“Tending the Wild:” Implications of land management by Native Americans in California

In our last post we told our readers about the usefulness of non-native plants which are closely associated with human civilization and are therefore found everywhere, but are considered weeds.  We don’t wish to leave our readers with the impression that native plants are not at least equally useful, so we will counter-balance our last post with this report based on a book about California Native Americans:  Tending the Wild:  Native American Knowledge and the Management of California’s Natural Resources. (1)  The author, M. Kat Anderson, is the national ethnoecologist of the United States Department of Agriculture’s Natural Resources Conservation Service and an Associate in the Department of Plant Science at UC Davis.

Aboriginal societies have been categorized by anthropologists as either hunter-gatherer or agricultural societies.  California Native Americans were considered hunter-gatherer societies because they were not sedentary, tied to a specific site where they tilled the land to grow crops, and they had no domesticated animals.  Tending the Wild challenges this categorization based on an exhaustive survey of the land management practices of California Native Americans.  The author proposes a middle-ground between the dichotomous categories to reflect the many ways in which Native Americans essentially gardened wild plants to produce their food and other utilitarian objects, while also acknowledging the seasonal mobility of Native American society.

Karok basket maker, 1894.  Smithsonian photo archive
Karok basket maker, 1894. Smithsonian photo archive

Fire was the essential tool

Million Trees has reported many times that California Native Americans intentionally set fires, but until reading Tending the Wild we did not appreciate how essential fires were to their culture, nor did we understand the many purposes for which fires were set.  Here is an incomplete list of the many reasons why Native Americans set fires:

  • Fires maintained grassland by eliminating shrubs that naturally encroach on grassland in the absence of fire.
  • In the absence of fire, thatch of dried grass accumulates when grasses die back during the dry season. This thatch retards the germination of a new crop of young grass.
  • Young grass which sprouts after a fire is attractive to grazing animals which were hunted. Young grass was also preferable for basket-making because it is straight and pliable.
  • Fire reduces shrub vegetation which competes with grasses for light and water. Land cleared by fires was then seeded with the plants most useful to Native Americans.
  • Fire recycles nutrients in the soil.
  • Fire was used to smoke small mammals from their burrows.
  • Fires were used to corral grasshoppers and other insects considered edible for harvesting.
  • Fire was used to reduce insect populations that feed on the plants eaten by Native Americans. For example, the duff beneath oaks was burned before acorns fell so that acorns were not eaten by insects.
  • Fire was used to germinate seeds of the many species of native plants that require fire for germination.
  • Periodic fire was considered a means of preventing wildfires fueled by accumulated dead vegetation.

Other land management methods

Pomo gathering seeds, 1924.  Smithsonian photo archive
Pomo gathering seeds, 1924. Smithsonian photo archive

Fire was one of many management methods used by California Native Americans to foster the plants that were most useful to them.  In some cases, these practices maximized their food sources and in others they produced useful materials such as those needed to make baskets or plants thought to have medicinal properties.

Tending the Wild reports that 60-70% of the diet of California Native Americans was from plants.  Miwoks report using 48 species of plants for fresh greens compared to just a dozen salad greens typically found in a modern market.  California Native Americans ate 15 of 31 native clover species. Clover seed was broadcast-seeded onto burned ground because it improved the fertility of the soil by restoring nitrogen to the burned soil.

Miwok mortars where seeds and nuts were ground.  Smithsonian archive
Miwok mortars where seeds and nuts were ground. Smithsonian archive

Baskets were equally important to their culture.  Every family typically had 22 different types of baskets for a variety of purposes such as storage, food gathering, beating seeds from plants, cooking, water storage and transport, fish traps, small-animal traps, etc.  Seventy-eight plant species were used by California Native Americans to make these baskets.

Here is an incomplete list of the methods used to foster the plants most useful to California Native Americans:

  • The seeds of favorite plants were planted to be available close to living quarters. Native tobacco is an example of a plant found around Native American settlements, presumably planted there.
  • The seeds, bulbs, corms, rhizomes etc., of favorite plants were collected and transplanted close to settlements.
  • Bulbs, corms, roots, rhizomes were harvested selectively to preserve the plants which were stimulated by the thinning of the plant.
  • Fields of useful plants were weeded to create monocultures that made harvesting more efficient.
  • Plants were pruned and coppiced to maximize fruit production.
  • Plants were pruned to produce the straight twigs and grasses useful to make baskets and arrow shafts.
  • Plants were irrigated to promote growth and maximize fruit production.
  • Plants were treated by cooking, soaking, etc., to remove toxins so they could be safely eaten.

Impact on the landscape

Over the thousands of years that California Native Americans practiced these land management practices, the landscape was altered by them:

  • Plants that did not tolerate frequent fires died out, creating a landscape that is dominated by plants that are adapted to fire. Jon Keeley (USGS) informs us that over 200 native plant species are “fire endemics,” requiring fire to germinate and dying out within a few years after a fire. (2)
  • The Europeans arriving at the end of the 18th Century found a landscape dominated by grassland because repeated fires prevented succession to shrubs and forests. The absence of shade produced a landscape of native plant species that require full sun.
  • Forests were open and park-like with little understory, which had been repeatedly cleared by frequent fires.
  • The plants which were most useful to Native Americans were more likely to survive than those that were not useful because they were tended and competing vegetation burned or weeded.
  • The natural ranges of the plants which were useful were altered by the land management practices of Native Americans. They were transplanted and grown from seed where they were accessible to the community.

What are the implications for ecological “restorations?”

