Suzanne Simard – Conservation Sense and Nonsense

Calaveras Big Trees State Park: To burn or not to burn?

Coast redwoods (Sequoia sempervirens) and sierra redwoods, often called giant sequoias (Sequoiadendron giganteum), are members of the Sequoioideae family, a sub-family of the Cypress family. Both are native to California. Dawn redwood (Metasequoia) is the third genus in the small Sequoioideae family. Although there is fossil evidence that dawn redwoods lived in California some 40 million years ago they are now native only to a small region in China.

Coast and sierra redwoods have a common ancestor that is now extinct. They evolved into different genera in response to the creation of microclimates by geologic changes that isolated their gene pools and gradually drifted apart in directions adapted to their respective regions. (1)

Coast redwoods live in wetter climates than sierra redwoods and they are heavily dependent on coastal fog that maintains a moist environment when interior regions of California are hot and dry. As our climate continues to change, the future of coast redwoods will depend on whether or not our coastal fog persists. In turn, the fog depends on the coolness of the ocean relative to the warmth of the land. The greater that difference in temperature, the more fog is created as water in warm air condenses when it meets cold ocean air.

Sierra redwoods tolerate a much drier climate than coast redwoods, but they have been tested by our prolonged drought. They are also threatened by wildfires that have ravaged California during our long drought. Only about 70 small, isolated groves of sierra redwoods still exist on the western slope of the Sierra Nevada. In 2020 and 2021, wildfires killed 13 percent to 19 percent of the world’s giant sequoias, according to the U.S. Forest Service. (2) The Mariposa Grove of giant sequoias in Yosemite National Park burned in 2022, but none of the sequoias were killed.

Public land managers are under intense pressure to do whatever is necessary to save our sierra redwoods. Extreme measures have been taken, such as wrapping their huge trunks in fire resistant foil, spraying trunks with water and canopies with gel when fires approach. (3)

The prevailing opinion about conserving sierra redwoods is that prescribed burns will reduce fuel loads and therefore fire hazards as well as kill shrubby understory that can carry fire from the ground into tree canopies. The understory is also considered competition for moisture in the soil. Kevin McCarthy, the speaker of the US House of Representatives, has introduced a bill titled Save our Sequoias Act (SOSA) that would enable logging to reduce fuel loads in giant sequoia groves without requiring environmental impact reviews. Many experts disagree about that strategy. We visited the sierra redwood grove in Calaveras Big Trees State Park at the end of May to see for ourselves and consider the pros and cons of the strategy that is being used there to save the big trees.

Calaveras Big Trees State Park

Calaveras Big Trees State Park is located near the town of Arnold at an elevation of about 4,700 feet. It is near the northern end of the narrow range of giant sequoias. The southern end of the range is near the city of Visalia in Sequoia National Park at about 6,000 feet elevation. Most of the big trees that were destroyed by recent wildfires are at the southern edge of the native range. Recent wildfires have not reached Calaveras Big Trees, but several giant sequoias in the park were badly damaged by prescribed burns and may not survive. These damaged trees are a testament to the risks of prescribed burns.

Below is a picture of one of the areas that was intentionally burned in 2022 to reduce fuel loads:

Calaveras Big Trees State Park, May 25, 2023

Below is a picture of a giant sequoia that was scorched by that fire. The right-hand side of the tree looks seriously damaged, suggesting that the tree may not survive:

Larger prescribed burns were also conducted on the northern edge of the park, where there are few sequoias. Below is a picture of one of several large areas of the park that were intentionally burned:

There are only two sequoias in this part of the park, named the Orphans because of their isolation from other sequoias in the park. The Orphans were severely burned by this fire. (see below) It isn’t clear if the Orphans will survive.

The Orphans, Calaveras Big Trees State Park. Photo by Alan Beymer with permission.

Land management or mismanagement?

