Why poisoning the soil contributes to failed “restorations”

We are members of an international team of people who are concerned about the destructive consequences of ecological “restorations.”  Trees, Truffles, and Beasts (1) was recommended to us by one of our collaborators in Australia because the book was written by several academic scientists in Australia and the Pacific Northwest of the United States.  The book compares and contrasts the forests of these disparate locations and finds that below the ground, they have much in common.

Much more is known about the important ecological functions performed by forests above ground than below ground.  However, there are many equally important things happening below ground that are essential to the health of forests:

  • The soil is inhabited by millions of microbes that decompose organic matter, making it available to plants as nutrients. These microbes recycle dead plants and wood back into usable material for living plants.
  • Nitrogen is essential to plant growth. Microbes and fungi in the soil convert nitrogen in the atmosphere into forms needed for plant growth.  Specific plant species (e.g., legumes, such as acacia and lupine), called nitrogen “fixers,” are mediators in this process.
  • Fungi in the soil deliver water and nutrients from the soil to the roots of trees in exchange for carbohydrates provided by the trees. This symbiotic relationship is essential for the health of trees and in the absence of fungi, tree growth and development are severely retarded.
  • Most carbon is stored in the soil, and soil fungi play a role in converting atmospheric carbon dioxide into carbon that is stored in the soil. “Recent research has shown that mycorrhizal fungi hold 50 to 70 percent of the total carbon stored in leaf litter and soil on forested islands in Sweden.” (2)

Relationships between animals and forests

The animals that live in the forests contribute to forest health and forests also benefit the animals.

Mature Parasol mushrooms - note hand for size comparison
Mature Parasol mushrooms – note hand for size comparison

Fungi in the soil produce “fruiting bodies” that are their means of reproducing.  Fruiting bodies above ground are called mushrooms.  Fruiting bodies below ground are called truffles.  In both cases, they are important sources of food for animals.  The animals in Australia are different from those living in the Pacific Northwest, but they have in common that the fruiting bodies of fungi are equally important sources of food for them.

In the case of mushrooms above ground, dispersal of their spores is accomplished primarily by wind.  But in the case of truffles, dispersal of their spores is dependent upon the animals that eat them and “deposit” them elsewhere.  So, animals are crucial to the reproductive cycle of fungi that fruit below ground.

Long-footed potoroo is an Australian marsupial that eats primarily mushrooms and truffles.
Long-footed potoroo is a rare Australian marsupial that eats primarily mushrooms and truffles.

In their search for truffles, the animals also till the forest floor, which contributes to the decomposition of leaf litter and the dispersal of nutrients into the soil.  As the animals defecate in the forest, they are also making contributions to forest health and there are species of microbes and insects that specialize in the use of animal feces.

Golden mantled ground squirrel, Western North America. Prefers to eat mushrooms and truffles.
Golden mantled ground squirrel, Western North America. Prefers to eat mushrooms and truffles. Creative Commons

What happens to the forest ecosystem when it is clear cut?

The forest is a complex and delicate ecosystem.  When the forest is destroyed, we should not be surprised to learn that this ecosystem is destroyed.  Here are a few of the consequences of clear-cutting a forest:

The Bay Area is often blanketed in fog. Courtesy Save Mount Sutro Forest.
The Bay Area is often blanketed in fog. Courtesy Save Mount Sutro Forest.
  • The forest precipitates fog and the shade provided by the canopy retains that moisture on the forest floor. When we destroy the forest, we lose that source of moisture.  The ground dries out in the sunshine.  The fruiting bodies of fungi—mushrooms and truffles—require moisture to bloom and they die quickly in the absence of moisture.
  • The herbicide (Garlon) used to prevent the trees from resprouting is known to damage the mycorrhizal fungi that are essential to forest health. The herbicide that is applied to the tree stump immediately after the tree is destroyed, travels though the cambium layer of the tree down through the roots of the tree.  The tree is killed by killing its roots.  Mycorrhizal fungi are essentially extensions of the root system.  When roots are killed, so are the mycorrhizal fungi.  In the absence of mycorrhizal fungi, the survival of “replacement” plants is compromised.
  • The loss of fruiting bodies as food for animals reduces animal populations and the contributions they make to forest health.
  • Glyphosate is the herbicide most commonly used to foliar spray non-native vegetation that colonizes the unshaded ground after a clear cut. Glyphosate was originally developed as an anti-bacterial agent.  Glyphosate kills bacteria in the soil (and in the mammalian gut, 4) that are playing a role in recycling nutrients to plants (and in digesting our food). (3)

