Study: Secondary forests help restore fresh water sources

New research, published in Scientific Reports by Smithsonian Tropical Research Institute (STRI) shows that bacterial communities in streams adjacent to young secondary forests can recover to resemble those of mature forest streams in as little as a decade after cattle has been removed from the land, and that these communities are robust throughout the year.

These results come at a critical time. 2021 marks the beginning of the United Nations Decade on Ecosystem Restoration, which aims to prevent, halt and reverse the degradation of ecosystems worldwide. The research took place at STRI’s Agua Salud Project site, which is a collaboration with the Panama Canal Authority and the Ministry of the Environment in Panama. With its various streams and rivers distributed throughout hundreds of hectares, Agua Salud offers a unique platform for hydrological studies.

When streams become impaired, microbial communities shift, risking their ability to help maintain natural processes and often allowing harmful bacteria to flourish. Chavarria and colleagues took weekly samples from streams surrounded by mature forest, young secondary forest, silvopastures and traditional pastures over a two-year period at STRI’s Agua Salud site.

They measured different aspects of water quality, and filtered water samples to extract and sequence the bacterial DNA in these streams. Silvopasture systems, where trees are planted on traditional cattle pastures and forest corridors are often maintained along streams, have gained a lot of attention in recent years.

They found similar communities in streams surrounded by young secondary and mature forests but different, less diverse communities in the cattle pasture stream. Notably, the bacterial community in the silvopasture stream shifted seasonally, with the wet season bacterial community being like the forests’ and the dry season community similar to the traditional pasture.

“Riparian forest helps to protect the silvopasture stream from the impacts of cattle in the wet season but in the dry season, when cows congregate in the stream to drink and seek shade as a way of avoiding the scorching sun, increased disturbance and fecal inputs make the bacterial community in the water more like that of traditional cattle pastures,” said STRI staff scientist Kristin Saltonstall, Chavarria’s advisor and collaborator on the project.

“It is important that cattle not access the streams, and that their drinking water is provided up slope during the dry season to ensure year-round water quality,” said Jefferson Hall, the director of Agua Salud and a collaborator on the project.

The team’s research shows that passive reforestation can restore many aspects of water quality in a matter of years.

“Our results add an important dimension to the growing body of research on the ability of biodiversity associated with young tropical secondary forests to recover rapidly, with implications for human health as well as a healthy environment,” said Chavarria.