It seems like they produce and trade with each other, even across species. Are trees and the fungi being selfish or altruistic? Adam Smith and Thomas Malthus make an appearance.
"Underground, trees and fungi form partnerships known as mycorrhizas:
Threadlike fungi envelop and fuse with tree roots, helping them extract
water and nutrients like phosphorus and nitrogen in exchange for some of
the carbon-rich sugars the trees make through photosynthesis. Research
had demonstrated that mycorrhizas also connected plants to one another
and that these associations might be ecologically important, but most
scientists had studied them in greenhouses and laboratories, not in the
wild."
"By analyzing the DNA in root tips and tracing the movement of molecules
through underground conduits, Simard has discovered that fungal threads
link nearly every tree in a forest — even trees of different species.
Carbon, water, nutrients, alarm signals and hormones can pass from tree
to tree through these subterranean circuits. Resources tend to flow from
the oldest and biggest trees to the youngest and smallest. Chemical alarm signals
generated by one tree prepare nearby trees for danger. Seedlings
severed from the forest’s underground lifelines are much more likely to
die than their networked counterparts. And if a tree is on the brink of
death, it sometimes bequeaths a substantial share of its carbon to its
neighbors."
"Since Darwin, biologists have emphasized the perspective of the
individual. They have stressed the perpetual contest among discrete
species, the struggle of each organism to survive and reproduce within a
given population and, underlying it all, the single-minded ambitions of
selfish genes. Now and then, however, some scientists have advocated, sometimes controversially, for a greater focus on cooperation over self-interest and on the emergent properties of living systems rather than their units."
"An old-growth forest is neither an assemblage of stoic organisms
tolerating one another’s presence nor a merciless battle royale: It’s a
vast, ancient and intricate society. There is conflict in a forest, but
there is also negotiation, reciprocity and perhaps even selflessness.
The trees, understory plants, fungi and microbes in a forest are so
thoroughly connected, communicative and codependent that some scientists
have described them as superorganisms. Recent research suggests
that mycorrhizal networks also perfuse prairies, grasslands, chaparral
and Arctic tundra — essentially everywhere there is life on land.
Together, these symbiotic partners knit Earth’s soils into nearly
contiguous living networks of unfathomable scale and complexity."
"Mycorrhizal networks were abundant in North America’s forests. Most trees were generalists,
forming symbioses with dozens to hundreds of fungal species. In one
study of six Douglas fir stands measuring about 10,000 square feet each,
almost all the trees were connected underground by no more than three
degrees of separation; one especially large and old tree was linked to
47 other trees and projected to be connected to at least 250 more; and
seedlings that had full access to the fungal network were 26 percent
more likely to survive than those that did not.
Depending on the species involved, mycorrhizas supplied trees and other
plants with up to 40 percent of the nitrogen they received from the
environment and as much as 50 percent of the water they needed to
survive. Below ground, trees traded between 10 and 40 percent of the
carbon stored in their roots. When Douglas fir seedlings were stripped
of their leaves and thus likely to die, they transferred stress signals
and a substantial sum of carbon to nearby ponderosa pine, which
subsequently accelerated their production of defensive enzymes. Simard
also found that denuding a harvested forest of all trees, ferns, herbs
and shrubs — a common forestry practice — did not always improve the
survival and growth of newly planted trees. In some cases, it was
harmful."
"Many were perplexed as to why trees of different species would help one
another at their own expense — an extraordinary level of altruism that
seemed to contradict the core tenets of Darwinian evolution."
"It’s now well accepted that resources travel among trees and other
plants connected by mycorrhizal networks. Most ecologists also agree
that the amount of carbon exchanged among trees is sufficient to benefit
seedlings, as well as older trees that are injured, entirely shaded or
severely stressed, but researchers still debate whether shuttled carbon
makes a meaningful difference to healthy adult trees. On a more
fundamental level, it remains unclear exactly why resources are
exchanged among trees in the first place, especially when those trees
are not closely related.
In their autobiographies, Charles Darwin and Alfred Russel Wallace each
credited Thomas Malthus as a key inspiration for their independent
formulations of evolution by natural selection. Malthus’s 1798 essay
on population helped the naturalists understand that all living
creatures were locked into a ceaseless contest for limited natural
resources. Darwin was also influenced by Adam Smith, who believed that
societal order and efficiency could emerge from competition among
inherently selfish individuals in a free market. Similarly, the planet’s
dazzling diversity of species and their intricate relationships, Darwin
would show, emerged from inevitable processes of competition and
selection, rather than divine craftsmanship. “Darwin’s theory of
evolution by natural selection is obviously 19th-century capitalism writ
large,” wrote the evolutionary biologist Richard Lewontin.