Prescribed burning is another land management method used to eradicate “invasive” plants.  In addition to polluting the air, releasing carbon into the atmosphere, and increasing the risk of wildfire, prescribed burns also damage the soil:  “Prescribed burning in California pine forest decreased the ectomycorrhizal biomass by almost 90 percent in the upper organic layers of the soil as compared to unburned sites.  A decrease of that magnitude in the mycorrhizal energy source of the fungi would affect not only fungal fruiting but also fungal populations.”  (1)

In the absence of fungi and bacteria, the soil is essentially sterile and is no longer capable of contributing to the health of a new generation of plants and animals to replace the forest.

Eucalyptus forest in California and Australia

Trees, Truffles, and Beasts was written by academic foresters who are primarily concerned about the destructive consequences of destroying native forests and replacing them with timber plantations, often of another, faster growing species.  Ironically, in the case of old growth eucalyptus forests in Australia, the choice of replacement species is often Monterey pines.  Since some of the species of mycorrhizal fungi are specific to certain species or types of trees, this change of species is not successful without the inoculation of appropriate species of fungi.  For example, some of the mycorrhizal fungi that grow on the roots of conifers are not found on eucalyptus species.

Before writing this article, we corresponded with the authors of Trees, Truffles, and Beasts to confirm that fungi are found in the eucalyptus forests of California.  Since eucalyptus was brought to California as seeds, rather than potted plants, we needed confirmation that our eucalyptus forests are also enjoying the benefits of mycorrhizal fungi.  We are grateful that the authors replied.  They report that eucalyptus forests in California are populated with fungi, including some species that are native to Australia, which implies that some eucalyptus were imported from Australia with native soil.  Therefore, we can assure our readers that our description of how the forest functions applies to the eucalyptus forest in California, as well as in Australia.

Predicting the consequences of destroying our urban forest

Plans to destroy non-native forests on 2,000 acres of public land in the East Bay will result in a dry, barren landscape populated primarily by non-native annual grasses.  Fantasies that the forest will be magically replaced by a landscape of native plants and trees are just that…fantasies.  Every reputable source of information about the planned project predicts this outcome, from the US Forest Service to the Audubon Society and the California Native Plant Society.  There are many reasons why this outcome is predictable:

  • UC Berkeley's "Vegetation Management"
    UC Berkeley’s “Vegetation Management”

    The ground will be covered by as much as 24 inches of wood mulch, which will retard the germination of any plant. The plants most likely to penetrate this physical barrier are those that are most competitive, such as broom and other non-native weeds considered “invasive.”

  • The moisture available to plants will be reduced by the loss of fog drip and shade provided by the tree canopy. Fog drip in eucalyptus and Monterey pine forests in the East Bay has been measured at 10 inches per year. (5) Young plants and trees require more water than established plants, so the water deficit will retard the growth of a new landscape.
  • The climate of the San Francisco Bay Area has changed in the 250 years since the arrival of Europeans. Plants that were native at that time are no longer competitive in the warmer, drier climate and an atmosphere higher in nitrates and carbon dioxide.  The rapidly changing climate is making the concept of “native” increasingly irrelevant.

And now we know that the damage that will be done to the soil and the forest floor by the destruction of our urban forest will further handicap the successful establishment of a new landscape.  Aside from the physical damage done by removing hundreds of thousands of trees with heavy equipment, the herbicides used to kill trees and plants considered undesirable by the perpetrators of this devastating project will sterilize the soil.  The resulting weed-dominated moonscape will probably recover in hundreds of years, although the eventual outcome is impossible to predict in our rapidly changing environment.  Neither the supporters of this project nor its critics will live to see the recovery.

  1. Chris Maser, Andrew W. Claridge, James M. Trappe, Trees, Truffles, and Beasts, Rutgers University Press, 2008
  2. https://en.wikipedia.org/wiki/Mycorrhizal_fungi_and_soil_carbon_storage
  3. http://www.nytimes.com/2013/09/20/business/misgivings-about-how-a-weed-killer-affects-the-soil.html?ref=todayspaper&_r=1
  4. http://www.fooddemocracynow.org/blog/2015/apr/13
  5. Harold Gilliam, Weather of the San Francisco Bay Region, UC Press, 2002