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Oak Trees in Rossmoor

“The creation of a thousand forests is in one acorn.” – Ralph Waldo Emerson

Magnificent oak trees can be found all over Rossmoor. The heritage oaks in Dollar Park and near the Buckeye tennis courts are spectacular. Most of the large oaks in Dollar Park are tall, branching Valley Oaks. There are many Coast Live Oaks too, with one majestic tree gracing the area with its spreading canopy.

Worshipped by the Celtics as a sacred tree, oak trees are symbols of wisdom, strength, and endurance. They are known as a “keystone species” as they form the foundation of the ecosystem, supporting the life of numerous plants, insects, birds, mammals, and people. Colorful acorn woodpeckers can be seen in Dollar Park, nesting and storing their acorns in holes in the trunk and branches of the oak trees.  

Valley Oaks, native to the hot, interior valleys of California, are the largest of the North American oaks and known as the “Monarch of Oaks”. Reaching almost a 100 feet, they can live for centuries, 150 - 300 years or longer. The Coast Live Oak is also native to California and can often live over 250 years.

Oak trees are climate change champions. They capture and store carbon dioxide (sequester) in their leaves, branches, trunk and extensive root system. The Coast Live oak is the most efficient of all trees at capturing large amounts of carbon dioxide. The larger the tree, the more carbon it can store. Like all trees, oaks also remove air pollution and purify the air, provide shade and cooling, and capture and store water in the soil.

Over 900 species of Lepidoptera (butterflies and mostly moths) have caterpillars that live and grow on oak leaves.

Understanding the key role oak trees play in combatting climate change is vital for a sustainable future. We have a responsibility to preserve and take special care of our Rossmoor oaks.

Photo: Towering Valley Oak in winter in Entry 2 Ptarmigan Drive

CA Native Oaks 'Best Practices' Checklist

Based on a report by Dr. Matteo Garbelotto, UC Berkeley

of a site visit to Rossmoor's Dollar/Event Center area on 11/24/22

Also: https://californiaoaks.org and https://www.nrcs.usda.gov

Watering

Mature established native oaks usually require no watering, except during periods of extreme drought.

☐   Give no water during dry season (July to October), except in dry winters (when rainfall is less than 2" per month).

☐   If water is provided, give at intervals of 3 weeks or less, to a depth of 12"–18". Irrigate slowly and outside the dripline—never near the trunk. Use MP Rotators or drip system with precipitation rate of .4 inches/hour or less. Bubblers are not appropriate.

Oaks in Lawns

Lawns are incompatible with native oaks, because lawns require regular watering, which promotes root pathogens in oaks.

☐   Remove lawn under entire canopy (dripline to dripline) of all native oaks by sheet mulching. Do not use a sod cutter, which will damage surface roots of oaks.

☐   Then for a full year, progressively reduce frequency and amount of water these oaks had been receiving, and water only outside their dripline.

Protecting Oak Root Systems

Primary reasons for oak decline are root pathogens and extreme soil compaction.

☐   Irrigate oaks only outside their dripline. This discourages development of root pathogens such as Phytophthora ramorum (the cause of Sudden Oak Death).

☐   Where possible, remove paved surfaces near oaks. Instead use permeable paving or permeable concrete.

Oaks Deemed Hazardous

Trees showing signs of decline—early browning of leaves, thinning of canopy, and loss of branches—may be hazardous if near areas with cars and people.

☐   For those oaks, consider excavating the root collar, and removing branches or stems that show loss of leaves, or obvious defects (e.g.,swellings, seepings, cankers, spotted leaves, cavities, mushrooms).

Replacing Oaks

Native oaks shouldn't be planted in areas requiring regular irrigation if replacement trees are needed.

☐   All plant stock obtained from outside Rossmoor should be tested for soil pathogens.

☐   Do not plant oaks with or near plants known to be foliar carriers of Sudden Oak Death, including California bay laurel, toyon, or Pacific madrone.

Construction Work Near Oaks

To protect mature oaks, avoid disturbing their root zone.

☐   Do not add fill or alter natural grade within the root zone (the area 1.5 times larger than trunk to dripline) so soil doesn't become compacted.

☐   Avoid paving or trenching in this area, and avoid or minimize human activities.

☐   Use permeable paving materials outside the area to reduce heat accumulation and avoid pooling of water.