Infrastructures of Sustainability

Introduction
This document intends to confront the theme of the relationship between the city and natural processes with regards to the eco-sustainable development of the urban environment, proposing a new approach to the theme of open spaces and green spaces, considering them as sites for activating the process of environmental regeneration of the city.
The hypothesis can be reassumed in the proposal for a system of open spaces and green spaces configured as a network. A green network which is complex and penetrates deeply within the urban fabric, which is constructed as a fabric for ecological regeneration and the improvement of the hygienic and sanitary conditions of the urban ecosystem, contributing to the “design” and the structure of its form, organising and activating relationships and connections between its various parts.
A green network which assumes the connotations of a true infrastructure for the environmental sustainability of the city and which, equal to other infrastructures, performs a precise function and plays an important role in the urban structure.
A continuous framework, a grid which is no longer geometric, but organic, which describes the city with clarity and qualifies its spaces (Dierna 1996), the pattern of which invests different scales, from those of the geography of river networks to the urban layout of tree lined avenues, unfolding an ample range of morphologies: from those of the wild landscape to formal gardens, from cultivation gardens to forests, from the mirrored surface of bodies of water to green pathways.

The choice of the term “network” underlines a reflection which the world of ecology has recently undertaken through the introduction of the concept of an “ecological network”, while at the same time it manifests the will to establish analogies between “green network” and “technical networks”, those which are made up of continuous physical infrastructures such as roads, railway lines and hydro lines, central to the most advanced hypotheses of underlining the services provided by spaces and corridors of the network in the urban environment, making possible a process of sustainable development.

The intervention context for green networks is that which may be identified in the idea of “urban environment”. An idea which manifests, already through the matching of the terms “environment” and “urban”, the constant oscillation of the contexts of application between two “natures”: the “urban” and the “environmental”, in human settlement.
We must then turn to a context which is characterised by the co-existence of natural or almost-natural sections, together with built works and anthropical infrastructures, the reciprocal interferences between which constitute sources of either conflict or opportunity. The urban environment about which we are thinking includes then both the urban territory in addition to the extra-urban territory which is experiencing phenomena of urbanisation, at varying intensities. All the different forms of the “urban condition”, the compact city, the periphery, the sprawl, urbanised territories, may then be gathered together in a programme for a network of green spaces.

Multi-Functional Networks
To anticipate the realisation of green systems according to a “reticular” model, with the role and attributes of a complex urban infrastructure, is equal to advancing the proposal of an innovation in the culture and practice of planning of urban green spaces.
The choice of the networks corresponds in fact in the first place with the objective of realising a “continuous” green system. Which is proposed as an alternative to the system of “fragments”, the result of a praxis, which attributes marginal activities to green spaces with a scare ability to compete with more remunerative uses of the urban lands.
The continuity of the system allows for green spaces to accept roles of ecological regeneration and the improvement of the hygienic and sanitary conditions of the urban environment, unthinkable through the use of the “fragments” model. An improvement in the ecological and environmental conditions may be activated only by guaranteeing the presence of green areas within the pervasive built fabric.

The objectives of the network, looked at as a whole, at the urban scale, are threefold:
1. assuming a role of “structure” within the urban context;
2. creating a “fabric” for ecological regeneration and the improvement of hygienic and sanitary conditions within the urban environment;
3. distributing green spaces and public services and providing spaces for free time activities. The objective expressed in the second point calls for the hygienic, sanitary and ecological services which the green networks may perform within the urban environment, hilighting its role of “infrastructure of sustainability”. Hygienic and sanitary services concern the possibility of using the units of the green network in order to contribute to the restoration and mitigation of the impact produced by human activities on the urban environment. Contributing to the reduction of pollution of both air and water, in addition to improving micro-climatic conditions.
The ecological services deal with the capacity to restore the natural cycles of primary resources, air, water and the ground plane; increasing the level of biological diversity and the capacity of the urban fabric to auto-regenerate.

