Deforestation, climate crisis could crash Amazon tree diversity: study
by Jenny Gonzales - 18 August 2019
- New research finds that when climate change and deforestation impacts are taken together, up to 58 percent of Amazon tree species richness could be lost by 2050, of which 49 percent would have some degree of risk for extinction.
- Under the deforestation/climate change scenario, half the Amazon (the north, central and west) could be reduced to 53 percent of the original forest. The other half (the east, south and southeast, where agribusiness occurs), could become extremely fragmented, with only 30 percent of forest remaining.
- Studies rarely take both climate change and deforestation into account. But the new study’s results bolster the findings of other scientists who have modeled results showing that when the Amazon is 20-25 percent deforested, it could cross a rainforest to savanna conversion tipping point, a disaster for biodiversity.
- Scientists warn that Jair Bolsonaro’s anti-environmental policies could result in a worst-case scenario, with severe damage to the Amazon rainforest and to its ecological services, including the loss of the sequestration of vast amounts of stored carbon, leading to a regional and global intensification of climate change.
The combined impact of ongoing deforestation and escalating climate change on the Amazon rainforest could radically transform its configuration by 2050, with the biome divided into two distinct blocks — one occupied by still significant but very seriously diminished rainforest, the other dominated by agribusiness and scattered forest inside conserved areas.
That shift, were it to occur, could result in a decline of up to 58 percent of Amazon tree species richness, of which 49 percent would have some degree of risk for extinction (with tree species becoming vulnerable, endangered or critically endangered), according to a new study published in Nature Climate Change.
The authors of the paper — four researchers from Brazil and the Netherlands — determined that both deforestation and climate change had to be examined together, and not separately as is typically done, in order to determine a realistic future scenario.
To the researchers’ surprise, when the effects were combined in their models, the tree species loss numbers were very high.
Under the deforestation/climate change scenario, one half of the Amazon (the northern, central and western portions) would be reduced to 53 percent of the original forest, although still with continuous areas. The other half (the eastern, southern and southeastern areas, where agribusiness activities currently take place), would become extremely fragmented, with only 30 percent of forest remaining; remnant vegetation would be found primarily in protected areas and indigenous reserves.
Two scenarios for 2050 were highlighted by the study, a more optimistic one — in which Paris Climate Agreement carbon targets are achieved and global temperature warms by less than 2 degrees Celsius (3.6 degrees Fahrenheit) — and a more pessimistic one based on recent rising trends in deforestation and CO2 emissions.
In the more pessimistic scenario, Amazonian tree species would lose up to 65 percent of their spatial distribution area (where they live and reproduce), and up to 58 percent of their diversity; 49 percent would be threatened with extinction, of which 22 percent would be critically endangered, according to IUCN’s threatened extinction criteria.
Even the more optimistic scenario “does not indicate a promising future,” Vitor Gomes, an environmental scientist at the Federal University of Pará and the lead study author told Mongabay. That scenario predicts a loss of tree species richness of up to 43 percent, and a decline in tree species distribution area of up to 53 percent; under that scenario, 48 percent of tree species would be threatened, of which 11 percent would be critically endangered.
“The study should be seen as a big warning,” said Ima Vieira, a researcher at the Museu Paraense Emílio Goeldi and a study co-author. “It shows that if deforestation is currently the biggest cause of habitat loss in the Amazon, over the next thirty years it will probably be surpassed by climate change, which operates throughout the whole biome and can alone reduce species diversity by up to 37 percent.”
“It was not so clear to us how much the climate could affect the forest in the future,” Gomes added. “Deforestation is no longer the only major threat to the Pan-Amazon,” a biome designation that includes portions of nine South American countries.
Excluding climate change impacts, deforestation alone could cause Amazon species diversity losses of 19 percent (in the best scenario) or 36 percent (in the worst), while climate change could cause reductions of 31 percent to 37 percent, respectively.
No time for migration
The researchers analyzed the current distribution area of 6,394 tree species with available data among the 10,071 known Amazon tree species. They then compared that present data with both historical data (1950-2000) and projected deforestation data (up to 2050), along with current and future climate scenarios as determined by the United Nations IPCC (UN Intergovernmental Panel on Climate Change).
From this total species data, they eliminated rare species with insufficient records available to produce distribution models, and species without statistically significant models, leaving a total of 4,935 species.
Mapping the locations where the species can be found today is important to obtain temperature and precipitation limits in which they are apparently comfortable.
“The trees will find less favorable conditions [as climate change escalates] to keep existing and propagating,” explained Gomes. “Because they are static, they are slow to migrate to new areas through dispersers and pollinators [such as wind, water and animals].” The study gives as a reference the Holocene, a geological period that started about 11,600 years ago, when climate change caused Amazonian tree communities to expand their distribution southward.
