Timing for urban forestry

Urban forests seem to be the superheroes of the contemporary city, due to the many kinds of requirements they should satisfy, such as beautifying the city, offering comfortable, safe, and inclusive public spaces, enhancing biodiversity, improving environmental indicators, ensuring ecological and financial sustainability. Therefore, urban forests are mostly intended as service-providers able to solve problems, carrying out specific tasks, making top-of-the-heap performance, giving guaranteed, certain, as well as thoroughly measurable and valuable results, optimized according to the imperative of ecological functionalism. When listing the data proving the profitable services generated by planting forests into the city, reference is rarely made to time, as if the quantities of the captured pollutants or the reduction of the heat island did not critically depend on the age of the trees’ population (time as growing or evolution) as well as on their seasonal features (time as recurring cycles) and disregarding that trees even die (time as expiration). Indeed, forestation is never an instantaneous action nor a stable condition; it is rather a ceaseless, ongoing process whose effects are not immediate nor constant. Therefore, putting urban forestry into a medium-long term horizon is an inescapable and constitutive projection for any design, which is fatally called to collaborate with both the biological rhythms of the living beings and the socio-economical rhythms of the urban metabolism. Time affects the architecture of urban forests, in terms of density, homogeneity, or diversification of the planting patterns, both driven by sylvicultural practices and by the forests’ self-reliant morphogenetic actions, such as self-thinning as a strategy of survival and regeneration. Already in 1827, in his Traité général des eaux et forêts, chasses et pêches Jacques-Joseph Baudrillart underlines the advantages coming from what we today use to name ‘polycyclic plantation’: in the board titled ‘Projet d'avenues perpetuelles’, he proposes to plant uneven-aged trees of different species and to cut some trees every few decades, to keep the landscape alignment (architecture) and sustainable wood resource (ecology and economy). More recently, some landscape projects of the last twenty-five years – conceived by well-known landscape architects, from Michel Desvigne to Studio Vulkan, from LOLA to TK Studio − can highlight some possible declinations of timing for urban forestry. For instance, some of them start with dense, obsessive plantings and then make room through subtraction and thinning; other ones operate in the opposite way, pushing the increase and thickening of the trees. In any case, these projects demonstrate that assuming time as a design tool for urban forestry is challenging because it requires a large degree of unpredictability: it asks for accepting that the outcomes are linked to contingencies that cannot always be foreseen and so it spoils the very idea of efficiency and guarantee of performance typical of ecological and economical determinism. Timing for urban forestry precisely asks for overcoming the idea of urban forests as appliances, such as machines or gadgets, because forests are spatial and ecological structures, continuously changing, and they develop, get stronger as well as vulnerable, certainly age and perish, according with the laws which rule the biological and social life of both trees and humans.