Doug's Mountain Journal
A Chronicle of Natural History on San Bruno Mountain

Doug Allshouse has been writing his seasonal Mountain Journal for many years. It appears in the quarterly newsletters of the Yerba Buena Chapter of the California Native Plant Society (CNPS). We are very pleased to share his reflections on the natural history of the Mountain. Together with David Nelson, he is writing The Natural History of the San Bruno Mountains. The book will be published by Heyday Books.

Summer on the Mountain is a bit quiet and a time to catch one’s breath after a busy spring. But it is prime time on the Daly City Dunes where we find the rare and endangered San Francisco lessingia and spineflower in full bloom just as the dunes’ four species of sun cups or evening primroses (whatever you prefer) are winding down. The first two are Camissonia contorta, plains evening primrose, and sandy-soil sun cup, C. strigulosa). Both have flowers so small, 6-7 mm, that they are easily missed, and their leaves are thread-like. The only difference between them is the minute hairs on the stems. Are they perpendicular to the stem (contorta) or pressed to the stem (strigulosa)? The other two are now in the genus Camissoniopsis, C. micrantha with a medium-sized flower, 6-9 mm, and California sun cup, C. bistorta) with a larger flower, 12-15mm. An astute botanist is thinking aloud that C. bistorta is a southern California plant, so what is it doing on an isolated, 125,000-year-old dune system? I don’t know how it got here, but it keys out to bistorta and until someone tells me differently, I’m going with it.

On MLK Day the County sponsored a volunteer work party and an area between the Old Guadalupe Trail and the upper Bog Trail was planted with native plants. Each plant species is assigned a color and pattern of field tape, which is tied to the top of a meter-long bamboo stick and stuck in the ground. One June morning, as I was walking by those markers a male Song Sparrow was climbing up the stick. Imagine this, he is perched sideways and leads up with his right foot and places his left foot a bit below it, and repeats this shimmying motion until, finally, he is perched atop the stick and above the tape. At this point he tilts his head skyward, utterly full of pride about his accomplishment and, like Caruso, belts out a beautiful song......and then promptly flies to a wax myrtle and sings again. This is free entertainment and comedy at its best as only nature can provide.

As we endure our typical summer of fog, it’s a good time to remember that many plants on San Bruno Mountain depend on this summer regime for survival. Summer fog brings water in the absence of rain, contributes water to the ecosystem by fog drip, increases humidity and decreases evapotranspiration, increases foliar uptake, decreases air temperature, and reduces solar radiation and soil evaporation.

Fog drip is caused by fog condensing on the leaves of trees, and even scrub, and dripping to the ground. The most significant example can be felt, seen, and heard in Fog Forest, the large plantation of eucalyptus and cypress trees encountered at the main parking lot and along the Day Camp Road and the Old Guadalupe Trail. The added moisture from drip supports epiphytic leather ferns (Polypodium), mosses, and creates boggy conditions to the delight of seep spring monkeyflower (Mimulus), horsetails (Equisetum), speedwell (Veronica), and water parsnip (Oenanthe). Near the summit of the mountain Monterey pine needles intercept moist fog and bathe mosses.

As strong winds blow fog over the summit ridge, a low-pressure area is created on the lee side causing fog to curl downward and back toward the ground, which moistens the mosses. Fog drip can add many inches of additional moisture to the measured annual rainfall. All our native members of the Ericaceae family (manzanitas, madrone, and huckleberries) live within a few hundred feet below the main ridge and take advantage of this added moisture.

Fog also increases the humidity and decreases evapotranspiration. Moisture is lost by plant and soil evaporation. The leaves lose water through surface pores called stomata and about 98% of the water uptake of roots exits through the stomata. The increased humidity slows this water loss. The presence of fog also decreases the ambient temperature, slowing evaporation. When you look west from Bayshore Boulevard and see the summit radio towers completely blanketed with marine fog and wind, there is good reason to believe that it’s darn cold and wet up there, and the sun is obscured. When it’s a chilly 55 degrees on the summit it can be a scorching 105 degrees in Livermore, or a balmy 70 in downtown Brisbane.

Many species of plants can absorb water directly into their leaves. Some species on San Bruno Mountain that are noted for their foliar uptake are sword fern, leather fern, California polypody, evergreen huckleberry and madrone. Mosses and lichens also obtain all their water through foliar uptake, and one genus of lichens, Niebla, occurs only on rocky outcrops in full face of the foggy marine winds. The name of the powerful Piemontese red grape of Barolo and Barbaresco fame, Nebbiolo, is derived from the Italian word for fog, nebbia.

I keep a professional rain gauge on my deck, which keeps track of the rainfall I tell you about throughout the year. The surface area of the collection funnel is about 9 square inches. The amount in my gauge that fog provides is not as striking as what falls to the ground from trees and scrub because they have thousands of leaves to catch more moisture. But on average, fog contributes about 2 inches of rain a year in my rain gauge. The months of July and August from the four rain seasons of 2014-15 to 2017-18 produced in order, 0.65”, 0.51”, 0.91” and 0.72”, all because of fog. Triple or quadruple those readings for what falls in Fog Forest. It truly is a coastal rain forest. This year from July 1 to August 2 we had 16 days of captured precipitation for 0.30 inches of fog rain.

The poison oak is turning red and exposing its greenish berries. The pink everlasting (Pseudognaphalium ramosissimum) has yet to show its gorgeous pink blooms in full color. Besides being my favorite cudweed, its minty-buttery aroma is seductive. It is also a larval host plant for the American Lady or Painted Lady (Vanessa virginiensis). The coffee berries are still green and a bit away from their mature black color. And I’m waiting to see the bright-white berries of snow berry fruits, which will come with the shorter days ahead when the bushes shed their leaves, exposing those tiny snowballs at the end of bare twigs. But, to my delight, the creek dogwood fruits are beginning their show.

Autumn is coming, I can hear it calling, “Doug, don’t despair, Indian summer is right around the corner.”

See you on the mountain...