The landscape selected by native plant advocates as the goal of ecological “restorations” is the landscape that existed in 1769 when Europeans first laid eyes on San Francisco Bay.  Now we know that it was a landscape that had been altered by thousands of years of occupation and cultivation by California Native Americans.  There are at least two major flaws in the selection of this landscape as the goal of “restoration:”

  • Native ranges reflect the choices made by the Native Americans. They do not necessarily reflect the forces of nature.  The modern obsession with “where plants belong” is based on a fantasy of why plants were found where they were when Europeans arrived in California.
  • The land management practices of Native Americans are no longer being practiced, which means that the plants they preferred are no longer receiving the care that ensured their survival in the past. Humans no longer set fire to the landscape every year.  Therefore, the landscape has changed and will continue to change to correspond to changed practices:

The relationship between humans and nature has changed since California was occupied solely by Native Americans.  Consequently, nature has changed in ways that reflect how humans now use the land.  The author of Tending the Wild acknowledges that her book conflicts with the goals of ecological “restoration:”

“If restoration is aimed at returning ecosystems to the condition in which they existed before Western settlement degraded them, then that condition is surely not an entirely natural one.  As we now know, many of the classic landscapes of California—coastal prairies, majestic valley oak groves, montane meadows, the oak-meadow mosaic of Yosemite Valley—were in fact shaped by the unremitting labor of generations of native people.  Moreover, these and other communities were managed intensively and regularly by these people, and that many have disappeared or changed radically in the absence of management shows they were not self-sustaining.” (1)

In our next post, we will think about how our relationship with nature has changed and what that means for the future of the management of our remaining open spaces. Given this revised understanding of the “native” landscape, how must we revise our goals for ecological “restoration?”

  1. M. Kat Anderson, Tending the Wild: Native American Knowledge and the Management of California’s Natural Resources, University of California Press, 2005 (This is the source of most of the information in this article.)
  2. Jon Keeley, et. al., Fire in Mediterranean Ecosystems, Cambridge University Press, 2012

Predicting the future of plants in a changed climate

Despite a minority of die-hard deniers and their corporate enablers in the fossil fuel industry, most scientists have quit debating that the climate has changed and will continue to change.  Nor is there much doubt that the primary cause of climate change is the significant increase in the greenhouse gases that trap heat on the Earth’s surface.  Scientists have now turned their attention to the huge task of understanding the consequences of a changed climate and predicting its future course.  Our best hope is that such knowledge can help us to devise strategies for coping with the consequences.

In this post, we will share with our readers some of the recent research about how plants and trees are responding to climate change. 

Non-native plants are more responsive than natives to higher temperatures

The State of Ohio has one of the most complete climate records in the country.  They have had weather stations in stable locations throughout the state since 1895.  From 1895 to 2009, these weather stations reported an average increase in temperature of 1.7 degrees Fahrenheit.  All of the weather stations were outside of urban areas, so we can be confident that the data were not confused by the separate, but associated, phenomenon of the urban heat affect as population and development in urban areas increased during this period. 

These data were combined with an equally rich source of information, the herbarium of the University of Ohio which contains 500,000 plant specimens.  These two sources of information enabled a graduate student, Kellen Calinger, to assemble “one of the six-largest such data sets in the world tracking the history of the wildflower life cycle in response to climate change.” (1)

When is the California poppy blooming?
When is the California poppy blooming?

Ms. Calinger compared the bloom time of 141 species of plants with the temperature at the time of bloom.  She reports that “…46% of the 141 species showed significant advancement in flowering in response to increased temperatures.  And more of this advancement was seen in introduced species [AKA non-natives] than in native plants.”

Ms. Calinger predicts that the non-native plants that bloom before their native neighbors have a competitive advantage.  Presumably, they are growing and occupying ground prior to the natives.  If, indeed, climate change is giving non-native plants an advantage that would help to explain why attempts to eradicate non-native plants and replace them with native plants are often unsuccessful. 

However, the report of this research then enters muddy territory.  It speculates, but without offering evidence, that there may also be disadvantages to blooming earlier:

  • Is the flower blooming prior to the arrival of its pollinator thereby decreasing its reproductive success?
  • Will the early bloom only become the victim of a subsequent frost because the growing season is not yet stable?
  • Will migrating birds pass through only to find that the nectar sources they have depended upon in the past have now completed their blooming period?

What do we know about the response of plants in urban areas?

So, how does this information apply to our urban area?  In general, temperatures in urban areas are higher than in rural areas because so much of our ground is covered with buildings and hardscape that absorb and retain heat.  This is called the urban heat affect.   It seems logical to assume that what has been observed in the rural setting would be exaggerated in the urban setting.  That is, plants in urban areas are likely blooming even earlier because the temperatures are higher, although there is probably an upper threshold, beyond which there is no growth benefit.

However, there are other factors in climate change that are more important in urban areas which are also affecting the growth of plants and trees.  Greenhouse gases are greater in urban areas than in rural areas because of industrial and transportation emissions. 

Carbon dioxide concentrations have increased 24% globally since 1960.  We should assume that increase is greater in urban areas.  Carbon dioxide is the primary fuel of photosynthesis, so we should not be surprised to learn that higher concentrations of carbon dioxide are associated with faster plant growth. (2)

Are the oaks growing faster?
Are the oaks growing faster?

Kevin Griffin (Columbia University) compared the growth of the native red oak in rural New York with their brethren in New York City over a period of 8 years.  The average minimum temperature in August was 71.6 degrees at the city site and 63.5 degrees in the country.  He also found elevated levels of nitrogen in the leaves of the trees in the city.  Nitrogen is a plant nutrient.  Griffen reported that, “The urban oaks, harvested in August 2008, weighed eight times as much as their rural cousins, mostly because of increased foliage.”  (2)

Unfortunately, like most stories about climate change, this one is also a mixed blessing.  While carbon dioxide and higher temperatures may benefit plants in the city, other elements in urban air do not.  Higher levels of ozone can severely damage plant pores, which slows their growth and some trees are more susceptible to this damage than others.  Cottonwoods are particularly susceptible to ozone damage.  Ironically, ozone levels are actually higher in rural areas than in urban areas because some of the ozone is converted to oxygen in the city, while the remaining ozone “blows out to the country.”  (2)

What are the implications for readers of Million Trees?

Here’s our take-away message from these research reports:

  • The consequences of climate change are complex and are incompletely understood.
  • Climate change and air quality conditions in the urban setting are probably giving non-native plants a competitive advantage over native plants which helps to explain the frequent failures of attempts to eradicate non-native plants.
  • There are pros and cons to every change in the environment.  To call change “good” or “bad” is to over-simplify the complexity of nature.
  • Finally, our usual rhetorical question, “Do the managers of native plant installations understand the complexity of their undertaking?”  We don’t think they do. 


