206 CLIMAX FORMATIONS OF NORTH AMERICA. 



Annuals first appear on the middle beach, especially Cakile and Corisper- 

 mum, and are followed also by biennials and perennials, which form an herba- 

 ceous cover upon the upper beach. The latter next passes into the heath 

 stage, marked by Juniperus, Ardostaphylus, Pteris, etc. The coniferous stage 

 begins apparently with jack pine {Pinus banksiana), which is followed soon 

 by the red or Norway pine (P. resinosa), and this by the white pine (P. strobus). 

 The balsam (Abies balsamea) and hemlock {Tsuga canadensis) often play a 

 prominent part in this stage. The latter is followed by the climax forest of 

 maple {Acer saccharum) and beech {Fagus ferruginea), in which the hemlock 

 often occurs on equal or nearly equal terms. The yellow birch {Betula lutea) 

 also has a constant place with the dominants. The development on clay 

 bluffs begins with Solidago, Aster, Elymus, etc., and passes quickly into a 

 scrub of Juniperus, Shepherdia canadensis, etc. The third or forest stage is 

 marked by conifers, poplars, and white birch, and this terminates in due time 

 in the maple-beech-hemlock cUmax. 



In the case of rock, the initial Uchens and mosses are followed by herbs, such 

 as Solidago, Potentilla, and Campanula, and by low shrubs, such as Arcto- 

 staphylus, etc. These are followed by arbor vitse {Thuja ocddentalis), junipers, 

 and pines, which finally yield to the climax. In the lakes and ponds the uni- 

 versal amphibious associes are succeeded by the stage crystaUized in the 

 CassandrorSphagnum zone, which makes conditions possible for the tamarack- 

 spruce zone. The latter in turn yields to the pines and the climax. When 

 the swamp becomes partially drained, arbor vitse replaces the tamarack, and 

 then, with its associates, Fraxinus, Abies, Pinus strobus, and Betula lutea, gives 

 way to the final forest. 



Bruncken (1902) has studied the succession of forest trees in southern 

 Wisconsin: 



The accumulation of leaf-mold under the oaks is such that in time there is 

 sufficient humus formed to enable the maple to enter. As the latter gains a 

 foothold, its dense shade prevents the reproduction of the oak, and in the 

 course of time the oak stage gives way to the maple. The earliest forests 

 known in the region were of white pine. This was probably followed by a forest 

 of yellow birch, hemlock, etc. Later the area was invaded by the oak for 

 some unexplained reason, and the oak then gave way to the maple, basswood, 

 and beech. 



Snow (1902 : 284) has found that the psammosere of the Delaware coast is 

 essentially identical in development with that of Lake Michigan, New Jersey, 

 Virginia, etc. : 



The middle beach shows two zones, the lower succulent zone of Cakile, 

 Salsola, Xanthium, and Atriplex, and the low AmmophilorAxxne zone, char- 

 acterized by Ammophila, together with Panicum, Cenchrus, etc. In the outer 

 series of the dunes, Ammophila, Euphorbia, and Leptilon characterize the 

 exposed slopes, while Cassia, Oenothera, Panicum, etc., on the protected slopes 

 pass into a heath of Lechea, Baptisia, Myrica, and Baccharis, followed by Pinus 

 rigida, Juniperus, and Qu£reus. The low dunes back of this series are covered 

 mainly by Hudsonia tomeniosa. The second dune series is covered with scanty 

 Ammophila, with Lespedeza, Sarothra, Panicum, and Pinus rigida. The heath 

 extends from the second series back to the forest. It consists chiefly of 

 Baptisia and Ruhus with Ammophila in reKct groups, while in it occur many 

 trees, shrubs and herbs. The thicket contains Aronia, Pyrus, Malus, Ilex, etc., 



