontail rabbit is common in the early stages, and 

 the fox squirrel invades with the first trees. 



FLOODPLAIN SERE 



A stream continuously deepens its chan- 

 nel, thus lowering the water table of the surrounding 

 land. At times of flood, the stream overflows its 

 banks. The flow rate of water declines as the water 

 passes over vegetated areas, and there is a deposition 



of silt which may sometimes amount to several inches. 

 In a valley, the lowland area between the river and 

 the bluffs on each side is called the floodflain. In the 

 course of time, the river meanders back and forth 

 across the floodplain, cutting new channels and aban- 

 doning old ones, and frequently leaving a sequence of 

 terraces between its present channel and the sur- 

 rounding upland. A study of these terraces com- 

 monly shows a variety of i)lant communities that 

 constitutes the plant sere. 



Plant communities 



Gravel, sand, or silt is deposited on the inner 

 side of river bends. Attached aquatic vegetation may 

 occur in the water. On land, such herbs as smart- 

 weed, cocklebur, ragweed, beggar's ticks occur. At 

 some bends small sand dunes may occur, displaying 

 their characteristic plants and animals : usually this 

 stage is narrow at most, and may be entirely absent. 

 On sandy islands in the river or on sandy shores, the 

 sandbar willow often forms dense, shrubby thickets. 

 The first tree stage is ordinarily black willow mixed 

 with eastern cottonwood, and sometimes silver maple. 

 On the floodplain of the Canadian River in Okla- 

 homa (Hefley 1937), the sere proceeds next to an 

 edaphic subclimax of either tall grass prairie or elm- 

 oak. The climatic climax on the surrounding upland 

 is mixed prairie. The normal sequence of stages in 

 this region has become considerably modified by the 

 extensive ecesis of the exotic tamarisk tree, intro- 

 duced from Asia. 



On the Mississippi floodplain in western Tennes- 

 see (Shelford 1954b) the mature cottonwood-willow 

 associes contains an abundance of vines of several 

 species that form such tangled masses as to be al- 

 most impenetrable. The next stage is one in which 

 sugarberry, sweetgum, American elm, and American 

 sycamore predominate: several other species are 

 present in small numbers. This leads to an oak- 

 hickory stage that includes a complex variety of spe- 

 cies, and eventually to the regional climax of western 

 mesophytic forest. Cypress becomes part of the com- 

 position of the early floodplain forest around the edge 

 of small oxbow ponds or other standing water. The 

 schedule for this sere, the time from the start to the 

 beginning of dominance by each successive plant com- 

 munity, has been estimated as follows : sandbar wil- 

 low, 3 years : cottonwood-willow, 35 years : sugar- 

 herry-sweetgum. 82 years : early species of oaks and 

 hickories. 260 years : intermediate species of oaks and 

 hickories. 350 years ; early climax of oaks and tulip- 

 tree, 440 years : full development of the climax, 600 

 years. 



Elsewhere in the eastern United States, the cot- 

 tonwood-willow stage gives way to a narrow zone of 

 sycamore. Two or three species of elm .white ash. 



Rock, sand, and clay 1 ]3 



