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Fungal "plant diseases" may not be the cause of dying trees

Several parks and reserves around Queensland are experiencing tree deaths, blamed on the brown root rot fungus Phellinus noxious and other “fungal pathogens.” The Moreton Bay fig tree (Ficus macrophylla) is one tree species susceptible to failure due to factors affecting their health.

Understanding the true role of decomposers

When a tree comes down for whatever reason, it is always recycled by decomposer fungi, returning the tree nutrients back to the soil as food for microbes and plants, supporting the ecology of the forest. Some decomposer fungi, which are visible while the tree is alive, as a bracket sporing body, are in fact endophytes (symbiotic fungi which support plant/tree growth while it is alive), turning into a decomposer as the sick tree signals the fungi to break it down.

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There is always a background cause which initiates failure of the tree and which happens long before any symptoms of “disease” are present. Fungi such as Phellinus noxious are not directly responsible for causing a disease and are therefore erroneously labelled as “fungal plant pathogens.” The various fungi which are thought to cause plant disease are often, if not always a secondary symptom. In fact, they provide a solution to the cause of the problem, which is a depletion in the soil microbiome required for nutrient cycling, and thus tree nutrition and defence.

Unfortunately because these fungi are being viewed as the causative disease agent, being blamed for the disease, aggressive treatment is often used to prevent their spread, often in a chemical form, further damaging the microbiome of the ecosystem and perpetuating the problem.

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Given its widespread distribution in subtropical and tropical forests where it is seen decomposing fallen wood, and having its presence recorded before any evidence of “causing disease,” suggests that Phellinus noxious is a healthy component of the forest microbiome, and an excellent generalist decomposer, which is its primary function. Its spores are ubiquitous wherever it forms sporing bodies and are present in the surrounding soil and vegetation, where it does not necessarily cause disease symptoms. Given the wide range of tree species being decomposed by Phellinus noxious, suggests its important role as a generalist decomposer. Additionally, the most severe cases of wood rot symptoms associated with Phellinus noxious are seen in agricultural and forestry situations, suggesting underlying ecosystem imbalance the Phellinus proliferation clearly indicates.

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Fungi like all organisms can only effectively begin to decompose an already dying plant. A healthy tree, like any other organism has a plethora of defence mechanism mainly in the form of its beneficial, protective microbiome. This supportive network of microorganisms including beneficial fungi must already be compromised within the tree, in order for it to succumb to the decomposer. The decomposer is only doing its job “knowing” that the tree is dying, receiving a signal from the tree that it needs to be decomposed, so the decomposer begins to fulfil its role. All we see, is the effect of it growing and performing its designated task, while blaming it for causing a disease in the tree, so we attempt to control it.

The real cause of tree failure

Reduced biodiversity due to deforestation and climate pressure

However, the cause of the tree failing, signifies a lack of support for the tree in the surrounding ecosystem to remain healthy and functional, which is always rooted in the decline of the plant and soil microbiome, and loss of biodiversity as a whole. Each ecosystem has its own necessary biodiversity limit, that it requires to support the function of individual plants and animals and therefore the whole system. As we keep diminishing the size of forests, ripping out entire ecosystems, reducing the biodiversity within them, we are destroying their defences, reducing the links and connectivity required for information and resource sharing within these living super-organisms. If we look at a forest one whole organism, every time an organ (a species or a functional group of species) is lost, the health and longevity of that forest is diminished, just as it happens in the human body. Add climate change, extreme and unseasonal temperature variations, frequent droughts, fires, flooding and water logging and we have a disaster ready to happen.

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Herbicide use

However, the most detrimental of all is our overuse of chemical herbicides to control weeds in parks and reserves. All herbicides, particularly glyphosate are biocides, meaning that they do not only kill plants but also the microbes in the soil that feed trees and other plants. Herbicides and insecticides kill the entire defence system of the forest, its microbiome, just as we do when consuming antibiotics frequently or in large amounts. Herbicide application destroys the very organisms that support the life of trees, causing a systematic decline in their root/soil microbiome. As the weakened hosts, continue to lose their nutrient delivery and defence system, they become so depleted that they can no longer support their microbial networks, their immune and communication systems, leading to death of the trees and their decomposition by fungi.

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The most commonly used herbicide, glyphosate (Roundup), kills fungi in the soil and this really restricts nutrient supply to the trees, especially if the affected fungi are the root symbiotic (mycorrhizal) fungi which majority of plants, especially trees require for nutrient supply and root defence. With continued use of herbicides, especially water based ones like glyphosate, which end up falling down back on vegetation and soil with rain, means that there is a continuous destruction of the soil/plant microbiome, and in fact, our own microbiome. We are effectively stripping any immunity of plants, animals and humans and as a results we and our ecosystems are continually more and more prone to supporting organisms we call disease causing, while they are simply trying to break down any sick organism down and return their nutrients to the soil, to build back the immunity and nutrient load of the entire ecosystem.

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The cut and paste method, reportedly being a friendly way to apply glyphosate to avoid spraying large areas of habitat is quite misleading and detrimental to ecosystem health. Since plants have bidirectional transport tissues (phloem and xylem) for nutrient and water transport, anytime glyphosate is applied to the stem entering these tissues, it will be translocated to the roots. This is how the plant is killed by this particular method of poisoning, as the toxin travels down to its roots. This affects and kills the root symbiotic (mycorrhizal) fungi living in the plant’s roots and before that happens the chemical will be transported and shared with healthy native plants if they are using and sharing the same mycorrhizal network as the target weed. So while we think we are killing a weed, we are in fact also poisoning, if not killing the native plants which are connected to the undesirable plant through their shared, symbiotic root fungal network. When we look at a forest, we must recognise it as an interconnected system, not see plants as individuals. In this view, we must treat the ecosystem as a whole, not as individual, isolated components within it. Everything within an ecosystem is connected to something else, and each ecosystem is connected to everything else, through transpiration of water, wind currents, animal distribution, we are affecting the entire planet with each damaging choice we make for an individual plant, fungus, microbe, insect, animal or human being.

