Urban Jungle
In Hong Kong, hanging gardens sprout on building walls
One fig tree sprouted from the 14th floor of an apartment house. Others clung to sheer facades, creating a kind of vertical urban oasis. Overall, a recent survey spotted nearly 700 trees and shrubs naturally sprouting from buildings in busy Hong Kong. The results highlight the unusual urban “forests” that have found a way to grow in some of the world’s densest cities.
“The walls and buildings in cities afford a third dimension for exploration by nature,” C.Y. Jim and Wendy Y. Chen report in Urban Forestry and Urban Greening. “They contain a surprising assemblage of vertical and horizontal niches, with a varied collection of surfaces and edges, to allow colonization by plants and other organisms.”
Past studies, for instance, found nearly 60 species of trees and shrubs growing from historic buildings in Italian towns. In the historic Czech city of Plovdiv, more than 131 species cling to walls. A recent study of modern buildings Christchurch, New Zealand, found 117 species. Few researchers, however, had surveyed “vertical forests” in rapidly growing cities of the humid tropics.
In Hong Kong, Jim and Chen surveyed three old and densely developed districts that have buildings dating back to the 1840s. Overall, they counted 692 arboreal, or tree-like, plants belonging to 11 species. Most were native fig (Ficus) trees, and tended to grow on buildings constructed before 1980. Three-quarters perched on the first six floors, but a few had a better view, rooting as high up as the 14th floor.
In forests, fig species routinely climb up and “strangle” other trees, and this habit probably explains “the ability of Ficus trees to grow on walls and buildings,” the authors note. “In the city, the seeds are deposited by birds and bats whilst they roost on the elevated perches of buildings, and in the joints and weep holes of stone walls.” And once the trees take root, residents are often kind, they note, pruning the plants instead of yanking them out by the roots. “From the viewpoint of urban ecological conservation and biodiversity enhancement, such a moderate “let live” tree treatment is commendable,” they write. “It can prevent eradication of a precious and interesting” flora that “adds a new dimension to urban ecology.”
These tenacious forests, they add, “deserve to be studied and conserved using innovative means to maintain…urban biodiversity of plants and their faunal partners.” – David Malakoff | January 27, 2011
Source: Jim, C., & Chen, W. (2011). Bioreceptivity of buildings for spontaneous arboreal flora in compact city environment. Urban Forestry & Urban Greening DOI: 10.1016/j.ufug.2010.11.001
Image © Vladimir Piskunov
