April 2022 – Conservation Sense and Nonsense

Weeds are making a comeback!

While the native plant movement remains strong in California and locally in the San Francisco Bay Area, some communities are waking up to the fact that weeds make valuable contributions to our gardens and the wildlife that lives in them. The British have always been ahead of us in welcoming plants from all over the world in their gardens. The British have bee n enthusiastic importers of plants from all over the world for hundreds of years. They had one of the biggest empires in the world, spanning the globe from India to Africa, Australia, New Zealand, and America, which put them in a unique position to sample the botanical riches of the world.

The English garden, where plants from all over the world are welcome

In a recent article in The Guardian, an English gardener describes her journey from fighting the weeds in her garden to her new relationship with them: “I remember writing, many years ago, about my fight to get rid of these dandelions. Clearly, I didn’t win. Now, when I am greeted by them, I am glad I lost the battle. These days, I truly consider them friends…they are welcome in my garden, because I know they do more good than harm.”

The English gardener reminds us that the war on weeds began only recently. Going deep into agricultural history, weeds were natural forage that were a part of our diet. Weeds fed our domesticated animals, stuffed our mattresses and made twine and rope. Many have medicinal properties, but most have marketable substitutes now. They were tolerated on the edges of agricultural fields and in our gardens.

The typical American lawn, maintained with pesticides and fertilizer is not habitat for pollinators or other insects. Source: Pristine Lawn Care Plus

The war on weeds began after World War II, when chemicals were introduced to agriculture. Pesticides were considered benign for decades. We have learned only recently of the dangers of some pesticides. The promotion of pesticides changed the aesthetics of gardening, initiating an era in which weeds were banished from our agricultural fields and our gardens.

Note the drone hovering over the children in a strawberry field. Drones are the latest development in chemical warfare. They are used to spot non-native plants in open space as well as to aerial spray pesticides. They are cheaper than other methods of application and for that reason are likely to increase the use of pesticides.

Do not underestimate the power of propagand a to promote the use of pesticides: “A publishing company linked to the most powerful agricultural lobby group in the U.S. is releasing children’s books extolling the benefits of pesticides and nitrogen fertilizers.” Industrial agriculture begins the indoctrination of the public at childhood.

Bumblebee in clover. Source: buzzaboutbees.net

Weeds made their way back into our gardens partly by evolving resistance to the pesticides we used for decades to kill them. There is growing awareness of the impact of pesticides on insects and wildlife. As populations of pollinators decline, we are more willing to indulge their preference for weeds such as dandelions and clover. Weeds are often the first to arrive in the spring garden, as native bees are emerging from their winter hibernation in ground nests. Weeds prolong the blooming season in our gardens, providing nectar and pollen before cultivated plants are blooming.

“No Mow May” comes to America!

“No Mow May” originated in Britain out of concern for declining populations of bees. Communities make a commitment to stop mowing their lawns in May to let the weeds dominate their lawns. Weeds such as dandelions and clover give the bees an early boost in the spring that studies show increases bee populations. Lawns maintained with pesticides and fertilizers provide poor habitat for bees.

Two professors in the Midwest of the US introduced “No Mow May” to their community in Wisconsin in 2020. They signed up 435 residences to participate in “No Mow May” and studied the impact: “They found that No Mow May lawns had five times the number of bees and three times the bee species than did mown parks. Armed with this information, they asked other communities to participate.” According to the New York Times, “By 2021, a dozen communities across Wisconsin had adopted No Mow May. It also spread to communities in Iowa, Minnesota, Illinois and Montana.”

Farmers climb on board

Hedgerows are the backbone of the English countryside. They are a complex bramble of woody and herbaceous plants that traditionally served as fences, separating roads from agricultural fields and confining domesticated animals. They nearly disappeared when industrial agriculture dictated that fields be cultivated from edge to edge. They are making a comeback in the English countryside as farmers realize that their loss contributed to the loss of wildlife. The concept of hedgerows as vital habitat is slowly making its way to America.

