SOIL ORGANISMS 



247 



per cent of humus. ^ In the Firmetum, as well as in the Festucetum 

 violaceae, the decomposition of organic matter proceeds more rapidly 

 than in the Elynetum and the Curvuletum, probably due to the higher 

 lime content. The Elynetum has a greater productive power than the 

 Curvuletum, since the annual growth of the former is greater, and since 

 there is more Hgnin in the plant body. 



In the Curvuletum, where humus destruction proceeds the most 

 slowly because of the high acidity, a certain equilibrium seems to be 



6^-5.9pH 



— . ' . ■ ■■..-«...>i 



25- zip H 





.... . t 15-20%:.. ■ ■,,//v. 



62-S.SpH 



S.Z-if.6pH 



Relafive produciion 

 of vegetable maifer 



Humus per cent 



Firmetum Festucet Eljjnetum Curvuletum 

 violaceae 



w^^ Saiuraied mild ^^ Unsafuraied acid 

 ^^ Humus ^^ Humus 



Fig. 123. — Relation of the annual production of vegetable matter, the pH optimum, 

 and humus production in associations in the Central Alps. 



reached between humus formation and destruction when about two- 

 thirds of the plant remains are destroyed (Fig. 123). 



The decay curve of the Curvuletum of the alpine slopes in the 

 eastern Central Alps gives a good idea of the general progression of 

 humus decomposition in an alpine climate (Fig. 124). The theoreti- 

 cally highest possible humus accumulation would amount to about 90 

 per cent, since Carex curvula contains around 8 to 12 per cent of 

 incombustible ash. The highest actually observed humus percentages 

 in the Curvuletum lie between 60 and 70, since the rapid initial destruc- 

 tion quickly removes the easily decomposed albumin, fatty compounds, 

 etc. 



In spite of a considerably greater production of material than 

 in the Curvuletum, the humus percentage of the meadow associations 

 of the Swiss lowlands averages only about 5 per cent. Decomposition 

 proceeds here much more quickly than in the perhumid alpine cHmate. 



^ The quantity of humus (thickness of humus layer) is not to be confused with 

 the degree of decay. The former attains in the Loiseleurietum 1 m., in the 

 Curvuletum 40 to 50 cm., in the Elynetum 15 to 20 cm; 



