Tropical rainforests are often described as the 鈥渓ungs of the earth,鈥� able to essentially inhale carbon dioxide from the atmosphere and exhale oxygen in return. The faster they grow, the more they mitigate climate change by absorbing CO2.
This role has made them a hot research topic, as scientists question what will happen to this vital carbon sink long-term as temperatures rise and rainfall increases.
Our findings fundamentally change a view of the tropical forest carbon cycle that has been published in textbooks and incorporated into models of future climate change for years."
鈥揚hilip Taylor
Conventional wisdom has held that forest growth will dramatically slow with high levels of rainfall. But 抖阴旅行射 Boulder researchers this month turned that assumption on its head with an unprecedented review of data from 150 forests that concluded just the opposite.
鈥淥ur data suggest that as large-scale climate patterns shift in the tropics, and some places get wetter and warmer, forests will accelerate their growth, which is good for taking carbon out of the atmosphere,鈥� said Philip Taylor, a research associate with the . 鈥淚n some ways, this is a good-news story, because we can expect greater CO2 uptake in tropical regions where rainfall is expected to increase. But there are听a lot of caveats.鈥�
Ecologists have long thought that forest growth follows a hump-shaped curve when it comes to precipitation: To a point, more rainfall leads to more growth. But after about 8 feet per year, it was assumed too much water can waterlog the ecosystem and slow the growth rate of forests. While working in the Osa Peninsula of Costa Rica, Taylor, who got his doctoral degree in ecology and evolutionary biology at 抖阴旅行射 Boulder, began to question this assumption.
鈥淗ere we were in a place that got 16 feet of rain per year, and it was one of the most productive and carbon-rich forests on Earth. It clearly broke from the traditional line of thinking,鈥� he said.
Intrigued, Taylor spent four years synthesizing data on temperature, rainfall, tree growth and soil composition from rainforests in 42 countries, compiling what he believes is the largest pan-tropical database to date.
The , published recently in the journal Ecology Letters, found that cooler forests (below 68 degrees F on average), which make up only about 5 percent of the tropical forest biome, seemed to follow the expected hump-shaped curve. But warmer forests, which are in the majority, did not.
Philip Taylor measures the growth rate of a tropical giant, the Ajo, on the听Osa Peninsula in听Costa Rica. The trees can grow听to 180 feet tall and can live 1000 years.
鈥淭he old model was formed with a lack of data from warm tropical forests,鈥� said Taylor, who describes such remote, often uninhabited forests as among the 鈥渇inal frontiers鈥� of scientific exploration. 鈥淚t turns out that in the big tropical forests that do the vast majority of the 鈥榖reathing鈥� the situation is flipped. Instead of water slowing growth down, it accelerates it.鈥�
Taylor cautioned this does not mean climate change won鈥檛 negatively impact tropical forests at all. In the short term, research has shown, droughts in the Amazon Basin have already led to widespread plant death and a 30 percent decrease in carbon accumulation in the past decade.
鈥淎 lot of climate change is happening at a pace far quicker than what our study speaks to,鈥� he says. 鈥淥ur study speaks to what we can expect forests to do over hundreds of years.鈥�
Because the carbon cycle is complex, with forests also releasing carbon into the atmosphere as plants die, it鈥檚 still impossible to say what the net impact of a wetter climate might mean for the forest鈥檚 ability to sequester carbon, said senior author Alan Townsend, a professor of .
鈥淭he implications of the change still need to be worked out, but what we can say is that the forest responds to changes in rainfall quite differently than what has been a common assumption for a long time,鈥� said Townsend.
Going forward, the authors hope the findings will set the record straight for educators and scientists.
鈥淥ur findings fundamentally change a view of the tropical forest carbon cycle that has been published in textbooks and incorporated into models of future climate change for years,鈥� said Taylor. 鈥淕iven how much these forests matter to the climate, these new relationships need to be a part of future climate assessments.鈥�
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