The ratio of hardwood to conifer trees in temperate forests is predicted to change under global warming, which could lead to major changes in ecosystem function.
We report historic landscape-scale evidence of this phenomenon: a significant increase over 70 years in the abundance and extent of hardwood trees along a 300 km conifer-hardwood ecotone. These changes were detected through comparison of two independent historical vegetation data sets to contemporary data. Change is found along an elevational ecotone measuring 300 km on the western flank of the Sierra Nevada mountains,
This change in vegetation physiognomy is emperical evidence of projected future climate change effects, captured over recent historic time, on an area of sufficient size to represent a lanscape-level trend. We expect mountain ranges in other arid and semi-arid regions to exhibit similar dynamics.