Naturaleza Urbana y Espacios Verdes

By Andre Mader, Montreal

Urban Nature and Green Spaces | Sustainable Cities Collective.

Me gusta simplificar lo que constituye la naturaleza urbana en un área dada. Por lo tanto, pensé que podría ser interesante proporcionar una visión general y preguntar si algo falta o fué erróneamente incluido. Este artículo expresa mi punto de vista sobre la variedad de formas que podrían incluirse en el marco de la “naturaleza de las ciudades”. En los mapas de planificación, la naturaleza está representada por polígonos, líneas y puntos. Los polígonos son formas, denotando el área. Las líneas son características lineales, aunque no necesariamente rectas. Los puntos son características individuales lo suficientemente pequeñas como para no requerir una forma que las represente

Formas

Las ciudades fragmentan el paisaje que ocupan. Si ese paisaje no estaba ya transformado por la agricultura, los fragmentos pueden contener remanentes de ecosistemas naturales. La sostenibilidad de estos ecosistemas relativamente prístinos depende de su tamaño, forma y conectividad entre sí, así como del tipo de presiones que experimentan desde el exterior. En zonas ‘calientes’ de biodiversidad como la Región Florística del Cabo en Suráfrica, cada residuo es considerado por los conservacionistas como una preciosa contribución a los blancos nacionales y locales para conservar muestras representativas como un porcentaje de la extensión original. Aunque éstas son la forma “más pura” de la naturaleza en las ciudades, varios estudios, de décadas atrás, sugieren que difieren de su estado anterior, sin fragmentar (véase, por ejemplo, Andren, 1994). Los fragmentos pueden incluir humedales, que están sujetos a las mismas presiones que otros remanentes, así como contaminación adicional y extracción de agua.

1) Natural vegetation. Credit Brian RalphsNatural vegetation. Photo: Brian Ralphs

Así como ciudades costeras adicionales pueden contar la franja de zona costera –tanto playas como el mar– como parte de los activos de naturaleza urbana. Aunque a menudo son muy utilizadas y sobreexplotadas, estas zonas están conectadas a ecosistemas lejanos y, alrededor del mundo, tienen características e incluso especies en común. A menudo, los gobiernos de las ciudades también son responsables de gestionarlos, mientras que los residentes y turistas dependen fuertemente de ellos para la recreación, –desde nadar en la playa hasta observar ballenas.

2) Camps Bay, Cape Town, Credit sat.greatstock.co.zaCamps Bay, Cape Town. Photo: sat.greatstock.co.za

Parques en la ciudad pueden tomar una variedad de formas, pero típicamente son segados y manicurados en cierta medida e, históricamente, poco esfuerzo se hizo para naturalizarlos. Hoy en día, muchos están rompiendo ese molde. El Tiergarten en Berlín, por ejemplo, tiene secciones en las que se permite que crezcan silvestres, mientras que otros se manicuran a la manera tradicional. Los parques son para la gente y su naturaleza será determinada en última instancia por lo que la población local prefiere. Con las ideas sobre la naturaleza de las ciudades evolucionando, podríamos ver un futuro, en el que el enfoque de Tiergarten se vuelve más común.

3) Urban Park. Credit Florent LannoyAn urban park. Photo: Florent Lannoy.

En la ciudad promedio, los jardines probablemente excedan por mucho los parques en área total. Sin embargo, están intensamente compartimentados, limitando el flujo de genes entre ellos excepto por los animales voladores y las plantas dispersadas por ellos y el viento. También es probable que los jardines contengan una variedad mucho mayor de especies que los parques en una ciudad dada, aunque muchos o la mayoría pueden ser especies exóticas que no desempeñan las mismas funciones que los mas grandes y originales ecosistemas. Pueden ser notablemente diversos, como se demuestra en el famoso ejemplo de 2.673 especies de plantas y animales registrados en el jardín de Leicester en el transcurso de 30 años (Owen 2010).

