Why Alpine Plants Are Ice Age Survivors: Warming and Deer Grazing Threaten Japan's Flower Meadows

What Are Alpine Plants—Living Fossils That Survived the Ice Age

When people hear "alpine plants," many picture delicate flowers like Komakusa or Chingoruma. But behind that delicacy lies a vast history: a global cooling that began roughly 2 million years ago, followed by repeated glacial and interglacial cycles. During the Pleistocene, Earth swung repeatedly between cold glacial periods and relatively warm interglacials, and each time, plant distributions shifted dramatically north and south, and between lowlands and highlands.

A 2-Million-Year Journey—Through Glacial and Interglacial Periods

During glacial periods, cold-adapted plants now found only in Hokkaido or high-latitude regions to the north are thought to have spread across a much wider area of the Japanese archipelago. But as the climate warmed into interglacial periods, these cold-loving plants either retreated north in search of cooler conditions, or chose to survive by moving "vertically" up into the mountains. Plants that could not fully escape the warming and were left stranded on high mountains make up no small part of what we today call "alpine plants."

Why Are They Called "Glacial Relict Species"?

Many of Japan's alpine plants have close relatives in Hokkaido or high-latitude regions further north. This is evidence that these plants were already widespread when the Japanese archipelago was colder, and biologists call such survivors "glacial relict species." Just as Yakushima's vertical zonation recreates climate zones from subtropical to subarctic through elevation alone, the alpine zones of central Honshu's mountains have functioned as "climate islands," locking in fragments of ice-age ecosystems to this day.

The Tiny Fraction of Japan That Is "Alpine Zone"

Generally, the "alpine zone" refers to areas above the tree line—the elevation limit at which forest can grow. In Japan, this is roughly around 2,400–2,500m, though it varies by region; above this, trees thin out and give way to a distinctive landscape of dwarf pine, grassland, and rocky scree. This alpine zone makes up only a tiny fraction of Japan's total land area, meaning ecosystems dating back to the ice age are compressed into a very limited space. That is precisely why even small environmental changes can have an outsized impact on the whole ecosystem.

The Alpine Zone: An Ecosystem With Nowhere Left to Go

For alpine plants, the summit is the last refuge. As temperatures rise, the tree line pushes upward from below, forcing them to climb ever higher to survive. But every mountain eventually has a top, beyond which there is nowhere left to flee. This "dead end" structure is precisely why alpine ecosystems are considered among the most vulnerable in the world to climate change.

Komakusa and Chingoruma—Familiar Examples of Glacial Relicts

Known as the "queen of alpine plants," Komakusa has survived by deliberately rooting in weathered scree slopes—a harsh environment where almost no other plant can grow—thus avoiding competition. It sends long roots deep into the gravel to secure moisture, and its structure withstands strong wind and UV exposure. Chingoruma, which grows in clusters at the edge of snow patches, must complete flowering and fruiting within the short summer right after snowmelt, having evolved its entire life cycle around the timing of snowmelt. These species-specific adaptations also translate into differing degrees of vulnerability to climate change.

Species like Komakusa, dependent on dry scree slopes, lose their habitat the moment surrounding vegetation changes, stabilizes the soil, and becomes covered by taller plants. Species like Chingoruma, dependent on snowmelt timing, see changes in snowpack patterns translate directly into failed flowering and fruiting. In other words, alpine plants each carry different "weak points," and it is too simplistic to say they are uniformly resilient or vulnerable to warming.

Moreover, many alpine plants have drastically slowed their growth rates as an adaptation to harsh conditions. Some species grow only a few millimeters a year, and it is not unusual for a plant to take nearly a decade from germination to first flowering. In other words, once a population is lost, it cannot be expected to recover naturally in a short time. We must approach this not as damage that can be undone in a few years on a human timescale, but as an ecosystem where impacts, once lost, persist for decades or longer.

