Month: February 2023

The Oxalis Obsession

As a long-time reader of Jake Sigg’s Nature News, I am very familiar with his passionate crusade against Oxalis pes-caprae.  When oxalis appears in the landscape in January, Jake gears up his campaign again. This year the Westside Observer published an article by Jake about oxalis that reaches a new level of urgency and asks land managers to increase their use of herbicides to kill the plant.

In the past, Jake has advised careful and relentless hand-pulling of oxalis with its bulb intact.  Now he acknowledges that hand-pulling is useless to eradicate oxalis.  Although herbicides have been used on oxalis in San Francisco’s parks for 25 years, Jake now wants MORE herbicides to be used. Over 20% of all herbicide spraying by the Natural Resources Division (NRD) of the Recreation and Park Department was applied to kill oxalis in “natural areas” in 2022. NRD sprayed oxalis 35 times in 2021 and 38 times in 2022.

Spraying Garlon on Twin Peaks in San Francisco, February 2011

From January to March, virtually all the herbicides sprayed by NRD in the so-called “natural areas” were sprayed on oxalis.  If it were possible to eradicate oxalis with herbicide, why is there more oxalis now than there was 25 years ago, when NRD (then known as the Natural Areas Program) started spraying herbicides in the “natural areas?”  A lot of herbicide has flowed under the bridge in the past 25 years, but oxalis thrives. What is the point of pouring more herbicide under the bridge of sighs?  We’re pouring more fuel on the fire with nothing to show for it. 

One of many pesticide application notices on oxalis in Glen Canyon Park in February 2023.

The University of California Integrated Pest Management Program explains why it’s not possible to eradicate Oxalis pes-caprae with herbicides: “Several postemergent herbicides including triclopyr and fluroxypyr (selective for broadleaf plants) and glyphosate and glufosinate (nonselective) effectively kill the top growth of this weed but are harmful to most ornamentals, so be careful these herbicides don’t drift onto desirable plants. These herbicides don’t kill the bulbs, and regrowth from bulbs should be expected.” In other words, you can kill the above-ground top growth and other non-target plants in the vicinity, but you won’t kill the oxalis. 

Chemical Warfare?

On one hand, Jake urges public land managers to escalate chemical warfare against oxalis.  On the other hand, he accuses oxalis of “chemical warfare” (AKA allelopathy), secreting chemicals that kill other plants. This accusation is pure speculation on Jake’s part.  He offers as “evidence” of his speculation that after oxalis dies back in April “we’re left with bare ground for the rest of summer and autumn.”  He ignores the obvious fact that annual spraying of gallons of herbicide on oxalis in the “natural areas” could be causing the bare ground. It has apparently not occurred to him that many herbicides are non-selective, killing everything they touch, not just targeted plants. And those herbicides that claim to be selective are very mobile in the soil, capable of killing adjacent plants through their roots.  If you don’t want to see bare ground, don’t spray herbicides!

Jake asks for more research on how oxalis interacts with other plants in his article published by Westside Observer. He is apparently unaware of the research that has been done by scientists at University of Montana to address the question of how competitive oxalis is in plant communities that include native plants:  “Oxalis is a poor competitor. This is consistent with the preferential distribution of Oxalis in disturbed areas such as ruderal habitats, and might explain its low influence on the cover of native species in invaded sites.”

The study explains why oxalis does not suppress the growth of other plants, including natives.  Oxalis makes more phosphorous available in the soil, which essentially acts as a fertilizer for other plants:  “These results are consistent with our field data and suggest that Oxalis may improve P availability in the field.”

This study was published in 2007.  It found that Oxalis pes-caprae does not suppress the growth of other plants and, in fact, increases nutrients in the soil.  Jake apparently doesn’t know about this study and related studies that found that pollinators are as interested in O. pes-caprae as they are in native plants.

Jake’s accusation that oxalis is waging “chemical warfare” against native plants does not come out of nowhere.  The same accusation was used against eucalyptus trees for decades until a definitive empirical study proved that eucalyptus is not allelopathic.  The California Invasive Plant Council removed that accusation from its evaluation of Blue Gum eucalyptus in 2015 (along with the accusation that eucalyptus kills birds).  As the readers of Jake’s Nature News know, his hatred of eucalyptus is second only to his hatred of oxalis.  There was never evidence that eucalyptus is allelopathic and there is no evidence that oxalis is allelopathic.

Does biodiversity justify poisoning nature?

Jake justifies his crusade against oxalis based on his belief that its existence threatens biodiversity.  Since there is no evidence that oxalis kills other plants, there is no reason to believe its existence threatens biodiversity.  