(1)    “Non-native plants show a greater response than native wildflowers to climate change,” October 5, 2012.  Available here.

(2)    Guy Gugliotta, “Looking to Cities, in Search of Global Warming’s Silver Lining,” New York Times, November 26, 2012.  Available here.

Is there a relationship between patriotism and the preference for native plants?

Drawing from a book by Andrea Wulff (1), we recently told our readers about the enthusiasm of the British for exotic plants from all over the world, particularly American plants.  Andrea Wulff has recently published a second book (2) which informs us that while American plants made the journey to Europe, this botanical transfer was not reciprocated by early Americans. 

Signing of Declaration of Independence, painting by John Turnbull, 1819

Our founding fathers were reluctant politicians, but devoted gardeners and professional farmers.  Although they grew many non-native plants for food and other practical purposes, they used almost exclusively American trees and shrubs when landscaping their properties.  The historical record suggests that this was a conscious choice on their part and a reflection of their patriotism.

Although George Washington was able to visit his home at Mount Vernon only once during the eight-year Revolutionary War, his correspondence suggests that it was always much on his mind.  As the city of New York prepared for the onslaught of British troops and warships in 1776, Washington wrote to his estate manager by candlelight, “Only American natives should be used, he instructed, and all should be transplanted from the forests of Mount Vernon…Washington decided that Mount Vernon was to be an American garden where English trees were not allowed.

As a farmer, Washington was innovative and practical.  He experimented with various methods of fertilizing and crop rotation.  He imported food crops and fruit trees from all over the world.  But when landscaping for ornamental purposes, he planted exclusively American plants which “…carried a symbolic message that this new nation would be independent, self-sufficient and strong.”

Shortly after Americans won their independence from Britain, our second and third presidents, John Adams and Thomas Jefferson, went to Britain hoping to negotiate a trade treaty with their former rulers.  This was a frustrating and ultimately unsuccessful effort, but while waiting in vain for a response to their proposal, Adams and Jefferson toured many of the famous gardens of England.  They were both avid gardeners and farmers and could think of no better use of the idle time imposed upon them.  They were proud to learn that the most lavish private gardens of England were composed predominantly of American trees and shrubs.  As we reported in our earlier post, these plants had been laboriously imported to England earlier in the 18th century.

Returning home, their horticultural choices were similar to Washington’s.  They made utilitarian choices when farming, but their ornamental choices were exclusively American.

Monticello, Thomas Jefferson's home

 Jefferson brought vegetable seeds from all over the world to his vegetable garden.  He kept meticulous records which enable us to marvel at the international population of vegetables in his garden during the first year of his retirement from the presidency:  “African early peas,” “Windsor beans,” “solid pumpkin from S. America,” “long pumpkin from Malta,”, “Lettuces Marsailles,” “Chinese melon,” “Spanish melon,” “Broccoli Roman,” “Kale Malta,” “Kale Delaware.” 

As the first American president to spend his entire term in residence in the White House (actually not yet named the White House), he was responsible for designing its first landscape:  “He envisaged an all-American garden…planted  ‘exclusively with Trees, shrubs, and flowers indigenous to our native soil.’”  When returning home to Monticello, he made the same ornamental choices for his own property.

Peter Coates, a British historian, examines the historical record of American fears regarding non-native species of plants and animals in his book, American Perceptions of Immigrant and Invasive Species (3), looking for a relationship between nationalism and those fears.  Although he finds many examples of similarity in the language used to describe human and non-human immigrants, he ultimately concludes that human xenophobia is not necessarily the source of anxiety about non-native plants and animals. 

One of the episodes in the historical record which Coates reports, is a long correspondence between Charles Darwin, the British scientist and his American counterpart, Asa Gray.  They engaged in a chauvinistic rivalry about the hardiness of their native plants.  Darwin jokingly asked, “Does it hurt your Yankee pride…that we thrash you so confoundedly?  I am sure Mrs. Gray will stick up for your own weeds.  Ask her whether they are not more honest, downright good sort of weeds.”  Gray replied that his wife, “allows that our weeds give up to yours,…[they are] modest…retiring things, and no match for the intrusive, pretentious, self-asserting foreigners.”

In this exchange, Darwin and Gray are referring to a botanical conundrum:  “The asymmetry between the preeminence of Eurasian weeds in North American and the weak presence of North American weeds in Eurasia has engrossed botanists on both sides of the Atlantic since Darwin and Gray’s exchanges.”  (3)  It is an intriguing question which we have considered in earlier posts, but cannot answer. 

The historical record suggests that there is an element of patriotism in Americans’ preference for our native plants and trees.  On the other hand, maybe our plants and trees are just more handsome!  But when plants perform a function—such as feeding us—Americans revert to their utilitarian ideals, abandoning natives if introduced plants are superior. 


 (1) Andrea Wulff, The Brother Gardeners, Alfred A. Knopf, 2008

(2) Andrea Wulff, The Founding Gardeners, Alfred A. Knopf, 2011

(3) Peter Coates, American Perception of Immigrants and Invasive Species, UC Press, 2006.

The Bees of Berkeley

Gordon Frankie is a Professor in the Department of Environmental Science, Policy and Management at UC Berkeley.  He has been studying the preferences of bees in northern California for over 20 years.  In 2002 he published an article in Fremontia, the journal of the California Native Plant Society, reporting on the preliminary results of his study.*

First, a word about the methods used in his study.  His research team visited the residential gardens of north Berkeley and Albany twice per week for three years, 1999 to 2002.  In the first stage of the study, the team identified the plants that were being visited by bees.  In the third year, they focused on counting the number of visits made to the identified “bee plants” by each species of bee.

The plants of Berkeley

Frankie’s team reports having identified 600-700 different varieties of non-native plants in the study area.  Native plants were defined as those that occur historically only in northern California.  Only 50 species of native plants were identified in the study area.