Features of Japan's Alpine Flora—Relicts at Their Southern Limit

Daisetsuzan, the South Alps, Hakusan—Different Faces on Every Mountain

Alpine plants can be found across a number of mountain regions in Japan, from Daisetsuzan in Hokkaido to the South Alps, North Alps, and Hakusan in central Honshu. Daisetsuzan National Park in particular is known for retaining an environment that has persisted since the ice age, with 365 alpine plant species confirmed there, 27 of which are found nowhere else. "Snow-patch meadows" that bloom where snow lingers late, and "wind-swept grasslands" spread across gusty ridges, combine in a mosaic to create the classic "flower meadow" landscape.

The Phenomenon of "Disjunct Distribution"

Central Honshu's mountains, on the other hand, represent the southern limit of distribution for many alpine plants. Some alpine plants growing in the South Alps, sustained by abundant remaining snow, are isolated hundreds of kilometers from populations of the same or closely related species to the north. This "disjunct distribution" resulted from once-continuous ranges being severed by interglacial warming, and it has allowed each mountaintop to develop its own distinct genetic character.

Isolated populations are thought to have evolved unique traits specific to each mountain over long periods. Even within the same species, populations in the South Alps and Hokkaido can show slight differences in leaf shape, flower size, and cold tolerance. These mountain-by-mountain differences are a valuable asset that raises the overall diversity of the species; losing the population on a single mountain range means more than a simple drop in numbers—it means losing the evolutionary history that mountain has nurtured.

The Fate of Southern-Limit Populations—Poor Genetic Diversity

Populations at the southern edge of a range tend to have low, isolated numbers, making them prone to poor genetic diversity. This factor is intertwined with the sika deer grazing damage discussed below, forming the underlying reason for the vulnerability faced by alpine plants in the South Alps.

The Plants That Make Up the Flower Meadows

Plants that color Japan's flower meadows include Hakusan-ichige, which bursts into white bloom right after snowmelt, the yellow-flowered Miyama-kinbai, scree-dwelling Komakusa, and Chingoruma along the edges of snow patches. Each species prefers a different environment—scree, snow patch, or grassland—and this slight difference in required conditions is what allows them to coexist within the narrow alpine zone. Because this ecosystem rests on such a delicate division of habitat, even small changes in temperature or snowpack pattern can wipe out individual species and trigger a chain reaction that destabilizes the entire plant community.

Growing Concern in the North Alps and Hakusan Too

Sika deer grazing damage was once seen as a problem unique to the South Alps, but in recent years sightings and feeding traces have also been reported around the North Alps and Hakusan. Japan's Ministry of the Environment and the Forestry Agency are now jointly examining deer countermeasures for the North Alps as well, meaning alpine plants in mountain ranges once thought safe from grazing can no longer be considered secure. The risk is gradually spreading to Japan's alpine zones as a whole, not just at the southern edge of distribution.

Warming Brings "Extinction With Nowhere to Flee"

Rising Temperatures and Upward Distribution Shifts

According to findings compiled by Japan's Climate Change Adaptation Information Platform (A-PLAT), alpine ecosystems are considered exceptionally vulnerable to rising temperatures precisely because they have "nowhere to flee." Indeed, shrubs and dwarf bamboo such as Siberian dwarf pine and Chishima-zasa have already been observed expanding into alpine zones in multiple mountain regions, shrinking the area of snow-patch meadows.

Daisetsuzan Climate Impact Projections (NIES, FY2022)

In FY2022, Japan's National Institute for Environmental Studies published research projecting the future of alpine vegetation and subalpine forest vegetation in Daisetsuzan National Park. The study modeled how suitable habitat would change under different climate scenarios for both the alpine vegetation that forms "flower meadows"—snow-patch meadows and wind-swept grasslands—and the subalpine forest vegetation below it.

Diverging Futures Under RCP2.6 and RCP8.5

The projections show that under "RCP8.5," a scenario in which greenhouse gas emissions continue at the current pace, suitable habitat for Daisetsuzan's alpine vegetation will nearly vanish by 2100, with subalpine forest replacing it all the way up to near the summits. Under "RCP2.6," a scenario closer to the emissions cuts targeted by the Paris Agreement, suitable habitat for alpine vegetation still declines substantially but is projected to partially persist—showing that the degree of emissions reduction makes a dramatic difference to the outcome.

