LocalAdapt is a cooperative research project aimed at studying the local adaptation of an endemic forest species in the Patagonia region of Argentina. Here we study Nothofagus pumilio, commonly known as lenga, which is one of seven endemic Nothofagus species in southern South America and the one with the widest distribution range. N. pumilio grows in the Andes mountain range, which is notable both for its length – at 7,000 kilometers, it is the longest on earth – and for its orientation, running almost perfectly north to south. The Andes also create a pronounced humidity gradient from west to east, with temperate rain forests on the western side and xeric steppe habitats to the east. Over time, N. pumilio has adapted to live in a variety of these local environmental conditions, from high steppe (300 mm of annual precipitation) to humid Valdivian forest (over 3000 mm) and from near sea level at high latitudes up to the timberline at low latitudes. By sampling and analyzing N. pumilio along these pronounced latitudinal, temperature, and humidity gradients, we can begin to elucidate the genetic, phenotypic, and environmental bases of local adaptation of N. pumilio.