Iceland was not always treeless. When Norse settlers arrived around AD 870, birch woodland covered a meaningful share of the island, and the near-total disappearance of those forests over the following centuries is the result of several forces acting together: human land clearing, relentless sheep grazing, harsh subarctic climate, catastrophic soil erosion, and the island’s volcanic geology. Today, forests cover roughly one percent of Iceland’s total land area, and vegetation of any kind covers only about 28 percent of the country.1ScienceDirect. Simulating vegetation cover dynamics with regards to long-term climatic variations in sub-arctic landscapes No single factor explains this. The treelessness is the product of a feedback loop in which each problem reinforces the others.
What Iceland Looked Like Before Humans Arrived
Before the Norse colonization, Iceland’s lowlands supported scattered but genuine birch woodland, dominated by downy birch (Betula pubescens) along with dwarf birch and several species of willow. Ancient sedimentary DNA studies show that plants colonized Iceland rapidly after the last ice age, and the island’s flora stabilized well before humans showed up.2Quaternary Science Reviews. Ancient sedimentary DNA shows rapid post-glacial colonisation of Iceland followed by relatively stable vegetation until the Norse settlement (Landnám) AD 870 The native woody plant diversity was never large. Iceland has only two native Betulaceae species (downy birch and dwarf birch) and four native willows, including three cold-tolerant dwarf arctic species and one shrub-like species.3eLife. Postglacial woody shrub colonization and diversity buildup in Iceland and the circum North Atlantic Compared to the floras of Scandinavia and the British Isles, which are about four times as species-rich, Iceland’s plant community is sparse. But that is not because the climate was too hostile for trees. It is because the ocean crossing filtered out most species before they could establish.2Quaternary Science Reviews. Ancient sedimentary DNA shows rapid post-glacial colonisation of Iceland followed by relatively stable vegetation until the Norse settlement (Landnám) AD 870
The birch woodlands that did exist were low-growing and scrubby by continental standards, with an average upper limit of only about 200 to 300 meters elevation.1ScienceDirect. Simulating vegetation cover dynamics with regards to long-term climatic variations in sub-arctic landscapes Still, they were forests. They stabilized the soil, sheltered other plant species, and held the landscape together in ways that became painfully obvious once they were gone.
How Norse Settlement Stripped the Land
The arrival of Scandinavian settlers marked the beginning of rapid deforestation. Pollen records from lake sediments across Iceland consistently show a dramatic drop in birch pollen percentages immediately following the Norse colonization around AD 870. At most studied sites, the decline was abrupt. At some locations in northern Iceland, the pattern was more gradual, with birch pollen declining steadily from the settlement period through about AD 1300, as the woodland was replaced by heathland species.4Boreas. Environmental impacts of the Norse settlement: palaeoenvironmental data from Myvatnssveit, northern Iceland Either way, the result was the same: widespread loss of tree cover within a few centuries of human arrival.
The settlers needed wood for buildings, fuel, and charcoal production. They also cleared land for hay fields and grazing. On an island with only a handful of tree species and a short growing season, the forests could not regenerate fast enough to keep up with demand. But the cutting alone might not have been fatal. What turned temporary clearance into permanent loss was the introduction of livestock, especially sheep.
Sheep and the Grazing Trap
Sheep have grazed Iceland’s highlands and lowlands for over a thousand years, and their effect on birch regeneration has been devastating. Birch seedlings are small and slow-growing in Iceland’s cool climate, and sheep eat them before they can establish. This creates what ecologists sometimes call a grazing trap: the adult trees that were cut or burned cannot be replaced because every seedling is consumed. Over centuries, as the remaining mature trees died, the landscape shifted to treeless grassland and heath with no mechanism for recovery.
The evidence for how powerful this effect is comes from fencing experiments. When researchers exclude sheep from degraded land, birch comes back. One study tracking two grazing-exclusion areas over nearly three decades found that tree density jumped from around 500 trees per hectare to more than 9,000 after grazing was removed. Seedling recruitment also increased, indicating that natural regeneration was actively underway once the sheep were gone.5Restoration Ecology. Successional patterns of Icelandic subarctic mountain birch woodlands after decades of grazing exclusion In some fenced areas, birch woodland expanded by natural seedling colonization as fast as or faster than deliberate planting efforts, sometimes leading land managers to abandon planting altogether and let nature do the work.6Restoration of Boreal and Temperate Forests. Restoration of birch woodlands in Iceland
That result is both encouraging and damning. It shows the land can still grow trees. It also shows that continuous grazing has been the primary obstacle preventing recovery for centuries. The forests are not gone because the climate became impossible for birch. They are gone because the seedlings keep getting eaten.
