sentence: this led him to evolve the agroforestry concept of the '' forest garden '' : based on the observation that the natural forest can be divided into distinct layers or ` storeys ' , he developed an existing small orchard of apple and pear into an edible landscape consisting of seven dimensions ; hart had a vision for the spread of the forest garden throughout even the most heavily built up areas , as he explains : bibliography inviolable hills : ecology , conservation and regeneration of the british uplands , stuart & w ( 1968 ) .