Central Chile is a narrow strip of land wedged between the Andes and the Pacific Ocean, stretching roughly from 30°S to 36°S latitude. It holds one of only five Mediterranean-type climates on the planet, with wet winters, bone-dry summers, and an unusual concentration of species found nowhere else on Earth. That combination of rarity and vulnerability has earned the region recognition as a global biodiversity hotspot, but it also means the landscape is under extraordinary pressure from drought, wildfire, invasive species, and centuries of land-use change.
A Mediterranean Climate in an Unlikely Place
When most people think of Mediterranean climates, they picture southern Europe, maybe coastal California. Central Chile’s version is the only one in South America, and it is geographically compact. The Mediterranean-type environment here occupies a band roughly 1,000 kilometers long on the western side of the Andes, defined by its pattern of winter rainfall and summer drought.1ResearchGate. The Physical Geography of South America The Pacific Ocean and the cold Humboldt Current running along the coast shape the region’s weather in ways that create microclimates packed tightly together. Move a few dozen kilometers inland and you shift from cool coastal fog to hot, dry interior valleys.
The fog itself plays a surprisingly important ecological role. Along the coast, the region’s prominent topography intercepts a persistent deck of marine stratocumulus clouds that sits over the southeast Pacific. At places like Fray Jorge Biosphere Reserve, around 30°S, fog frequency follows a seasonal rhythm: it drops during winter and peaks in spring, aligning with the growing season for the reserve’s trees.2Journal of Geophysical Research: Biogeosciences. Interannual variability of the coastal fog at Fray Jorge relict forests in semiarid Chile These fog-dependent forests are ecological relicts, patches of lush evergreen vegetation that survive in an otherwise semiarid landscape thanks almost entirely to moisture wrung out of passing clouds.
The climate was not always like this. Pollen records from Laguna de Tagua Tagua show that during the late Pleistocene, cooler and more humid conditions prevailed, with southern beech and podocarp forests extending into latitudes that are now dominated by dry-adapted scrub. The modern Mediterranean pattern, with its sclerophyll vegetation adapted to seasonal drought, developed during the Holocene.3PubMed. Quaternary pollen record from Laguna de Tagua Tagua, Chile Pollen records from Lake Laja further south document fluctuations over the last 2,800 years, with a drier period between roughly 1561 and 1894 AD that lines up with the tail end of the Little Ice Age in Europe, followed by clear evidence of human impact on vegetation in the twentieth century.4Review of Palaeobotany and Palynology. Vegetational and climatic history during the late Holocene in Lake Laja basin (central Chile) inferred from sedimentary pollen record
Built on a Subduction Zone
Central Chile sits directly above one of the most seismically active boundaries on the planet, where the Nazca Plate dives beneath the South American Plate. The geometry of that collision varies along the coast in ways that matter for everything from earthquake behavior to mountain building. Between about 26°S and 33°S, the descending slab flattens out at intermediate depths, probably because a buoyant underwater ridge (the Juan Fernández Ridge) is being dragged into the trench. South of roughly 33°S, the slab steepens to a constant angle of about 27 degrees, creating a sharp change in the subduction geometry that influences where and how earthquakes happen.5Journal of South American Earth Sciences. Seismotectonic and stress distribution in the central Chile subduction zone
The Andes themselves owe much of their height in this region to relatively recent uplift. Geological evidence from relict peneplains, essentially ancient flat surfaces now stranded at high elevations, shows that portions of the mountains rose more than two kilometers in a geologically brief span of about two million years. The eastern Coastal Cordillera at 33–34°S was pushed up somewhere between 1.5 and 2.1 kilometers, while parts of the Principal Cordillera exceeded 2.5 kilometers of uplift. Erosion responded dramatically, with sharp knickpoints in river profiles retreating upstream as the landscape adjusted.6Tectonics. Late Miocene high and rapid surface uplift and its erosional response in the Andes of central Chile (33°–35°S) This rapid uplift, beginning somewhere around four to ten million years ago, created the steep topographic gradients that define the region today: a compressed transition from ocean to towering peaks in barely 200 kilometers.
