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Plant Focus

Quercus peninsularis
A Red Oak (Section Lobatae) endemic to inland ranges of northern Baja California, Mexico

The Oak Collection at Santa Barbara Botanic Garden

Santa Barbara Botanic Garden is the oldest garden dedicated to California’s native plants. Our Garden was founded in 1926, in direct response to what we today would call the biodiversity crisis. Our founders saw the rapid development of California’s wildlands after the railroad boom and the growth of cattle ranching, and they were motivated to create a botanic garden to display and protect these species. From the beginning, a high value was placed on wild-collected specimens from across California, as indicated by our earliest records.

Fig. 1 – A scan of our accession records, showing the wild source for two species of Quercus acquired in October 1935
 A scan of our accession records showing the wild source for two species of Quercus acquired in October 1935

Beginning in 1926, the Santa Barbara Botanic Garden became a space that harbored the wild oaks native to the Santa Barbara area, as well as a selection of specimen oak trees from across the state of California. There are around 20 species of oak that are native to California. These resilient trees are found in almost every habitat from the Quercus douglasii (blue oak) groves in the foothills of the Sierra Nevada to the Q. john-tuckeri (Tucker’s oaks) looking out over the Mojave Desert. Around a fifth of oak species in California are rare and threatened, often due to habitat loss or human-introduced pathogens and, of course, climate change.

Quercus engelmannii (Engelmann oak in the meadow which is a personal favorite tree)
Quercus engelmannii (Engelmann oak in the meadow, a personal favorite tree)

Our Garden is home to robust wild populations of Q. agrifolia (coast live oak) as well as a rare species of scrub oak, Q. dumosa (Nuttall’s scrub oak). Like many chaparral species, Q. dumosa is threatened in the wild by development. Chaparral is still being developed in coastal California, but the wild spaces of the Garden help preserve groves of this species in situ. The other species native to the site is the coast live oak. Many of largest trees in the garden are spontaneous plants from the Q. agrifolia population native to Mission Canyon. Compare below the historic photo of our desert section with a photo of the same area today. The slope in the background is now totally blocked out by the oak woodland that was simply allowed to reestablish itself.

Fig 2. Desert section circa 1930s Photo SBBG Archives – note the bare slopes in the background of the Desert Section
A photo in the Santa Barbara Botanic Garden archives showing the desert section circa 1930; note the bare slopes in the background
The same section today, with a healthy oak woodland behind it.
 The same section today, with a healthy oak woodland behind it

Our collection of oak trees is a marvel; nearly all species are either site native (like the coast live oaks and Nuttall’s scrub oaks) or collected from their native habitats in the wild. In our Garden we have around 30 species and naturally occurring hybrids of oaks, six of which are considered rare or threatened.

Quercus pacifica acorns
Quercus pacifica 

Our collection of species from the Channel Islands and Baja California is a point of pride. Santa Barbara Botanic Garden is home to multiple specimens of Q. tomentella (island oak), Q. pacifica (island scrub oak), and Q. cedrosensis (Cedros Island oak) collected from across their native ranges. One of our Q. tomentella holds the distinction of being the National Champion, i.e., the largest specimen on the mainland. That plant was collected from the Central Valley of Santa Cruz Island in 1965. It was noted at the time of collection as having especially large acorns.  

The National. Champion Quercus tomentella on a lovely day in October 2023.
The National. Champion Quercus tomentella on a lovely day in October 2023  

The oak trees here in the Garden all do double duty: in addition to supporting wildlife and humans, the trees in our collection are also an important conservation tool. Acorns are large seeds with a high fat content. These types of seeds are referred to by researchers as “recalcitrant seeds” since these properties make them difficult to store in a seed bank. For this reason, oak trees must be conserved in the wild or in the living collections of botanic gardens. Santa Barbara Botanic Garden is part of the Global Conservation Consortium for Oak (GCCO)'s efforts to address the conservation gaps for Californian oak species (more info here).

Quercus kelloggii (Black oak in our collection since 1947)
Quercus kelloggii (California black oak), in our collection since 1947

If you ever find yourself in Santa Barbara, please come visit us! I love talking about the collection and telling the stories of our plants. If there is a species you’re particularly interested in hearing more about, please reach out and ask. You can find out more information about our collection, get my contact info, and more on our website here.

Quercus × ganderi Gander oak thriving in our collection since 1941
Quercus ×ganderi (Q. agrifolia × kelloggii, Gander oak) thriving in our collection since 1941

 

Christina Varnava

Living Collections Curator
Santa Barbara Botanic Garden 


Photos © Christina Varnava unless specified otherwise