US Department of Agriculture reports improvements in agricultural practices in the past 10 years: more no-till farming that reduces fossil fuel use and carbon loss from the soil; more efficient irrigation methods; broader field borders for pollinators and wildlife; more crop rotations that reduce disease and insect pests; reduction of nitrogen and phosphorous run-off; reduction in diesel fuel use, etc. These are all well-known methods of reducing environmental damage from industrial agriculture, but there is now evidence that farmers are actually adopting them.

Nativists are late to the game

We see progress being made to reduce pesticide use and provide more diverse habitat for wildlife, but nativists drag their feet. They continue to use pesticide to eradicate non-native plants and they deny the value of non-native plants to insects and wildlife, despite overwhelming evidence to the contrary.

In a recent commen t posted on Conservation Sense and Nonsense, a nativist explains the justification for using herbicides to eradicate non-native plants: “No one likes herbicides, but in the absence of a labor force willing to abandon its modern conveniences to do very hard work, they are important tools in restoration ecology, and methods are improving as a result of careful science to determine how the least amount of them could be used to gain the greatest amount of benefits to the maximum amount of species. Throwing those tools away is about like tossing chemotherapy or vaccinations because of that “all-or-nothing” black or white point of view that native plant supporters are being (unjustly) accused of.”

For nativists, the harm done by non-native plants is greater than the harm done by pesticides. This equation does not take into consideration the benefits of many non-native plants to wildlife and it underestimates the damage caused by pesticides to the environment and its inhabitants.

Argentine Ants: An “invasion” that wasn’t

Bay Nature published an article about Argentine ants with an alarming title and disturbing accusations, such as:

“…from its home range around the Paraná River region in Northern Argentina, this ant has spread to six continents and numerous islands, including Hawaii. In numbers, it is probably the most successful invasive nonhuman creature in California.”
“Argentine ants have been documented aggressively going after other, bigger species of ants.”
“…most native ants cannot resist well and are wiped out by the Argentine ants.”
“When native ants are displaced, it can disrupt whole ecosystems and reduce the diversity of other arthropods in the region.”

After establishing the Argentine ant’s credentials as a dangerous “invasive species,” the article abruptly changes directions by contradicting itself. According to a 30-year monitoring survey of Argentine ant populations at the 1,200 acre Jasper Ridge Biological Reserve, “…the ants had, counter to expectations, actually retreated from some areas they had occupied in previous years at Jasper Ridge…” Early survey data showed the Argentine ants spreading rapidly in the preserve. They reached a stable distribution around 2001, and have since declined.

The monitoring survey at Jasper Ridge speculates that the decline in Argentine ant populations was caused by drought. However, that theory is not consistent with similar declines in Argentine ant populations elsewhere, where and when there was no drought.

Jasper Ridge is just one of many places that have reported declining populations of Argentine ants over many years. In 2011, Scientists in New Zealand reported the disappearance of the Argentine ant from 40% of sites they populated in the past and their populations have shrunk significantly where they are still found. Native ants have “reinvaded” the areas vacated by the Argentine ant. The scientists reporting this finding “concluded the species naturally collapses after 10 to 20 years.”

In an unpublished communication in 2011 with an entomologist at UC Davis, I learned that Argentine ant populations in Davis were declining.

In 2008, a study of ants in San Francisco’s “natural areas” in city parks reported that the existence of non-native Argentine ants does not have a negative impact on populations of native ants. (1) They report that Argentine ants occupy the perimeter of the “natural areas” where native ants generally are not found. This observation contradicts the usual nativist claims that non-native plant and animal species have negative impacts on native species.

The “invasion” curve

Introduced species are often accused of being invasive and there is a range of explanations, including the bias against non-native species that assumes every non-native species will eventually becoming invasive. In some cases, a new species spreads aggressively because it is better adapted to disturbed conditions to which it has been introduced. The initial success of an introduced species is sometimes enabled by the absence of its predators in its new home. This is called “predator release,” which does not confer permanent protection to a new species that will eventually encounter new predators. These and likely other factors are probably operating simultaneously.