Soil Erosion and the Desert Feedback Loop
Deforestation and overgrazing did not just remove the trees. They set off a chain reaction of soil loss that is arguably harder to reverse than the loss of the trees themselves. Iceland’s soils are mostly Andosols, volcanic soils that are thick, fertile, and light. When vegetation holds them in place, they support rich ecosystems. When the vegetation is removed, they erode with alarming speed.
A distinctive Icelandic erosion feature called a rofabard illustrates the process. Rofabards form where loose Andosols sit on top of harder material like glacial till or lava. Once the vegetation at the edge is breached, the soft soil beneath the root mat gets undermined by wind and water, creating retreating escarpments. On top of the escarpment sits a fully vegetated ecosystem; behind it lies barren desert. These features are common across a roughly 20,000-square-kilometer area of Iceland, and the total land they have stripped of vegetation and fertile soil is estimated at 15,000 to 30,000 square kilometers.7Earth Surface Processes and Landforms. The Icelandic ‘rofabard’ soil erosion features For context, Iceland’s total land area is about 103,000 square kilometers, so this erosion has potentially denuded up to a quarter of the country.
The feedback loop is straightforward: trees and vegetation hold soil, soil supports trees, and once the vegetation is gone, the soil blows away, leaving behind surfaces that cannot support new trees even if seeds arrive. Large areas of Iceland’s interior highlands are now classified as desert or semi-desert, and many of those areas had fertile Andosols before the vegetation was lost. Replanting on these degraded surfaces is possible but slow, because the soil that would nurture seedlings has been stripped down to rock or hardpan.
Climate at the Margins
None of this would have been so catastrophic if Iceland had a forgiving climate. It does not. The growing season is short, summer temperatures are cool, and the island sits right at the climatic margin for tree growth. The mean upper limit of continuous vegetation cover is between 600 and 700 meters elevation, and birch woodland tops out at just 200 to 300 meters on average.1ScienceDirect. Simulating vegetation cover dynamics with regards to long-term climatic variations in sub-arctic landscapes Trees can survive at these latitudes and altitudes, but they grow slowly and recover slowly from disturbance. A birch seedling in southern Norway might grow out of reach of sheep in a season or two. In Iceland, it may take years.
This marginal climate means the system has very little buffer. A landscape that can support trees under undisturbed conditions can permanently lose them when human pressure and climate stress combine. During the Little Ice Age, roughly the 14th through the 19th centuries, temperatures dropped further, making conditions even harder for any remaining woodland fragments. The trees were already in trouble from cutting and grazing. Colder temperatures pushed the survivors closer to their physiological limits and slowed any attempted recovery to a crawl.
What Determines Whether Birch Can Come Back
Researchers studying natural birch colonization in Iceland have identified a range of factors that determine whether trees can reestablish on degraded land. The early establishment phase turns out to be the bottleneck, and it depends on several things lining up at once: the availability of suitable microsites where seedlings can take root, wind speed and direction (which affect both seed dispersal and seedling survival), and critically, whether or not sheep are present.8Restoration Ecology. Natural colonization as a means to upscale restoration of subarctic woodlands in Iceland If a seed source exists nearby and grazing is excluded, natural colonization can be remarkably effective. But remove any one of those conditions and the process stalls.
The genetic health of Iceland’s remaining birch populations adds another layer. Despite centuries of fragmentation, the surviving forests still harbor similar levels of genetic diversity from site to site, suggesting that fragmentation and hybridization between downy birch and dwarf birch have not dramatically eroded the genetic variation within individual forests. There is genetic divergence between forests in different regions, likely reflecting historical isolation, but the raw material for adaptation appears to still be present in the population.
Exotic Species and the Forestry Question
Iceland’s reforestation efforts have not relied solely on native birch. Since the early 20th century, land managers have experimented with introduced tree species, and one of the most successful has been Sitka spruce, a North American conifer that grows well across much of the country.9Icelandic Agricultural Sciences. Individual-tree growth models for Sitka spruce (Picea sitchensis) in Iceland Other species planted include Siberian larch, lodgepole pine, and various other spruce and pine species. These trees often grow faster than native birch, which makes them attractive for commercial forestry and carbon sequestration goals.
The use of exotic species is not without controversy. Native birch woodland supports a suite of Icelandic plant and invertebrate species adapted to it, while dense spruce plantations create a very different habitat. The ecological trade-offs become especially sharp when you look at birdlife. Ground-nesting wader species, which are an important part of Iceland’s biodiversity, are sensitive to the presence of tree plantations even when the plantations are small. A study found that densities of five out of seven wader species in the area surrounding forest plantations were roughly half those found farther away.10Journal of Applied Ecology. Subarctic afforestation: Effects of forest plantations on ground‐nesting birds in lowland Iceland The pattern held regardless of plantation height or type. One species, the snipe, actually showed higher densities near plantation edges, but it was the exception.
