Mapping an Invasive Species? Eucalyptus in Berkeley, CA

The mapping of invasive species on land or sea provides one of the clearest ways of visualizing our shifting ecosphere:  in mapping of the threat of invasive marine species to coastal ecosystems, Michelle Slosberg developed her marine map of the spread of invasive species in 2011 when an undergraduate at MIT.  She did so by mapping sites of high-risk areas of marine “invasions” along coastal waters, geo-referencing data on ballast water of ships to determine the risks of the presence of invasive species that were carried by ships from one ecosystem to another and specific to the northeastern coast of the United States.

Invasive Marine Species Mapped

The vectors of travel in ballast water are shockingly widespread, and the container ships traveling from China to across the Pacific, or along the Atlantic, increasingly import species accidentally that are rarely noticed until they propagate:  the number of harmful alien species mapped worldwide have so grown that some 84% of the world’s 282 marine ecosystems are documented to contain invasive species, and in 2008 coastal regions with harmful alien species were dense in ecoregions in the Mediterranean, in the North Sea, and along the California shore and Hawai’i.


Blue waters note areas where fewer harmful alien species were found to dwell.

The complex vectors of marine migration of alien species have only begun to be mapped, but heighten anxieties about the definition of “national waters” or marine borders, increased by shifting temperatures of ocean habitats and lend new meanings to the maelstrom of modern life:

Major Pathways of Marine Invaders

Fears of the heightened potential of geographic relocation of species by mapping points of transfer paths of airline flights offer by linking regions of similar temperate zones:

map invasive_species

The category of the “invasive” redraws spatial boundaries–and inflects taxonomic identifications–to suggest a shifting map of the natural world, combining nature and culture and resisting the stability of a fixed map.  But mapping the spread of “invasive species” often charts less an invasion in early stages of development than a process of resettlement, as in this map of wild carrots that flourished after they arrived in our national borders 250 years past, but still classified as weeds in mid-western and north-western agricultural fields:

WIld Carrots in US

The wild carrot seems relatively benign, and was introduced at about the same time as domesticated carrots to US farms. But the introduction of eucalypts from New Zealand redefined the Bay Area, where I live, and the exploding trees that are native to Australia–where they are known as “exploding trees” and played such a large role of combustibility in the recent bushfires where they provided exploding fire balls in the air that led to the advance of walls of flame when sustained drought increased the volatility of what became an explosive landscape, a flammability transmitted through the flammable fumes created by vaporized eucalyptus oil.

Australian residents have long called the native species “gasoline trees,” rooting them in an anthropocentric landscape or imaginary, whose highly combustable oils are released in fires, and whose explosions–sometimes sending parts of their crowns to spatially removed sites–create their ability to magnify grass fires into explosive threats of devastating scope, ramping up the danger and scale of the bushfire in what seem spontaneous combustions geographically removed from one another without any predictable pattern. The explosion of euclyptus crowns that can travel fourteen miles in the air increased not only the intensity but geographic distribution of the Australian fires. But the explosion of eucalypts immediately known in the Bay Area was revealed in the Oakland Hills Fire of 1991, when the explosion of blue gums contributed some 70% of the energy during the devastating fires that destroyed upwards of 3,000 homes over days, leading to calls to remove the tens of thousands of blue gums and other non-native species from the ridges that had so long seemed to be a part of the local landscape for Northern California residents who had celebrated their health benefits soon after since their arrival in the late nineteenth century. While they soon exploded, the density of thin Eucalyptus crowding once open spaces raise questions of whether they belong or don’t in this landscape–and what sort of roles the eucs have and what they are even doing there.

Dan Rademacher, Eucalypts North of Claremont Avenue, East Bay

The danger of labeling an “invasive species” by mapping its lines of incursion is to constitute a category that elided the existence of external environmental influence.  But how to chart the undeniable impact of commercial practices or climactic shifts that serve to facilitate the geographic dispersion of an ‘invasive’ species?   The piles of perfumed litter that fill the roadsides of many of the East Bay hills, cascading downhill into the road, provide a nice remembrance of nature, but also are undeniably dangerous kindling for future potential fires, releasing oils in the air not only powerful in fragrance but combustible. And the multitude of Eucalypts that we see locally echoes the spread of blue gums and other eucs across delicate habitats across Malawi, South Africa, and Chile, crowding out local species, as in Patagonia; these large fast-growing plants of Australian origin suck up water and cast shade over other plants, and foliage, crowding out other native plants, in ways that don’t create calls for nativism–but biodiversity.

