Regional opportunities for tundra conservation in the next 1000 years

The biodiversity of tundra areas in northern high latitudes is threatened by invasion of forests under global warming. However, poorly understood nonlinear responses of the treeline ecotone mean the timing and extent of tundra losses are unclear, but policymakers need such information to optimize conservation efforts. Our individual-based model LAVESI, developed for the Siberian tundra-taiga ecotone, can help improve our understanding. Consequently, we simulated treeline migration trajectories until the end of the millennium, causing a loss of tundra area when advancing north. Our simulations reveal that the treeline follows climate warming with a severe, century-long time lag, which is overcompensated by infilling of stands in the long run even when temperatures cool again. Our simulations reveal that only under ambitious mitigation strategies (relative concentration pathway 2.6) will ∼30% of original tundra areas remain in the north but separated into two disjunct refugia.</jats:p

Evolutionary adaptation of trees and modelled future larch forest extent in Siberia

With changing climate, the boreal forest could potentially migrate north and become threatened by droughts in the south. However, whether larches, the dominant tree species in eastern Siberia, can adapt to novel situations is largely unknown but is crucial for predicting future population dynamics. Exploring variable traits and trait adaptation through inheritance in an individual-based model can improve our understanding and help future projections. We updated the individual-based spatially explicit vegetation model LAVESI (Larix Vegetation Simulator), used for forest predictions in Eastern Siberia, with trait value variation and incorporated inheritance of parental values to their offspring. Forcing the model with both past and future climate projections, we simulated two areas – the expanding northern treeline and a southerly area experiencing drought. While the specific trait of ‘seed weight’ regulates migration, the abstract ‘drought resistance’ protects stands. We show that trait variation with inheritance leads to an increase in migration rate (∼ 3% area increase until 2100). The drought resistance simulations show that, under increasing stress, including adaptive traits leads to larger surviving populations (17% of threatened under RCP 4.5 (Representative Concentration Pathway)). We show that with the increase expected under the RCP 8.5 scenario vast areas (80% of the extrapolated area) of larch forest are threatened and could disappear due to drought as adaptation plays only a minor role under strong warming. We conclude that variable traits facilitate the availability of variants under environmental changes. Inheritance allows populations to adapt to environments and promote successful traits, which leads to populations that can spread faster and be more resilient, provided the changes are not too drastic in both time and magnitude. We show that trait variation and inheritance contribute to more accurate models that can improve our understanding of responses of boreal forests to global change

Vegetation pattern along micro-relief and vegetation type transects in polygonal landscapes of the Siberian Arctic

QuestionHow important is the effect of micro-relief and vegetation type on the characteristics of vascular plants and bryophytes in low-centred polygons? LocationSiberian Arctic, Russia. MethodsEight low-centred polygons in northern Siberia were surveyed for vegetation along transects running from the rim to the pond via the rim-pond transition of each polygon and across a vegetation type gradient from open forest to tundra. ResultsThe cover of vascular plants and bryophytes displays no significant differences between the rim and rim-pond transition but is significantly lower in the pond section of the polygons. Alpha-diversity of vascular plants decreases strongly from rim to pond, whereas bryophyte diversity in pond plots is significantly distinct from the rim and the rim-pond transition. There is no clear trend in cover for either plant group along the vegetation type transect and only a weak trend in -diversity. However, both gradients are reflected in the compositional turnover. The applied indicator species analysis identified taxa characteristic of certain environmental conditions. Among others, we found vascular plants primarily characteristic of the rim and bryophyte taxa characteristic of each micro-relief level and vegetation type. ConclusionsThe observed gradual pattern in -diversity and composition of polygonal vegetation suggests that micro-relief is the main driver of changes in the vegetation composition, while vegetation type and the related forest cover change are of subordinate importance for polygonal vegetation patterns along the Siberian tree line

What drives the recent intensified vegetation degradation in Mongolia - Climate change or human activity?

