Fire smoke provides unexpected fertiliser for Amazon rainforest
Forest fires in the tropics cause enormous damage to nature and the climate. However, new international research shows that the smoke from these fires also has an unexpected and positive side effect: it carries phosphorus to the heart of the Amazon rainforest, where it stimulates tree growth. This ‘fertilisation’ compensates for some of the carbon loss caused by deforestation.
Let there be no doubt: forest fires are a disaster for humans and animals and endanger biodiversity. However, research at the University of Antwerp (Global Change Ecology Centre, Research group PLECO) and at the Barcelona research institute CREAF (Centre de Recerca Ecològica i Aplicacions Forestals) has revealed a positive aspect. Adrià Descals, Ivan Janssens and Josep Peñuelas report on their research in the journal Nature Geoscience.
Forest fires are widespread in South America. Most fires occur in the so-called ‘deforestation arc’ in the southern Amazon region. During the dry season, winds carry the smoke deep into the intact rainforest. The smoke contains nutrients such as phosphorus that can fertilize the forest and boost plant growth.
Photosynthetic activity
Satellites record increased concentrations of fire-related smoke in the southern Amazon, along with a clear increase in the photosynthetic activity of trees. "We measured this activity using solar-induced fluorescence (SIF), a faint signal that plants emit during photosynthesis. Photosynthesis allows plants to use sunlight to produce sugars and oxygen. The stronger the light signal, the more actively the forest removes carbon from the atmosphere," explains Adrià Descals.
Strikingly, regions with higher smoke and phosphorus deposition systematically show higher photosynthesis. Phosphorus proved to be the strongest predictor of spatial differences in forest growth. Descals: ‘Phosphorus is essential for tree growth in the Amazon rainforest, where it limits growth. Even small additional amounts can make a measurable difference to carbon uptake.’
Connected ecosystems
According to the scientists, the extra phosphorus not only makes photosynthesis more efficient, but also results in a denser canopy. This allows forests to develop more leaf surface area, enabling them to utilise more sunlight and capture extra carbon, which in turn is good for the climate.
On average, every additional milligram of phosphorus per square metre leads to an annual increase of 7.4 grams of carbon storage. Because the Amazon basin is enormous, this amounts to substantial quantities. ‘This absolutely does not mean that fires are “good”,’ the researchers emphasise. ‘But it does show how strongly ecosystems are interconnected, even through pollution. While fires release carbon locally, they enhance the ability of intact forests to absorb CO₂ elsewhere.’
Photo's: Worldview
