Reforestation and Genetic Diversity: Dr. Carlos Navarro Presents the Case of the Leucaena

Dr. Carlos Navarro

On July 27, Dr. Carlos Navarro, the Azuero Earth Project’s new Director of Agroecology and Forest Restoration, spoke to the Pedasí community about what he knows best: trees.

Dr. Navarro studied forestry in the Technological Institute of Costa Rica, completing his undergraduate thesis on floristic studies of secondary forest on the Peninsula de Nicoya. After working in CATIE he received a fellowship to study his master’s degree at the postgraduate school, preparing his dissertation on Bombacopsis quinata, a native species of Costa Rican and Panamanian dry forests. He has been involved in restoration of both forests and endangered species in several countries and has been a consulted authority for CITES, Bioversity International, CATIE, among others. He received his PhD in the University of Helsinki and his doctoral thesis explored the Genetic resources of Cedrela odorata L. and their efficient use in Mesoamerica.

Dr. Navarro’s talk focused on the best practices for reforestation projects, using the story of the Leucaena tree as a cautionary tale.

The Leucaena, a species native to Mesoamerica, was widely considered a “miracle” tree in the 1970s and 1980s. Leucaena grows quickly, produces many seeds, fixes nitrogen in the soil, and serves a good source of firewood and fodder for cattle. However, when the trees were introduced in Panama some 20 years ago, they had little success.

Dr. Navarro speaks about the different varieties of Leucaena

Dr. Navarro explained that a major reason for the trees’ lack of success in Panama and in other countries is a lack of genetic diversity. Seeds of Leucaena leucocephala, the principal subspecies chosen for propagation, were collected from a limited number of mother trees, and thus many of the new plantings shared similar genes. People soon discovered that Leucaeana was susceptible to cold and drought, and that it also tends to form dense stands not useful for timber.

Only later did researchers realize that the Leucaena family contains a much wider variety of species with rather distinct traits. Creating healthier Leucaena populations could involve spreading seeds from these other species and thus increasing the genetic diversity of pioneer Leucaena populations.

Dr. Navarro told attendees that when collecting seeds for a reforestation project, one should aim to collect seeds from a minimum of 20-30 mother trees in different locations in order to ensure healthy genetic diversity among new plantings. Trees, like humans, can experience problems with consanguinity. Seeds produced by closely related parent trees will do poorly.

I didn’t realize how much we need to work on diversity with regards to planting trees,” said Derek Mazerolle. “That makes our job a bit more difficult but also more exciting.”

Dr. Navarro’s Powerpoint Presentation (Spanish)

Bioversity Video about the Leucaena tree

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