Causes of tree line stability: stem growth, recruitment and mortality rates over 15 years at New Zealand <i>Nothofagus</i> tree lines

Abstract Aim Abrupt tree lines are relatively rare world‐wide and are poorly understood. We studied demographic processes at abrupt tree lines to better understand the factors governing their dynamics. Location Five Nothofagus ‐dominated tree line sites across the South Island, New Zealand. Methods All Nothofagus stems at or above the tree line were tagged and their spatial locations and heights recorded on three occasions over 15 years at each site. We estimated rates of stem height growth, recruitment and mortality, and used these data to develop a demographic model to project stem numbers into the future. Results Stem numbers had increased above the tree line at most sites over the last 15 years, but with little evidence of tree line…