Ancient human impacts in Amazonia – the debate continues…

How well can you ever really know 5.5 million km2 of hyperdiverse forest? The Amazon region, and this question, are at the heart of several ongoing debates in the natural sciences – why are there so many species? how much carbon can the forest store? how much did ancient humans impact the forests, and can we still see their effects today?

How fully can you really know a forest as huge and diverse as the Amazon?

This last question was the subject of a paper by Caroline Levis and colleagues published in the prestigious journal Science in March this year, which caused significant ripples within and outside the scientific community. In a nutshell, the article found that tree species humans have cared for are five times more likely to be forest ‘hyperdominants’ than you’d expect. Past human impacts also help explain where these species are found now, accounting for up to 20% of the variation in their distribution (for comparison, environmental factors explained up to 30%). The paper’s conclusion, as picked up by the media, is that “modern tree communities in Amazonia are structured to an important extent by a long history of domestication by Amazonian peoples.”

Theobroma cacao – the tree cocoa beans come from – was one human-influenced species in the Levis et al study

So, debate settled? Not quite. Responding to the paper some critics pointed out that the potential influence of soil nutrients hadn’t been adequately considered; others suggested the data showed that human effects were only significant within 20km of archaeological sites; and yet another argued that most of the human-influenced trees are so short-lived that pre-colonial individuals would be dead by now. Furthermore, another study published around the same time showed these Amazon forest plots are disproportionately close to places highly affected by ancient humans, so maybe it was inevitable that the sampled areas would still be showing their influence.

This, perhaps, goes to the heart of the problem with trying to uncover the human history of all Amazonia: there isn’t much detailed region-wide environmental data, the non-random tree plots cover a vanishingly small fraction of the forest, and there are many archaeological sites we may never find. Reflecting on the paper and its findings at a recent TPRG meeting, it was sobering to consider how this can limit the conclusions of wide-ranging studies like this.

It was also striking how, when it comes to ancient human impacts on forests, people can draw very different conclusions from the same data. As I embark on my research into the effects of past humans and climate change on southern Brazil’s Araucaria forests, these will certainly be important things to bear in mind!



The original paper by Caroline Levis and colleagues can be found here: Some scientists have responded to the paper in its eLetters section (, and Christopher Dick posted his thoughts on his research group website ( The paper on the link between forest plots and areas of ancient human impact was published by Crystal McMichael et al., and can be found here:

Thoughts on PAGES OSM- with photographic evidence

I am aware that not many people had the great opportunity like me to attend PAGES OSM 2017. Therefore, I wanted to share some of the key things that got stuck with me after the conference.



There was an outstanding list of presentations and strong sessions. I am not aiming to pick a favourite, but I would like to highlight the following ones: “From the Mediterranean to the Caspian: paleoclimate variability, environmental responses and human adaptative strategies” with convener Ana Moreno et al, “Do species move or die” with convener N. Whitehouse et al, and specially “Disturbance dynamics across special and temporal scales” with convener Graciela Gil-Romera et al. Papers discussed there were largely multidisciplinary, and generated good discussions.

I felt that the plenaries weren’t as broad, strong or focused as I would have expected. I felt some of them were a little scattered in ideas, and one of them not really tackling the issue of climate change. Nevertheless, I really enjoyed Erik Wolf’s presentation on “Warm worlds”, his presentation was not full of great research and facts, but also felt genuine, and quite fun.

What was a kind of surprise for me, but not for others, was the high quality of research in poster presentations. Back in my time of undergrad and Master studies, a poster presentation was for those that didn’t have a strong enough study to make it to the presentation. Now I can see poster presentation as the new place to showcase research. Having had two posters for PAGES OSM myself (details of presentations below), I can see this as the largest opportunity to actually share and especially discuss, about my research. Added to that is the fact that your work will have a much larger exposure as posters are generally for a whole day which does not compare with the only 15 minutes of oral presentation. I really enjoyed both my posters ads well as oral presentations anyway.


At one of my posters


Fun time!


Heather certainly made a difference with her poster



PAGES OSM really worked as a hub for researchers of common interest in past climate and the environment coming from different disciplines and geographical areas. I met not just colleagues from various institutions from the UK, but also from Chile and Brazil. I also meet new people, especially from Spain, that are doing similar studies in the Mediterranean that I would have not known otherwise. There were great networking opportunities, which is always welcome you can end them up having some quality tapas in a fantastic old town centre.



I think this has been one of the best organisations I have seen in a conference. I did not notice major issues besides the change of the timetable for the plenaries in the very first day, and some queuing for the lunch time (we really needed those 2 hours lunch break to do this and rest the great lunch afterwards).  I saw everything very well thought and programmed, from the rooms and the system for the presentations to be loaded, up to the timing of the food for breaks and lunch. There was always plenty of bottled water available for us to drink, and of course, a good Wi-Fi (which wasn’t available for free at the Palynology meeting in Bahia last year!)