A Biodiversity Hotspot Under Siege
Central Chile qualifies as a biodiversity hotspot because it harbors an unusually high number of endemic species alongside intense human pressure.7Regional Environmental Change. Consequences of land-use change and the wildfire disaster of 2017 for the central Chilean biodiversity hotspot The native vegetation is dominated by sclerophyllous forest and matorral, communities of tough-leaved, drought-resistant shrubs and trees adapted to the long dry summers. Species like boldo (Peumus boldus) and arrayán (Luma apiculata) are characteristic of these forests, though they respond quite differently to shade and water stress. Under experimental conditions, height growth in response to shade ranged from essentially zero in boldo to a tripling in arrayán, yet all species showed similar physiological adjustments to drought, suggesting a shared strategy for coping with the region’s dry summers.8PubMed Central. Early Growth and Physiological Acclimation to Shade and Water Restriction of Seven Sclerophyllous Species of the Mediterranean Forests of Central Chile
One iconic resident of these forests is the Chilean wine palm (Jubaea chilensis), the world’s southernmost palm species and one that produces the largest seed of any palm. It is also in deep trouble. A field experiment tracking 300 seedlings over 18 months found that only 14 percent survived. The primary killer was not drought but vertebrate herbivores, mostly rabbits and hares introduced from Europe. Unfenced seedlings had virtually zero survival regardless of whether they grew in the open or beneath shrub canopy, meaning that the shrubs native vegetation typically provides as nurse plants offered no protection against browsers.9PLOS ONE. Recruitment Dynamics of the Relict Palm, Jubaea chilensis: Intricate and Pervasive Effects of Invasive Herbivores and Nurse Shrubs in Central Chile Without active control of invasive herbivores, the palm cannot regenerate, no matter how many seeds it drops.
Birds That Hold the Ecosystem Together
Central Chile’s ecosystems depend on ecological interactions that are easy to overlook. Seed dispersal by birds turns out to be critical for shrubland regeneration. Research on five native shrub species found that passage through a bird’s gut boosted germination in four of them, primarily by stripping away the fruit pulp that otherwise inhibits sprouting. The implication is sobering: if bird populations decline due to habitat loss, the shrublands may lose their ability to recover from disturbance, because seeds that are not dispersed and processed by birds germinate poorly.10Plant Ecology. Avian gut-passage effects on seed germination of shrubland species in Mediterranean central Chile
Two bird species illustrate these tight ecological links especially well. The green-backed firecrown (Sephanoides sephaniodes), a hummingbird, pollinates a pair of sympatric mistletoe species (Tristerix aphyllus and T. verticillatus), while the Chilean mockingbird (Mimus thenca) disperses their seeds. Camera trap surveys over two years revealed that these two generalist birds are the primary mutualists for both mistletoe species, with pollination and seed dispersal partitioned in time.11PubMed. Temporal partitioning of pollination and seed dispersal interactions in two sympatric mistletoes Lose one of those bird species and two plant species lose either their pollinator or their disperser, cascading effects that would ripple through the food web.
Water from Ice and Snow
Central Chile is home to Santiago, a metropolitan area of more than seven million people, and the water that sustains it comes overwhelmingly from the high Andes. In the Maipo River basin, the primary water source for Santiago, snowmelt accounts for about 60 percent of total annual runoff, with ice melt adding another 37 percent. On average, glaciers contribute roughly 16 percent of total annual discharge, but during summer months that share can spike to nearly 60 percent.12The Cryosphere. Glacier runoff variations since 1955 in the Maipo River basin, in the semiarid Andes of central Chile
Those numbers take on a different character during drought. Between 2010 and 2018, as central Chile endured its worst multi-year drought in modern records, glacier melt became a critical buffer. Research combining field measurements, satellite data, and climate reanalysis showed that unsustainable ablation of glaciers, meaning ice loss not replaced by new snowfall, strongly propped up late-summer river discharge. Without glaciers, water availability in the Maipo would have dropped by about 31 percent during March.13Earth’s Future. Glacier Contributions to River Discharge During the Current Chilean Megadrought That is water borrowed from the future. Every year the glaciers shrink, the buffer for the next dry spell gets thinner.
Chile’s approach to managing this scarce resource is unusual. Since 1981, the country has operated under a water code that privatized water rights and attempted to stimulate a free market in water trading, an experiment more radical than anything tried elsewhere. The results have been uneven, and the broader lesson is that creating functional water markets turns out to be far more complicated than theory suggests, even in a relatively straightforward setting like irrigation transfers.14Journal of South American Earth Sciences. Bringing water markets down to earth: The political economy of water rights in Chile, 1976–1995 In a region where water supply is increasingly unreliable, the tension between market mechanisms and equitable access is growing sharper.
The Megadrought
Central Chile has been in the grip of what researchers call a megadrought since roughly 2010, the longest and most severe dry spell in the instrumental record. The drought is not simply a matter of less rain. Observations show it results from a persistent atmospheric circulation pattern: a high-pressure ridge sitting over the subtropical Pacific blocks extratropical storms from reaching central Chile, while a low-pressure anomaly over the Amundsen-Bellingshausen Sea reinforces the block. This dipole pattern has been remarkably stable for over a decade.15International Journal of Climatology. The Central Chile Mega Drought (2010–2018): A climate dynamics perspective
The causes are a mix of natural variability and human influence. The Pacific Decadal Oscillation, a long-cycle pattern of ocean temperature variation, explains roughly half of the precipitation decline. But the rest is not easily attributed to natural phenomena. Climate modeling suggests that about a quarter of the rainfall deficit since 2010 is anthropogenic in origin, driven by greenhouse gas increases and stratospheric ozone depletion that together strengthen a climate mode called the Southern Annular Mode, which in turn reinforces the blocking pattern.16Geophysical Research Letters. Anthropogenic and natural contributions to the Southeast Pacific precipitation decline and recent megadrought in central Chile In other words, this is not purely bad luck. Human-caused warming has loaded the dice.
