Emilio Bruna

Seed germination is lower in fragmented rainforest

Contributed by Lily Johnson-Ulrich @hyenacognition and Emilio Bruna @BrunaLab


Biodiversity, Conservation, Demography, Ecology, Experimental, Field, Global patterns, Latino/a/x, Plants, Population ecology, Rainforest, South America, Terrestrial



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Bruna, E. M. (1999). Biodiversity: seed germination in rainforest fragments. Nature, 402(6758), 139.



Slide 1: Researcher’s Background

Dr. Bruna is a professor at the University of Florida. His research focuses on how landscape alterations influence plant-animal interactions and populations in South America’s largest biomes: the Amazon and the Cerrado. 

Photo credit (left): Stephen Perz in the western Amazon (Acre state, Brazil).


PB: Why did you become a biologist?

EB: As long as I can remember I’ve been fascinated by the natural world. I also love being outside, and grew up backpacking all over the southwestern US.  Ecology is the perfect match for those two passions.


PB: What is your favorite part about your job?

EB: There is nothing better than field work – a bad day outside is still a day outside! I also love working with students, especially helping them figure out how to best convey to different audiences how exciting the results of their months (or more) of hard work are.


PB: What obstacles have you overcome to get where you are?

EB: I do my research abroad, and that can be tough – long stretches away from family and friends, worries about how I’m going to get funding to pay for the research, struggling to communicate in a foreign language…And of course, a healthy dose of Imposter Syndrome!


PB: What advice do you have for aspiring biologists?

EB: Read, but not just about biology. I am a better biologist for having read history, graphic novels, science fiction, biographies…read.  It helps make you a better writer, too, and that’s a huge part of this job. 


PB: Do you feel that any dimension of your identity is invisible or under-represented/marginalized in STEM?

EB: I’m Latino – my mother is from Mexico and my father is from Cuba — and I was born and raised in the border region of the Southwest. I now live in Florida, where 23% of the residents of my state are Latinx. But only 6% of the faculty at my university are Latinx, and the percentage of Latinx members in the most important professional organization for my discipline is even lower (about 3%). These numbers have barely changed since I finished my PhD in 2001, in fact, I can count on one hand the numbers of Latinx Ecologists I know who are Full Professors. 

Slide 2: Research Overview

Take home message of study

Habitat fragments, which are left behind after forest is cleared for cattle pasture and other activities, is a huge threat to biodiversity. However, the reasons for local extinction in habitat fragments are unclear. Bruna (1999) showed that seed germination was significantly lower in Amazonian forest fragments, leading to lower numbers of seedlings there than in nearby areas of unbroken forest. He suggested this was caused by changes in temperature and humidity, as well as greater accumulation of leaf litter on seeds, preventing their germination. 


Study system

Heliconia acuminata is pollinated by Phaethornis hummingbirds (Photo by E. M. Bruna)


Slide 3: Key Research Points

Main figure

Seed germination is significantly higher in continuous rainforest relative to rain forest fragments. across all three planting conditions (planted directly on the soil surface, in a cup to prevent removal by ants, and in a cup covered by mesh to prevent leaf-litter accumulation. 

Caption from paper: 

Mean proportion (+ s.e.m. of seeds germinating in continuous forest and fragmented sites in different experimental treatments. Differences in the proportion germinating in each habitat and treatment were assessed by ANOVA. The square root of the percentage germinating in each plot was arcsine-transformed, and habitat type and treatment were treated as fixed effects. The effect of habitat type was highly significant (F1,24 = 22.623, P<0.0001), but that of planting treatment was not (F2,24 = =2.336, P=0.118). The planting treatment x habitat type interaction was also nonsignificant (F2,24 = =0.028, P=0.973). Bars with different letters are significantly different from each other.


Societal Relevance

Rainforests are homes to millions of people, reservoirs of biodiversity, and provide ecosystem services such as rainfall, water, food. As carbon sinks they play a vital role in the Earth’s climate cycle, and deforestation contributes to carbon emissions and climate change.

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