A walk in an oak forest

The breeze blew cool and clear. There was no one close by on the path up to Zero Point inside Binsar National Park, so I pulled my mask down to smell the trees around me. Oak forests don’t have the pleasant resinous smell of pines, but they are so much more alive. At this height, about 2400 meters, the Himalayan white oak (banj, or Quercus leucotrichophora) should be close to its upper limit, but they looked like they were thriving away from the hard competition with chir pines (Pinus Roxburghii) on lower slopes.

Oak forests are alive. Langurs prefer banj oaks as roosts. A yellow throated marten streaked across our path, it is another inhabitant of banj forests. I could hear a woodpecker looking for lunch, and, from a distance, the call of the Great Barbet. This forest was full of birds: seed eaters, acorn gatherers, and insectivores. The oaks themselves harbour life: fungi, lichens, ferns, orchids, and mistletoe. Butterflies flitted about on the sun dappled path. On gentler slopes the canopies merge together to provide complete shade under them, making it hard for younger trees to grow. But up here, the slope was steep enough that there was always a gap in the canopy, and rhododendron and other trees could spring up. Still, the forests of the western Himalayas do not seem to have the exuberance of the east. The monsoon winds create this difference.

The smaller number of large trees here gives me a chance to slowly begin to recognize most of them. A few years ago I made myself a small and incomplete field guide to trees of the middle heights. I’ve added to that by now, and I realize I can recognize most of the trees around me as I walk. But the herbs are another matter. I stop and look at the small plants poking out of the muddy cliff on one side of the path. I haven’t the faintest clue about them.

I could stick to the trees for now. The path is surrounded by oaks. I’ve aways been a little surprised by that. Oaks, mistletoe, holly all sounded exotic to me when I grew up surrounded by mango, guava, jamun, and silk cotton trees. But to my surprise the genus Quercus, oaks, seems to have its origins in a part of an ancient continent which is today East Asia, in the middle of the Eocene Epoch, perhaps about 45 million years ago. That was just after the earth had gone through one of its temperature maxima (there were no ice sheets anywhere on the planet) and the Indian plate had just banged into Asia. Over the geological ages after that, the oaks adapted to the cooling climate, and crossed the Himalayas into Europe. The five Himalayan species found themselves settled at various heights, Q. leucotrichophora at the lowest altitude. During the multiple ice ages of the Pleistocene Epoch the white oaks seem to have covered a very large part of the lower slopes.

Most observers agree that the oaks are slowly being crowded out by pines on the lower slopes. I asked why, and got different replies. The literature is also a little confused, but I tried to make sense out of what I read and heard and got an interesting story. The two main threads in the plot are how fast the trees grow and how they respond to fire. Once the acorns germinate, the oak seedlings can halt growth until conditions are just right. This requires a moderate disturbance of the forest to let in some light. In the days of Jim Corbett, this was provided, at least partially, by human intervention, as villagers chopped off a few branches of older trees for kindling, and removed some of the leaves for fodder. But now this activity is forbidden, for reasons that were well-intentioned. As a result seedlings lie in arrested growth for long times in unattended forests. The trouble is that in recent decades a “fire season” has become part of the annual cycle in the ecology, probably due to direct human intervention. I have read no account of it in the older literature on Kumaon. Fire affects the slow-growing oak seedlings disproportionately.

Pines, on the other hand, are adapted to grow in degraded land, and can reach a height of 20 meters or so in a decade. Fire also causes pine cones to open up and release spores. As a result, chir pines out-compete and out-grow oaks. They are also more immediately useful for commerce, so the forest department manuals on planting and harvesting of pines are widely used. Oaks provide more ecosystem services, but they are not seen as commercially viable products. As a direct result, I could not find any manual on oak silviculture. When I reached the end of the walk I could look down at the surrounding slopes. The nearer ones, inside the park, still held many stretches of oak forests. Further off, there seemed to be more pines.

[Note added later: much of my understanding behind this paragraph may have to be revised in the light of new scientific findings about pines and their stabilizing role in the previously unrecognized biome called Himalayan grasslands. Through the 20th century they were thought to be degraded forests, but are now recognized as a separate biome with support for a different set of species. The dynamic balance between oak forests and these grasslands is still being studied.]

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