This study examines the course and driving forces of recent vegetation change in the Mongolian steppe. A sediment core covering the last 55 years from a small closed-basin lake in central Mongolia was analyzed for its multi-proxy record at annual resolution. Pollen analysis shows that highest abundances of planted Poaceae and highest vegetation diversity occurred during 1977–1992, reflecting agricultural development in the lake area. A decrease in diversity and an increase in Artemisia abundance after 1992 indicate enhanced vegetation degradation in recent times, most probably because of overgrazing and farmland abandonment. Human impact is the main factor for the vegetation degradation within the past decades as revealed by a series of redundancy analyses, while climate change and soil erosion play subordinate roles. High Pediastrum (a green algae) influx, high atomic total organic carbon/total nitrogen (TOC/TN) ratios, abundant coarse detrital grains, and the decrease of δ13Corg and δ15N since about 1977 but particularly after 1992 indicate that abundant terrestrial organic matter and nutrients were transported into the lake and caused lake eutrophication, presumably because of intensified land use. Thus, we infer that the transition to a market economy in Mongolia since the early 1990s not only caused dramatic vegetation degradation but also affected the lake ecosystem through anthropogenic changes in the catchment area

Responsiveness of Dichrostachys cinerea to seasonal variations in temperature and rainfall in central Namibia

Woody plants provide natural archives of climatic variation which can be investigated by applying dendroclimatological methods. Such studies are limited in Southern Africa but have great potential of improving our understanding of past climates and plant functional adaptations in the region. This study therefore investigated the responsiveness of Dichrostachys cinerea to seasonal variations in temperature and rainfall at two sites in central Namibia, Waterberg and Kuzikus. Dichrostachys cinerea is one of the encroacher species thriving well in Namibia. A moving correlation and response function analysis were used to test its responsiveness to seasonal climatic variations over time. Dichrostachys cinerea growth rings showed relationships to late summer warming, lasting up to half of the rainy season. The results also revealed that past temperatures had been fluctuating and their influence on growth rings had been intensifying over the years, but to varying extents between the two sites. Temperature was a more important determinant of ring growth at the drier site (Kuzikus), while rainfall was more important at the wetter site (Waterberg). Growth ring responsiveness to rainfall was not immediate but showed a rather lagged pattern. We conclude that D. cinerea differentially responds to variations in rainfall and temperature across short climatic gradients. This study showed that the species, due to its somewhat wide ecological amplitude, has great potential for dendroclimatological studies in tropical regions

Assessing arctic flora composition in the Siberian treeline ecotone by vegetation mapping, pollen analyses and sedimentary DNA metabarcoding

Arctic environments are one of the most climatically influenced areas worldwide. These influences are currently causing major changes in vegetation composition, for example in the Taymyr lowlands, which harbour the northernmost boreal-arctic treeline areas of the world. The most dominant species of the treeline ecotone in this region are Larix gmelinii, Betula nana and Alnus viridis. They are presently shifting in density and range, and have done so multiple times throughout the Holocene. To understand the vegetation changes it is necessary to investigate the current state, before deducing changes for other time phases of the Holocene. To this end a field campaign was carried out at the Taymyr lowlands in 2013 to perform a multidisciplinary investigation by combining methods from vegetation mapping, palynological records and sedimentary DNA metabarcoding. We sampled lake sediments and mapped the vegetation along a transect spanning the treeline ecotone, with changing vegetation composition and density. Our results of the surveyed vegetation will help to investigate the current state of vegetation and will also be used as calibration of the pollen and DNA metabarcoding records. The comparison of the vegetation and pollen record will allow the assessment of over- or underrepresentation of certain taxa within the pollen signal, and this will enable a more secure interpretation of historic pollen records. We will also test this for the DNA metabarcoding data, which has not yet been systematically done for lake sediments in arctic latitudes. This multidisciplinary investigation will draw a more comprehensive image of the current vegetation composition at the Taymyr lowlands than has been possible to date, and will enable a more secure interpretation of historical vegetation change in this highly dynamic area

