NAC | Working Trees for Treating Waste

Waste from one species can benefit another.

Trees require sunlight, carbon dioxide, water, and nutrients to grow. Waste from municipal sewage treatment plants, livestock operations, irrigated farming operations, and industrial processing contains nutrients that can be used by trees. Trees can often be substituted for more costly engineered practices.

Of the nutrients commonly found in these wastes, large amounts of nitrogen, phosophorus, potassium, magnesium, calcium, and sulphur are needed by trees in large quantities.

The nutrients taken up are distributed throughout cells in the tree, with the highest concentration ending up in the leaves. The leaves conduct photosynthesis, the process by which sunlight is used to convert carbon dioxide into sugars that accumulate primarily in the wood. Year after year, as the tree grows, nutrients are stored in the wood of branches, stems, and roots. Rapidly growing trees provide a better sink for these wastes than older trees.

In addition to the benefit of using the nutrients from wastes, the trees can be harvested after six to 15 years, depending on species and climate. Products derived from the wood can provide a substantial cash return to the landowner or operator.

Fast growing trees, such as hybrid poplars, can take up large amounts of nutrients, making them ideal for treating wastes.

Which Trees?

Success in using trees to remove wastes depends on the species and the length of the growing season. Trees that are well-suited for treating wastes include several species with rapid growth rates, which allow more nutrients to be absorbed than trees that grow more slowly. Extensive and deep root systems are also desirable, enabling nutrients to be effectively filtered out and keeping them from moving into ground water.

Fast growing tree species that can be planted for nutrient uptake include:

Hybrid Poplar (grows in many regions of the U.S.)
Hybrid Willow (Northeast U.S.)
Sweetgum, Sycamore, and Yellow Poplar (Mid-Atlantic and Southeast U.S.)
Loblolly Pine (Southeast U.S.)

Both hybrid poplar and hybrid willow are especially attractive because of their ease of regeneration.

When selecting trees for eventual harvesting, check with local mills on the potential market for wood products.

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Last updated 12.13.2000.
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