Oaks of the Putah-Cache Watershed (Quercus spp.)

December 2021

Valley oakAs the giving season approaches, what better trees to feature in our spotlight than oaks, which give an abundance of shelter, forage, and life to our region. Quercus, the genus that encompasses Oaks, has 20 species and 30 subspecies of Oaks currently persist in California. Oak species that can be found within the Putah-Cache Watershed include: Valley Oak (Q. lobata), Blue Oak (Q. douglasii), Interior Live Oak (Q. wislizenii), Coast Live Oak (Q. agrifolia), Black Oak (Q. kelloggii), Scrub Oak (Q. berberidifolia), Leather Oak (Q. durata), Canyon Live Oak (Q. chrysolepis) as well as a few other more inconspicuous Oak species. Please reference the dialogue within the pictures above for information on a few of these listed species.

Oaks are a foundational species. They maintain the obvious ecosystem services one would consider, like aesthetics, forage and habitat. For example, Oaks interact with over 300 vertebrate species and over 5,000 insects making them key habitat. Additionally, Oak acorns make up approximately 40% of deer forage and sustenance in their fruiting season. While walking along Putah Creek’s open-spaces, Oaks can be used for respite from the hot sun or the occasional rain storm.

A less obvious, but considerable ecosystem service that Oak species provide relates to their carbon sequestration potential. In general, global carbon storage is estimated via measurements of above ground biomass in each vegetation type and/or biome. However this is not the case for the genus Quercus. This general global model that estimates the sum of the biomass of the above ground portion of species, lacks confidence in regards to Oak species. This is due to Oaks unique regeneration and recruitment, as well as growth rates that are unpredictable down to an Oak stand and even an individual Oak level.

Blue oakOak regeneration and recruitment is at risk, as there is an absence of the recruitment size class. This is significant as recruitment is insufficient to maintain the current Oak populations, so is insufficient to maintain the current rate of carbon sequestration. This is central when considering our current climate crisis and the anthropogenic input of greenhouse gases.

Further, Oaks are opportunistic and plastic, meaning that the organism (genotype) has the capacity to vary in development (phenotype) according to the current environmental conditions. The genus does maintain a great range in California by maintaining the ability to track precipitation as well as other necessary resources, by being a transitional species. This gives each Oak organism a unique growth habit as discussed above, and therefore a unique carbon storage and accumulation potential. The climate and water crisis will likely decrease the range in which Oaks can grow, as necessary resources become limited. Without necessary resources the species must limit the size in which the biomass can grow regardless of age, so reductions to the amount of carbon sequestration that can occur may be inevitable.

Because of these idiosyncrasies and variation among individuals, scientists are creating individual-tree based models that allow for grouping among size class, oak demography, as well as calculations of how many Oaks will survive into the next age class or persist among the current age class and being prepared to justify the deviations. Further, Oaks have immense root systems. From when the radical first emerges the organisms have a rare adaptation that allows for a deep, persistent tap root, that most other tree species do not maintain. That tap root makes way to astonishing lateral roots and fine roots that also act is an accumulator of carbon. These substantial root systems allow for beneficial fungal interactions and an eventual build-up of organic matter that also maintains a high carbon storage potential.

Black oakOaks are of the utmost importance as the climate and water crisis intensifies. Human intervention by planting Oaks in areas in which it is appropriate, allows for helping to combat the Oak recruitment gap. Oaks are a keystone to the environment and possess countless ecosystem services that can help to mitigate the carbon footprint humans have imposed.

With the giving season upon us, consider giving back to Putah Creek Nursery, where Oaks are integral trees that we grow each year. Your support allows us to grow and plant more Oaks within our watershed! Check out more oak plant cards on PCC’s Instagram page!

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Putah Creek Council

PO Box 1258, Winters, CA 95694
530-795-9000

info@putahcreekcouncil.org

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