The bees of Berkeley

Frankie was surprised by the diversity of the bee population found by his research team.  They report having identified 74 different species of bees (updated on his website to 81).  Of those, only two were non-native bees (the European honeybee and the leaf cutting alfalfa bee).  Putting these numbers into perspective, there are approximately 1,600 species of bees in California and about 4,000 known to occur in the U.S.  Frankie reported that the population of European honeybees in the study area has declined significantly in the past 10 to 15 years.

What do the bees of Berkeley want?

The bees were observed visiting a small number of the total number of flowering plants available to them.  Only 72 species of flowering plants were visited by bees often enough to be counted by this study as “bee plants,” about 10% of the total number of flowering plants available to them.  Fifty-three of the “bee plants” were non-native and 19 were natives. 

Native bumblebee on non-native cotoneaster, Albany Bulb, Albany, California

While the bees of Berkeley are using a higher percentage of the available native plants (38%) than they are of non-native plants (8%), the percentage of non-native plants they are using is nearly 75% of all the flowers they are using.   Clearly, the non-native plants are important to the bees of Berkeley.

Frankie explains that many non-native plants are not useful to bees because they have been cultivated for looks, rather than for the nectar and pollen needed by the bees.  However, on his website, he updates his research with some strong recommendations to include both natives and non-natives in our gardens both for the benefit of the bees and the benefit of native plants.

Non-native plants extend the blooming period in our gardens, which provides food to the bees for a longer period of time:

“California native [plants] tend to flower in early spring and summer, while non-native ornamentals bloom mainly in late summer to fall, so a combination of both would be ideal for attracting the highest potential density of bees.”

Also, when our gardens attract more bees, all the plants in our gardens benefit from their pollination services, which will also benefit the native plants in our gardens:

“If your priority is a healthy garden, it makes good ecological sense to consider your plants’ bee-attractiveness, rather than focusing exclusively on whether one hundred percent of your plants are natives.  Even if your priority is to have a native garden, it can be highly advantageous to include even a couple of exotic plants on the basis of their bee-attractiveness.  The bees they attract will help your natives thrive.”

Frankie reminds us that the bees don’t care about the nativity of the plants that they use. 

Insects and other wild animals make no distinction between weeds and plants we put in our gardens.  From the perspective of the bee, any plant that provides quality pollen and nectar is attractive.  For the short period they are in bloom, weeds such as dandelions and white clover provide bees with good sources of pollen and nectar.”

Opening our minds to the benefits of non-native plants

The bees of Berkeley remind us that the obsession with native plants is a human hang up that is not shared by animals.  They consider the nativity of the plants that are useful to them to be irrelevant.  So should we. 

* Gordon Frankie, et al, “Bees in Berkeley,” Fremontia, July/October 2002

The Living Roof: A failed experiment in native plant gardening

Living Roof, California Academy of Sciences, March 2011

When the California Academy of Sciences reopened in San Francisco in August 2008, its “living roof” was considered its most unique feature.  Thirty species of native plants were candidates for planting on the roof.  They were planted in test plots with conditions similar to the planned roof and monitored closely.  Only nine species of native plants were selected for planting on the roof because they were the only plants that were capable of self-sowing from one season to another, implying that they were “sustainable.”  A living demonstration of “sustainability” was said to be the purpose of the living roof. 

So, 2-1/2 years later, what have we learned from the living roof about the sustainability of native plants in San Francisco?  The results of monitoring the roof since June 2009, are reported on the “fromthethicket” blog about Golden Gate Park.

Two of three of the predominant species on the roof after 2-1/2 years are native.  The third–moss–is not.  It is described by “fromthethicket” as “varieties of early succession mosses, the types that commonly show up in disturbed soil.”

The monitoring project has divided the roof into four quadrants.  Non-natives now outnumber natives in two of the quadrants, those which are not being weeded.  Although natives outnumber non-natives significantly in the other two quadrants, non-natives are also growing in these quadrants.

California Academy of Sciences, April 2011

We had the privilege of meeting the ecology consultant who designed the plant palette for the  living roof for the academy and many other institutions around the world.  He would not be surprised by this monitoring report.  He advised the Academy to walk the streets of San Francisco and identify the plants growing from the cracks in the sidewalks.  These are the plants he advised the academy to plant because these are the plants that are adapted to current conditions in the city.  The Academy rejected this advice because they were committed to planting exclusively natives on the roof.

The designer also advised the academy not to irrigate the roof, because the point of the roof is that it is a demonstration of sustainability.  Again, the Academy refused because they knew that without irrigation most of the native plants would be brown during the dry season, roughly half the year.  They wanted the public to believe that the plants that are native to San Francisco are beautiful year around.

There is a lesson to learn here for anyone who is willing to learn from it.  The living roof is not natural because it is irrigated and intensively gardened (e.g., weeded, fertilized, replanted, reseeded), yet non-natives not only found their way there on their own, but are dominating it within only 2-1/2 years.  Native plants are not sustainable in San Francisco without intensive gardening effort.

Peter Del Tredici has been telling us this for several years.  He is a Senior Research Scientist at the Arnold Arboretum at Harvard University and a Lecturer in the Department of Landscape Architecture at the Harvard Graduate School of Design.

In a recent publication*, he advises the managers of public lands in urban areas to abandon their fantasy that native plants are sustainable in urban settings:

“The notion that self-sustaining, historically accurate plant associations can be restored to urban areas is an idea with little credibility in light of the facts that 1) the density of the human populations and the infrastructure necessary to support it have led to the removal of the original vegetation, 2) the abiotic growing conditions [e.g., temperature, salinity, moisture, etc.] of urban areas are completely different from what they were originally; and 3) the large number of non-native species that have naturalized in cities provide intense competition for the native species that grew there prior to urbanization.”

Sure, he says, we can grow native plants, but they require at least the same amount of effort as growing any other plant and are therefore just another form of gardening:  “Certainly people can plant native species in the city, but few of them will thrive unless they are provided with the appropriate soil and are maintained to the same level as other intentionally cultivated plants.”

He concludes that native plant advocates are making a “cultural value judgment:”

“…people are looking at the plant through the subjective lens of a cultural value judgment which places a higher value on the nativity of a given plant than on its ecological function.  While this privileging of nativity may be appropriate and necessary for preserving large wilderness areas or rare native species it seems at odds with the realities of urban systems, where social and ecological functionality typically take priority over the restoration of historic ecosystems.”

