The greening of a rock

At a place called Urulanthanni near Thattekad is a rock poking out of the surrounding rain forest. The area is a ecological hot spot. The dense canopy of the forest holds a very large variety of endemic birds, which are invisible from the ground. The rock provides a great vantage point from which to view the activity in the canopy. In fact, as you can see in the featured photo, the canopy itself is a grand view.

While walking in the forest I’d noticed basaltic rocks poking out of the ground at various places. So the whole rain forest here has been formed by sedimentation and erosion of the volcanic rock. This knoll that I stood on was a rougher rock. On the surface I could see a flowing texture created by weathering. You can see this in the photo below. But when I looked at a broken face in the rock, as in the photo above, I could see the grainy texture of the rock. It seems that the rock here is a mixture of two kinds called gabbro and syenite. Both have this texture, but are different in the minerals that they contain. So this giant rock must have been created by a separate upwelling of magma within the volcanic rocks underlying the land around us. The red insect is the nymph of a bug which I saw later.

How did inhospitable rock become the bed of a rain forest? Observations on Mount Saint Helens has given us a wonderful insight into how biology covers geology. Could I see the beginnings of the cycle on this dome? Almost certainly the bare rock was covered by bacteria. But the smallest things I could see were mosses. I regretted not bringing my macro attachment. I would have got wonderful photos here. At the next level of organization, I could see soil blown into little hollows in the rock, as in the photo above. Was this enough to support plants?

It seemed that it was. I could see clumps of bushes growing in these thin mats of soil. As they grow and shed leaves they add to the soil. They also present a barrier to winds which cause the air to drop soil around them. Right at the exposed top, the process of bootstrapping the creation of soil is slow. But just behind the flat top, it proceeds faster, accelerating even more as you go down the slope. In the photo above you can see the scant bushes at the flat top growing in a thin mat of soil, and the larger thickets of bush lower down. You can also see a few trees which have taken root in the upper slopes. Eventually, the bacteria, moss, bushes and trees will erode the stone into soil, and this dome will be covered in vegetation!

Author: I. J. Khanewala

I travel on work. When that gets too tiring then I relax by travelling for holidays. The holidays are pretty hectic, so I need to unwind by getting back home. But that means work.

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