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.