Organisms classified as mosses. 72nd plate from Ernst Haeckel’s “Kunstformen der Natur” (1904, public domain)
We have read little fiction in the past few years, as we struggle to keep pace with the scientific literature that is revising conservation biology. Happily, we were recently given the opportunity to read a charming work of fiction that is firmly in the center of our interest in botanical issues.
The Signature of All Things was written by Elizabeth Gilbert. Its title refers to a botanical myth about which we have published an article that is available here. The Doctrine of Signatures seemed a logical botanical belief at a time when plants were one of man’s few medicinal tools and religion was a powerful influence in human society. The Doctrine of Signatures, which was actively promoted by the church in 17thcentury Europe, was based on a belief that God had “signed” plants with certain suggestive shapes and colors to inform humans of their medicinal properties. For example, a heart-shaped leaf was considered God’s message to us that a particular plant would be beneficial to the human heart and this message was strengthened by a flesh-colored flower. Every plant was believed to be useful in some way if man could only discern its purpose. Else why would they have been created, since the Garden of Eden was created for the benefit of man? The church encouraged man’s study of plants as a way to worship God’s creation.
After reading a rave review by one of our favorite authors, Barbara Kingsolver, we were unable to resist the diversion to this story that is inspired by botanical history. Kingsolver concludes, “The Signature of All Things is a bracing homage to the many natures of genius and the inevitable progress of ideas, in a world that reveals its best truths to the uncommonly patient minds.”
Signature begins in Kew Garden in London during the 18th Century reign of one of our great horticultural heroes, Joseph Banks.We featured Banks in an article about the English garden. He began his career as an intrepid collector of exotic plants when he joined one of Captain Cook’s voyages into the Pacific. He returned with thousands of plants from all over the world and they became the core of Kew Gardens, one of the greatest horticultural collections in the world.
The hero of Signature is sent by Banks on expeditions to collect valuable plants and his adventures are an historical account of early explorations of the New World. We learned from Richard Henry Dana’s Two Years Before the Mast that the physical hardships of these voyages are not exaggerated by Signature’s fictional account. The hero of Signature eventually makes his home in Pennsylvania and his extensive garden there is reminiscent of the garden of John Bartram, the Early American collector of plants about whom we have also written.
So you see, Signature covers familiar ground for us and we enjoyed revisiting it in the company of an extraordinary heroine, Alma Whittaker. She is gifted with a remarkable mind and her equally intelligent parents provided her with the education and tools needed to make life-long good use of her talents. She “discovered” her own version of evolutionary theory based on a deep understanding of mosses, which model the mechanics of natural selection.
We don’t wish to give away too much of the plot because we hope you will be intrigued to read it. Readers will have the privilege of eavesdropping on a fascinating (fictional) conversation with Alfred Russel Wallace, a contemporary of Darwin. Although Darwin and Wallace shared a belief in evolution, they diverged on a variety of other topics. Wallace’s busy mind strayed into spiritualism, hypnotism, and mesmerism as well as left-wing politics. Wallace was as eccentric as Darwin was sensible and cautious.
Alfred Russel Wallace
Our heroine, Alma, confides to Wallace that despite a tortuous path in life, she considers herself lucky: “I am fortunate because I have been able to spend my life in study of the world…This life is a mystery, yes, and it is often a trial, but if one can find some facts within it, one should always do so—for knowledge is the most precious of all commodities.”
Alma’s confession was a welcome reminder of why we persist in our effort to inform the public of the destruction of our public lands by native plant “restorations.” Although we make little visible progress, we have learned a great deal about nature. That is our reward. Thank you, Alma, for the reminder of our mission to understand and inform and to Elizabeth Gilbert for the very pleasant entertainment of The Signature of All Things.
Kaweah Oaks Preserve is a 322-acre remnant of riparian woodland in the Central Valley of California, near the town of Visalia. The land was purchased by the Nature Conservancy in 1983 and turned over to a land trust 14 years later. That’s the usual Conservancy strategy. They buy the land to preserve it, engage in an initial restoration to its pre-settlement condition if necessary, but they look for partners to maintain the land for the long-term.
When we parked our car, we were instantly greeted by the chatter of birds. In a brief visit of less than 2 hours, we saw or heard 15 species of birds. (1) In late fall, many of the plants were dormant, but there was still much of interest to see.
There was no water in the creek. We wondered if we would find water in the creek in the late fall during a more typical rain year. We have had almost no rain in California yet this year.
Valley Oak
Valley Oak (Quercus lobata) is the tallest oak in California, reaching 70 feet or more according to Sunset Western Garden.
California wild cucumber, also called manroot (Marah fabacea)
California wild cucumber covered much of the ground and climbed high into the trees.
Native blackberry was also thriving in the understory. We were reminded of its non-native cousin, Himalayan blackberry, which is eradicated for the same “invasive” behavior exhibited here by its native counterpart.
Native willow grows densely near the creek, sprawling on the ground, creating tunnels on the trails.
There were oak galls on the trees and lying on the ground under the trees. “The valley oak trees on the Preserve are hosts to at least nine different kinds of gall wasps. These tiny cynipid wasps sting the stems of oak leaves in the early spring and lay their eggs there. The tree responds to the chemicals the wasp leaves behind and quickly produces a growth that the wasp larva live in and consume until they become adult wasps and chew their way out. The oaks can look like an apple, a tiny pink-and-white chocolate kiss, a wooly ball, a bright pink sea urchin, a brain or even a tiny ball the size of a pinhead that jumps around!” (2)
This Valley Oak fell over a long time ago, but doesn’t appear to be dead yet. It is left on the ground to continue to contribute to the ecosystem. Dead trees are valuable members of the forest community. As they slowly decay, the nutrients they have accumulated during their long lives will be returned to the soil.
The lessons of the Kaweah Oaks Preserve
These were our thoughts, as we ended our late fall walk in the woods:
Native plants sometimes spread just as non-native plants do. However, they are never called “invasive” as non-native plants are. We would like to retire the word “invasive” from our horticultural vocabulary. We don’t wish to call native or non-native plants “invasive.”
Nature is wild and free in the Kaweah Oaks Preserve. It isn’t being manicured to suit the preconceived notions of humans. Why can’t we leave our public lands in the Bay Area alone to grow as nature dictates? Human “management” of nature does not achieve better results than nature left to its own devices.
An occasional downed tree or trail obstructed by a sprawling limb adds to the adventure of a walk in the forest. The resulting tangle provides superior habitat for every creature in the forest.
Toby Hemenway is the author of Gaia’s Garden: A Guide to Home-Scale Permaculture and the founder of Pattern Literacy, an organization which sponsors courses and workshops in permaculture design and practice. We share many of the same opinions about the native plant movement. Visit one of our earlier posts to learn more about permaculture.
We are republishing an article from Toby’s Pattern Literacy website today with his permission. Readers of Million Trees will find many of the themes in Toby’s article familiar, but his examples are from Oregon, rather than our usual examples in the San Francisco Bay Area. We hope Toby’s examples help to make the point that the native plant ideology doesn’t make much sense wherever it is applied.
********************************* Native Plants: Restoring to an Idea
Let me tell you about the invasive plant that scares me more than all the others. It’s one that has infested over 80 million acres in the US, usually in virtual monocultures. It is a heavy feeder, depleting soil of nutrients. Everywhere it grows, the soil is badly eroded. The plant offers almost no wildlife habitat, and since it is wind pollinated, it does not provide nectar to insects. It’s a plant that is often overlooked on blacklists, yet it is responsible for the destruction of perhaps more native habitat than any other species. Research shows that when land is lost to this species, native plants rarely return; they can’t compete with it. It should go at the top of every native-plant lover’s list of enemies. This plant’s name: Zea mays, or corn. Corn is non-native. It’s from Central America. Next on my list is the soybean, with 70 million acres of native habitat lost to this invasive exotic. Following those two scourges on this roll call of devastating plants is the European invader called wheat.
