The Cathedral Forests
Posted by: David Orme
As I placed my hand on the trunk of the giant tree towering over me, I felt a sensation of awe and exhilaration, as though the tree was transferring some of its life energy to me. Once a tiny seed, this goliath had likely germinated during an ancient mast-fruiting event and had survived over the centuries, against the odds, to emerge through the canopy around 60 m above the forest floor. All around it, as far as my eyes could travel, were similar-sized or even larger trees. Giant lianas thicker than the torso’s of two adult men looped down from the branches of the trees and almost touched the forest floor. The understory was clear of the tangle of secondary vegetation that is rife in forests that have undergone logging and a springy layer of leaf litter carpeted the forest floor.
I felt as though I was in a gigantic cathedral, an incredibly peaceful and soothing cathedral created by the giants of the rainforest. The sunlight filtered through the trees, illuminating sections of the forest floor in dappled light while dark shadows concealed the parts the sunlight could not penetrate. The silence of the cathedral was punctuated by a gentle breeze as it whistled high above through the branches of the trees and descended to rustle the leaf litter on the forest floor. The sounds of birds chirping and the gibbons singing in the distance enhanced the air of calm. As the day wore on, the birds became quieter in the afternoon heat and only the occasional cicada penetrated the silence. Borneo’s rainforests are among the oldest in the world. The ancient trees in the Maliau Basin have been fortunate to escape being logged, by random chance of having grown in an area that is currently protected. Among the most magnificent forests I have ever had the privilege of walking in, OG1 or Seraya as it is better known among the researchers of SAFE, is one of three old growth control sites in the Maliau Basin, the other two being Belian (OG2) and Gravity (OG3). It is the most distant of the three control sites from the Maliau Basin Studies Center (MBSC) as well as the most challenging in terms of its terrain, with the steepest plots being approximately 3 hours away on foot.
However, the stiff trek is well worth it when one cools off on the ridge that overlooks the valley below with its fine forest full of mighty trees. I particularly remember a misty morning when I made my way to the steepest plots from the makeshift campsite around 20-30 minutes away. It had been raining lightly since 4:00 AM and the trees looked particularly magical in the pre-dawn light as the mist swirled around the trunks. At the top of the ridge, the mist was lighter and the valley below was cloaked in a swirling sea of white. As the sun rose, it shaded the mist pink, followed by orange and finally red. The trees performed the role of filters, individual beams of sunlight rippling through them and playing on the forest floor. The sound of the raindrops seemed rather magnified in the vastness of the cathedral, the drops seeming to echo as they pattered on to the leaf litter. Spotting movement in the valley below, I watched quietly from the ridge as a muntjac made its way along an animal trail. Gibbons were calling vociferously that morning, a family almost above us proclaiming their right to their territory to the neighboring family, their joyous whoomps echoing and traveling far through the trees.
Most of the trees in the cathedral belong to a family known as Dipterocarpaceae. This family of trees dominates Borneo’s rainforests. What makes Borneo’s rainforests unique among the rainforests of the world is the manner in which the Dipterocarps reproduce. Every 4-9 years, the Dipterocarps come into flower synchronously and then fruit en masse in a phenomenon known as mast fruiting. The exact timing of such masts is difficult to predict but they are known to occur during El Nino years. The drought caused by an El Nino likely stresses the trees and makes them want to set seed. Many other families of trees follow the Dipterocarps and also come into flower and fruit during masts. The grandeur of a mast fruiting event has to be witnessed to be believed. I was fortunate to be in the Maliau Basin during the 2014 mast event. During February-June, the trees slowly became covered by what looked as dull brown fuzz, the effect of thousands of winged fruits maturing on the branches. From mid July, the winged fruits began to gyrate from the tops of the trees, whirling down to the forest floor. The effect of millions of seeds of multiple species on the forest floor was akin to that of a unbroken carpet – initially formed by seeds and subsequently, by seedlings. It was literally impossible to step on any part of the forest floor without stepping on a few seeds or seedlings.
It has been hypothesized that the most likely reason for the phenomenon of mast fruiting is to satiate seed predators. Numerous species of insects, fungi and vertebrates such as rodents and bearded pigs find the seeds nutritious and eat large quantities of them. The sheer number of seeds produced in a very short time likely fills up most predators and allows some seeds to germinate and survive into seedlings. A proportion of seedlings survive to become saplings and an even smaller proportion to become adults. This phenomenon of mast fruiting and predator satiation has been occurring in Borneo’s rainforests over millennia.
The situation in logged forests, however, was nothing like that in old growth forests in the Maliau Basin. Most large adult Dipterocarps are removed during the first round of logging. Subsequent rounds of logging remove even more reproductive adult trees. The few remaining trees are small and are likely not reproductively as active. Furthermore, if the remaining trees are spatially isolated from each other, cross-pollination may be adversely impacted. I observed few seeds in the logged forest at SAFE during the mast, a fraction of what I observed at Maliau. There were no seed and seedling carpets to be seen. In such a scenario, the few seeds that fell to the forest floor were vulnerable to being eaten by seed-eating animals and fungi. The few seedlings that germinated were also vulnerable to the altered microclimatic conditions of logged forests.
As recently as a hundred years ago, much of Borneo was covered in rainforests that must likely have formed similar cathedrals. The advent of man, subsequent timber extraction and agricultural expansion altered the landscape drastically. Furthermore, ongoing climate change may pose a problem for mast fruiting, even in protected areas. Trees invest much energy into reproductive events such as masting. Consecutive or rapid masts are known to occur but are usually rare since trees have little energy for back-to-back masts. There was a mast in some parts of Borneo in 2015. The 2016 El Nino has been rather severe, causing the river that supplies the SAFE camp with water to run dry. It is unknown whether such frequent droughts may interfere with the mast fruiting cycle of trees. Of the many seedlings produced during a mast, most will not survive the onslaught of seed predators. Of the handful that do, how many will withstand the onslaught of climate, logging and agricultural expansion to poke their heads above the canopy of the cathedral forests a few hundred years from now?