What of the habitats they afford or create? In the East Bay, the euclypts that crowd the hills are improvised shelters and sights of nesting for the elevated platforms that red-tailed hawks take as their eyries, advantageous for their height and stability to allow them to swoop down, and the great horned owl who often succeed them in the same sites of roosting. But the benefits that eucalypts afford these larger predators are cause for worry in themselves as creating imbalances in the delicate dynamic of the biodiversity of any place, as Allen Fish, who directs the Golden Gate Raptor Observatory, and has noted the advantages that shelter in tall trees can give to some species over those that, as raptors, occupy more specialized ecological niches: the eucs may often afford the larger avian predators a privileged position to swoop down into the smaller birds such as kestrels, spotted owls, screech owls, saw-whet owls, and and Coopers’ hawks, or even provide habitat for red-tails who will crowed out sensitive species from the grasslands and savannah, including long- and short-eared owls, and barn owls, that provide a fundamental role in habitat. How to map the effects of such invasive species in dynamic ways, as altering the ecosystems we often separate from maps?

Indeed, mapping the species’ ‘invasive’ nature–or even the term “invasive”–effectively renders transparent the identity of the pernicious plant as a bacillus, deflecting agency from economic practices to the collective species labelled nonindigenous; such maps become distorting lenses to foreground effects of a species’ dangerous tendencies to spread over space that remove blame (or responsibility) from the economic or climactic change to locate it in the species it tracks, and indeed flatten temporal change:  maps of invasive species prove a perfect example of the strategies for the power of map-signs to reframe the experience of nature illuminated by Denis Wood and John Fels.  A classic case is the dangers of rapidly reproducing predatory lionfish through the Florida keys, which having migrated or “arrived” from warmer ocean habitats threaten to destroy local marine life, whose presence can be highlighted, removed from its environment, in a striking map of its marine spread:


This sort of cartographical compartmentalization circuitously brings us to the battle over local eucalyptus trees, conducted largely around the invasive nature of nonindigenous Tasmanian blue gums long rooted in groves in the landscape of Bay Area hills.  Invasive species of plants are nonindigenous plants that spread in uncontrolled ways to an area they have never lived and lack predators, creating environmental problems and contributing to the extinction of native species and animals.  But how long can a plant be present in an ecosystem and continue to be labelled invasive?

Although airline traffic, like routes of ships, expands the network and increases the speeds at which seeds migrate across the earth, increasing the vectors of moving invasive species by accelerating contact between regions that did not share borders, introduced species–some 50,000 now exist in the United States–is conditioned by the suitability of the environments they arrive–few of which are on the west coast, although the travel of weeds alone cost California at least $82 million per year.  The very virulence of terminology to identify plants and animals as invasive–perhaps the biological threats of a postmodern age–has conditioned how we see the landscape before our eyes.

Recent debates around the proposals to clearcut 22,000 non-native trees in Strawberry Canyon and Claremont Canyon reveal a pitched battle in the Berkeley Hills and Claremont Canyon around labelling the Tasmanian blue gum eucalyptus as ‘non-native.’  Whether or not the Tasmanian blue gum eucalyptus  (Eucalyptus globulus) is correctly labeled as invasive is not only a question of fact, however, but reflects how one maps the place of the towering blue gum trees in the landscape they have created and long lived–and how one maps them as signs of fire-risk.  The removal of the trees that cover a large part of the hills, especially on the west-facing hills of Berkeley and Oakland, from the environment when mapped for clear-cutting, revises their place in Bay Area landscapes, and the struggle that emerges among environmentalists and planners (or local constituent groups, since the division is not so clear) reveals a battle between landscape and map, or a naturalized landscape of welcoming groves and a firescape dotted with unwanted risks, but also offering transcendent moments of their own.


Many land-owners share deep-running concerns about the fire-dangers created by the branches, shaggy bark, leaves, and seed-pods, all containing highly flammable oils, and explosive proclivities of eucalyptus trees:   multiple vectors of encouraging fire-risk have led the tree to be demonized as primary culprits of the disastrous 1991 fire in the Oakland hills that destroyed so much property and claimed 27, as well as forest habitat.

