From Trees to Coquis, an Earthwatch Scientist Explores Puerto Rico’s Rainforest

By Stan Rullman

As a terrestrial ecologist, entering a new ecosystem to me is like a child entering a new candy store. All my senses tingle with the novelty, every corner reveals some new treasure that I try to fit in to that which I am familiar and understand as a scientist. Such was the case this past December, when I had a chance to participate in our Puerto Rico’s Rainforest project. As Earthwatch’s Research Director, I was particularly excited about this journey, as it would be my first official Earthwatch expedition.


Puerto Rico’s rainforest

During my life, I’ve explored and conducted research in various tropical forests around the globe, from Borneo and Sumatra to the Congo Basin to Central America’s ‘paseo pantera’ to the heart of Amazonia- always looking for those common threads of form and function, of predator and prey, and always listening for that unique collective song of each forest system.

In Puerto Rico, the lead singer of that forest song is the common coqui, a frog that has leaped into a formal mascot role for the island nation.

Listen to the coqui call as a researcher records observations in the field.

I’ll come back to frogs in a bit. As much as these landscapes are influenced by what is there, they are also defined, in many ways, by what is not. And what was conspicuously absent in the secondary growth rain forest of the Patillas district was, in short, bugs. In few of those aforementioned tropical forests could I plop myself down on the ground for lunch without being swarmed by ants or buzzing bees and wasps or, later in the day, mosquitoes. Puerto Rico, in truth, has all of those, but in this mountain forest, they are not abundant, and therefore not a nuisance, allowing for explorations without slathering oneself in plastic-melting DEET, or layers of protective clothing and facial nets. And a big part of why those accoutrements are not needed comes back around to the frogs.


A ‘Critically Endangered’ mahogany coqui, so named for its rich bronzy coloration.

Frogs and anolis lizards are the dominant vertebrate predators of insects. Birds play a part too, both native residents and neotropical migrants that overwinter in Puerto Rico. But frogs and lizards rule the show. The sound of common coquis calling, particularly after an evening rain, is the sound of Puerto Rico’s forest. And a trained ear can tease out several more species. Norman Greenhawk has such an ear, and leads the project’s ongoing herpetofaunal research, helping to answer such questions as how the different forestry treatments applied at the site affect frog and anole diversity and abundance.

While in the field this past winter, we also collected frogs to assess the presence and impact of chytridiomycosis, a fungal disease that is linked to the decline of amphibian populations around the globe. Our team of intrepid volunteers drew on those childhood frog-catching skills and collectively caught a total of 74 frogs, sampled them for the fungus, and released them back where we caught them. Included in our captures were several ‘critically endangered’ species, like the mahogany and locust coquis.


Earthwatch volunteers swabbing a frog to test for chytridiomycosis, a fungal disease that is wiping out amphibian populations around the globe.

As a wildlife biologist, I loved the herp work. But at the core, the Earthwatch Puerto Rico’s Rainforest project is about restoration, not only of the forests themselves, but also restoring the skillsets to effectively and sustainably utilize forest resources (wood and non-timber projects) to the Puerto Rican community, strongly linking healthy ecology and economy for this small island nation. A large component of the field research we worked on assesses valuable hardwood tree growth in control vs. thinned plots (plots in which trees that might compete for light and nutrients are removed from the plot, thereby releasing focal timber trees from that competition and hopefully promoting increased growth). We collected several metrics on over 250 trees, including dbh (diameter at breast height), crown class (an indicator of competition for light), and the surrounding forest basal area (a measure of how crowded the focal tree is by the trees surrounding it).

Earthwatch volunteer Colleen Casey and Co-PI Thrity Vakil assess the health and growth of a young Palo de Jazmin transplant.

Earthwatch volunteer Colleen Casey and Co-PI Thrity Vakil assess the health and growth of a young Palo de Jazmin transplant.

Working with co-PI Thrity Vakil, we also assessed the growth and health of two of the most critically endangered species of plants in the world, Palo de Jazmin (down to four mature trees in the wild), and Palo de Nigua (known by only seven mature plants in the wild). Seedlings provided by the US Fish and Wildlife Service were planted at Las Casas de la Selva just over a year ago, and the research team checked in on nearly 150 of those, measuring the trees, checking for damage, mold and insect infestations, and liberating them from vines and crowding. It was amazing to have such a “hands-on” interaction with these critically endangered plants- not unlike handling California Condor or Whooping Crane chicks. The team also collected 30 seedlings of the caimitillo tree for later transplanting throughout the forest. Though birds are the target seed dispersers for these trees, sometimes we ‘two-legged mammals’ can play that role too.

Which leads me to wrap up with another target of restoration: the restoration of members of the public as contributing participants in vital research, and that is what Earthwatch is all about.