Introduction
You find yourself at the lowest point in a green-space nestled between the peaks of the waves of San Francisco urbanization. Glen Canyon has existed through many incarnations of history. A place for recreation and escape from the sidewalks, Glen Canyon Park epitomizes the compromise between native organismal diversity and the terraforming of industrial development and incursion of invasive species. As you move through the park, consider how this novel ecosystem has emerged from this alchemy. Glen Canyon is not a pristine California landscape, but it is functional and fabulous, and its existence serves the betterment of people who visit here, it is a haven for native plants, and it serves as an important habitat corridor for animals on the move.Walking up from the Bart station, it may be a surprise to find the tide of boxy houses giving way to an open island of grass and trees. How this park came to be—and why the swell of the city stops at the intersection of Bosworth and Elk—speaks to the history of this incredible place.
Giant Powder Company
In 1868, this area was the short-lived home of the Giant Powder Company, the first site in the United States where dynamite was produced. Dynamite—which was invented by Alfred Nobel the previous year—was patented as a safer alternative to nitroglycerine which had killed Alfred’s younger brother four years earlier. Nobel would make his fortune from the invention and production of dynamite. While Nobel saw the application of his products in mining, dynamite would be adapted for use in war. Nobel became burdened by a heavy conscience, which was exacerbated by a misprinted obituary that eulogized Nobel as a “merchant of death.” Nobel donated over 90% of his fortune to the Royal Swedish Academy of Sciences to create an international award program to support the work of scientists, thinkers, artists, and changemakers who sought to improve the human condition. Though dynamite was safer than nitroglycerin to ship and handle, manufacturing was just as deadly. People were not keen to build their homes near the factory. In 1869 the Giant Power Company was destroyed in an explosion, and nine workers were killed. The plant was relocated to the edge of the city in what is today the Outer Sunset district. A year later, that plant also exploded. Giant Powder would later be forced out of the city entirely. After that, factories were constructed in multiple locations in Berkeley, Albany and Pinole. Each factory met a similar fate.Dynamite that was manufactured here was mostly sold to mining operations and prospectors in the Sierra Nevada and Shasta Trinity Mountains. The cost of the intermittent, devastating incidents at the factories was outweighed by lucrative sales. By 1852, the easy-picking of gold from panning and sluice box had come to an end. Mining operations consolidated into the hands of the well-financed barons and companies who could invest in hydraulic extraction. Hydraulic mining relied on high-powered jets of water that obliterated gravel bars and river banks throughout the state. Extraction of the gold through this process relied on use of mercury. Today, the effects of hydraulic mining are still evident in the Bay Area. Three feet of sediment was added to the North Bay, brought as runoff from the state's northern drainages. Mercury that washed down the rivers and streams continues to haunt the communities where it settled. Many of the low lying communities that hug the bay shoreline were built on the dredges of the bay. Mercury soaks the soil that was used as infill, and this mercury continues to magnify through the food chain, polluting the fish that people eat and poisioning osprey and other predators.Dynamite, like hydraulic mining, was physically destructive to the landscape, but in its application, mercury was not required. The portable and affordable explosive provided economic opportunity for small-holders who had been boxed out by the big hydraulic operations. The windfall of dynamite manufacturing in California—as well as the gold, ore and other minerals extracted from the earth—accelerated the growth of the state economy.
