The Udzungwas: What a full forest of beauty

Luscious rainforest, stunning waterfalls and unbounded wildlife: the Udzungwa Mountains National Park in southern Tanzania was the location for some special hiking.

Situated on the edge of the Kilombero valley, the Udzungwa mountains host an exciting array of flora and fauna, with many unique species found nowhere else. This high level of endemicity combined with the high biodiversity, characteristic of tropical forests, makes these mountains an important global biodiversity hotspot. Taking a break from our busy work schedule, we were fortunate to spend two days exploring this beautiful ecosystem.

Our stay involved two day-long hikes through the national park: the campsite 3 and Sanje waterfall circuits. Combined they would involve 15 hours and 20km of walking through mountainous jungle terrain, encountering some of the most incredible wildlife found on our planet!

Before we even began our hiking though, the sheer abundance of animals awaiting us inside the park was evident as we were able to see five species of monkey just along the roadside: yellow baboons, black-faced vervet monkeys, mitis monkeys, Angolan black and white colobus monkeys and the endemic Iringa red colobus monkey. Such a variety of primates emphasised the abundance of food available inside the forest to support these animals. However, their presence alongside the road reinforced their vulnerability in a country with a rapidly growing population and frequent human-wildlife conflict. Nevertheless, it was fantastic to observe the behaviours of these monkeys – some brave, some shy – as they swung between the trees. It was fascinating to see too how the two colobus monkey species formed mixed troops, a unique occurrence to the Udzungwas, as the Iringa red colobus monkey cannot be observed anywhere else.

As we began our hike proper inside the national park, we were instantaneously presented with a beautiful forest, passing through the dry semi-deciduous forest first before reaching the evergreen montane rainforest. As we walked, our senses were on overload as we listened, watched and smelt the wildlife that surrounded us. Everywhere I looked, a species had colonised the dense habitat filling every available niche.

As in all other rainforests it was possible to see the intense competition for light between plants with thousands of climbers trying to reach the canopy to gain access to the energy they need for photosynthesis. The competition for nutrients between trees was also evident with extensive root systems on display. Moreover, the key role of animals supporting the diversity of plants in the forest was clear to see: Forest elephants had helped generate clearings, allowing species requiring high light levels on the forest floor to flourish; dung beetles were recycling scat, improving the soil’s fertility; whilst butterflies flew between flowers, pollinating as they went and helping produce the next generation of plants. And then you have the primate species we had encountered earlier, who alongside many bird species were helping with the dispersal of the seeds that embody the next generation.

As we walked, the forest could not help but relax and rejuvenate me, even if the gradient and humidity were posing a major challenge. As we climbed higher and higher through the forest, we could feel the conditions change as the temperature began to cool. With this environmental gradient, we could observe how some species had evolved to fill a small environmental range, whilst others were able to survive across a range of conditions. This made me concious of the impact climate change could have on these forests, especially the specialists that will be forced to move up the mountain or adapt to survive, and the desperate situation for the mountain-top species that will have nowhere to go! The pristine nature of the forest and the protection it was getting from its rangers helped reassure me though that it would have the best possible chance to adapt under new climatic conditions.

Another feature of the forest I noticed during the hike was the array of convergent evolution on display. Having visited the rainforests of south-east Asia and the Amazon within the last year and a half, I was able to make direct comparisons across these ecosystems. All around me, there were reminders of the tropical forests from across the planet. In fact, the forests here showed such extreme convergence that I could have been walking through Kubah National Park in Sarawak, Borneo, had it not been for the different families of plants and animals present. In both forests, there were giant trees that emerged from the canopy, an abundance of climbers fighting for light, and similar defences to herbivores such as vicious spines on branches and vines. My favourite example of convergence though must be the enormous trees that have gigantic buttress roots that provide stability with their otherwise shallow root system. It was also fascinating to hear that indigenous people had equally converged on their use of these trees for communication. By banging these roots with rocks, forest dwellers across all three continents have been able to transmit signals over substantial distances (>2km), including to call for meetings, celebrations and most importantly for help when lost.

The most impressive feature of these forests however must surely be the abundance of water found there. Despite massive drought across the neighbouring Kilombero valley, water within the Udzungwa mountains was plentiful. Combined with the elevational effect of the mountains, transpiration from the forest is able to generate a unique microclimate, trapping moisture to form clouds in the forest canopy of the upland cloud forests. This unique meteorological phenomenon ensures a continual supply of water to these forests even during Tanzania’s dry season, and consequently  supports a rich biodiversity.

The vast quantity of water in the forest has also been key in structuring the geology of the forest. Water descending down the forest can provide a powerful erosional force. Here, it has been able to carve out rivers and numerous waterfalls, including the spectacular Sanje waterfalls that descends over 800m from top to bottom! These stunning features not only provide beauty to the landscape but also play a key role in creating clearings in the canopy and pools for butterflies and amphibians that thrive in these conditions. They also provide a unique habitat for mosses and ferns that are able survive on the rock surface with minimal soil, escaping competition from larger plants. Seeing these magnificent waterfalls was a privilege and felt very special indeed!

Overall, the Udzungwa mountains provided an exquisite backdrop to our hiking, with breathtaking scenery and beautiful wildlife. I fell in love with these forests during our short stay there and they definitely provide the highlight of my travels in Tanzania so far. Being able to spend time in these incredible forests felt very special and reinforced my love for tropical forests and my desire to study them in my career. I cannot wait for my next adventure to a tropical rainforest!

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