Cornfield
Wait, you say: these plants are deliberately spread by people; that’s different! But to an ecologist, it is irrelevant that the dispersion vector of these plants is a primate. After all, we don’t excuse holly or Autumn olive, even though without bird dispersal, they could not spread. Why are corn, soy, and wheat not on any blacklists? Because we think of them differently than plants spread by non-humans. This suggests that an invasive species is an idea, a product of our thinking, not an objective phenomenon. When we restore land, we restore to an idea, not to objective criteria.
Let me give another example of how our ideas dictate which species we’ll tolerate and which we won’t. The wooded hillside in rural Oregon where I once lived was thick with 40- to 120-year-old Douglas fir and hemlock. But as I walked these forests, I noticed that scattered every few acres were occasional ancient oak trees, four to six feet in diameter, much older than the conifers and now being overtopped by them. I realized that in these ancient oaks I was seeing the remnants of the oak savanna that had been maintained for millennia by fire set by the original inhabitants, the Calapuya people. The fir forest moved in when the whites arrived and drove off the Calapuya, and suppressed fire. So what I was seeing was a conifer forest created by human-induced fire-suppression, and it had replaced the oak savanna that had been preserved by human fire setting. Which was the native landscape? Both were made by people. If we say, let’s restore to what existed before humans altered it, we’d need to go back to birches and willows, since humans arrived as the glaciers retreated. But clearly that’s not appropriate.
Native Americans setting grass fire, painting by Frederic Remington, 1908Willamette Valley, Oregon. Creative Commons
In a similar vein, one of the rarest and most valued ecosystems in the Northwest are the native prairies, such as those found in the Willamette and other valleys. Yet these prairies are also the product of human manipulation. Prairies were predominant in the Willamette over 5000 years ago, but began to disappear not long after that. Ecologist Mark Wilson has written “As climate turned cooler and moister 4,000 years ago, oak savanna and prairie ecosystems were maintained only by frequent fires set by native people to stimulate food plants and help in hunting.” The local people used fire technology to maintain an environment that supported them even when the climate no longer supported that ecosystem.
So I applaud and encourage efforts to preserve native prairie in the region—they are valuable as endangered species habitat, examples of cultural heritage, and a way of preserving planetary biological wisdom. But we should restore these prairies with the strict recognition that we are creating—not recreating or restoring–a state that can not be supported by current climate and other conditions. Prairies are artificial in the Willamette Valley. The preservation of prairies there isn’t a matter of simply repairing and replanting a degraded landscape and then watching the prairie thrive, but constructing a species community and an environment for it that must remain on intensive life support, with constant intervention, for it to survive at all, as long as the climate remains unsuitable to it. The Willamette prairie remnants can’t be considered native; the only criteria they meet is that they were here in small patches when botanists first catalogued them. But so were dandelions. Botanists knew dandelions weren’t native, but they didn’t know that the prairies were human created, so the prairies were catalogued as native. Prairies in the Northwest haven’t been indigenous for 4000 years.
We love the local prairies and I firmly believe in the efforts to preserve them. But I want us to be clear that we are restoring to an idea. We are restoring because we want these things here, and not because there is a master blueprint that says they are the right ecosystem for the place. Ecosystems exist because current conditions favor those particular assemblages. Change the conditions, and the ecosystems will, absolutely, change. Both the climate and humans have changed the conditions plenty. Environmental change is the driving force behind shifting species makeup. With plants and most animal species, no evil species showed up and through sheer cussedness, killed off the locals. Instead, the conditions changed.
The very concept of wild land, for most Americans, is founded on a misunderstanding: a very brief ecological moment during which a once-managed ecosystem was at the height of its degradation due to loss of its keystone species. The dark and tangled primeval forests, written about by Thoreau and Emerson, are simply the declining remnants of open and spacious Eastern food forests, turned to thicket after a century or two of neglect once their human tenders were killed. But this idea of wilderness is deep in our mythology, national imagery, and consciousness.
Let’s look at some of the causes of species change. First: terminology. The word “invasive” is loaded. We hate invaders. The term also places focus solely on the incoming species, yet the ability of a species to survive is due to interactions with the biological and physical environment. So I prefer a more neutral, and I think, ecological more correct and descriptive term, such as opportunistic. Kudzu is not a problem in its native habitat, but it will take advantage of opportunities.
Cedar Waxwings in crab apple tree. Wikimedia Commons
What creates those opportunities for species shifts? Intact ecosystems are notoriously hard to invade. We know this because, for example, seed dispersal rates are truly astounding. Birds are a major dispersal agent. They can carry seeds from multiple plant species in their gut, stuck to their feathers, and in mud on their feet. So picture billions and billions of birds, for 60 million years or so, traveling tens to thousands of miles, seeds dropping off of them every wing-beat of the way. Add to that bats, which are actually more effective at seed dispersal, per bat, than birds. Plus land-animal dispersals, not as far-ranging as birds but bringing much larger seed loads via droppings and fur. Include water-rafted trees and other plants, wind-dispersed species, and more.
This gives a picture of the whole planet crisscrossed with billions of birds and animals for millions of years, seeds and spores going everywhere, eggs being carried to new environments, dispersal, dispersal, dispersal! So why isn’t the whole planet a weedy thicket? Because the mere arrival of a new species, even in large numbers, is not what causes a successful colonization. Ecosystems are very hard to invade, and several conditions must be present for that to happen.
A major reason for ecosystems being tough to invade is that nearly all the resources in undisturbed ecosystems are being exploited. Nearly every niche is filled, every nutrient flow is being consumed, almost every opportunity is taken. Two major changes make ecosystems invasible: disturbance, and the appearance of new resources. Take disturbance. Perennially disturbed places, like riparian zones, are sensitive to opportunistic species. So is farmland, or developed areas, or anywhere that humans or nature cause disturbance. It drives me nuts when I read that “species X” has destroyed 50,000 acres of habitat. When you do a little digging you find that, no, that area was farmed, or new roads cut, or logged, or polluted, or otherwise disturbed, and then the new species moved in.
Brown tree snake, Guam. Wikimedia Commons
For example, one poster child of invasion biologists is the brown tree snake, blamed for invading Guam and killing off several species of birds. The untold story is that for decades the US Navy used over half of the island as a bombing range, leaving most of it unfit for life. Much of what remained was crowded by displaced people, and developed by the military, and thus turned into poor and disturbed habitat. The tree snake just cleaned up the struggling remnants that were vulnerable in their poor habitat and already in serious decline.
Stop the disturbance, and you’ll almost always eliminate or reduce the effect of the new species. Land I lived on was clear-cut in the early 1970s and not replanted with fir until the 1980s, and was covered with patches of Himalayan blackberry and Scotch broom when I arrived in the early 1990s. By the late 1990s, both species were gone from most places and nearly dead everywhere else, because the trees had grown back and shaded them out. The problem is disturbance, not that a species pushes out others because it’s tough or mean.
