The high dynamism of Western Amazonian lowlands: a long-term view of the vegetation communities of Yasuní National Park (Ecuador)

Abstract

Since the first pollen diagram presented in 1916 by von Post, the study of the vegetation long-term (>50 years) dynamics through the use of palynology has spread worldwide. However, this increment in the number of analyses has been patchy, with locations densely studied and other areas with still limited knowledge, as it is the case of the tropics. For instance, South American tropics and specially the lowlands (Amazonia sensu lato), represents a region largely understudied, thus limiting obtaining accurate information of the plant communities¿ dynamics of such an ecologically and economic important area. Some of the reasons for this low density of available studies are the difficulty of arriving and exploring the study area or the finding of suitable locations. Among the problems for finding suitable records, western Amazonia has been highlighted as a very geomorphologically active location, preventing the development of long, continuous, sediments spanning several thousand years without a sedimentary gap or hiatus. Here we present a Holocene sequence of western northern Amazonian lowlands, in the Ecuadorian Yasuní National Park. The sequence (PATAM25_B16, 0º41¿07.1¿¿S-76º25¿58¿¿W, 217 m asl), spans the last 6000 years, and pollen, non-pollen palynomorphs, and charcoal analyses have been performed. The beginning of the record is characterised by the presence of some disturbance indicators such as Cecropia, and Asteraceae and Anacardiaceae. Around 5000 years ago, the forest was characterised by high abundances of Urticales, Araliaceae, Virola, Sterculia and Mimosa. Other rainforest elements became important around 3000 years ago, including Acalypha, Alchornea and Malpighiaceae. Finally, the modern forest composition was established during the last millennium, with important contributions from Hyeronima, Geonoma/Euterpe, Iriartea, Ficus, and more recently, Machaerium and Mauritia. The results show the continuous presence of a rainforest, but with a high dynamism changing the abundance of the dominant taxa several times during the last 6000 years. In this sense, the forest with a higher evenness is the present-day one, established during the last millennium. It is suggested that the changes in the vegetation were primarily driven by geomorphological activity including changes in the drainage system, as well as human occurrence, which could have been only sporadic in the study area. Today, the study site is inhabited by Waorani indigenous, and it is subjected to oil extraction activities. The high dynamism of the forest and the unidirectional trends of the taxa shown in this record highlight the importance of studying in more details the trends of the current vegetation in order to secure the present and future ecosystem services of such unique location. Project refs.: 2014 BP-B-00094 and IJCI-2015-24273.