Eucalyptus
There are many conflicting stories about why eucalyptus were first brought to the Bay Area, but every story ultimately returns to the tree's ability to grow fast and grow big. Blue Gum Eucalyptus, seen here, were first introduced to the region on a large scale for timber production. These native Australian trees grew straight and tall in the fog-drenched Mediterranean climate of the Bay Area. But Blue Gum Eucalyptus proved unwieldy to harvest and mill. The dense wood is tough to cut and heavy to move. Saps and terpenes locked in the wood were hard on both the saw and the workers. And the wood, when cured, is wont to split and fray. Look at the bole of one of the trees, and note how it spirals upward as it grows. If you were to follow the path of water from the roots to the canopy you would wrap many times around the trunk. The twist of the wood gives the tree stability. It is also an adaptation found in many plants that evolved in drier parts of the world. When the timber barons learned this about the tree, they cursed the flaw that made the blue gum’s hardy growth a reality.The trees at Glen Canyon were not planted for timber. Because so much of the landscape here was devoid of trees, and the eucalyptus could quickly take root in the drylands, eucalyptus was planted for shade and windbreaks. The trees also were planted to provide the people who lived here cover from the sights and sounds of the factory that was built before the maze of houses. Eucalyptus at this site and at other Giant Power factory locations mark the perimeter of the old dynamite plants. The trees were planted by the company to create a shield to buffer neighboring properties and homes against noise and the risk of explosion. Yet the volatile oils of the eucalyptus—the phenolics and terpenoids that give the tree its pleasant fragrance—could carry a conflagration and spread the fire beyond its catastrophic origin.The history of eucalyptus in California is complicated. In the early 20th century artists incorporated the beautiful, gestural forms of the trees into their painting and woodblocks. The eucalyptus became synonymous with the bucolic landscape of the California Coast. Having adapted to a similar ecology in Australia, the trees appear at home here. The pale blue and olive leaves match the palette of the chaparral, and like the sage and oak, the muted colors reflect the heat of the sun. The leaves hang from the branches so that only their edges feel the intense mid-day sun, with the rest of the leaf shielded by the oblique angle. The proud silhouette of the tree flattens like the anvil of a thundercloud, similar to a Monterey cypress. The branches perch atop tall bare trunks like the pruned bole of a coastal pine. The shapes and colors of these trees tell the story of adaptation to drought and fire.When these trees were planted here, it was doubtful there was much native life. The Spanish and later Mexican ranchers had transformed the dappled landscape of native grasses, wildflowers and coastal brush into a wide expanse of annual grasses that came in the feed and guts of the cattle they brought with them. As the eucalyptus grew, other plants germinated around them. These plants could grow here because of the environment created by the tree. Over time the grassland was replaced by the forested ecosystem you see here today.
Succession
In ecology, we call the gradual and unimpeded replacement of one ecosystem for another succession. Ordinarily, the path of succession follows a replacement of more ephemeral species, such as annual grasses and forbs, with more hardy perennial species such as chaparral, oak woodlands and conifer forests. Early American ecologists saw succession as uni-directional with the replacement of ecosystems culminating in what was called a climax community—a maximally stable, maximally complex system. The concept of climax community has since been discredited, but it has had a profound effect on how American scientists managed our open spaces, particularly with regard to wildfire. Today, scientists recognize that all ecosystems, particularly those in dynamic places like California, exist on a sort of conveyor belt, with disturbances and periodic interruptions creating a mosaic of systems that diversifies the living landscape and creates resiliency.Here the eucalyptus trees are being replaced by redwoods, optimistically planted by the County of San Francisco. Like the eucalyptus, redwoods are adapted to tolerate fire and can be resourceful when it comes to drought. But the redwood may feel less at home here than the eucalyptus, in spite of its California roots. Redwoods thrive where there is water, and while native to California, redwood trees were unlikely to have grown in the sandy soils of the San Francisco Peninsula. Like the eucalyptus, the redwood self-prunes its lower branches as it grows above the lick of ground fires that historically swept the understory. Unlike the eucalyptus, the redwood’s needles are dark and dense and they face the afternoon sun. This is a plant adapted to cool, shaded places, not the stark bright slopes of San Francisco.
