The study found that the breeding success of the hornbills collapsed over a decade-long monitoring period (2008 – 2019), corresponding with rapid warming due to climate change. During the monitoring period, sub-lethal effects of high temperatures, including compromised foraging, provisioning, and body mass maintenance, reduced the chance of hornbills breeding successfully or even breeding at all.

“These temperature effects occurred even in good rainfall years,” said Nicholas Pattinson, a researcher at UCT’s FitzPatrick Institute of African Ornithology.

“While drought did negatively affect breeding success, our findings suggested that the rapid warming in the region was responsible for the collapse in breeding success: temperatures have been rising but drought return rates have remained stable in this area.”

The hornbills have an incredible breeding strategy, whereby the female actually seals herself inside the nest and moults all of her flight feathers. This strategy helps them avoid predation, and while it is common to many hornbills, it is a truly remarkable method of breeding.

Writing in the Frontiers in Ecology and Evolution journal, Pattinson said the study supports the proposition that even in the absence of large-scale mortality events associated with heat waves, cumulative sub-lethal consequences of increasing temperatures can and will likely cause population declines and even local extinctions.

Pattinson and his colleagues were surprised by how rapid climate warming acted so quickly on the breeding success of the hornbills.

“Within just a single decade we see a collapse in breeding success, correlating to the warming in the region and related to the inability of the hornbills to breed successfully at high temperatures. The most surprising thing is the finding that the hornbills, as we were monitoring, were fighting extirpation,” he said.

Commenting on the findings, Pattinson said there is rapidly growing evidence for the negative effects of high temperatures on the behaviour, physiology, breeding and survival of various bird, mammal, and reptile species around the world.

“Heat-related mass die-off events over the period of a few days are increasingly being recorded, which no doubt pose a threat to population persistence and ecosystem function,” he said. A team of researchers monitored the breeding of a population of the hornbills breeding in nest boxes at a study site in the Kalahari Desert from 2008 to 2019. They analysed the breeding success at the scale of entire breeding seasons and individual breeding attempts within seasons and correlated those with weather variables. The team also analysed South African Weather Service data for the Kalahari region to look at long term temperature and rainfall patterns to determine the onset and rate of warming due to climate change.

Out of the 118 breeding attempts the team monitored over the decade period, not a single attempt succeeded where the average air temperature during the attempt was equal to or greater than 35.7 °C. According to Pattinson, this shows a clear, dramatic negative effect of high temperatures on the breeding success of the hornbills.

“Current climate change predictions make it very unlikely that hornbills will persist across the hottest parts of their range even over the next decade. However, if they are going to occur anywhere across their current distribution in the future, the temperatures will have to remain below this threshold of 35.7 °C during their breeding,” he said.

This study may be about the hornbills in the Kalahari Desert, but it is relevant to people and systems worldwide, said Pattinson.

“Much of the public perception of the effects of climate change is related to scenarios calculated for 2050 and beyond. This renders the concept of the effects of climate change abstract to much of the general public not directly affected by extreme weather events, given that the effects are considered to concern future generations,” he said.

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Issued by: UCT Communication and Marketing Department
Photo: Marc/Unsplash

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The world’s most famous tropical forests found on lowlands, like those of the Amazon or Borneo, are celebrated for their ability to store carbon. The Amazon rainforest itself holds up to twenty years’ worth of fossil fuel carbon emissions in its trees and soil.

While tropical forests can also be found on tropical mountains such as Mount Kinabalu in Borneo, these have long been assumed to store much less carbon. On mountains, temperature decreases with increasing elevation, negatively affecting tree growth. Also, common mountain features such as thick fog, wind and steep slopes tend to constrain tree height.

If trees are smaller, and grow slower, then mountain forests should contain less carbon sequestered from the atmosphere through growth processes: a hypothesis which has been reflected in studies of tropical mountains in the Andes and southeast Asia.

But our research, recently published in Nature, shows that tropical mountain forests in Africa actually store as much carbon per hectare as those found in African lowlands – a finding specific to the continent.

This is because, although African tropical mountain forests have fewer trees (about 450 per hectare compared to 600 in other continents) than their lowland counterparts, they have a greater abundance of large trees (over 70 cm in diameter), whose increased mass means they hold on to more carbon.

We wondered if this unusual finding was thanks to elephant populations resident in many African tropical mountain regions, who eat and destroy smaller tree stems – creating room for others to grow larger – and also transport nutrients which are limited in mountain soils.

But we didn’t find significant differences in tree height between forests with and without elephants, although unfortunately our data only showed us if elephants were present in a given area and not how many were around. Other explanations could include the low frequency of tropical cyclones or active volcanoes in Africa, making it less likely for trees to be destroyed before they grow tall.

Carbon storage

A group of 101 researchers working at different institutions across Africa, Europe, North America, Asia and New Zealand measured 72,336 trees with trunks of over 10cm diameter on 44 mountains in 12 countries within the African continent. For each tree we recorded trunk diameter, species and height.

We used an equation to estimate the carbon stored in these forests, since actually cutting, drying and weighing trees – technically the most accurate method for analysing carbon capture – would rather undermine our aim to mitigate climate change.

