In the alpine zone – above the treeline, where the wind never stops and the snow lies deep – mosses are the giants. They are the only plants that can survive the cold, the wind, the thin soil. And there was once an alpine moss that grew taller than any alive today – a moss whose stems rose 20 centimetres from the rocks, forming a dense, spongy carpet that held the mountain together. It was the giant alpine moss, and it is gone. Height and cold tolerance made it special. A 20-centimetre moss in the alpine zone is a forest – a dense stand of upright stems, each one a tiny tower, packed together so tightly that the stones beneath were hidden. It was a living blanket, insulating the soil, holding moisture, providing habitat for the tiny creatures of the mountain. It built the alpine soil. In the harsh alpine environment, soil is precious – a thin layer of organic matter over rock, easily eroded. The giant alpine moss captured wind-blown dust, held water from melting snow, and added its own decaying leaves to the ground. It was the engineer of the alpine zone, the plant that made it possible for other plants to grow. Its dense mats provided shelter for alpine insects, mites, and springtails. Its leaves held moisture through the dry winter, releasing it slowly in spring. It was the heart of the alpine ecosystem. Mosses reproduce by spores, released from capsules on slender stalks. The giant alpine moss produced spores in large quantities, but its growth was slow – a few millimetres per year. A 20-centimetre moss might be a century old. That strategy works when the mountain is stable. It fails when the grazers arrive and the climate warms. Introduced grazers and climate warming destroyed it. European settlers introduced goats, chamois, and thar to the mountains. These animals love alpine plants. They ate the moss, trampled the mats, tore up the soil. A slow-growing moss that takes a century to reach full size cannot survive annual grazing. At the same time, the climate warmed. The alpine zone began to shrink. The giant alpine moss, adapted to extreme cold, could not survive in the milder conditions that crept up the mountain. Its range contracted, then disappeared. By the 1910s, it was gone. The last patches were probably eaten by a goat or withered in a warmer spring. No one knew they were the last. The smaller alpine mosses survived. They are lower-growing, tougher, more adaptable. They are the survivors, the ones that kept their heads down, the mosses of the cracks and crevices. But the giant alpine moss is extinct. A few pressed specimens in a herbarium, a few spores in a core sample, and the memory of a moss that used to carpet the alpine slopes, 20 centimetres tall, dense and green. We brought the grazers. We warmed its world. Then we wondered why the mountain felt so bare.