268 SUCCESSION IN EURASIA. 



In the development of the moor, there is a striking departure from the usual 

 sequence. At the bottom of the moor lies the usual aquatic deposit, but this 

 is followed, not by reed-swamp peat, but by a swamp-forest deposit, which 

 passes into reed-swamp peat. This is then followed by heath-moor peat in 

 the form of Eriophorum peat. Sphagnum peat, etc. The layers indicate that 

 the original water-level decreased to a point where swamp forest developed, 

 and that this was then flooded, resulting in the appearance of reed swamp, 

 followed by the normal development into Sphagnum and heath moor. 



Ahlfengren (1904) has studied the development and melioration of west 

 Prussian moors, grouping them as follows: 



(I) Reed swamps: (2) green land moors (Amblystegium), (a) reed-swamp 

 moors (chiefly Cariceta, C. paniculaia-type), (b) reed moors (Phragmiteta), 

 (c) sedge moors {Cariceta, C. rostratortype, (d) Juncus moors {Junceta), 

 (e) mixed moors; (3) high moors {Sphagnum), (a) sedge {Car ex s^r-icta-type) 

 (6) shrub {AndromedirOxycocceta), (c) hill high moor (Eriophoreta) , (d) forest 

 moor; (4) wood moors (Arboreta), (a) Saliceta, (Jb) Betuleta, (c) Alneta; 

 (5) meadow moors, (a) peat meadows, (6) culture meadows; (6) mixed forma- 

 tions; (7) field formations. 



Schreiber (1906, 1910) deals exhaustively with the concepts of moor and 

 swamp, and with the structure and classification of these communities in 

 Austria: 



Moor is defined as a habitat with at least 50 cm. of peat soil. Peat is 

 described as consisting of more or less decomposed plant remains, bearing 

 insignificant impurities, watery when fresh, capable of being burned when dry, 

 and formed since Quaternary time in cold, wet regions. The author uses the 

 term "moos" (mossland) for "hochmoor" and defines it as an area with at 

 least 50 cm. of peat consisting of Sphagnum or some substitute. The term 

 "reed-swamp" is used for "flachmoor" or "niedermoor." Horizons which 

 consist of reed-swamp fossils below and Sphagnum moor above are called 

 "reedmoss;" a meadow converted into "hochmoor" or "lowmoor" is termed 

 respectively "meadow moss" and "meadow swamp." The characteristic 

 plants of the different moors, and the communities which they form, are 

 considered at length. 



Graebner (1907) points out the following reasons why he concludes certain 

 heaths will never be invaded and controlled by trees without the interference 

 of man: 



The chief cause is not the lack of soil nutrients, but the presence of direct 

 or indirect limiting factors. Of these the layer of raw humus is the most 

 important, since it not only hinders the aeration of the soil, but also uses up 

 the oxygen directly in oxidation. In addition, it tends to promote the 

 leaching out of nutrients from the upper layers of the soil. The relation of 

 air and water in heath soils is such that the roots are mostly superficial, and 

 in consequence subject to critical variations in water-content, a condition 

 often emphasized by the strong root competition for water. 



Hill (1909) has traced the progress of marsh-building in theBouche d'Erquy, 

 in connection with the study of this area made by Oliver and his associates: 



In certain areas the vegetation, mainly Salicomia radicans and Suaeda 

 maritima, had advanced over the bare sand. In one place, an advance of 

 12 m. was recorded. Salicornia radicans had made marked advance over the 

 hummocks in the bed of the channel, and in the case of older hummocks was 

 already giving way to Glyceria and Suaeda. 



