Fungi in treeline ecotones – Halting or causing abrupt ecosystem change?

Abstract

Climate warming is currently expanding the low-temperature-limit for tree survival – the treeline – further into arctic and alpine areas. This may enable the encroachment of trees into previously treeless areas if no other limitations of tree growth prevail. As trees benefit from the activities of both symbiotic and saprotrophic soil fungi, and vice versa, concurrent range expansion of trees and fungi may facilitate forest development, alter ecosystem nutrient and carbon balances and potentially lead to an ecosystem tipping-point with altered climate feedbacks. The roles of fungi in vegetation shifts and subsequent climate feedbacks are poorly characterized. In this minireview, we outline potential roles of soil fungi in tree colonization and carbon balance and discuss the fungal-driven soil processes that may halt, precede or ultimately cause abrupt changes in treeline ecotones.