middle | Ecology of the past

Cárdenas, M.L. (2011) The response of western Amazonian vegetation to fire and climate change: A palaeoecological study. PhD Thesis, Department of Earth & Environmental Sciences, The Open University.

MLC Ecuador (2008)

Abstract:

Amazonia is one of the most biodiverse regions of the world, a reputation largely earned by the floristic richness of western Amazonia, namely the Ecuadorian Andes. In particular, montane cloud forest in western Amazonia on the Andean flank has been identified as of high ecological value because of its large floristic diversity. Unfortunately, montane forests’ biodiversity have suffered a strong detrimental impact due the ongoing human activity and climate change. Consequently, understanding the dynamics of montane forest and identifying the main factors that control them is fundamental to manage and protect these ecosystems.

This thesis focuses upon paleoecological data obtained from organic sediments from Erazo (Ecuador), located today within the lower montane forest. Examination of modern vegetation and pollen rain close to Erazo revealed florist variation at the kilometer scale related to human disturbance. Modern data provided the basis for interpreting the fossil record. Radiometric dating of interbedded volcanic ash indicates the sediments were deposited c. 324,000-193,000 years ago, well before the arrival of humans in America. Fossil pollen and wood preserved within organic sediments suggest that the composition of the forest was different to modern and changed significantly during the middle Pleistocene. Taxonomic changes in the fossil pollen assemblage, coupled with the presence of Podocarpus spp. macrofossils within the sediments, indicate that temperatures reached c. 5oC cooler than modern. Given the timing and magnitude of vegetation cha

nge observed in the Erazo sediments it therefore seems likely that the variations were instigated by global temperature changes associated with Marine Isotope Stage (MIS) 9 and the MIS 7-6 transition from interglacial-glacial conditions.

The palaeoecological data from Erazo indicate that far from being a relatively stable ‘museums’ tropical forests are in fact dynamic systems undergoing long term floristic re-assortment as well as being susceptible to abrupt short term floristic reorganization.

Supervisors: Dr. William D. Gosling , Dr. Sarah Sherlock, Dr. Vincent Gauci (all The Open University), Prof. Toby Pennington (Royal Botanic Gardens Edinburgh), and Dr. Imogen Poole (University of Aberdeen).

Examined by: Dr. Juan-Carlos Berrio (University of Leicester), and Prof. Simon Kelley (The Open University).

To borrow a copy from The Open University Library click here.

Photo taken close by the study site. The road that pass through Eastern Andes, and the magnificent Montane forest of western Amazonia behind. (Photo by M. L. Cárdenas)

Who would have thought that building a road in Andes would have allowed us to gain new and unique insight of pristine western- Amazonian forests? (I would have thought completely the opposite). Initially Patricia Mothes, chief of the volcanologist section of the Intituto de Geofisica in Ecuador, was called to look at sediments exposed by road works on the eastern flank of the Ecuadorian Andes. Arriving at the site she found thick (>20 vertical meters) deposits of grayish and dark brown interbedded layers of sediments which looked like they have been recently deposited. At closer inspection Patricia discovered that there were even wood pieces and leaves within the dark sediments (now known to be highly organic) that had the appearance of have been deposited within modern time. She wanted to know more. So a PhD student was recruited (a.k.a. Macarena Cárdenas) to work with the sediments at the Palaeoenvironmental Change Research Group at the Open University under the supervision of Dr William Gosling… And so the study began.

After several years spent dating the sediments, analyzing their composition (physical and elemental) and the fossils (pollen and wood) contained within them preliminary insights into vegetation change on the eastern Andean flank during the middle Pleistocene (c. 200,000-300,000 years ago) were revealed and published (Cárdenas et al., 2011a; Cárdenas et al., 2011b). Further work covering stratigraphically lower sediments (older than those previously published; c. 500,000 year) and more detailed sedimentary and fossil analysis of the entire sequence completed a PhD thesis (Cárdenas, 2011).

I am now pleased to announce that the extended work included in my PhD thesis has now been published in a new article in Palaeogeography, Palaeoclimatology, Palaeoecology (Cárdenas et al., online). The new paper is an extended version from previous publications from the same research and provides further evidence of the unique insights that can be gained from palaeoenvironmental studies in this region. These are some of the oldest Quaternary sediments ever discovered and studied from the mid-elevation eastern Andean flank / western Amazon and upon their analyses we were able to get for the first time an insight of how human-untouched Amazonian forests were back in time (up to 500,000 years ago!), how was their diversity and how they responded to intense volcanic activity and climatic change.

By Dr Macarena L. Cárdenas

REFERENCES

Cárdenas, M.L. (2011) The response of western Amazonian vegetation to fire and climate change: A palaeoecological study. In: Department of Earth & Environmental Sciences, p. 242. The Open University, Milton Keynes

Cárdenas, M.L., Gosling, W.D., Pennington, R.T., Poole, I., Sherlock, S.C. & Mothes, P. (online) Forests of the tropical eastern andean flank during the middle pleistocene. Palaeogeography, Palaeoclimatology, Palaeoecology. DOI: 10.1016/j.palaeo.2013.10.009

Cárdenas, M.L., Gosling, W.D., Sherlock, S.C., Poole, I., Pennington, R.T. & Mothes, P. (2011a) The response of vegetation on the Andean flank in western Amazonia to Pleistocene climate change. Science, 331, 1055-1058. DOI: 10.1126/science.1197947

Cárdenas, M.L., Gosling, W.D., Sherlock, S.C., Poole, I., Pennington, R.T. & Mothes, P. (2011b) Response to comment on “the response of vegetation on the Andean flank in western Amazonia to Pleistocene climate change”. Science, 333, 1825. DOI: 10.1126/science.1207888