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Why are there so few mushrooms in the tropics?

March 7, 2011

The tropics are characterised by an overwhelming biodiversity: coral reefs with enchanting fish, mountains with thousands of plant species, colourful butterflies….but actually not so many mushroom species! In fact, my humble and unscientific observation is that boreal forests are richer in mushroom fruitbodies than the tropical monsoon forests surrounding Chiang Mai in northern Thailand.

How can that be?

My hypothesis after studying the Dokmai Garden ecosystem is that termites degrade wood so quickly there is only limited substrate left for the fungi. Indeed there are mushrooms, many of which are mycorrhizal, i.e. live in symbiosis with trees (Dipterocarpaceae, Pinaceae and Fagaceae), but wood degrading mushrooms are not as abundant as in for example Sweden. When we recently went up on the mountain Doi Inthanon, we could study a sphagnum bog at around 2500 meters altitude, Lobaria lichens and logs indicating brown rot. Such mushrooms degrade wood slowly, extracting cellulose and leaving the lignin skeleton. In Sweden where we have no termites, fungi are the main wood decomposers. In Sweden we also have thick litter and humus layers, while here the degradation is so fast there is hardly no humus.

Maybe Sweden should announce mushroom tours for people in the tropics?

Eric Danell

Brown rot is identified by its blocks of brown lignin, a left-over from a fungal feast where the main course was cellulose. These lignin blocks are like the bones after eating a chicken. Other fungi will decompose this lignin, but very slowly. Such a sight is common in cool boreal ecosystems, but rare in the tropics. This picture is from the summit of Doi Inthanon mountain in Thailand.

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4 Comments leave one →
  1. November 10, 2011 12:28 PM

    Eric, I passed on your post to a mycologist friend who is retired from the University of Hawaii at Hilo. He replied:

    “Yes, he may be correct about the wood-rotting mushrooms. I had a student work on that exact project, and he found that it is a race between the fungi and the termites as to who gets the log. Once the wood-rotting fungi have taken a hold they secrete chemicals that inhibit the termites. In areas where the termites dominate, they may be winning this food source. My colleague Dennis Desjardin has been working in Thailand for years, and let me tell you there are lots of mushrooms there even though they may not be growing on wood.”

    I hope that is of interest.

    Ken

    • November 11, 2011 9:19 AM

      Thanks a lot for this information! I was not aware there was a chemical warfare about the resources. Indeed there are mushrooms around here, but the abundance in species and specimens you experience during a one-day foray in say Sweden or the American Pacific Northwest can not be seen here.

      I have a faint memory I attended a lecture on Hawaiian mushrooms about 17 years ago, possibly held by Dennis Desjardin, and my impression was the mushroom diversity was quite low there. Not so strange due to the isolation.

      Cheers, Eric

  2. November 17, 2011 12:59 PM

    Eric, my friend, Dr. Don Hemmes, went out exploring for fungi every week; he told me he discovered new species almost every trip because the fungi of Hawaii were so poorly investigated. He published Mushrooms of Hawaii with Dr. Desjardin in 2002, and it may be that at the time you attended the lecture by Dr. Desjardin there were indeed few mushrooms described for Hawaii. Dr. Hemmes is an incredible guy, one of the most congenial and generous people you could hope to meet. At over 65 years of age, he is a competitive table tennis player and track athlete.

    Aloha, Ken

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