Erika Gobet

A palaeoecological attempt to classify fire sensitivity of trees in the southern Alps

Using pollen percentages and charcoal influx to reconstruct the Holocene vegetation and fire history, we differentiate six possible responses of plants to fire of medium and high frequency: fire-intolerant, fire damaged, fire-sensitive, fire-indifferent, fire-enhanced and fire-adapted. The fire sensitivity of 17 pollen types, representing 20 woody species in the southern Alps, is validated by comparison with todays ecological studies of plant chronosequences. A surprising coincidence of species reaction to fire of medium frequency is character istic for completely different vegetation types, such as woodlands dominated byAbies alba (7000 years ago) andCastanea sativa (today). The temporal persistence of post-fire behaviour of plant taxa up to thousands of years suggests a generally valid species-related fire sensitivity that may be influenced only in part by changing external conditions. A non-analogous behaviour of woody taxa after fire is documented for high fire frequencies. Divergent behaviour patterns of plant taxa in response to medium and high fire frequencies (e.g., increases and decreases ofAlnus glutinosa) also indicate that post-fire plant reactions may change with increasing fire fre quency.

Influence of human impact and bedrock differences on the vegetational history of the Insubrian Southern Alps

Vegetation history for the study region is reconstructed on the basis of pollen, charcoal and AMS14C investigations of lake sediments from Lago del Segrino (calcareous bedrock) and Lago di Muzzano (siliceous bedrock). Late-glacial forests were characterised byBetula andPinus sylvestris. At the beginning of the Holocene they were replaced by temperate continental forest and shrub communities. A special type of temperate lowland forest, withAbies alba as the most important tree, was present in the period 8300 to 4500 B.P. Subsequently,Fagus, Quercus andAlnus glutinosa were the main forest components andA. alba ceased to be of importance.Castanea sativa andJuglans regia were probably introduced after forest clearance by fire during the first century A.D. On soils derived from siliceous bedrock,C. sativa was already dominant at ca. A.D. 200 (A.D. dates are in calendar years). In limestone areas, however,C. sativa failed to achieve a dominant role. After the introduction ofC. sativa, the main trees were initially oak (Quercus spp.) and later the walnut (Juglans regia). Ostrya carpinifolia became the dominant tree around Lago del Segrino only in the last 100–200 years though it had spread into the area at ca. 5000 cal. B.C. This recent expansion ofOstrya is confirmed at other sites and appears to be controlled by human disturbances involving especially clearance. It is argued that these forests should not be regarded as climax communities. It is suggested that under undisturbed succession they would develop into mixed deciduous forests consisting ofFraxinus excelsior, Tilia, Ulmus, Quercus andAcer.

Climatic and human impacts on mountain vegetation at Lauenensee (Bernese Alps, Switzerland) during the last 14,000 years

Lake sediments from Lauenensee (1381 m a.s.l.), a small lake in the Bernese Alps, were analysed to reconstruct the vegetation and fire history. The chronology is based on 11 calibrated radiocarbon dates on terrestrial plant macrofossils suggesting a basal age of 14,200 cal. BP. Pollen and macrofossil data imply that treeline never reached the lake catchment during the Bølling–Allerød interstadial. Treeline north of the Alps was depressed by c. 300 altitudinal meters, if compared with southern locations. We attribute this difference to colder temperatures and to unbuffered cold air excursions from the ice masses in northern Europe. Afforestation started after the Younger Dryas at 11,600 cal. BP. Early-Holocene tree-Betula and Pinus sylvestris forests were replaced by Abies alba forests around 7500 cal. BP. Continuous high-resolution pollen and macrofossil series allow quantitative assessments of vegetation dynamics at 5900–5200 cal. BP (first expansion of Picea abies, decline of Abies alba) and 4100–2900 cal. BP (first collapse of Abies alba). The first signs of human activity became noticeable during the late Neolithic c. 5700–5200 cal. BP. Cross-correlation analysis shows that the expansion of Alnus viridis and the replacement of Abies alba by Picea abies after c. 5500 cal. BP was most likely a consequence of human disturbance. Abies alba responded very sensitively to a combination of fire and grazing disturbance. Our results imply that the current dominance of Picea abies in the upper montane and subalpine belts is a consequence of anthropogenic activities through the millennia.

HyRAD‐X, a versatile method combining exome capture and RAD sequencing to extract genomic information from ancient DNA

