A few weeks ago I had the luck to visit Hluhluwe-Imfolozi National Park in South Africa. This amazing landscape is tucked into the lush green hills of Kwazulu-Natal towards the south-eastern end of South Africa.
The park has a long history, being the first game park established in Africa, and before that a hunting reserve for the Zulu kings. It has also been a pioneer in thinking about how to manage wildlife and landscapes throughout the 20th century (in ways good and bad, including extensive culling of wildlife in the mid-20th century to eliminate the region of tsetse-fly. Perhaps its most significant contribution is that was the last refuge of the southern white rhinoceros or southern square-lipped rhinoceros (Ceratotherium simum simum), which because of overhunting was reduced to just around 20 individuals hanging out in this reserve in the early 20th century. Thanks to Operation Rhino, perhaps one of the biggest conservation successes in history, this population has recovered and rhinos have been airlifted to reserves and private lands across southern Africa, such that there are around 20,000 southern white rhinos alive today, all descended from this Hluhluwe-Imfolozi population. They are now under renewed pressure, however, as poachng pressure intensifies and becomes more sophisticated.
In addition to rhinos, the reserve has abundant herbivores including elephants, giraffes and water buffalo, and predators including lions, leopards, cheetahs and wild dogs. It has played an exceptional role in our understanding of the interactions between animals, vegetation, climate and landscapes. Particularly notable are the seminal work by Norman Owen-Smith on the role of megaherbivores in ecosystem ecology, and the work by William Bond and his former students on the role of both herbivores and fires as consumers and shapers of ecosystems. To me, this work has been hugely influential in shaping our recent thinking and papers on how the the whole planet may have functioned differently at the time of the megafauna. So many of these ideas can be traced back to this corner of South Africa. It is also an area where the widespread phenomenon of woody encroachment of savannas has been studied in detail, a phenomenon many think to be a response to global increases in carbon dioxide
A detailed history and review of the science of the park has just come out as a book.
Conserving Africa's Mega-Diversity in the Anthropocene: the Hluhluwe-iMfolozi Park Story
I was privileged to be able to spend a few days in this landscape on scientific ramble, in the company of William Bond, soil fauna expert Kate Parr from the University of Liverpool, and PhD students Heath Beckett and Anabelle Cardoso. We explored how herbivores, drought and fire shape the landscape, and looked at the impact of excluding herbivores or excluding fires. These experiments show that changes are not simple or obvious, that ecosystems to not just "flip" when fire or herbivores are removed, but that key events such as droughts appear to be needed as tipping points.
As a predominantly forest ecologist, I relished hanging out with a group of people with a "savanna and grassy biome" eye, looking at the dynamic interplay between trees, grasses, forbs, animals, drought and fire. It was immensely insightful and educational (even with the tick bytes I picked up on the way!)
After my visit to Moorea in French Polynesia, I spent a spellbinding day and night at Tetiaroa. Tetiaroa (Tahitian for "far in the ocean") is a coral atoll sitting north of Tahiti and Moorea, a Tahitian "leh" (garland) of tree-wreathed coral sand islands (“motus”) wrapped round a turquoise lagoon. This is probably as close to an apparent archetypal tropical island paradise as it is possible to imagine. The archipelago was inhabited by Polynesians for many centuries, and was a retreat for Tahitian royalty. As elsewhere, its population went into decline following European contact, and it was sold by the Tahitian king to his American dentist a century ago. He converted the vegetation of many of the motus to dense coconut plantations for the production of copra from the fibres, but these were abandoned a few decades later as the copra market went into decline. The dentist’s daughter then lived almost alone on the atoll into her old age.
In the 1960s Marlon Brando, at the peak of his Holywood stardom, came upon the islands while looking for sets for the filming of Mutiny on the Bounty. He was bewitched by the place and bought the entire archipelago. He visited it often as a retreat from the world of Holywood, and also set up a basic hotel on one motu. But is his later decades the hotel struggled to survive and the island went into slow neglect, while also avoiding the expansive development of many other Polynesian atolls. Soon after Marlo Brando’s death, the atoll was bought up by a very high-end eco-resort, the Brando, which has established an aesthetically and environmentally discrete hotel on the south-western motu, Onetahi that has won a Platinum LEED (Leadership in Energy and Environmental Design) award.
Thus, by historical circumstances Teriatoa offers a chance to study a coral atoll with a modest contemporary human footprint, but one which faces many of the legacies issues and future challenges faced by many Pacific atolls (see below). I have been invited to look at the potential for terrestrial ecosystems science at Tetiaroa. My host is the Tetiaroa Society, a non-profit environmental organisation that manages conservation and scientific research in the atoll in collaboration with the hotel.
