Tropical treelines are critical zonesfor observing and understanding regional responses to climatic change(Diaz et al. 2003), especially because the low latitudes play a prominentrole in the global climate system(Hoerling and Kumar 2003), and mountain areas regulate downstream availability of water resources (Brad-ley et al. 2004). In North America,tropical treelines are also part of theNorth American Monsoon System(NAMS); this system?s control over summer precipitation, thunderstorm activity, and lightning patterns in the southwestern US extends to other regions via atmospheric connections(Vera et al. 2006; Dominguez et al.2009). Few weather stations with uninterrupted data series exist above 3000 m in rural areas throughout the entire American Cordillera, fromAlaska to Tierra del Fuego (Bradleyet al. 2004), making it difficult to test hypotheses, calibrate models, and detect landscape feedbacks to human activities.