This suggests that we need to take care of naturally disturbed areas like riverbanks, since most of the species we’ve labeled as problematical thrive on disturbance. Even in these riparian zones, though, conditions are altered from what they once were because of the loss of the beaver and from damming. Thus nature is just trying to deal with our changes as best as she can, and she’ll use whatever resources she can find. A return to the former, natural disturbance regime may allow the once-present vegetation to return, if that is our choice for that land,
Purple loosestrife, Cooper Marsh, Cornwall, Ontario. GNU Free
The second cause of successful invasion is the appearance of new resources. Often the new resources that allow an otherwise intact ecosystem to be colonized are pollution and fertilizer runoff. For example, a number of aquatic opportunists, such as purple loosestrife, thrive in more polluted and higher-nutrient environments than the plants they replace. Many species that evolved in clean water are harmed by pollutants and they then decline. Loosestrife, though, has high rates of nutrient uptake, and this trait allows it to out-compete many other species in polluted water. But in permaculture, we say that every problem carries within it the seeds of its own solution. And so loosestrife can be used in constructed wetlands and in natural environments to clean nutrient-rich water. They are an indicator of a problem, a response to it, and nature’s way of solving a problem, not the problem itself. If you really hate loosestrife and want it to go away, clean up the water. Without doing that, you’ll be flailing away at the problem forever. Spraying and yanking is not an effective strategy to remove unwanted species. Nature is far more patient and persistent, and has a bigger budget, than we do. To remove an unwanted species, change the conditions that made it more favored than the desired vegetation.
Unwanted species generally arrive because humans have changed the environment to make conditions more favorable for the new species. And when we “restore” landscapes, or more often, introduce a set of species that we have decided are the ones we want to see there, we are altering the landscape to suit our idea of what should be there, not to match some divine plan. These two understandings burden us with a huge responsibility to make intelligent choices, but more importantly, to recognize that we are often arbitrarily making a choice based on our own preferences, not because there is only one right choice for a landscape, When we put resources into landscape management, however, we direct the shape of that landscape toward only one choice. That’s the best we can do. Thus I’d like to see us be less dogmatic in the way we cling to those choices.
Unfortunately, dogma is present on all sides. Friends of mine approached the Portland city government with a plan to create some edible plant corridors along Springwater Trail, a 40-mile bicycle and pedestrian loop around the city. Their idea was for bikers and pedestrians to be able to snack on berries and fruit. The city official in charge said, “Nope, we have a natives-only policy on the trail.” The trail is a paved pathway that goes through industrial areas and along backyards, road right-of-ways, and scrubby vacant lots. It probably goes through a dozen or more different environments, based on soil, water, sunlight, and all the other factors that determine what plant communities will grow there. But the policy is natives only. Wouldn’t it make sense for the primary species that will be using that trail to have a habitat that suits that species’ needs for food and comfort, particularly since it’s in a busy urban area? But instead the landscaping is to be driven by an idea, by dogma. I totally support the idea of having natives-only areas on the trail. But let’s allow the new landscaping to serve those that it’s being built for, too.
I began this with corn and soybeans. One of my favorite snarky questions for natives-only people is: “What did you eat for breakfast?” I ask that because it is our choices that determine how much of our landscape is going to be consumed by non-native species. I didn’t eat camas cakes with pink-flowering currant syrup this morning, and I’ll bet you didn’t eat any local plants either. Of course, I’d rather see someone growing indigenous species in their yard rather than having a sterile, resource gobbling lawn. But my urban yard is not, in my or several other lifetimes, going to be part of a natural ecosystem. I might be able to cultivate some endangered native species in an attempt to pull a rare plant back from extinction. That’s one good reason I can see for growing indigenous plants in my yard. But the most frequent native plants I see grown in yards are salal, Oregon grape, and others that are in no danger of extinction and don’t, to my knowledge, support specialist species dependent only upon them. And since much of my yard is watered, it is inappropriate for me to grow natives that are adapted to our dry summers. It’s always struck me as bizarre to see Northwest natives being irrigated.
But even more than indigenous plants, I’d rather see someone providing for some of their own needs from their yard. When we eat a bowl of cornflakes for breakfast, or oatmeal, or store-bought eggs, we are commissioning with our dollars the conversion of wild land into monoculture farms. I’ll bet that a large percentage of people reading this buy local food, shop organic, and so forth. But the farms growing that food are almost all moncultures, and out of the urban matrix. In other words, it is farmland that, if consumption decreased, has a far better chance of being restored to a functioning ecosystem than does a home lot. If I grow some of my own food, that means that somewhere out in the country, a farmer won’t have to plow so close to the riverbank, or could let some of that back field go wild. That land has a far better chance of functioning as an ecosystem than my yard will. Oh, I have visions of how city and suburban landscapes could be functional ecosystems, but that’s another subject. My point is, we need to be putting money and energy into growing indigenous species where they will do the most good, where they can truly contribute to ecosystems and their functions. Many of our efforts in eliminating exotics are a terrible waste of resources at best, and at worst are repeated use of poisons to destroy a hybrid habitat whose function we don’t yet grasp. Let’s be honest at what we are restoring to: an idea of what belongs in a place. If we want to get rid of an invasive exotic, let’s get rid of some monocultured corn, and let a bit of farmland return to being a real ecosystem.
Recommended Viewing: Video: Native Plants and Permaculture
Copyright 2007 by Toby Hemenway
(presented at the Native Plants and Permaculture Conference, Lost Valley Educational Center, Dexter, Oregon, in May 2007.)
In the fifteen years that we have debated with native plant advocates about their desire to destroy our non-native urban forest, the arguments they use to justify their plans have changed many times in response to our push-back against their plans. In the latest round of argument about plans for the Sutro Forest in San Francisco, the justification devolved to the claim that “thinning” the forest would improve its health and reduce fuel loads. We will set aside the claim about fuel loads in this post because we have published many articles to address the bogus claim that the existing Sutro Forest is a fire hazard. Although we don’t agree that “thinning” is an accurate description of a project that intends to destroy 90% of the trees on 75% of the Sutro Forest, we will set that issue aside for the moment as well.
The dense and healthy Sutro Forest. Courtesy Save Sutro
As we often do on Million Trees, we will challenge the conventional wisdom that a “forest” with few trees is healthier than a dense forest, based on the assumption that the trees are released from competition with their neighbors for available resources. We will report on a new argument for the advantages of dense forest for optimal forest health, i.e., that the forest is essentially a community which functions best when it is densely populated:
“It is the evolutionary nature of a tree to be part of a forest or plant community. Trees do not grow as lone individuals under natural conditions. This principle of cooperation referred to by biologists as mutualism appears to have governed organisms from their beginnings.
“Despite the universal gregarious nature of trees, they are almost always discussed and depicted as solitary specimens. Children’s books, technical publications, and literature on gardening only illustrate and discuss the atypical form of a tree—the symmetrical, low-branched, open grown form. All of our knowledge about trees is colored by this cultural archetype. We celebrate the singular specimen.
“Observe trees growing on a natural woodland site. The tall erect trunks of closely spaced forest trees and branch configurations shaped to admit light are two of the more obvious adaptive responses of trees to forest conditions. Each layer of the forest contains examples of this kind of adaptive geometry. The result is that trees can grow very well in dense forest conditions, and in fact are uniquely suited to what we regard as close spacing. For example, it is not unusual to find northeastern forests growing at densities of 400 trees per acre. This is equivalent to trees ten feet apart in both directions. Much higher and lower densities also occur naturally. It is significant that trees can adapt to such a wide range of conditions. A group of Maple trees growing five feet apart is just as healthy or at least better able to survive than a single tree growing in an open meadow. The slower growth rate of trees growing close together is part of their adaptive response and does not indicate that they are less healthy than faster growing trees.
A lone eucalyptus trees in the Mountain View Cemetery.
“The popularized open grown individual tree has an adapted form that is not as sturdy as the forest shaped tree.The tree needs the lower, more spreading branching as protection for its trunk and roots. Its faster growth rate actually produces less sturdy wood.
