The World’s Largest Forest Wilderness Seems to Be Shrinking

The World’s Boreal Forests May Be Shrinking as Climate Change Pushes Them Northward

Earth’s boreal forests circle our planet’s far northern reaches, just south of the Arctic’s treeless tundra. If the planet wears an Arctic ice cap, then the boreal forests are a loose-knit headband wrapped around its ears, covering large portions of Alaska, Canada, Scandinavia and Siberia.

The Sustainable Development Goals (SDGs)

1. Goal 13: Climate Action
2. Goal 15: Life on Land

The Importance of Boreal Forests

• Boreal forests are among the most important ecosystems on Earth.
• They support numerous species of mammals, fish, plants, insects, and birds.

Climate Change and Boreal Forests

For over two centuries, scientists have recognized that climate plays a key role in determining the geographic zones of plant communities. Because boreal forests and soils face subzero winters and short summers, these forests and the animals that live in them are shifting northward as temperatures rise.

Concerning Evidence of Shrinking Forests

However, boreal forests’ northward advance has been spotty and slower than expected. Meanwhile, their southern retreat has been faster than scientists predicted. As scholars who study northern ecosystems, forests, and wetlands, we see concerning evidence that as the world warms, its largest forest wilderness appears to be shrinking.

The Largest Wilderness on Earth

Boreal forests contain billions of trees. Most are needleleaf, cone-bearing conifers, but there also are patches of broadleaf species, including birch, aspen, and poplar. They support millions of migratory birds and iconic mammals like brown bears, moose, and lynx.

Regulating Earth’s Climate

• The trees and soils in boreal forests help regulate Earth’s climate by storing carbon dioxide and preventing it from entering the atmosphere.
• Changes to the forests will have an impact on global climate.

Warming and Carbon Storage

These forests are warming at rates well above the global average. Rising temperatures directly affect the growth and survival of trees and their ability to store carbon.

Forests on the Move

As atmospheric warming frees trees from cold temperatures, they can respond by growing faster. Milder temperatures also allow young seedling trees in the most northern boreal forests to gain a foothold where previous conditions were too harsh for them to become established.

In the warmer, southern boreal forests, conditions have become too warm for cold-adapted boreal trees, slowing their growth and even leading to their death. With warming comes dryness, making trees more susceptible to insect infestation and fires.

If this happens at a larger scale, southern boreal forest boundaries will thin and degrade, retreating farther north where temperatures are still suitable.

Tracking Forests from Space

Satellites are invaluable for tracking how boreal forests have changed in recent decades and whether these changes are consistent with an overall northward shift. Researchers can use satellites to monitor year-to-year changes in forest characteristics, such as annual tree growth and tree cover.

Recent studies using satellite data showed that tree growth and tree cover increased from 2000 to 2019 throughout much of the boreal forest, mainly in the coldest northern areas. However, there was limited evidence to indicate that forests were expanding past current tree lines.

Tree growth and tree cover often decreased from 2000 to 2019 in warmer southern areas of the boreal forests. Hotter and drier conditions frequently reduced tree growth or killed individual trees, while wildfires and logging contributed to tree cover loss.

Satellite data makes it clear that climate change is affecting both the northern and southern margins of the boreal forest. However, if tree cover loss in the south occurs more rapidly than gains in the north, then the boreal forest will likely contract, rather than simply shifting northward.

Zooming in to Understand Forest Change

Forests advance when individual tree seeds germinate and grow, but boreal trees grow slowly and require decades to reach a size that’s visible from space. Finding young trees whose presence would signal tree-line movement requires data from the ground.

Field studies have shown that young boreal trees are growing beyond established tree lines, indicating a northward movement. However, these expansions are localized and do not yet happen everywhere along the northern tree line.

The Future Face of Boreal Forests

Boreal forests are responding to rising temperatures, but the rapid rates of climatic change may prevent them from moving northward at a pace that keeps up with their loss in the south. The future of boreal forests and their ability to compensate for carbon losses in the south remains uncertain.

If boreal forests contract, it will harm native and migratory animals, reduce habitat for birds, and have cultural implications for communities that rely on these forests. Monitoring boreal forests using satellite data and on-the-ground measurements is crucial to understanding their future.

The Sustainable Development Goals (SDGs)

1. Goal 13: Climate Action
2. Goal 15: Life on Land

Ronny Rotbarth, Ph.D. Candidate of Arctic and Sub-Arctic Ecology, Wageningen University; David J. Cooper, Senior Research Scientist Emeritus, Colorado State University; Logan Berner, Assistant Research Professor of Global Change Ecology, Northern Arizona University; Roman Dial, Professor of Biology and Mathematics, Alaska Pacific University

This article is republished from The Conversation under a Creative Commons license. Read the original article.