Solar Totems
Before you are three redwood logs. These logs serve as a record of the past in two ways. In the first, the wood itself inscribes a physical and chemical history of the passage of time. The study of tree rings, or dendrochronology, is one of the most common ways of exploring the past with plant cellulose, in particular the plant’s wood, or vasculature. In the anatomy of a plant, water must travel from the roots to the leaves because water and carbon dioxide from the atmosphere are the building blocks of sugars which is both energy and the basic units for cell construction. Those sugars also need to get to the roots to build, maintain and feed the root cells. Just like in any supply line a complex transportation network has emerged to facilitate this exchange. This network is the vascular tissue and can be divided into xylem (wood) and phloem (bark). Looking at a cross section of a tree, the rings you see are a concentric pattern of xylem tissue that the plant uses to move water from the roots to the stems and leaves. The appearance of rings emerges because the xylem cells produced across a given year are of different diameters. During the growing season, when there is more access to water and the need for transport of that water, the xylem cells grow to a larger diameter. These bright bands are separated by darker areas where the xylem cells grow smaller and in greater density. In the flux of rainy winters and parched summers, each ring represents a year of growth. The ring patterns are not even, and the interval between rings fluctuates between thick and thin like the lines of a barcode. This is governed by environmental and climatic factors. Where these patterns can be found to repeat between two or more trees, we can use the cross sections to peer into the past. By matching the pattern of tree rings dating back thousands of years, archeologists have been able to determine the age of ancient pueblos in the American Southwest. A study of xylem chemistry can tell us specific details about climate conditions at any point in time during the tree’s life. Stable isotope ecology has been important to our reconstruction of past climates and our understanding of anthropogenic impacts on the natural world.But another meteorological history is also inscribed into the wood, in the form of the burnt black lines that run perpendicular to the grain of each log. The lines that cover each log represent the sunlight over a single year. The installation, created by artist Charles Sowers, represents three years of records. To create the burnt line, Sowers constructed a sort of magnifying glass. Each day, as the sun tracked across the sky it would focus through the lens of the glass and burn these black marks into the wood. Notice that each line is not complete or as deeply etched. This indicates times when the sun was blocked by fog, clouds, aerosols or physical aspects of the landscape. Each line chronicles a single day. The logs scars have been oriented south. In the Northern Hemisphere, far from the equator the sun tracks it’s daily arc ever-so slightly toward the southern horizon. This is most noticeable in the winter, when the sun’s zenith does not fall directly overhead. Looking at the totems, do you notice any patterns? When are the sun’s rays the most intense during the day or throughout the year? This totem was etched nearby in the Twin Peaks neighborhood. How do you think this pattern would change if the logs were positioned down in the Glen Canyon, the clear-skied Mission district, or in the forever foggy-swept outer-Richmond neighborhood?
Bat Boxes
Even though the eucalyptus and some of the other species found in this grove are not from California, they can still create habitat for the wildlife that lives here. On a spit of land overgrown with buildings and pavement, there are few places for the small animals to take shelter. Voles, deermice, chorus frogs, fence lizards, and songbirds can all be found in this park. If you listen you may hear the rustle of a Brown Creeper as it balances on the dry curls of eucalyptus brands, or you might hear a Spotted Towhee sifting the fallen litter for grubs and goodies. The trees provide the structure in which birds roost or find nesting materials. The trees offer protections from threats on the ground.City stewards, in their upkeep of the park, have added bat boxes to the sides of some of the trees. If you look above on the tree trunks, you will find trim wooden frames shaped like a postbox. At the base of each box a cavity is open. Though only an inch or two wide, this crevice is ideal for bats. Over the past decade, bat populations nationwide have been decimated by a fungal infection called white nose syndrome. As the disease makes its way into California, researchers are hopeful that places like Glen Canyon will be a foundation for rebuilding dwindling populations. In a partnership between state and federal agencies, the USGS regularly monitors bat populations across the Bay Area via radio telemetry, tracking the movements of tagged bats.