“To retain their vitality when growing close together, trees adjust their form and growth rate. In this way, they are able to share the more limited amount of sunlight and root space. Trees of the same species do not kill each other off in a fight for survival. This more dramatic image has greater popular appeal but limited accuracy. In the natural process of forest succession, a certain species will dominate all other trees for a given soil type and climate. This is a long term process that occurs because less tolerant trees tend to grow on a site first and would not occur if the climax species were planted first. It is true that in natural repropagation of a clear area, a superabundance of seedlings is often produced, and later thinned by competitive survival of the stronger individuals. This process is limited for the most part to the seedling and early stages of forest succession, and is a lesser factor to later development of the forest when the adaptive process assumes a more important role than competition…
“Through observation of trees growing in natural habitats, a designer can conclude that there is no biological basis for keeping trees far apart, since they grow at every possible spacing” (1) (emphasis added)
An analogy to human society
The community of trees in a forest reminds us of a civilized human society in which individuals cooperate for the collective benefit of society. Like a healthy forest, a civilized human society is one in which cooperation trumps competition. It doesn’t seem to be a coincidence that native plant advocates consider competition more powerful than cooperation both in a forest of trees and in human society. Many native plant advocates seem to share a dark outlook about both human society and our healthy urban forest.
Update: We are pleased to report that UCSF announced on Thursday, November 21, 2013, a significant revision of their plans. Onlytrees 6″ in diameter will be destroyed,* which means fewer trees will be destroyed than originally planned. Only the perimeter of the forest will be thinned to reduce perceived fire hazards to the surrounding residential neighborhood. They do not plan to use herbicides. The details of the revised plan and the timeline for its approval and implementation are available on the Save Sutro website.
*Update: UCSF has corrected this information in response to an inquiry from the Save Sutro webmaster: “The correct information is that the proposed Hazard Reduction Measures recommend removing trees with a stem diameter of less than 10” in the North and South project areas, and to remove trees with a stem diameter less than 6” in the West project area.”
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(1) H.F. Arnold, Trees in Urban Design, 1993, pgs 49-50
Still, the myth persists that eucalyptus forest is devoid of life. In this article we will address this specific statement in the assessment of the California Invasive Plant Council (Cal-IPC) of Blue Gum eucalyptus:“loss of native plant forage and migratory disruptions may have greater long-term impact on wider diversity of wildlife species, including invertebrates and microorganisms in soil.” Cal-IPC provides no studies to support this speculative statement. Therefore, we will tell you about a specific study that refutes the assumption of Cal-IPC: “Similar breakdown rates and benthic macroinvertebrate assemblages in native and Eucalyptus globulus leaf litter in Californian streams” (1)
First, we will provide a few definitions for our readers who may not have encountered some of the more esoteric jargon before. The benthic zone is the sub-surface layer of bodies of water. Here is a brief list of some of the common names of macroinvertebrates that lay their eggs in water that were found in this study: mayflies, caddisflies, stoneflies, and midges. These insects and their larva are food for fish and birds and in turn, fish are food for other animals.
Cerritos Creek. Not one of the creeks in the study, but typical of an East Bay creek with native vegetation.
Three small streams in Alameda and Contra Costa counties in the East Bay were selected for this study because they have sections of shore with eucalyptus forest and sections with native trees (oak, bay, big leaf maple, and alder). Like many ecological studies we have read over the years, this study hypothesized that it would find reduced abundance and diversity of insect populations in the streams bordered by eucalyptus based on the assumption that eucalyptus is “lower-quality food resource for macroinvertebates than a mixture of native litter.” As we will, see, they did not find evidence that supported their theory. We are fortunate that their study was published, because the chances that a negative finding will be published are significantly smaller than studies with positive results.
We will briefly describe the methods used by this study because they establish the credibility of the study. They sampled insect populations directly from the streams as well as using mesh bags of the litter of the two types of forest: eucalyptus forest and an assemblage of native tree species. The sampling was done in three different seasons and the litter bags were sampled after 26, 56, and 90 days. They used two measures of diversity and two metrics related to pollution tolerance, as well as two measures of abundance of invertebrate species in litter bag samples to describe the insect population.
Here are their key findings:
“[Differences in y]early litter input rates in reaches bordered by Eucalyptus and by native vegetation were not statistically significant.”
Species diversity and pollution tolerance did not differ significantly between eucalyptus and native sites, with one exception. There was a higher proportion of one complex of insects (Ephemeroptera, Trichoptera, Plecoptera) in the eucalyptus samples.
The abundance of the five most common taxa (species or genus) did not differ significantly between eucalyptus and native sites with the exception of mayflies which were on average twice as abundant in eucalyptus sites.
One metric of diversity (Shannon Diversity Index) found greater species diversity in eucalyptus sites compared to native sites.
The decay of litter in the bags of eucalyptus litter was similar to the bags of native litter, i.e., “leaf mass loss was not significantly different between eucalyptus and native leaves.” Decay of litter is a proxy for the amount of litter consumed by insects and microorganisms in the litter and by extension the population of these organisms in the litter: “…the importance of biotic factors (bacteria, fungi, macroinvertebrates) in litter breakdown is greater than that of the physical fragmentation.”
The study then compared these findings with similar studies conducted all over the world. When they found differences between their results of those of other scientists, they explained them in terms of local differences in conditions. For example, in European native forests, more deciduous trees are found than in Californian native forests.
Only one similar study was conducted in North America, specifically in two streams in southern California: “… [it] compared the decomposition of Eucalyptus litter to native species and found it slower than that of Alnus [alder], faster than that of Rhus [sumac] and similar to Quercus agrifolia [coast live oak]. Both the decomposition rate and the biomass of macroinvertebrate colonizers differed much more between…two streams than among the litter species.”
Both the results of their study, and the review of the literature of similar studies, led the researchers to this conclusion:
“In coastal California, we conclude that presence of small patches of riparian Eucalyptus even though it influences the species composition of plant litter in streams, has no noticeable influence on diversity and composition of benthic macroinvertebrates that colonize the litter. Furthermore, based on similarities in leaf decomposition, Eucalyptus litter appears likely to be as suitable a substratum for macroinvertebrate colonization as some of the components of the native litter in the three streams tested. Thus, the overall condition of these small streams is not markedly degraded by the presence of patches of riparian Eucalyptus and is unlikely to be improved by their removal.”
Looking for Godot
Looking for evidence of the harm that eucalyptus does to our ecosystems is like waiting for Godot. No one has found any evidence yet. We venture to say that they can keep looking, but we think they are looking for something that isn’t there. If we keep pointing out that there is no evidence to support their indictment against eucalyptus, will they give it up eventually? All we can do is keep trying.
We congratulate those with the tenacity to slog through this tedious post. Your reward is more good news for our harmless eucalyptus.
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Igor Lacan, Vincent Resh, Joe McBride, “Similar breakdown rates and benthic macroinvertebrate assemblages in native and Eucalyptus globulus leaf litter in Californian streams,” Freshwater Biology, 55, 739-752, 2010.
Many plants, both native and non-native have such allelopathic properties. Therefore it is important both to determine if eucalyptus has such properties, and to compare eucalyptus to native tree species to determine if suppression of germination of competing species is any more likely under eucalyptus than native tree species. One of the references provided by Cal-IPC compares germination success of three native plant species using both eucalyptus leaves and oak leaves: “The Effect of Eucalyptus and Oak Leaf Extracts on California Native Plants” (1)
This unpublished master’s degree thesis does not prove that eucalyptus leaf extracts inhibit growth of native plants. The study uses two different methods to test the hypothesis that eucalyptus leaf extracts inhibit growth of native plants.