One thing worth mentioning: the food was fan-tas-tic.  We were almost a 1000 delegates, and the food was always ready, and delicious. The best for me, there was catering for vegetarians and people that have a gluten free diet… and it wasn’t boring! The one not minor issue was that the amount of food for people with special dietary was limited. I saw several colleagues struggling to get enough to eat in most days. Nevertheless, there was something that was never missing: red wine always available at the tables for lunchtime.


Gluten free and vegetarian options at the opening ceremony


Coffee breaks with fruits!


Tasty salad and creamy butternut squash soup for lunch!



The Auditorio de Zaragoza is a spacious place, modern and of a very professional feeling. We could all fit well -yet cosy- for the poster sessions, and at the main room for the plenaries (having in mind that not all people attend the very early talks). Just one thing I found disappointing, which was that two rooms for oral sessions were located in a hotel that was nearby the Auditorio. These rooms were not near to the quality of rooms inside the Auditorio and they felt a little isolated. Still, the organisation on those and the rest of rooms worked out very well, at least in the sessions I was attending.

Zaragoza is a fabulous city to visit, plenty of places of cultural and historic importance, the Goya Museum and archaeological sites amongst them, as well as rich architecture. Places to go for dinner or tapas were plenty, and all at reasonable prices.

Nuestra Senora del Pilar Cathedral and the Ebro River


Gorgeous Aljaferia! Vestiges of the time of the caliphs



I am quite pleased to have attended in PAGES OSM, I’ve got a lot from it. Looking forward to the next one!


by Macarena



H. Plumpton; F. Mayle; B. Whitney. Impact of mid-Holocene drought upon Bolivian seasonally-dry tropical forests

J, Iriarte; M. Robinson; J. de Souza; M. L. Cárdenas; F. Mayle; R. Corteletti; P. DeBlasis. The Making of the Forest: Human-induced spread of Araucaria forest out of their natural range in the southern Brazilian highlands

Iriarte; R. Smith; J. Gregorio de Souza; F. Mayle; B. Whitney; M. L. Cárdenas; J. Singarayer; J. F. Carson; S. Roy; P. Valdes. Out of Amazonia: Late-Holocene climate change and the Tupi-Guarani trans-continental expansion

M. L. Cárdenas; F. E. Mayle; J. Iriarte; J. Gregorio de Souza; P. Ulguim; M. Robinson; R. Corteletti; P. DeBlasis. Past vegetation changes in the context of land use and late Holocene expansion of the Jê pre-Columbian culture in Southern Brazil

Freeman, M. L. Cárdenas; V. Iglesias; J. M. Capriles; C. Latorre; J. Freeman; D. Byers; J. Finley; M. Cannon; A. Gil; G. Neme; E. Robinson; J. DeRose. PEOPLE 2K (PalEOclimate and the PeopLing of the Earth): Investigating tipping points generated by the Climate-Human Demography-Institutional nexus


PhD opportunity with us


NERC ‘Scenario’ DTP PhD project at University of Reading:

 Assessing the resilience of Brazil’s iconic Araucaria forest

to past and future climate change




Lead Supervisor: Francis E. Mayle, Dept. Geography & Environ. Science, Univ. Reading.


Staff profile 

Broader context of the project 

Co-supervisors: Richard Walters, School of Biological Sciences, Univ. Reading; Joy Singarayer, Dept. Meteorology, Univ. Reading; Macarena Cárdenas, Dept. Geography & Environ. Science, Univ. Reading.

Collaborator: Jose Iriarte, Dept. Archaeology, Univ. Exeter.



The Parana pine (Araucaria angustifolia) of southern Brazil is an iconic ‘living fossil’, dating back to the Mesozoic, when it was likely grazed upon by Sauropod dinosaurs.  This evergreen conifer once dominated highland areas of Brazil’s southern Atlantic Forest (a global biodiversity hotspot) until the colonial period, but is now critically endangered and is a key conservation priority.  To gain a robust understanding of the likely response of Parana pine to future climate change, a better understanding of the underlying reasons for its current biogeographic distribution is first needed, which can only be gained via knowledge of the long-term dynamics of this species over the past several millennia, in relation to both past climate change and pre-Columbian (pre-1492) human land use.  The overall aim is to determine the relationship between Araucaria forest, climate change, and human land use over the past ~ 6,000 years in southern Brazil, and thereby improve understanding of the likely response of this species to future climate change and the implications for conservation policy.  This PhD project complements an ongoing AHRC(UK)-FAPESP(Brazil)-funded project which provides the archaeological context.