The study's projections for 2050 are also worth noting. Even without waiting until 2100, suitable habitat for alpine vegetation is expected to shrink substantially by the middle of this century—meaning the flower meadows we see on mountains today could look dramatically different within a matter of decades, not in some distant future. This is not a story of impacts "someday, far away," but a scale of change projected to materialize within the lifetimes of people alive today—and that is what makes this research so significant.

The impact of global warming on natural ecosystems is considered most pronounced and severe in alpine and polar ecosystems.

— Takashi Kudo (Faculty of Environmental Earth Science, Hokkaido University), "Alpine Plants and Climate Change"

What "Being Replaced" Really Means

Alpine vegetation being "replaced" by subalpine forest doesn't simply mean more greenery. As trees like Siberian dwarf pine and Erman's birch grow taller and cast shade, alpine plants that need light lose their habitat. Furthermore, for plants specifically adapted to snow-patch or wind-swept meadows, a forest environment itself becomes unsuitable for growth. Even if the landscape looks lush and green, many of the glacial relict species that once lived there will have lost their place and disappeared.

What Monitoring Sites 1000 Has Captured

Earlier Flowering Times

Japan's Ministry of the Environment's Biodiversity Center has run the "Monitoring Sites 1000" alpine zone survey since the 1990s, conducting long-term observations of the relationship between ground surface temperature and flowering time for plant species growing in both snow patches and wind-swept sites. The results confirmed that, for many of the species studied, flowering tends to occur earlier in years with higher ground surface temperatures. Even within the same mountain area, plants growing in snow patches where snow melts later flower later than those in wind-swept sites, and in years when snowmelt is delayed, flowering is delayed by a corresponding amount—revealing a tight relationship between snowpack and flowering timing.

The survey analyzed the relationship with ground surface temperature across multiple species growing in both snow patches and wind-swept sites, and found a clear tendency for many species to flower earlier in years with higher ground temperatures. It is also notable that not all species respond the same way—differing sensitivity to temperature among species suggests that the once-synchronized flowering timing of a plant community may no longer stay aligned. If flowering times among co-occurring plants drift apart, competitive relationships and competition for pollinators could shift as well, gradually altering the composition of the community itself.

Rising Summer Temperatures Since 1990

Since this long-term monitoring began in the 1990s, summer temperatures have shown a rising trend. A slight shift in flowering time might seem minor on its own. But it can lead to phenological mismatches with the activity periods of pollinating insects, or to failures in seed production—and if these effects accumulate, they can threaten the very survival of a population.

• Expansion of shrubs and dwarf bamboo such as Siberian dwarf pine and Chishima-zasa into the alpine zone
• Shrinking area of snow-patch meadows
• Earlier flowering and the resulting risk of mismatch with pollinators
• Continued rise in summer temperatures since 1990

What 20-Plus Years of Continuous Monitoring Reveals

Changes in alpine plants are hard to notice from just one or two years of observation. Some years have earlier snowmelt, others later, and a single year's data alone cannot distinguish "chance" from "trend." It is precisely because Monitoring Sites 1000 has accumulated records at the same locations using the same methods for over 20 years that researchers could identify a statistically supported trend of rising temperatures and earlier flowering. Patient, ongoing fixed-point observation is the only way to scientifically capture change in alpine ecosystems.

Sika Deer Grazing—An Added Threat on the Ground in the South Alps

Why Deer Started Heading for the Alpine Zone

In the South Alps, sika deer began appearing near mountain ridgelines around 1998, and their numbers have increased since then. This is attributed to factors such as declining snowpack and an expanding deer range driven by population growth at lower elevations, and deer have come to graze on the alpine zone's rare plant communities as well.

