A University of Florida professor visited the University of Connecticut on Thursday, Feb. 5, to discuss the impact of habitat fragmentation and drought on tropical plants.
Emilio Bruna spoke to the UConn community at the Biology/Physics building about his long-term research in the Amazon rainforest as part of the Ecology and Evolutionary Biology (EEB) department’s weekly “Seminar Series,” where experts in the field talk about their research.
Before diving into his findings, Bruna had the audience laughing with a series of self-aware jokes comparing Florida to Connecticut, a sign of the lighthearted and engaging lecture style that followed.
Bruna said that fragmented rainforest habitats — which are portions of rainforest that have been downsized to small patches due to human development — typically have lower species diversity and a higher rate of local extinction than continuous forests. However, there is not much information on what specific factors cause this decline in plant species.
Some experts speculate that plant decline in habitat fragments come from having fewer required pollinator and seed dispersal species, reducing reproduction and growth, Bruna said. But others attribute plant struggles to changes in environmental factors because of the habitat’s fragmentation itself.
Portions of Bruna’s research assess how these factors impact Heliconia acuminata, a tropical plant native to South America. But he also wanted to explore how climate change-induced drought affects plants in fragmented rainforest habitats.
“Life seems terrible, especially if you’re a fragmented forest,” Bruna said. “But it gets worse, and that is that species in tropical landscapes — all landscapes — fragmented tropical landscapes are also dealing with the consequences of changing climates.”
The impact of drought on plant species can be unpredictable, sometimes even leading to short-term flourishing, Bruna said. Drought effects can also be delayed, taking time to influence plant growth and even overlap with future drought impacts.
“The plant is going to have grown a certain amount, but you don’t necessarily know whether it’s because it’s a lingering effect or a new delayed effect,” Bruna said. “And not only do you have the effects of the first drought, you’ve got the subsequent effects layered on top of the effects of the first drought.”
Bruna’s synergy hypothesis presumed that drought would reduce the growth rate of tropical plants in fragmented habitats more severely than it would for tropical plants in continuous forests.
To test this, Bruna studied over 10 locations near Manaus, Brazil. Six were continuous forests, three were 10-hectare plots of fragmented forest and four were one-hectare plots of fragmented forest. Over time, only the continuous forests exhibited a positive growth rate for the studied plant species in all locations, while most of the fragmented locations had a negative growth rate.
The process of evaluating drought’s impact on plant growth, survivability and fertility was less simple. Bruna compiled over 10 years of data, and through complex computational equations, determined a way to discern the consequences of each drought, including their lingering effects. He found that droughts can take up to 36 months before having an effect on plant growth.
These models also allowed Bruna to predict how — at the current rate of climate change and drought prevalence — these tropical plants might fare over the next few decades, taking into account habitat fragmentation. In both the models with the most and least extreme drought predictions, plants in continuous forest fared much better than those in fragmented forest in the long term.
While his research demonstrated how different environmental changes interact with one another, it also showed that these changes can be unpredictable and difficult to study, Bruna said. He hopes other scientists apply similar studies to different plant species in different climates for a broader understanding of how climate change and habitat fragmentation make it harder for species to survive.
“We are living in a fragmented world whether we like it or not,” Bruna said. “So, we need to understand what’s happening in fragmented ecosystems.”
Margot Gagnon, a graduate student in the EEB program, attends each of the department’s “Seminar Series” events because she is enrolled in the program. Her current focus is on dissections and she liked hearing how these habitat-wide studies differed from her own work, she said.
“I’m always really interested in the logistics, the practical aspects of doing tropical studies,” Gagnon said. “Because it’s very technology-limiting to do research in the dead center of the Amazon, and I’m really interested in how they navigate that.”
There needs to be more research on drought and habitat fragmentation like Bruna’s, Dr. David Wagner, an entomology professor at UConn, said. Plants are necessary for everything in nature, so Bruna’s research is relevant for all ecologists regardless of their species specialization, he said.
“We don’t know why we lose species, so that’s a very important problem,” Wagner said. “Why do we lose species from cutting up a rainforest? We have small fragments, so we need to understand that problem so we can practice preventing it.”
Upcoming events in the “Seminar Series” program can be found on the EEB website. The research and data from Bruna’s lab can be found on his website.