The three teachers on our Tropical Biology Association field course here in Kibale abandoned the station for a day trip to the Rwenzori mountains, around two hours drive away (if nothing goes wrong, which it did). These fabled peaks are known as the Mountains of the Moon and comprise the tallest mountain range in Africa*. The Rwenzori Mountains National Park runs along the border with DR Congo where it merges with Virunga NP on the other side. Both are UNESCO World Heritage Sites.
We began at the main park gate at around 1700 m and were led by our guide through several kilometres of valley floor which had been cultivated prior to the park’s gazetting. This remained in a rather sorry state, with little evidence of regeneration. I wondered why this might be the case, and whether this was a site where assisted regeneration through tree planting would be justified. Regardless of the stature of the vegetation, however, it makes good habitat for several of the endemic chameleon species, as well as an easier habitat for the bird watchers**.
After a while the gradient steepened considerably as we ascended a knife-point ridge which afforded spectacular views on each side, as well as supporting a forest vegetation quite unlike the steep slopes. I say steep; if you fell then you wouldn’t bounce many times before reaching the white water at the bottom. It’s a wonder any vegetation clings to them at all, though in fact they’re covered by a mosaic of wooded patches and tangles of vines and shrubs.
After a 1000 m climb we reached the top of the ridge, panting and with burning muscles in our legs. We emerged into some delightful cloud forest. Trees were shrouded in the characteristic straggly Usnea lichens, and branches bore dense carpets of aerial-rooted epiphytes. Combined with the fresh breeze blowing across the mountains it was a narrow strip of paradise.
Above this, at around 3000 m, lay what I was really interested in — bamboo forest. I’ve heard about it but never had the opportunity to see it for myself. It was majestic; giant bamboos tower above you to a height of around six metres, and scattered amongst them are ancient Podocarpus trees which frequently exceed a metre in diameter.
Almost all the trees were large, with relatively few smaller stems. This made me wonder about the processes regulating these forests. I presume that episodic dieback of the bamboo (which happens after they flower en masse) opens up occasional opportunities for tree regeneration, perhaps only a few times a century. Those lucky recruits which manage to establish can then survive until the bamboo crowds around them again. This is my guess; once I get back to a reliable internet connection there will be plenty of reading to do.
We made it all the way to Lake Mahoma at 3000 m then returned after a thorough workout. Sadly there wasn’t time (or energy) to explore the heath forests that form the treeline, nor the endemic montane flora that lies above them. I’m intrigued enough by this landscape to already be planning a return.
I’ve completed the set! I have now seen in Kibale (drumroll please) black and white colobus, red colobus, red-tailed guenons, blue monkey, grey-cheeked mangabay, L’Hoest’s monkey, olive baboons and chimpanzees. Seven diurnal primates in one site and none of them hard to find (the nocturnal bush baby and potto are slightly trickier). It helps that so many of the groups are habituated thanks to generations of primatologists passing through.
Why are there so many primates here? I can’t give a definitive answer (though I’m sure that more informed people than me have speculated before), but suspect that part of the story lies in the age of these forests. Even those defined as primary show every sign of being in late stages of regeneration. Their canopies are short, dominated by long-lived pioneers which begin branching quite low, and with basal areas below 40 m2/ha. Whether they were cleared by humans or some catastrophic disturbance, the forests I’ve seen appear to be no more than a few hundred years old.
Why should this matter for primates? Long-lived pioneer trees have large leaves with high nutrient content, and often produce fruits which are animal-dispersed (and hence much favoured by frugivorous primates). Compare this to, for example, a much taller dipterocarp forest in Southeast Asia, where most of the leaves are practically inedible and most trees only fruit once every five or so years. Such forests are described as food deserts and primates exist at comparatively low densities.
It’s only a guess, but I can’t help feeling that the extraordinarily high diversity and abundance of primates here owes much to the relative youth of the forests.
Finally, some sad news. We heard this week that Dr Jerry Lwanga, the director of the Makere University Biological Field Station (MUBFS) at Kanyawara, and an instrumental force in the gazetting of Kibale Forest National Park, has died. I never met Dr Lwanga, but the sombre mood among the staff here is a reflection of the high regard in which he was held by all and their fondness for him. Everyone has spoken of him as a good man of impeccable probity and decency. Writing now from the field station which he founded, in the park to which he dedicated his career, it was certainly a life with many accomplishments.
* As individual mountains, Mt Kilimanjaro and Mt Kenya are taller than anything in the Rwenzori range, but they are both stand-alone peaks of volcanic origin. The Rwenzori peak of Mt Margherita is the third-tallest in Africa at 5109 m and is surrounded by a cluster of others which come pretty close.
** Apparently we saw the Rwenzori endemic purple-breasted sunbird. Or something. I include this information purely to irritate twitchers.