Why are wetlands common in boreal and tropical regions?

Wetlands are most abundant in boreal and tropical regions primarily because these areas possess environmental conditions that promote an excess of water, where local water input consistently exceeds output.1

In boreal regions, the prevalence of wetlands is largely driven by the presence of permafrost. This perennially frozen ground acts as an impermeable layer that prevents surface water from percolating into the soil, effectively trapping it on the surface. Additionally, the landscape in many boreal areas was shaped by past glaciation, which created low-relief topography and impeded drainage patterns that favor the development of bogs, fens, and peatlands.23

In tropical regions, the abundance of wetlands is supported by high levels of humidity and precipitation characteristic of the tropical rainforest biome. These conditions allow for the accumulation of organic matter, such as the thick peat deposits found in peat swamp forests, which are sustained by the region's consistently wet climate.12

Across both biomes, the specific distribution of these ecosystems is determined by the net balance of precipitation and evaporation, alongside the geomorphology of the land, which dictates how water gathers and remains on the surface.4