When Gaudi, the great Catalan architect and urban artist, designed a new basilica for his beloved Barcelona late in the 19th century, he had trees rather than stone in mind. The great building is not yet finished but his grand design shows clearly through. The huge supporting stone columns and arches are carved as vast trunks and branches of an enveloping forest. For he believed that buildings were akin to immense, protective trees. Standing inside the columns and arches of the half-built basilica, the connection between human-built structures and natural ones comes alive. Gaudi’s greatest work was to capture this vital link.

Many people think that we have built an urban jungle from which we must escape, destroying all in our path. But this ‘urban jungle’ is not tamed by clear felling, slash and burn; for it creates a wealth of diversity that keeps us alive. The most micro-level ecosystems of cities make up the whole. So as with sustainable forestry we must always make good and replace what we take out. We must follow the rhythm of nature in energy use, water, waste and air; we must support healthy growth and regrowth from within, responding carefully to any incursions and unexpected shifts in patterns; we must create light-footed settlements that we constantly recycle; and keep the scale of activity to the lowest and least damaging level. This way we follow the hidden rules of survival using only what we need.

In the earliest human communities, sharing, reusing, cooperating, restraining, supporting and protecting led to our dominance of the planet. In modern cities, with all their resource constraints and intense global competition, we need these communal skills again. If we think of cities as ‘rainforests’ instead of ‘urban jungles’, we will recognise their immense potential value as richly diverse, crowded and intense medleys of colour, sound and constant renewal to be harvested and protected simultaneously. Our urban future depends on thinking of cities as the human equivalent of trees, as Gaudi envisioned his great basilica – dense, diverse, light and dark, self-regenerating, strong, tall and small, life-supporting and longlasting.