We journeyed at dawn by dinghy from Moorea to Tetiaroa, a bumpy journey of 2.5 hours. It’s a short journey, but halfway through in a small dinghy I gained a huge sense for the vastness of of the Pacific, and respect for the Polynesian navigators who made this vast ocean and its ever-shifting swells their home. Soon after we sighted the motus of Tetiaroa as thin slivers of trees on the horizon. As we approach we were greeted by a young humpback whale joyfully breaching clear of the water, followed soon after by an encounter with a mother and child humpbacks, and a host of spinner dolphins buzzing our boat. The waters of the lagoon are higher than the surrounding ocean, filled by waves crashing against the surrounding reef, so we had to navigate a precarious cascade to work our way into the light turquoise waters of the lagoon and dock on a sandy beach. Black tipped reef sharks, striking but only a metre in length, circled curiously as we waded on shore. We stayed at the Ecostation, a comfortable research facility with excellent labs within the hotel grounds.
There is a fair amount of marine research occurring on Tetiaroa, but almost nothing on the terrestrial ecosystems. One of the downsides of being an ecologist is that we know too well that there is often trouble in paradise (beware of taking an ecologist on honeymoon!). Most tropical islands hold a legacy of extinction and invasion - the extinction of over a thousand species of birds in the Pacific following human settlement was probably the biggest extinction event of the Holocene.
There are two main current terrestrial environmental issues on the atoll: the challenge of of rat invasion, and the legacy of the dense coconut plantation. To a holiday visitor the white sandy beach lined by dense groves of coconuts is archetypal paradise. Indeed, the Polynesians found a multitude of uses for the coconut and it is an indispensible part of the cultural heritage of the Pacific islands. But this is an ecosystem out of kilter. The coconut groves, especially if untended, form dense stands with fallen palm fronds suppressing regeneration by other plant species, and providing a poor habitat for nesting birds. It is debatable whether coconut was naturally found in Polynesia, or was brought by the Polynesians. But dense coconut stands are a legacy of copra plantation. There are two species of rat on the atoll, the smaller Polynesian rat or kiore (Rattus exulans), which arrived with the first Polynesian settlers (deliberately - it was regarded as a luxury food), and the black rat (Rattus rattus), which arrived after European contact. Both rats negatively affect the ecosystem but the larger black rat is particularly problematic, by eating up seeds and preventing new plant recruitment, and by raiding nests and eating young chicks. They also feed off the plentiful coconuts, which results in a large and active rat population. Hence there is an ecological meltdown, with dense coconut stands reducing bird habitat and support an large rat population, and the rat population suppressing plant diversity and consuming young birds. Land birds are long gone. And as sea birds now largely avoid the most rat-abundant islands, the inflow of nutrients from ocean to land through bird guano is greatly reduced.
I visited with James Russell of Auckland University (see his National Geographic blog here), who hopes to implement a rat eradication effort on some of the motus, and others are also thinking of reducing coconut abundance in some areas. A key ecological question here is: “can we restore plant and animal diversity and ecosystem nutrient cycling function here by removing rates and/or reducing coconut abundance?”. To do this we are contemplating arranging an array of small ecosystem monitoring plots across various motus, covering a range of invasion and disturbance histories. The spatial patterns across these motus now will be interesting in themselves, but they plots would also provide a baseline for future experiments with rat eradication or coconut thinning.
A different, longer-term question is climate change: how will these low-lying atolls cope with sea level rise? Will the rate of coral aggradation and motu deposition be sufficient to keep up with the rising seas, and how will vegetation and biodiversity respond to these shifts? Again, establishing a baseline plot network now could provide valuable insights into how these ecosystems cope, and what interventions might help.
Last week I visited the Pacific island of Moorea, which sits just next to Tahiti in the Society Islands, in French Polynesia, an array of islands widely scattered across the Central Pacific. The islands form a progression of volcanic seamounts, with youngest in the south-east peaking in the 2100 m peaks of Tahiti, and the oldest in the north-west subsiding into perfect coral atolls. My host was Neil Davies, Director of the Gump Research Station in Moorea, and I am here to discover a little more about the forests of Polynesia, to find ways of supporting and devleoping some of the forest research here, and to bring in some of the ecosystem process studies that we do elsewhere across the tropics, with the potential of bring some of these forests into our Global Ecosystems Monitoring Network. Moorea is the focus of the IDEA Digital Avatar project, and effort to digitise an entire island ecosystem from 'genes to satellites'. There is an article about this project in Nature. As a result the biodiversity of the land and marine ecosystems in Moorea is particularly well catalogued.