5) Kirstenbosch National Botanical Gardens, South Africa. Credit sat.greatstock.co.zaKirstenbosch National Botanical Gardens, South Africa. Photo: sat.greatstock.co.za

Los jardines botánicos merecen mención aparte debido a la experiencia educativa que ofrecen sobre los parques y la experiencia más expansiva (y más cara) de la naturaleza que ofrecen sobre jardines privados. A menudo emparejados con invernaderos, exposiciones educativas y restaurantes, concentran la experiencia de la naturaleza en un espacio bien gestionado mientras a menudo maximizan la biodiversidad. Algunos, como el impresionante Jardín Botánico Nacional Kirstenbosch  de Ciudad del Cabo, que transita a la vegetación natural. Al penetrar más lejos dentro de Kirstenbosch y lejos de los restaurantes, el jardín se vuelve más salvaje mientras que las multitudes se vuelven más escasas.

4) Cottage garden. Credit Garry KnightCottage garden. Photo: Garry Knight

Brownfield sites are the neglected cousins of the preceding categories. They have the added ignominy of an uncertain or terminal future, with many being earmarked for future development. Studies have shown, however, that they play a role in supporting biodiversity and even in providing a natural experience (Bonthoux et al. 2014). Importantly in the context of urban nature, a perceived value (often based on the presence of a single, iconic-enough species such as a breeding pair of birds) may be motivation enough for enhancing such sites or retaining a portion when they are developed, for the sake of nature.

6) Brownfield site. Credit Russell James SmithBrownfield site. Photo: Russell James Smith

Lines

A variety of green infrastructure can fulfill the purpose of a natural green corridor. In systematic biodiversity planning, however, corridors are considered to be strips of natural vegetation and the ecosystems they support, which connect more substantial fragments of natural vegetation. Their effectiveness depends on their length and breadth, and the species that need to use them to traverse the urban matrix, and entire books have been written on the questions of how they should look in terms of width, length and quality (see for example Hilty J and Lidicker WZ. 2006).

7) Green corridors through a city. Credit La Citta VitaGreen corridors through a city. Photo: La Citta Vita

Avenues of trees or shrubs along roads are, in some ways, the linear equivalents of parks. They are, however, typically less diverse and imaginative, despite offering an undeniable improvement on a treeless road. Singapore is a world leader in re-thinking the concept of an avenue. In this crowded city, where space is paramount, biodiversity authorities have responded accordingly by planting multi-species, multi-layer “avenues” that contribute to the biodiversity of the city as much as to its aesthetics.

8) Multi-species avenue in SingaporeA multi-species avenue in Singapore. Photo: Jeremy Woon

Water lines” in cities range from relatively sterile concrete canals that carry only water, to rivers with a variety of plant and animal life and vegetated banks. The former is often a wasted opportunity to bring nature to the city, although it may be necessary where space is severely limited. The ecosystem services provided by naturalized water lines, such as flood attenuation, water purification and recreation may, however, surpass the benefits of a canal even in economic terms. Perhaps the most popular option is a compromise between these two ends of the spectrum. In Seoul, the Cheonggyecheon Stream—re-engineered after the demolition of a highway —attracts thousands of visitors but is expensive to maintain because water needs to be piped in from elsewhere. Retrofitting often tends to be expensive—a reminder of the importance of design in early-stage city planning.

9) Cheonggyecheon stream in Seoul. Credit d'n'cCheonggyecheon stream in Seoul. Photo: d’n’c

Points

Many members of the public don’t think of any of the shapes and lines discussed above when considering nature in cities—they think of wild animals. Many “cosmopolitan”, or widespread, species play a role in various parts of the world. Some are appreciated by the public (squirrels, ducks), others abhorred (rats, cockroaches), and still others produce mixed feelings (pigeons, seagulls). Many such species have little value in terms of biodiversity due to their ubiquity and uniformity; nevertheless, they are nature, and must be counted as residents of cities. One common phenomenon regarding urban wildlife is that the rarer the species is, the more it is valued. This is demonstrated, for example, by the excited reaction of tourists having their first experience of a species that may be common and problematic in a city they are visiting for the first time, such as foxes, raccoons or mallard ducks. Animals in the city are usually mapped (i.e. treated as points) only if they are relatively rare.

