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.
Last week we hosted a stimulating debate on Ecomodernism.
Last year a number of thinkers launched The Ecomodernist Manifesto, a striking statement that at its core argues that the best way to protect the Earth;s natural ecosystems is to "decouple" from them, to embrace a high-technology, highly urbanised future where humans and intensive agriculture are concentrated in intensely managed areas, leaving room for other parts of the natural world to be protected or "rewild".
These ideas have been very controversial, with proponents arguing the provide a much-needed positive environmental agenda for the Anthropocene (a "good Anthropocene") and detractors arguing they encourage a laissez-faire approach to the very actions that are causing so much damage to the biosphere. For this debate we hosted author Mark Lynas, an original signatory of the manifesto, who was followed by short commentaries from faculty and research fellows Connie McDermott, Paul Jepson and Richard Grenyer, and ending with questions from the audience
The debate can be watched below.
Seven of our ECOFOR GEM intensive forest plots in Brazil have experienced fire in the past two months. This includes old growth forests and previously logged forests.
Wildfires are raging through Eastern Amazonia and Indonesia, a product of this year's intense El Niño together with land use change and forest clearance pressure. Some things have been written about Indonesia (but not enough), but there has been even less written about what is happening in Amazonia. One exception is this piece in the Conservation by our team member Erika Berenguer and colleague Jos Barlow.
Erika is conducting fieldwork in our carbon monitoring plots near Santarem, and yesterday she reported that two of the plots have just been been burnt through before her eyes. These are forests that are not adapted to fire, so the consequences can be devastating.
The loss is devastating, but Erika is working hard to get the plot reestablished as quickly as possible so we can understand the changes in carbon cycling and process of forest recovery after this event, to better inform our understanding of how tropical forest drought and fire affect the carbon budget of the planet.
Here is a wonderful short clay animation made by some of our students from the Environmental Change and Management MSc class. It is derived from lectures I give on the history of the biosphere and arguments for various start dates for the Anthropocene.
At the end of the module the students get into groups and have to create a "presentation" on a theme from the lectures. Responses ranges from videos to a long rap/poem to a folk band singing songs about nutrient transfer by whales ("Eat Deep, Poop Shallow") and global warming ("Oh no, where did the Ice Age go?")
Very proud of and impressed by this deeply committed but also talented and fun group of students.
Here is an dance video made by my DPhil student Tahia Devisscher, which has been submitted to the "Dance Your PhD" contest. Her DPhil looks are the role of fire in the dry forest landscapes of the Chiquitania, Bolivia. She takes an interdisciplinary approach that examines this social-ecological system, trying to understand how people can manage to live with and work with fire as a tool for adapting to climate change.
This is the link to the video:
And this is the link to the 'Dance your PhD' global contest:
We have a paper in PNAS today (as part of the megafauna and ecosystem function special features), led by Chris Doughty, on global nutrient in a world of giants.
Because of their high food consumption rates, long gut residence times and large diurnal movement ranges, megafauna can also play a disproportionate role in the lateral movement of nutrients across landscapes through their faeces and urine. Animals can diffuse significant quantities of nutrients along concentration gradients even without net mass flow of faeces out of the fertile area, merely by eating and defecating back and forth across the nutrient concentration gradient. A world with its Late Pleistocene composition of giant megaherbivores is likely to have had much more efficient lateral diffusion of nutrients across landscapes. Today many megafauna are lost, and remaining wold or replacement domestic megafauna (such as cattle) are restricted in movement. Our recent studies attempted to quantify this megafaunal diffusion effect by compiling mass-based scaling data for terrestrial mammals within a random-walk mathematical framework and concluded that larger animals are disproportionally important in transferring nutrients across landscapes, acting as “arteries” that increase nutrient diffusion rates by at least an order of magnitude.
In the oceans a similar megafaunal nutrient transfer occurs, with whales and other marine mammals consuming nutrients in the deep ocean and transferring them to the surface through faeces and physical mixing. The decline in marine mammal abundance in recent centuries may have reduced this oceanic vertical nutrient pump by around 80% . It is possible that these oceanic and continental megafaunal nutrient pumps were connected via marine-to-terrestrial nutrient transfers by migratory anadromous fish such as salmon at mid- and high latitudes, and by seabirds. This raises the possibility of a global megafaunal nutrient pump that works against abiotic entropic flow of nutrients from weathering continents to oceanic sediments, an interlinked system recycling nutrients with whales moving nutrients from the deep sea to surface waters, anadromous fish and seabirds moving nutrients from the ocean to land, and terrestrial megafauna moving nutrients away from hotspots such as river floodplains into the continental interior. The PNAS paper explore the magnitudes of these nutrient fluxes, and estimate that the vertical ocean pump has declined by 77%, the sea-to-land pump has reduced by 94%, and the terrestrial diffusion of these nutrients has decreased by 92%.
This paper just raised the possibility of this megafaunal pump and how large it might have been. More work is needed to understand better the processes involved, and the geography and ecology of this megafaunal poo pump.
Yadvinder Malhi is an ecosytem ecologist and Professor of Ecosystem Science at Oxford University