The landscapes of Tahiti and Moorea (and many other Pacific volcano islands) are truly breath-taking, with the basalt volcanoes eroding way into almost vertical-sided mountains and towers, some of the most astounding topography I have seen anywhere. As Darwin noted when stopping at Tahiti after his explorations of South America: “in the Cordillera, I have seen mountains on a far grander scale, but for abruptness, nothing at all comparable with this". The high mountains hold on to native cloud forest and rocky scrub, but the lower levels are a lush green mosaic of invasive species, farms and light green fernlands. The islands are surrounded by a skirt of coral reef holding in a lagoon of perfect turquoise waters.
In between meetings and visiting the forest and lagoon, I tried and absorb all I could about this mesmerising land I found myself in and knew so little about. My sources on the geology and vegetation history were “Vegetation of the Tropical Pacific Islands” by Dieter Mueller-Dombois and Raymond Fosberg. I also borrowed off Neil an excellent biography of James Cook by Frank McLynn, and read particularly closely the descriptions of Cook’s several contacts with Tahiti and the societies he found there, and how both reacted to the “other” in this collision of worlds. A highly recommended book that highlights how astonishing both Cook and the Polynesian societies were, and captures the astonishing nature of the first contacts.
We visit the Opunohu valley, a lush mosaics of forests, farmlands, archaeological remains. This area was densely populated and farmed at the time of European contact, and suffered a population crash and almost complete depopulation over the 18th and 19th centuries. Feral chickens, first brought over by the Polynesians, run wild over the landscape, itself almost entirely free of predators. The mapae are rectangular stone enclosures that were used for religious ceremonies, and are now groves of Tahitian chestnut trees (Inocarpus fagifer) with wonderful fluted buttress roots.
Some of the key trees that may have been brought by the Polynesians or that may be native include Hibiscus tiliaceus, Pandanus tectonis, Casuarina equisetifolia. As in many islands, the main environmental story is one of biological invasion, Big invasive species here include Tecoma stands, Psidium cattleianum (strawberry guava) and most recently, the all-smothering Miconia calvescens.
The view from Moorea is of an ocean planet. Polynesia sits in the middle of a hemisphere that is probably over 95% ocean, with what continental area there is is ringing its fringes, and scattered throughout this planet-sized ocean are small islands that are legacies of volcanic hotspots. Every wave of “discovery” of these is an astounding tale. First the various species of plant, bird and insect that manage to make it across thousands of miles, often by accident, to stumble on an island refuge. There they slowly specialise and diverge and take advantage of this new ecosystem that they build. Then the human discovery, an amazing tale of Polynesian adventures reading the stars, winds and swells to cross vast distances and create unique cultures. Then the Europeans, with adventurers such as Cook and his sailors expanding the known world with their exploration of a new ocean world and civilization. Each "discovery" has been accompanied by ecosystem disruption and loss, as well as the creation of something new.
We have just completed a full recensus of our 18 ha plot in Wytham Woods, where we are tracking around 20,000 trees (all trees with greater than 1 cm stem diameter). The plot was set up in 2008, and then remeasured in 2010. Now a team of six people are remeasuring it six years later, working all day five days a week for a couple of months. This measurement is particularly important in establishing the long-term dynamics of the plot (what trees are growing fast, what trees are doing OK, what trees are dying). It is also at a critical time, because ash dieback is likely to arrive in Wytham Woods some time over the next couple of years. Ash trees account for around one third of the trees in the plot, and if many of them die off, as seems likely over the next few years, it will have major consequences for the structure and ecology of the woods. Currently ash is the best performing of the most common tree species, and accounts for a large proportion of the increasing biomass and carbon sink in Wytham, an increase that is large a result of relative "abandonment of the woodlands following intensive use in the first half of the 20th century.. This sink may well turn into a carbon source within the next decade. Waves of pathogen are part of the natural long term ecology of a forest, but the forces of global interconnectedness and movement of goods and people mean that the frequency of arrival of new pathogens has greatly increased. This may well be the most important source of contemporary and future change in temperate woodlands.
The data collected form this census are freely available to researchers. Please contact me if you would like to use these data.
Many thanks to the amazingly thorough and efficient census team, comprising Rebecca Banbury-Morgan, Micol Chiesa, Alex Morrice, Claire Paulus, Cian McGlinchy, Angelica Martinez Bauer and coordinated by Sam Butt.
The Wytham Woods plot forms part of a global network of plots, the Forests Global Earth Observatory (ForestGEO), coordinated by the Smithsonian Institution. There are similar temperate plots across North America, China and other parts of Europe.