Like most so-called “invasions,” introduced plants and animals may briefly expand, but eventually most find their niche in the ecosystem without causing permanent harm to their neighbors. The assumption that introduced plants and animals threaten native species is usually unsupported by empirical evidence

Journalistic due diligence

If the author of the Bay Nature article about Argentine ants had searched research literature about Argentine ants, she could have learned that the negative tone of the article and its hyperbolic title were not justified. In the author’s defense, the demonization of non-native plants and animals is routine in mainstream media. The bad news about introduced species always precedes their eventual participation in ecosystems and the record is seldom corrected when they do, as in the case of Argentine ants. The reader can compensate for this journalistic bias by reserving judgment about non-native species until more is known about their fate.

Kevin M. Clarke, et. al., “The influence of urban park characteristics on ant communities,” Urban Ecosyst, 11:317-334, 2008

A Natural History of the Future

“The way out of the depression and grief and guilt of the carbon cul-de-sac we have driven down is to contemplate the world without us. To know that the Earth, that life, will continue its evolutionary journey in all its mystery and wonder.” Ben Rawlence in The Treeline

Using what he calls the laws of biological nature, academic ecologist Rob Dunn predicts the future of life on Earth. (1) His book is based on the premise that by 2080, climate change will require that hundreds of millions of plant and animal species—in fact, most species–will need to migrate to new regions and even new continents to survive. In the past, conservation biologists were focused on conserving species in particular places. Now they are focused on getting species from where they are now to where they need to go to survive.

In Dunn’s description of ecology in the future, the native plant movement is irrelevant, even an anachronism. Instead of trying to restore native plants to places where they haven’t existed for over 100 years, we are creating wildlife corridors to bypass the obstacles humans have created that confine plants and animals to their historical ranges considered “native.”

The past is the best predictor of the future. Therefore, Dunn starts his story with a quick review of the history of the science that has framed our understanding of ecology. Carl Linnaeus was the first to create a widely accepted method of classifying plants and animals in the 18^th century. Ironically, he lived in Sweden, one of the places on the planet with the least plant diversity. Colombia, near the equator, is twice the size of Sweden but has roughly 20 times the number of plant species because biodiversity is greatest where it is hot and wet.

Global Diversity of Vascular Plants. Source: Wilhelm Barthlott, et. al., “Global Centers of Vascular Plant Diversity,” Nova Acta Leopoldina, 2005

Humans always have paid more attention to the plants that surround us and the animals most like us. Dunn calls this the law of anthropocentrism. We are the center of our own human universe. Consequently, our awareness of the population of insects that vastly outnumber us came late to our attention in the 20^th century. In the 21^st century we learned that all other forms of life are outnumbered by the microbial life of bacteria, viruses, and fungi that preceded us by many millions of years. Our knowledge of that vast realm of life remains limited although it is far more important to the future of the planet than we realize because those forms of life will outlast our species and many others like us.

Tropical regions are expanding into temperate regions

The diversity and abundance of life in hot and wet tropical climates give us important clues about the future of our warming climate. We tend to think of diversity as a positive feature of ecosystems, but we should not overlook that tropical regions are also the home of many diseases, such as malaria, dengue fever, zika, and yellow fever that are carried by insects that prey on animal hosts, including humans. In the past, the range of these disease-carrying insects was restricted to tropical regions, but the warming climate will enable them to move into temperate regions as they warm. The warming climate will also enable the movement of insects that are predators of our crops and our forests into temperate regions. For example, over 180 million native conifers in California have been killed in the past 10 years by a combination of drought and native bark beetles that were killed during cold winters in the past, but no longer are. Ticks are plaguing wild animals and spreading disease to humans in the Northeast where they did not live in the cooler past.

Human populations are densest in temperate regions: “The ‘ideal’ average annual temperature for ancient human populations, at least from the perspective of density, appears to have been about 55.4⁰F, roughly the mean annual temperature of San Francisco…” (1) This is where humans are most comfortable, free of tropical diseases, and where our food crops grow best. As tropical regions expand into temperate regions, humans will experience these issues or they will migrate to cooler climates if they can.

