At high elevation or latitude, the margin of life-form tree is set by low temperature, with trees defined as upright woody species taller than 2–3 m. Globally, temperature limit occurs whenever growing season mean soil declines to 6.7 ± 0.8 °C. Disturbance and human land use, however, can cause be absent from climatic treeline. After addressing definitions concepts related treeline ecophysiolog...