Soil conditions crucial for tropical forestation

By Drake Baer

More than half of all tropical forests are degraded in some way due to urban development, extensive agriculture, logging and mining.

“We are losing tropical forests at an unprecedented rate,” said Jim Dalling, associate professor of life sciences at the University.

In order to manage and restore these forests, humanity must achieve greater understanding of how soils, nutrients and other factors influence individual tree species’ ability to regenerate, Dalling said.

Dalling and his team, including Robert John, a former graduate student at the University, and scientists from across the country, have recently completed a study concerning the relationship between woody plants and their soils.

The results of the study provide insight into how undisturbed forests are organized and indications of how soil conditions are likely to affect successful tree growth.

“We had three tropical forest sites, including Ecuador, the mountains in Columbia, and central Panama,” Dalling said.

The Ecuador site has as many species of woody plants in the span of two football fields as is found in the U.S. and Canada combined, said Robert Stallard of the US Geological Survey, principal researcher in the study and professor at the Univeristy of Colorado.

“Perhaps the biggest unresolved question in ecology is how biodiversity is maintained in species-rich communities (like tropical forests),” Dalling said. “Some of the sites that I work at contain more than a thousand tree species in an area the size of the lawn between Foellinger and the Union.”

Such diversity has fascinated scientists for decades, but the matter of soil has yet to be thoroughly investigated. Within this diversity, each tree species has a different set of nutrient requirements.

“There is not a lot of data concerning soil nutrients, and so our approach was to collect a tremendous amount of data,” said Joseph Yavitt, researcher and professor at Cornell University. “This is where Jim Dalling used some very innovative statistical methods in order to draw correlations.”

Trees are often drawn to soil with specific nutrient sets, or micro-environments, said Kyle Harms of Louisiana State University.

“In our study we mapped and identified half a million individual trees in three tropical forests and measured the concentrations of essential nutrients in the soil,” Dalling said. “We show that rather than being randomly distributed in space, individual species are often sensitive to soil conditions.”

Dalling is at the cutting edge of community ecology and has been a rising star in tropical biology ever since he was in graduate study at Cambridge, said Harms.

The greater understanding garnered in this study underscores the importance and appeal of tropical forests, Stallard said.

“At the aesthetic level, I personally find biologically-diverse landscapes more appealing. A tropical forest is more appealing than a plantation; tall grass prairie is more appealing than a corn field,” Stallard said. “Diverse systems are often more robust in the face of gradual environmental change, understanding how diversity engenders this robustness can teach us much about ourselves as a social species and provide tools for dealing with practical issues such as disease.”