We tend to think of land and water as two different environments. But there's a very rich intermediate zone, which scientists call the riparian zone, where land and water overlap and influence one another.

In a cold, dry climate like much of the Yukon's, riparian habitat is very important, says Wendy Nixon, biologist with Environment Canada in Whitehorse.

"Think of water as a nutrient," she says. "In fact, it's the most essential nutrient. And that's the most significant aspect of riparian sites: they have terrestrial vegetation but they're tremendously influenced by the presence of water."

You'll find riparian habitat along the banks of streams and rivers, around wetlands and lakes, in floodplains -- any area where land and vegetation are influenced by the presence of a body of water and where the water, in turn, is influenced by surrounding land and vegetation.

The water in riparian habitats helps plants take up nutrients and grow faster and more densely. The vegetation provides food and shelter for everything from insects to moose, and to their predators. The water also facilitates the final stage of the nutrient cycle, the decomposition of plant and animal matter back into its component nutrients.

"Things rot faster if there is moisture present," Nixon explains.

In turn, the vegetation on land contributes to the aquatic environment, she says. Leaves fall into the water, where they decompose and provide food for a myriad of microorganisms and invertebrates. Those tiny creatures become food for larger creatures, which feed still larger predators like pike, salmon, eagles, and bears.

Terrestrial, or land-based, vegetation also provides shelter, Nixon adds. When the riverbank erodes and trees topple into the stream, they become important shelter for smaller aquatic creatures such as invertebrates and juvenile fish.

"In fact, I was on a river recently where an old spruce had fallen into the water," says Nixon. "There were hundreds of chinook salmon fry all clustered in under this sweeper."

A kingfisher was hunting in the area and larger fish were gathered nearby, she says, but the fry were safe as long as they stayed in the small spaces between the branches of the fallen tree.

The diversity and density of life in riparian areas is remarkable, says Nixon. Plants and animals that survive in drier habitats thrive in riparian habitats. In addition, there are species that appear nowhere else, such as otters and beaver, water thrushes and a couple of warblers, including the common yellowthroat and blackpoll warbler.

Insectivores like bats and swallows hunt in riparian areas because of the high numbers of insects. Plants grow more densely in riparian areas, and some plants, such as some kinds of willow, grow nowhere else.

In riparian areas, even things that look like waste are often essential parts of the nutrient cycle and important habitat, she says.

For example, standing dead trees, drowned out by rising water levels, suit many forest birds perfectly as nesting sites, food sources, and cover from predators. Tangled, half-dead undergrowth along a bank might be unsightly and block access to the water, but it's exactly what an otter is looking for when it picks a place for its den. In the Yukon, three species of ducks nest in tree cativies, while several others nest on the ground in riparian areas.

In southern Canada, millions of dollars have been spent to restore riparian habitat destroyed in the pursuit of agriculture or in the spread of human habitation. Only after it was gone did people realize the importance of the riparian zone in the smooth functioning of the larger ecosystem.

"It's a unique combination of features, and it provides habitat for a myriad of species," Nixon says. "You can't restore it easily."

For more information about riparian habitats, contact Wendy Nixon, Environment Canada, at 667-3929.