The spatial layout of planting matters too. Simulations in the same study suggested that concentrating tree planting into one large block rather than scattering it across many small blocks in similar habitat could reduce the total impact on bird populations by roughly 90 percent. This kind of finding has practical implications for how Iceland plans its forestry: planting strategy, not just total area planted, determines the ecological cost.
Carbon in the Soil
One of the more compelling arguments for reforestation in Iceland is carbon sequestration, but the story is more complicated than simply “plant trees, store carbon.” Iceland’s degraded volcanic soils have lost enormous amounts of organic carbon since deforestation, and restoring birch woodland can begin to rebuild those stocks. After 50 years of birch growth on severely degraded soils, soil organic carbon was significantly higher than in the degraded state but still lower than in naturally established birch woodland, suggesting the sequestration process takes well beyond 50 years to complete.11SOIL. Evaluating the carbon sequestration potential of volcanic soils in southern Iceland after birch afforestation
There is also a wrinkle in how the carbon is stored. In the first decades after planting, the new carbon entering the soil accumulates primarily in labile pools, meaning it is in forms that decompose relatively easily. Whether that plant-derived carbon will eventually stabilize in mineral-associated forms or partly return to the atmosphere during the transition remains an open question.11SOIL. Evaluating the carbon sequestration potential of volcanic soils in southern Iceland after birch afforestation A more recent study found that soil carbon accumulation rates in regenerating birch woodlands were modest in the first 30 years but accelerated substantially as the woodland matured. If applied to large-scale birch restoration plans, those rates could offset roughly 20 percent of Iceland’s total CO₂ emissions.12PubMed. Soil carbon stocks of regenerating Icelandic native birch woodlands: Effects of space and time That is a meaningful number for a small country, though it depends on restoration happening at a scale that has not yet been achieved.
Climate Change and the Future Treeline
Warming temperatures are already changing conditions for trees in Iceland. Pollen analysis spanning the Holocene shows that periods of warmer climate in Iceland’s past corresponded with expanded birch woodland and increased hybridization between downy birch and dwarf birch. A new wave of birch hybridization appears to have started in recent decades as temperatures have risen, and researchers expect birch woodlands to become more widespread as warming continues.13PubMed. Microscopical palynology: Birch woodland expansion and species hybridisation coincide with periods of climate warming during the Holocene epoch in Iceland
A warmer climate could push the potential treeline higher in elevation and farther into Iceland’s interior, theoretically opening up large areas to woodland that currently cannot support trees. But climate alone is not the limiting factor right now. Sheep grazing, soil degradation, and the slow pace of natural dispersal all constrain how quickly trees can take advantage of warmer conditions. If grazing pressure is not reduced in parallel, warmer temperatures alone will not bring forests back. The seedlings will simply be eaten in a slightly warmer climate.
There is also a tension between Iceland’s treeless landscapes and the country’s conservation priorities. Iceland’s open heathlands and wetlands are internationally important for breeding wader populations. Bringing back forests, whether through natural regeneration or planting, inevitably changes the habitat. The question facing Icelandic land managers is not simply “how do we get the trees back?” but “where do we want trees, and where do we want open habitat?” Strategic planning that accounts for both carbon goals and bird conservation is becoming a central part of the conversation, especially as the pace of afforestation picks up.
Why Recovery Is So Slow Even Where It Is Happening
Even under the best conditions, reforestation in Iceland is a slow process compared to tree planting in temperate climates. The short growing season means birch puts on modest height each year. Natural seed dispersal is limited by wind patterns and the distances between surviving forest patches. And the degraded soils in the most eroded areas cannot support vigorous tree growth without decades of organic matter accumulation first. The 50-year afforestation sites studied in southern Iceland still had not caught up to the soil carbon levels of naturally established woodlands, which gives some indication of the timescale involved.11SOIL. Evaluating the carbon sequestration potential of volcanic soils in southern Iceland after birch afforestation
Iceland’s volcanic activity adds yet another variable. Eruptions periodically deposit tephra, or volcanic ash, across the landscape, which can bury vegetation and set back recovery. While a single tephra fall does not necessarily kill established woodland, it can smother seedlings and alter soil chemistry in ways that slow regeneration. Over the long sweep of Icelandic history, periodic volcanic disturbances have been one more factor resetting the ecological clock.
The interplay of all these forces is what makes Iceland’s treelessness so persistent. It is not one problem with one solution. It is a system of interlocking constraints, each of which makes the others harder to address. Remove the sheep, and trees come back, but slowly on eroded soil. Fix the soil, and trees grow better, but sheep still eat them. Warm the climate, and the potential range for trees expands, but the soil and the sheep are still there. Iceland’s landscape is a case study in how quickly a subarctic ecosystem can be degraded by human activity and how stubbornly it resists repair, even when the original cause of the damage is understood.