698 PROTECTION AGAINST SWA Mi's. 



carbohydrates instead of carbon-dioxide in the soil. Healthy 

 growth and activity of roots is consequently much impaired. 



iii. Increased damage by frost, sometimes killing off young 

 plants (p. 499). 



iv. Difficulties in forest management in regeneration and 

 harvesting, also in transport. The wetness of the soil increases 

 the difficulty of cultivating it, and often renders spring-planting 

 quite impossible ; seeds do not germinate in too wet a soil, and 

 young plants often perish. 



v. The tendency of a swamp to increase in area is another 

 cause of danger to the forest. 



b. According to Species. 



Hardly any forest species can withstand continuous stagnant 

 wetness of the soil, but the degree of resistance to it shown by 

 different species differs considerably. Experiments made in 

 the Palatinate, where there is an impermeable subsoil, show 

 that trees resisted a very wet soil in the following order: 



Pedunculate oak, elm, poplars, willows, hornbeam, common 

 alder ; ash, sessile oak ; Scots pine, spruce ; beech, silver-fir. 



It is strange to find the alder so low in this scale, as other 

 observations tend to prove that this species can withstand 

 more moisture than the elm. The birch, and especially Betala 

 pubescens, Ehr., will withstand much moisture in the soil, and 

 so will the rowan (Pyrus Aucuparia, Gaertn.) 



c. Age of Wood. 



Young plants are frequently killed by inundations. Poles 

 and trees on swampy ground suffer generally from root-decay, 

 especially the spruce, larch, and Scots pine. 



d. Locality and Nature of Soil- Covert/ if/. 



Swamps are more frequent in lowlands than on hills and in 

 mountain districts, on massive than on stratified rocks, and on 

 heavy stiff soil than on loose soil. Local swamps may occur 

 where the substrata are horizontal, as on the Buntersandstein 

 in the Black Forest. 



Certain forest weeds, such as sedges, reeds, peat-plants, and 



