If you’ve ever been to some of the Talk and Walks, you might have met Andy MacKinnon. Andy is one of those rare individuals who is a natural born teacher. He combines his expertise in forest ecology, his passion for our wild lands and his innate sense of humour to produce unforgettable presentations that leave you spellbound and open to the mysteries that still abound in science.
Such was the case on November 9, 2012 as we listened to Andy’s Talk on Making Connections in Metchosin, Mycorrhizal or Romantic?
|Ancient Douglas-fir (and my grandson!)|
Andy began the talk by reminding us that 5,634 ha (76%) of Metchosin is forested and the signature organism of our District is the Douglas-fir, named after David Douglas, an early explorer and plant collector. In 1825 Douglas measured one fir that was 227 ft tall and 48 ft in circumference! We don’t have many old giants left in Metchosin as most of the District has been previously logged, but there are a few.
The area bounded by Parry Bay to William Head Rd is shown on old maps as a Garry oak woodland, one of Canada’s most endangered ecosystems, most of the remaining District is forested with a mixture of tree species, of which Douglas-firs and conifers are predominant.
Andy posed the question “Why do we have Douglas-firs in Metchosin?” and the answer, as you would suspect, is partly from climate - the sun, moisture, heat and cold, partly because of the soil composition – the depth, the nutrients and drainage, and also, and perhaps most importantly, because of mushrooms.
The mushrooms we see are the above ground fruiting bodies of underground organisms. Andy likens them to the apples on a tree or you can think of them as the tip of the iceberg, where most of the bulk is concealed below. This association between plant roots and fungi is called mycorrhizae from the Greek mykos for fungus and riza for root. These very fine, microns thick, fungal filaments attach themselves to the roots of plants in various ways. In the case of most of our conifers (except western redcedars), the association is with fungus filaments that surround the root hairs, called ectomycorrhizae. Almost any large mushroom you will find in our forests belongs to this group. The mass of mushroom filaments gather water and minerals and supply them to the trees, which in turn, makes sugars that are shared with the mushrooms.
Under the title “Lifestyles of the Rich and Fungal” Andy divided mushrooms in four lifestyles.
Saprophytes feast on decaying organic matter and include oyster, fairy ring, witch’s butter and magic mushrooms.
Parasites feed on living creatures, the edible honey mushrooms, the world’s largest organism belong here. Through DNA testing, one fruiting honey mushroom was identified to be twenty km across in size! Another of the parasites is the lobster mushroom, which invades a mushroom, usually the short-stemmed russula, and in the process produces a delicious, edible fungus. Conks found on trees are also parasites and there was an enormous artist conk (so called because the white underside stains brown when scratched) on display at the talk, courtesy of Kevin Trim.
Not many people realize that lichens also have a relationship to the fungus family. They are the product of an association between a fungus and an alga and/or with cyanobacteria. The fungus makes up to ninety to ninety-five percent of the lichen. In this case the fungus cultivates the alga/cyanobacteria inside itself, to produce sugars that are shared with the fungus and in return, the alga and/or cyanobacteria use the fungus as a protective home.
|Camas with Reindeer Lichen|
Some mushrooms can also be predators; the jellys are in this group, secreting a substance that traps amoebas, roundworms and rotifers. After they are immobilized, the fungus inserts one of its filaments into the prey, killing it and consuming the organism.
Two thousand species of fungus have been documented having a mycorrhizal association with Douglas-firs. At any one time there can be a dozen species of fungus attached to any one tree, which might also be attached to further trees nearby, even to different tree species, this has been termed, somewhat tongue-in-cheek, the wood-wide web. In a study by Suzanne Simard (Nature, Aug 1997), it was shown that nutrients are shared among trees by the fungal mycorrhizal networks and that when one of these partnerships is stressed (such as a tree being shaded), additional nutrients are shipped to that tree to help it survive. It has been conjectured that saving multiple tree species gives the fungus an advantage if a natural disaster or cycle, such as fire or disease should wipe out a species. You could make a case that the mushrooms are farming the trees!
In a January 2010 article of New Phytologist, research was described that mapped the belowground connections between two fungus species and Interior Douglas-firs in a 100m x 100m plot. It was shown that these associations promote the health and development of juvenile trees. Additionally, it seems to be that the old veteran trees have more connections to more trees (one old tree was connected by the mycorrhizal network to forty-seven other trees), than do younger trees. The myriad connections which are possible with older trees, the ability to shunt nutrients and water between so many trees, helps to stabilize the forest ecosystems. Something that should be considered in future forest management plans.
Other plants besides trees have beneficial relationships with mycorrhizal fungus, in fact 94% of all plant species in the world have these associations.
Coralroots, some of our beautiful orchid species that lack chlorophyll, were previously thought to be saprophytes, plants that feed on decaying wood. That theory as been proved inaccurate and we now know that coralroots are part of the fungal web that is also associated with conifers. Spotted coralroots have a relationship with the various Russulas, as does Indian-pipe and striped coralroots with Tomentella fungal species.
Candysticks are another intriguing species that lack chlorophyll and are associated with mushrooms. In this case, where you find candysticks, you will find the delectable pine mushrooms.
Salal, huckleberries, blueberries, arbutus and other ericoid species, generally found in nutrient poor soils, have beneficial relationships with ericod mycorrhiza, which extract nitrogen from decaying organic matter so that it is available to their plant partners.
Tracing the thousands of kilometers of myriad fungi filaments that shunt water and nutrients between plants, DNA sequencing, all of this underground, presents huge challenges to the research of associations and relationships between plant species and mycorrhizal fungi. There is a growing awareness that the old concept of survival of the fittest through competitive forces is not the only survival story in nature. The beneficial mycorrhizal relationships of mushrooms with other plants are based on a cooperative approach that nature has taken. From looking at our forests through a single species lens, to the acknowledgement that forest species are all interconnected will have far ranging consequences for ecosystem management.
Next time you are in forest and spy a few mushrooms, so small and almost insignificant compared to the towering conifers and wide-spreading maples, consider that without the mushroom networks, there would be no forests.