We have a new paper led by Ana Malhado, on the ecological biogeography of Amazonia. It can be downloaded from here. It provides a nice concise overview of recent insights into the distribution and variation in function of Amazonian trees, and the complex interviewing of deep history, past environmental variation and current climate and soils.
This is based off the literature review Ana did for her DPhil a few years ago, but updated with more recent insights.
Scale-dependent relationships between tree species richness and ecosystem function in forests
Our 18 hectare research plot at Wytham Woods, where we are tracking the growth rate of over 20,000 trees, is part of a global network of research sites, SIGEO (http://www.sigeo.si.edu) and currently the only one in Europe. This global network conducts analyses of forest structure, composition and diversity at fine spatial scales.
The network has a new paper in Journal of Ecology, by Chisholm et al., the explores the relationship between tree species richness and forest biodiversity and function. The paper can be downloaded here.
The paper was selected as Editor's Choice for the issue. Below is the editors' nice summary of this paper.
The argument for biodiversity conservation is increasingly being framed in terms of maintaining ecosystem functions and services. However, just how important a role biodiversity plays in guaranteeing the provisioning of these services remains contentious. Experimental and field-based studies that have explored the relationship between biodiversity and ecosystem functioning have often reached contradictory conclusions. This issue’s Editor’s Choice, “Scale-dependent relationships between tree species richness and ecosystem function in forests” by Ryan Chisholm and co-authors makes progress in reconciling these seemingly contrasting results. As it turns out, spatial scale is critical.
The conceptual basis of the study is as follows. At small spatial scales any environmental effects are likely to be drowned by other effects arising from stochastic variation in diversity, such as sampling effects and niche complementarity. All things being equal, diverse patches are therefore expected to have higher ecosystem function than species-poor ones at small scales (i.e. those at which most experiments are conducted). At larger spatial scales, there is less stochastic variation in diversity among quadrats and so what is left is the environmental effect. Under these circumstances diversity is expected to play a much smaller role in shaping ecosystem process compared to the environment: this may explain why observational studies have traditionally considered productivity to be the driver of diversity patterns, and not the other way around.
To put these ideas to the test, Chisholm and his co-authors take advantage of a globally distributed network of permanent forest plots (http://www.sigeo.si.edu). Relying on this unique dataset, they explore how two key ecosystem services provided by forest – the capacity to sequester and store carbon - relate to tree species richness, and ask how spatial scale affects this relationship. At a grid size of 0.04 ha, diverse stands generally sequestered more carbon into woody stems and stored greater volumes of live biomass per unit area than species-poor ones. However, when the spatial grain was increased to 0.25 ha, and then further still to 1 ha, differences among diverse and species poor communities faded. Although small patches of diverse forest pack a greater density of stems and utilize available resources with greater efficiency, environmental heterogeneity is what ultimately determines the carbon dynamics of forest landscapes.
Recent studies have suggested that the effects of biodiversity loss on the ability of ecosystems to function and provide services will be comparable in magnitude to those of other drivers of global change. The work by Chisholm and his co-authors points to a more complex scenario, one in which ecosystem responses to global change are scale dependent
This town sits in the Sacred Valley before Machu Picchu, and is the starting point for trains to Machu Picchu. It is a gorgeous little down in a spectacular setting, and in many ways perhaps evening more amazing than Machu Picchu itself.
A spectacular Inca fortress and temple complex looks over the town, and this was the major holdout of the rebel Inca emperor Manco Capac as he tried to wrest back the empire from the Spanish usurpers. Here he inflicted a major defeat on the besieging Spanish. What is perhaps even more remarkable is that the whole town and surrounding mountains appear to have been a massive observatory with which to observe and celebrate the cycle of the seasons. Again we see this Andean habit of using and modifying the wider landscapes as extensions of the urban and ceremonial living space
This first becomes apparent when you realise that the sacred mountain opposite the temple-fort has been subtly carved to show the shape of a giant bearded face, and behind the face is a giant storehouse containing granary store houses. This is thought to be Tunupa, who in Inca legend roamed the lands at the creation of the Incas and froze into the mountainside here. Then, higher up you notice the silhouette of an Inca face. At the winter solstice, the time of renewal of the annual cycle, the sun rises through this point and casts its light directly through the doors of the solar temple. Moreover, it turns out that the whole mountain is used as a giant sundial, with tree-lined boundaries in the fields marking the points with the mountain casts a shadow at the solstices.