Here are some wonderful images from my student Anabelle Cardoso working at Lope National Park in Gabon. She is studying how animal and fire affect the transition between tropical forest and its variation over time. As part of this work she records the movement of forest elephants along the forest-savanna boundary using camera traps. Hence these amazing photos. I am sure there will be many more to come
Last week, following the excellent ATBC (Association for Tropical Biology and Conservation) meeting in Montpellier, we organised a workshop on our traits campaigns in the Spanish Pyrenees. We stayed in dorms in a wonderful little hostel (La Farga) tucked away in a lush forested valley with a gushing river, descending down a magnificent waterfall-lined gorge etched into magnificent mountains.
The aim of this workshop was to bring together the results from the various field campaigns across the tropics that I have some involvement in, where we are measuring both plant traits and carbon cycling. This ranges from elevation gradients in the Andes and Australia, through forest-savanna gradients in Ghana and Brazil, and disturbance gradients in human-modified tropical forests in Borneo and the Amazon and Atlantic rainforests of Brazil. The workshop was the first time these various projects had been brought together, and was a chance to both share results and brainstorm grand syntheses and analyses for the coming two years.
The workshop was funded by my European Research Council funded project GEM-TRAIT. Like many British scientists, I have benefited both financially in terms of close collaboration by being part of the European Union, and it bis tragic to see world-class science cast into such uncertainty by the self-inflicted wounds of Brexit.
There's been some wonderful work going on at our plot in Wytham Woods.
Kim Calders (at the National Physical Laboratory and University College London) and Mat Disney (at University College London) have been scanning parts of the plot with Terrestrial Laser Scanners in summer and winter 2015. Kim has also been working on the airborne lidar data over Wytham, provided by David Coomes' team at Cambridge, and originally collected by NERC ARSF as part of the AIRSAR campaign.
Mat has written a nice post about this work here
The image show shows a transect and shows what is possible. The red dots indicate laser returns from the summer (mainly from leaves). The green dots are returns from the winter scans (manly from wood and evergreen leaves). The blue dots show what is detected from the airborne lidar in summer (mainly the top surface of the canopy).
In combination, these data depict an wonderfully detailed 3D representation of the woodland of which this is just a cross-section. This patch contains a dense patch of ash and sycamore of roughly even age and size, a legacy of recovery form disturbance in the 1940s and early 1950s. Hence the dense canopy of crowns tightly packed and competing for space, and the lack of gaps in canopy space from tree mortality. We can also begin to estimate and map leaf area and biomass by comparing winter and summer scans. Data such as these open new prospects in not just forest mapping, but in understanding forest ecology, dynamics and animal habitats. They look gorgeous too!
Below is an image of the same landscape I have taken from a drone last week (our canopy walkway is in the foreground), which when combined with the laser imagery above adds additional potential to map the distribution, shape and phenology of every tree in exquisite detail. The leaves are just beginning to come out in Wytham in the sycamore and some oak, but not yet the ash.
And finally here is a lovely video (edited together by my son Luke Malhi) showing some lovely footage of the woods and study plot from the air. We are hatching plans to do a more systematic series of drone maps to captre the seasonal shifts in the canopies of individual trees
I have just returned from a week's visit to Lope National Park in Gabon, Central Africa. The reason was to kick off a couple of new projects (a DPhil project by Anabelle Cardoso on how fire and elephants mediate the transition between forests and savannas, and a Royal Society-Leverhulme project by Kate Parr on how large mammals and soil termites and ants interact to affect soil function. We also had a workshop on our long-term ecosystem monitoring in Gabon, where we spent two days with our Gabonese colleagues working through the data we have collected over the past three years, to come up with the first measurements of productivity of Central African forests.
It is a gorgeous place, one of the loveliest landscapes I have experienced in the tropics: a landscape of ancient soft curving hills, decked by a patchwork of deep green forests, soft green-brown grasslands and bright green fern savannas on some hill slopes. The lowlands between the hills are a similar mosaic, but also interspersed with damp marsh grasslands, forest island "bosquets" that represent the sites of long-abandoned villages, and green fingers of riverine gallery forests that are snaking through the grasslands. The savannas are always hot in this time of year, April, when an relentless equinox sun beats down overhead and noon. But this year is particularly unusual as we are experiencing the unusual heat and drought of a strong El Niño. On top of the long term warming trend this makes it potentially one of the hottest month this landscape has experienced for a century and probably more.
