Māris kļaviņŠ, azamat azizov, JĀnis zaļoksnis environment, pollution, development: the case of uzbekistan

Figure 4.12. 
Ecological 
succession in terrestrial 
ecosystems
A field becomes over‑
grown and transforms 
into a spruce forest 
within a period of ap‑
proximately 80‑100 years. 
Several stages can be 
distinguished in this pro‑
cess. During each stage, 
there is a distinctive bio‑
logical community with 
a specific composition of 
plant and animal species.

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4. HUMANS AND THE ENVIRONMENT
 57
becomes shallower and shallower. Overgrowing also takes place 
from the lake’s shores; consequently, the open water area becomes 
smaller and smaller – until it disappears completely.
The main characteristic feature of ecological succession is the 
changing composition of species in an ecosystem. The total bio-
mass of living plants and animals and its productivity within the 
ecosystem change with that. Parallel to that, the mass and product-
ivity of organic substances produced in the ecosystem also change. 
Thus, another feature of ecological succession is changing amount of 
biomass produced within a specific unit of time. There are two main 
types of succession: primary and secondary. In the case of primary 
succession, the development process of an ecosystem starts on 
bare rocks, for example, on volcanic lava, in a sand dune or gravel 
pit.  Micro-organisms,  algae,  lichen  and  moss  appear  first.  When 
these  organisms  die  off,  organic  substances  gradually  accumulate, 
and  the  soil  is  formed.  After  that,  plant  and  animal  species  start 
to propagate, successively replacing one another along with the 
develop ment of the ecosystem. 
In the case of secondary succession, an ecosystem starts to 
develop following the impact of some forceful external factor, for 
example,  forest  fire,  hurricane,  deforestation,  ploughing  the  soil 
and the like. In this case, succession takes place on pre-existing soil