The use of non-tropical wood for the back and sides is traditionally very old old and not just a requirement for environmental protection. Violins have always been made of maple, lutes used to be made primarily of yew and flamenco guitars of cypress.
It is therefore logical that the use of European woods does not result in any loss of sound. On the contrary, non tropical wood, which is softer than rosewood, can be used to build round and velvety sounding guitars.
Next to maple, yew, and cypress Philipp Neumann has also differrent sets of walnut, plum, pear and apple tree in stock. For the neck there is maple, walnut and alder available.