We hope that the managers of our public lands in the San Francisco Bay Area will soon catch up with the scientific literature as well as acknowledge the actual experience of years of failed “restorations.”  Aside from the waste of scarce resources, these efforts are poisoning our parks with toxic herbicides and destroying beautiful and healthy plants and trees to no useful purpose. 

* “Spontaneous Urban Vegetation:  Reflections of Change in a Globalized World,” Nature and Culture. Winter 2010, 209-315.

Climate Change: Not just global warming anymore

When climate change first became a hot topic (pardon the pun) about 10 years ago, it was consistently described as “global warming.”  When scientists observed the effect that global warming was having on plants and animals in California, they reported that the ranges of native plants and animals were moving to higher elevations and northern latitudes in search of cooler temperatures. 

A study published in Nature magazine in December 2009 found that plants and animals must move as much as 6 miles every year from now to the end of the century to find the conditions they occupy now. When the plants move, the animals that depend on them must adapt or move with them to survive.  Professor Art Shapiro (UC Davis) has been studying California butterflies for over 35 years.  He reported (1) that native butterflies are moving to higher elevations, where temperatures are lower, but that ultimately, “There is nowhere else to go, except heaven.”

More recently we have experienced extreme weather that cannot be adequately described as “global warming.”  We have seen epic storms that have resulted in unprecedented flooding, while other places have experienced prolonged drought.  We are as likely to have an extremely cold winter as we are to have an extremely hot summer.  So the phrase “global warming” has evolved into the more accurate description:  “climate change.”  Aside from our anecdotal observations of these extreme weather events, science is beginning to catch up to provide an analytical understanding of our observations.  The story of climate change is now much more complex and the challenges it presents have become correspondingly more difficult and unpredictable.

Changes in Precipitation

Although places like Pakistan, Australia and some states in the US have recently experienced more rain and flooding than history has recorded, scientists have been reluctant to attribute this to climate change until very recently.  Computer modeling of nearly 50 years of weather data has finally enabled scientists to confirm that these increases in precipitation are the result of “…the effects of greenhouse gases released by human activities like the burning of fossil fuels.” (2)

And, like increases in temperature, changes in precipitation also result in the movement of plants and animals to “find” the conditions to which they are adapted.  Scientists have recently challenged previous assumptions about the movement of plants and animals to higher elevations.  They now report (3) that in some places in California in which precipitation has increased, plants have responded by “moving” to lower elevations.  Scientists acknowledge that the affect on the animal populations in their historic ranges is unpredictable because insects, for example, are more sensitive to changes in temperature and may not be able to move downhill with the plants they presently depend upon. 

Changes in Fog Patterns

Fog is another weather event that is important in California, particularly along the coast, where the warm air from the interior meets the cold air from the ocean.  The result of this confluence of cold and warm air is fog, particularly during the summer when the difference in temperatures is greatest. 

The redwood is our native tree that is closely associated with the foggy coastal conditions in California.  The redwood requires the fog drip to irrigate it during the dry California summer and its range is limited to sheltered areas because it does not tolerate wind.  The range of the redwood in California is therefore limited to a few hundred miles along the coast.  Its narrow range makes it particularly vulnerable to climate change. 



Redwood National Park, NPS photo



In Muir Woods, for example, higher temperatures have reduced coastal fog by 30% in the past century.  Scientists expect this loss of summer fog drip to result in a significant loss of water to the trees and they predict that it will affect the survival of the redwoods in the long-run.(4)

Implications of climate change for native plants?

Clearly, we still have much to learn about climate change:

  • Which weather events are indicators of long-range trends?
  • Climate change is apparently not just one trend, such as increased temperatures.  It is probably many different types of weather events, such as increases or decreases in snow and rainfall, hurricanes and typhoons, fog and wind.  Obviously, we don’t yet have the complete picture of what or where long-range changes have occurred or which are likely in the future. 
  • We know little about the affect that climate change will have on the natural world.  How will plants and animals respond to climate change?  Which plants and animals will survive and, if so, where will they survive?

We marvel at the confidence that the local native plant advocates have in their agenda.  How did they select the pre-European landscape of the late 18th century to replicate?  What makes them think that plants and animals that lived here 250 years ago are still sustainable here, let alone that they will be sustainable in the future? 

These are rhetorical questions, which we will presume to answer for our readers:  Native plant advocates may compensate for radically changed environmental conditions by using intensive gardening methods.  The use of herbicides, irrigation systems, prescribed burns, constant weeding, soil amendments, fences and boardwalks, etc., may artificially mimic the conditions of 250 years ago.  However, the result is a native plant garden that is neither natural nor more biodiverse than what can be achieved with less effort, with less toxicity and fewer scarce resources.  While we can see the value of a native plant garden to preserve our horticultural heritage, we find it more difficult to justify the large-scale efforts that we currently find in all of our public lands.  Is it realistic to garden all of our public lands in perpetuity? 

(1) Arthur Shapiro (UC Davis), Contra Costa Times, 1/19/10

(3) “Mountain plant communities moving down despite climate change, study finds,” Los Angeles Times, 1/24/11


(4) “Fog burned off by climate change threatens to stunt Muir Wood’s majestic redwood,” Marin Independent Journal, 2/5/11   http://www.marinij.com/marinnews/ci_17297751?IADID=Search-www.marinij.com-www.marinij.com

Stephen Jay Gould examines the concept of “native plants”

The native plant ideology is inconsistent with the basic principles of evolutionary theory and has dangerous political implications which have been applied in the past.  In his article (“An Evolutionary Perspective on Strengths, Fallacies, and Confusions in the Concept of Native Plants”), published by Arnoldia, the journal of Harvard University’s arboretum, Stephen Jay Gould describes the concept of “native plants” as “a notion [which] encompasses a remarkable mixture of sound biology, invalid ideas, false extensions, ethical implications and political usages both intended and unanticipated.”(1)

First, who is Stephen Jay Gould and why should we care what he thinks about the ideological construct of “native plants?”  Professor Gould taught geology and paleontology at Harvard University and biology and evolution at New York University, while also working at the American Natural History Museum in New York.  His most significant achievements as a scientist were in the field of evolutionary theory.  He is one of the most frequently cited scientists in the field of evolutionary theory.  But he is best known as a writer of essays and best-selling books on natural history for the general public.  Incidentally, he had a life long interest in civil rights and he brought that interest to his scientific inquiries with his abiding opposition to the use of pseudoscience to promote racism or sexism.(2) It is that interest that led him to his analysis of the concept of “native plants.”