The potential loss of a few giant sequoias at Calaveras Big Trees may seem trivial, but their loss must be put in the context of the small and shrinking population of giant sequoias as well as their very long lifespan of roughly 3,000 years. The survival of the species is threatened by these unintentional deaths that could have been avoided.

Many major wildfires have been started when burn crews lost control of prescribed burns. In April 2022, the US Forest Service conducted two prescribed burns in the Santa Fe National Forest in New Mexico that merged and became a major wildfire that burned for months, ultimately destroying over 341,000 acres of forest. Although it was one of the most destructive of wildfires started by a prescribed burn, it is only one of many.

Logging to thin the forest is another strategy used by public land managers to reduce fuel loads, but we did not see any evidence of logging at Calaveras Big Trees. The giant sequoias in Calaveras County reside in a mixed conifer forest of ponderosa pine, incense cedar, white fir, and sugar pine. These tree species are valuable timber and therefore vulnerable to pressure from the logging industry. It seems likely that the Save our Sequoias Act sponsored by Republicans is a gift to the logging industry, rather than to the sequoias.

In 2017, the National Academy of Sciences published an evaluation of fuels management project s in the US. The authors of this publication reported that managing forest fuels has been ineffective: “Mechanical fuels treatments on the US federal lands over the last 15 years totaled almost 7 million hectares, but the annual area burned has continued to set records. Regionally, the area treated has little relationship to trends in the area burned, which is influenced primarily by patterns of drought and warming.” Where fuels treatment was done, wildfires subsequently occurred:“10% of the total number of US Forest Service forest fuels treatments completed in the 2004-2013 period in the western United States subsequently burned in the 2005-2014 period.” This suggests that “most treatments have little influence on wildfire.” In any case, only 40% of wildfires occurred in forests since 1984, with most fires burning grasslands and shrublands.

The authors of the study published by the National Academy of Sciences, recommend a new approach to forest management. Whereas past policies were designed to maintain forest conditions to historical conditions, this is no longer considered a realistic goal. The recommended goal is now “supporting species compositions and fuel structure that are better adapted to a warming, drying climate with more wildfire.”

The other, equally important new goal is to reduce the vulnerability of communities to wildfire by “changing building codes to make structures more fire-resistant…and providing incentives, education, and resources to reduce vulnerability to future wildfire.” The only tree removals that make sense to the authors are those immediately around residential communities, “strategically located to protect homes and the surrounding vegetation.” That is the principle of creating “defensible space” immediately around structures: “fuels management for home and community protection will be most effective closest to homes…where ignition probabilities are likely to be high.” The strategies used in Calaveras Big Trees to protect giant sequoias may not be the best strategies for surrounding residential communities.

Land managers who conduct prescribed burns in sequoia groves also believe they are assisting forest regeneration because the heat of fires is said to release the seed-carrying female cones from the tree canopy and open the cones to release their seeds. The track record on forest regeneration after wildfires depends partly on the severity of fire, but the results of studies are mixed. (4)

The purpose of prescribed burns is to reduce fuel loads with low-severity fire in order to prevent more destructive high-severity fires. However, in the case of giant sequoias, high-severity fires may be necessary for long-term survival of the species: “High-severity fires create robust seedling establishment and survival. For example, in a report on sequoia ecology, NPS researcher Nate Stephenson concluded: ‘Before the arrival of European settlers, successful recruitment of mature sequoias depended on fires intense enough to kill the forest canopy in small areas. Thus, sequoia is a pioneer species, and this conclusion has specific management implications.’” (5)

We saw an example of forest regeneration after a severe wildfire in the sequoia grove in Calaveras Big Trees. Below is a photo of the Mother of the Forest that was burned by a wildfire in 1908. That tree was particularly vulnerable to wildfire because the thick, spongy bark layer that protects sequoias from fire (as well as insects and disease) had been removed by entrepreneurs (more accurately called vandals) who reassembled the bark as a tree replica for display and profit.