Islay Creek
Islay Creek takes its name from a Salinas word for the native cherry that grows here. The Creek which originates against the southwestern slopes of Twin Peaks was once the city's largest naturally occurring body of water. Not far from here, a Ramaytush Ohlone village stood for thousands of years, fed by the waters of this creek and the abundance of plants and animals that thrived along the stream. The wide, short channel of the creek was so fertile that as many as 10,000 people made their home here. The Spanish expelled the natives, turn loose European cattle along the banks. Islay creek would later support the pasturage of the dairy farm of José de Jesus Noe, for whom Noe Valley was named. After the Mexican-American War, this would become an epicenter for German and Swiss immigrants who grazed dairy cattle along the length of this creek.Glen Canyon Park was altered dramatically by the urban growth of the 19th and 20th centuries, but native species still take refuge along the creek bank. Look closely and you'll find the San Francisco forktail damselfly, one of the rarest damselflies in North America due to anthropogenic habitat modification. The Bay Area is rich in many species that are found in few other places. The protection of rare, threatened and endangered species such as this damselfly are one of the reasons why these urban parks are so valuable. With its slender green iridescent body, the forktail damselfly may be seen flexing its wings as it perches on low branches beside the creek. The damselfly needs to be around fresh water because in its earliest life stage, as a larva, it requires cool streams.In the waning years of the Gold rush, the creek became a dumping ground for byproducts of the meat processing plants that occurred at the outskirts of the growing city. The creek became putrefied. To deal with the problem, after the 1906 earthquake, the city buried the creek under the rubble of the city. While much of Islay Creek remains under subdivisions and roadways, the creek reemerges at the bayshore. There, the lower reaches of the stream that at one time formed a meandering slough through tidal marshland, has been straightened into a wide channel that throughout its recent history has been a harbor for small shipping vessels in the Hunters Point neighborhood of San Francisco. Like much of the creek, Hunters Point carries the legacy of ecological contamination, and the soil with the naval shipyards at the mouth of the creek is a superfund site. According to the EPA, the soil, dust, sediment, surface water, and groundwater are contaminated with petroleum, pesticides, heavy metals, polychlorinated biphenyls, volatile organic compounds, and radionuclides. Soil at the site also contains naturally occurring asbestos and gold-rush era mercury and heavy metals. Quite a stew.Nevertheless, water from Islay creek supports plants that stay green throughout the year. Unlike the dry slopes on either side of the canyon, in the presence of the creek, perennial plant species abound. We call the verdant ecosystem typical of stream corridors a “riparian” habitat. Not only does the creek provide water, but in these basins, it moves nutrients from the surrounding landscape, accumulating the building blocks of plant life. Temperatures are moderate next to the creek channel. During the day, when the city bakes, the creek is shaded. The warm air rises through the ravine of the canyon displacing the cool air of evening. By morning the warm air has cooled at the higher elevations of Twin Peaks and will reside in the canyon throughout the day, until the evening cycle is repeated. This process, known as cold-air drainage, is familiar to anyone who has spent a day by the river and felt the strong warm breeze develop in late afternoon.We can see in Glen Canyon three strategies for coping with the long dry summers of the California Central Coast. The annual plants set seed between winter and spring, escaping the driest parts of the year by dying. In their short life, the adult plant will never know the summer. The riparian species instead centers their lives around location. Because of the water and moderate climate found in the riparian strip, the plants that live here decouple from the Mediterranean climate. A final strategy can be seen farther away from the creek. Woody plants that stay green year-long grow slowly and cautiously. In their austerity they find ways of surviving the dry summers, and they rely on association with microbes and the thrifty use of fog-drip to sustain themselves.As you walk, notice that in some places along the creek there is very little vegetation beside the water. In other places the creek channel will be thick with willow and green herbs. What do you think causes this variation? How might overstory species like eucalyptus impact what grows beside the creek and how might the footsteps of people off trail affect the vegetation.
