All life contains water. From distant space, Earth appears as a mosaic of blue and green, blue for water, green for plants. This book is about the ecological communities that occur where green meets blue: wetlands. Wetlands are intimately associated with water. They are one of the most productive habitats on Earth, and they support many kinds of life. This book explores the general principles that control the distribution and composition of wetlands around the world. The cover (Figure 1.1, artwork by Howard Coneybeare) illustrates a typical temperate zone wetland. Common wetland plants shown include floating-leaved water lilies (Nymphaea odorata), emergent pickerelweed (Pontederia cordata), and shoreline reed canary grass (Phalaris arundinacea). The food web is largely composed of invertebrates that feed upon decaying plants. Near the top of the food web are vertebrates such as fish (yellow perch), reptiles (snapping turtle), and birds (great egret). The surrounding forests interact with the wetland. Amphibians, such as tree frogs, over-winter in the forest, while nutrients and runoff from the forest enter the wetland.

Wetlands have always influenced humans. Early civilizations first arose along the edges of rivers in the fertile soils of floodplains. Wetlands continue to produce many benefits for humans – along with fertile soils for agriculture, they provide food such as fish and waterbirds. Additionally, wetlands have other vital roles that are less obvious – they produce oxygen, store carbon, and process nitrogen.