Relict high-Andean ecosystems challenge our concepts of naturalness and human impact

Steven P Sylvester,Johanna M Toivonen,Harrie J M Sipman,Hermann F Jungkunst,Michael Kessler,Carlos A Gonzales Inca,Mitsy D P V Sylvester,Juan C Ospina,Felix Heitkamp

doi:10.1038/s41598-017-03500-7

Abstract

What would current ecosystems be like without the impact of mankind? This question, which is critical for ecosystem management, has long remained unanswered due to a lack of present-day data from truly undisturbed ecosystems. Using mountaineering techniques, we accessed pristine relict ecosystems in the Peruvian Andes to provide this baseline data and compared it with the surrounding accessible and disturbed landscape. We show that natural ecosystems and human impact in the high Andes are radically different from preconceived ideas. Vegetation of these ‘lost worlds’ was dominated by plant species previously unknown to science that have become extinct in nearby human-affected ecosystems. Furthermore, natural vegetation had greater plant biomass with potentially as much as ten times more forest, but lower plant diversity. Contrary to our expectations, soils showed relatively little degradation when compared within a vegetation type, but differed mainly between forest and grassland ecosystems. At the landscape level, a presumed large-scale forest reduction resulted in a nowadays more acidic soilscape with higher carbon storage, partly ameliorating carbon loss through deforestation. Human impact in the high Andes, thus, had mixed effects on biodiversity, while soils and carbon stocks would have been mainly indirectly affected through a suggested large-scale vegetation change.

Highlights

The omnipresent effects of humans on ecosystems makes it almost impossible to properly assess past and present anthropogenic influences
Some researchers argue that the drastic Holocenic forest declines can be attributed to natural climate change[9,10,11,12], whilst others point to human impact[4, 13,14,15,16]
It is disputed whether primitive hunters, early livestock farmers or nomads, likely to have been present in small numbers, were capable of causing this large-scale forest decline and whether it was purely a result of natural causes[10]

Summary

Introduction

The omnipresent effects of humans on ecosystems makes it almost impossible to properly assess past and present anthropogenic influences. Palynological inferences, the mainstay for baseline inferences, are further hindered by a lack of precision, with taxa only being identified to family or genus level, and an overrepresentation of taxa with windborne pollen[4] Due to these limitations, heated debates continue over the “true” natural states of present-day ecosystems[2, 5]. Palynological studies report a high abundance of Polylepis forest in the high Andes prior to the appearance of humans, but which suffered a drastic decline around 11,000 years ago[7, 8, 14], which some researchers attribute to human activity[14, 16] It is disputed whether primitive hunters, early livestock farmers or nomads, likely to have been present in small numbers, were capable of causing this large-scale forest decline and whether it was purely a result of natural causes[10]. As our study sites have clearly always been isolated from possible human impact by steep rock walls that can only be climbed with mountaineering equipment, we can confidently say that the data we present is from ecosystems with no direct human impact

Methods

Results

Conclusion