Flower Meadows Vanish, and Some Populations Lose 90% of Genetic Diversity

Deer tend to favor flowers and tender leaves, and when these are consumed before flowering or fruiting, that year's seed production is lost entirely. If this repeats year after year, a population cannot store up seeds for generational turnover even if its roots survive, and it gradually declines. The visible decline in flowers is, behind the scenes, the result of many years' worth of lost reproductive opportunities.

Deer grazing has left parts of the South Alps' "flower meadows" as bare ground, causing the secondary problem of soil erosion. Even more serious is the less visible genetic toll. Much like warming-driven shifts in species distribution, South Alps alpine plant populations—already small due to being at the southern limit of their range—have seen their numbers further reduced by deer grazing, and some research shows they have lost about 90% of their genetic diversity compared to high-latitude populations. Poor genetic diversity weakens a population's ability to adapt to new environmental stresses such as disease or climate change.

Deer Fencing and Population Management as Countermeasures

In response, Japan's Ministry of the Environment established the "South Alps Alpine Plant Conservation Liaison Council," bringing together relevant government agencies, in 2009, and formulated a policy for countermeasures. On the ground, three types of deer-proof fencing—year-round, summer-only, and low fences—are used to protect flower meadows, alongside population management through deer culling, fixed-point monitoring surveys, and measures to prevent soil erosion from bare ground.

1. Grasping the extent of grazing damage through monitoring surveys
2. Installing deer-proof fencing (year-round, summer-only, and low-fence types)
3. Managing deer populations through culling
4. Preventing soil erosion in areas that have become bare ground

Behind deer advancing into the South Alps' alpine zone lie multiple intertwined factors: declining snowpack, deer densities remaining high because population management in lower-elevation forests hasn't kept pace, and reduced hunting pressure due to an aging and shrinking population of hunters. Because this is not a single-cause problem but one arising from the overlap of climate, land use, and changes in hunting culture, no single countermeasure alone is likely to be fully effective.

Inside vs. Outside the Fence—Visible Results of Conservation

Where deer-proof fencing has been installed, a striking contrast can be seen: flower meadows recovering inside the fence, while soil continues to erode on bare ground outside it. This is clear proof that countermeasures work, but the very fact that alpine plants cannot survive without an artificial enclosure also speaks to the severity of the situation. Maintaining these fences requires ongoing labor and cost, and given the difficult conditions of mountainous terrain, building a system that can sustain these measures over the long term remains a key challenge.

The Invisible Risk of Genetic Diversity

Why Southern-Limit Populations Are More Vulnerable

Populations with fewer individuals and greater isolation tend to lose genetic diversity more easily. Alpine plant populations at the southern limit of their range, like those in the South Alps, already have low numbers and rarely exchange pollen or seeds (gene flow) with other populations. When deer grazing and shrinking habitat from climate change are layered on top of this, population decline and loss of genetic diversity can reinforce each other in a vicious cycle.

Extinction Risk That Can't Be Measured by Numbers Alone

Research published by Hokkaido University in 2025 found that plant species that have recently been declining in Daisetsuzan's flower meadows share common features in the morphology of their underground parts (roots and rhizomes). This finding suggests that even when the number of individuals visible above ground appears stable, differences in underground traits affect resilience to environmental change—offering a way to identify high-risk species in advance. Rather than tracking population numbers alone, evaluating genetic diversity and physiological traits is becoming an essential perspective for future conservation.

To assess genetic diversity, researchers often compare small variations occurring in specific regions of DNA (molecular markers) across populations. Even within the same species, the type and amount of variation held by each population differs, and the greater that difference, the more "robust" a population is considered to be. The poor genetic diversity found in South Alps alpine plant populations only came to light through this kind of molecular-level analysis—a type of risk that could never be noticed by simply observing the number of blooming flowers.

Why Visible Population Counts Alone Aren't Reassuring

Even if many flowers bloom in a given year, that doesn't necessarily mean the population is healthy. A population with low genetic diversity may maintain its numbers temporarily, but faces the risk of being hit hard all at once when confronted with a new environmental stress such as a disease outbreak or a sudden climate shift. Populations with more diverse genotypes are more likely to have at least some individuals survive, which in turn raises the species' overall resilience. When thinking about alpine plant conservation, it's important to look not just at "how many are blooming right now," but also at the invisible metric of "how genetically diverse that population is."