In the first method, the seeds of three native species (two bunch grasses and a perennial forb) were germinated in petri dishes in sand soaked with a solution of the masticated leaves of eucalyptus and oak. Two of the species of seeds grew shorter roots in the eucalyptus solution than in the oak solution. The third species of seed grew longer roots in the eucalyptus solution than in the oak solution. The percent of germination was lower in the eucalyptus solution than in the oak solution for two of three of the species of seeds and the same in the third species of seed.
The second method used by this study was to test germination success in the soil of eucalyptus compared to oak soil. No significant difference was found in germination success when seeds were planted in the soil:
“The Eucalyptus soil treatment did not result in germination inhibition relative to the control which suggests that allelochemicals present in the leaves are reduced or absent in the soil.” (1)
Since natural germination occurs in the soil rather than in petri dishes soaked in concentrated solutions, this study does not substantiate the statement that E. globulus “inhibits germination and growth of native species.”
Using our eyes to test the theory
We don’t doubt that the leaves of eucalyptus contain chemicals. But the leaves of other trees do as well. The question is not whether or not the leaves of trees contain chemicals, but rather do they prevent the germination and growth of other species of plants? The fact is no study has proved that the chemicals in the leaves of eucalyptus are more likely to prevent the survival of native species of plants than any other tree species, whether native or non-native. We can see with our own eyes that eucalyptus forests often have a thriving understory of both native and non-native plants. Here are just a few examples of local eucalyptus forests that have such an understory:
The management plan for San Francisco’s Natural Areas Program describes the eucalyptus forest on Mount Davidson as follows:
“Although the overstory is dominated by eucalyptus, when all species were considered within the urban forest at Mount Davidson (point data), native species accounted for 36 percent of the understory cover and 21 out of 50 species were native…Pacific reed grass (Calamagrostis nutkaensis) does not have a state or federal special-status rating, but San Francisco is at the southern edge of this species’ range. This species can be found in several locations on Mount Davidson”
Native Pacific reed grass under girdled eucalyptus tree on Mount Davidson
“The eastern portion of the eucalyptus forest has a [native] toyon understory as identified in 1991. The toyon appears to be a wider band than shown in 1991 and covers approximately 2.0 acres…It was noted in a 1972 article in the California Native Plant Society publication Fremontia that the toyon has been introduced by either man or birds. Native species [in the eucalyptus forest] include toyon, coast live oak, coyote brush, blue wild rye grass, and poison oak.”
Native toyon under eucalyptus on Albany Hill
Finally, the understory of the dense eucalyptus forest on Mount Sutro is the richest understory we have personally witnessed. Its understory is composed of both native (most notably elderberry) and non-native species.
The lush, green understory on Mount Sutro. Courtesy Save Sutro Forest.
We give the last word on the scientific question of the allelopathic properties of eucalyptus to R.G. Florence of the Department of Forestry at The Australian National University. An Australian scientist is not under the same pressure to find a negative story to tell about eucalyptus. Professor Florence reports that a world survey of 3,000 articles about allelopathy found “…that the phenomenon of direct chemical interaction in natural communities, in the face of natural selection pressure, must be regarded as rare.” And further, “While [allelopathy] is an attractive concept, there is no certainty that this occurs to any appreciable extent in nature.” (2) These observations are certainly consistent with the reality of the eucalyptus forest in the San Francisco Bay Area, where an understory of both native and non-native plants is often found.
If not allelopathy, then what suppresses understory growth?
We have hiked as often in oak woodland in California as we have eucalyptus forests. We find the understory in the oak woodland as varied as any eucalyptus forest. Sometimes we don’t find much understory in either type of forest. A redwood forest has the sparsest understory of any of these three tree species.
What these forest types have in common is that there is a layer of leaf litter under them that suppresses germination and growth of other plants because it forms a physical barrier to the soil. And the limited sunlight on the floor of both forests is surely a factor in suppressing the development of an understory. When an understory persists through the limiting factors of low light and heavy leaf mulch, there are obviously mitigating factors such as more moisture, better soil, and other resources that understory plants need. Furthermore, some species of native plants seem to be suited to conditions in the eucalyptus forest.
The leaves of eucalyptus contain chemicals–as do the leaves of all plants– but if they do not prevent the growth of an understory or they are not any more likely to suppress the growth of competing plants than chemicals in native tree species, this is not a legitimate argument against eucalyptus. Cal-IPC has not provided any scientific justification for indicting eucalyptus based on its allelopathic properties.
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(1) Kam Watson, “The Effect of Eucalyptus and Oak Leaf Extracts on California Native Plants,” 2000.
(1) R.G. Florence, Ecology and Silviculture of the Eucalypt Forest, CSIRO, 1992?, pgs 71 & 103
Recently, we have been writing about the classification of eucalyptus as “invasive” by the California Invasive Plant Council (Cal-IPC). Judging by the traffic to those posts and the volume of comments, this topic has been of interest to our readers. Therefore, we plan to continue mining the Cal-IPC assessment of eucalyptus.
However, we are making a brief digression today to discuss an interesting comment we received from one of our subscribers that speculates that the “aesthetics” of the native compared to the non-native landscape is yet another reason why it is so difficult to find common ground. Here is the comment from Presley Martin:
“It was the eucalyptus page on the Cal IPC that made me realize that much of this debate comes down to aesthetics. They don’t like it because it’s “encroaching on the ocean view.” And from the Cal IPC website, “Stature and growth form are distinctive and unlike native tree species, which compromises the visual quality of natural landscapes.” They’re upset about the “visual quality” of the landscape, which I see as, man those trees are tall, they’re blocking my precious view. This is not really about loss of habitat and dead birds, it’s about what we think our view of the land should look like. That is why I think art can be one of the most effective tools in this fight to stop the destruction of living plants and animals. You can see my efforts to this end here: http://presleymartin.com/invasive-species-project.html”
We visited Mr. Martin’s website and were even more intrigued by his suggestion that “art can be one of the most effective tools in this fight to stop the destruction of living plants and animals.” Here is his explanation from his website of how art can be a weapon to fight against the pointless eradication of non-native species.
“With the precariousness of our environmental situation ever more apparent, the cultural discourse surrounding our place in the environment is still dominated by an outdated paradigm. My works present images, forms, and performances that are contrary to the dominant environmental discourse surrounding so called invasive plants and animals. They highlight the inseparability of natural and man-made phenomena.
Snail Tenement at Montalvo Arts Center. By Presley Martin with permission
The work provides documentation of the pockets or gaps in the urban metropolitan environment, under freeways, along rivers, so called waste places. These are places where the disaffected, and homeless congregate, and also where nature stakes a claim. Most of the plants and animals that are willing and able to grow in such places are non-native. Plants and animals that have wandered the globe and taken up residence far from where they originated. It should be pointed out that the movement of plants and animals is tied directly to the movement of people. These “invasive” species are global citizens of the non-human world. The places they occupy are the newest “wild” places, and they are precisely the breeding ground of a new relationship with the environment and way out of our environmental predicament. These works are examples, sign-posts on the path to a future where our culture no longer suffers an invisible impoverishment because of looming environmental catastrophe. If our culture is to survive we will need a blossoming of empathy for all living creatures”
We applaud the generosity of spirit expressed in Mr. Martin’s explanation of his work. It brings to mind the open arms of the Statue of Liberty and the poem engraved on it: “Give me your tired, your poor, Your huddled masses yearning to breathe free, The wretched refuse of your teeming shore Send these, the homeless, tempest-tost to me, I lift my lamp beside the golden door!” We welcomed our immigrants at one time and they have made us a great nation. Why not welcome the plants and animals that inevitably made the trip with them?