“It took them 3,000 years to advance nearly 100 kilometers (62 miles). Man-induced climate change is happening now, and trees will be unable to move in 30 years or so more than 300 kilometers (186 miles), the distance to which the most suitable climates may be in relation with the current distribution areas [by 2050]. Not to mention that deforested areas [caused by agribusiness and other human development] make it even more difficult for trees to move forward once that barrier has been created,” Gomes said.
Tree species found in the lower half of the Amazon — such as the Protium altissimum (Aubl.) Marchand, the second most abundant in the biome, for example — may face a serious threat of extinction as the species suffers losses of up to 50 percent of its suitable distribution area. While Eperua falcata Aubl., common in the Guiana Shield, could lose up to 63 percent of its suitable distribution area.
Agreement with previous studies
Carlos Nobre, a respected Brazilian climatologist and senior researcher at the University of São Paulo, along with Thomas Lovejoy, a U.S. ecologist at George Mason University, have estimated that deforestation and climate change combined could cause a large part of the Amazon biome to experience a rainforest to savanna conversion tipping point when around 20 to 25 percent of the biome is deforested.
Nobre commented on the new study: “The results are quite credible as projections of the synergistic effect of climate change, due to global warming, and deforestation, on the distribution of species in the Amazon. In our studies, we looked at the rainforest as a biome, not species by species, as in their study, and we analyzed the risks of change in the type of vegetation — that is, the forest being replaced by a savanna.”
However, “The results of these two kinds of analysis are similar: higher impacts in the south and east of the Amazon, while the forest would remain in the west,” Nobre said. “The study strongly reinforces our projections and recommendations for a development model with zero deforestation or, better still, the restoration of large deforested areas” in the Amazon.
Paulo Brando, an ecologist at the Woods Hole Research Center in Massachusetts, USA, noted that “the division of the Amazon in the middle is not necessarily a surprise. Previous studies, such as Duffy et al. 2015, have shown that the Eastern Amazon could be[come] drier and hotter with climate change, while the west would be more rainy. That said, the results are of immense importance for the conservation of the rainforest.
“With the reduction of deforestation, Brazil could avoid the loss of occupation areas of hundreds of species. Without a global effort to stabilize the climate, however, some species would still be threatened. Thus, reducing deforestation would help not only to stabilize the climate but also to prevent habitat loss,” Brando concluded.
The new research also highlights the crucial role of the currently existing network of protected areas and indigenous lands in the Amazon. Those areas can help buffer the loss of species diversity against future impacts.
“Even though [trees inside protected areas] are not totally immune to climate change, our models show that forests outside protected areas can lose up to a third more species,” said Gomes. “That’s why the preservation [of conserved areas] and the creation of corridors between them are so necessary, allowing biological dispersion and the migration of animals. Otherwise there will be only forest patches left in the Amazon.”
Vieira, of the Museu Paraense (linked with the Brazilian Ministry of Science, Technology, Innovation and Communications), said that it’s not difficult to imagine the most pessimistic study scenario becoming reality, given the trouble the world’s nations are having in achieving their carbon reduction goals as expressed in the 2015 Paris Agreement, as well as the difficulty Brazil has had in controlling deforestation, first under the Temer administration and now under the Bolsonaro administration.
June 2019 deforestation in the Brazilian Amazon increased by 88 percent as compared to the same month in 2018, and while this result is preliminary many analysts fear that 2019 could show a significant annual rise in deforestation.
However, the nation isn’t responding by curbing deforestation, rather its policies appear to be encouraging the opposite. In May, Brazilian Environment Minister Ricardo Salles proposed a reevaluation of all 334 federal conservation units, with an eye on reducing the size of some, and abolishing others. More recently he declared without offering any scientific evidence that Brazil has already reached “zero relative deforestation,” that is, deforestation in the Amazon represents, according to him, “0.002 percent of the biome.” Later he said the correct number is 0.16 percent.
Vieira responded: “There is a political scenario unfavorable to the environment in the country [of Brazil], with budget cuts in the environmental and scientific areas, reduction of operations in environmental control and inspection, setbacks in environmental legislation, freezing of indigenous lands demarcations and the threat of opening [indigenous reserves] to mining activities.
“To save the Amazon from destruction, initiatives should consider an integrated vision of the region, long-term public policies, respect for environmental legislation, as well as for indigenous territories and peoples, and there should be strong economic pressure to restrict the sale of products from deforested areas and protected areas of the Amazon,” Vieira concluded.
Gomes, V. H. F., Vieira, I. C. G., Salomão, R.P., & ter Steege, H. (2019). Amazonian tree species threatened by deforestation and climate change. Nature Climate Change, 9(7), 547-553.