10) Falcon chick. Credit Metropolitan Transportation Authority of the State of New YorkFalcon chick. Photo: Metropolitan Transportation Authority of the State of New York

Plants constitute many of the features discussed under shapes and lines, but in the urban context, or the context of the planner, they can also be points. This is especially true for large and iconic trees (see also Trees as Starting Points for Journeys of Learning About Local History and Heritage Trees of Cape Town (Continued) by Russell Galt), which may be located in a concrete matrix, as well as individuals of rare species in parks or gardens. Individual trees may have great natural and cultural relevance. In the seaside town of Mossel Bay, in South Africa, for example, the “post office tree” is an ancient milkwood (Sideroxylon inerme) and a national monument that acted as a mail system for sailors in the 1500s, who hung their shoes with notes in them for safe delivery.

11) Credit London TreesPhoto: London Trees

Others

It’s not always so clear whether a feature should be regarded as point, line or polygon. For example, a cluster of points can constitute a shape. A population of sedentary organisms (i.e. mostly plants), especially a rare species, may therefore be represented by a polygon of the area in which they are distributed, rather than by individual points.

12) Cluster of points constituting a polygonCluster of points constituting a polygon.

Green roofs and, to a greater extent, green walls, are difficult to categorize in the spatial sense but are also important contributions to urban nature.

13) Flower growing in a sandwich space. Credit Anderson ManciniFlower growing in a sandwich space. Photo: Anderson Mancini

As we get further into more-difficult-to-define features, we should not forget the “sandwich spaces” discussed by Timon McPhearson and Victoria Marshall—the spaces between buildings, rooftops, walls, curbs, sidewalk cracks, and other small-scale urban spaces that exist in the fissures between linear infrastructure (e.g. roads, bridges, tunnels, rail lines) and our three dimensional gridded cities. These spaces can be reservoirs for species, assist with water infiltration and offer other benefits discussed in McPherson and Marshall’s piece.

14) Green wall. Credit Swiss.pitonGreen wall. Photo: Swiss.piton

Lastly, in cities, representations of nature are to be found in the intensively managed and artificial confines of zoos, aquariums, and museums. If urban nature is to be defined as that which provides us with an approximation of a natural experience, and if it contributes to the conservation of biodiversity, these cannot be excluded. Especially if education and awareness are our goals, these features need to be considered a part of the nature of cities.

15) Penguins at Edinburgh Zoo. Credit Glen BowmanPenguins at Edinburgh Zoo. Photo: Glen Bowman

Concluding remarks

This was a brief blow-by-blow summary of urban nature in categories, as seen through the eyes of a conservation biologist. The tools that are used to map and appoint attributes to these features, to indicate their location and importance, is often a geographic information systems (GIS)—a digital mapping device. We all use the resulting maps to get around cities with which we are not familiar, while city administrations increasingly focus on a network of green spaces as a key component of conserving biodiversity in the urban environment. For these reasons a holistic, spatial view of the nature of cities will always be an important contribution to our understanding and conservation of the nature of cities.

Andre Mader is a conservation biologist specializing in subnational implementation of the Convention on Biological Diversity, seconded to the Secretariat for a third year by ICLEI.

On The Nature of Cities

References

Andren H. 1994. Effects of habitat fragmentation on birds and mammals in landscapes with different proportions of suitable habitat: a review. Oikos. 71:355-366.

Bonthoux S, Brun M, Di Pietro F, Greulich S, Bouché-Pillon S. 2014. How can wastelands promote biodiversity in cities? A review. Landscape and Urban Planning. 132: 79-88.

Hilty J and Lidicker WZ. 2006. Corridor Ecology: The Science and Practice of Linking Landscapes for Biodiversity Conservation.

Owen J. 2010. Wildlife of a Garden—a thirty year study. Royal Horticultural Society

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