The aesthetics of native vs. non-native landscapes
We have rarely discussed the question of aesthetic judgment of native compared to non-native landscapes on Million Trees. The one exception to that general rule is a report of the reaction of early explorers to the Bay Area to the dry, summer landscape. Frankly, they didn’t think it was very appealing. Visit that post HERE to see what they said.
Although we happen to agree with the opinions of the early explorers, we have rarely used that argument on Million Trees because we consider aesthetics strictly a matter of opinion. As they say, “beauty is in the eye of the beholder.” Consistent with that opinion, we always urge native plant advocates to plant whatever they want, but just quit destroying everything else and we always say, “we respect your horticultural preferences.” We have horticultural preferences too, but it never occurred to us that we had the right to impose them on those who don’t share them.
Although we believe those statements and stand by them, fall is a good time of year to illustrate the stark contrast between the native and non-native landscapes. Virtually all of our fall color is absent in the native landscape. Here are a couple of photos to illustrate that point. The first photo was taken recently. It shows a colorful house flanked by colorful trees that complement the color scheme of the house. Could anyone dispute that this house would not be nearly so lovely without its surrounding landscape?
Ginkgos & Japanese Maple
The second photo is of the Serpentine Prairie in Oakland. The photo was actually taken in June, but that landscape will continue to look brown and dead until the rains start. As Bay Area residents know, the rain is late this year and so our brown natural landscape persists.
Serpentine Prairie restoration. East Bay Regional Park District
The Serpentine Prairie is one of many “restorations” by the East Bay Regional Park District. EBRPD destroyed 500 trees to return the landscape to a treeless prairie. Many of the trees were native oaks and bays. The prairie is predominantly non-native annual grasses, but the hope is that native bunch grasses can be restored there because the serpentine rock suppresses the growth of plants that would otherwise compete with the bunch grasses and other rare native plants. The prairie will have to be burned periodically to prevent natural succession to shrubs and eventually trees.
We assume native plant advocates like the look of the Serpentine Prairie. Since they demanded this particular “restoration,” they are surely obligated to defend it. But what do you think? Do you think it was worth destroying 500 trees, including many oaks and bays? And do you think aesthetic arguments against the destruction of non-native species deserve more coverage on Million Trees? If so, please give us some examples of suitable comparisons that support your viewpoint?
This is a guest post by a member of Communities United in Defense of Olmstead (CUIDO) Olmstead is a 1999 Supreme Court decision affirming the civil rights of people with disabilities. We have added links to articles about the issues about which they were demonstrating.
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CUIDO demonstration on November 2, 2013. Photo by Luke Hauser
Eighteen activists –including a blind woman, a deaf man, numerous wheelchair riders, people with invisible disabilities, and nondisabled allies–paraded single file through the Farmers Market and downtown Berkeley, California on Saturday, November 2, 2013. The action was called by CUIDO, a local disability action organization.
The protesters carried signs —“DEAF SAY: READ OUR HANDS! NO CLEAR CUTS, NO PESTICIDES, DEFEND EAST BAY FORESTS” and “DEATH BY 1,000,000 CUTS!!”— as they passed out hundreds of leaflets warning of the impending destruction. Protesters also carried, attached to their wheelchairs, enlarged photographs of graceful tall trees that are targeted for elimination, including a photo of a bald eagle parent and chick, nesting in a “non-native” eucalyptus tree.
Their action took place on All Souls Day, El Dia de los Muertos. Protesters identified with the souls of the trees and forest life endangered by this plan. Stephanie Miyashiro’s wheelchair bore a photo of large trees. A paper chain connected her heart with the trees. Her sign proclaimed: “Our lives are inextricably linked.”
Two CUIDO activists will discuss the issue in greater detail at 2:30 pm Friday, November 15, 2013, on “Pushing Limits,” a radio program on KPFA (94.1 FM) which addresses issues relevant to the disability community. Update: Marg Hall and Jean Stewart did a terrific job with this interview which is available HERE
More protests are planned. Community members who would like to join in future CUIDO actions are encouraged to contact the group at: cuidoaction@gmail.com.
CUIDO, Communities United in Defense of Olmstead, is a grassroots rights organization of people with disabilities, including chemical injuries caused by pesticides. Olmstead is a 1999 Supreme Court decision affirming the civil rights of people with disabilities.
This is the flyer that CUIDO distributed at their demonstration:
DAY OF THE DEAD TREES
Trees are sacred and beloved friends; ancient living trees link us to our ancestors.
A plan is afoot to cut down hundreds of thousands of tall trees on over 2000 acres of forest, from Richmond to Castro Valley. A great many have already been destroyed. In observing Day of the Dead, we mourn their loss, celebrate their spirits, and treasure—and pledge to protect—those that remain.
Some of our most popular parks will have almost no trees left. In place of tall trees we will see vast acres of woodchips, as there are no plans for replanting. Similar projects are proposed for other Bay Area locations, such as Sutro Forest (SF).
The pretext is fire hazard mitigation, but the result will be a dry and barren landscape which will actually increase fire danger. A complex, delicate ecosystem will be destroyed, and massive amounts of carbon will be released, contributing to global warming. Deforestation is one of the principle causes of climate change, which already threatens the planet.
There are alternative approaches to fire hazard mitigation, but project sponsors (UC Berkeley, East Bay Regional Parks District, and the City of Oakland) have dismissed safer and less destructive alternatives. Instead, they propose clear-cutting and long-term, extensive use of toxic herbicides, which they intend to apply for up to 10 years. One of these pesticides has been shown to cause acute skin, eye, & respiratory illnesses; the other has been linked to blood, kidney, liver, & nervous system toxicity. One of the targeted tree species is listed as Endangered. The funding for this project is all public money, including a Wildfire Prevention Assessment District special tax on Oakland residents. (mail-in ballot due Nov. 13-VOTE NO!) IS THIS HOW YOU WANT YOUR TAX DOLLARS SPENT?
Distributed by: CUIDO (Communities United in Defense of Olmstead)
Contact: cuidoaction@gmail.com ; http://www.cuido.org
CUIDO is a grassroots rights organization of people with disabilities, including chemical injuries caused by pesticides.
Monarch butterflies overwintering in California are using predominantly tall non-native trees, especially eucalyptus. There is no evidence that the monarchs overwintered in California prior to the planting of these non-native trees, contrary to the claim of Cal-IPC.
In this post, we will look at the “evidence” provided by Cal-IPC that Blue Gum eucalyptus is invasive in California. Here is how Cal-IPC described the “local rate of spread with no management” of Blue Gum eucalyptus:
“Once a tree matures and produces seed, it can produce a profusion of progeny within a few years; doubling of stand area within 10 years possible but not well documented Without quantitative data, this response is conservative; stands have certainly expanded far beyond initial plantings in many locations, based on unpublished photodocumentation (1, 2) and personal observations (3)” [numbers refer to cited “references”]
And here is the “evidence” Cal-IPC provides in support of this rather dire prediction of the invasiveness of Blue Gum in California:
“Potts, Michael. 2003. About this edition. Caspar News. Online @ http://casparcommons.org/Press/News0305.htm. 2. Site Stewardship Program, Parks Conservancy. Unpublished photographs of Oakwood Valley, Marin Headlands, Golden Gate National Recreation Area. 3. Warner, PJ. 2004. Personal observations from 1980-2004 working in and adjacent to Eucalyptus stands in Marin, Sonoma, and Mendocino Counties, CA. 707/937-9172; pwarner@mcn.org.”
