University research focuses on little-studied forests

An experiment led by University of Minnesota researchers sheds light on restoration efforts in an often-overlooked environment.

The research, conducted with foresters in Costa Rica, identifies trait-based screenings — which use measurable plant characteristics — as the best way to choose plant species for restoration projects in tropical dry forests. Some experts say these areas have been under-studied and hope the findings will be useful in climate change research worldwide.

Leland Werden, a graduate student in the plant biological sciences program, and Jennifer Powers, associate professor with the College of Biological Sciences, led the study along with foresters from Estacion Experimental Forestal Horizontes in the Area de Conservacion Guanacaste in Costa Rica. Their findings were published late last month. 

This region is a tropical dry forest, an environment common in Central and South America that covers more area worldwide than tropical rain forests. This type of forest has a strong dry season of at least three to four months with little to no precipitation, which makes restoring the areas especially difficult.

“One of the challenges in restoring tropical dry forests is their seasonal nature. Finding species that are resistant or tolerant of drought is challenging,” said Juan Dupuy, a researcher with the Centro Investigacion Cientifica de Yucatan.

The research focused on a type of soil called vertisol, which shrinks and cracks during the dry season, then swells during the rainy season. This causes flooding, which kills many seedlings. 

The study suggests that plant functional traits are the most efficient way to determine which species will survive in the degraded soil. In the tropical dry forests, drought-tolerant species had higher survival rates in the vertisols, Werden said.

Of the 32 species tested, over a third were considered “restoration-viable,” meaning they had survival rates of at least 10.9 percent, according to the study. Seven of those species had survival rates over 30 percent.

These results were encouraging for tropical dry forest restoration efforts, Werden said, because they showed that restoration is difficult, but still possible, even on degraded vertisols. 

Plus, these findings can be applied to other environments beyond tropical dry forests, he said.

The UMN researchers worked closely with foresters from Estacion Experimental Forestal Horizontes. Powers said that they “shared the goal of restoration.”

“[University researchers] brought ideas on how to think about species and functional traits, while [Costa Rican foresters] brought a vast knowledge of native species. It was a great collaborative effort,” she said.

Historically, tropical dry forests have been overlooked in conservation and restoration efforts, Depuy said. More people study humid forests, he said.

While tropical dry forests are home to fewer species overall than their humid counterparts, they have more endemic species that are only found in one place, he said.

“This means that when you lose tropical dry forests, even when it’s not on such a large scale, it’s likely that you are going to lose a large number of species that are unique to that place,” Depuy said.

Tropical dry forests could also be crucial to the study of climate change, since experts predict drought will become more common in the future, Depuy said.

“Tropical dry forests are important because they have plants that have different adaptations to dealing with drought,” he said. “Understanding how plants and trees deal with drought is important. The obvious place to study that is tropical dry forests because they are already subjected to drought conditions.”