Sugarloaves in the Atlantic Forest

Isolated stone mountains (monoliths) that rise abruptly from the landscape – mainly composed of granitic and/or gneissic rocks – are called inselbergs (from German, insel = island and berg = mountain). In Brazil, when they have a rounded shape and are embedded in a forest matrix, they are called ‘sugarloaves’. These formations date back millions of years and are distributed across all continents, with the tropics being centers of their biological diversity.         

The term ‘Sugarloaf’ given to the Rio de Janeiro mountain dates back to the time of Portuguese colonization. During sugar production, clumped crystals were removed from conical molds in blocks, taking on their shape. This process resembled the production of bread, which was also baked in molds; thus, by analogy, the sugar crystal obtained began to be called ‘sugarloaf’. Later, the Rio mountain and conical monoliths were given the same name due to their shape.

In the book ‘Travels in Brazil,’ Martius wrote about "Tours around Rio de Janeiro": “Next to the Carioca waterfall, the path moves away from the aqueduct and passes over a dry ridge, full of shrubs and low trees, and returns through the virgin forest that covers the slope of Corcovado. (...) To the south the mountain is sheer, and one’s gaze is lost in the deep abyss, bordered by the blue bay of Botafogo around it; beyond rises the bold rock cone of the Sugarloaf.”

However, these mountains harbor a biodiversity that few are familiar with. Several species of cyanobacteria – part of the first groups of organisms that appeared on Earth millions of years ago – form crusts on the rock, giving it the grayish color we see. There are also very small plant groups, such as bryophytes, and lichens (fungi and algae), that adhere to the surface. Thus, there are no truly bare rocks, but instead slopes covered by a mantle of microorganisms.

Living beings capable of surviving in these places have different types of adaptations, as they need to withstand, for instance, temperatures that reach over 60°C. There are plants that can adhere directly to the rock, without fissures or soil, that climb vertical walls and are called hyperepilithics. Examples include bromeliads of the genus Stigmatodon.

Another curious strategy is desiccation tolerance. Some sugarloaf plants, like sedges, ferns, and canelas-de-ema, have the ability to dehydrate and rehydrate several times, depending on water availability. Because of this ability, they are called “resurrection plants”.

In various regions of Brazil, these rocky formations face severe threats because they are not considered priority areas for conservation. Mining, illegal collection of ornamental plants, fire, invasion of exotic species (not native to these places), and urban growth have contributed to the destruction of the natural vegetation of these environments. Even on the iconic ‘Sugarloaf’ in Rio de Janeiro, construction companies are planning to build ziplines and malls on its summit.