CHAP, xcn DECIDUOUS DICOTYLOUS FOREST 335 



Ash-forest. 



On the east coast of Jutland, in lower Austria, and elsewhere, Fraxinus 

 excelsior, the ash-tree, on a loose moist soil produces true forests, with 

 a dense ground-vegetation composed of tall herbs that, apart from this, 

 usually occur in open, moist fields or meadows. 



Alder-forest. 



Alnus incana in the north of Sweden gives rise to forest with a ground- 

 vegetation of Spiraea Ulmaria, Geranium sylvaticum, Geum rivale, Aira 

 caespitosa, Milium effusum, Urtica dioica, mosses, and others. 1 



Other Deciduous Forests. 



In a similar manner several other indigenous European trees give rise 

 to pure or mixed associations, whose character differs with the humidity 

 of the soil and the conditions of illumination in the forest. 



In Sweden there is a mixed forest, wood-meadow, consisting of such 

 deciduous trees as oak, elm, maple, lime, and hornbeam, beneath which 

 there is an undergrowth of shrubs and tall herbs that is very luxuriant 

 and rich in species ; it is open, well lighted, and park-like, has a rich 

 humus-soil, and possibly represents forest that has been more or less 

 changed by cultivation. Hesselman 2 has studied it in detail, particularly 

 as regards the demands for light, the assimilatory activity and transpira- 

 tion of the perennial herbs, and in general the mode in which these per- 

 form their vital functions under various external conditions. 



In the region of the Danube, about half-way from the source of this, 

 the forests are remarkably mixed in nature, and include a profuse mixture 

 of Fagus, Carpinus, Quercus sessiliflora, Acer, Betula, Prunus Cerasus, 

 Pyrus communis, Populus, Tilia, and Coniferae. The underwood consists 

 of Berberis, Cornus sanguinea, C. Mas, Euonymus europaea, E. verrucosa, 

 species of Prunus, Juniperus communis, and others. In addition, dwarf - 

 shrubs belonging to the Ericaceae, and Polygala Chamaebuxus, occur. 3 

 This complexity indicates closer proximity to the tropics, and probably 

 also has a geological cause, namely, that the land has been free from ice 

 for a longer time than, say, Scandinavia, so that the immigration of 

 species has been more effective here than in the case of Scandinavia. 



In Mediterranean countries on mountains there are other forests, 

 formed by Castanea sativa, Platanus orientalis, and so forth. Populus 

 nigra and P. alba give rise to ' poplar-meadow ' in Servia. 4 



North America has its belt of deciduous dicotylous forest corresponding 

 to that of Europe. A strong admixture of species is characteristic of 

 North American forests. In addition, the underwood is denser and taller. 

 Lianes are more abundant. Yet the physiognomy of the forest is much 

 the same as in Europe. Excepting in the south, epiphytes are confined 

 to mosses and lichens. The yellow and red autumn tints are unusually 

 deep, particularly in species of Quercus, Crataegus, and others. The 

 flora is different. Many genera are indigenous to the temperate zone, 



1 Grevillius, 1894. * Hesselman, 1904. 



a G. Beck, 1890-3; Kerner, 1863; Vierhapper und Handel-Mazetti, 1905. 



4 Adamovicz, 1898. 



