Oak woodlands and in particularly the Portuguese montados and Spanish dehesas have high conservation and socio-economic value.

For maintaining the sustainability of such systems it is necessary to understand the dynamics of oak natural regeneration.

Herbage layer is one of the main factors affecting tree regeneration.

Although most research on the effects of herbage layer on tree and, particularly, oak regeneration has been centered on competition between herbs and tree seedlings.

In Mediterranean systems, due to microclimatic effects created by the herbage layer (e.g. less variable temperatures and low soil evaporation) it is possible that processes such as facilitation between herbs and tree seedlings occur.

In this project we used stable isotope analyses (C13 and N15) to assess how is the herbage layer affecting water and nitrogen use efficiency by cork and holm oak seedlings.

In particular we want to assess how do oak seedlings respond to species composition and standing crop biomass of the herbage layer.

Results obtained may be use in projects aiming to promote restoration of Mediterranean oak woodlands and, in particular, montados and dehesas.