Our ability to cope with the warming climate is greatly complicated by the extreme variability of the climate that is an equally important feature of climate change. It’s not just a question of staying cool. We must also be prepared for episodic extreme cold and floods alternating with droughts. Animals stressed by warmer temperatures are more easily wiped out by the whiplash of sudden floods or drought.

Diversity results in resiliency

Diversity can be insurance against such variability. If one type of crop is vulnerable to an insect predator, but another is not, growing both crops simultaneously increases resiliency. That principle applies equally to crops that are sensitive to heat, cold, drought, or floods.

Agricultural biodiversity. Source: Number of harvested crops per hectar combining 175 different crops. Source: Monfreda et al. 2008. “Farming the planet: Geographic distribution of crop areas, yields, physiological types, and net primary production in the year 2000”. Global Biogeochemical Cycles, Vol. 22.

Historically, cultures that grew diverse crops were less likely to experience famine than those that cultivated monocultures. The Irish potato famine of the mid-19^th century is a case in point. The Irish were dependent upon potatoes partly because other crops were exported to Britain by land owners. When the potato crop was killed by blight, more than one million people died in Ireland and another million left Ireland. The population dropped about 20-25% due to death and emigration. The diversity of crops in the United States (where corn is the commodity crop) and Brazil (where soy is the commodity crop) is very low, compared to other countries. This lack of diversity makes us more vulnerable to crop failure and famine, particularly in an unpredictable climate.

Change in total use of herbicides, antibiotics, transgenic pesticide producing crops, glyphosate, and insecticides globally since 1990. Source: A Natural History of the Future

Instead of increasing crop diversity, we have elected to conduct chemical warfare on the predators of our crops by using biocides, such as pesticides for agricultural weeds and insects and antibiotics for domesticated animals. The scale of our chemical warfare has increased in response to growing threats to our food supply. This is a losing strategy because as we increase the use of biocides we accelerate evolution that creates resistance to our biocides. We are breeding superweeds, insects, and bacteria that cannot be killed by our chemicals. This strategy is ultimately a dead end.

Evolution determines winners and losers

Inevitably, evolution will separate the survivors of climate change from its victims. Dunn reminds us that “The average longevity of animal species appears to be around two million years…” for extinct taxonomic groups that have been studied. In the short run, Dunn bets on the animals that are most adaptable, just as Darwin did 160 years ago. The animals most capable of inventing new strategies to cope with change and unpredictability will be more capable of surviving. In the bird world, that’s corvids (crows, ravens, jays, etc.) and parrots. In the animal world that’s humans and coyotes. We aren’t helping adaptable animals survive because we are killing abundant animals based on a belief it will benefit rare animals. Even in our urban setting, the East Bay Regional Park District contracts Federal Wildlife Services to kill animals it considers “over-abundant,” including gulls, coyotes, free-roaming cats, non-native foxes, and other urban wildlife throughout the Park District. We are betting on evolutionary losers.

If and when humans create the conditions that cause our extinction, many of our predators are likely to disappear with us. Bed bugs and thousands of other human parasites are unlikely to survive without us. Many domestic animals will go extinct too, including our dogs. On the bright side, Dunn predicts that cats and goats are capable of surviving without us.

Timeline of the evolution of life. Source: CK-12 Foundation

However, in the long run Dunn bets on microbial life to outlast humans and the plants and animals with which we have shared Earth. Humans are late to the game, having evolved from earlier hominoids only 300,000 years ago, or so. The plants and animals that would be recognizable to us preceded us by some 500 million years, or so. But microbial life that is largely invisible to us goes back much further in time and will undoubtedly outlast us. Dunn says microbial life will give a big, metaphorical sigh of relief to see us gone and our environmental pollutants with us. Then microbial life will begin again the long process of rebuilding more complex life with their genetic building blocks and the tools of evolution.

Some may consider it a sad story. I consider it a hopeful story, because it tells me that no matter what we do to our planet, we cannot kill it. For the moment, it seems clear that even if we are not capable of saving ourselves at least we can’t kill all life on Earth. New life will evolve, but its features are unfathomable because evolution moves only forward, not back and it does not necessarily repeat itself.

A Natural History of the Future, Rob Dunn, Basic Books, 2021