Native plant advocates believe in the inherent superiority of native plants.  This belief is based on an assumption that native plants “belong” in a particular place and that their presence in the proper location represents an “optimal” landscape for that place.  This belief is based on a lack of understanding of the concept of natural selection. 

As Gould explains, “Natural selection does not preferentially lead to plants that humans happen to regard as attractive.  Nor do natural systems always yield rich associations of numerous, well-balanced species.  Plants that we label ‘weeds’ will dominate in many circumstances…weeds often form virtual monocultures, choking out more diverse assemblages than human intervention could maintain.”   The mechanism of natural selection does not produce the optimal adaptation, but only the adaptation that is better than its competitors at any particular point in time, which is why introduced plants are frequently more competitive than their predecessors deemed “native.” 

The argument that native plants “belong” in a particular place is equally fallacious because it assumes that the plants are there because they are best suited to conditions in that location.  In fact, plants are “products of a history laced with chaos, contingency, and genuine randomness.”  Plants have been moved—and continue to be moved—about the planet by weather, by birds and animals, including humans.  “’Natives’, in short, are the species that happened to find their way…not the best conceivable for a spot.”  (see video, “The Fallacy of Native Plants“)

A closely related argument used by native plant advocates to justify their crusade against non-native plants and trees is that the natives have “co-evolved” with other species of plants and animals and that they therefore fit together like some magic puzzle, implying that if the native plants disappear, native animals will also disappear because they are dependent upon the plants.  Gould says, “this notion, however, popular among ‘new agers,’ must be dismissed as romantic drivel.” 

Gould credits the native plant movement for efforts to preserve biodiversity, a goal that is defeated if other plants are simultaneously eradicated by their efforts.  He counsels native plant advocates to balance their efforts to achieve an inclusive biodiversity and we share that view.  We encourage native plant advocates to preserve the plants they prefer and plant more if they wish, but to quit destroying the plants they do not prefer.

But Gould does not come to this topic solely from his knowledge of the principles of evolution and his desire for the public to correctly understand its mechanisms.  He is also concerned about the “slippery slope” of nativist ideology from application to plants to application to humans.  This is not a theoretical anxiety on his part.  It is based on historical precedents. 

Wikimedia Commons

In Nazi Germany and in the United States around the same time, horticultural theories abounded about the superiority of native landscapes and those theories were inextricably linked to the belief that non-native humans were also inferior.  For example, “In 1942 a team of German botanists made the analogy explicit in calling for the extirpation of Impatiens parviflora, a supposed interloper:  ‘As with the fight against Bolshevism, our entire Occidental culture is at stake, so with the fight against this Mongolian invader, an essential element of this culture, namely, the beauty of our home forest, is as at stake.’”   And similar sentiments from an American horticulturalist, Jens Jensen, “’The gardens that I created myself shall…be in harmony with their landscape environment and the racial characteristics of its inhabitants.  They shall express the spirit of America and therefore shall be free of foreign character as far as possible…Latin spirit has spoiled a lot and still spoils things every day.”

Having debated many times with native plant advocates about their plans to eradicate non-natives, and listened to their justifications for those plans, we know that no counter argument inflames them more than the suggestion that their plans are reminiscent of similar efforts to eradicate human non-natives.  However, for the vast majority of the public who have not engaged in this debate, we provide the scientific evidence that the native plant movement is an ideology not based on scientific principles which has been associated in the past with horrific discrimination against non-native humans. 

"The New Case Against Immigration: Both Legal and Illegal" Book cover in the public domain

 We cannot dismiss these historical precedents as irrelevant at a time when anti-immigration sentiments are rampant in our society.


(1) All quotes are from “An Evolutionary Perspective….” 

CHANGE….the only constant

The conventional wisdom amongst native plant advocates is that native plants will return to the landscape if non-native plants are eradicated.  In this post, we will examine this assumption and refute it.

Several different methods are used to eradicate non-native plants, but it doesn’t matter which method is used because the results are the same:  native plants do not return when non-native plants are removed. 

Spraying herbicides is a popular method of eradicating non-native plants because it is considered the most cost-effective method. In addition to the obvious health risks, the downside of herbicide use is that they are as likely to kill the natives as the non-natives.  This problem is illustrated by a USDA study of the effects of a one-time aerial spraying of herbicides on grassland after 16 years.  Although the herbicide is assumed to “dissipate” within a few years, the negative effect on the natives persisted 16 years later:  “…the invasive leafy spurge may have ultimately increased due to spraying.  Conversely, several desirable native herbs were still suffering the effects of the spraying,,,” 

Even when native plants are removed, non-native plants occupy the cleared ground.   Environmental scientists at UC Berkeley removed native chaparral from experimental plots in Northern California to test fuel reduction techniques using two different methods (prescribed burns and mechanical), in different seasons, over a period of several years.  In every test, the result was on average from 23% (for prescribed burns)to 61%  (for mechanical methods) non-native plants where they had not previously existed.  

Jon E. Keeley (USGS) finds the same tendency for non-natives to replace natives in forests:  “Forest fuel reduction programs have the potential for greatly enhancing forest vulnerability to alien invasions.” (1)

A scientist (2) arrived at the same conclusion after attempting to restore an oak-studded grassland on Vancouver Island.  He tried several different methods of removing invasive grasses for several years only to find that “…the decline of the native plant species accelerated…” 

Crissy Field, NPS photo

Those who observe native plant restorations in the San Francisco Bay Area aren’t surprised by these studies.  We know that native plant restorations are unsightly failures unless they are aggressively planted, irrigated for several years, and fenced.  Examples of successful restorations can be seen at Crissy Field and the summit of Mt. Sutro.  The East Bay hills provide examples of the opposite strategy.  Where UC Berkeley has clear-cut all non-native trees and vegetation, non-native weeds quickly occupied the barren ground.    After a particularly wet winter, the non-native poison hemlock in the East Bay hills is 6 feet tall along the roads. 

