We have just completed the installation of tree water use measuring equipment at the Bobiri field site in Ghana. This is one of our key intensively monitored sites which run in a wet-dry gradient in Ghana, from wet rainforest to woody savanna. Bobiri sits in the middle of the transect, a patch of forest reserve just east of Kumasi and conveniently close to the Forest Research Institute of Ghana (FORIG). With our FORIG colleagues we have been monitoring the carbon cycle of this forest in detail for the last five years, and have shown it to be the most productive tropical forest we have ever monitored. We are still trying to puzzle out why this site is so productive.
I am with Lucy Rowland from Exeter University (who has worked on studying water flow in a drought experiment in Brazil for many years) and our Ghanaian colleagues Stephen Adu-Bredu, Akwasi Duah Gyamfi, Mickey Boakye and Patrick.
Now, with the installation of water flux sensors, we are adding an understanding of the use of water by different trees. Our main measurements are done using sap flow sensors, which measure water flow (transpiration) through the stem by looking at the rate of dissipation of heat injected into the tree via electrodes. The more sap flow, the faster the dissipation. Installation involves hammering electrodes into the tree (often perched precariously on a ladder in the case of large buttressed trees).
Initial data suggest phenomenal levels of water flow through these trees, much higher than we have seen at previous work in eastern Amazonia. This may be related to the high productivity and fertility that we see at the Ghana site, with the fast growth rates requiring high water use, at least in the wet season. These are amongst the first (and maybe the very first) sap flow measurements in the wet tropical forests of Africa, and there is much to learn in the coming years.
A wonderful June day, and we have a Biodiversity cluster day out to Windsor Great Park, the expansive grounds of Windsor Castle. Our hosts are Ted Green, the wonderfully indomitable and opinionated ecologist of the park (picture below), and Jonathan Spencer from the Forestry Commission. Ted has played a major role in bringing some ecology-focussed management to the park.
The park has been managed as a royal hunting ground and private estate since the Norman Conquest almost a thousand years ago, and was a Saxon hunting ground before then.
We started off by looking at some wonderfully ancient oak trees that are around one thousand years old (the dating is very approximate). These are amongst the oldest broadleaf trees in Northern Europe (coniferous yew trees can frequently be older). The oaks are withered and often hollowed out by heart wood decay, but still very much alive and hosting a wonderful array of biodiversity. Ted argues that the hollowing out actually increases the likelihood of surviving high wind speed events (something he observed after the Great Storm of 1987), and may also be a strategy to recycle nutrients locked away in heartwood.
Beyond the ancient trees, another focus of interest was the role that large animals play in shaping ecosystems (something I talked about at the ZSL Raffles lecture last week). There is a vigorous debate about how the presence of large animals "opened up" closed forests into a woodland-glade mosaic. These would have been aurochs and bison in the early Holocene before they were hunted out, and even elephants and rhinoceros in the previous interglacial, before the Late Pleistocene megafaunal extinctions.
In Windsor there has been some implementation of these ideas, with an old breed of magnificent longhorn cattle left free to roam through some woodland pastures. The resulting ecosystem of open woodland glades and some magnificent ancient trees is just magical. Ted emphasises again and again how important it is to maintain and conserve soil diversity and function in these systems.
Thank you Ted and Jonathan for a magnificent day of insight, exploration and sheer admiration of these wonderful trees and ecosystems.
Last Tuesday our DPhil student Claudia Comberti was tragically killed in a bicycle accident involving a bus. Many of us in the ecosystems team, in the Environmental Change Institute, and in Oxford, are still reeling and devastated as we try to come to terms with with the loss of a talented colleague and friend taken from us so suddenly. There are many tributes to her flowing on Facebook and other fora. Here is mine.
Claudia was original, smart and had a passion for the Amazon and its indigenous peoples, in particular the Tacana II peoples of the Bolivian Amazon, with whom she lived both before and during her DPhil studies. I first met her in 2011. I was living in Ghana at the time, she had just come back from Bolivia, and she contacted me to fix a meeting at Heathrow airport on one of my short visits to Oxford. I immediately saw what potential she had and encouraged her to apply for the MSc Programme. Such was her quiet force of persuasion that by the end of the short meeting she had convinced be to pay for her to attend an ecology conference in Cambridge! She came from a natural sciences background but was moving to a social sciences and policy focus. She cared deeply about the reciprocal relationships between indigenous peoples and their environment, relationships she thought were often misrepresented, poorly understood or just ignored. Whenever our lab group discussions veered into the heavily ecological, Claudia would put up her hand and I could always predict that her interjection would be some variant of “but what about the people?”. She felt strongly that many traditional peoples did not just benefit from nature’s “services” (a form of thinking that has become very popular in our field in recent years), but many peoples actually nurtured and cultured the natural world, providing “services for nature”. I sometimes suggested to her that her ideas sometimes verged on overly romantic idealisation of indigenous peoples, and this always provoked stimulating and vigorous debate that occupied the rest of our meetings. But her ideals were also blended with a passionate pragmatism. She had already written some important papers which have had a significant influence in high level debates on indigenous peoples within the UN climate change and biodiversity conventions. For the last two years she had also been a much-loved teaching assistant on the Environmental Change and Management MSc course.
She had so much to contribute to the world and is taken from us far, far too soon.
In the day after her death there was a spontaneous and moving cycle ride tribute where we rode from the city centre to lay a white bicycle at the scene of her death. The bike was soon decked with the most lovely flowers, scarves and poems. On Friday at 11 am around a hundred of her colleagues in the department gathered in a moment of tearful silence, followed by a few words of tribute by her co-supervisors that remembered the quirky and unique individual she was. The laughs this generated did not feel out of place – I feel she would have been there laughing with us.
We (her supervisors and colleagues) are thinking of other ways to honour her legacy, and some ideas will be announced in the coming weeks. In the meantime, Claudia, may the webs of connection and hope that you have spun throughout your life continue to resonate to your name.
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
Yadvinder Malhi is an ecosytem ecologist and Professor of Ecosystem Science at Oxford University