Invasive Species
As a generalist, invasives must be able to tolerate a wide range of environmental conditions, otherwise they would be restricted in where they can grow and would be of no concern. And in order to be able to spread to these places they must be able to easily disperse. Easy dispersal means a possibility, and probability that seeds will travel over greater distances. Adaptation to disperse over great distances isn’t of value if the organism can’t thrive in those new habitats. So these two attributes go hand-in-hand. Rapid reproduction is another important attribute of the invasive, because colonization often comes down to the number. Volume of offspring will dictate the likelihood that a population can establish itself and gain territory. But not all invasives reproduce in this way. Some aggressive varieties of Cape Ivy and Clematis, that you can find in this park are sterile. Other times, an invasive species may not be compatible with the local pollinators. So asexual reproduction, through bits of stem, bulbs, or runners is another valuable strategy associated with highly invasive plants. Because reproduction via flowers and fruit is also energy expensive, plants that can spread clonally have an added advantage in terms of reproductive cost. Rate of growth is also worth considering. We find in many systems that invasive species, like the blue gum eucalyptus or the Armenian blackberry, with its thorny, hexagonal vines, are quick to colonize habitats that are free of vegetation such as after some disturbance. To be able to quickly disperse into a system and dominate that system is an important strategy.We also need to include in this conversation the idea of introduction. There are varying definitions of what constitutes an invasive species. For most people, what comes to mind are the transplanted species that have come from somewhere else, maybe an escaped ornamental, agricultural species, or hitchhikers on your pant leg. These introduced species bring with them novelty. That novelty means there may not be a native species that will consume that species (thereby keeping it in check) or it may have some sort of strategy that gives that species an advantage, (what is sometimes called the Novel weapons hypothesis.) But we must also consider that some native plants can also be considered invasive (or weedy) within their native range. In California, the USDA considers shrubland species such as Baccharis pilularis (coyote brush) and Douglas-fir which grow prolifically along the central and northern coast to sometimes act as invasives, even while in their native range.Here, rather than the imbalance and invasiveness being the result of the novel qualities of an introduced species, the imbalance that leads these native species to be considered invasive is a result of changes to the system itself. For example the loss of pleistocene herbivores, a changing fire frequencies and intensities, or human mediated dispersal can prevent the natural reductions of these prolific species. In the absence of these disturbances, or the presence of new variables like the habitat fragmentation found in urban wildland encroachment or certain forestry and agricultural practices, these plants are rapid colonizers that may displace other native life or ecosystems. So here what we are introducing is some variable that changes the ecological paradigm allowing for imbalance in what species will succeed.Surveys for invasive species known as EDRR of Early detection, rapid response is one way that land managers stay vigilant. If we can identify an invasive species early, we can root it out and mitigate the need for expensive, labor intensive or destructive invasive species management approaches to abatement of these undesirable plants. If you are interested in learning about weeds to watch out for CalIPC, the California Invasive Plants Council website is a great place to start. They have lists of all the known offenders.
Grasslands
The natural history of the native grasslands of the California coast is a history of interruption, disturbance, and change. The grassland garners no epithet for an enduring presence—it is the antithesis of stability and permanence, existing on a continuum between bare soil, coastal scrub, and oak woodland. Words such as old-growth, virgin, or decadent do not apply to the coastal prairie as they do to an old intact forest, because the grassland is a forest on stand-by, a chaparral under construction. Coastal meadow is an ecological scaffold, destined—if left undisturbed—to morph into the systems that surround it. For all these reasons, there is much uncertainty as to how we define and discuss grassland ecosystems: even the most focused snapshot of a meadow must be blurred by the transient motion of the space.Grasslands are pivotal to the health of native diversity. Native grasses, and the habitats they create, provide unique benefits to adjacent systems; they are a cornucopia for wildlife. Grasslands host a diversity of small mammals and their predators, and they are an important stop along the migratory routes of raptors. But native grasslands are also a repository for rare and endemic plants. Grassland ecosystems hosts 90% of California’s rare and endangered species, and 40% of the native vegetation found in California is in grasslands. When you consider the moderate, mild ecosystem of a coastal grassland, it's little wonder why it is a nursery to so many different organisms, and why it constantly cedes and capitulates to woody vegetation. Grasslands form the bottom rung of a successional ladder that