The Same Phenomenon Is Advancing in Mountains Worldwide

"Squeezed Toward the Summit" Reported in the Alps and Rockies Too

The vulnerability of alpine ecosystems with nowhere to flee is not unique to Japan. IPCC reports have repeatedly pointed out that mountain ecosystems are among those affected earliest and most severely by climate change. In the European Alps and the North American Rockies too, alpine plant distributions have been reported shifting upward, with suitable habitat near summits shrinking—showing that the phenomena seen in Japan's Daisetsuzan and South Alps are part of a structural problem common to mountains worldwide.

What "Climate Islands" Tell Us

Alpine plants are living records that survived the climate change of the past ice age, and at the same time, they are indicator species that are among the first to reflect the ongoing impact of present-day climate change. Tracking how their distribution changes offers an important clue for thinking about how we should confront the climate change ahead of us.

A phenomenon reported commonly across mountains worldwide is plant species being "pushed upward" from lower to higher elevations, and some researchers liken mountain ecosystems to a natural instrument for measuring the impact of climate change. The fact that the same structural crisis is unfolding across borders and languages shows that alpine plant conservation is not an issue any single country or region can resolve alone—it cannot be separated from global climate action.

Mountain regions are also reservoirs of freshwater in the form of glaciers and snowpack, so changes in alpine ecosystems are not limited to plants and animals alone. As discussed in our piece on how snowmelt supports agricultural water supplies, mountain snow and ice are closely tied to livelihoods and industry downstream, and the changes now underway in the alpine zone could affect a much broader range of the foundations of daily life than we might assume.

What We Can Do to Protect Alpine Plants

Small Actions Hikers Can Take

Conserving alpine plants isn't only the job of government agencies and researchers. There is much that individual hikers can do. Staying on trails and not stepping into vegetation, cleaning mud off boot soles to avoid carrying in the seeds of non-native plants, and never picking or taking home alpine plants are basic yet highly effective conservation actions.

Mountain huts, trailhead notice boards, and municipal nature conservation centers often provide panels and materials introducing the alpine plants and conservation efforts specific to that mountain area. Simply reading through this information before a hike can help you recognize whether the flower in front of you is a species that survived the ice age, or a rare species vulnerable to poaching—knowledge that can change behavior. Knowing itself is the first act of conservation.

Participating in Citizen Science and Monitoring

Citizen science initiatives, in which the public records flowering and growth conditions to support research, are spreading across the country, including through the Ministry of the Environment's "Monitoring Sites 1000." Even a photo of a flower taken during a hike can become part of the data used to capture long-term change.

The Link to Climate Action

Ultimately, the single biggest factor determining the fate of alpine plants is global climate change. As the Daisetsuzan projections show, whether greenhouse gas emissions are cut will make a huge difference in whether alpine flower meadows "partially survive" or "nearly disappear." The energy choices and consumption habits of our daily lives are connected to alpine ecosystems far away.

There are also ways to financially support on-the-ground activities such as installing deer fencing and conducting monitoring surveys, through donations or crowdfunding organized by mountain huts, municipalities, and research institutions. Even without the chance to visit the mountains yourself, there are multiple ways to help support the survival of plants that have endured since the ice age.

The situation surrounding alpine plants—facing the simultaneous threats of warming and deer grazing damage—is by no means something to be optimistic about. Even so, the flower meadows recovering inside deer fences, and the data steadily accumulated through patient fixed-point observation, show that there is still room to change the outcome depending on the countermeasures taken. Whether the story of these plants, which have survived for 2 million years, can continue depends on the choices we make over the coming decades.

• Stay on trails and avoid trampling vegetation
• Clean mud off boot soles to avoid introducing non-native seeds
• Never pick or take alpine plants home
• Participate in citizen science projects such as Monitoring Sites 1000
• Keep climate action in mind in daily life