Tropical treelines are critical zones for observing and understanding regional responses to climatic change(Diaz et al. 2003), especially because the low latitudes play a prominent role in the global climate system(Hoerling and Kumar 2003), andmountain areas regulate downstream availability of water resources (Brad-ley et al. 2004). In North America, tropical treelines are also part of the North 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 theentire American Cordillera, from Alaska to Tierra del Fuego (Bradleyet al. 2004), making it difficult to testhypotheses, calibrate models, and detect landscape feedbacks to human activities.