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O 0 Preliminary Arborist Report. Ponderosa Homes HortScience,Inc. Valley Trails,Pleasanton Page 4 Suitability for Preservation Trees that are preserved on development sites must be carefully selected to make sure that they may survive development impacts,adapt to a new environment and perform well in the landscape. Our goal is to identify trees that have the potential for long-term health,structural stability and longevity. Evaluation of suitability for preservation considers several factors: • Tree health Healthy,vigorous trees are better able to tolerate impacts such as root injury,demolition of existing structures,changes in soli grade and moisture,and soil compaction than are non- vigorous trees. • Structural integrity Trees with significant amounts of wood decay and other structural defects that cannot be corrected are likely to fail. Such trees should not be preserved in areas where damage to people or property is likely. • Species response There is a wide variation in the response of individual species to construction impacts and changes in the environment. In our experience,for example,drought-stressed coast redwoods are more sensitive to construction impacts;while coast live oak is tolerant of site disturbance. • Tree age and longevity Old trees,while having significant emotional and aesthetic appeal,have limited physiological capacity to adjust to an altered environment. Young trees are better able to generate new tissue and respond to change. • Species invasiveness Species which spread across a site and displace desired vegetation are not always appropriate for retention. This is particularly true when indigenous species are displaced. The California Invasive Plant Inventory Database(htto://www.cal- loc.orotirdinventorv/weedlist.phoMev)lists species identified as having being invasive. Pleasanton is part of the Central West Floristic Province. None of the species assessed at the Valley Trails site are considered invasive. Each tree was rated for suitability for preservation based upon its age,health,structural condition and ability to safely coexist within a development environment. Table 2,following page,provides a summary of suitability ratings. Suitability ratings for individual trees are provided in the Tree Assessment Forms(see attachments). We consider trees with high suitability for preservation to be the best candidates for preservation. We do not recommend retention of trees with low suitability for preservation in areas where people or property will be present. Retention of trees with moderate suitability for preservation depends on the intensity of proposed site changes.