The characterization of the tree as an invasive–and even as a weed–are all rooted in its change on the landscape, as much as unquantifiable expansion of fire risks.  None seem greater than the piles of as the bark that, shed, create a dry ground cover that inhibits future plant growth, and raises the specter of quickly igniting kindling that stimulate powerful underdrafts after its combustible oils ignite that would push a wildfire’s growth out of control, as updrafts push flaming bark ahead of the actual fire-front, onto the roofs of nearby houses, at the same time crown-fires spread the canopy of leaves create crown-fires among towering trees that carry the level of flames into the atmosphere.  Once their combustible oils ignite, leaves and litter are feared to fuel a raging fire, offering firewood as groves of Eucalyptus themselves explode and ignite.  Hence the fears summoned by imagined firescapes expanding by burning crowns and flaming bark thrown by winds that are provoked by those leaves’ presence.


So what are the abilities to contain this vegetation whose vigorous spread seems to obstruct the growth of other plants in the ground area they cover by displacing native plants?  Attempts to map areas for their elimination reflect the fears of property owners, recently saddled with newfound legal liability for responsible land management, and responsive to the availability of federal funds to land management in the hope that future fires would not consume the lands they manage or impinge on nearby houses, and create any suits of environmental liability.  If causing huge financial damages is hoped to be avoided, the question of legal liability seems to have been the primary factor that motivated further attention from large-scale land-owners as the University of California or regional parks.  Already by 1991, the University of California at Berkeley began to clear thousands of “invasive” eucalyptus within the purple section, as part of a larger ten-year plan to remove 25,000 trees from its property–or the grove in the below aerial view in the Claremont Canyon, in projects of “land management” directed to such a reduction of risk.

Claremont Canyon Fire Mitigation

In December 2009, these plans received a setback as FEMA denied four separate grants to the University of California, Oakland and the park system for $5 million to remove eucalyptus, pine and acacia trees from the ridges above Oakland and Berkeley, but plans to for clear-cutting some 82,000 Berkeley and Oakland trees, a quarter of which lie in the protected Claremont and Strawberry Canyons, to be followed up by 700-1400 gallons of herbicide in land belonging to Regional Parks.  Similar interventions clearing eucalyptus encouraged the large-scale project to clear-cut the eucalyptus from the hills–dramatically revising the landscape of the region to be reforested by “native” plants whose seeds may lie buried by eucalyptus litter, and would be re-introduced after careful extraction of each and every blue gum.

The hills were colonized and indeed filled by eucalyptus, and most especially the Australian import of the Tasmanian blue gums, around UC Berkeley’s campus, in Regional Parks that could be said to themselves litter the  Berkeley and Oakland hills–Tilden, Wildcat, Kennedy Grove, Anthony Chabot, Lake Chabot, Redwood, and Sibley–where the planting of eucalyptus replaced grasses and wildflowers that covered the region, as in this image of the stately eucs that provide posts for Kennedy Grove.

Kennedy Grove

Yet there is some evidence–not widely acknowledged–that cast the eucalyptus as something of a windshield whose presence in dense groves, by blocking winds, would actually fights wind-driven fire, acting both to break and interrupt the flow of the wind that bears the fire and as a screen to trap flying embers that might be in danger of spreading and starting wildfires.

The decision of UC Berkeley to once more seek needed FEMA funds of $5.6 million to fund for the clearcutting began in 2013, with hopes target an expanse of some 22,000 non-native trees from Claremont and Strawberry Canyon, in order to mitigate fire risks for residents haunted by the devastating firestorm that swept through the Oakland Hills in 1991 Oakland Hills that destroyed some 3,000 homes in the hills.  Many residents remember the Eucalyptus as fostering the rapidity with which the flames of the raging fire spread across the hills:  as “fuel-productive” trees that produce huge quantities of combustible litter, they are readily labeled high fire risks, and have few protectors.  Even though some 19,000 non-native acacia, blue gums, and Monterrey pines have already been destroyed, the destruction of the expansive grove destined to be felled and chipped would potentially end a major protective windshield, but would no doubt reduce how we quantify fire risk.  

And the current thinning of Eucalyptus and other invasive species as acacia and Monterrey pine in the regional parks in the East Bay hills, despite the mobilization of a community-based Hills Conservation Network (HCN) to protect them, will cover 2,000 acres, targeting diseased and dying non-native trees as much as converting the region to grasslands, leave a forest spotted with chemically treated stumps where trees once grew.


