It is the International Day of Forests. The theme this year is “Forests and Sustainable Cities”, so I’ve chosen a tree associated with urban landscapes (particularly in India!). Banyans, or banyan figs, can become so massive in both girth and canopy spread that they become destination sites for tourists.
Ficus benghalensis are evergreen or semi-evergreen trees native to India and Pakistan. However, they have been introduced to other tropical and subtropical regions of the world. Thought to only carry a moderate risk of invasiveness due to a complex pollination mechanism requiring species-specific wasps, Ficus benghalensis is still considered invasive in the Bahamas, Australia, Singapore, Western Samoa, and the Chagos Islands. Both birds and bats play a role in dispersing seeds by eating the pinkish-red fruits (figs). In addition to establishing in soil, these seeds can germinate inside other tree species, growing as an epiphyte that eventually strangles the host.
The far-reaching roots and expansive nature of these trees can cause damage to buildings, sidewalks, and other structures. As illustrated in today’s photograph, older trees form aerial prop roots that can develop into accessory trunks. Though massive, the main trunks can become hidden by the surrounding mix of dense aerial roots and accessory trunks. Over time, a single genetic individual can generate a forest-like landscape. The largest of these banyans (by gross area) is the Kabir Vad Banyan; it covers almost 21,000 square meters (~5.2 acres) of land. If one were to consider canopy cover as the primary measure of tree size, some of these banyan trees would be among the largest trees on Earth (perhaps after Pando?).
I couldn’t help myself from investigating banyans after attending a lecture where they were given as an example of the importance of large, old trees in urban landscapes. Banyan trees are considered sacred in India, commonly planted beside temples and throughout cities such as Delhi. In the case of Delhi, these trees were planted on roadsides and near monuments established by past rulers of the city. Their heritage value in religion and urban landscapes is now being complemented by a recognition of the ecosystem services they provide in urban landscapes (ecosystem services are benefits provided by nature for which we can assign a value; they are considered pivotal in debates about the utility of conserving species and landscapes). The services from banyan trees include beauty, cultural significance, urban animal habitat (e.g., trees provide essential daytime roosting habitat for fruit bats), and shade (ameliorating the urban heat effect in a warming climate).
Many of the old trees in Delhi were recently declared as natural heritage trees, joining almost one thousand such trees recognized for their heritage value throughout India. Conservation of Indian Heritage Trees, by Y. D. Bar-Ness, describes a project to document each heritage tree in India. This article includes a section that notes the size of each Ficus benghalensis, providing both locations of notably large specimens and aerial photos showing their canopy spread.
Botany resource links (added by Daniel): also on the topic of trees, TreeLib is a “collection of high-quality tree photographs for educators, students and lay persons”, assembled (and primarily photographed) by local resident Blake Willson. At the core of TreeLib is the search area, where you can drill down through the taxonomic hierarchy to see photos of species and cultivars (for example, try Styracaceae -> Melliodendron -> Melliodendron xylocarpum). Although based near Vancouver, Canada, TreeLib contains photos from around the world through Blake’s travels and collaborators.