A Network of Networks
The structure that is schematically proposed as a model for the formation of the green network in urban environments is the result of the combination of open spaces and green spaces. Each different in nature and morphology, the typological articulation of which may be based on various criteria, reacting to change from the specific point of view adopted. That which we intend to privilege is a point of view which looks above all at the infrastructural role played by the network, attributing particular importance to the services being offered. In this way the considerations relative to the ability of space to be effective in processes of ecological restoration and in compensating the damage cause by urban activities, acquires particular significance. Capacities which vary as a function of the dimensions of space, the context of the intervention, the form of use tied to them and the characteristics of the project.
The network is schematically composed of green spaces and green corridors, which represent the “nodes” and the “patterns” of the network.
The nature of the spaces and the corridors may vary widely in a gradual system which moves from the forest to the course of a river, from a garden to a tree lined avenue. The range of functions performed by the green spaces and green corridors, dependant upon numerous factors, is influenced by their scale and the contexts in which they are located. In this way for example, the ecological functions are at a maximum in large spaces and corridors in low density urban contexts, where insertions of natural elements with a high biological value become plausible. While they are minimum at the small scale in densely constructed areas, as a benefit to those functions tied to human fruition.

The green network idea may be described as a “network of networks”. A network formed by the coming together of many networks; the hydrographical network, the network of road infrastructures, the network of technological infrastructures, the network of reserved areas, the network of parks and gardens, etc.
Networks with substantial differences and special attributes, whose role within the urban green network is defined by context and design objectives, other than by internal rationalities.
The networks which contribute to the construction of a green urban network will in fact have specific rationalities of realisation and management. In this way, the network tied to systems of mobility will undertake those functions which are prevalently hygienic and sanitary, as the network tied to the hydrographical network will largely provide ecological services.

Conclusions
The hypothesis of green networks as infrastructures for sustainability, as defined, requires a new outlook on the part of those researching spaces and their concrete relationships. The conditions for the feasibility of this proposal, above all in territories of urban dispersion, are in fact tied to the capacity to retrace, in the multitude of open spaces which mark the form of the contemporary city, the implicit potential for the creation of policies of green infrastructures.
According to this hypothesis, the role of open spaces, even in light of the recent reflections on the concept of the urban ecosystem, assumes a new centrality in policies for urban sustainability. For this reason we propose to look at open spaces not as free areas waiting to be built upon, but as a “resource”, taking advantage of the opportunity they offer as spaces for re-balancing the environment.
Seen in this way, green networks as infrastructures for the environmental sustainability of urban contexts, if considered as public works offering hygienic, sanitary and ecological performances, may be compared to the mobility network and other technical networks, public works which require a collective force in terms of cost, but which in return offer “services”.

Naturally this approach, which underlines the functional nature of open spaces and green spaces, does not intend to exclude other approaches, from urban composition to the design of the landscape and the different and alternative methods of using spaces within the urban environment which may be imagined. Vice versa, it is held to be useful, in the design of this green network, to bring together these various hypotheses, which investigate, from different angles, the role and meaning of open spaces, focusing attention for example on their role in the urban landscape, on the history of transformations which they have created, etc.
We are not then proposing to turn the design of green networks into a piece of sectorial politics, but more importantly we are aiming at the acceptance of an integrated vision which makes green networks a space for experimenting with policies of urban sustainability, the latter to be understood in its most ample definition.


References
Angrilli, M., 2003. Reti ecologiche. Lo spazio europeo tra pianificazione e governance. Ecological Network. The European Space Between Planning and Governance. eds. F. Karrer, S. Arnofi, Alinea Editrice, Florence.
Angrilli, M., 2002. Reti verdi urbane. Urban Green Networks, Palombi Editori, Rome. Angrilli, M., 1999. Greenways, Urbanistica, 113, pp. 92-96, INU, Milan.