13.1 Ecosystem mycology

  • Fungi are the saprotrophs that perform the decomposition processes that contribute to organic and inorganic nutrient cycling. Clearly, fungal decomposition of dead organic matter, be it wood or other plant litter, animal dung, or cadavers and bones, is an essential ecosystem function because it maintains soil nutrient availability (see below). But there is another significant contribution along the way: fungi that decay wood soften the timber sufficiently to allow small animals (birds, reptiles, amphibians, insects and mammals) to make burrows and nests.
  • Fungal products aggregate soil particles and organic matter, improving drainage and aeration; and by so doing they create habitat diversity for many other organisms (see our discussion of glomalin in Section 6.8).
  • Fungi serve as both prey and predators of many soil organisms, including bacteria, other fungi, nematodes, microarthropods, and insects (Wall et al., 2010; Crowther et al., 2012; Menta, 2012; Ngosong et al., 2014) (see Sections 1.5, 11.2, and Chapter 15).
  • Mushrooms and truffles are consumed by many animals including large mammals like primates, deer, and bears, and many small mammals rely on mushrooms and truffles for nearly their entire food supply. The fungal mycelium is an equally important nutritional resource for many microarthropods (see Section 11.2).
  • The significance of fungi in nature means that changes in the composition and functioning of fungi in a community can have sweeping effects on the diversity, health and productivity of our natural environment. Fungal diversity is also called richness (Andrew et al., 2019) and molecular methods  (‘metagenomics’) are now allowing this to be studied directly (Lindahl & Kuske, 2013). Although it is species of fungi, bacteria, nematodes, and arthropods that typically dominate terrestrial ecosystems in terms of species richness, most conservation work is unfortunately concentrated on vertebrates and vascular plants. Yet there is evidence that land management practices can affect fungal diversity.

In most environments, most of the larger, showy and fleshy mushrooms that are readily seen, as well as truffles beneath the surface, are mycorrhizal. Obviously, diversity of mycorrhizal species will be influenced, if not determined, by plantings of their potential hosts. However, management practices can also affect the diversity of saprotrophic fungi; indeed, in Northern Europe intensive management of forest is associated with decline in species diversity of wood-degrading saprotrophic fungi. This appears to result from management regimes that remove woody debris from managed forests. Diversity of such species is positively correlated with both the quality and quantity of woody debris left in a forest and coarse woody debris even promotes the abundance and diversity of truffles. It is counterproductive to allow this to occur as change in the diversity and abundance of wood-degrading fungi will adversely affect the recycling of key nutrients and the provision of ecological niches in the managed community. Ironically, although the overall fungal community composition is mostly determined by host tree species, because forest management has a generally negative impact on wood-inhabiting fungal diversity, the overall species richness increases as the forest naturalness increases (that is, as management by humans is removed) (Jenna et al., 2021). Forest resilience is compromised by human-induced environmental influences, potentially resulting in major shifts in the ecosystem that might be difficult to reverse. Such a shift is called a tipping point. The theoretical basis for ecosystem tipping points has been developed in recent years largely to assess the effects of present and future climate change on the Earth’s ecosystems. Applying tipping point theory to forests, including their belowground components like ectomycorrhizal fungi, is at an early stage but may enable understanding of feedback mechanisms and predict forest ecosystem tipping points that might be addressed (Suz et al., 2021).

The result is that the influence extends beyond the plant communities to all those other organisms that interact with fungi, from insects and slugs that depend on fungi for food, to the vertebrates that eat the invertebrates. And, of course, it’s not just the commercial forests to which this applies. Amenity land (public garden and park land) is an increasingly important aspect of the urban environment which so many of us inhabit, but here, too, excessive tidiness can adversely affect the biodiversity and diminish the recreational value of the resource (Czederpiltz et al., 1999; Floren et al., 2015; Juutilainen et al., 2014; Heilmann-Clausen et al., 2017; Stevenson et al., 2020).

From several aspects of the above it is evident that fungi contribute to human welfare, both directly and indirectly, and therefore represent part of the total economic value of planet Earth. But these are just a few examples of the ways that fungi make this contribution; descriptions of many other examples occur throughout this book. This is the fungal part of the interface between economics and biology. Overview of the many benefits that the natural world offers to humans views those benefits as a range of services (first called Nature’s Services; Daily, 1997) to which monetary value (the natural capital) can be attached. The hope being that understanding the value of the natural systems on which we are all vitally dependent will encourage greater efforts to protect the Earth’s basic life-support systems before it is too late (on the principle ‘money talks’). The description ‘ecosystem services’ was adopted by Costanza et al. (1997), and this name is now the most widely used. Costanza et al. (1997) estimated the (minimum) economic value of the entire biosphere to be an average of US$33-trillion (that is, US$33 × 1012) per year. This is equivalent to US$50-trillion at 2018 prices. To put this into perspective, the Gross Domestic Product of the United States of America ran at a rate of $20-trillion a year during the second quarter of 2018. Ecosystem services is now the principal concept in ecology. By March 2017, the paper in the journal Nature by Robert Costanza et al. (1997) had been cited over 17,000 times and Gretchen Daily’s book (Daily, 1997) had been cited over 6,000 times, making them among the most highly cited works in ecology to date (Costanza et al., 2017). In Resources Box 13.1 (below) we provide a few more reference sources for Ecosystem Services and a Table listing the fungal examples you can find in this book.

Resources Box 13.1

View the pages hyperlinked below for reference sources dealing with Ecosystem Services and a Table listing the fungal examples you can find in this book

CLICK HERE to view the Resources Box of references and explanation (opens in a new window)

CLICK HERE to view Table 13.1 listing fungal examples discussed in this book (opens in a new window)

CLICK HERE to download a PDF that combines these data

World agriculture’s vulnerability to climate change is increasingly being expressed as its resilience. Agricultural resilience, defined as the capacity of the system to absorb shocks and stresses (to agricultural production and farming livelihoods), has become a distinct policy objective for sustainable and equitable development (Bousquet et al., 2016). The resilience concept and its relationships to biodiversity, ecosystem services, and socioeconomics are explored fully by Gardner et al. (2019).

The 2019 Global Assessment Report on Biodiversity and Ecosystem Services produced by the United Nations’ Intergovernmental Science-Policy Platform has demonstrated that the natural environment across most of the globe has now been significantly altered by human activities, with most indicators of ecosystem health and biodiversity showing rapid decline. At the time of writing this text the full Report (which is expected to exceed 1,500 pages) has not been published, but you can access the 39-page Summary for Policymakers that was released in May 2019 at: https://www.ipbes.net/news/ipbes-global-assessment-summary-policymakers-pdf.

In Chapters 14 to 16 we will add detail to the brief descriptions given above of the ways that fungi contribute to the Earth’s ecosystems (and see Suz et al., 2018). In this Chapter we will concentrate attention on some saprotrophic activities to begin with, but our main topic will be the various associations between plants and fungi.

Updated September, 2021