Tropical forest research has evolved significantly over the past 30 years, with an increased emphasis on the function of the forest canopy. A recent review in BioScience magazine, co-authored by former Earthwatch principal investigator Dr. Roger Kitching (Griffith University
), highlights the importance of canopies both in harboring most of the biodiversity of tropical forests and providing ecosystem services such as climate control.
Earthwatch's first efforts to understand the ecology of tropical forests began in 1975, when volunteer teams helped Dr. Daniel Janzen (University of Pennsylvania) collect leaves, seeds, and fruits for phytochemical analysis in Costa Rica's Santa Rosa Park. Janzen's later work there was the foundation for one of the most celebrated conservation, research, and education initiatives, leading to the establishment of the Area de Conservacion Guanacaste (ACG) in Costa Rica.
Janzen's forest biodiversity research in Costa Rica has been recently expanded on by two other Earthwatch-supported researchers, Dr. Eric Olson (Brandeis University) and Dr. Lee Dyer (Tulane University). Olson has pioneered a method to accurately quantify the timing and extent of insect herbivory in the Costa Rican tropical dry forest, effectively taking the pulse of the ecosystem, by sampling the caterpillar frass (feces) that rains down from the canopy and understory. He has also investigated many other aspects of tropical forest ecology with the help of Earthwatch teams on Costa Rica's Tropical Forest, including the discovery of the first herbivorous spider known to science.
Dyer's partial list of the 5,000 caterpillar species in a lowland wet forest is linked to Janzen's comprehensive database of Costa Rican dry forest biodiversity. Many of the 550 caterpillar species reared by Dyer's Earthwatch teams were newly identified, having only been known previously as adult moths or butterflies, and 10 adults were new species as well. Realizing that caterpillars eat more leaves than all other herbivores combined, Dyer has documented ways in which they are important regulators of biodiversity in the La Selva rainforest ecosystem. Working with Earthwatch teams on Rainforest Caterpillars, he has explored the intimate relationship between plants, caterpillars, and parasitoids. They've found more than 50 new species of the latter, parasitic wasps, flies, and nematodes whose immature stages live inside the caterpillar host and kill them as part of their life cycle. Dyer has found that elaborate defense mechanisms developed for predators actually attract these parasitoids, improving their chances for survival. Teams also contributed to the first clear demonstration of a terrestrial "diversity cascade," in a clever field experiment, suggesting that tropical forests are even more sensitive to perturbations than suspected.
In the 1980's, Earthwatch supported a canopy researcher who shook up the tropical forest research community. Dr. Terry Erwin (Smithsonian Institution) implemented a new fogging technique to test his revolutionary estimate of the total number of insect species. His research suggested that there were nearly 30 million insect species in the world, a far cry from the 1.5 million previously estimated. Although more recent studies have revised estimates down to a more moderate 5 or 6 million, the impact of Erwin's research on the field of canopy studies and on forest conservation was enormous. His findings on species distributions suggested that preserving a few large areas of forest would not necessarily preserve a large share of biodiversity, and thus new conservation techniques would need to be explored.
In Peru's Amazon Basin, Earthwatch supported the work of Drs. David Nickle (Smithsonian Insitution) and James Castner (University of Florida) on the biodiversity of katydids in the forest canopy. Earthwatch teams in the late 1980s and early 1990s collected thousands of samples, including 400 katydid species previously unknown to science, increasing the number of known neotropical katydid species by 25 percent. Nickle and Castner's research also demonstrated that katydids were a major foundation of the rainforest food chain.
On the other side of the world, Dr. Margaret Lowman (Williams College) explored insect herbivory in the canopy with Earthwatch teams in the early 1980s. Putting in 2,000 person-hours, teams measured leaf loss in 59 tree species at four sites and collected 20,000 insects, including 5,000 herbivores. Canopy walks allowed the monitoring of individual leaves, leading to the discovery that leaves can live between three and fifteen years. Leaf loss to herbivores was a staggering 35 percent, which showed that Australian rainforest trees were more resilient than had been thought.
"Earthwatch projects and outreach in Queensland has had a positive impact on conservation and raising the visibility of rainforests as a precious treasure for all Australians," said Lowman, author of Life in the Treetops. Research data from Lowman's Earthwatch teams presented at court hearings helped contribute to the conservation of the Washpool rainforest region in Queensland.
"I am totally grateful to Earthwatch volunteers who increased the eyes, ears, and brains that were present in the rainforest canopy to assist in surveying this biodiversity hot spot with me," added Lowman. "Without these extra bodies, I do not think we could have possibly collected so much detailed information on this complex ecosystem."
Lowman and Drs. Roger Kitching (Griffith University) and Susan McIntyre (University of New England) went on to survey Australian forest canopies at Cape Tribulation, one of the wettest areas in Queensland, Lamington National Park, and the Atherton Tablelands. Kitching, author of Arthropods of Tropical Rainforests, later documented the astounding diversity of rainforest canopies on the island of Borneo. In a one-hectare plot in Brunei, Earthwatch teams working with Kitching in the late 1990s counted 281 species of trees belonging to 46 families, as well as 800 species of moths, making it among the world's most diverse rainforests. Kitching's methods for assessing the diversity of forest arthropods, developed with four Earthwatch teams, were adopted as the standard for the 2001 International Biodiversity Observation Year, a global survey of biodiversity status.
More recently, Earthwatch has supported the work of Drs. Nigel Stork and Steve Turton (James Cook University) in the treetops of Queensland's rainforest, conducted from the first canopy crane in the southern hemisphere. The forests of the Wet Tropics World Heritage area reach as high as 40 meters, and support 800 species of vertebrates and 5,000 species of plants, many of them found nowhere else in the world. Earthwatch volunteers on Life in the Rainforest Canopy are helping Stork and Turton investigate the ecology and diversity of treetop mammals, birds, reptiles, amphibians, and insects to see how they use canopy resources. This project is part of Earthwatch's North Queensland regional initiative, with findings that can be integrated with those from other projects in this rich rainforest ecosystem.