Jake also asks us to include only native plants in the measure of biodiversity, but he is alone in that belief.  Scientific measurements of biodiversity include all species of plants and animals, whether considered native or non-native.  The Recreation and Open Space Element of San Francisco’s General Plan explicitly acknowledges that both native and non-native plants contribute to biodiversity:  “Parks and open spaces in San Francisco include both native and non-native species, both of which can contribute to local biodiversity.” (Policy 4.1, Recreation and Open Space of San Francisco General Plan)

Jake ups the ante against oxalis by claiming that wildlife requires solely native plants, a fundamental tenet in native plant ideology.  Again, this claim is unsupported by evidence.  As Professor Art Shapiro (UC Davis) says in his Field Guide to Butterflies of the San Francisco Bay and Sacramento Valley Regions, “Most California natives in cultivation are of no more butterfly interest than nonnatives, and most of the best butterfly flowers in our area are exotic.”

coyote hunting in oxalis field. Copyright Janet Kessler

On one hand, Jake claims that oxalis deprives birds and other foragers of food.  On the other hand, Jake acknowledges that oxalis is foraged by gophers and scrub jays (based on one observation).  Jake wants it both ways because that serves his purpose. 

If native plants were any benefit to wildlife, that benefit is quashed by the widespread use of herbicides being used in the “natural areas.”  For example, Himalayan blackberries are an important source of food for birds and other wildlife in San Francisco’s parks and are also eaten by children visiting the parks.  The blackberries are routinely sprayed with herbicides in the so-called “natural areas.”  Wildlife is exposed to the herbicides and they are also deprived of important sources of food.

A recent survey of 24,000 gardens in the UK found that pesticide use had a significant effect on bird life. The study found that gardens that used pesticides had fewer species of birds than similar gardens that did not use pesticides:

“Pesticide spraying impacted the positive effect [surrounding habitat quality] had on bird richness. Specifically, ‘species richness [number of species] increases with the surrounding quality, both for gardens that do not use pesticides and for gardens that applied pesticides, but this effect is significantly less strong when pesticides are applied’ the study indicates. Scientists zeroed in on three active ingredients: the weed killer glyphosate, the neonicotinoid insecticide acetamiprid, and the synthetic pyrethroid deltamethrin as resulting in the most damaging pesticide impacts to bird species’ richness.” Note that the study’s definition of “surrounding habitat quality” made no distinction between native and non-native plants.  The British are not strong supporters of native plant ideology. 

Nativists keep using huge quantities of herbicide to kill vegetation they don’t like, while also claiming that their eradication projects benefit birds. This is a fundamental contradiction. Their eradication projects are harmful to birds and other creatures that live in our parks and open spaces.

Jake’s Lament

In his article, Jake laments that people are accepting changes in the landscape because they don’t remember what the landscape looked like 100 years ago.  His “baseline view” of what landscapes should look like is much further in the past than most people’s memories of the landscape. 

The climate has changed significantly in the past 100 years.  When the climate changes vegetation changes.  We should welcome the changes because they are required for the survival of any landscape.  When the climate changes, plants and animals must move, adapt, or die.  The changing landscape is an indication that plants are adapting to changing conditions. 

We cannot stop evolution, nor should we try.  Herbicides are a futile attempt to stop evolution.  Herbicides cannot stop evolution, because plants evolve a resistance to them.  After 25 years of constant herbicide use in San Francisco’s parks and open spaces, we should assume that they are less effective every year. 

While San Francisco’s Recreation and Park Department has significantly reduced its use of herbicides since 2010, the Natural Resources Division that is responsible for the “natural areas” has not. Natural Resources Division is now using more herbicides than the rest of the parks. Source: San Francisco IPM Program, Department of Environment

What does “restoration” mean?

I welcome comments on my website because I often learn from them.  This comment on a recent post inspired me to think about why I often put the word “restoration” in quotation marks when describing projects that are more destructive than constructive:

Oh my, we are back to putting quotes around words we don’t like. An excerpt from this article:

“Many ecological studies and associated “restoration” projects adopt the same viewpoint that destruction is a justifiable method of studying and “restoring” ecosystems. “Restoration” projects often begin by killing all non-native plants with herbicides before attempting to create a native landscape.”

Often? We do a fair amount of underburning around here, primarily to “restore” ecosystem structure and function in mixed conifer. Of the burns I have been involved with, not one involved herbicides and pesticides. I think you put the lie to your own article by this one exaggeration. I suspect if I bothered to look I would find many others.

