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Friday, March 18, 2011

Quercus agrifolia - Coast Live Oak

First off, I am a huge oak fan, especially of huge oaks. There are so many oaks available, but lets have a look at the native oak that so dominates our urban forest canopy. This is me under a huge one in Santa Barbara area.



My new favorite tree, in Carmel CA.



This is a nice pair located at Filoli Garden. Notice what a great job they have done of minimizing the damage from summer water and compaction from pedestrians by using a huge circle of mulch. The mulch helps with compaction and keeping the summer water off the trunk of the tree seems to be key in fighting root rot.



Coast live oak is an evergreen tree 30-75' high and potentially as wide or wider. Trunk usually splits very close to the ground into 2 or more main leaders creating a broad spreading habit. Some specimens are more upright while others seem more broad. I suspect it has a lot to do with where they are growing, for example in a crowded canopy they will likely grow taller while an open grown specimen like you might see at Wilder State Park will be very broad with the lowest branches almost touching the ground.




Even though I grew up in the bay area I still think of the typical oak being a deciduous tree and having leaves that look "oak-like". These below are from the scarlet oak, Q. coccinea and are more or less what I would think of if someone said "oak-like".



So, lets have a look at the foliage of the coast live oak. One of the most frustrating things about these and many oaks is the foliage is so variable from tree to tree and from leaf to leaf. These leaves are all from one branch on the same tree.




Leaves are evergreen, alternately arranged, oval to broadly elliptical to almost round in shape. They are stiff, medium to dark green and glabrous above, slightly paler beneath with some axillary tufts of hairs. The margins are usually revolute (rolled over), making the leaf appear narrower, margins finely to coarsely spine tipped or sometimes entire. 1-3" long, 3/4 - 2" wide. They last only 1 year and fall off when the new foliage emerges. Terminal buds clustered as usual for oaks and notice the goldish colored hairs on the stems when young.




The obvious flowers are the males, in catkins that are often called tassel-like. Females are small and red borne further back from the tip of the shoot.






Acorns maturing the first year 1 - 1.5" long, narrow, pointed, brown in color. Cap is about 1/3 the length of the nut. Found these on the ground in January, just starting to germinate. And to be frank, this tree is a weed, beautiful but they come up everywhere.




The bark is quite beautiful. Most of the time it is smooth, silver gray colored but eventually develops deep furrows of darker brown or blackish. This image is a reasonably young tree. I love the wrinkly bark. Look where the two stems split.




This is the trunk of an old specimen located near Aptos park. Notice the gray is being replaced by deeply furrowed areas of dark gray or black.




Here is an old tree tree at a Monterey Bay Nursery showing the nice branching pattern and colors of the bark. Also pretty common is the longitudinal splitting of the bark.



This oak is a fast grower. It reseeds quite easily and new trees develop rapidly where you might not have wanted them. I do think they would make great hedges but they don't transplant easily unless the roots have been cut several times to encourage more lateral roots.

Every so often we see an infestation of oak leaf moth. These little buggers like to eat the foliage, then pupate, emerge as moths, mate, then lay another set of eggs which will hatch later in the same season. Generally they cause minimal damage to healthy trees, but those suffering from drought or root compaction or pruning abuse can be seriously damaged. The plant generally needs all the energy from the leaves and stores the extra in the stems. Damaged leaves mean less stored carbs for growth.

Another big problem is with the root systems. These oaks are quite susceptible to oak root fungus and the new disease on the block Sudden Oak Death. This can be a really big problem when the grade or soil levels have been altered when landscaping around an old specimen.

There are some seemingly conflicting information about watering oaks. They seem to be quite drought tolerate when older, but they do best with added moisture. They seem to grow well in lawns up to some age, then they start to suffer from water hitting the trunks. I think its best to do what Filoli does, mulch and cut back on the water hitting the root and trunk area.

There are so many beautiful specimens around that you just need to go looking for them.

Related oaks, yes, oaks are hard to ID sometimes.

Misidentification:
Another similar oak Q. wislizeni Interior live oak grows among our coast live oak and looks similar but the foliage is a bit narrower and does not roll over on the margins.

Location:
Santa Cruz
111 Hammond Ave wow, one of the nicest and largest

Soquel
Robertson Rd, by the Soquel Drive intersection

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