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

www.nature.com/scientificreports OPEN Received: 7 December 2016 Accepted: 2 May 2017 Published: xx xx xxxx Relict high-Andean ecosystems challenge our concepts of naturalness and human impact Steven P. Sylvester1,2, Felix Heitkamp3, Mitsy D. P. V. Sylvester1,4, Hermann F. Jungkunst5, Harrie J. M. Sipman6, Johanna M. Toivonen7, Carlos A. Gonzales Inca8, Juan C. Ospina9 & Michael Kessler1 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. The omnipresent effects of humans on ecosystems makes it almost impossible to properly assess past and present anthropogenic influences. Evidence is accumulating that Neolithic populations had already fundamentally changed landscapes across the globe and that, today, only completely inaccessible ecosystems remain without a direct human footprint1, 2. The lack of knowledge about true natural conditions2 is leading to a shifting baseline syndrome, with perceptions of what is “natural” becoming biased towards anthropogenically affected ecosystems3. Current understanding of human impact on Earth’s ecosystems stems largely from paleo-environmental proxies, but the use of such data to infer present natural ecosystem states is constrained by changed environmental conditions and because many ecosystem properties, e.g. vegetation structure and local-scale composition, cannot be readily derived from paleo-environmental proxies4, 5. 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 pollen4. Due to these limitations, heated debates continue over the “true” natural states of present-day ecosystems2, 5. This is never more apparent than with regards to high mountain ecosystems which presently are composed largely of grassland (3.8 × 106 km2)6, while paleo-ecological evidence suggests that forests once covered large proportions in the early Holocene that since declined4, 7–14. Some researchers argue that the drastic Holocenic forest declines can be attributed to natural climate change9–12, whilst others point to human impact4, 13–16. The 1 Institute of Systematic and Evolutionary Botany, University of Zurich, Zurich, Switzerland. 2Department of Geography, Philipps-Universität Marburg, Marburg, Germany. 3Section of Physical Geography, Faculty of Geoscience and Geography, Georg-August-Universität Göttingen, Göttingen, Germany. 4Universidad Nacional del San Antonio Abad del Cusco, Cusco, Peru. 5Institute of Environmental Sciences, Geoecology & Physical Geography, Universität Koblenz-Landau, Mainz, Germany. 6Botanischer Garten und Botanisches Museum Berlin-Dahlem, Freie Universität Berlin, Berlin, Germany. 7Department of Biology, University of Turku, Turku, Finland. 8Department of Geography and Geology, University of Turku, Turku, Finland. 9Instituto de Botánica Darwinion (ANCEFN-CONICET), Buenos Aires, Argentina. Correspondence and requests for materials should be addressed to S.P.S. (email: steven_sylvester@ hotmail.com) Scientific Reports | 7: 3334 | DOI:10.1038/s41598-017-03500-7 1 www.nature.com/scientificreports/ challenge here is discerning causality in a situation of concurrent climate change, human population expansion, and forest decline. In the Andes, humans are known to have been present above 4,000 m a.s.l. since as far back as 12,800 years ago17 but the ecological impact of these early inhabitants remains unknown. Interestingly, 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 ago7, 8, 14, which some researchers attribute to human activity14, 16. However, 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 causes10. When considering natural ecosystems, most would say they have more species, are more fertile, and store more carbon. Actually, grazing may increase local plant species richness by altering competitive interactions18 while conversion of forest to grassland can increase soil organic carbon (SOC) stocks19. These insights, however, stem from grazing exclosures, which allow assessment of ecosystem recovery but not of natural conditions20. Here we use inaccessible relicts of natural vegetation in the Peruvian high Andes, located close to human habitation and associated ecosystem-shaping disturbances of grazing and burning, to infer modern baselines and gain an understanding of human impact on these ecosystems. We consider sites that are completely inaccessible to anthropogenic disturbance to host pristine vegetation that is certain to have never received direct human impact and is representative of the potential natural vegetation based on current ecological conditions of our study area. Evidence of natural grazers (i.e. mountain deer, Hippocamelus antisensis d’Orbigny and viscacha, Lagidium peruanum Meyen) and isolated natural fires (i.e. trees damaged by lightening) were found at these inaccessible sites and they can, thus, be considered representative of natural ecosystem processes. Much controversy and debate centre around similar research from lowland Amazonia21–23 that attempt to infer natural vegetation from sites which “found little to no evidence of either human occupation or forest/landscape modification”23 as it is argued that these sites could have been accessed by humans. As our study sites have clearly always been isolated from possible hum (...truncated)