Function

A Giant Living Sponge
A Conserver of Water
A Reef Saver
Our defense against drought and flood

The Hawaiian forest is the ultimate watershed.

Millions of years of evolution have made the Hawaiian forest highly efficient at capturing and retaining water.

Generally speaking, the more complex the structure of a forest, the more enhanced its watershed functions. 

The Hawaiian rain forest, with its multi-layered structure - tall canopy, secondary trees, shrubs and fern layers, ground-hugging mosses and leaf litter - act like a giant sponge, absorbing water and allowing it to drip slowly underground and into streams.

Even without rain, the forest can pull moisture from passing clouds.  In Hawai'i, this interception can push water capture above and beyond total annual rainfall by as much as 30 percent.

The Hawaiian rain forest is a great conserver of water.  The tall, closed canopy shades out the sun, resulting in less water lost to evaporation and transpiration.   The dense vegetation also blocks wind, which would otherwise pull moisture from the land.

The many layers of vegetation blunt the erosive effects of rain, and once saturated, buffer the release of stored water, reducing immediate flow in wetter times, maintaining it in dry.  Long after rain subsides, the forest delivers fresh water for human use.

There is a direct correlation in Hawaii between the health of our forested watersheds and the health of our reefs and beaches.

Without a healthy forest to anchor the soil and temper the erosive effects of heavy rain, large amounts of sediment wash off our steep mountains and into the ocean, polluting streams, destroying coral reefs, and degrading coastal fishing resources.

Perhaps the greatest value of the thousands of native species in the West Maui Watershed is the function they perform together, as parts of a complex, natural ecosystem.

The balance achieved among these species over the millennia has produced forests that can best weather the typical cycles of drought and flood in the region, and are uniquely adapted to the climate and soils of the mountain.

Because of the buffering effects of the forest, our human communities enjoy a more comfortable climate with a lowered risk of extreme conditions.

Adapted from "Last Stand - The Vanishing Hawaiian Forest" prepared by The Nature Conservancy, Hawaii.  For a free copy, contact TNC.