As Darwin well knew, however, ruthless competition was not the only way
that organisms interacted. Ants and bees died to protect their colonies.
Vampire bats regurgitated blood to prevent one another from starving.
Vervet monkeys and prairie dogs cried out to warn their peers of
predators, even when doing so put them at risk. At one point Darwin
worried that such selflessness would be “fatal” to his theory. In
subsequent centuries, as evolutionary biology and genetics matured,
scientists converged on a resolution to this paradox: Behavior that
appeared to be altruistic was often just another manifestation of
selfish genes — a phenomenon known as kin selection. Members of
tight-knit social groups typically share large portions of their DNA, so
when one individual sacrifices for another, it is still indirectly
spreading its own genes.
Kin selection cannot account for the apparent interspecies selflessness
of trees, however — a practice that verges on socialism. Some
scientists have proposed a familiar alternative explanation: Perhaps
what appears to be generosity among trees is actually selfish
manipulation by fungi. Descriptions of Simard’s work sometimes give the
impression that mycorrhizal networks are inert conduits that exist
primarily for the mutual benefit of trees, but the thousands of species
of fungi that link trees are living creatures with their own drives and
needs. If a plant relinquishes carbon to fungi on its roots, why would
those fungi passively transmit the carbon to another plant rather than
using it for their own purposes? Maybe they don’t. Perhaps the fungi
exert some control: What looks like one tree donating food to another
may be a result of fungi redistributing accumulated resources to promote
themselves and their favorite partners.
“Where some scientists see a big cooperative collective, I see
reciprocal exploitation,” said Toby Kiers, a professor of evolutionary
biology at Vrije Universiteit Amsterdam. “Both parties may benefit, but
they also constantly struggle to maximize their individual payoff.”"
"plants and symbiotic fungi reward and punish each other with what are
essentially trade deals and embargoes, and that mycorrhizal networks can
increase conflict among plants. In some experiments, fungi have
withheld nutrients from stingy plants and strategically diverted
phosphorous to resource-poor areas where they can demand high fees from
desperate plants."
"Some researchers have proposed that cooperation within or among species
can evolve if it helps one population outcompete another — an altruistic
forest community outlasting a selfish one, for example. The theory
remains unpopular with most biologists, who regard natural selection above the level of the individual
to be evolutionarily unstable and exceedingly rare. Recently, however,
inspired by research on microbiomes, some scientists have argued that
the traditional concept of an individual organism needs rethinking and
that multicellular creatures and their symbiotic microbes should be
regarded as cohesive units of natural selection. Even if the same exact
set of microbial associates is not passed vertically from generation to
generation, the functional relationships between an animal or plant
species and its entourage of microorganisms persist — much like the
mycorrhizal networks in an old-growth forest. Humans are not the only
species that inherits the infrastructure of past communities."
[At a mycorrhizal network] "She handed me a thin strip of root the length of a pencil from which
sprouted numerous rootlets still woolly with dirt. The rootlets branched
into even thinner filaments. As I strained to see the fine details, I
realized that the very tips of the smallest fibers looked as though
they’d been capped with bits of wax. Those gummy white nodules, Simard
explained, were mycorrhizal fungi that had colonized the pine’s roots.
They were the hubs from which root and fungus cast their intertwined
cables through the soil, opening channels for trade and communication,
linking individual trees into federations. This was the very fabric of
the forest — the foundation of some of the most populous and complex
societies on Earth."
"Five hundred million years ago, as both plants and fungi continued
oozing out of the sea and onto land, they encountered wide expanses of
barren rock and impoverished soil. Plants could spin sunlight into sugar
for energy, but they had trouble extracting mineral nutrients from the
earth. Fungi were in the opposite predicament. Had they remained
separate, their early attempts at colonization might have faltered or
failed. Instead, these two castaways — members of entirely different
kingdoms of life — formed an intimate partnership. Together they spread
across the continents, transformed rock into rich soil and filled the
atmosphere with oxygen.
Eventually, different types of plants and fungi evolved more
specialized symbioses. Forests expanded and diversified, both above- and
below ground. What one tree produced was no longer confined to itself
and its symbiotic partners. Shuttled through buried networks of root and
fungus, the water, food and information in a forest began traveling
greater distances and in more complex patterns than ever before. Over
the eons, through the compounded effects of symbiosis and coevolution,
forests developed a kind of circulatory system. Trees and fungi were
once small, unacquainted ocean expats, still slick with seawater,
searching for new opportunities. Together, they became a collective life
form of unprecedented might and magnanimity."
