Native tree rehabilitation in Costa Rica’s biggest urban park

During a recent trip to Costa Rica, CCSD scientist Leighton Reid toured La Sabana, Costa Rica’s largest urban park, with Wilmar Ovares, an instructor at the Universidad Estadal a Distancia who has been studying the recovery of bird diversity following large-scale replacement of exotic trees with native ones.

The first time I visited La Sabana Metropolitan Park in downtown San Jose was in 2005. At that time it was essentially a eucalyptus woodland; the tall trees with peeling bark stretched upwards above the soccer fields and hiking trails. No longer. La Sabana has gotten a makeover in the last few years – and for the better.

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The old La Sabana (exotic eucalyptus trees in background – slated for removal in the near future) and the new (native trees and a eucalyptus stump in the foreground). The tree at right (unidentified species; Solanaceae) is a natural recruit, dispersed to the site by a bird or a bat. The slightly curved tree at center-right has died, but it can still serve as a bird perch and might facilitate the dispersal and establishment of a new, native tree in its place.

The project was initiated as a collaboration between three institutions: the National Biodiversity Institute (INBio), the National Sports and Recreation Institute (ICODER), and Scotiabank. Beginning in 2010, this collaborative removed most of the exotic trees in La Sabana and replaced them with more than 5000 native trees, representing 234 species. Not all of the species are native to the central valley, but all are native to the country.

Although the planted trees are still quite small, one short-term indicator of project success is the recovery of bird diversity in the park. On my first visits to La Sabana prior to 2010, the birding was slow, with occasional excitement when I would stumble on a eucalypt in flower – abuzz with warblers, orioles, and hummingbirds. Now, Wilmar Ovares finds that the number of bird species has increased by more than a third. Many of the new species are migrants, which breed in North America and winter in Central America. Others have drifted in from nearby riparian forests along the Rio Torres and the Rio Maria Aguilar. In some cases, birds and other animals have carried in and deposited native tree seeds, complementing the plantings.

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Vainillo (Tecoma stans, Bignoniaceae), a beautiful, native addition to La Sabana.

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This Annona cherimola (Annonaceae) recruited on its own at this site in La Sabana. Its large seed may have been dispersed by a bird, a squirrel, a raccoon, or even a human. The source of the seed may have been the Rio Torres, which flows through a riparian forest not far from the park. This tree species is a conservation priority species in the Central Valley.

To be clear, this project is not strictly ecological restoration; below the new trees is a manicured lawn, and it is likely to remain that way for some time. The work is better classified as rehabilitation – a return of some elements of the local biodiversity, but by no means all of it. This approach is sensible given that the park is a resource for human recreation – not just a habitat for plants and animals. Still, if the park administration wished to go further, they could consider introducing some native, understory shrubs, ground-layer plants, and epiphytes, all of which would enhance bird diversity and enrich the experience of visitors.

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Jicaro (Crescentia alata, Bignoniaceae) is a champion of forest restoration efforts in Guanacaste, and it looks good in La Sabana as well. The large flowers are pollinated by nectar-eating bats, and the fruits are used by some indigenous people as water canteens.

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Acerola (Malpighia glabra, Malpighiaceae) in a recent planting in La Sabana. This tree/shrub produces edible fruits, which are not very sweet. (Thanks to Amy Pool for correcting a previous misidentification!)

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The last vestiges of the old La Sabana. This area near the stadium is dominated by eucalyptus (from Australia) and Cupressus lusitanica (from Mexico and northern Central America). Wilmar Ovares finds a lower diversity of bird species in these exotic tree groves, despite their much greater stature. Though it cannot be denied that when the eucalyptus are flowering, warblers, orioles, hummingbirds and others may be found in large numbers feeding on the nectar and nectar-eating insects.

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Wilmar Ovares has been monitoring changes in the bird community in La Sabana as a result of the native tree rehabilitation.