The Krummholz and the Fury
The Magellanic Subpolar Forests are the planet's southernmost forests, an ecoregion clinging to the tip of South America. Here, violent subpolar winds and cold summers, with an average temperature of around 6°C (43°F), dictate the rules of life. The relentless westerly winds are so powerful they permanently deform the trees, creating a phenomenon known as krummholz, a German term for "crooked wood". Trees like the Lenga beech (Nothofagus pumilio) and Ñire (Nothofagus antarctica) grow horizontally, their branches swept eastward into a "flag tree" formation, as if perpetually pointing away from the wind. This stunted, dense growth is a survival strategy, allowing the trees to persist where vertical growth is impossible.
This ecosystem is a refuge for Antarctic flora, sharing many plant families with the temperate forests of New Zealand and Australia, a legacy of the ancient supercontinent of Gondwana. The dominant trees are three species of southern beech: the evergreen Magellan's beech (Nothofagus betuloides) in the wetter western areas, and the deciduous Lenga and Ñire beeches in the drier east. The forest floor is often a soggy carpet of mosses and peat, adapted to the high rainfall which can reach 4,000 millimeters (157 inches) annually in the west.
An Invasion of Engineers
In 1946, the Argentine government imported 20 North American beavers (Castor canadensis) from Manitoba, Canada, to Tierra del Fuego. The plan was to create a fur trade. The industry never materialized, but the beavers, with no natural predators in the region, flourished. Their population has exploded to over 100,000, transforming the area in what has been called the "largest landscape-level alteration in subantarctic forests since the last ice age."
The southern beech trees of the Nothofagus genus are uniquely vulnerable to the beavers. Unlike their North American counterparts like willows and poplars, they cannot resprout from the stump after being felled. When a beaver cuts down a southern beech, the tree is gone forever. The beavers' primary impact comes from their dams. The flooding creates ponds and meadows that drown the existing forest. The inundated soil kills the trees' root systems and destroys the seed banks within the soil. Studies show that 88% of tree death in affected riparian zones is from drowning. These "phantom forests" of pale, dead trees cover an area estimated to be twice the size of Buenos Aires.