Forests are ecological superheroes—they ventilate the planet, nurture the most biodiverse habitats on Earth, and regulate global climate and carbon cycles. From the poles to the equator, our survival is completely dependent on healthy woodlands.
But according to the latest issue of Science, which is devoted to forest health, every major forest biome is struggling. While each region suffers from unique pressures, the underlying thread that connects them all is undeniably human activity.
For example, the first of the special issue's studies, led by forest ecologist Sylvie Gauthier, outlined the threats faced by boreal forests, which represent the largest forest habitats on Earth. These high-latitude woodlands are primarily coniferous, made up of pines, spruces, and larches, and stretch from the expansive forests of Canada to the Russian taiga.
Gauthier and her colleagues note that boreal forests have been traditionally very resistant to environmental changes that would devastate other biomes. "The resilience of these systems is well illustrated in the boreal forest of eastern North America," noted the team, "where the regional tree species pool has remained mostly unchanged over the past 8,000 years despite large fluctuations in climate and regional disturbance regimes."
But the adaptive prowess of boreal forests can only be pushed so far, and industrial logging of these timber-rich woodlands is beginning to take its toll. Gauthier's team estimates that two thirds of the world's boreal forests are now subject to heavy resource extraction, which has resulted in widespread pollution, deforestation, wildfires, and a less genetically diverse tree population.
Compounding these issues is the projected effect of climate change on northern forests. "Over the course of the 21st century, the boreal biome is expected to experience the largest increase in temperatures of all forest biomes," the team said. "Warmer temperatures would [...] lift the climate barriers to population growth or range expansion of native or invasive forest pests, resulting in severe outbreaks."
"The health of the immense and seemingly timeless boreal forest is presently under threat, together with the vitality of many forest-based communities and economies," the researchers said.
Temperate forests aren't faring much better, according to another study from the issue written by US Geological Survey ecologists Constance Millar and Nathan Stephenson. Temperate forests are primarily composed of deciduous trees that shed their leaves seasonally, and are common in mid-latitude regions around the world.
As with boreal forests, climate change is the most devastating threat facing temperate woodlands, which are especially vulnerable to droughts and wildfires. Deciduous trees have evolved to withstand these pressures to a certain degree, but the authors pointed out that the steep upward trend of rising temperatures is ushering in "megadisturbances" that will not be so easy to brush off.
"For millennia, drought has been a key disturbance agent in temperate forests," Millar and Stephenson said. "Over the past few decades, however, rising global temperatures have contributed to droughts of a severity that is unprecedented in the last century or more."
"[E]xceptional droughts, directly and in combination with other disturbance factors, are pushing some temperate forests beyond thresholds of sustainability," the team concluded.
Forests that have been severely dehydrated by megadroughts suffer from water depletion, and they also turn into enormous tinder piles that can feed megafires. On top of that, temperate forests coincide with heavy population densities, so there a lot of anthropogenic stressors on them as well, like pollution, industrial development, and invasive species.
"[T]he actions we take now in temperate forests can ease and guide transitions, diminishing effects to forest ecosystems and human societies," Millar and Stephenson said.
Last but not least, researchers led by geography professor Simon Lewis assessed one of the most biodiverse habitats on the planet—the tropical forest, characterized by evergreen broadleaf trees.
While Lewis and his colleagues noted that climate change is a major risk for tropical forests, they concluded that this biome is much more threatened by direct anthropogenic contact.
Along those lines, the team outline the ecological disturbances induced by human settlements over the course of several millennia, beginning with extinctions of tropical megafauna and ending with "today's global integration, dominated by intensive permanent agriculture, industrial logging, and attendant fires and fragmentation."
"The 21st century will see large increases in demand for products from tropical lands," the authors wrote. "Thus, the greatest threats will likely continue to be conversion and degradation but will be increasingly combined with the impacts of rapid climatic changes."
So, to sum up: Every forest biome on Earth is actively dying right now, and if this course isn't corrected, the deterioration of these valuable ecosystems will accelerate over the coming decades.
Of course, in each of the studies, the authors pointed out numerous ways to slow the alarming decline of forests worldwide, such as stricter conservation policies, better forestry management, and a global framework for policing climate change. These kinds of actions "would lessen the unwelcome shocks that living in the Anthropocene will bring this century," as Lewis's team put it.
In other words, it is absolutely possible for humans to curb the damage to forests, or perhaps even reverse it in some places. Indeed, given that our own fate is inexorably tied to that of the world's forests, it seems suicidal to consider any other option.
But whether we can pull this kind of turnaround off depends almost entirely on the human capacity to plan for the long-term health of the planet. If humans intend to survive this anthropogenic age we brought to the planet, we will have to up our game.