As the world warms, higher latitude climates are changing faster than anywhere else - and plant distributions are changing with them. The forests of Tierra del Fuego represent a global treeline, a point where woody plant distribution should be changing in the most visible way. Here, we describe the worlds southernmost forests on Isla Hornos, Chile, a forest never before described quantitatively. Plots were installed within and spanning the edge of the world's southern treeline. To explore expansion or contraction associated with climate change, we measured multiple variables: Remote sensing/GIS measurements to plot the extent and location of forest, dendroecological data from cores taken from all mature individuals surveyed, plant community composition, and soil C and N concentrations. The purpose is to test the hypothesis that southern treeline is limited by temperature and expanding due to climate change.
Results/Conclusions
Southern treeline does not appear to be temperature or substrate limited but rather limited by wind and competition. The forests are embedded in a thick combination of grasses and woody shrubs with a mean height of 50cm, which likely constrains seedling establishment. Where topography provides shelter from the wind, the forest (density averaging ~1600 trees/ha) averages ~4 meters height with an open understory of bryophytes. The trees are generally old (>100 years), with little evidence of recent establishment. In contrast, the edges of the forest indicate a period of recent dieback. Together with the biogeochemical results, this suggests treeline is undergoing a series of expansions and contractions over decadal time periods (for causes unknown) rather than directional movement south. Thus constraints imposed by wind and potentially substrate competition appear to be limiting migration in the world's southernmost forests.