This is my reply to this comment:

When the word restoration is used appropriately, it is a powerful, positive word.  There is a multitude of potential projects in California that would be restorative.  Here is a brief list:

Superfund Sites in California

Prescribed burns are currently popular and some don’t use herbicides before burning, but they are NOT a panacea.  Many prescribed burns have become destructive wildfires.  Here are two presentations made at the October conference of the California Native Plant Society that were critical of the over-reliance on prescribed burns:

Source: Jon F. Keeley, CNPS Conference, October 2022
  • Dr. Jon Keeley is a respected fire scientist with US Geological Service with expertise in chaparral ecosystems.  He explained that 60% of native chaparral species (notably manzanita and ceanothus) are obligate seeders that do not resprout after fire and therefore depend on their dormant seed bank for regeneration.  In recent decades the fire interval in chaparral has decreased due to climate change and associated drought.  In many places the fire interval has become too short to establish the seed bank needed for regeneration.  In those places Dr. Keeley has observed vegetation type conversion to non-native annual grasses.  Dr. Keeley Is concerned that vegetation type conversion from forests in some cases and shrublands in others to non-native annual grassland may be the result of shortening fire intervals further “because of the upsurge in state and federal programs to utilize prescription burning to reduce fire hazard.” 
  • Another presentation about a 20-year effort to convert non-native annual grassland to native grassland using prescribed burns at the Santa Rosa Plateau Ecological Reserve reported their failure: “Non-native grass cover significantly decreased after prescribed fire but recovered to pre-fire cover or higher one year after fire.  Native grass cover decreased after prescribed fire then recovered to pre-burn levels within five years, but never increased over time.  The response of native grass to fire (wild and prescribed) was different across time and within management units, but overall native grass declined.” The audience was audibly unhappy with this presentation.  One person asked if the speaker was aware of other places where non-native grass was successfully converted to native grass.  The speaker chuckled and emphatically said, “NO.  I am not aware of any place where native grasses were successfully reintroduced.” 

When describing projects that are more destructive than constructive, I put the word “restoration” in quotes.  I stand by that choice.

Projects that are truly restorative

Days after responding to this comment, the New York Times published an article about the successful effort to clean up the New York City harbor that deserves to be called a restoration:

“Fifty years ago, Congress voted to override President Richard Nixon’s veto of the Clean Water Act. It has proved to be one of the most transformative environmental laws ever enacted.

“At the time of the law’s passage, hundreds of millions of gallons of raw sewage was dumped by New York City into the Hudson River every day. This filth was compounded by industrial contaminants emptied into the river along much of its length. The catch basin for all of this was New York Harbor, which resembled an open sewer. At its worst, 10 feet of raw human waste blanketed portions of the harbor bottom, and certain reaches held little or no oxygen to sustain the life of its fishery. Trash floated among oil slicks.

“Health advisories against eating fish from the Hudson remain, but its ecology has largely recovered, thanks to the law, which imposed strict regulations on what could be discharged into the water by sewage treatment plants, factories and other sources of pollution….”

The NYT article also describes how many animal species benefitted from the reduction in pollution in New York City’s harbor.

NYT also published an article about the pollution of the water surrounding Cape Cod that is destroying that ecosystem. 

“The algal explosion is fueled by warming waters, combined with rising levels of nitrogen that come from the antiquated septic systems that most of the Cape still uses. A population boom over the past half-century has meant more human waste flushed into toilets, which finds its way into waterways.

“More waste also means more phosphorus entering the Cape’s freshwater ponds, where it feeds cyanobacteria, commonly known as blue-green algae, which can cause vomiting, diarrhea and liver damage, among other health effects. It can also kill pets.

“The result: Expanding aquatic dead zones and shrinking shellfish harvests. The collapse of vegetation like eelgrass, a buffer against worsening storms. In the ponds, water too dangerous to touch. And a smell that Ms. Fisher characterizes, charitably, as “earthy.”

“Together, the changes threaten the natural features that define Cape Cod and have made it a cherished destination for generations.”

Cape Cod. Source: NASA

This an example of the many missed opportunities to restore the environment.  Instead of addressing the sources of pollution, such as leaky septic tanks and sewage systems, we invest in projects that contribute to pollution by spraying harmless vegetation with herbicides, killing harmless animals with pesticides and contributing to air pollution by burning vegetation. 

Closer to home, the recent torrential rain soaking California is a reminder of our inadequate sewer systems now overflowing from storm drains into city streets and being dumped into the ocean when the drainage gets that far.   San Francisco’s antiquated sewage system is an extreme case.  When it was built, it funneled storm runoff from city streets into the city’s sewer system, combining residential sewage waste with storm water runoff.  When it rains heavily, San Francisco’s sewage system is not capable of treating the increased flow. Such systems have been illegal for decades, but San Francisco has not made the necessary improvements to its sewer system.  As the SF Chronicle reports, city streets are now flooded with a toxic mix of rain water and human sewage. 

“Restoration” is not a dirty word when used to describe projects that reduce pollution.  When projects contribute to pollution they cannot legitimately be called “restorations.”