Over the last decade, protocols aimed at reproducibly sequencing reduced-genome subsets in non-model organisms have been widely developed. Their use is, however, limited to DNA of relatively high molecular weight. During the last year, several methods exploiting hybridization capture using probes based on RAD-sequencing loci have circumvented this limitation and opened avenues to the study of samples characterized by degraded DNA, such as historical specimens. Here, we present a major update to those methods, namely hybridization capture from RAD-derived probes obtained from a reduced eXome template (hyRAD-X), a technique applying RAD sequencing to messenger RNA from one or few fresh specimens to elaborate bench-top produced probes, that is, a reduced representation of the exome, further used to capture homologous DNA from a samples set. In contrast to previous hybridization capture methods, the reference catalogue on which reads are aligned does not rely on de novo assembly of anonymous RAD-sequencing loci, but on an assembled transcriptome obtained from RNAseq data, thus increasing the accuracy of loci definition and single-nucleotide polymorphisms (SNP) call, and targeting, specifically, expressed genes. Finally, the capture step of hyRAD-X relies on RNA probes, increasing stringency of hybridization, making it well suited for low-content DNA samples. As a proof of concept, we applied hyRAD-X to subfossil needles from the coniferous tree Abies alba, collected in lake sediments (Origlio, Switzerland) and dating back from 7200 to 5800 years before present (bp). More specifically, we investigated genetic variation before, during and after an anthropogenic perturbation that caused an abrupt decrease in A. alba population size, 6500–6200 years bp. HyRAD-X produced a matrix encompassing 524 exome-derived SNPs. Despite a lower observed heterozygosity was found during the 6500–6200 years bp time slice, genetic composition was nearly identical before and after the perturbation, indicating that re-expansion of the population after the decline was most likely driven by local specimens. To the best of our knowledge, this is the first time a population genomic study incorporating ancient DNA samples of tree subfossils is conducted at a moderate cost using reproducible exome-reduced complexity.

Reconstruction of Holocene vegetation dynamics at Lac de Bretaye, a high-mountain lake in the Swiss Alps

A deeper understanding of past vegetation dynamics is required to better assess future vegetation responses to global warming in the Alps. Lake sediments from Lac de Bretaye, a small subalpine lake in the Northern Swiss Alps (1780 m a.s.l.), were analysed to reconstruct past vegetation dynamics for the entire Holocene, using pollen, macrofossil and charcoal analyses as main proxies. The results show that timberline reached the lake’s catchment area at around 10,300 cal. BP, supporting the hypothesis of a delayed postglacial afforestation in the Northern Alps. At the same time, thermophilous trees such as Ulmus, Tilia and Acer established in the lowlands and expanded to the altitude of the lake, forming distinctive boreo-nemoral forests with Betula, Pinus cembra and Larix decidua. From about 5000 to 3500 cal. BP, thermophilous trees declined because of increasing human land use, mainly driven by the mass expansion of Picea abies and severe anthropogenic fire activity. From the Bronze Age onwards (c. 4200–2800 cal. BP), grazing indicators and high values for charcoal concentration and influx attest an intensifying human impact, fostering the expansion of Alnus viridis and Picea abies. Hence, biodiversity in alpine meadows increased, whereas forest diversity declined, as can be seen in other regional records. We argue that the anticipated climate change and decreasing human impact in the Alps today will not only lead to an upward movement of timberline with consequent loss of area for grasslands, but also to a disruption of Picea abies forests, which may allow the re-expansion of thermophilous tree species.

Ein palaookologischer Beitrag zum besseren Verstandnis der naturlichen Vegetation der Schweiz

ZusammenfassungWie natürlich oder naturnah ist eine Pflanzengemeinschaft oder eine Landschaft? Diese Frage ist von Interesse, wenn wir verstehen wollen, wie unsere heutigen Landschaften entstanden sind. Noch wichtiger ist sie aber, wenn abgeschätzt werden muss, welche Massnahmen zum Schutz und zur Bewahrung der Funktionen eines bestimmten Vegetations-, Umwelt- oder Landschaftstyps notwendig sind. Wir fassen hier die Erkenntnisse aus über 30 paläoökologischen Untersuchen zur postglazialen Vegetationsgeschichte in der Schweiz zusammen. Die Kombination von Pollen- und Makrorestauswertungen sowie die Untersuchung von mikro- und makroskopischen Holzkohle-Partikeln und der Vergleich mit Klimaindikatoren ermöglicht es, die Vegetationsentwicklung mit hoher zeitlicher und räumlicher Auflösung zu rekonstruieren. Gemeinsame Trends bei der Vegetationsentwicklung gehen vorwiegend auf die Klimadynamik zurück, es gibt aber nennenswerte Unterschiede in Abhängigkeit vom Bodentyp, der menschlichen Aktivität (besonders unter Einsatz des Feuers) oder der Höhenlage. Verschiedene Waldtypen, die bis anhin unter den jeweiligen Klimabedingungen als natürlich betrachtet wurden, sind das Resultat menschlicher Landnutzung über die Jahrtausende, insbesondere ist die Dominanz einzelner weniger Baumarten in den Wäldern der Schweiz anthropogen bedingt. Umgekehrt wurden lokale, isolierte Bestände nicht als Relikte natürlicher Wälder betrachtet. Die Vielfalt der Waldvegetation hat also stark abgenommen, während dem die gesamte Biodiversität stark zugenommen hat, vorwiegend als Folge der Ausbreitung von Offenlandarten durch landwirtschaftliche Tätigkeiten. Die Paläoökologie hat also dazu beigetragen, die Natürlichkeit von Pflanzengesellschaften neu einzuschätzen und die Reaktionsweisen auf Störungen besser zu verstehen. In diesem Sinne stellen wir neue Projekte vor, in denen die Paläoökologie eingesetzt wird, um Kenntnisse zu gewinnen, die für Naturschutz, Waldbau und die Planung von Nationalparks unentbehrlich sind.AbstractHow natural is a plant community or landscape in a given region? This question is essential for understanding the origin of today’s vegetation as well as for nature conservation and vegetation management. Here we summarize results of over 30 recent paleoecological studies about postglacial vegetation development in Switzerland. The combination of pollen and macrofossil analyses, charcoal analyses and climatic indicators allows the reconstruction of vegetation development with high spatial and temporal resolution. Natural changes, largely related to climatic fluctuations, could be distinguished from changes induced by human land use. Results show general trends across Switzerland as well as remarkable regional differences in vegetation development according to local climate, altitude, bedrock, fire regime and human activity. Several forest types, which used to be regarded as natural vegetation under the current climate, could only establish after extensive human disturbance, so that their dominance is partly anthropogenic. Conversely, local isolated stands were not recognized to be relicts of formerly widespread natural forest types. The diversity of the forests strongly decreased whereas total biodiversity increased, mainly as a consequence of the creation of open land for agricultural purposes. Thus, paleoecology has shed new light on the naturalness of plant communities and their vulnerability to disturbance. We conclude by giving examples of how paleoecological knowledge can be applied in nature conservation, forest management and projects for national parks.

