THE STREET AS A RAVINE, LANDSCAPES OF NEGOTIATION
Although landscape in urban contexts is almost exclusively associated with the rural state of the cities’ periphery, or to urban parks as “healing nature,” in this column the street is approached as the most daily way to live the urban landscape. Like ravines, these linear grooves are microclimates but of an artificial topography. In the city, they are also a meeting place between natural systems and anthropic systems, a negotiation process where, in most cases, the natural systems are the big losers.
Although the native vegetation of the Metropolitan Region − understood as thorny bushes and meadows − is adapted to a Mediterranean climate of a prolonged dry season and therefore is resistant to water scarcity, the lushest vegetation in the area − the sclerophyllous forest − is associated with runoff from the Cordillera, located beside the ravines (1) where the water from spring thaws drains. These are places of shade that escape the summer heat and create favorable micro-environments for the proper development of vegetation. When the ravines correspond to a “narrow passage between mountains,” their slopes which are predominantly-north and predominantly-south are distinguished by their vegetation, which responds to the conditions of sun exposure and shade respectively. However, the main characteristic of these ravines is that they are dynamic due to the effects of the passage of water, which because of its speed erodes and builds a wild landscape, steep and with varied vegetation. As the ravines descend from the high mountain, they meet the valley in the concave spaces of the Cordillera, which are as architect Rodrigo Pérez de Arce A. describes, “spaces essentially oriented by their declination in plan, as well as their topographic decline” (2).
(1) The ravines as grooves or crevices of a territory with a prominent slope, where water flows permanently or intermittently. Definition according to the Royal Spanish Academy,Diccionario de la Lengua Española de laReal Academia Española (09 Dic. 2013), <www.rae.es>
(2) Rodrigo Pérez de Arce, “Los Márgenes Posibles del Valle del Alto Aconcagua: el Valor Propositivo de la Representación Arquitectónica” (The Possible Margins of the Valley of the Aconcagua: the Proactive Value of Architectural Representation) in ARQ 34 (Dic. 1996), 52-61
In the context of the city of Santiago, the urban topography is physically defined by the buildings in height and by the air that distances them. The street emerges analogously to the ravine, as a cleft where the water tends to go and, therefore, where the vegetation tends to grow. The street as a suitable ravine for the development of ecologies and environmental services in the city has not been properly exploited due to the systematic waterproofing through pavement of the soils, the limited space for growth of trees between the concrete slabs, poor practices of pruning, and the inefficient interaction between infrastructure − electrical, telecommunications, drinking water and waste water pipes − and flora.
Part of the benefit of understanding the street as an ecological system can be deduced from studies presented in the magazine Urban Forestry & Urban Greening, where it is explained, for example, that treetops have the capacity to intercept rainfall, thus reducing floods and helping urban drainage. In this sense, making space for natural systems can even improve the functioning of urban systems. In fact, the protection of the tree tops not only protects the surfaces of earth but is also a benefit for paved sectors as it protects these sectors from the corrosive action of direct rain and thereby minimizes maintenance costs (3). The street vegetation not only consists of public trees and the low vegetation that could exist on the median strips or sidewalks; the gardens of private homes also contribute to existing natural systems. Although the limits of private plots are defined, roots and tree tops do not distinguish these limits and criss cross these according to their needs. However, processes such as high-rise construction transform these drainage sites and micro-ecologies into high-traffic soils. In this context, the trees of the street acquire a more prominent role for regulating heat and diminishing soil erosion. In addition to the benefits mentioned, the foliage also improves the air quality of the city. As David Nowak, an American expert on urban forests, human health, and environmental quality, points out, trees remove pollutants from the air by absorbing them through their stomata, while others are trapped on the plant surface (4). According to Nowak, plants act during the day at the time of year when the trees have leaves and produce evapotranspiration (5). Based on the text, Removal of Air Pollution by Urban Trees and Shrubs, it can be deduced that deciduous species renew the filtering capacity of their contaminated stomata precisely by losing their leaves, while perennials catch pollutants throughout the year on their surfaces, thus both types contribute to diminish the amount of suspended particles (6).
(3) Ver D. Armson, P. Stringer y A.R. Ennos, “The Effect of Tree Shade and Grass on Surface and Globe Temperatures in an Urban Area” in Urban Forestry & Urban Greening Journal www.elsevier.de/ufug
(4) See David J. Nowak, Daniel E. Crane and Jack C. Stevens, “Air Pollution Removal by Urban Trees and Shrubs in the United States” in Urban Forestry & Urban Greening Journal (10 Dic. 2013) www.elsevier.de/ ufug
(5) See Nowak, Crane and Stevens.
(6) See Nowak, Crane y Stevens.
While we could continue to mention the benefits of caring for vegetation and the multiple water systems and other natural resources within the urban space, through these examples, we can understand the importance of the natural dynamics and the ecological systems on a larger scale and how they benefit urban environments. The street, as accumulator of runoff and linear arborization, is a propitious medium for the proliferation of new ecologies, provided that the operation of the natural elements involved is understood. Enhancing the forestation of Santiago’s interior not only brings aesthetic benefits, but also − and mainly − environmental benefits: drainage, thermal regulation, reduction of soil erosion and reduction of air pollution. It is time to conduct a fair negotiation, without prioritizing anthropic infrastructures by establishing short-term solutions: that the street should be a balanced meeting place between the urban and the natural, so that social encounters take place in a dynamic and pleasant atmosphere.
Camila Medina Novoa. Architect, and holds a Master’s degree in Landscape Architecture from UC, 2014. Professor in theory courses at PUC, UDP, and UFT universities. Independent Landscape Architect.