We then calculated how much tropical mountain forest had been lost in the African continent over the past 20 years, using data from satellites. We estimated that 0.8 million hectares had been lost, mostly in DRC, Uganda and Ethiopia.

Unexpectedly, given the steep terrains which make logging operations or large-scale farming challenging, we found that in many African countries deforestation rates were higher in the mountains than the lowlands.

So if these mountain forests store more carbon than expected, we are releasing more carbon dioxide into the atmosphere than previously assumed. In fact, the 0.8 million hectares of mountain forest destroyed since 2001 has emitted more than 450 million tonnes of carbon dioxide into the planet’s atmosphere, accelerating global warming.

Biodiversity loss

African tropical mountain forests are not only carbon-rich: they are also rich in biodiversity. Among their huge trees live elephants, mountain gorillas, chimpanzees, and numerous species of birds, amphibians and snakes found nowhere else in the world. Continued deforestation will push many of these creatures further towards extinction.

These forests also act as “water towers” (like giant water tanks), irrigating agricultural land and supplying numerous vital river systems including the Congo and the Nile. This makes them crucial for local and regional crop growth, hydropower systems providing renewable energy, and inland fisheries supporting nutritious diets and livelihoods for local communities.

Mountain forests often collect water droplets from fog in a process known as “occult precipitation”. This makes local landscapes much more humid than if the forests were not present. Destroying these forests is therefore not only terrible for our global climate, but also for regional weather and biodiversity, since many species require the specific conditions created by this humidity to thrive.

But our study also provides some hope. If these forests store more carbon than previously assumed, it could allow us to increase the economic benefits awarded to developing countries who successfully decrease deforestation, meaning greater incentives for forest conservation – and better futures for those who call the mountain forests home.

Aida Cuní Sanchez, honorary fellow, University of York; Martin Sullivan, Lecturer in Statistical Ecology, Manchester Metropolitan University, and Phil Platts, Research Fellow, University of York

This article is republished from The Conversation under a Creative Commons license. Read the original article.
Featured photo by Hamsavani Raja Komaraim/Scopio

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Dr Emma Bush and Dr Robin Whytock, of the Faculty of Natural Sciences, along with Professors Kate Abernethy and Lee White, are lead authors of ‘Long-term collapse in fruit availability threatens Central African forest megafauna’ published in renowned journal Science. It reveals that a significant reduction in fruit production by trees in Lopé National Park, Gabon, has coincided with a decline in the physical condition of fruit-eating forest elephants.

The study found an 81% decline in fruit production between 1986 and 2018, alongside an 11% drop in the physical condition of fruit-dependent forest elephants since 2008.

This means that, on average, elephants and other animals would have encountered ripe fruit on one in every 10 trees in the 1980s, but need to search more than 50 trees today.

The region’s climate has changed since the 1980s, becoming warmer and drier, and it is believed this may be behind the decline in rainforest fruit production. Mean temperature has increased by almost 1oC during the course of the study. Some tree species in Lopé National Park are dependent on a dip in temperature to trigger flowering but warmer temperatures may mean that this vital cue to producing fruit is being missed.

Dr Emma Bush said: “The massive collapse in fruiting among more than 70 tree species studied at Lopé National Park, Gabon may be due to species missing the environmental cue to bear fruit, because of increased temperatures and less rainfall. Less fruit in the ecosystem will have huge impacts on forest dynamics such as seed dispersal, plant reproduction and food availability for wildlife such as forest elephants, chimpanzees, and gorillas.”

The University of Stirling is a pioneer in tropical ecology research, having established the world-renowned Station d’Etudes des Gorilles et Chimpanzes (SEGC – The Gorilla and Chimpanzee Research Station) with the Centre Internationale de Recherches Médicales de Franceville (CIRMF, The International Medical Research Centre in Franceville) in Lopé National Park, central Gabon, in 1983.

This 37-year, on-going collaboration between the University and the Government of Gabon has generated a unique data set that allows researchers to monitor how the rainforests and wildlife of the Congo Basin are responding to climate change.

Dr Robin Whytock said: “Large animals like forest elephants are already under severe pressure in Central Africa due to hunting, habitat loss and habitat degradation. If important protected areas like Lopé National Park in Gabon can no longer support them because there is not enough food, then we may see further population declines, jeopardising their survival in the long-term.

“We know that large bodied animals, like elephants, are disproportionately important for the healthy functioning of ecosystems and their loss could result in broad changes to forest systems and even reduce the amount of carbon stored there.”

Functioning tropical ecosystems are important for global climate regulation and global health. This research highlights how global climate change might be affecting plants and animals locally, through decreased forest food production. It also adds to the global body of evidence highlighting the ongoing biodiversity crisis and the consequences of rapid climatic change.

Professor Lee White, Gabon’s Minister of Water, Forest, Sea and Environment, and an Honorary Professor at the University of Stirling, said: “Long-term ecological research such as ours is unfortunately extremely rare in the tropics, and it is possible that similar processes are underway, but undetected, throughout the tropical rainforests of our planet.

“It is alarming that climate change may be resulting in forest elephants going hungry, and we need to seriously consider whether this is forcing elephants out of the forests to approach rural villages in search of food, resulting in an increase in crop raiding.”

Source: University of Sterling
Photo: Family of forest elephants (credits: Malcolm Starkey)

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