Dear Nature Lovers,
Greetings from oikos !

Grasses being very hardy serve as pioneering species in succession.

Pioneering species are hardy species, first to colonize damaged ecosystems. 
e.g. In Western Ghats forests slashed & burnt for making way for cultivation. 
Once this cultivation is over, land becomes devoid of nutrients and 
original species are not able to cope up in such soil. 
In this condition, grasses like Themeda find the opportunity. 
So these are also called as opportunistic species. 
These species act as pioneering species and
improve the organic matter in the soil to improve its fertility.
So that the original conditions of the soil are attained 
which can support earlier superior forest species. 
Though it may takes years to restore back original forest,
species like Themeda help to start that process on a barren land.
Those are essential raw material to begin a chain of ecological succession 
that ultimately leads to a more biodiverse steady-state ecosystem.