As global temperatures rise, temperate forests are not moving northward to cooler latitudes as quickly as scientists expected, creating a dangerous mismatch between where the trees are and where their ideal climate is heading. This lag, observed in key studies, suggests that many tree species could face significant stress and decline as they become stranded in environments that are increasingly too warm for them to thrive.
This failure to migrate at the same pace as climate change stands in stark contrast to other global ecosystems. Tropical species, for example, are shifting their ranges to higher, cooler elevations on mountainsides at a significantly faster rate. The sluggishness of temperate forests raises urgent questions about their long-term survival and the stability of the ecosystems they support, prompting researchers to investigate the complex factors that appear to be holding them in place.
A Lagging Response to Warming
Studies have documented a significant disparity in migration rates between different global biomes. Research comparing mountain regions globally found that tropical species are moving upslope 2.1 to 2.4 times faster than their temperate counterparts. Tropical forests, in particular, are shifting their ranges uphill at a rate 10 times faster than temperate forests are. This suggests tropical species may be more immediately sensitive to temperature changes, given the relatively stable climate they are adapted to.
The lack of responsiveness from temperate forest ecosystems is a major concern for scientists. Prior research in North America showed that many young trees were not successfully establishing themselves in cooler habitats farther north, a phenomenon described as a “failure to migrate.” While some upslope shifts are occurring in mountainous temperate zones, these movements are still far behind the pace of warming. This inertia suggests that these forests are not adapting to climate change through geographic shifts as effectively as other ecosystems are.
The Continental Divide in North America
Across North America, the story of tree migration is not uniform, revealing a clear split between western and eastern regions. A continental-scale analysis found that a poleward migration of northern species is currently underway in the West. In these areas, both seed production, known as fecundity, and the successful establishment of new seedlings are contributing to the northward spread of tree populations.
In the eastern United States, however, the migration is notably stalled. The primary limiting factor appears to be fecundity; the centers of seed production for many species have not yet shifted northward to follow the warming climate. This creates a critical bottleneck, as successful germination and seedling survival at the northern frontier cannot compensate for the lack of seed production in those areas. This regional contrast highlights that the ability of a forest to migrate depends on more than just warming temperatures; it is also constrained by the complex life cycles of the trees themselves.
Defining a Forest on the Move
Contrasting Rates of Change
The speed of migration can depend heavily on what is being measured. Some research distinguishes between the movement of individual tree species and the shift of an entire forest type or biome. One study based on records of over 9 million trees found that, on average, North American forests as ecosystems migrated at a remarkable velocity of 205.2 kilometers per decade. This rate is more than twice as fast as the migration of individual tree species ranges, which averaged 95.6 kilometers per decade. This suggests that changes in the abundance and composition of species within a forest can cause the entire ecosystem type to shift faster than any single species can move on its own.
The Slow Spread of Seeds
Other researchers argue for a much slower rate of migration, pointing to the physical limitations of seed dispersal. A forest ecologist with the Cary Institute of Ecosystem Studies, Charles Canham, has noted through computer modeling that the seeds of most temperate tree species land within 15 to 20 meters of the parent tree. This physical tether severely restricts how quickly a species can establish new populations in more distant, cooler regions. While some light seeds from trees like aspens can be carried many miles by wind, this is not the norm for the majority of species that make up the forest.
Barriers to a Northern Trek
Several underlying factors may explain why temperate forests are struggling to keep pace with climate change. One theory is that some species are attempting to adapt in place by altering their seasonal timing rather than shifting their geographic location. Processes like blooming, shedding leaves, or entering dormancy may be shifting in response to changing temperatures. However, scientists remain uncertain whether this strategy of temporal, rather than spatial, adaptation will be sufficient to cope with the accelerating rate of environmental change.
The different life stages of trees—adult, seed production, and seedling—respond to climate differently, creating potential hurdles. In the eastern U.S., for example, limited warming combined with the specific climate needs for robust seed production may be preventing adult trees from reproducing effectively in potential new northern habitats. The conditions that allow an adult tree to survive are not necessarily the same as those required for it to produce a large crop of viable seeds.
Ecological Risks and Future Outlook
The failure of species to track their optimal climate zones puts them at a heightened risk of decline and, eventually, extinction. For trees and other organisms in mountainous areas, the only option is to move to higher elevations. As they move upslope, however, the available land area shrinks, leading to a phenomenon dubbed the “escalator to extinction,” where species eventually run out of habitat at the mountain’s peak.
While temperate forests lag, other biomes are already visibly transforming. Boreal forests, the vast belt of conifers across the planet’s northern regions, are actively shifting northward. Satellite observations over 40 years show that these colder forests are becoming more productive and expanding into arctic tundra at their northern edge. At the same time, they are experiencing more stress, browning, and tree death along their warmer southern margins due to hotter and drier conditions. This clear biome shift in the north underscores the unusual and concerning inertia observed in temperate ecosystems.
