Grasslands of the World.pdf - Disasters and Conflicts - UNEP

388
Plate 10.1
Agropyron pectiniforme.
Grasslands of the world
vegetation occur. Ramenskii’s classifications are known as “phytotopological”
with major emphasis on the habitat . First, all natural grassland is divided into
dryland or floodplain. Second, subdivisions are based on topography and
moisture conditions. No less than 50 categories were formulated, each with
22 subdivisions based on moisture conditions. Within similar habitats, several
plant associations occur.
For instance, on dark-chestnut loamy soil of the dry steppe plains, Ramenskii
found the following associations as grazing intensity increases:
• in virgin steppe, a low-grass sward with Stipa lessingiana (Plate 10.2), but less
Festuca sulcata ;
• after a few years, predominantly Festuca sulcata ;
• under intensive grazing , Poa bulbosa associations; and
• finally, after excessive grazing , an association with Polygonum aviculare .
This is typical succession-regression (see also Table 10.2). Ramenskii’s
analysis of the constituents of the vegetation itself was not quantitative, but
estimated by so-called vertical “projection”, by simply estimating the degree
of cover at one particular date. No mechanical devices for ranking constituent
species or for weighing samples were employed. Potential yields were estimated
from empirically established standard graphs (see also section below on
Botanical condition ).
After ploughing and cropping steppe for several years, the following appear
in the fallow :