Daniel Janzen and the long work of bringing back a forest

In northwestern Costa Rica, a dry forest ecosystem devastated by cattle ranching and fire has been slowly rebuilt over more than fifty years through the joint work of ecologist Daniel Janzen, his wife and scientific partner Winnie Hallwachs, and a large Costa Rican network of park staff, parataxonomists, teachers, and government officials.

Janzen, now 87 and Chief Scientist of the Guanacaste Dry Forest Conservation Fund, helped develop the Janzen-Connell hypothesis explaining tropical tree diversity, and his decades of biodiversity inventory work in Área de Conservación Guanacaste underpin recent studies, including a June 2026 PNAS paper estimating Earth may hold 14 to 20 million insect species.

The piece stresses that the outcome was never the work of one man with a camera and a theory, but of sustained funding, political agreements, local trust, and people who stayed long after the initial attention faded.

The full dispatch is available from the source below.