The whole landscape seems layered in significance and hidden meanings. I wonder how much more is out there, in this culture and maybe in other lost cultures, that we are no longer aware of.
Machu Picchu, Peru
Machu Picchu is of course world famous, but in ten years of working in Peru very close to the site I have never been there (though I went as a backpacker in the 1990s). This time I have my family here as a wonderful excuse to slow down explore more rather than work intensely in the forest then rush back home. So we take the “vistadome” train to Aguas Calientes as visit this famous ruin.
The most startling, memorable thing about Machu Picchu is not the ruins themselves (which are spectacular), but the location. The mountain on which the lost city was located is incredibly steep-sided and thickly clad in lush mid-elevation cloud forest (around 2400 m above sea-level), as are the surrounding peaks. In typically Inca style, the design and layout of the city mirrors the surrounding natural landscape, with rocks and sacred points within the ruins designed to mimic surrounding peaks. Hundreds of metres below, the sacred Vilcanota river casts a wide meander around the mountain peninsular, literately a sacred snake in Inca mythology signifying the potency of the underworld. The combination of mountains, clouds, lush forest, stonework and raging sacred river is mesmerising and unforgettable.
The wider geography is also startling, and after years working on the Andean slope I appreciate its context in a way I did not before. Machu Picchu sits north of Cusco, at the end of the Sacred Valley which was a central ceremonial centre of the Incas. The various archaeological complexes along the Sacred Valley take the shape of constellations, which mirror constellations in the sky. The valley itself mythologically extends into the sky to become the Milky Way. This concept of geoarchitecture, of shaping cities like sacred creatures and altering landscapes to look like mythological beings, is something that amazes me about the Andes. I have never come across it at this scale anywhere else in the world (though that may reflect my or our collective ignorance).
Machu Picchu sits perched in the zone where the fairly dry uplands transition into the lush Andean slopes and lowlands, and hence was probably a critical waypoint in accessing supplies from the lowland frontiers of the empire (such as coca, feathers), much like the Kosnipata Valley north-east of Cusco where my work has been focussed. But the city seems too carefully constructed (and in such an spectacularly inaccessible location) to be a way station. It seems like a special ceremonial and sacred centre, perched on the each of the vast Amazon lowlands, which appears dangerous and impenetrable even to the mighty Incas at their peak. It seems like a citadel from which to respect and worship the mystery and power of the blending of peaks, sun, clouds and endless, magnificent and mysterious forests.
The legacy of the lost giants
We have a couple of new papers out this week, presenting an intriguing new idea. They are focussed on the idea that large animals play a disproportionate role in transferring nutrients around landscapes through their dung.
The papers can be downloaded as pdfs from my publications list here or directly from here (Nature Geoscience paper) and here (PLOS One paper).
There is coverage of these papers on the BBC here, and also in New Scientist and the Independent among others.
Until very recently in Earth history, just before the dawn of farming, large animals were everywhere. The landscapes of North and South America, Eurasia and Australia looked very much like how African safari parks do today, teeming with giant creatures, the megafauna. In most continents these megafauna disappeared around the time of the arrival of the first human hunters. There is still some debate as to the relative role of humans vs. climate change (particularly in North America) but from my perspective the evidence looks pretty overwhelming that humans played a major role. In Africa the megafauna held out, perhaps because they co-evolved with humans and learnt to become cautious of these puny-looking but dangerous primates.
In a paper in Nature Geoscience we explore the consequences of this megafaunal loss on nutrient cycling in the Amazon forest. We develop a mathematical model, calibrated off modern data from Africa, showing that large animals act like major nutrient arteries pushing nutrients through landscapes. Large animals matter because they eat more, the food sits longer in their guts, and they travel further each day. Using this model we estimate that the nutrient pump in Amazonia diminished 50-fold after the megafaunal extinction.
In a parallel paper in PLOS One we look at the contemporary world. We test our model against data from Kruger National Park in South Africa. Then we use global animal size and range data to look at the size of the modern nutrient pump across the world. Apart from bright patches in parts of Africa and southern Asia, the pump is effectively switched off across the world, a legacy of the megafaunal extinctions.