The ecological consequences are already visible. Satellite measurements of vegetation greenness show significant browning in close to a third of the region’s forests, with the worst declines in semiarid sclerophyllous forests, the very communities that are supposed to be adapted to drought.17Ecological Indicators. Forest browning trends in response to drought in a highly threatened mediterranean landscape of South America Tree-ring analysis reveals that growth in sclerophyllous species began declining around 2002 and has worsened since, driven mainly by reduced winter-spring rainfall and increasing water deficit. These trees evolved to tolerate dry spells, but a drought that persists for more than a decade appears to be pushing them beyond their adaptive limits.18Ecosystems. Sclerophyllous Forest Tree Growth Under the Influence of a Historic Megadrought in the Mediterranean Ecoregion of Chile
Wildfire and the Exotic Plantation Problem
Drought and fire feed each other. During the megadrought, the number, total area burned, simultaneity, and duration of large fires in central and south-central Chile all increased significantly compared to the preceding period, and large fires even began occurring in winter, something essentially unheard of before. The sustained rainfall deficit was the most critical factor, more important even than rising temperatures.19Ecosphere. The 2010–2015 Megadrought and its influence on the fire regime in central and south‐central Chile
What burns most, though, is not native forest. The expansion of industrial plantations of radiata pine and eucalyptus has fundamentally reshaped the fire landscape. In the Concepción metropolitan area, exotic plantations cover about 55 percent of the land surface, and the pattern of fire risk follows them faithfully: 100 percent of the areas classified as very high fire hazard fell on plantations, along with about 70 percent of high-hazard areas.20Natural Hazards and Earth System Sciences. Data-based wildfire risk model for Mediterranean ecosystems – case study of the Concepción metropolitan area in central Chile These species are fast-growing and economically valuable, but they are also highly flammable. Their leaf litter is rich in volatile oils, their canopies dry out faster than native sclerophyll, and their uniform structure allows fire to spread rapidly. The catastrophic 2017 fire season, which burned more than half a million hectares across central Chile, hammered this point home.21Regional Environmental Change. Consequences of land-use change and the wildfire disaster of 2017 for the central Chilean biodiversity hotspot
After fire sweeps through, exotic species often regenerate faster than natives, locking the landscape into a cycle where plantations expand at the expense of the native ecosystems that used to occupy those hillsides. For a biodiversity hotspot, this feedback is a serious threat.
Restoration in a Transformed Landscape
Central Chile’s dry forests have undergone profound historical transformation, with considerable deforestation stretching back centuries.22Ecosphere. Identifying suitable multifunctional restoration areas for Forest Landscape Restoration in Central Chile Land clearing for agriculture, livestock grazing, firewood collection, and more recently industrial forestry have all left their marks. Today, intact native forest covers a fraction of its former range, and what remains is fragmented.
Restoration efforts face a set of interlocking obstacles. The megadrought makes it harder for planted native seedlings to establish. Invasive herbivores like European rabbits and hares mow down regenerating palms and shrubs, as the Jubaea experiment demonstrated. Exotic plantations occupy much of the land that might otherwise be restored, and the economic incentives favor keeping them. And the fire cycle preferentially destroys what native vegetation hangs on at the margins.
Researchers have begun mapping where multifunctional restoration could deliver the biggest returns, identifying areas where biodiversity recovery, erosion control, water regulation, and carbon storage overlap. The approach acknowledges that restoration in a region this transformed cannot aim to recreate pristine wilderness. Instead, it targets landscapes where restoring native cover delivers multiple benefits at once, a pragmatic framework for a place where ecological and human needs collide in a shrinking water budget and a warming climate.
Fog Forests as Living Laboratories
The fog-sustained relict forests scattered along central Chile’s coast deserve attention as something more than ecological curiosities. Places like Fray Jorge, where patches of Valdivian-type evergreen forest survive hundreds of kilometers north of their main range, function as natural experiments in how plant communities respond to isolation and climate stress. These forests have been cut off from their parent ecosystems for thousands of years, maintained by fog moisture in a region that receives negligible rainfall during the growing season.23Journal of Geophysical Research: Biogeosciences. Interannual variability of the coastal fog at Fray Jorge relict forests in semiarid Chile
Because their survival hinges on the marine stratocumulus deck, these forests are sensitive indicators of large-scale climate shifts. Changes in sea surface temperature, atmospheric stability, or wind patterns that alter cloud cover over the southeast Pacific could starve the forests of their primary water source. In a region already deep into a megadrought, with anthropogenic warming altering atmospheric circulation patterns, the fog forests represent a canary in the coal mine. Their persistence or decline in coming decades will tell us something important about how far the climate has moved beyond what even resilient ecosystems can tolerate.