The Mother of the Forest is surrounded by a young forest of trees, including many giant sequoias. (See below. Trees with reddish bark are young giant sequoias.) “The [1908] fire created ideal growing conditions for giant sequoia seedlings and today there is a healthy stand of young sequoias there. Many of these trees are the result of natural regeneration that happens after a fire, while others were planted during the 1930s by members of the Civilian Conservation Corps.” (6)

Mountain dogwood (Cornus nuttalli) and hazelnut (Corylus cornuta) are the predominant understory shrubs in the forest of Calaveras Big Trees. After an unusually long, cold winter most weren’t blooming yet at the end of May. A few dogwoods were blooming where sunshine penetrated the tree canopy. (see below)

Unfortunately, these lovely small trees are seen as competitors of the giant sequoias for available water and nutrients in the soil. Therefore, destroying the understory in Calaveras Big Trees is one of the management goals. According to the Calaveras Big Trees Association, most of the dogwoods were chopped down by park staff about 9 years ago. Dogwoods are vigorous resprouters, so they quickly grew back more densely than their taller predecessors. Pesticides (including herbicides) aren’t used in Calaveras Big Trees, so resprouting was inevitable. I wonder if those who destroyed the dogwoods understood that would be the outcome of their effort.

Management strategies of the timber industry are based on an assumption of competition. When clear-cut harvests are done by the timber industry they are typically sprayed with herbicides from helicopters to destroy the understory that they assume competes with the tree seedlings they plant for the next timber crop. Public land managers often use the same strategy.

The research of Suzanne Simard has informed us that there is more cooperation in the forest than there is competition. A lifetime of observing healthy forests taught her that the soil is occupied by vast networks of fungi that connect the plants and trees. These mycorrhizal fungi transfer moisture and nutrients from the soil to the trees and plants, to their benefit. She speculated that the destruction of all vegetation in clear cuts was eliminating that support structure and she designed experiments to test her hypothesis.

The specifics of fungal associations between tree species varies, which requires that we describe a specific relationship. Simard’s original studies focused on the fungal associations between Douglas fir and birch trees in the understory. Birch trees were destroyed in the clear cuts that were then planted with Douglas fir seedlings that were not doing well. Simard’s experiments eventually revealed that birch trees and firs mutually benefit one another through their fungal networks. Carbon stored and the sugar produced by photosynthesis by firs are shared with deciduous birch during winter months while they are leafless. In summer months when birch are foliated, they store more carbon that is shared with firs. Birch is resistant to a root pathogen to which firs are susceptible. In a sharing fungal relationship between birch and firs, birch confers some of that resistance to the root pathogen onto their fir neighbors. Is there a similar relationship between dogwoods and sequoias and other conifers in the forest at Big Trees?

The understory also shades the forest floor, which retains moisture in the soil that would otherwise evaporate in the absence of shade. The canopy of giant sequoias is near the top of mature trees and doesn’t cast much shade. In other words, the shaded forest floor provides more moisture for all members of the plant community in sequoia groves. Furthermore, a shaded forest floor is less likely to ignite a fire because of the moisture it retains.

Collaboration triumphs over competition in the forest

“Ecosystems are so similar to human societies—they’re built on relationships. The stronger those are, the more resilient the system.” Suzanne Simard, Finding the Mother Tree

Suzanne Simard is an academic scientist of forestry of some renown because her research has revealed that the forest is a community of plants and trees that share resources to their mutual and communal benefit. Her recently published memoir, Finding the Mother Tree, about her 40-year career in forestry is deeply personal and informative.

Simard grew up in the forests of British Columbia in an extended family of traditional loggers who used manual methods to selectively remove individual trees, leaving forests intact. This is physically demanding and dangerous work, making it a predominantly male occupation.

After her education as a forester, Simard joined the Canadian Forest Service and a profession dominated by men and committed to maximizing profit by clear cutting patches of forest with mechanized methods. This policy requires the destruction of all vegetation in clear cuts considered potential competition for the next crop of timber. After mechanical removal, the ground is sprayed with herbicide from helicopters before being replanted with tree seedlings. This policy is called “free to grow,” a misnomer that was eventually revealed by Simard’s research. The plant and tree neighbors of the seedlings are their collaborators in the enterprise of the entire forest, functioning as an ecosystem that creates a home for every life form in the community.