Modern and ancient DNA in lacustrine sediments – Vegetation signals unraveled

Current climatic changes, mostly triggered by global warming, influence broad parts of the northern latitudes all over the world, and reliable assessments of present and past vegetation are highly relevant to predict the future development of Arctic ecosystems. The northernmost Siberian arcto-boreal treeline areas in the Taymyr lowlands may be particularly affected by climatic changes, with latitudinal shifts of the treeline ecotone and resulting vegetation changes from tundra to taiga. Obtaining reliable information about present vegetation composition in such remote arctic locations is difficult, as vegetation surveys in the field can typically only be carried out during brief visits, and the flowering season is short. Although these techniques are time consuming, methods like vegetation assessment by ground surveys or palynological analyses are common tools to evaluate floral composition and provide valuable, complimentary information. While vegetation surveys mainly provide information about the status quo, pollen analyses also allow investigation of vegetation back in time. In recent years, sedimentary DNA has emerged as an additional and effective tool to improve knowledge about past vegetation. DNA metabarcoding of lake sediments and sediment cores has become more and more relevant as a tool for such research, but an explicit assessment of lake sediment DNA data in comparison to data obtained from pollen and vegetation surveys is still lacking. Here, we present a study comparing these three vegetation assessment methods for 31 lakes within a 300 km transect in arctic Siberia, reaching from Tundra, through the treeline area, to the light Taiga. Surface sediments of lakes were taken, subsampled for DNA and pollen analyses and processed in the respective laboratories. Together with six representative vegetation surveys, we present results of this comparative study. Our results show that taxa assigned by DNA sequence analyses are comparable to those found in the pollen and vegetation analyses. Overall, the DNA provides a higher taxonomical level of identification, while the pollen grains mainly identify to genus level. Compared to the vegetation survey, pollen and DNA provide more information, as they are able to track vegetation elements, which could not been surveyed at the time of the year the surveys were carried out. The results show that the combination and comparison of pollen, DNA and vegetation seems to serve as a calibration set for future investigations of such remote and highly dynamic ecosystems. Our investigation draws a multidisciplinary, comprehensive image of the current composition of the Siberian lowland vegetation by combining well established and promising, newly emerging methods

Characterisation of East Siberian paleodiversity based on ancient DNA analyses of the Batagay megaslump exposure

With the ongoing Arctic warming, permafrost thaw accelerated during the last decade as much as it is now a global concern for biodiversity loss, food webs and biogeochemical cycling. This rapid permafrost degradation forms features such as massive retrogressive thaw slumps that give access to exceptional records for Quaternary biodiversity change investigations. The Batagay megaslump located in northern Yakutia, East Siberia, is the world’s largest thawslump known to date, and along its ~55m high headwall it gives access to Late and Mid Pleistocene permafrost deposits up to more than 500 kyrs in age. During an expedition to this unique site in 2017, sediment samples were collected with ages from more than 500 kyrs to modern time for the analysis of ancient DNA (aDNA). Our aim is to characterise the biodiversity and changes over geological timescales of this region in East Siberia. Using the aDNA extracted from these ancient environmental samples, we first performed a metabarcoding analysis (chloroplast trnL) to investigate past vegetation composition. We then performed a shotgun metagenomic analysis, which enabled a much higher depth of sequence data and allowed us to access the entire biodiversity, from Eukaryotes to Prokaryotes, Archaea and Viruses. This approach opened up new horizons, making it possible not only to investigate biodiversity composition and changes but also to infer on potential interactions across taxa and kingdoms. Both methods together allowed comparison and ensured robustness of the results obtained. We present here one of the very first studies done on the global, past and modern, biodiversity of permafrost regions which holds an enormous potential to reveal new insights into the evolution of this fragile ecosystem

Late Holocene forcing of the Asian winter and summer monsoon as evidenced by proxy records from the northern Qinghai-Tibetan Plateau

Little is known about decadal- to centennial-scale climate variability and its associated forcing mechanisms on the Qinghai-Tibetan Plateau. A decadal-resolution record of total organic carbon (TOC) and grainsize retrieved from a composite piston core from Kusai Lake, NW China, provides solid evidence for decadal- to centennial-scale Asian monsoon variability for the Northern Qinghai-Tibetan Plateau during the last 3770 yr. Intensified winter and summer monsoons are well correlated with respective reductions and increases in solar irradiance. A number of intensified Asian winter monsoon phases are potentially correlated with North Atlantic climatic variations including Bond events 0 to 2 and more recent subtle climate changes from the Medieval Warm Period to the Little Ice Age. Our findings indicate that Asian monsoon changes during the late Holocene are forced by changes in both solar output and oceanic-atmospheric circulation patterns. Our results demonstrate that these forcing mechanisms operate not only in low latitudes but also in mid-latitude regions (the Northern Qinghai-Tibetan Plateau)