More generally, we argue that in the world of the megafauna nutrients moved freely across landscapes, mixed around by the large beasts, and that the current patchy distributions of nutrients in weathering regions and floodplains is a legacy of megafaunal extinctions. If humans played a major role in these extinctions, as I suspect, our alteration of biogeochemical cycling and planetary function at global scales began long before even the dawn of agriculture.
Today, some of the remaining the megafauna are still being slaughtered, particularly the forest elephants of the Congo Basin. Over half of the remaining elephants have been slaughtered in the last decade because of the illegal ivory trade. In March I was in Gabon in Ivindo National Park, one of the last strongholds of the forest elephant. I gained an immense respect for these giant, intelligent and complex creatures. Our new papers show that their ongoing loss may have consequences for more than the elephants alone.
After five days of intensive but wonderful meeting in Lima, a few of us (me, Miles Silman, Patrick Meir, Ken Feeley, Sassan Saatchi, Norma Salinas and Eric Cosio) head to Lima for a day of meetings with government officials and key NGO stakeholders. Our aim is to give a summary of what ABERG has achieved over the last decade, and to discuss how it can help the Peruvian government and NGOs with their environmental planning and decision makers. We leave Pisaq at 4 am, driving through silent windy mountain roads for a 6 am flight from Cusco airport. I try to tidy up our presentation on the plane to Lima but cannot stay awake. Then a taxi in Lima to the venue, grabbing some coffee just before entering the meeting and tidying up slides until the last second.
The meeting goes well I think, with two hours of presentations by our team on themes ranging from the effects of climate change to the mapping of biomass and forest function. There are plenty of discussions and suggestions, and a new meeting is arranged that afternoon at the Ministry of the Environment (MINAM). So after a great lunchtime cerviche (food in Lima is so good...) we head to MINAM with a new, shortened presentation to about 25 MINAM employees and advisors, and discussions continue until 8 pm. Topics of discussion range from biomass mapping of Amazonia, through fire control in parks and assisting with Peru’s national forest inventory.
By the end of the day we are exhausted and head for a restaurant meal and a few celebratory pisco sours…
We have a week of workshop and presentations for our Peruvian research consortium (the Andes Biodiversity and Ecosystems Research Group – ABERG). The venue is the wonderful and spectacular town of Pisaq, in the Sacred Valley north of Cusco and surrounded by steep mountains decked in Inca ruins and terraces. In the town, we use a beautiful house owned by La Catholica University, which is hosting the meeting.
ABERG is a consortium focussed on the transect we have set up in the Andes-Amazon, ranging from the high Andes (up to almost 4000 m above sea-level), stretching down through the Kosnipata Valley on the edge of Manu national park, and stretching out into the Amazon lowlands and Tambopata national park. The consortium started ten years ago as three research teams (myself, Miles Silman from Wake Forest University, and Patrick Meir from Edinburgh University) but has since grown rapidly and in many new directions into a huge group involved more than a dozen research groups, around one hundred international and Peruvian researchers. The project is now an international flagship of tropical research and produced close to a hundred scientific papers. Now many new scientists are being attracted to the transect, bring new dimensions ranging from aircraft remote sensing to river biogeochemistry.
The meeting in Pisac lasts for five days packed with presentations and discussions. There are many new ideas and results floating around, and new projects kicking off (including my big traits collection campaign – CHAMBASA). A key highlight of this year’s meeting (the first big one in Peru) is the large number of presentations (over 25) by Peruvian students. This experience is a key chance for them to be exposed to the breadth of research being conducted by them – often they are embedded in a particular project and do not get the chance to see the big picture. They also get a first experience of presenting their work to an international scientific audience, a huge chance and step in their scientific development. They all do just fantastically and present with amazing confidence and clarity.
This meeting is the tenth anniversary of our first foray down the stunning Kosnipata valley, and in the end we have a broad discussion about where we have come and where we are going. It is wonderful, inspiring and surprisingly emotional at times. What a unique and fantastic week!
Yadvinder Malhi is an ecosytem ecologist and Professor of Ecosystem Science at Oxford University