Approach and Methods:

The student will use a novel, multi-disciplinary approach, which combines palaeoecological and archaeological data with ecological and climate models.  Fossil pollen will be analysed from bog sediments and fed into land-cover models (REVEALS, LOVE) to reconstruct the history of Araucaria forest over the last ~ 6,000 years.  These data will be integrated with ongoing archaeological studies and previously published palaeoclimate records to determine the respective roles of people versus climate change in driving late Holocene Araucaria expansion.  Climate models and ecological niche models (e.g. MAXENT) will be tested against these palaeo data and used to map the environmental niche of Araucaria through time, in response to past and future climate change.

Training opportunities:

Training will be given in field- (bog coring) and laboratory-based (pollen microscopy) palaeoecological skills (Mayle & Cárdenas), climate (Singarayer) and ecological (Walters) modelling, and integration with archaeological data (Iriarte).  Sediment cores have already been collected, but there will be scope to visit the field area and collect further material if necessary and any relevant ecological data.

Student profile:

Applicants should hold a minimum of a UK honours degree at 2.1 level, or equivalent, in a relevant subject such as biology, geography or environmental science.  A strong background in numerical/statistical techniques is essential and knowledge of ecology, microscopy and coding/modelling would be advantageous.


How to apply:

Full details of how to apply, as well as a podcast of this advert, can be found at:

The deadline for applications is 25th January 2016, although later applications may be considered.  For further details about the project, please contact the lead supervisor, Francis Mayle.



Where Palaeoecology leads us 2: A&E


Figure 1.  The Hospital, for most people, a dreaded place. For us, a place of revelation


This is the sequel to the post about “Guns” where we talk a little bit about where palaeoecology leads us when we follow our quest for investigating the past using lake/bog sediments.


An unusual patient

If you are worried about the consequences of working in palaeoecology, I can assure you that my recent visit to A&E was not because of an accident (and was not an accident either). This was a very well planned visit to the hospital to become more familiar with my beloved Brazilian patients, my bog cores.


Having taken over 110 Russian cores from numerous bogs across southern Brazil, between Frank Mayle and I (check out the Je Landscapes Project website to know more), I needed a quick non-destructive technique to visualize the internal structures of the cores so I could select the best ones for the project. I therefore decided to take x-rays of these half-metre cores. This relatively low-cost technique allows us to identify any key lithological changes through the core which are not apparent to the naked eye. The differences in density are seen in the resulting images as shades of light and dark. The lighter the colour of the image, the denser the sediment is. That is why features such as clastic material and tephra layers appear light, in comparison with organic peats which are usually dark.



So I arrived at the hospital with two oversized suitcases (Figure 2), completely filled with sediment cores (I am glad to say that I didn’t have to rush there). Carrying the cores this way allowed me to navigate easily through the labyrinthine hospital and get to the subterranean x-ray room.



Figure 2. Just arrived at the Hospital


The X-ray manager was very helpful, and we worked together as a great team, with me unwrapping the cores and placing them on the plate, taking notes and hiding behind the x-ray shield; while he was pressing the button and inputting the information into the computer (Figure 3). It was a relief to be on the other side of that shield.



Figure 3a. Our view to the patient. Behind the shield



Figure 3b. Not sick looking, one of the bog cores being analyised


The cores just about fitted on the x-ray plate (in diagonal) (Figure 4). I am glad I checked that beforehand! If you are considering taking x-rays of your cores, its important to call the hospital beforehand to make sure they have the plate size you need. It seems that most of the x-ray facilities only have the 23cm length plate, which is no where near large enough for a half-metre Russian core.



Figure 4. X-ray of one of the bog cores


I am pleased with the results. The images allow me to distinguish internal structures and therefore enable me to select the best cores (some cores look fine from the outside, but with the x-rays I can see some small gaps in the sediment). On the other hand, the lithological changes revealed by the x-rays enable me to cross-correlate overlapping and duplicate cores. A particularly useful further step is to undertake grey scale analysis of the x-ray image, which can reveal even greater detail (Figure 5), especially when correlating with XRF and magnetic susceptibility results.



Figure 5. Grey scale analysis performed with ImageJ in one of the cores


This was my first experience of undertaking x-ray analysis of bog cores, and I must say that I am very pleased with how useful this technique has proven to be.


By Macarena Cárdenas





Where Palaeoecology leads us 1: Guns



Our quest for understanding the past, using sediments pushes us to find ways to extract the information in what is sometimes quite an exotic manner, as well as making us visit unexpected and fun places (soon to come, a blog post about the places we have visited lately in our field trips). Here is an example of the fun things we get to do.


No blood involved

One fun activity we have been doing is: holding a gun. Not any gun, but a galactic-looking laser-shooting one. I am talking about the portable x-ray fluorescence (XRF) analyser (Thermo), a fantastic piece of technology that allows us to analyse a wide range of elements from the Periodic Table (Figure 1). The gun is very easy to use, with touch-screen and flexibility to customise it, depending of the nature of your sediments. Beware that, because of the nature of this piece of kit, you will need to undertake training in radiation. And: make sure that if you are using it in hand-held format for long periods, that you have strong biceps!