Poison hemlock, East Bay hills

Why are non-native plants apparently more competitive than native plants?  Because the conditions that supported native plants 250 years ago, prior to the arrival of Europeans, have changed.  The native plants are no longer well adapted to the current conditions.

Higher levels of CO2 and the associated climate change are promoting the growth of non-native plants.  A USDA “weed ecologist” (3) studied the effects of higher temperatures and CO2 on the growth of non-natives (AKA weeds) by growing identical sets of seeds in a rural setting and an urban setting with higher temperatures and CO2 levels.  Seeds grown in the urban setting produced substantially larger plants with much more pollen and therefore greater reproductive capability. 

Other scientists reach the same conclusions by studying the changing ranges of native plants and insects.  An ecologist at UC Berkeley (4) says that “California’s flora face a potential collapse…as the climate changes, many of these plants will have no place to go.”   A scientist at the California Academy of Sciences (5) predicts that redwoods will disappear from California by the end of the century.

As the plants move, so do the insects and animals that need them.    A study published in Nature magazine in December 2009 found that plants and animals must move as much as 6 miles every year from now to the end of the century to find the habitat they occupy now.  An ecologist at UC Davis (6) has been studying native butterflies for over 35 years.  He recently reported that native butterflies are moving to higher elevations, where temperatures are lower, but that ultimately, “There is nowhere else to go, except heaven.”

The local environmental organizations and public policy-makers must wake up to this reality and reorder their priorities.  Instead of demanding that all non-native plants and trees be eradicated and that native plants be restored where they are no longer sustainable, they must make climate change their highest priority.  The easiest and cheapest step to take to address this issue is to quit destroying healthy trees—just because they are non-native–that are sequestering tons of carbon.

(1) “Fire Management Impacts on Invasive Plants,” USGS, Jon E. Keeley, April 2006

(2) Andrew MacDougall, University of Guelph, Ontario, Canada, NY Times Magazine, 6/29/08

(3) Lewis Ziska, USDA, Beltsville, MD

(4) David Ackerly, UC Berkeley, Los Angeles Times, 6/25/08

(5) Healy Hamilton, Cal Academy, Center for Biodiversity Research

(6) Arthur Shapiro, UC Davis, Contra Costa Times, 1/19/10

What is natural?

The branch of San Francisco’s Recreation and Park Department dedicated to the preservation and restoration of native plants to the city’s parks calls itself the Natural Areas Program (NAP).  And the 32 parks or portions of parks within NAP’s jurisdiction are called Natural Areas.  In this post we will visit a few of these areas to ask if they are accurately described as “natural.”

Parcel 4, Balboa & Great Highway, 1868

The Natural Area known as Parcel 4 is at the corner of Balboa and the Great Highway.  A photograph taken in 1868 of that location indicates that it has been continuously built upon for nearly 150 years.  Long-term residents of San Francisco will remember it as the location of Playland by the Beach.  After Playland was closed, the city purchased the property for $3.05 million in 1993 with the intention of putting a sewer pipe under it, then restoring it to dune vegetation.  The soil was essentially building rubble, so the city had to buy $47,000 of sand and disk it down 18 inches to amend the soil in preparation for planting dune vegetation.  The sand was bulldozed into simulated dune shapes and planted in 2002.  The restoration was described in the newsletter of the Coalition of San Francisco Neighborhoods in April 2003, in an article entitled “Sand Francisco.”  Does this sound “natural” to you?

Parcel 4 under construction, 2002
Eight years later, 2010

India Basin is a Natural Area on the east side of the city, on the bay.  The east shore of the city was where most industrial development was located until industry left the city beginning in the 1960s.  Much of the soil was landfill.  Like Parcel 4, the landfill was bull-dozed into a simulated wetland, hoping to restore tidal action.  Native pickle-weed was planted several times in the mud-filled basins.  We haven’t visited this area for several years.  Perhaps they have finally been successful in that effort.  This is what we found there on our last visit:  native plants along the trail, surrounded by plastic and woodchips to discourage weeds and huge, empty, mud basins off shore.    It didn’t look natural to us.

India Basin, 2003

Many of the Natural Areas in San Francisco are less artificial than these two extreme examples.  Some of the Natural Areas weren’t built upon in the past, but had no native plants in them when they were designated as Natural Areas.  Pine Lake is an example of such a Natural Area.  Even where native plants actually existed, their populations were small and isolated in comparison to the acreage designated as a Natural Area.  Over 1,000 acres of city-managed parkland have been designated as Natural Areas, 25% of all parkland in San Francisco and 33% if Pacifica is included in the calculation.

Sculpture of “Albany Bulb Greeter”

Now we will visit the Albany Bulb for contrast.  Albany Bulb is also landfill that was for many years the Albany city dump.  When the dump was closed, the Bulb became a park.  It is a wild and wonderful place.  There are few native plants, other than the ubiquitous coyote bush that seems to thrive almost anywhere.  In the spring, Albany Bulb is a riot of color.  These are the competitive non-natives that native plant advocates wring their hands about.  They are there because they are best adapted to the current conditions in this location…the heavily amended soil, the higher levels of CO₂, the warmer climate, the use by humans and their animal companions. 

Valerian and wild mustard, Albany Bulb. Both are non-native plants.

If all of these non-native plants and trees were eradicated from the Albany Bulb, would native plants magically appear?  Based on our experience, we don’t think so.  The conditions that supported the plants that are native to the Bay Area are gone for good.  It is a fantasy that the existence of non-native plants is the only obstacle to the return of the natives.  Visiting a few places where this strategy has been tried will confirm this.  Unless the natives are aggressively planted, irrigated for several years, fenced for protection, weeded or sprayed with herbicides regularly, they do not return.  Can such intensive gardening be called “natural?”

