Monodominant tree species within an ecosystem are defined by their overwhelming dominance in terms of abundance and biomass compared to other tree species present. They typically occupy at least 60-70% of the total tree population in the area, creating a near-monoculture stand.
I agree with Tesfaye Humnessa but I would give a percentage of 51 or more to be monodominant. Of course, this is opinion, since there are no rules in ecology and statistics :)