Peatlands and Climate Change

Abstract

The fundamental reason for the presence of peatlands is a positive balance between plant production and decomposition. Organic matter accumulates in these systems because prolonged waterlogged conditions result in soil anoxia (i.e., exclusion of oxygen), and under these conditions decomposition rates can be lower than those of primary production. Climate therefore plays an important role in peat accumulation, both directly by affecting productivity and decomposition processes, and indirectly through its effects on hydrology/water balance and vegetation (for a summary, refer to Yu, Beilman & Jones 2009). Climate provides broad-scale constraints or controls on peatland extent, types and vegetation, and ultimately, ecosystem functioning, carbon accumulation, greenhouse gas exchange and all of the other ecosystem services that peatlands provide. Peatlands can play a vital role in helping society mitigate and adapt to climate change, because of their carbon and water regulating functions, while at the same time, the climate sensitivity of peatlands makes them potentially vulnerable to future global warming and changes in spatial and temporal patterns of precipitation, especially if they are in a degraded state. Climate change is likely to alter the hydrology and soil temperature of peatlands, with far- reaching consequences for their biodiversity, ecology and biogeochemistry. Their involvement in the global carbon cycle will also be affected, with the possibility of drier conditions allowing peatland erosion and increases in CO2 emissions that would result in a positive feedback to climate change (Turetsky 2010). This highlights all the more the need for restoration to ensure peatlands are resilient to change so that they continue to deliver ecosystem services for human well-being. This chapter describes the interactions between climate and peatlands, in three sections. The first section explains how present climate influences peatlands, by documenting how climate limits peatland geographical extent globally, and how bioclimatic envelope models can predict peatland extent. We indicate how each type of peatland is linked to a specific climate range, and introduce the concept of ecosystem function in relation to climate. The second section looks into the past. It describes how peat preserves a record of past climates and environmental conditions that can be deciphered to reveal the history of peatland vegetation, hydrology and carbon accumulation changes in relation to past changes in climate. We highlight lessons that can be learned from the palaeorecord preserved in peat. The final section discusses the potential effects of present and future climate change on peatlands, their extent, carbon accumulation rates, fire frequency, water table and greenhouse gas exchanges. We also consider how increases in sea level and CO2 concentration, and decreases in the extent of permafrost, are likely to affect peatlands.