This is a fascinating landscape, where the forests of Central Africa are encroaching on the remnants of forest grasslands that once stretched across much of the current forest zone of Gabon. But what makes this landscape special is that it has been intensely studied as a labour of love by scientists over 30 years. These scientists - Lee White, Kate Abernethy, Kath Jeffery, Riczard Oslisly and many others - have dedicated much of their lives to unpicking the story of this landscape, and through this understanding trying protecting it for future generations.
The picture that has emerged is of a dynamic dance between savanna and forest that plays back over hundreds of thousands of years. Early hominids appear to have occupied this landscape for at least 700,000 years ago and more modern Neolithic farmers arrived several thousand years ago, farming palm oil and bananas, opening the forest and smelting iron, but also undergoing periods of mysterious population collapse, such as in the period 700-1400 years ago, when they disappear from the landscape.
Since the ice age the overall story has been of forest advance into the savanna, leaving now only pockets of savanna hugging the might Ogoué river in the drier northern fringes of the park. Occasionally in history human activity as slowed or stopped this advance, and at the moment fire management in the park aims to preserve these last pockets of unique savanna.
This landscape gives us a chance to understand in exquisite detail the processes that lead forest to advance in to or retreat from savanna. One way to do this is to walk from the savanna into the forest zone.
We walk towards an advancing front of this forest. The savanna around is dominated by metre-high grass, and only two or three woody, contorted savanna tree species 1 or 2 metres high: Nauclea latifolia with broad leaves golf-ball sized round, spiky fruit, Crossopteryx febrifuga with pale grey bark and a twisted form. The savanna is surprising species poor in trees - is this because this is an outlying zone and isolated pocket of the vast savannas that stretch across much of Africa?
We move into the transition along an elephant trail about a foot wide. Local experienced researchers stay at the front and back of our group, alert for a hint of elephant. The forest elephants are beautiful here, but are particularly aggressive, perhaps because they are the survivors of hunting episodes in the 1970s and 1980s. The front troops of the march of forest trees are the wonderful Lophira alata (Azobe), its young leaf tips flushed bright red. The grasses peter out in the shade of forest trees, taking this risk of fire with them, but the twisted savanna trees linger on, increasingly crowded out and shaded out by their youthful new forest neighbours. Then we are in older forest, dominated by surprising large trees including Lophira alata (azobe), Aucoumea klaineana (okoumé) and the elephant-dispersed Sacoglottis gabonensis (ozouga). What happens to these early forests in terms of fire or elephant events seems to shape the path of these forests for centuries to come.
Moving beyond the colonising forest we enter regions a few hundred years old, dominated now by towering stands of mainly okoumé. One fascinating aspect of okoumé's biology is that the root systems of different trees are often joined below the ground and nutrients are exchanged between individuals, helping a damaged tree to survived through a support of its neighbours.
As we walk on through the okoumé forest, eventually we reach a phase where the forests are more than 400 years old. This first cohort of okoumé trees has begun to die, opening up the forest canopy. But instead of younger trees surging up to fill the gaps, the ground is smothered by an almost impenetrable thicket of wild gingers and Marantaceae (arrow roots), which also climb up form towers which engulf dead stumps and small trees, and which suppress the emergence and growth of young trees. These plants provide valuable and accessible food for elephants, gorillas and others animals - the air is thick with the odour of giant creatures in a way I have never experienced in a forest, and everywhere we see signs of plants and fruit being eaten, trees heavily damaged by elephants feeding on their bark, and the dung of elephants, gorillas and chimpanzees. There is a tinge of excitement, mixed with an edge of alertness, listening out for every sound in the bush and being prepared to run quickly if necessary.
A troop of mandrills rustles the bushes nearby, and a hidden gorilla lets of a warning cry. Why does this Marantaceae forest occur? There may be a mutually beneficial interaction between the Marantaceae and the large animals - the plants attract animals to feed on them but can regenerate leaves and shoots quickly. The animals trample and damage small trees, preventing their ability to grow and shade out the Maranaceae. Whatever the reason, the Marantaceae freeze the process of forest regrowth, large trees die but are not replaced, and the canopy becomes more open.
Another amazing example of a tree-animal interaction is the tree Cola lizae, a species that is common in Lope but was only scientifically described in the 1980s. It produced bright crimson fruit that are particularly delicious for gorillas, bur fairly unpalatable for elephants. The gorillas then tend to nest in clearings with a dense growth of herbaceous vegetation, deposit their dung nearby, and in the process create conditions that let the young Cola trees establish and thrive.
Eventually, after at least 500 more years, the Marantaceae appears to be edged out. Maybe by chance a few trees to manage to escape the Marantaceae and grow and shade it out, which the enables more shade-tolerant trees to grow. Even 1500 years after colonisation of the savanna, the forest appears still some way from a stable old-growth form.
