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A four-year study was conducted to evaluate the effects of treeshelters on the growth and survival of three oak species and Douglas fir growing in a Mediterranean climate. Trees were planted in irrigated and nonirrigated plots, enclosed in treeshelters or tree guards, and measured annually for height and diameter growth. In nonirrigated plots, both treeshelters and tree guards improved oak survival, but generally did not produce significant height or diameter growth increases over unprotected controls. In irrigated plots, plant growth and survival was substantially greater than that in nonirrigated plots. Irrigated trees with protection (shelters or guards) showed substantially greater survival levels than unprotected trees. Height growth was greatest in treeshelters and diameter growth was roughly equivalent for all irrigated treatments. Irrigated trees continued to grow when irrigation was discontinued after three years, and treeshelter trees exhibited little or no lean when shelters were removed. Trees without irrigation in Mediterranean climates should not be expected to exhibit growth enhancement effects from treeshelters equivalent to those found in temperate climates.

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