ECOLOGY AND WILD LIFE CONSERVATION 473 



Succession 



A mature biological community remains the same for a long time, 

 unless the area is affected by some natural or human agency such as a 

 fire, flood, or glacier. When the community is completely destroyed, 

 one type of vegetation after another will appear in a regular series of 

 steps which may require hundreds or even thousands of years. Eventu- 

 ally such a region will again reach a climax in development in which 

 dominant species of trees and animals will take over the region. For 

 example, after the continental glaciers melted in the northeastern states 

 some 20,000 years ago, they left the landscape completely bare of soil 

 and denuded of all life, both plant and animal. Many serai stages, one 

 after the other, occurred in the region before the climax forest was re- 

 stored. As the glaciers receded, animals such as the caribou, arctic 

 hares, arctic foxes, and many birds migrated across the region carrying 

 the seeds and spores of plants which started growing, and it was not 

 long until some plant life was re-established. The first plants were 

 species of lichens and mosses which require little soil, and the first ani- 

 mals were insects, the larvae of which feed on such low plants. As 

 soon as a little soil had accumulated in low patches, fast-growing annuals 

 became established. These were followed by perennial herbs and pio- 

 neer shrubs such as blackberries, dewberries, raspberries, blueberries and 

 huckleberries. Ground nesting birds such as pipits, longspurs, and 

 horned larks now found a suitable habitat along with some predatory 

 mammals and birds. As the soil deepened, larger shrubs became com- 

 mon and tough, pioneer trees became established. Rabbits now found 

 suitable cover, deer began to browse on the shrubs and small trees, a 

 varied fauna of birds which nest in shrubbery became established, and 

 the larger carnivores, such as foxes and wolves, followed. Next a 

 growth of pioneer trees such as swamp maples, sassafras, persimmon, 

 cedars, and pines began to crowd out the low vegetation, and squirrels, 

 tree-nesting birds, wood-boring insects, and many other forms of ani- 

 mal life now found a suitable home. Birds and mammals of the open 

 country were then crowded out or reduced to a few colonies in open 

 spots. Finally, such slow-growing but dominant trees as sugar maple 

 and beech, or white spruce farther north, gained a foothold and raised 

 their crowns above the forest and gradually crowded out many of the 

 smaller, short-lived trees. Rabbits no longer found their favorite brier 

 patches, deer had to search elsewhere for tender twigs on which to 

 browse, and birds of the shrubby habitats became scarce. However, as 

 old trees developed dead branches and hollow trunks, more woodpeckers 

 found food and homes, and more dens became available for raccoons. 