Suzanne Simard’s lonely professional journey in forestry

One of Simard’s first assignments as a forester was to assess the health of seedlings planted in a clear cut. The seedlings were not doing well. It became her mission to find out why. A lifetime of observing healthy forests had taught her that the soil is occupied by vast networks of fungi that connect the plants and trees. These mycorrhizal fungi transfer moisture and nutrients from the soil to the trees and plants, to their benefit. She speculated that the destruction of all vegetation in clear cuts was eliminating that support structure and she designed experiments to test her hypothesis.

Douglas fir forest, MacMillan Provincial Forest, Vancouver, British Columbia

Her experimental plots were divided into areas with varying degrees of vegetation clearance. At one extreme, seedlings were isolated by sheets of metal buried deep into the soil that prevented development of mycorrhizal networks to support the seedlings. Decades later, these isolated seedlings were the most likely to have died. The seedlings that survived most often were on the perimeter of clear cuts, with access to the surrounding intact forest.

The relationships between tree and plant species and their mycorrhizal networks vary by plant and fungi species. There are thousands of mycorrhizal fungi species associated with trees and about half are generalists that associate with most tree species. Specialist species of fungi are confined to a narrower range of tree species, genera, or families. There are fewer species of mycorrhizae associated with plants and most are generalists.

The specifics of fungal associations between trees also varies, which requires that we describe a specific relationship. Simard’s original studies focused on the fungal associations between Douglas fir and birch trees. Birch trees were destroyed in the clear cuts that were then planted with Douglas fir seedlings that were not doing well. Simard’s experiments eventually revealed that birch trees and firs mutually benefit one another through their fungal networks. Carbon stored and the sugar produced by photosynthesis by firs are shared with deciduous birch during winter months while they are leafless. In summer months when birch are foliated, they store more carbon that is shared with firs. Birch is resistant to a root pathogen to which firs are susceptible. In a sharing fungal relationship between birch and firs, birch confers some of that resistance to the root pathogen onto their fir neighbors.

Nitrogen is essential to plant and tree health, but not all species are capable of converting atmospheric nitrogen to soil nitrogen available to plants. When a nitrogen-fixing plant is associated with a plant without that capability, it can share its nitrogen with its neighbor through their fungal network.

A mature tree can store more moisture than its young seedlings without extensive root structure. The mature tree can share its stored moisture with struggling seedlings through its fungal network. Seedlings with access to that network are more likely to survive while establishing their own root structures. Research of Simard’s graduate students and collaborators eventually found that such sharing of resources between mature and young trees occurs more frequently within the same species, but sharing also occurs with unrelated tree species. The mature trees nurture their offspring, enabling their survival and the survival of the species. They are, in effect, Mother Trees.

MacMillan Provincial Forest, Vancouver, British Columbia

Herbicides used to kill vegetation in clear cuts

Another early assignment by the forest service required that Simard determine the most effective herbicide regimen to kill plants in clear cuts perceived to be potential competitors of the seedlings of the next timber crop. Simard and her sister applied several different concentrations of herbicide to vegetation and predictably determined that the most concentrated formulation of herbicide was the most deadly. Glyphosate is the most commonly used herbicide for this purpose.

This particular episode in Simard’s early career was disturbing in view of the fact that she eventually developed breast cancer that nearly killed her. Simard and her sister were uncomfortable about their assignment and they suited up cautiously as best they knew how while applying herbicide. The Simard sisters felt ill after an application and they sought medical help from whom they learned that their masks did not contain the necessary filters. Required safety measures for herbicide applicators are only as good as the knowledge on which they are based. That knowledge moves slowly forward and becomes more alarming as we learn more.

What has the timber industry learned from Simard’s research?

