In this work we present a P system based model of the ecosystem dynamics of
plant communities. It is applied to four National Hunting Reservoirs in Catalan Pyrenees
(Spain). In previous works several natural high- mountain- ecosystems and population
dynamics were modeled, but in those works grass was considered unlimited and changes
in plant communities were not taken into account. In our new model we take advantage
of the modularity of P systems, adding the plant communities to an existing model on
scavengers dynamics. We introduce the plant community production and two possible
changes or evolutions in communities: due to less grazing pressure, and due to
recovering pastures with human management as for example re or clearing
