Lowland plant migrations into alpine ecosystems amplify soil carbon loss under climate warming

Climate warming is releasing carbon from soils around the world1–3, constituting a positive climate feedback. Warming is also causing species to expand their ranges into new ecosystems4–9. Yet, in most ecosystems, whether range expanding species will amplify or buffer expected soil carbon loss is unknown10. Here we used alpine grasslands as a model system to determine whether the establishment of herbaceous lowland plants in alpine ecosystems influences short–term soil carbon storage under warming. We found that warming (< 1 year) led to negligible alpine soil carbon loss, but its effects became significant and 52% ± 31% (mean ± 95% CIs) larger after lowland plants were introduced at low density into the ecosystem. We present evidence that soil carbon loss likely occurred via lowland plants increasing rates of root exudation, soil microbial respiration and CO2 release. Our findings suggest that warming–induced range expansions of herbaceous plants may yield a rapid positive climate feedback in this system, and that plant range expansions among herbaceous communities may be an overlooked mediator of warming effects on carbon dynamics.

MAIN STAGES OF DEVELOPMENT OF THE LATE CARBONIFEROUS FLORA AND VEGETATION IN THE DONETS BASIN AS THE BASIS OF JUSTIFICATION OF REGIONAL STRATIGRAPHIC UNITS AT THE PALAEOECOSYSTEM LEVEL

Four stages of development of the late Carboniferous vegetation cover have been established that correspond to the time intervals of four regional subdivisions of the Donets Basin − the Toretsian and Kalynovian Regional Stages, the Luganskian and Vyskrivskian Horizons of the Myronivskian Regional Stage. The analysis of phytostratigraphic and paleophytocenological data showed that the stages of vegetation development are characterized by the dominant plant communities in rank of orders of widespread landscapes. Сhanges from one stage to another are considered as the paleophytocenotic events, which are expressed by the changes of dominant communities of certain landscape types. The levels of paleophytocenotic events coincid with the bases of regional subdivisions The bases of the Toretsian and Kalynovian correspond to the levels of paleophytocenotic events, which were manifested by the formation of new communities types as a result of the evolutionary renewal of composition of wetland calamitean-fern and fern-pteridosperm forests of coastal lowlands as well as lycopsid and calamitean-fern forests of deltaic plains. The base of the Myronivskian (Luganskian Horizon) corresponds to the level of the paleophytocenotic event that was expressed by, firstly, the appearance of new communities types of seasonally dry pteridosperm woodlands of river valleys as a result of the evolutionary renewal of their composition, secondly, the appearance of new communities types of wetland calamitean-fern woodlands of coastal lowlands and calamitean-fern and pteridosperm woodlands of deltaic plains, the formation of which were due to the reduction of species compositions and the changes of dominants. The lower boundary of the Vyskrivskian Horizon corresponds to the level of the paleophytocenotic event that was expressed by the appearance of new communities types of wetland calamitean-fern and fern-pteridosperm woodlands of coastal lowlands and seasonally dry fern-pteridosperm woodlands of lacustrine-lagoon plains, the formation of which were associated with plant migrations and the appearance of new dominants. The considered paleophytocenotic events are manifestations of phytocoenogenetic processes, which led to paleophytocenotic changes, and mark main palaeoecosystem transformations in view of vegetation development stages.

Brazilian montane rainforest expansion induced by Heinrich Stadial 1 event

The origin of modern disjunct plant distributions in the Brazilian Highlands with strong floristic affinities to distant montane rainforests of isolated mountaintops in the northeast and northern Amazonia and the Guyana Shield remains unknown. We tested the hypothesis that these unexplained biogeographical patterns reflect former ecosystem rearrangements sustained by widespread plant migrations possibly due to climatic patterns that are very dissimilar from present-day conditions. To address this issue, we mapped the presence of the montane arboreal taxa Araucaria, Podocarpus, Drimys, Hedyosmum, Ilex, Myrsine, Symplocos, and Weinmannia, and cool-adapted plants in the families Myrtaceae, Ericaceae, and Arecaceae (palms) in 29 palynological records during Heinrich Stadial 1 Event, encompassing a latitudinal range of 30°S to 0°S. In addition, Principal Component Analysis and Species Distribution Modelling were used to represent past and modern habitat suitability for Podocarpus and Araucaria. The data reveals two long-distance patterns of plant migration connecting south/southeast to northeastern Brazil and Amazonia with a third short route extending from one of them. Their paleofloristic compositions suggest a climatic scenario of abundant rainfall and relative lower continental surface temperatures, possibly intensified by the effects of polar air incursions forming cold fronts into the Brazilian Highlands. Although these taxa are sensitive to changes in temperature, the combined pollen and speleothems proxy data indicate that this montane rainforest expansion during Heinrich Stadial 1 Event was triggered mainly by a less seasonal rainfall regime from the subtropics to the equatorial region.

Palynological evidence for vegetation patterns in the Transvaal (South Africa) during the late Pleistocene and Holocene

Palynological evidence relating to the nature of Late Quaternary vegetation types and plant migrations in the Transvaal is briefly summarized. It is suggested that, after an early temperate, relatively moist phase and a subsequent relatively dry phase lasting until about 25 000 yr B.P., a vegetation-type with ericaceous elements developed. It resembled belts presently occurring above the treeline and was possibly widespread over the plains of the Transvaal during the last glacial maximum period. In the central parts of the province, warm semi-arid savanna subsequently expanded during the early Holocene and was followed by a more broad-leafed type of woodland in the late Holocene. This change probably resulted from slightly wetter and, at times, also slightly warmer and cooler conditions.

Pleistocene changes in the flora of the high tropical Andes

Geological data show that high Andean habitats have been available for plant colonization only since the end of the Tertiary. The manner in which plant species moved into these habitats, the times during which, and the methods by which they differentiated during the Pleistocene varied altitudinally and latitudinally along the tropical Andes. The process of speciation in all areas, however, was the same as that in temperate environments, namely, geographic isolation and subsequent divergence. Except on the Altiplano, most plant species expanded their ranges during glacial periods when vegetation zones were lowered. In the northern paramos at elevations above treeline, colonization was greatest during glacial periods but has always occurred in a manner similar to that of oceanic islands. At lower elevations in the northern Andes, and along the Eastern Cordillera, direct migration was possible in glacial times because of increased contiguity of upper montane forest habitats. On the upper slopes of the west coast of Perú, glacial-age plant migrations were fostered more by changes in precipitation than by the lowering of vegetation belts. In all of these areas, interglacial periods were, and are, times of isolation and differentiation. Across the Altiplano in contrast, glacial periods were times of population fragmentation accompanied by differentiation and/or speciation.