New Study Shows Forests Growing Shorter, Dying Younger, Storing Less Carbon

The world’s forests are growing shorter, dying younger, and storing drastically less carbon due to the combined effects of climate change and illegal logging, according to a new study published last week in the journal Science.

The research conducted by the U.S. Pacific Northwest National Laboratory (PNNL) and Britain’s University of Birmingham shows forests “transforming as the Earth heats up and as more frequent and severe droughts, wildfires, and disease outbreaks destroy trees,” CNBC reports.

“Reductions in average forest age and height are already happening and they’re likely to continue to happen” due to climate change said PNNL scientist and report author Nate McDowell.

“A future planet with fewer large, old forests will be very different than what we have grown accustomed to,” as “older forests often host much higher biodiversity than young forests and they store more carbon,” he added. But already, “over the last hundred years we’ve lost a lot of old forests, and they’ve been replaced in part by non-forests and in part by young forests. This has consequences on biodiversity, climate mitigation, and forestry.”

“Increasing rates of tree mortality driven by climate and land use change—combined with uncertainty in the mix of species that will form the next generation—pose big challenges for conservationists and forest managers alike,” agreed co-author Tom Pugh, a scientist at the Birmingham Institute of Forest Research.

The changing profile of forests also has an impact on biodiversity, which in turn affects their role in mitigating global heating. “Forests not only have less capacity to store carbon dioxide released by burning fossil fuels but are also unable to host certain species that normally reside there,” CNBC writes, citing McDowell. With 80% of the world’s land species living in forests, according to World Wildlife Fund, “widespread tree mortality and deforestation has disrupted the habitats of now critically endangered animals like the Sumatran tiger and the orangutan.”

The report singles out the Amazon rainforest as the “biggest deforestation front in the world, with more than 20% of the forest already destroyed” by cattle ranching and wildfires. It also points to a rise in forest disease outbreaks and fungi, including vines that use other plants as “host structures” and are choking some trees in tropical forests to death.

“Tropical forests are huge reservoirs of carbon, storing 250 billion tonnes in their trees alone—an amount equivalent to 90 years of global fossil fuel emissions at current levels,” the Thomson Reuters news agency explains. “Large swaths of rainforest, including in Indonesia, Malaysia, Brazil, and the Democratic Republic of Congo, help regulate rainfall, prevent flooding, protect biodiversity, and limit climate change. Trees also absorb carbon dioxide, the main pollutant heating up the Earth’s climate, and store carbon, which they release when they are cut down, or when they are burned or rot.”

Which is why the tree loss documented in the PNNL-Birmingham study will make it that much harder to stabilize average global warming at 1.5°C.

“In order to reach those temperature change targets, it would require even stronger reductions in emissions because the forests are taking up less. Therefore we either have to put less in the atmosphere or find a way to take it out,” Pugh told Thomson Reuters. “It implies a hotter world,” as well as a shift in forest conservation practices.

“There is a need for adaptive forest management, which takes into account…the climate we expect trees to be experiencing in the next decades, and making sure that the trees that are being planted take account of that,” he said.

CNBC cites a separate study, published last year in the Proceedings of the National Academy of Sciences, that found carbon storage lost each year to invasive insects equivalent to the emissions from five million internal combustion vehicles.