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Davis, California

Thursday, July 18, 2024

A view from the treetops


A closer look at the significance of heritage trees on campus

UC Davis is home to a number of iconic symbols: the classic mustang insignia painted in bike roundabouts, the picture-perfect water towers, and, most prolific of all, the impressive heritage trees that reside all over campus.

According to campus arborist Melanie Gentles, there are over 10,000 trees on the main campus plus another 3,000 or more in the Arboretum — as well as over 1,000 in the peripheral areas of land owned by UC Davis. Roughly 700 of those in the Arboretum are different species of oaks. Many of these oaks, in the Arboretum and on central campus, are considered “heritage.”

“‘Heritage’ is a human value — if something is valuable culturally, aesthetically or has great age, then you refer to it as ‘heritage,’” said Warren G. Roberts, a superintendent emeritus and Arboretum volunteer. “If you think about it, these trees [in the Arboretum] were here when there were grizzly bears, and [these trees] watched covered wagons come through. In fact, one pair of my grandparents came through the arboretum in the 1850’s because that was the main road coming west, and they would have seen some of these trees.”

The Arboretum is home to a number of trees that are more than 300 years old. In fact, the Central Valley used to be dominated by one of California’s most unique and native trees: the Valley Oak. This species of oak tree, however, was decimated when settlers began agricultural practices in the area. Today, the Valley Oak is the most abundant oak tree in the Arboretum and on the UC Davis campus.

Many of the trees that line the Quad and other parts of central campus are Cork Oaks, most likely planted in the 60’s and 70’s. These oaks are easily distinguishable from their characteristic cork-like bark, which, historically, is harvested in their native lands and fashioned into various cork products. The largest Cork Oaks on campus are unequivocally deemed heritage trees, their massive trunks towering above passersby on the north side of the Memorial Union and just south of Hickey Gymnasium.

“Most of the oaks here thrive in a Mediterranean climate, which means dry summers, wet winters,” said Kamyar Aram, a plant pathology Ph.D. student in the Rizzo Lab at UC Davis. “Oaks have been intimately connected with human civilization, there’re a lot of old references in Roman literature to acorn eating, and of course the Native Americans.”

Aram and his colleagues focus on forest pathology as well as forest ecology related to the influences of disease in forests. He studies a group of pathogens called phytophthora and how the pathogens can induce Sudden Oak Death, which, he pointed out, only infects and kills trees in a collection of oak species called red oaks. The Cork Oaks that can be seen around the Quad are not susceptible to this disease, but other species on campus, like the Coastal Oaks that line Howard Way into the MU bus stop, do have the potential to be infected by this pathogen.

“[Sudden Oak Death] was introduced in the coast, most likely through the nursery trade,” Aram said. “It has a complex lifestyle, it mainly grows on bay trees, [where it] produces spores […] and [the spores] find their way underneath the bark of an oak tree and that’s when they kill the oak tree.”

Fortunately for UC Davis and the Central Valley, Sudden Oak Death is not a big issue as it mostly affects trees in more coastal habitats and live in environments where contact with bay trees is probable. There are, however, other challenges that are more relevant to the trees on campus.

“As a tree grows older, it can become more susceptible to pests and diseases,” said Emily Griswold, the director of GATEways Horticulture and Teaching Gardens. “In the urban landscape, often what kills oaks is things like construction impacts and compaction of the soil, so the roots don’t have as much access to oxygen. Also irrigation, a lot of our native oaks evolved in this climate that is summer-dry, so there can be certain diseases that […] can affect roots of oaks if they get water in the summertime.”

Griswold, Gentles, Roberts, Aram and other interested experts at UC Davis are all members of the Tree Committee. Whenever there is a development on campus, the committee convenes on the tree site to determine if any trees in the area are worthy of being saved — especially heritage trees.

“The first [category] is the heritage tree category,” Roberts said. “The second is trees that are beautiful and valuable but not quite heritage tree status, third is it’s a good tree but it’s going to need some help — in other words you can’t leave it as it is or problems will occur in the future. The fourth category is that the tree is dying or out of shape.”

Management practices of trees at UC Davis have become less reactive and increasingly proactive since Gentles began working here full-time about 10 years ago. The urban setting means that safety is the number one concern for Gentles and her fellow groundskeepers, but managing the trees for health and beauty is extremely important, especially considering the heritage oaks are what attract many people to Davis in the first place.

This past January, a storm swept through the Central Valley and eight large trees on campus toppled over, including a large oak tree that fell onto Haring Hall.

“This storm was the perfect combination,” Gentles said. “It was soil saturation, [so] the roots couldn’t hold on, especially on the taller top-heavy trees. All the ones we lost were evergreens, which means they have a heavier load in their canopy. It acts like a sail, and the high gusts of wind meant that the roots couldn’t hold on.”

Thanks to the proactive management of the grounds crew on campus, evidence of these trees’ deaths has already been erased. Gentles and her team keep close track of which trees struggle and which thrive in the area, and replacement planting is the main route for dealing with the loss of trees on campus.

With a quick glance around, it’s not hard to notice the great diversity of tree species at UC Davis. The oak trees lend a characteristic appeal to the school and instill a sense of pride in students. Neither a scientific or historical knowledge of oaks nor a complete understanding of what designates a tree as “heritage” is necessary to appreciate the inherent value in nature so present and beautiful.

“I love when people I know [understand] the natural world around me, and oak trees are something I see everyday in my life,” Aram said. “When we get to know the world around us, we put on new lenses, and seeing more of the world is knowing more of the world.”
Written by: Marlys Jeane — features@theaggie.org


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