Plant communities as bioclimate indicators on Isla Navarino, one of the southernmost forested areas of the world

Resumo

Variation in climactic vegetation with altitude is widely used as an ecological indicator to identify bioclimatic belts. Tierra del Fuego is known to undergo structural and functional changes in forests along altitudinal gradients. However there is still little knowledge of the changes in plant-community composition and plant diversity –including both forests and tundra and their area of contact (krummholz)– and their relation to climatic factors along an altitudinal gradient. This study focuses on Isla Navarino (Chile), at the eastern part of Beagle Channel, included in the Cape Horn Biosphere Reserve. Numerical analysis revealed four community types along the cited gradient: a) mixed forest of Nothofagus betuloides and Nothofagus pumilio distributed at lower altitudes (0-300 masl); b) pure forests of Nothofagus pumilio distributed at higher altitudes (350-550 masl); c) krummholz forest of Nothofagus pumilio near the tree line (500-550 masl); and d) pulvinate-cushion vegetation –tundra– of Bolax gummifera and Abrotanella emarginata at altitudes above 600 masl. Species turnover showed that the most abrupt change in plant composition occurs from 550 to 600 masl, producing a drastic landscape change when the high-altitude tree limit formed by dwarf forest of deciduous N. pumilio yields to tundra at a calculated biotemperature of 2.9 ºC. Two other minor changes occur in the understory of pure Nothofagus pumilio forests: a transition from a thermophilous element to a more orophilous element at a calculated biotemperature of 4.3 ºC, and a drop in the number of species as the erect forest changes to low krummholz forest at a calculated biotemperature of 3.3 ºC. The identification of bioclimatic belts based on changes in vegetation and the calculation of biotemperature along the altitudinal gradient suggests that the following plant communities are reliable regional bioclimatic bioindicators: lowermiddle-oroantiboreal mixed forest of Nothofagus betuloides-Nothofagus pumilio; oroantiboreal pure forest of Nothofagus pumilio; hemi oroantarctic krummholz of Nothofagus pumilio; and oroantartic tundra of Bolax gummifera and Abrotanella emarginata.