If I didn’t know any better, I would guess that apricot trees were native to the Santa Clara Valley because they were once so much more common. In the early 1970’s, all the neighborhood kids and I played in a forest of them until this forest was replaced by the lawns, basketball courts, playground and recreation center of San Tomas Park. We were so deprived and had nowhere to play with our forest gone!

Native species have been increasingly displaced from urban areas by exotic (non-native) species during the previous two centuries or so, but the natives still persist and are still popular among many garden enthusiasts.

It would seem that because the local climate is so mild that native species would not need to have developed any special adaptations. Such adaptations would seem more necessary where weather can become severely cold during winter or hot during summer. Local climate does neither, but can be quite arid at times. This is why several native species have developed the capacity for variable dormancy.

For example, California horse-chestnut and California sycamore may emerge from dormancy during spring, but may partially defoliate if weather becomes unseasonably warm and dry during summer or even spring. If this happens, they can ‘refoliate’ as weather allows but prior to cool winter weather that stimulates complete dormancy. Sycamores can also behave like this in response to fungal infection, as was so common last spring as anthracnose proliferated during alternating warm and rainy weather.  

Spring seems to have arrived early this year and weather has recently been warmer than it has been for this time of year since 1965. If this weather pattern continues, foliage may subsequently become dingy among sycamore, London plane (which is a hybrid of Japanese sycamore and California sycamore) and even valley oak. Sycamores that are not within irrigated areas or near an active creek may eventually begin to partially defoliate.

Just as some species are sensitive to frost during winter, a few species are sensitive to unseasonable warmth while foliage is only beginning to emerge from dormancy. Foliage typically matures and becomes more resilient as weather slowly warms from spring to summer. However, if weather becomes too warm too rapidly, tender new foliage may be damaged by direct exposure to sunlight, particularly if humidity is minimal or a breeze enhances evapotranspiration.