Future warming could cause trees to dominate peat bogs

Peat bogs cover 3% of the earth’s surface but contain 30% of global terrestrial carbon stores. Rising temperatures could have drastic effects on how these bogs are structured and how they contain carbon – or don’t. The spectre of drying peat bogs raises concerns about the amount of stored carbon this could release into our atmosphere.

Summer droughts allow trees to establish a firmer hold in peat bogs that are predominantly moss-covered (those found in the Northern hemisphere), but do not fundamentally alter the structure of the bog. A climate warming of 1°C, however, sees trees replacing grasses, though not moss, and a rise of 1.5°C sees a ‘tip’ in the structure of the bog, from moss-covered to tree-covered, particularly under prolonged drought conditions (more than nine dry summers). Lower water tables and higher temperatures encourage tree growth and discourage moss growth: rising temperatures kick off a vicious cycle of increasingly more trees and lower water tables, and a corresponding continual drop in moss growth. During shorter droughts, there is more hope for the moss: shade from the trees prevents evaporation and lets moss take advantage of wetter summers.