Secondary forests restore fresh water sources in degraded landscapes

Chavarria and his colleagues collected weekly samples from streams that were surrounded by mature and young secondary forests, silvo and traditional pastures at STRI's Agua Salaud site over a period of two years to determine the bacteria content. Credit: Jorge Aleman (Smithsonian Tropical Research Institute).
Research by Karina Chavarria, a Smithsonian Tropical Research Institute postdoctoral fellow, and her colleagues has shown that streams near young secondary forests can recover to look like mature forest streams within a decade. These communities also remain strong throughout the year.

These results are crucial. The United Nations Decade on Ecosystem Restoration will begin in 2021. It aims to stop, halt, and reverse global ecosystem degradation. One of the many initiatives at STRI that aims to understand the causes and consequences of environmental changes is the Agua Salud project, which was a collaboration between the Panama Canal Authority (Panama) and the Ministry of the Environment in Panama.

Long-term studies of forest ecosystems across various land uses and extreme weather events at Agua Salaud have provided valuable insights that will help us to maintain and restore tropical forests. Agua Salud offers unique hydrological opportunities because of its many streams and rivers that run across hundreds of hectares.

Water is essential for all life. People depend on rivers and lakes for their water supply and recreation. Although microbes are not well-known, they are important components of aquatic systems. They are the engineers behind water quality and energy cycling. Microbial communities can shift when streams are polluted or the environment is degraded. This affects their ability to maintain natural processes and sometimes allows harmful bacteria to thrive.

Chavarria and his colleagues collected weekly samples from streams that were surrounded by silvo-, traditional pasture, and mature forest over a period of two years at STRI's Agua Salaud site. They took samples of water from different sources to measure water quality and extracted and sequenced the bacterial DNA.

The stream was surrounded by mature and young secondary forests, but the communities found in the cattle pasture stream were different. The silvopasture stream's bacterial community changed seasonally. The wet season bacterial community was similar to that of the forests, while the dry season community was more like the traditional pasture.

Karina Chavarria, a postdoctoral fellow at STRI, has shown that bacteria communities found in streams near young secondary forests mimic those in mature forest streams within a decade of cattle being removed. Credit: Kristin Salzonstall, Smithsonian Tropical Research Institute

"Riparian forests help to protect silvopasture streams from the impacts cattle in the wet and dry seasons, but when cows congregate into the stream to drink and seek shelter as a way to avoid the scorching sun," Kristin Saltonstall (STRI staff scientist, Chavarria's adviser and collaborator) said.

Jefferson Hall, director of Agua Salad and collaborator in the project, stated that it was important for cattle to not have access to streams and that they are provided with drinking water up slope during dry seasons. This will ensure that year-round water quality.

Silvopasture systems are where trees are planted on traditional cattle ranches. Forest corridors are also maintained along streams. These systems have been gaining a lot of attention over the years. Although the jury is still out on whether these systems offer all the environmental benefits claimed by their promoters it is evident that having a forest buffer surrounding a stream is beneficial in terms of water quality and stream water bacteria communities.

Chavarria stated that "our results add an important dimension" to the growing body research on the potential of biodiversity associated with young, tropical secondary forests to rapidly recover. This has implications for human health and the environment.

The quality of our lives for the future will depend on how we manage to mitigate the impacts of this Decade of Ecosystem Restoration. Chavarria's research shows that passive reforestation (where forests are allowed to recover from cattle being removed) can restore many aspects water quality within a matter of years. These studies provide important data, and show how science can be used to inform policy and practice. This will help us create a sustainable planet.

The Smithsonian Institution includes the Smithsonian Tropical Research Institute. It is located in Panama City, Panama. The Institute promotes conservation and furthers knowledge of tropical nature and its importance for human welfare. It also trains students to conduct research on the tropics.

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Further information: Karina Chavarria and colleagues, Land use influences stream bacteria communities in lowland tropic watersheds, Scientific Reports (2021). Information from Scientific Reports Karina A. Chavarria and colleagues, Land use influences stream bacteria communities in lowland, tropical watersheds. (2021). DOI: 10.1038/s41598-021-01193-7