Last millennial environmental dynamics in the western Peruvian Andes inferred from the development of a cushion-plant peat hillock

Abstract

For the first time, an isolated cushion-plant peat hillock was investigated, a so far neglected feature of high-Andean spring ecosystems. These small hillocks typically cluster around springs within the upper catchment areas of larger cushion-plant peatlands at altitudes ranging from 4000 m to 5000 m a.s.l.The size of the investigated peat hillock, located within the Río Viscas catchment area (Lucanas province, District of Ayacucho) at 4250 m a.s.l., is relatively small (about 10 m in diameter). Due to its dome-shaped and densely green habitus, it overlooks the surrounding vegetation by about 1–2 m and stands out by its color. Terrestrial laser scanning (TLS) techniques are used in order to provide insights into the spatial extension of the Distichia muscoides-dominated vegetation stand.For the reconstruction of environmental dynamics during the past millennium, plant micro-/macrofossil analyses and total carbon/total nitrogen measurements were applied. Based on radiocarbon dating, the peat archive provides a chronology for the past 1050 years. We interpret phases of relatively high abundances of Poaceae pollen in our record as an expansion of Andean grasslands during humid phases. Drier conditions are indicated by a decrease of Poaceae pollen and higher abundances of Asteraceae pollen. The results reflect significant climate oscillations and provide evidence for a sustained dry phase between AD 900 and AD 1100. A more humid and cooler phase prevailed from around AD 1300 to AD 1825, during the Little Ice Age.Our data provide evidence that such a spatially defined peat-accumulating ecosystem, as represented by the studied peat hillock, is capable to survive pronounced climatic oscillations as long as it does not lose its protective cushion-plant surface. As peat hillocks are heavily affected by grazing, multitemporal studies should be carried out to document changes and to provide new insights into adaption strategies of vegetation to changing environmental conditions.