920x920-3Paul Chin (S.F. Chronicle)/July, 2015

Native Americans regularly burnt grasses to encourage their growth and spread their seeds, inhibiting the spread of trees. This allowed a massive spread of eucalyptus was so extensive in the grassy hills, where they were planted, erroneously to impede further local grass-fires.  The importation of the eucalyptus plant from 1850 was not only for ornamental ends, but to create fast-growing hard-wood forests was originally celebrated–if incorrectly–and presented, strange to say, as a further reduction of hazards of fire that regularly broke out in the grasslands.   They were also screens, to be sure, for further construction of residences and houses in the hills, valued as protective natural obstacles for privacy as houses gained increasing density on the hillsides, placing neighbors in greater proximity than they had wanted–and perhaps offering an even more welcome screen during Prohibition for private parties, as the eucs became part of the Northern California atmosphere, viewed largely as benevolent, convenient ways of adding further salubrious greenery.

The arrival of the trees in the Bay Area was spawned by unsuccessful lumber schemes, designed to meet the needed infrastructure and housing materials for the region’s growing population.  When the Judson Dynamite and Powder Company first introduced the tree in the 1880s to use their canopies and dense foliage in order to hide ravages of construction and muffle sounds of explosion or construction, the trees’ arrival was greeted in local papers as offering relief from the regular grass fires “that almost every year swept over the hills,” as was argued in the Oakland Tribune–a somewhat common-sense theory that research as now revived, although the argument that they offered wood that resisted burning was openly fraudulent.   At any event, the species robustly grew on plantations of trees as Frank Havens’ land company–the Mahogany Eucalyptus and Land Company–planted some three million eucalyptus and Monterrey pine in plantations of 400-900 trees/acre across 3,000 acres in the East Bay, billing the tree as “the most valuable on the face of the globe,” offering hardwood for fences, firewood, shingles, telegraph poles or “ecclesiastical furniture.”  

The tree seemed magically powerful not only in the rapidity of their growth, quickly attained huge heights, but the multiplying of trunks from their bases so their wood could be regularly re-harvested:  yet as it was realized not to be quite so suitable for milling, and  readily cracked, Eucalypt monoculture became jungles able to suck water out of the ground, leading to calls to thin the population that crowded out native species.  As the difficulty of combatting its fires became clear, the survival of the eucalyptus became something of an economic dinosaur that had outlived schemes for the sudden profits of crops of wood.

One can map the spread of the species first planted to disguise sites of construction, mitigate disturbing sounds, or create miniature parks or groves, to a mini-industry of plantations.  But can one ever map the losses or the density of Eucalyptus trees in the Oakland hills?  One can hardly call the tree non-naive to the state, given the century-long spread of the mid-nineteenth century arrival across different micro regions and environments from coasts to valleys to foothills to dry desert:

Eucalyptus globus state-wide

The prime danger that the trees pose to fire is in shedding their foliage, particularly after colder weather:  the 1972 freeze led trees to shed some 50 tons of debris per acre, over an expanse of 3,000 acres, creating a tinderbox of bark; the shedding was cleared by federal disaster funds.  The 1990 freeze played a considerable contribution to the disastrous 1991 East Bay hills blaze which consumed over 3,300 homes, and led East Bay landowners to work to prevent risks of future fires.  Regular clearing in times of intense shedding of shaggy bark–the eucalyptus trees’ “litter”–surely poses a more economic response to the need to mitigate fire risk.

But the characterization of “match sticks loaded with freeze dried fuel” shifted the blame from dead grass, wooden houses, and vacant lots–and points the finger at the invasive tree, and particularly to question its proliferation on public lands.  Loni Hancock, then Berkeley’s mayor proposed chainsawing down thousand of these “invasive species” or “weeds,” to reduce the dangers of fire-risk–albeit while creating dangers of soil erosion and changing the habitat.  The wide planting of the tree throughout the state not only served needed screens or decorative cover, but valuable fence- or scrap-wood and firewood, given its quick growth.)


The “disorderly” trees that did not clean up for themselves were labeled “invasive” and even identified by the evocative term  “unwanted immigrants” that needed to removed from public parks and lands conceals the risks equally posed by landscaping with non-native shrubs or Monterrey pines.  Tasmanian blue gums have, no doubt because of their visual presence, coppicing, rapid growth, and towering size been seen as weeds, and also been defended as “native enough”–as residents of over a century and a half–continuing the arboreal personification and obscuring debate.  