Use of fire

Another key microbial killer is fire, a method used extensively and often times indiscriminately in bush management, severely reducing the microbiome of the soil and ecosystem biodiversity at large. While we can argue that fire provides nutrients to the soil, most minerals do not survive fire and are therefore lost with smoke into the atmosphere causing air pollution. Logically if we think about it, fungi grow on decaying wood, and rarely if at all on charcoal, so when we burn wood to charcoal, we drastically reducing fungal foods and killing all of the fungal mycelium within the wood. Sadly, fungi are the very thing that is missing from our soils through the repeated harsh treatments we employ to control the disease or weed symptoms, further perpetuating disease and weedy conditions to proliferate, all the while believing that we are saving the ecosystem. While some fungal spores do have some heat resistance, their tolerance varies, some fungi are very sensitive to increases in temperature, so we reduce fungal survival and diversity drastically by applying fire to ecosystems.

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Any reduction in fuel within the ecosystem, means reduced food sources for fungi in particular, and therefore other organisms relying on fungi and their power of decomposition. It must also be pointed out that reducing fresh plant biomass, reduces food sources for animals directly by burning, leaves, bark, grasses, flowers and seeds. In fact animals like snails, termites, ants (important fungal feeders and spore distributors), flightless insects and all insect larvae, bird and reptile eggs and young, and any wildlife that cannot escape in time, is burnt to death, dramatically reducing species abundance and diversity in any burnt ecosystem. This in turn sets back the ecosystem’s succession, reducing its capacity to maintain high successional species like trees.

Solutions

So how can we achieve an ecosystem balance in which trees are healthy and supported by their microbiome, especially in the face of climatic pressure? How can we create resilience in forest and other ecosystems, where opportunists such as Phellinus noxious will no longer signal that something is awfully wrong in the ecosystem?

Removing herbicides and fire

From the above discourse, it is obvious that we must maintain a high level of plant and thus microbial diversity in any given ecosystem and its soil. This means encouraging expansion of reduced forest ecosystems to a level required for their self sustenance and ongoing survival, ensuring plant diversity. Most importantly it means eliminating any use of biocidal chemicals and other biomass destructive tools like fire. These are far more damaging and the real cause of compromised ecosystem and tree health. Any removal of biomass which is done on mass when clearing vegetation, burning or removal of weeds, must be compensated for by application of an equal or greater amount of biomass to prevent nutrient depletion through loss of microbial life. This is difficult to achieve, especially since living plant biomass once removed, cannot be returned immediately, and it is the living, photosynthesising plants that provide the necessary carbohydrates that fuel the soil microbiome. This is where using native ground cover species which grow rapidly is essential and seldom if at all implemented in restoration efforts, but which is a must to maintain the soil microbiome. While living plants will take time to reestablish, organic matter from dead trees can be useful to maintain fungal diversity and thus nutrient cycling in the soil.

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Using the fallen trees to repair the soil

The dead “diseased” trees can be of value here, if properly managed their decomposing wood can be safely returned to where they came from. The wood chip from the trees can be composted off site and returned once composting has been completed. Alternatively and preferably, it can be treated with microbial inoculants in situ, which contain the entire soil food web (all the organisms needed for efficient nutrient cycling), to extract the nutrients present in the mulch, returning these nutrients to the compromised soil, and reestablishing the soil microbiome that is required for healthy plant growth.

Using weeds as ecosystem restorers

Any weeds removed form a given ecosystem should also go through a similar process, preferably through a worm farm system to extract and return the nutrients that were removed with the weeds, while replenishing the soil microbiome. Anytime we remove weeds off site, we are mining nutrients from the soil, continually depleting essential biomass and the nutrients contained within it, while destroying the microcosm the weeds supported. Constant plant cover is absolutely essential to maintain in any given ecosystem and if it is comprised of native species, weeds become unnecessary in colonising the soil. However, as fungal biomass is reduced in the soil, through removal of woody vegetation and woody biomass, plants belonging to the lower successional stages (we call herbaceous weeds) will proliferate, feeding on the nitrates provided by bacterially dominated soils. Trees require ammonium provided by fungi to sustain their growth, so if we want to prevent the growth of undesirable plants and want to support tree growth, we must feed fungi first.

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Increased fungal diversity in fire prevention

Another method for increasing particularly fungal diversity in the soil to encourage the ecosystem’s succession towards an old growth forest habitat, is to actively build up the soil organic mulch layer by chopping and dropping branches to the ground. The thicker the decomposing mulch matter buildup, the more fungal diversity will colonise the mulch and the more moisture will be retained in the litter providing moisture to plants through drought, as well as resilience to fire. Not only will the fuel on the ground be moist and fire retardant as it holds onto moisture, the fuel load in the vegetation layer will also be reduced through ongoing chop and drop management. Some of this dropped biomass accumulation can be achieved through weed removal, reducing their growing biomass, and thus managing these plants, but also exploiting their fast growth as a continuous vegetation cover and provision of photosynthetic carbohydrates to maintain the soil microbiome. Such management practices can build the soil microbiome to a level that will support the growth of native trees and understory plants. These changes in ecosystem care practices can all be achieved and tested through regular analysis of the soil food web organisms and measurement of the bacterial to fungal biomass ratio using microscopy.

To learn more, investigate these methods or request a soil microbiome analysis contact

loveoursoils@gmail.com⁠

or visit

Love Your Soil⁠

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