With the exception of an article in “Caspar News,” all evidence provided by Cal-IPC is unpublished. Although the one written source is described as “Caspar News,” in fact its title is “Caspar Newsletter.” The edition of this newsletter that is cited is the first unprinted edition of the “Caspar Newsletter.” Some of the unpublished “evidence” cited by Cal-IPC is described as “personal observations” of Peter Warner, who is the author of the Cal-IPC assessment for Blue Gum eucalyptus.
Therefore, the only source of information about the invasiveness of Blue Gum that we can evaluate is the one that is available on the internet HERE.
First a word about the town of Caspar, which is located 4 miles north of Mendocino on the coast of California. According to the 2010 census, it has a population of 509 souls. We celebrated New Years Eve there many years ago in a rocking bar, so we have fond memories of it. It is a lovely little town. We mention its small size to put its newsletter into perspective. It’s hardly mainstream journalism.
The article in the “Caspar Newsletter” starts with the recommendation of Peter Warner to eradicate all eucalyptus in Caspar:
“In this newsletter you find several articles written by strong advocates of dire means, including the authoritative Eucalyptus indictment written by State Parks’ expert on managing exotics Peter Warner, who advocates a draconian solution: cutting and then careful application of a dire chemical to eliminate every tree.”
In other words, the “Caspar Newsletter” is merely a repetition of Peter Warner’s agenda to eradicate eucalyptus and poison them with herbicides to prevent them from resprouting. It’s not an independent source of information.
Photographic evidence of invasiveness?
The only photographic evidence of the invasiveness of Blue Gum eucalyptus provided by Cal-IPC’s assessment is in the article in “Caspar News:”
“Eucalyptus encroaching on the ocean view”
There are three problems with this photograph with respect to the claim that it is evidence of the invasiveness of eucalypts:
We are asked to trust the memory of the photographer about the history of this eucalyptus grove. Credible evidence of spread of the eucalyptus grove would provide dated photographs taken at each period of time represented in this photo, i.e., 1989, 1994, 1999, and 2003.
We see the ocean in the far distance, west of this grove of trees. As the forest approaches the ocean, we see that the trees are smaller. This is as we would expect, because the wind from the ocean has suppressed the growth of the trees on the windward side of the grove. The fact that wind suppresses the growth of trees was established by Joe R. McBride in his study of trees in the San Francisco Presidio which the Presidio contracted with him to conduct: “Wind at the Presidio affects tree growth, form, and mortality. Exposure to winds in excess of 5 mph usually results in the closure of the stomata to prevent the desiccation of the foliage (Kozlowski and Palhardy, 1997) Photosynthesis is thereby stopped during periods of moderate to high wind exposure resulting in a reduction in tree growth…Eucalyptus showed the greatest reduction in growth with trees at the windward edge being only 46 percent as tall as trees on the leeward side.” (1) (emphasis added)
The photographer asks us to believe that the eucalyptus forest is spreading towards the ocean. Given that the seeds of eucalyptus are dispersed by gravity and wind and that the wind is coming from the ocean, we would not expect the eucalypts to spread towards the ocean, but rather on the leeward side of the forest.
In other words the “evidence” provided by the Cal-IPC assessment that E. globulus is very invasive is not supported by the evidence that is provided.
It is possible to document invasiveness with photographic evidence. We have provided our readers with two such examples that indicate that Blue Gum eucalyptus is not invasive in the San Francisco Bay Area:
In “Vegetation Change and Fire Hazard in the San Francisco Bay Area Open Spaces,” William Russell (USGS) and Joe McBride (UC Berkeley) used aerial photos of Bay Area parks taken over a 60 year period from 1939 to 1997, to study changes in vegetation types. They studied photos of 3 parks in the East Bay (Chabot, Tilden, Redwood), 2 parks in the North Bay (Pt Reyes, Bolinas Ridge), and one on the Peninsula (Skyline). These photos revealed that grasslands are succeeding to shrubland, dominated by native coyote brush and manzanita. Eucalyptus and Monterey pine forests actually decreased during the period of study. In those cases in which forests increased in size, they were native forests of oaks or Douglas fir. In other words, they found no evidence that non-native trees are invading native trees or shrubs.
Another example of photographic evidence that E. globulus is not invasive is from Mount Davidson in San Francisco. Adolph Sutro purchased Mount Davidson in 1881. He planted it—and other properties he owned in San Francisco—with eucalyptus because he preferred a forest to the grassland that is native to the hills of San Francisco. Here are historical photos of what Mt. Davidson looked like in 1885, 1927 and 2010:
Since Sutro didn’t own all of Mt. Davidson, there was a sharp line between the forest and the grassland when this photo was taken in 1927.
Over 80 years later, in a photo taken in 2010, there is still a sharp line between the forest and the grassland. We see more trees in the foreground where residential areas have been developed and home owners have planted more trees, but the dividing line on the mountain is nearly unchanged.
There is one well-documented case of significant expansion of planted E. globulus on Angel Island. Using historical records of planting of E. globulus on 23.6 acres as well as observations of uniform spacing of those plantings, McBride et. al., determined that E. globulus spread to 86.1 acres. The trees were planted starting in the mid-1870s to 1933 and their spread was measured in 1988. The authors of the study reported that most spreading occurred in areas of high soil moisture, such as swales, and in disturbed areas such as road cuts. This is also the only documented case of significant expansion of planted E. globulus mentioned in the US Forest Service plant data base. (2)
The one exception to the general rule that Blue Gum eucalyptus has not been invasive in California is consistent with what we know about Angel Island and about the limitations of seed dispersal and germination rates of Blue Gum eucalyptus:
Angel Island is an extremely windy and foggy place because it is located in the San Francisco Bay, close to the Golden Gate to the Pacific Ocean, where wind and fog enter the bay.
Eucalyptus seeds are dispersed by gravity and wind. Therefore we can expect seeds to travel further in a very windy place.
Optimal soil moisture increases the success of seed germination. Fog drip increases soil moisture and spreading of the eucalyptus forest on Angel Island occurred in drainage swales, where moisture would be greatest.
How invasive is Blue Gum eucalyptus?
Blue Gum eucalyptus is rarely invasive. The only documented case of significant spread of eucalyptus forest occurred in ideal conditions for seed dispersal and germination. Therefore, Cal-IPC’s claim that Blue Gum eucalyptus is extremely invasive is exaggerated at best and fabricated at worst.
If our readers are aware of any other documented cases of spreading of eucalyptus, we invite them to inform us. We are committed to accurately informing ourselves and our readers of the reality of invasiveness of Blue Gum eucalyptus.
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(1) “Presidio of San Francisco, Wind Study, First Phase,” Joe R. McBride, circa 2002, page 6. (unpublished, contracted study)
(2) “Focused Environmental Study, Restoration of Angel Island Natural Areas Affected by Eucalyptus,” California State Parks and Recreation, July 1988, pg 47 & 51.
The claim that eucalyptus trees kill birds originates with an article in the publication of the Point Reyes Bird Observatory, written by Rich Stallcup. (1) Mr. Stallcup was well known as a knowledgeable birder, but he was not a scientist. He based his claim that eucalyptus trees kill birds on his observation of two dead birds in two different eucalyptus forests over a period of many years.
Bird mortality rates
Given that Mr. Stallcup was a serious birder who spent much of his time in the field observing birds, we begin our critique of his hypothesis by pointing out that a sample of two is absurdly small from which to extrapolate to a general rule about bird mortality in eucalyptus forests.
