Is half of the trees




A new study just provide the most accurate estimates to date and the results are surprising, for better and for worse. Until now it was thought that there are 400,000 million trees worldwide, or 61 per person. The count was based on satellite images and estimates of forest area, but not in field observations. Then in 2013, based on direct counts studies confirmed that only the Amazon there are nearly 400,000 million trees, so the question was in the air. And it is crucial to understand how, especially the carbon cycle and climate change, but also the distribution of animal and plant species or the effects of human activity on the planet works all global data.

The recount, which publishes the journal Nature, shows that there are actually three billion trees across the planet about eight times more than previously estimated. On average there is 422 trees per each human.

The country has uncovered a huge inequality, with rich and Bolivia, with more than 5,000 trees per person, and paupers like Israel, where two barely touch. Much of the contrast is due to natural factors such as climate, topography and soil characteristics, but also the unmistakable effect of civilization. The greater the human population, most trees decreases account. In part this is because more vegetation thrives where there is more moisture, places that also prefer humans to establish farmland.

Work estimates that every year, human activities end up with 15,000 million trees. The net loss, offset by the emergence of new trees and reforestation is 10,000 million. Since the beginning of civilization, the number of trees on the planet has been reduced by 46%, almost half of what it was, says the study, published today in Nature.

If this rate of destruction continues unchanged, the trees disappear from the planet in 300 years. There are three centuries, some 12 generations. “That’s the time left if we do nothing, but we hope that we can slow the pace and increase reforestation in the coming years to alleviate human impact on ecosystems and climate,” says Thomas Crowther, researcher Yale University (USA) and first author of the study.

Europe deforested

Two years representatives of the “Campaign 1,000 million trees” UN ago to replant some of the lost vegetation needed to know how much impact were tending their efforts. They contacted Crowther, who works at the School of Forestry and Environmental Studies Yale, to ask how many trees are there in the world and many in the regions where they work. It was the beginning of this study, signed by 38 researchers from 14 countries. Together they collected data on forest density taken in more than 400,000 points every continent except Antarctica. They divided the land into 14 types of biomes, or bioclimatic landscapes, estimated the density of trees in each based on satellite images and proved its reliability with action on the ground. Finally they made up the global map of trees more accurate than has ever been done, in which each pixel is one square kilometer.

The results show that the highest density of trees in boreal forests and subarctic regions of Russia, Scandinavia and North America. The largest expanse of forests are in the tropics, with 43% of all trees on the planet. The northern forests contain only 24% of total copies and 22% is in temperate zones.

Europe is one of the hardest hit areas. “Before civilization, all of Europe was a great forest, but human pressure due to agricultural, industrial and urban development make this region one of the most deforested in the world,” explains Crowther. In Spain there are 11,300 million trees, 245 per person.

Tropical tree species could be in much bigger trouble than scientists had thought: A new study, which involved collaboration from dozens of researchers, suggests that at least 36 percent and up to 57 percent of all Amazon tree species are likely at risk of extinction, depending on future deforestation rates. If true, this information would raise the number of threatened plant species on Earth by about 22 percent.

The research, which was published Friday in the journal Science Advances, combined spatial distribution models of the Amazon with both historical and projected data on deforestation to determine the conservation status of more than 15,000 Amazonian tree species, about two-thirds of which the authors considered rare species. The researchers used listing criteria from the International Union for Conservation of Nature (IUCN), which maintains a “red list” of threatened species on Earth, to decide which species should be considered in danger of extinction.

Using the IUCN framework is one of the paper’s major strengths, said Nigel Pitman, a senior conservation ecologist at the Field Museum in Chicago and one of the paper’s co-authors, during a teleconference about the paper on Friday morning.

“The problem is there are lots of definitions of the word ‘threatened,’” Pitman said at the teleconference. “Each country — oftentimes agencies with a country, NGOs, researchers — have different definitions. One thing that’s special about this paper is that we’ve made a real point of reporting our results using the most common currency of conservation status, the IUCN red list framework.”

However, Pitman added, about 90 percent of plant species on Earth have yet to be assessed by the IUCN, as it requires an enormous amount of resources to go through every species one by one.