Berkeley-based poet and Poet Laureate Robert Hass, longtime friend of the eucalyptus’ shaggy bark and camphor smells, got in on the fun when vaunting the blue gum as “California’s largest naturalized citizen,” aware of the serious stakes.  The debate on the trees’ status as alien immigrants set the stage for Verlyn Klinkenborg to enter the debate about “non-native” status of the blue gum eucalyptus, noting that the tree’s exclusion from a “native” land that existed over five hundred years ago relies on a pretty “imaginary snapshot of this continent taken just before European contact,” and, in omphalocentric New York-ese, questionably comparing their place in the landscape to the evolving arboreal landscape of Central Park, whose variety has long welcomed interlopers and foreigners in ways often imagined as a microcosm that reflects the urban population.   The point being that the landscape evolves.

But to shift from a human-centered approach to the place of eucalypts in our environment, it may make more sense to ask the overall environmental impact of the shedding trees.

Yet the California Native Plant Society deems “native” only species predating European contact, and the concerted efforts of public lands to strip the areas that they administer of fire risk have led to a huge investments of regional park and utilities corporations, no doubt eager to respond to insurance threats, to eradicate the blue gum from the local landscape, labeling it as a tinderbox to be uprooted.  A broad range of local authorities who administer parklands–UC Berkeley; City of Oakland; East Bay Regional Park District–have tried to secure up to $5.6 million  from FEMA’s Pre-Disaster Mitigation Grant Program to mitigate fire risk by a plan to remove tens of thousands of eucalyptus.  The group of suspicious non-natives—eucalyptus, Monterey pine and acacia—would be removed in over 1,000 acres, in hopes to expand the indigenous oaks that eucalyptus first replaced.

The 2010 result was to put a mosaic of vegetation management on view:

Proposed Actions on Eucalyptus

The 2010 report proposed Hazardous Fire Risk Reduction measures largely administered by the East Bay Regional Park Development:


Or, in the most focussed picture of mitigation in the regional parks of the Oakland and Berkeley Hills:

Tilden Termination of Eucs

Yet local environmentalists’ have resisted a plan to begin with clear-cutting of Eucalyptus trees, followed by annual application of herbicides, and then five to seven years of pulling seedlings–not only for posing risks to local endangered wildlife, from the whipsnake or California red legged frog, as members of the Hills Conservation Network argue, but may well stand to create even greater fire risks.

Yet the classification of the tree as “non-natives” is to some extent laughable–to judge by the crude state-wide choropleth of their spread, which is in many senses a basic counter-map to the final solution of arboreal demolition.  Indeed, the demand for their clear-cutting or selective clearing in residential areas reflects a desire to mitigate risks to expensive property, and no doubt lower insurance rates, as much as it reflects a direct tie between the growing risk of fires in California in an age of rising temperatures:

Eucalyptus globus state-wide

Elwood Cooper, no mere booster of Californian wildlife, wrote in his 1876 Forest Culture and Eucalyptus Trees, distinguished the value of the trees by noting that they “possess qualities which place it transcendentally above all other plants; . . . rendering localities healthy in which to sleep a single night was almost certain death,” placing on their doorsteps credit for making healthy the environment. Recent recent attack on these non-natives for increasing fire-risk on account of their contribution of dry leaves–or “litter”–to the underbrush may contribute to fires spread by their oil-rich tree crowns and highly flammable litters, but contrast to the majesty of the tree that was once seen as a basis for encouraging local forests.


It is hard to imagine the loss of the trees from the landscape, whose branches hold birds’ nests and whose flowers feed hummingbirds and monarch butterflies, whose groves smell “of camphor and the fog-soaked earth,” in Robert Hass’s organic poetics, themselves word maps of the physical experience of the Bay Area he loves.

1 Comment

Filed under alien species, EBMUD, ecosystems, eucalyptus, FEMA, invasive species, mapping environmental risk, mapping invasive species, mitigating environmental risk, University of California

One response to “Mapping an Invasive Species? Eucalyptus in Berkeley, CA

  1. Pingback: The East Bay’s burning question: how flammable are eucalyptus? – Student Environmental Resource Center

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