Our Native Oak Trees

Long before housing tracts, shopping malls and office building were built here, majestic old oaks formed woodlands on the slopes and along the creeks of Roseville. Many of these old trees survive, giving character, shade and beauty to our city. These trees are tough survivors, living only with rainwater that falls in the winter. The oak woodlands preserved by the City of Roseville are a good place to see oaks and the native birds, reptiles, insects and mammals that depend on them for food and shelter.

Large native oaks may be several centuries old. These old trees do not adapt well to changes in their environments. As more homes and businesses are built near native oaks, drastic environmental changes such as summer irrigation, soil compaction and grading threaten the health of our oaks. The effects of these changes may not appear for years, yet the tree may be irreparably damaged. Prevention is less expensive than maintaining an ailing oak or removing it when it becomes hazardous.

Root damage, fill soil and compaction impacts the health of an oak tree shown on the left, while the tree on the right is vigorous because its roots have mulch and minimal irrigation.

Use this quick guide to give you general information on your native oaks,  for more information we recommend that you consult an Certified Arborist who has experience with native oaks and who can give you specific information on your tree.

One of the most important steps you can take to preserve the health of your oak tree is to carefully observe your tree several times a year. This will help you will notice subtle changes which may signal a change in health or structural stability. Knowing what is normal for your tree, and trees of the same type can help you. Watch for changes in leaf color, early loss of leaves in the fall, oozing lesions, loose bark, mushrooms or other fungal growth on the trunk, branches or close to the tree are changes that may need attention.

Knowing which type of native oak you have can help you recognize what is normal. Identify your oak by comparing the leaves, bark and acorns to these illustrations and descriptions.

n-a-t-2Blue Oak leaves are blue-green in color and shallowly lobed, they drop in the fall. 

Blue Oaks are usually found growing on dry hills and slopes.  They have shallowly lobed leaves (lobes do not reach the midrib of the leaf) that are distinctly blue-green in the summer. They drop their leaves in the fall. The acorns are stocky with small caps and the bark is whitish-grey or patchy grey. Blue oaks grow slowly and are not very tolerant of root disturbance or summer irrigation.

n-a-t-3Valley Oak leaves are deeply lobed and rich green color. They drop in the fall.     

Valley Oaks prefer to grow where there is deep groundwater-near streams or ponds. Their leaves are deeply lobed (lobes reach the midrib of the leaf) and large, often 4-6″ long, and rich green in color. Leaves drop in the fall. The acorns are large and pointed with a small cap. Large “oak apple” galls may grow in the branches. They are light brown in color and very lightweight. They do not harm the tree and are caused by a reaction to small insects depositing their eggs in the bark. The bark is brown and breaks into blocky shapes on tree trunks and larger branches. Valley Oaks grow rapidly when they are in favorable situations and can reach large sizes with branches that hang to the ground on old trees. They often seem to tolerate some summer irrigation.

Interior Live Oaks grow in both dry and moist locations. Their leaves are leathery and edged with prickles. Interior Live Oaks are evergreen so they have leaves year round. Their  acorns are narrow with subtle stripes on the sides. The bark is smooth and grey when young and becomes rougher as it age. Interior Live Oaks can grow rapidly in favorable conditions or more slowly in very dry areas. Old trees can have very large trunks and branches. They may tolerate root disturbance or summer irrigation without loss of vigor when they are young.