2 - Peatlands across the globe

Summary

Introduction

More than 80% of the globe's 4 million km² peatland area is still in a largely natural state. In contrast, hardly any mire has survived in regions with a large population pressure. Degraded peatlands, i.e. 0.3% of the global land area, are responsible for a disproportionate 5% of global anthropogenic CO₂ emissions (Joosten 2009c). For such a small area of the globe to generate such substantial emissions suggests that peatlands have some remarkable qualities.

This chapter describes the main characteristics of peatlands, provides an overview of peatland distribution across the globe, presents trends in peatland use, describes peatland degradation and its root causes in various parts of the world, and discusses consequent restoration potentials and necessities.

Peatland characteristics and ecosystem services

Introduction

In most natural ecosystems the production of plant material is counterbalanced by its decomposition through the actions of bacteria and fungi. However, in wetlands where the water table is stable near the surface, the dead plant remains do not fully decay but partly accumulate as peat. Such wetland is called a mire, whereas an area with peat is called a peatland (see Box 2.1; Figure 2.1; Joosten and Clarke 2002). The rate of peat accumulation (‘peat growth’) in mires is generally in the order of magnitude of 1 mm per year. Where accumulation has continued for thousands of years, the land may thus be covered with peat layers that are many metres thick (Charman 2002).

Peat formation

The accumulation of peat requires an imbalance in the production and decay of dead organic (plant) material. The most important reason for peat accumulation is retarded decay due to water saturation (Clymo 1983). The limited diffusion rate of gases in water leads to a low availability of oxygen, whereas the large heat capacity of water and the large energy demand for vaporisation induce lower than ambient temperatures (Denny 1993; Ball 2000). The resulting anaerobic and relatively cold conditions inhibit the activities of decomposing organisms (Moore 1993; Freeman et al. 2001). An important role is played by the recalcitrance of the produced plant material, with some species, organs or substances decaying more easily than others. The production of acids, humic substances and phenolic inhibitors during initial decay also contributes to limiting decomposition.