leads to many of the other ecosystems we find in California.Before the Spanish carved the hills into ranches and townships, the prairies of the Central Coast were maintained and created through the carefully tended fires of the many tribal groups that made this coastline their home. In a distant time prior to the extinction megafauna, the massive Pleistocene grazers maintained the open grasslands with their bulk and appetite. Scraped bare by the scars of fires, landslides, and erosion, new meadows emerged in the wake of disturbance—breaching the scrub—and replacing the areas overgrown by forbs and sage-brush.While fire and large indigenous herbivores had both been extinguished from the San Francisco Peninsula, cattle ranching filled this niche, expanding grasslands for more than 100 years. But ranching was unkind and stark in its pruning of these meadows. Brought in the bellies and on the hooves of the cattle were many non-natives plants. The loss of these historic features upset the pattern of this landscape, and that disruption was further magnified by impacts of habitat fragmentation and non-native, introduced species that have since proliferated in these spaces.As the land has been allowed to rest, you can see a patchwork quilt of native diversity returning, integrated amongst the sun-bleached European annuals. Looking out toward the West-facing slopes, you can spot in the gullies and stoney outcroppings an archipelago of green islands. Low growing coyote brush, a hardy coastal variant known as Baccharis pilularis consanguinea, forms flat, even rings, radiating out from a single plant that has grown into an ever larger community. Under the watchful eye of hawks, these patches of brush provide safety for the anxious quail and rabbit that inhabit these meadows.For restoration ecologists and land-managers, piecing together a historic and sustainable system that is dominated by natives is a bit like solving a jigsaw puzzle without the picture on the box for guidance. Even worse, due to local extinction, some pieces may be missing, and in heavily urbanized areas, the changes to the abiotic factors have make the puzzle still more complex.
Geology
The spurt of jagged tumbled rocks before you are the crumbs leftover from the devoured Farallon plate which melted and subducted in the late Jurassic—collateral damage to the collision of the North American Continent and the Pacific Plate. Here, we are looking at Marin Headlands Chert, a hard gray stone that cleaves into sharp rectangular pieces with sufficient force. We can find this chert all along the boundaries of these colliding plates from the Monterey Bay to Point Reyes. The chert you see in this canyon, is the same rock that crowns the peaks of many of San Francisco’s highest summits, formed at the bottom of the ocean—sediments compacted under the weight of water. As you walk this canyon, look to the places where the soil is too or steep for grass to grow. The bathtub ring of the canyon reveals rust red earth and rock that snakes and folds back upon itself. This rock is also the outcome of this long-waged geological battle and is called radiolarian chert. Here, the reddish color is indicative of the iron, other oxidizing minerals and organic pigments found within this dense material. The name of this cherts barrows for the radiolarian, and protozoa that are found in great abundance with this rock. Because of the cherts strength it has been a popular spot for bouldering and top-rope practice for many years. As early as the 1930’s outdoor clubs and universities used these rocks especially the outcrops known as the Miraloma to train for expeditions.
Twin Peaks
The second highest summit in San Francisco, The wide rolling hills of Twin Peaks stands at 925 feet. To the Spanish who ranched these areas, the equivalently sized summits, now named Eureka (to the North) and Noe (to the South), were called Los Pechos de la Chola or the Breasts of an Indian Maiden. On most days, as the later afternoon fog rolls in it catches like wool in the comb of this ridgeline, promising the sun's warm golden rays in the neighborhoods of Noe Valley and the Mission to the East. As the fog is carried up over the grass and chaparral of the southwest slopes it snags on every blade of grass, leaf or branch in its path. In the long dry parched summer months, the fog offers relief. Walking to the summit in August when the fog hangs heaviest along the coastline, the summit of Twin Peaks is often damp and dewy.Some of the fog and the rain that the peaks collect will evaporate, some is used by hardy perennials that cling to these slopes and some of the water will percolate into the soil and make its way to Islay Creek and Glen Canyon.
Closing remarks
Here, under the shadow of Twin Peaks we concluded our hike. In walking this trail we have explored a space that is modest in its importance. Glen Canyon shows us the dramatic resculpting of the local topography and ecology. Glen Canyon and the waters that lead from this ravine into the Bay have been irreversibly transformed. And yet, this park remains a place of growth and hope for native plants and animals. The trees, vines and shrubs that were introduced here may not be native, but they could not be disentangled from this emergent system without destroying the special habitat they function to create. Here, in the heart of the city, this park is an island. The diversity both native and non-native is bound by a sea of houses and roads making this place a special and unique retelling of the centuries of history that have brought this park into being
