The importance of the globe’s five biggest forests

A new book outlines the outsized role of the five remaining big forests in the world:

Photo by thiago japyassu on

All forests can help, but large forests are of supreme importance for the climate. The five largest ones left—the megaforests—include boreal forests in Russia and North America, and the tropical forests in the Amazon, Congo, and New Guinea. Intact forests are 20 percent of the tropical total and store 40 percent of the aboveground forest carbon in the low latitudes. New research led by Sean Maxwell, of the University of Queensland, and 11 collaborators suggests that the carbon benefit of intact tropical forests is six times greater than the Intergovernmental Panel on Climate Change and others have estimated to date. That’s because in the years after a big forest is broken up by roads or farms, its edges dry out and winds whistle through, blowing over big trees. Fires invade it more readily, and overhunting eliminates animals that disperse seeds. And on top of all the carbon vaporized from the space actually deforested, over the next several decades the climate will be stuck with 14 metric tons of extra carbon per acre that the lost tropical forests would have absorbed had they remained standing…

This experiment began in 1979. It ended up with five plots measuring two and a half acres, four at 25 acres, and two covering 250 acres. Matching control plots in continuous forest were also established. By 2002, the project had produced a simple answer about fragmentation: Large intact areas are very important, the larger the better. Even the 250-acre reserves were too small for forest-interior bird species, half of which vacated these patches in less than 15 years. The edges were hotter and drier, with great mats of desiccated leaves from trees either dying or losing foliage to wind. There were more vines, thicker undergrowth, and fewer mushrooms.

Species that need continuous tree cover decamped. Black spider monkeys, for example, who move fast through large areas of forest eating fruit from widely spaced trees, abandoned all the forest fragments immediately. They stayed in nearby continuous forest. Howler monkeys, by contrast, are leaf eaters and not particularly choosy. They remained in all the fragments. The white-plumed antbird, so named for the spiky crest between its eyes, could not persist in the fragments. Antbirds follow raiding ant armies and eat the bugs flushed out by the lethal column. Though 250 acres is sufficient territory for one ant colony, each colony marches only about a week per month. So, to avoid going hungry for weeks at a time, the white-plumed antbirds need to follow several colonies on a rotating basis. The 250-acre fragments were at least three times too small for the birds. No antbirds means no antbird droppings, which deprives shimmering blue-and-black skipper butterflies their sustenance. They left too…

Big forests are a linchpin in a planetary system. They are vivid stages for stories about energy and matter that we describe severally with our physical, biological, and chemical sciences, but are really a single story whose intricacies and meaning we don’t fully understand. Orchid bees make Brazil nuts, feed agoutis, take carbon from the air, breathe water back into it, make clouds that make rain a hundred miles away that feeds a stream, where a catfish, having migrated from the mouth of the Amazon, is caught by an otter or by a person, surrendering its protein to enliven the woods. The bee makes all these things, and these things make the bee.

One takeaway from this research: the way trees and nature are often treated in urban and suburban settings does not fully grapple with the larger impact of trees and forests. Isolated pockets of green are not necessarily bad but there is a difference in scale between those possibilities in more densely settled locations and large unbroken forests.

Another interesting aspect to consider is the human interaction with these large forests. Coming off reading the The Dawn of Everything, the shift to agriculture and living in larger cities in metropolitan areas did really create a divide between certain natural settings where humans could thrive and what became the settings for much of human activity.

This book also reminded me of this January 2022 piece on a man who has explored the old growth forests of New England and how much this differs from many contemporary experiences with trees and forests.

McMansions being built in the wildland urban interface

Here is an argument that more McMansions are being built in the wildland urban interface and this is leading to problems with forest fires:

But in go-go America, these scientific truisms were no match for McMansion fantasies. As coastal folk headed to the Rocky Mountain frontier with visions of big-but-inexpensive castles far away from the inner city, the term “zoning” became an even more despised epithet than it already had been in cowboy country.

Rangeland and foothill frontiers subsequently became expansive low-density subdivisions, and carbon-belching SUVs chugged onto new roads being built farther and farther away from the urban core. That is, farther and farther into what the federal government calls the Wildland Urban Interface (WUI) and what fire experts call the dangerous “red zone.”

The numbers are stark: According to The Denver Post, between 1990 and 2000, 40 percent of all homes built in the nation were built in the WUI — and “a Colorado State University analysis expects a 300 percent increase in WUI acreage in the next couple decades.”

In the last two decades in fire-scorched Colorado alone, I-News Network reports that “a quarter million people have moved into red zones,” meaning that today “one of every four Colorado homes is in a red zone.”

I had never heard of the wildland urban interface before. To put it in other terms, it sounds like many new homes are being built in exurban areas, the leading edges of metropolitan areas. There are advantages and disadvantages to this: the land is likely quite cheaper and people can have bigger pieces of property and newer homes. But, there are negative consequences such as having to drive further to get places and the environmental impact.

Here is more information on the wildland urban interface in Colorado from Colorado State University. And here is an interesting opinion piece in the Denver Post about how to improve the narratives about WUI fires.