Carbon budgets in deciduous and evergreen treeline species

The growth limitation hypothesis proposes that treelines form because carbon sinks are more restricted by low temperatures than by carbon sources, but most supporting evidence comes from evergreen species. Fajardo et al. examine tree growth and concentrations of non-structural carbohydrates (NSCs) at four elevations in six deciduous–evergreen mixed-species forests in the southern Andes and the Swiss Alps, and find that both foliar types are sink-limited when faced with decreasing temperatures. Despite the deciduous tree species having significantly higher NSCs than evergreens, no indication is found of carbon limitation in deciduous species in the alpine treeline ecotone.