Trees in savanna areas of Cerrado produce three times more bark than species in forest areas, shows study

In tropical regions of the planet, savannas and forests often coexist in the same area and are exposed to the same climate. An example is the Cerrado, a Brazilian biome that includes several types of vegetation, from broad-leaved and sclerophyllous in dense woodland or shrubland (cerrado sensu stricto) to semi-evergreen in closed-canopy forest (cerradão), as well as grassland with scattered shrubs (campo sujo) and even semi-deciduous seasonal forest.

Areas of cerradão develop in the absence of fire, in both poor and moderately fertile soil (dystrophic to mesotrophic).

This coexistence intrigues botanists and ecologists since savannas and forests are home to different species and have different dynamics and functions. Savannas are dense and highly flammable grasslands that burn fairly frequently, with a direct impact on other types of vegetation.

Forests, on the other hand, have a broad, mostly continuous canopy that provides shade for undergrowth, bushes and smaller trees, and prevents the growth of flammable grass.

Savanna species evolved over millions of years in the presence of fire and have thick bark to protect them. After burning, they form new branches and leaves from asexual buds called gemmae.

A study conducted at the Santa Bárbara Ecological Station, an environmental protection unit in São Paulo state, investigated how much bark is produced by savanna and forest species in the Cerrado, whether savanna species that produce more bark also protect their gemmae more effectively, and whether generalist species (occurring in both savanna and forest) produce different amounts of bark depending on the environment in which they grow. An article on the study is published in the journal Annals of Botany.

The principal investigator for the study was Alessandra Fidelis, a professor in the Department of Biodiversity at São Paulo State University’s Rio Claro Institute of Biosciences (IBRC-UNESP). The first author of the article is Marco Antonio Chiminazzo, a Ph.D. candidate at IBRC-UNESP. The other co-authors are Aline Bombo, a postdoctoral fellow at IBRC-UNESP, and Tristan Charles-Dominique, a researcher at the Sorbonne in Paris and the University of Montpellier, both in France.

“We observed that savanna species produce about three times as much bark as forest species, while generalist species are intermediate, producing more bark in savanna than forest areas. This ability to adjust bark production to the environment is known as phenotypic plasticity and may be a deliberate strategy. We also found that species that produce more bark protect their gemmae and internal tissues better,” Chiminazzo told Agência FAPESP.

“Our study shows that fire is an important factor for savanna-type vegetation in the Cerrado, promoting the woody species that can cope with this disturbance and couldn’t live in shady forest areas.”

The study provides evidence that strongly supports those who advocate the carefully controlled use of fire to manage the savanna areas of the Cerrado. Properly managed fire requires zoning and a timetable. Zoning establishes a mosaic framework within which to burn designated areas rotationally in accordance with the timetable.

“Plant species in the Cerrado have adapted to fire, producing thick bark and strongly protecting their gemmae. These traits, which are the result of a long evolutionary process, enable them to survive fires and regenerate after burning,” said Fidelis, who is Chiminazzo’s thesis advisor.

Located in the municipality of Águas de Santa Bárbara, the ecological station where the study was conducted is an important native Cerrado remainder in São Paulo state and contains all the different types of savanna and forest found in the biome.

“We sampled shrub and tree species from four different types of vegetation with varying frequencies of burning and light availability. We investigated the amount of bark they produce as they develop and how they protect their gemmae against the effects of fire. We then separated the species according to the environment they prefer to inhabit, forming three groups: savanna specialists, forest specialists and generalists [capable of growing in both],” Chiminazzo said.

Future research should set out to understand how and why certain species can adjust bark production, whereas others cannot, he added. “In the context of climate change and changes in fire regimes, garnering deeper knowledge of these species offers a major opportunity to understand and predict which organisms will be more or less endangered, in accordance with their ability to adapt to varying environmental conditions,” he said.