Furthermore, the scientific literature about bird mortality informs us that a sample of two does not justify the assumption that these deaths were caused by eucalyptus trees. For example, the annual survival rate of adult song sparrows has been reported as only 30%. That is, in a single year, 70% of adult song sparrows will die of predation, disease, starvation, or other factors including old-age. Mortality rates are greater for small birds. (2)
Mortality rates for young birds are substantially greater than for adult birds. For example, a longitudinal study of Eurasian kestrels found that 51% of 245 kestrels were dead within their first year. All of the 245 kestrels in this study were dead by the end of 10 years. (2)
We have a beautiful Coast Live Oak tree on our property, under which we have found dead birds. Yet we have not concluded from those observations that the birds were killed by the tree. Of course, they were not. Although there were probably many different causes of death of these birds, we don’t feel the need to speculate about those causes because bird death is not a rare or unusual event unless, of course, you are looking for an excuse to blame the tree.
Flowers of Blue Gum eucalyptus. Photo by John Hovland
Stallcup’s Theory
Spotted pardalote is an Australian bird with a short beak that feeds in eucalyptus forests in Australia. Creative Commons
Stallcup speculated that eucalyptus trees kill birds by “gumming” up their beaks or nostrils with the nectar of the eucalyptus flower which blooms from about December to May in California. He supports this theory by claiming that the birds that are found in Australia, where eucalyptus is native, have long, curved beaks which enable them to eat nectar from the flower without gumming up their beaks or nostrils.
This theory is not consistent with the “evidence” that Mr. Stallcup uses to support his theory:
He found a dead ruby-crowned kinglet. The kinglet is an insect-eating bird, not a nectar eating bird.
Years before that sighting, he found a dead hummingbird. Hummingbirds eat nectar, but they have long beaks.
Many Australian birds that feed in eucalyptus forests do not have long, curved beaks; e.g., spotted pardalote, striated thornbill, and white-naped honeyeater. (3)
One study in Santa Cruz, California found many small birds feeding on insects in red gum eucalyptus, including yellow-rumped warblers, Townsend’s warblers, ruby-crowned kinglets, and bushtits. The beaks of these birds are not shorter than those found in eucalyptus trees in Australia mentioned by the same study. The study reported no dead birds or gummed beaks. (3)
The nectar of eucalyptus flowers is not “gummy.” It feels watery to the touch. Eucalypts are not called “gum” trees because of the nectar in their flowers. They are named for the sap under their bark.
Ruby-crowned kinglet is a North American bird that feeds in the eucalyptus forest in California. USFWS
We can compare Mr. Stallcup’s “data” of two dead birds with a database of a local wildlife hospital. The report of this database was posted to SFBIRD (San Francisco Bird is an email listserve that anyone can subscribe to and report the birds they see in San Francisco) by Richard Drechsler on March 12, 2012 and is quoted here with his permission:
“I have access to a database containing 56,960 records of birds brought to a local wildlife hospital between 1992 and 2010. During this period this facility also accepted 2500 birds who were classified as DOA (dead on arrival). I volunteered in that facility for seven months during 2010 where I worked with ‘small birds’ in order to get a better idea of how birds are being injured. I was aware then of the belief that resin, gum, nectar, etc. from Eucalyptus trees might harm feeding birds. During my time there I did not encounter any birds whose passages were blocked with any natural resins that would have prevented them from eating or breathing. This evening I compared my observations with the 19 years of data by searching on the following words: ‘euc,’ ‘euk,’ ‘bill,’ ‘beak,’ ‘tree,’ ‘asphy,; ‘breath,’ ‘mouth,; ‘nar,’ ‘gum,’ ‘resin,’ ‘nectar,’ ‘nostril,’,’ starv,’ ‘horn,’ ‘stick,’ ‘stuck,’ ‘glue.’
Preliminary Data Findings:
(1) There is no reference to Eucalyptus or any of its byproducts.
(2) There is one reference to a bill or mouth being restrained…by a synthetic adhesive.
(3) There is one vague reference to an Anna’s Hummingbird that was “Stuck in Resin”…treated and released one day later.
(4) Querying on ‘sticky,’ ‘stuck,’ or ‘glue’ yields many records and a wide variety of species being trapped by synthetic adhesives such as rodent traps and building adhesives.”
Given the ubiquitous presence of Eucalyptus in this area and the birds craving for its nectar one would expect more incidents of starving birds or ones surrendered DOA. Also, if birds did not have the capacity to preen or molt away this nectar, wouldn’t every (indulging) bird ultimately display this residue?”
Bird anatomy trumps the absence of data
There is no empirical evidence to support the claim that eucalyptus trees kill birds, but the most compelling evidence that this claim is not factually correct is that it contradicts the basic facts of bird physiology and anatomy. That is, birds can and do clear their beaks and nostrils with their feet or by rubbing their beaks on branches when necessary. If their nostrils are obstructed, they can breathe through their mouth and vice versa.
Ask yourself this question to appreciate the absurdity of the claim that birds would passively suffocate rather than using the tools they have at hand: If you were suffocating because there was something stuck in your mouth or nose, wouldn’t you raise your hands to your face and clear the offending obstacle? Is there any reason to assume that birds are not physically or mentally capable of the same defensive behavior? If you have a cold and your nose is stuffed up, don’t you breathe through your mouth?
In 2010, a student taking the Cornell Lab of Ornithology correspondence course on bird biology asked his instructor this question: “Do eucalyptus trees kill North American birds?” This is the email reply from his instructor:
“I have no firsthand knowledge of the effect of eucalyptus gum suffocating birds (or not), but I share your skepticism for the reasons you mention. The story has birds feeding in flowers and getting gum on their faces. The first bird mentioned in this saga appears to have been a Ruby-crowned Kinglet. They don’t feed on or in flowers much; they’re leaf gleaners and flycatchers. Is there even “gum” to be picked up on the flowers? Again, that seems unlikely. Birds can breathe through their mouths, so just plugging up the nostrils won’t kill them. (Nestling crows often get the feathers covering their nostrils so encrusted with food matter that there is no way they could breathe through them, but the young are fine. I chip it off when I band them.) It seems like this story could be investigated rather easily, but I see nothing about it in the scientific literature. I would need to see evidence before I believed it.”
Those who love to hate eucalyptus
The Cornell ornithologist would need to see evidence before he believed the claim that eucalyptus trees kill birds. Native plant advocates apparently don’t need any evidence. They have been repeating this absurd, baseless claim since 1996, when it was originally fabricated. One subscriber to the SFBIRD email listserve mentions this claim often, although he never offers any new actual dead birds to add to the two that were used to fabricate the story.
This story has been repeated by native plant advocates for nearly 20 years without any supporting evidence. It has taken on a life of its own until those who repeat it apparently are unaware that there is no evidence to support the myth.
The US Forest Service social scientist, Dr. Paul Gobster, interviewed native plant advocates while a visiting professor at UC Berkeley about ten years ago. At the end of his visit, he delivered a lecture at the Randall Museum about his observations of the local native plant movement. He said they were victims of “incestuous amplification,” the trading of misinformation in a vacuum caused by their isolation. The ridiculous story about eucalyptus trees killing birds is surely an example of incestuous amplification.
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(1) Rich Stallcup, “Deadly Eucalyptus,” Point Reyes Bird Observatory, Fall 1996
(2) Handbook of Bird Biology, Cornell Lab of Ornithology, Princeton University Press, 2004
(3) Julie Lockhart and James Gilroy, “The portability of food-web dynamics: reassembling an Australian psyllid-eucalypt-bird association within California,” Global Ecology and Biogeography, 2004, 13, 445-450
Conservation Sense and Nonsense 