If we climb up the hills we come across a much more ancient forest, a forest that has been continuous since the last ice age and probably much longer. A low layer of cloud bathes these forests in the dry season, and the cool and humidity ensure that these hill tops remained forest even in the most arid and carbon dioxide starved phases of the ice age. The forest has a very different feel, with an open understorey easy to walk around, and many magnificent giant trees. Small termite mounds are everywhere. Most magnificent of all must be the mighty moabi tree (Baillonella toxisperma), it's elephant-scarred trunk an astounding 2.5 metres in width, its branches arching out across the forest. In the fruiting season it drops fruit from a great height. The strong odour and maybe the thud of these fruit attracts animals from miles around, but only elephants are able to swallow the fruit whole and disperse the seeds.
It is this mosaic of savannas and forests of different ages and histories, combined with intense interactions between animals and trees, that makes Lope such a fascinating landscape.
In both the Marantaceae forest and the ancient forest, we have installed our GEM ecososyem monitoring plots and have been tracking the growth and carbon cycling of these forests. Up to now, our only published studies are from South America (some from Borneo are imminent). There has never been a direct measurement of the productivity of an African forest, and in both Gabon and Ghana we have been working hard over the last few years (with post-doc Sam Moore and a large host of local collaborators and research assistants) to develop the first data for African forests.
In Lope we run a two day workshop for our local research assistants who have been diligently collecting field data every month for several years. The aim of the workshop is to use Excel to show how to move from field data to estimates of productivity, and to gain a greater understanding about what are the most important aspects of data collection. A key output of the workshop is to produce the first estimates of net primary production for African forests. Below shows the crowning moment. The bars on the left are from Amazonia, the bars on the right are from Borneo. The six bars in the middle are from Gabon. In the next month we hope to add another 16 bars from Ghana, and another two from Ethiopia. Within a few months, from a starting point of zero, we will have more data points in Africa than in any other continent. Then we will pore over the data and work out how they relate to climate, soils and history. Africa arise, your time has come!
Last week I visited our rainforest-savanna transect in Ghana. We have been monitoring ecosystem carbon cycling and plant traits there for the last few years, and currently are tracking the plots through this hot and dry El Niño year.
This time I was visiting with colleagues from Wageningen University in the Netherlands, in particular Harm Bartholomeus and Juha Suomalainen. Our purpose was to map our plots with Unmanned Aerial Vehicles (UAVs or drones). The main instrument was a hyperspectral sensor aiming to map the forest canopy at wavelengths ranging from 450 nm to 950 nm. We hope to relate this to the canopy leaf traits (leaf thickness, water content and chemistry, and photosynthesis rates) that we have been monitoring through painstaking climbing of canopy trees and collection of branches. In our work in Peru we have been exploring the links with airborne hyperspectral remote sensing - in Ghana we are exploring the potential of drones to collect similar data, albeit at a much smaller spatial scale. In addition to this main drone, the team had a smaller, niftier Phantom drone, which was able to provide wonderful photographic mapping and video footage.
In addition, another team from Wageningen have been scanning the plots with a 3D Terrestrial Laser Scanner (TLS), joined at the Ankasa rainforest site by Mat Disney's team from UCL. Overall, we hope to have detailed understanding of the canopy and structure of almost every tree in our study plots.
The work is in collaboration with the Forest Research Institute of Ghana (Dr Stephen Adu-Bredu), and funded by my European Research Council Advanced Investigator Award, GEM-TRAIT, with the traits work supported by a Royal Society-Leverhulme Africa Award.
Video footage of the week's work (including stunning footage from the drone) can be seen below.
A Columbian mammoth, which existed in North America until 11,000 years ago. The Columbian mammoth is one of over 100 large herbivores and carnivores that went extinct as modern humans spread around the world. Large animals are particularly important in shaping the structure and function of ecosystems. Cover image of PNAS courtesy of Carl Buell, with the original on display at The Mammoth Site, Hot Springs, South Dakota.
This week sees the publication of two special features, in Proceedings of the National Academy of Sciences and Ecography with 24 papers examining how megafauna - large animals - affect ecosystem and Earth System function. This topic is based on a conference we held on Oxford in March 2014, and features on the cover of both journals.
