A Methodological Framework for Quantification and Valuation of Ecosystem Services of Tree- Based Intercropping Systems Mahbubul Alam, , Alain Olivier, Alain Paquette, Jérôme Dupras, Jean-Pierre Revéret, Christian Messier 2 nd European Agroforestry Conference June 4 - 6, 2014 – Cottbus, Germany