Thursday, 15 July 2010
[lichen and leaf mold, Pandani Grove walk, near Lake Dobson, Tasmania]
My senior high biology teacher, Mr Harnack, was fond of asking questions. Nothing unusual about that, I suppose, except that it was always the same question. And he would ask it every single lesson: What is life?
I’m sure he thought he was being deep, dramatic, and more than a little cosmic. To our shame, my classmates and I focussed less on the depth of his question than on his nerdish mode of delivery and his American drawl (“Boyzz – Whaart izz larrff?”)
Spending time among lichens in recent days brought Mr Harnack’s question to mind. It’s not that I doubt lichens are a lifeform. They are actually one of the more complex and interesting forms of life on earth: a symbiosis between two other living forms, algae and fungi.
Because the algal part of the partnership processes light via photosynthesis, lichens have some plant-like characteristics. However unlike plants, if they experience extended periods of heat, drought or cold, they can go into a suspended state – known as cryptobiosis – until conditions improve. They may appear dead, hanging as crisp and lifeless as dead leaves, when they are actually full of life. Hence my asking the Harnack question.
Cryptobiosis enables them to grow in locations impossible for most plants, including bare rock, sterile soil or sand, and human-made structures like walls, roofs and tomb-stones. And they can grow on other plants, even in the darkest depths of a rainforest.
That’s where I most recently encountered them, luscious and luminescent on the trunks of rainforest trees. But I’ve also seen the more demure forms that blotch granite boulders or daub dark dolerite. And the Harnack question comes to mind wherever I observe this intimacy between lichen and its substrate. The growth habits of lichen seem to blur the distinction between the living and the dead. Where, for instance, does the rock or dead bark end and the lichen begin? Does the fungal part of the organism reach deep into the rock as fungi will in soil. And can the substrate really be excluded from the symbiosis if the lichen “protects” the rock or bark?
[lichen on granite, Maria Island National Park, Tasmania]
I observed its role in bridging the living and the dead when visiting some Alaskan glaciers a few years ago. There lichen plays the part of John the Baptist, preparing the way for the lifeforms that will come after it. As glaciers retreat – and they have long been seen to do so in Alaska – bare rock sees the light of day for the first time in millennia. Lichen colonises the fresh faces, slowly doing its rock-breaking, soil-producing work. The soil then enables other pioneering species, plants like willow, fireweed and alder, to gain a foothold. In Alaska it takes 70 to 80 years from glacial retreat to full-blown coniferous forest. That’s a startlingly short time in earth history, and a testament to the influence of the easily overlooked wonder that is lichen.