1920] CLA Y BERG— UPLAND SOCIETIES 3 7 



{Soil stratum: here lie roots, youngest farthest up. 

 Leaf stratum : thin crisp continuous layer. 

 Herbage stratum: includes seedlings also (age 1). 

 {Sapling trunks: first really open stratum; shrubs here. 

 Death stratum: layer of dead twigs below sapling foliage. 

 Sapling synfolium: sapling foliage layer. 



UDoer forest /Tree trunk stratum: ample light first reached. 



[Upper synfolium: broken zone of adult tree foliage. 



The strata of any one generation are best shown and fullest 

 developed at the sapling age. They are not so well formed in the 

 seedling and are breaking down in ages 3 to 5. Only major layers 

 are listed. For this reason the seedling synfolium is not accorded 

 separate rank (although thicker than leaf stratum). 



Synfolium. — The synfolium is the layer formed by leaves of 

 trees of the same age. It is the result of photosynthetic need in 

 crowded sessile individuals. It must be dealt with not only as 

 compound, with the unit the foliage leaf, but also as a mass. The 

 placing together of all the synthetic tissue of a group of trees is of 

 serious ecological importance. The leaf placing, together with the 

 crowding of the trees, makes the vertical section of an individual 

 show a nearly rectangular foliage mass. The synfolium governs 

 its depth by means of the light relation. It also controls the amount 

 and composition of the herbage below. In the general discussion 

 here given, the synfolium of the sapling is taken as type. 



While the synfolium continually and gradually ascends as the 

 trees grow (no sudden jumps), the history of the foliage layer shows 

 characteristic stages. Since the seedlings are scattered, their 

 foliage layer is discontinuous horizontally. It is very close to earth 

 level and is but 20-40 cm. vertically. As the sapling age 

 approaches, the small foliage masses fuse into a continuous layer, 

 having a much greater vertical section, and both upper boundaries 

 parallel, horizontal, and nearly flat. This is the ecologic climax 

 of the synfolium ; here it reaches its greatest definition and density. 

 Most of the growth is strictly limited to the top at this age, but 

 later ages show the maple in its true light as more typically a 

 deliquescent tree. 



At the sapling age the synfoliar depth (from its top to its bottom) 

 is 3-4 m. As it recedes from the ground its upper surface becomes 



