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.

Questions: Have millennia of human land use fundamentally altered the vegetation of a large proportion of the high Andean puna biome, with natural vegetation now restricted to inaccessible areas? Can inaccessible ledges be used as surrogates to infer the potential natural vegetation (PNV) in heavily impacted areas of the puna ecosystem of the high Andes? Is there a difference in plant community composition and diversity between the potential natural puna vegetation, represented by areas inaccessible to grazing and burning, and the anthropogenically disturbed vegetation found on nearby, but accessible, slopes?Location: Abra M alaga Private Conservation Area, Cusco, southern Peruvian Andes.Methods: Four study habitats were chosen that comprised ledges and slopes from within and outside of the conservation area. For each habitat, vegetation composition was recorded using eight to twelve 2 9 2-m 2 plots studied for species cover and abiotic variables.

Human activity affects properties and development of ecosystems across the globe, to such a degree that it is now challenging to get baseline values for undisturbed ecosystems. This is especially true for soil development, which is potentially affected by land-use history and holds a legacy of past human interventions. Therefore, it is still largely unknown for most ecozones how soil would have developed ‘naturally’. Here, we show undisturbed soil development, i.e. the processes of weathering and accumulation of soil organic matter (SOM), by comparing pristine with grazed sites in the high Andes (4500 m) of southern Peru. We located study plots on a large ledge (0.2 km2) that is only accessible with mountaineering equipment. Plots with pristine vegetation were compared to rangeland plots that were presumably under relatively constant grazing management for at least four millennia. Vegetation change, induced by grazing management, led to lower vegetation cover of the soil, thereby increasing soil surface temperatures and soil acidification. Both factors increased weathering in rangeland soils. Formation of pedogenic oxides with high surface area explained preservation of SOM, with positive feedback to acidification. Higher contents of pyrophosphate extractable Fe and Al oxides indicated the importance of organo-mineral associations for SOM stabilization on rangeland sites, which are likely responsible for a higher degree of humification. This higher degree of humification induced melanization (darker colour) of the rangeland soils which, together with sparse vegetation cover, also feeds back to soil temperature. With this work, we present a conceptual framework of positive feedback links between human-induced vegetation change, soil development and accumulation of SOM, which is only possible due to the unique baseline values of a pristine ecosystem. Using ‘inaccessibility’ as a tool to quantify human impact in future interdisciplinary studies may push research forward on evaluating anthropogenic impact on Earth’s ecosystems.

We provide an updated checklist and key to the 30 Poa species with open panicles from Peru which includes previously circumscribed Dissanthelium and Aphanelytrum species, new taxon records, and three undescribed species. Poa compressa, Poa grisebachii, and Poa leioclada are recorded from Peru for the first time. A number of species are placed in synonymy: Poa carazensis, Poa ferreyrae and Poa tovarii are synonymized under the name Poa fibrifera; Poa adusta (tentatively) and Poa pilgeri are synonymized under Poa candamoana; Poa superata is synonymized under Poa grisebachii; and Poa paramoensis is synonymized under Poa huancavelicae. Included within this treatment are three new species, Poa ramoniana, Poa tayacajaensis and Poa urubambensis, which are described and illustrated. Poa ramoniana, found growing near lakes in high elevation Puna grasslands of Junín, is similar to a small form of Poa glaberrima, but differs in having rhizomes and growing to only 5 cm tall. Poa tayacajaensis, found from shrublands on Andean slopes of Huancavelica and Huánuco, bears similarities to Poa aequatoriensis but differs in having shorter lemmas which are pubescent between the veins, densely scabrous sheaths with smooth, glabrous throats, and shorter ligules. Poa urubambensis, a common element of the undisturbed Polylepis forest understory of the Cordillera Urubamba, Cusco, is distinct from all other members of open-panicled Poa’s by having glabrous lemmas with a smooth and glabrous callus, and notably small anthers. The type material for the name Poa adusta is discussed and a lectotype is selected.

The highest elevation epiphytic vascular plant flora ever recorded on a worldwide basis is described from the Cordillera Vilcabamba, southern Peruvian Andes. Three species of fern (Melpomene, Polypodium: Polypodiaceae) were recorded from Polylepis pepei forests at elevations above 4,250 m, with Melpomene peruviana reaching almost 4,550 m. A new high-elevation world record for arboreal hemiparasites is also documented, with Tristerix longebracteatus (Loranthaceae) being found at c.4,620 m. Climatic conditions of these sites were assessed and are discussed in the light of existing hypotheses on the abiotic conditions limiting epiphytism.