The Effect of Tree Shelters on Blue Oak Seedling Growth

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Introduction:

California’s blue oaks reduce rangeland soil erosion, absorb deep soil nutrients other range species cannot reach, and provide wildlife habitat.  Unfortunately, blue oak populations are declining, due in part to browsing.  British ranchers and farmers have used tree shelters to protect young trees from browsing.  Also, translucent, but colored plastic tree shelters may promote growth in comparison with wire mesh tree shelters.  The objective of this experiment was to compare the growth of blue oak seedlings sheltered by wire mesh or colored plastic shelters.

Materials and Methods

The study site – a private ranch --is in the foothills about 3 miles southwest of Elk Creek, Glenn County, CA.  In January 1998 the ranch manager planted acorns on the ridge and slopes of a small hill.  In the spring of 1998 the emergent seedlings were randomly assigned to four treatment groups: wire mesh cylinder, Tree-pee, Blue-ex and Tree-Pro shelters.  After the shelters were installed over the seedlings, a mat mulch was placed around the trees and a 5’ diameter “hog wire” cylinder was installed around the tree-sheltered seedlings and secured with two T-posts. 

Rodents killed some trees, with cattle damaging many more, because the wire cylinders failed to exclude them.  Five wire mesh and five Tree-pee trees survived.  Four Blue-ex and four Tree-Pro trees survived.  Heights of the surviving trees were measured in April, 1999.  These data were analyzed as a completely randomized design.  Treatments did not significantly differ as p = 0.45.  See Figure 1.  Also wire mesh did not differ from the three commercial tree shelters asp>0.05.

The major problem to overcome in studies as this one continues to be the protection of seedlings from cattle and deer.  Efforts to compare tree shelters will likely be wasted unless trees can be protected from large browsers.

References:

• Gerlach, T. Hill slope troughs for measuring sediment movement. Revue de Geomorphologic Dynamique. 1967. State of California: Department of Transportation, Division of New Technology. Control (Type D). 03-11-96.
• Thomas, Fred. CERUS ConsultinR. Interview. Sept. 1997.