The short answer to that question is very little. The strategy of the timber industry in both Canada and the US remains clear cuts that destroy all trees and vegetation followed by herbicide application by helicopter to kill all herbaceous vegetation before seedlings are planted. Simard reports that concentrations of herbicide have been reduced recently. She also says that a few large, mature trees are sometimes spared by clear cuts.

Recent knowledge of the health effects of glyphosate is causing some concern, but few changes in policy or practice have been made. Declining moose populations in a region of Canada led to decreased h erbicide applications. Legislators in the State of Maine recently passed a law to ban herbicide applications in timber clear cuts. That legislation was then vetoed by the Governor of Maine.

Strangely, none of these reports of reduced herbicide use by the timber industry mention that herbicides are known to damage mycorrhizae. Health concerns are cited as the sole reason for reducing herbicide use despite the fact that we now know the importance of mycorrhizal networks to the health and survival of forests. While Simard opposes the use of herbicides in forests, she does not explicitly connect herbicides with the destruction of mycorrhizal networks that enable the survival of tree seedlings.

Are these studies relevant to our urban forest?

Those who are looking for support for our urban forest in Simard’s work will be disappointed. Her focus is on the health and preservation of native forests. In fact, she has harsh words for “exotic weed invasions:” She says they are accelerating the decline of native grassland “possibly by sending the native grasses some poisons or an infection to finish the murder. Or starving them, taking over their energy, degrading the native prairie. Like the invasion of the body snatchers. Or the colonization of the Americas by Europeans.” Note that her indictment is speculative and not the conclusion of an empirical study.

But the principles of Simard’s findings are relevant to our concerns for the destruction of our urban forests and the herbicides used for that purpose. Mycorrhizal fungi are as essential to urban forests as they are to native forests. Herbicides used in our urban forests are as damaging to fungal networks as they are to clear cuts of native forests.

Trees, Truffles, and Beasts (1) was written by academic foresters in Oregon and Australia 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 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.

I 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, I 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 indeed populated with generalist fungi, including some species that are native to Australia. Therefore, we can assure our readers that our description of how the forest functions as a community applies to the eucalyptus forest in California, as well as in Australia.

When eucalyptus is destroyed in California their stumps are immediately sprayed with herbicide (usually Garlon) so the tree does not resprout. The herbicide is carried into the roots of the tree through the cambium layer that is briefly functional after the tree is destroyed. Garlon is kno wn to damage mycorrhizal fungi.

Herbicide is also used to destroy the non-native vegetation that thrives in the full sun after trees are destroyed. Glyposate th at is c ommonly used for that purpose is known to kill microbes that are essential to soil health, handicapping any replacement planting.

Suzanne Simard’s mission

Before leaving the Canadian Forest Service, Suzanne Simard made every effort to inform her colleagues of the damage being done by the timber industry and the potential for more successful planting of a new generation of timber if policy and practice were revised to preserve soil health. In a male-dominated profession that was committed to the methods being used, her message fell on deaf ears. In fact, her colleagues were openly hostile to her message, making the offer of an academic position welcome relief that gave her more freedom to conduct research and deliver her message.

After recovering from a nearly fatal bout of breast cancer, Simard became more committed to bringing her research to the attention of the public. She has delivered inspiring and wildly suc ce ssful TED talks and she was immortalized as the heroine of The Overstory (2), the barely fictional account of defenders of the forest that made Simard’s research accessible to the general public.

Finding the Mother Tree, Suzanne Simard’s memoir, is a sad reminder of the difficulty of bucking conventional wisdom that is deeply rooted in the profit motive. In the case of the timber industry, competition remains the dominant narrative that drives policy and the consequences of that approach are unnecessarily destructive.

Chris Maser, Andrew W. Claridge, James M. Trappe, Trees, Truffles, and Beasts, Rutgers University Press, 2008
The Overstory, Richard Powers, W.W. Norton and Company, 2019.

Tag: Suzanne Simard