International Symposium on Greener Cities for More Efficient Ecosystem Services in a Climate Changing World

The idea of garden is expressed, for the first time in history, by the Mesopotamian civilization as early as the IV millennium BCE as drawings and poetry texts showing a wall fencing one single tree. This is the first representation of the idea of sheltering/protecting a tree by human artifacts and, in its simplest form, brings the idea of the tight relationship between horticulture and urban environment. The "jardinu" of Pantelleria, a drystone wall shaped into an open-top tower encircling a single citrus tree, fully matches both in its founding idea and its physical implementation the elemental idea of the Mesopotamian garden. Such traditional growing system, developed in Pantelleria to cope with water scarcity, is an artifact at the service of households, fully integrated into the urban settlements of the Island and providing a valuable source of fresh fruit to families despite the lack of irrigation water. Currently, as many as 500 of such structures are still active in Pantelleria, standing as the distinguishing landmarks of the island. The simple, albeit expensive, principle of enclosing a tree inside a protective wall has many effects on the surrounding environment and on the eco-physiological behavior of the tree itself. We discuss here this system from the point of view of the interactions between the tree and the enclosing wall, focusing on the ability of the "Pantelleria citrus garden" to affect the water cycle of the tree and to avoid irrigation at all. Our analysis shows beyond simple, easily recognizable effects such as wind protection and the related reductions in transpiration, diurnal thermal dynamics of wall's stones actively affects the water balance of the system. Implications of this analysis suggest that the knowledge behind the empirical building-rules developed over the years for the construction of such structures are expression of the physical principles underlying the environmental dynamics of the "Pantelleria citrus garden".