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B. Fill Soils in New Developments May Hasten Tree Death

Narrator: This is Science Today. As new urban housing development continues to expand into former open space and forested areas, the expansion has altered the existing landscape. University of California environmental horticulture advisor, Larry Costello, explains.

Costello: It's been observed that the tree may decline, growth will be much slower, leaves may yellow - in some cases, the whole tree dies.

Narrator: Part of the problem is using fill soils in new urban housing developments to grade and level ground. Costello says this process can restrict air and water penetration in the root zone of growing trees.

Costello: If the tree is in good condition and it's a minimal amount of fill, just on part of the root zone of the tree, you may see little or no impact. If it's a large amount of fill, very deep on an old tree that perhaps is not in good health and the fill is very fine textured soil, the tree can be dead in a year.

Narrator: For Science Today, I'm Larissa Branin.