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4.7 BIOLOGICAL RESOURCES A high probability exists that many trees on the project site whose root zone (as denoted by the crown circumference) are located adjacent to proposed grading sites for the roadway and building pads would experience surface soil compaction during the construction process. In the areas which have been prematurely cleared for fairway construction, this impact may have already taken place. Such soil compaction greatly decreases the oxygen availability in the root zone area which can lead to the weakening and eventual death of the tree. Another latent cause of tree death could result from the positioning of lawn and garden watering systems upslope and adjacent to native oak species which would experience wet summer root soil that can promote oak root fungus (Armillaria mellea), the main cause of death of oak trees in California. Finally,unwarranted or incorrect pruning of heritage trees could,and in some cases has already occurred, reduce their vigor and visual value. All of these are considered potential significant adverse impacts. Mitigation Measures 4.7-4(a) Incorporateprotective measures for mature native trees into the development construction and finished plans. These should be similar to those outlined in the Buckeye Ranch Management Plan. They should include the enclosing of each native tree within and adjacent to the construction zone with a temporaryfence situated 4 feet outside the edge of the leaf canopy to prevent root zone soil compaction and limb/trunk damage from grading vehicles. Lots and streets situated upslope from oak trees should be designed with gutter systems which will shunt summer surface rwwfj`'water away from the root zones of native oaks. Also, sprinkler systems should be installed so that water is not directly applied to the root zone area of these trees. 4.7-4(b) A zone of potential impact should be established around mature trees which are located in close proximity to construction/grading activities. These trees should be inventoried and state of health and condition noted to facilitate future monitoring of the trees' condition. 4.7-4(c) Prohibit the cutting of all or part of any native tree within as well as outside the developable areas. The one exception would be a weakened limb overhanging structure that could cause damage or present a hazard to residents if it fell. This last item is in opposition to the Buckeye Ranch Management Plan recommendation that an arborist direct the pruning and culling of native oaks along the lines that might be employed in a city park. In a natural area a dead or dying tree is often as valuable to wildlife as a live one,and when these do not directly pose a threat to the well being of the new human residents, they should be allowed to complete their natural cycle. Impact 4.7-5 Human activities could cause potential impacts to the adjacent natural community. 4.7-33