Trees in the City

I have a backlog of pieces I've been meaning to write about and a number of them all share a theme: urban trees. Many cities, particularly dense ones like New York (especially Manhattan) or sprawling, concrete filled ones like Los Angeles, have a pronounced lack of greenery and what trees do exist are often sickly, ugly, unkempt, or isolated. Often they are also pollution tolerant species like the honey locust and Norway maple or evolutionary survivors like the ginkgo. This leads to uninteresting monoculture landscapes that can be more depressing than a barren street on its own. It also can lead to the spread of non-native species which can become invasive. Lake of greenery and open spaces generally can also contribute to the heat island effect, in which paved and built up spaces absorb more heat during the day which is then radiated back in the evening leading to higher temperatures (both minimums and maximums) than in surrounding areas that are kept cooler by evapotranspiration, higher albedo, and other effects.

First up is a story from China this summer. China, as we all know, is a rapidly growing nation that is quickly urbanizing and converting any open space in and around its cities into factories, offices, housing, and business uses. The nature of the Communist Party's rule also means that any action is essentially indisputable and impossible to block. That, combined with the fact that China has a weak and nearly non-existent environmental movement, means that if some trees are going to be cut in the name of progress, nothing is going to change that. In the city of Nanjing, however, local activists were able to save at least a few of the cities enormous wutong trees from a proposed subway expansion. While an incomplete victory, the subway will still be built and a large number of the trees will still be removed, it is progress for a notoriously single-minded, authoritarian, and anti-environment nation.

Moving back to the US, there are two pieces I see as companions, of a sort. New York City is trying to plant 1,000,000 trees to green up the city. In doing so it has taken an approach of too many, too soon, too haphazardly, at least in the views of some critics. While I think that the city has a noble purpose that is generally to be applauded, there are some elements of the program that are potentially troubling. Some are mentioned in the article and are trivial (neighbors complaining, seriously people, who doesn't like trees?), others are more serious, at least financially (roots buckling sidewalks). A more substantial criticism is that trees are being planted at the wrong time or year or in the wrong place and are therefore struggling or dying. While I am not a botanist or arborist and the article does little to resolve the he said/she said, from what I know of the Bloomberg administration it would not surprise me if the mayor just decreed that trees be planted and that they be planted by a date certain, details be damned. Two additional problems were not mentioned in the article. One is that as the climate changes, so will the suitability of the urban environment for certain species. Trees live a long time and care should be taken to select trees that are fit to survive in both the present and warmer, wetter city of the future so as to mitigate future losses and replacement costs. This was one element of Chicago's climate change plan (which I hope to write about in the future in more depth). The other is that trees, like most organisms, have a finite lifespan and planting huge numbers of trees at the same time can set up future problems, like those seen in Atlanta where drought and development pressures have combined with age to kill off a huge number of the city's trees.

And finally, a fully positive story about rescue and rediscovery. The Franciscan manzanita was long thought extinct in the wild until it was discovered growing in the middle of a traffic island in San Francisco's Presidio district in the path of a road project. The project was suspended and the plant was moved to a more protected location within the park (click here to see a picture of the process). Now it is eligible for protection as an endangered species and botanists are looking for cuttings in botanical gardens and nurseries to plant near the wild one in the hopes of fostering enough genetic diversity to create a self-sustaining recovery population.