“What we’ve tried to do with this paper is a kind of shortcut, a kind of triage, that can give us a preliminary look at the conservation status of all these species,” he said. And what he and his colleagues found is that “several thousand Amazonian trees that aren’t currently on the red list probably deserve to be.”

The tree inventory data the authors used came from the Amazon Tree Diversity Network, which includes more than 1,700 tree inventory plots throughout the Amazon. And their deforestation data came from published work on deforestation up through 2013 and projections for future deforestation in the year 2050. The IUCN red list framework takes future threats into account when determining a species’ conservation status, which is why the authors included future projections for deforestation in their study.

They considered two different future scenarios: a “business-as-usual” scenario, in which deforestation continues at its current rate, and an “increased governance” scenario, in which deforestation is slowed in the future. Under the business-as-usual scenario, 57 percent of the Amazonian species can be considered threatened, and under the increased governance scenario, 36 percent.

In 2009, a similar study was conducted on the extinction risks of Amazonian plants. Kenneth Feeley, the lead author of that study and an associate professor of biology at Florida International University, told The Post that this new paper helps confirm the results he and his colleagues produced at the time. Feeley was not involved with the new paper.

“We came up with very similar numbers,” Feeley said. “That’s a great thing in science. The fact that we have different assumptions, different sources of potential errors, and we still came to this similar number really helps to say that this is something we can believe in.”

Although Feeley’s paper did not use the IUCN framework to draw its conclusions, he noted that the strategy “is very useful because it’s a language a lot of policymakers are used to and comfortable with and know how to act on. This new paper will be very useful in pushing conservation and leading us into hopefully what needs to be done next to reduce these possible extinction rates.”

And what needs to be done, according to the authors, is an improvement in the management of protected areas in the Amazon. The authors noted that about 52 percent of the Amazon basin is currently composed of protected areas, although the degree of protection they offer varies. And even in these protected zones, trees can still be threatened, if logging is still permitted to take place under certain exceptions or if not enough resources are allocated to combating illegal deforestation.

However, there’s hope, according to the authors: In their analysis, they found that if deforestation were not permitted to occur within protected areas, the percentage of threatened species would fall to 32 percent under the increased governance scenario and 44 percent under the business-as-usual scenario.

“If we can protect these areas… the Amazon could be a showcase of large-scale conservation worldwide,” said Hans ter Steege, the paper’s lead author and a research fellow at the Naturalis Biodiversity Center in the Netherlands, during the teleconference.

Cracking down on deforestation will be one challenge moving forward — but not the only one, according to Feeley. This paper only takes deforestation into account when considering the trees’ conservation status. But there are other significant future threats to the trees as well, most notably climate change. “My guess would be, yes, the number of extinctions is potentially even higher than what the authors estimate,” Feeley said.

And to add to the alarm bells, the new study could imply that other tropical tree species, in places other than the Amazon, are also in worse shape than we thought.

“The vast number of threatened plant species uncovered by this new approach begs the question: how many others have been overlooked at a global scale?” said Thomas Crowther, a postdoctoral fellow at Yale University’s School of Forestry and Environmental Studies, in an e-mail to The Post. Crowther was not involved with this study, but was the lead author on a recent, high-profile paper mapping tree density across the world.

And, indeed, Pitman — the new study’s co-author — noted at the teleconference that “most tropical forests have lost a lot more forest coverage than the Amazon. It may be the case that most tree species in the tropics, if we were to do this same sort of analysis, would qualify as globally threatened.”

So there’s work cut out for conservationists hoping to prevent a large-scale extinction of tropical tree species in the future. Cutting down on global deforestation, particularly in the tropics, will likely be a topic at the UN’s climate conference in Paris, which begins on Nov. 30. Protecting trees is a safeguard against the loss of biodiversity, but forests are also valuable carbon sinks, meaning they absorb carbon emissions that would otherwise end up the atmosphere and contribute to global warming. So there are climate-related reasons to be concerned about the loss of tropical trees, as well.

With any luck, the study will be taken by policymakers as a clear warning that action is needed, Feeley said.

“What this study shows is that we already have a significant number of species that are likely to be threatened,” he said. “If we keep going in the direction we’re going, we’re going to put a lot more species at risk of extinction very quickly.”


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