Quercus douglasii blue oak

Native remnant Quercus douglasii, Rogers House, showing characteristic finely furrowed bark (compared to the coarser and deeper furrows of thick Q. lobata trunks). Sairus Patel, 20 Mar 2020

Quercus douglasii leaves. From Trees of Stanford and Environs, by Ronald Bracewell

The second most common oak indigenous to the Dish area, blue oak – deciduous, with picturesquely twisted branches – is often assumed to be valley oak when seen from a distance, whether driving past the foothills or walking their trails, even by those with some familiarity. But it doesn’t attain the great height and size of that species, and its compact, dome-shaped crown can usually be recognized from afar by the trained eye.

The leaves appear as if someone had been asked to sketch – within a second – the rough outline of a leaf with wavy edges: irregular, each one quite different, the lobes shallow if present at all. They emerge a tender green in spring, harden through the season, and by late summer display the distinctive blue-green of their upper surface, the result of a waxy coating that helps them withstand the blistering heat of the Great Central Valley foothills.

Blue oak also dots the Outer Coast Ranges, including the foothills of our Santa Cruz Mountains, extending right into campus proper, especially West Campus, where venerable indigenous patriarchs still stand, drawn and identifiable on 1880s surveys of Stanford lands: a splendid tree in front of Dinkelspiel Auditorium, another behind Rogers House, a pair where Lomita Court leaves Lomita Drive, a group south of the barbecue facility at Lagunita, and numerous others in the parking lot north of the O’Donohue Farm and near Los Arboles Avenue.

Thousands of blue oak acorns planted since the mid-1980s in the Dish foothills and on campus by Magic have reportedly performed “abysmally,” in stark contrast to valley and coast live oak acorns. Where they survived, they have grown slowly. At Jasper Ridge blue oak saplings remain stunted in what is despairingly nicknamed the Bonsai Forest – a patch of sandstone substrate at the north end of exposed ridgetop grassland at the Preserve’s eastern end, just beside magnificent mature blue oak woodland. Deer likely browse the tender new growth. Across the species’ range, regeneration has languished for nearly a century, hindered by intensive grazing, invasive weeds, and drought – even though it is regarded as the most drought-tolerant of California’s tree-sized oaks.

Blue oak hybrids

Blue oak hybridizes with valley oak (Q. lobata), accounting for as much as five percent of native oaks in the Dish area. The hybrid is named Q. ×jolonensis, after large trees seen at Jolon, Monterey County and its environs. The name Jolon, once explained as “valley of dead trees,” is more recently interpreted from the local Salinan dialect as “it leaks,” likely referring to a local seep or spring. The characteristics of Jolon oak – including bark and crown form – vary widely, with each tree showing its own mixture of the two parent species. The largest on campus is just west of the immense Torrey pine at the northwest corner of Palm Drive and Arboretum Road. The southwest corner of Forsythe Hall was clearly designed around the tall Jolon oak there. Numerous others can be found in the Golf Course, along with blue oak. Jolon seedlings have sprung up among the manzanita bushes at the southeast corner of the parking lot north of O’Donohue Farm, no doubt from the large native valley and blue oaks in that lot. The Jolon closest to the Bay in our area – and one of the largest – is in Palo Alto near the east corner of El Camino Way and West Meadow Drive.

Blue oak may also cross with Q. durata; both belong to the white oak section, though Q. durata is evergreen. A small tree on the left of the driveway at 70 Pine Ridge Way, Portola Valley may be such a hybrid; it mostly retains its leaves in winter. A curious tree at the southeast corner of the Papua New Guinea Sculpture Garden does the same, and may be a similar hybrid. From there to the south of Windhover and beyond into the parking lot are scattered a dozen or so blue oaks that look to be native.

Illustrations: Jasper Ridge plant photo archive.