We live in the shadows of lost giants. Until relatively recently almost every major vegetated land area on Earth possessed an abundance of large animals that we now only associate with African game parks. Mesmerizing early art shows how much these giant creatures dominated the psyche of our ancestors. They included larger relatives of familiar creatures such as elephants and lions, but also exotic wonders such as giant sloths, car-sized glyptodonts in the Americas, rhino-sized marsupials in Australia, and gorilla-sized lemurs in Madagascar. The oceans also hosted a high abundance of giants, which linger on in greatly reduced populations after the advent of commercial whaling.
Over the last 50,000 years, a blink of an eye in geological and evolutionary time, something extraordinary happened. These giants have disappeared completely from many continents, and been greatly reduced in diversity, abundance and range in other continents. In almost all land regions the decline and disappearance of these large animals, the megafauna, has been associated with the sudden arrival of modern humans, with only Africa and southern Asia, with a longer human prehistory, having pockets of substantial remaining megafauna. The evidence of strong decline is earliest in Europe and Asia, but most dramatic in Australia, the Americas and islands such as Madagascar and New Zealand. Much has been written about the size and cause of this decline, but much less on its consequences on the broader environment.
Too little of our thinking about contemporary ecosystems, whether marine or terrestrial, reflects that these are ecosystems missing a major functional component with which they co-evolved. It is likely that there are many “ghosts” of the megafauna in the structure and function of the contemporary biosphere. When we wander out into the closed woodlands of, say, Europe or North America, the woody savannas of South America or the fire-dominated drylands of Australia, it is worth reflecting on the elephants or other giants that were there just recently, and how even the most apparently pristine ecosystems may still resound with the echoes of their absence.
In March 2014, we convened a major international workshop at St John’s College Oxford, supported by the Oxford Martin School, and gathered a large number of international experts from disciplines ranging from paleoecology and anthropology through to conservation science and policy . The workshop was the first international meeting focused on the impacts of megafauna and megafaunal loss. It started by looking at the causes and impacts of past megafaunal loss, and then moved on to looking at contemporary studies around the world, ranging from work in savannas of Africa to “megafaunal rewilding” experiments in Europe and Russia. Finally it examined the challenge on ongoing loss of megafauna, and explored the potential and consequences for bringing back megafauna in selected landscapes, and what it means for conservation thinking and science. The proceeding of the conference have led to two special features in scientific journals, which were published on January 26th 2016. Ten papers are published in Proceedings of the National Academy of Sciences, and 14 in Ecography.
Collectively, the studies show emphatically the large impact that megafauna have on various aspects of the environment, ranging from vegetation structure and composition, species composition, through fire patterns, soil fertility and nutrient flow in both land and oceans, and even regional and global climate by affecting land surface reflectivity and atmospheric methane concentrations. The loss of megafauna cascades through all levels of functioning of ecosystems. Even the apparently wildest contemporary landscapes likely carry the legacies of lost megafauna, and the consequences of contemporary decline of elephants and other megafauna may be felt for centuries or millennia to come. This improved understanding of the many ways that megafauna have influenced ecology and biogeochemistry may also help identify hitherto underappreciated and unidentified “ecosystem services” that our planet’s remaining giants provide – or could provide if megafaunas were allowed to recover.
Taking the latter perspective, the special features conclude by looking forwards, and exploring the potential of a “megafaunal rewilding” agenda to shape how with think about nature conservation, and how we maximize landscape vitality and resilience in the changing and pressured environments of the Anthropocene. Much of the world is still suffering ongoing loss of its remaining wild large animals, often even within protected areas, as illustrated by dramatic and urgent rhino and elephant poaching crisis in Africa. However, in some regions a new dynamic is taking place, where megafaunas are undergoing unprecedented recoveries. These involve spontaneous recolonizations in response to societal changes, e.g., the return of wolves to Western Europe in recent years. It, however, also includes an increasing number of megafauna reintroductions, not just to aimed at restoring these magnificent species, but also their ecological effects. We need to understand how best to implement rewilding in the human-made landscapes that increasingly cover the Earth and its functionality in such settings. It is important think practically about how to develop strategies for implementing rewilding in ways that will allow it to realize its potential transformative role for nature conservation in the 21st century. The ghosts of the past megafauna may still have lessons for how to maintain life on a human-dominated planet.
