I took these photos with my Iphone in Flood Park off Bay Road in Menlo Park. Not too shabby for a camera in a phone!
The park has gorgeous old Oak trees- Coast Live Oaks and Valley Oaks that are many hundreds of years old.
Coast Live Oaks are evergreen and have rounded leaves with slightly spiny edges. Valley Oaks have lobed leaves and are deciduous. These are the most common Oaks in our area and many folks have them in their yards or neighborhoods.

I wanted to blog about them because they are so much a part of our lives in the Bay Area.  Where I grew up in San Rafael we had Oaks all around our home and even one in the middle of the house! The home is actually built around a Valley Oak forming an “L” around the trunk. We climbed them, gathered the acorns to play games with and threw the galls at each other as kids. I have spent many happy hours gazing up into the branches of the contorted Oak covering our deck.

 We lost a huge Live Oak in the front of the home last year and it was heartbreaking. It was akin to losing a member of the family.  Although Oak trees seem to live forever they definitely succumb to age, disease and natural disasters.
Living under the canopy of an Oak is not always easy.  They are huge trees that drop leaves, acorns and spent blossoms. They are often the home of caterpillars and insects that can also cause honeydew drip, leaf drop and other assorted messiness.  But we thank them for the shade, beauty and bird activity that thrives in their canopies.

That is actually the most exciting fact about large trees- they are a giant environment and ecosystem in their own right. Supporting birds, moths and insects, bacteria and fungus that larger animals live on and that are food for even larger creatures, these trees are a big part of the food chain. Shelter and structure is also a part of their role as well as the action of the root system in preventing erosion. The leaf drop of trees breaks down and provides organic matter for the soil essentially feeding the tree and organisms in the soil. Gardeners should leave the leaves below trees because of this action. Obviously, with trees over paving this doesn’t apply.

 When living below an Oak it is important to remember that they are adapted to summer drought- which is very long here. It is dry from May through October most years, and in the un-irrigated areas native plants have the ability to survive in this climate. They do not like a lot of extra water in the summer, so irrigation systems often cause damage to native trees and plants due to overwatering. Oak also have a fungus that lives in unison with them called Oak Root Fungus. This fungus lives in all parts of the trees. Oaks can live fine with it as part of their lives, unless there is a lot of extra watering going on or a very rainy year. The fungus becomes over active with the increased amount of water and can block the vein system of the trees and other plants in the garden near the Oaks. 
You will often hear advice that Oaks should not be watered under the canopy and especially not at the base of the trunk. This is due to disease issues- crown rot, fungus’ and even termite damage. Fungus at the tree crown is the disease that killed two of our large Oaks even though we were not irrigating them. The crown of a tree is where the trunk meets the soil and the roots start. Sometimes the crown becomes buried over time or is buried by folks adding soil or cobbles around the tree trunk. This makes a place that stays moist and is vulnerable to rot and fungus. In one of our trees the trunk had a cavity that collected water and a shelf fungus grew in the gap gradually breaking down the core of the tree. It lived with this for many years but finally fell pulled down by the weight of a bumper crop of acorns.

There are a lot of things that live in and among the Oaks that don’t hurt them, including beneficial fungus! Confusing I know but nature has its supportive systems while also having the survival of the fittest aspect.

 Pictured here is a twig with lichen on it. Lichen is a neat organism that is actually a fungus and an algae intertwined together to form one structure. You see it on rocks, trees, signs, roofs etc….. It only latches on to their supports and does not harm the trees or structures. Lichen is really a cool plant and I love the many colors and shapes it can have. Used for dyes, food for some animals, decorative projects and the Native Americans even used it to absorb moisture away from babies in their diapers.

Often Oaks will have cavities where a branch has died out. The cavities may or may not be a problem for the tree- mostly not. These holes become homes for birds, bee hives, small animals and even other plants.
Do not fill the cavities with anything like concrete or tar- this can damage the trees. Have a professional arborist look at the cavity and have them treat it as needed.

This funny looking ball is a gall. It is made by a wasp and is the nursery for their larvae. These are common in Oaks and do not hurt the trees. Some folks call them “Oak Apples” but they are not a fruit- well, maybe for the wasp larvae but not for us.
Galls are kind of interesting too. They come in a variety of shapes and sizes and on an Oak you may find 5 or more different kinds of galls. This type is one of the largest Galls.

Another aspect of living below Oaks and other large trees is compaction. Trees do not benefit from having a lot of traffic running over their roots. Paving below trees is hard on the trees and the paving!  Best to stay back from the trunks 8-10′ or more with paving and path areas. This is usually impossible in our tight urban settings but if there is a choice this is the rule of thumb.

Last note on large trees and Oaks- attaching things to them isn’t a great idea.  Building a tree house? Use posts and beams around the trunk and branches rather than nailing into the tree. Hanging a pot, swing or sign? Allow plenty of chain or rope instead of using a tight loop so the tree can expand and surround the chain or rope with rubber to avoid abrasion. Remove tight tree ties or bracing so the tree won’t be strangled or girdled over time.

Think of an Oak as a huge community supporting hundreds of organisms and providing oxygen for hundreds more. An Oak is more than “just” a tree it is a complex living being and structure that asks for little and gives and gives and gives. Amazing!