(UN)controlled Burns

Today’s SF Chronicle reports that yet another “controlled” (AKA “prescribed”) burn is responsible for a wildfire in California.  This fire in the Santa Cruz Mountains burned 485 acres in October 2009, injuring 4 of the 1,700 firefighters who fought it at a cost of $4 million.  That cost doesn’t include the claims for damages of the property owners who lost their homes.

This isn’t the only controlled burn that has caused major wildfires in California and elsewhere.  For historical perspective, let’s start with the Bandelier Monument Fire in New Mexico.  This fire, began in May 2000 as a prescribed burn and eventually burned over 45,000 acres, threatened the Los Alamos National Laboratory and destroyed 235 structures.  The Department of the Interior suspended all prescribed burns while an inquiry was conducted and policy was revised to theoretically prevent similar accidents.

Did revision of policy stop so-called controlled burns from causing wildfires in our national parks?  No, it did not.  In October 2009, the Big Meadow Fire in Yosemite began as a prescribed burn and eventually burned 7,425 acres.  NPS apparently hadn’t learned much from their bad experience 9 years earlier at the Bandelier Monument.

Yosemite Big Meadow Fire, NPS photo

The National Park Service isn’t the only manager of public land that has had bad luck with controlled burns.  In 2003, the California State Park Department was responsible for starting a fire on San Bruno Mountain in South San Francisco intended to burn 6 acres that eventually burned 72 acres and came perilously close to homes, according to the SF Chronicle.

We should not be surprised by the unpredictable results of prescribed burns.  Fire scientists at UC Berkeley conducted a series of experimental prescribed burns in chaparral in Northern California, hoping to arrive at a model of fire behavior that would improve the predictability of such burns.  They arrived at the conclusion that “…it is extremely difficult to predict with certainty where the fire will spread…For more than half of the transects installed, the flaming front did not traverse the transects as predicted…” (1)

You might ask, “If these prescribed burns keep causing major wildfires, why do we continue starting them?”  Good question, and we are going to answer that.  The conventional wisdom is that because fires have been suppressed in the past century or so, fuel has built up that has become extremely dangerous.  Theoretically, we must restore the “natural” fire cycle to prevent this dangerous build up of fuel that will inevitably cause a huge wildfire if we don’t reduce the fuel load with smaller (hopefully) fires.  Sounds like a good argument, but is it true?  Some scientists say it isn’t.

Jon E. Keeley, Ph.D. (Biologist, US Geological Service) says in “Fire Management in the California Shrublands,”

“Fire management of California shrublands has been heavily influenced by policies designed for coniferous forests, however, fire suppression has not effectively excluded fire from chaparral and coastal sage scrub landscapes and catastrophic wildfires are not the result of unnatural fuel accumulation. There is no evidence that prescribed burning in these shrublands provides any resource benefit and in some areas may negatively impact shrublands by increasing fire frequency. Therefore, fire hazard reduction is the primary justification for prescription burning, but it is doubtful that rotational burning to create landscape age mosaics is a cost effective method of controlling catastrophic wildfires.”

Obviously, there isn’t scientific consensus that prescribed burns reduce fire hazard, so perhaps there is another reason why we pursue this dangerous course.  Yes, there is, and once again we turn to the native plant movement to explain why we are harming our environment and posing unnecessary dangers to animals, including humans.

The scientific literature is rampant with evidence that periodic fire is essential to the health of native plants.  Here is an example from a renowned academic book about California’s ecology that has the status of a standard textbook:

“The [chaparral] community has evolved over millions of years in association with fires, and in fact requires fire for proper health and vigor.  Thus it is not surprising that most chaparral plants exhibit adaptations enabling them to recover after a burn.  Many species are sprouters; the aboveground parts may be killed, but new growth arises from roots or buds at the base of the stem…Other species have seeds that require fire in order to break dormancy; they will not germinate unless they have been heated.  The cones of some chaparral conifers open only after they have been heated.  Some herbaceous species will not germinate unless there is ash on the ground when it rains…In the absence of fire, a mature chaparral stand may become senile, in which case growth and reproduction are reduced.”  (Schoenherr, A Natural History of California, 1992, UC Press)

This is also an opportunity to show how the native plant agenda has been adopted by local managers of our public lands. The “Wildfire Hazard Reduction and Resource Management Plan” of the East Bay Regional Park District announces its intention to conduct prescribe burns for the following purposes:

  • “Grassland and Herbaceous Vegetation…broadcast burns in the summer or early fall [fire season] are known to favor native plants.” (page 128)
  • “Maritime Chaparral…This [native] vegetation type and the Manzanita it supports are also fire dependent. Without disturbance by fire the Manzanita does not reproduce, becomes decadent, and is replaced by shade tolerant species.” (page 132)
  • “North Coastal Scrub…This plant community [of native plants] is adapted to natural fire cycles, and most species found within this plant community resprout easily to rejuvenate individual specimens after fire, or require fire to trigger germination.”  (page 139)
  • “[Native] Coyote Brush Scrub…is adapted to natural fire cycles.  Most species resprout easily to rejuvenate individual specimens after fire, or requires fire to trigger germination.” (page 149)

Are any of these purposes related to reducing fire hazard?  You be the judge.

The management plan of San Francisco’s Natural Areas Program also announces its intention to use prescribed burns in the Initial Study (the first stage of environmental review under CEQA) of the program, but offers no information about the effect of these burns on the environment.  In a city such as San Francisco, in which there is no history of wildfire, we must assume that the sole purpose of these burns will be to benefit native plants.

Clearly controlled burns frequently cause major wildfires.  Fires, whether intentional or not, also release harmful particulates into the air and reduce air quality.  There is no evidence that controlled burns prevent wildfires.  Yet, there is considerable evidence that they benefit native plants.  We conclude that the primary purpose of controlled burns is to benefit native plants. 


(1) Scott Stephens, et. al., “Measuring the rate of spread of chaparral prescribed fires in Northern California,” Fire Ecology, Vol. 4, No. 1, 2008