Yadvinder Malhi, Environmental Change Institute, School of Geography and the Environment, University of Oxford, South Parks Road, Oxford OX1 3QY, UK.
tel: +44 7855 418919, email: Yadvinder.firstname.lastname@example.org
Chris Doughty, Environmental Change Institute, School of Geography and the Environment, University of Oxford, South Parks Road, Oxford OX1 3QY, UK.
tel: +44 7855 418919, email: Chris.email@example.com
Felisa Smith, Department of Biology, University of New Mexico, Albuquerque, NM, 87131, USA. Email: firstname.lastname@example.org
Jens-Christian Svenning, Department of Bioscience, Aarhus University, Denmark cell# 45+ 28992304, email: email@example.com
John Terborgh, Center for Tropical Conservation, Nicholas School of the Environment and Earth Sciences, Duke University, Durham, NC 27708, USA
List of papers
Synthesis and Perspective
Malhi, Y., Doughty, C.E., Galetti, M., Smith F.A., Svenning, J.-C. and Terborgh, J.W. (2015) Megafauna and ecosystem function from the Pleistocene to the Anthropocene. Proceedings of the National Academy of Sciences USA, 113, 838-848.
Smith, F.A., Doughty, C.E., Malhi, Y., Svenning, J-C. and Terborgh, J. (2015) Megafauna in the Earth System. Ecography.
Causes of Pleistocene megafaunal extinction
Bartlett, L.J., et al. (2015) Robustness despite uncertainty: regional climate data reveal the dominant role of humans in explaining global extinctions of Late Quaternary megafauna. Ecography
Surovell, T.A., Pelton, S.R., Anderson-Sprecher, R. and Myers, A.D. (2015) A test of Martin's overkill hypothesis using radiocarbon dates on extinct megafauna. Proc Natl Acad Sci USA.
Impacts on vegetation structure
Bakker, E.S., et al. (2015) Combining paleo-data and modern exclosure experiments to assess the impact of megafauna extinctions on woody vegetation. Proc Natl Acad Sci USA.
Asner, G.P., Vaughn, N., Smit, I.P.J. and Levick, S. (2015) Ecosystem-scale Effects of Megafauna in African Savannas. Ecography.
Villavicencio, N.A., et al. (2015) Combination of humans, climate, and vegetation change triggered Late Quaternary megafauna extinction in the Última Esperanza region, southern Patagonia, Chile. Ecography.
Doughty, C.E., Faurby, S. and Svenning, J-C. (2015) The impact of the megafauna extinctions on savanna woody cover in South America. Ecography.
Barnosky, A.D., et al. (2015) The variable impact of Late-Quaternary megafaunal extinction in causing ecological state shifts in North and South America. Proc Natl Acad Sci USA.
Johnson, C.N., et al. (2015) Geographic variation in the ecological effects of extinction of Australia's Pleistocene megafauna. Ecography.
Terborgh, J. and Davenport, L.C. (2015) Megafaunal influences on tree recruitment in African equatorial forests. Ecography.
Terborgh, J., et al. (2015) The African rainforest: odd man out or megafaunal landscape? African and Amazonian forests compared. Ecography.
Doughty, C. et al. (2015) Megafauna extinction, tree species range reduction, and carbon storage in Amazonian forests. Ecography.
Bakker, E.S., Pagès, J.F., Arthur, R. and Alcoverro, T. (2015) Assessing the role of large herbivores in the structuring and functioning of freshwater and marine angiosperm ecosystems. Ecography.
Trophic cascades and impacts on animal communities
Estes, J.A., Burdin, A. and Doak, D.F. (2015) Sea otters, kelp forests, and the extinction of Steller sea cow. Proc Natl Acad Sci USA.
Van Valkenburgh, B., Hayward, M.W., Ripple, W.J., Meloro, C. and Roth, V.L. (2015) The impact of large terrestrial carnivores on Pleistocene ecosystems. Proc Natl Acad Sci USA.
Pardi, M.I. and Smith, F.A. (2015) Biotic responses of canids to the terminal Pleistocene megafauna extinction. Ecography.
Smith, F.A., et al. (2015) Unraveling the consequences of the terminal Pleistocene megafauna extinction on mammal community assembly. Ecography.Megafaunal impact on global climate and nutrient cycles.
Doughty, C.E., et al. (2015) Global nutrient transport in a world of giants. Proc Natl Acad Sci USA.
Doughty, C.E., et al. (2015) Interdependency of plants and animals in controlling the sodium balance of ecosystems and the impacts of global defaunation. Ecography.
Smith, F.A., et al. (2015) A mammoth amount of methane: exploring the influence of ancient and historic megaherbivore extirpations on the global methane budget. Proc Natl Acad Sci USA.
A wilder Anthropocene
Svenning, J., et al. (2015) Science for a wilder Anthropocene - synthesis and directions for rewilding research. Proc Natl Acad Sci USA.
Jepson, P. (2015) A rewilding agenda for Europe: creating a network of experimental reserves. Ecography.
Yadvinder Malhi is an ecosytem ecologist and Professor of Ecosystem Science at Oxford University