Figure 1. The portable x-ray fluorescence (XRF) analyser (Thermo) in action. Russian core being measured.



Results from this technique have several applications that go from cross-correlating cores within a site to understanding the past environmental characteristics and deposits of the sediments. The fast processing time and resolution available with this method (1cm) enable results to be obtained very quickly, and allow one to understand the nature of the sediments in a non-destructible way (which is very much appreciated when you have only small volumes of sediments at your disposal with Russian cores!). The results can be imported into the computer and easily opened in an excel spread sheet (Figure 2).



Figure 2. Excel spreadsheet with XRF results from a bog core


Next steps will be correlating the XRF results with other analyses, such as magnetic susceptibility and pollen analysis. I am really looking forward to seeing what these multi-proxy analyses reveal.


By Macarena Cárdenas



Fieldtrip SE Brazil

TPR to the South East of Brazil: Je Landscape Palaeo fieldtrip



Pedra Furada, Sao Joaquim National Park (1890masl), Urubici area


It is not long since I came back from the Jê landscapes Project field trip in the South east of Brazil.

The experience was truly fantastic. I had the pleasure to meet and know incredible landscapes and generous people. As a result we found fantastic sites and collected what we believe are the best representative materials for our project.

Focusing in the vegetational, environmental and climate reconstruction during the existence of the Proto- Jê culture, the aim of the field trip was to collect sediments from bogs at the main three geographical areas where the project is studying the Jê culture: Urubici (Highlands), Rio Fortuna (were the Atlantic forest is) and Campo Belo do Sul (Highlands). Armed with dutch gauge and Russian corer, me and my fantastic assistant Álvaro Costa toured over 200 kilometres within Santa Catarina region looking for deep bañados.

Alvaro Costa_Macarena Cardenas

In the Atlantic forest, fundamental piece of the field trip Álvaro Costa next to myself

Our experience in Urubici started very challenging. The very first bog we tried coring was what  I would say the most difficult of the whole trip. We simply couldn’t extrude it. It was a clay and silt grey sediments with a large proportion of silica that would stick to the inside of the Russian corer like leeches, and not even using spatulas to do toggle we could extrude them. Long story short, we managed to find a way to extrude without disturbing the sediments and from that moment onward nobody stopped us. We cored 13 sites within the area, all with overlapping and duplicate drives.

Disturbed Araucaria forest

Human impact is evident in this Araucaria forest, Urubici area (800masl)

peat bog

Santa Bárbara peat bog, at 1800masl in the Araucaria forest-Campos (grasslands) boundary

Santa Barbara_core

Like black butter. Sediments from Santa Barbara peat bog


Our experience in Rio Fortuna, towards the littoral side of Santa Catarina, was indeed a very different but not an easier landscape to core. To find a bog that didn’t suffer the consequences of agriculture or cattle, or that wasn’t converted in a fish tank to grow trout was the first but not only barrier; being able to cut across with the Russian corer the dry and sandy sediments was another one.  We would not give up, and using as much of our patience as well as our weight to push we recovered sediments from four sites very close (~100m) to archaeological finds.

flecha rio fortuna

Arrow point found as we were walking by one of the study sites in Rio Fortuna area

drive_rio fortuna

Sediments from one of the Rio Fortuna sites (600masl)


Campo Belo do Sul gave us a little truce. Thanks to Frank Mayle, who already went to the area in April 2014 and cored eight fantastic sites, we weren’t in much need to core much more. I personally enjoyed this part of the field by joining to the archaeological team that was in the site excavating Abreu e Garcia (funerary) and Baggio (oversized pit-house) sites. An army of students, plus researchers Dr Mark Robinson, Dr Rafael Corteletti, PI Professor Jose Iriarte, PhD students Jonas Gregorio and Priscila Ulguim and of course, loads of yerba mate there were many hours of tireless digging.

Abreu e Garcia

Students working at Abreu e Garcia funerary site, Campo Belo do sul

Another fruitful stop was in Gateados farm, a timber company committed to preserve and protect native vegetation. With the crucial help of Professor Lauri Schorn and his student Alyne Rugiero from University of Blumenau, we collected moss pollsters from the most pristine Araucaria forests available in the area. We will use the pollen rain contained in these natural traps to understand how modern Araucaria forest vegetation expresses in the pollen record.

It was almost two very intense months of travelling, coring and falling, but I would definitely do it again. Now the next step is face the many hours of work in the field translated in sediments to unveil what the past of vegetation and climate was like when Jê culture inhabited these areas.


Almost forgot… I also found mosquitos…

mosquito bite

One mosquito bite in my arm, above my wrist… unfortunately not the only one I had



Post by Macarena