Ein paläoökologischer Beitrag zum besseren Verständnis der natürlichen Vegetation der Schweiz

ZusammenfassungWie natürlich oder naturnah ist eine Pflanzengemeinschaft oder eine Landschaft? Diese Frage ist von Interesse, wenn wir verstehen wollen, wie unsere heutigen Landschaften entstanden sind. Noch wichtiger ist sie aber, wenn abgeschätzt werden muss, welche Massnahmen zum Schutz und zur Bewahrung der Funktionen eines bestimmten Vegetations-, Umwelt- oder Landschaftstyps notwendig sind. Wir fassen hier die Erkenntnisse aus über 30 paläoökologischen Untersuchen zur postglazialen Vegetationsgeschichte in der Schweiz zusammen. Die Kombination von Pollen- und Makrorestauswertungen sowie die Untersuchung von mikro- und makroskopischen Holzkohle-Partikeln und der Vergleich mit Klimaindikatoren ermöglicht es, die Vegetationsentwicklung mit hoher zeitlicher und räumlicher Auflösung zu rekonstruieren. Gemeinsame Trends bei der Vegetationsentwicklung gehen vorwiegend auf die Klimadynamik zurück, es gibt aber nennenswerte Unterschiede in Abhängigkeit vom Bodentyp, der menschlichen Aktivität (besonders unter Einsatz des Feuers) oder der Höhenlage. Verschiedene Waldtypen, die bis anhin unter den jeweiligen Klimabedingungen als natürlich betrachtet wurden, sind das Resultat menschlicher Landnutzung über die Jahrtausende, insbesondere ist die Dominanz einzelner weniger Baumarten in den Wäldern der Schweiz anthropogen bedingt. Umgekehrt wurden lokale, isolierte Bestände nicht als Relikte natürlicher Wälder betrachtet. Die Vielfalt der Waldvegetation hat also stark abgenommen, während dem die gesamte Biodiversität stark zugenommen hat, vorwiegend als Folge der Ausbreitung von Offenlandarten durch landwirtschaftliche Tätigkeiten. Die Paläoökologie hat also dazu beigetragen, die Natürlichkeit von Pflanzengesellschaften neu einzuschätzen und die Reaktionsweisen auf Störungen besser zu verstehen. In diesem Sinne stellen wir neue Projekte vor, in denen die Paläoökologie eingesetzt wird, um Kenntnisse zu gewinnen, die für Naturschutz, Waldbau und die Planung von Nationalparks unentbehrlich sind.AbstractHow natural is a plant community or landscape in a given region? This question is essential for understanding the origin of today’s vegetation as well as for nature conservation and vegetation management. Here we summarize results of over 30 recent paleoecological studies about postglacial vegetation development in Switzerland. The combination of pollen and macrofossil analyses, charcoal analyses and climatic indicators allows the reconstruction of vegetation development with high spatial and temporal resolution. Natural changes, largely related to climatic fluctuations, could be distinguished from changes induced by human land use. Results show general trends across Switzerland as well as remarkable regional differences in vegetation development according to local climate, altitude, bedrock, fire regime and human activity. Several forest types, which used to be regarded as natural vegetation under the current climate, could only establish after extensive human disturbance, so that their dominance is partly anthropogenic. Conversely, local isolated stands were not recognized to be relicts of formerly widespread natural forest types. The diversity of the forests strongly decreased whereas total biodiversity increased, mainly as a consequence of the creation of open land for agricultural purposes. Thus, paleoecology has shed new light on the naturalness of plant communities and their vulnerability to disturbance. We conclude by giving examples of how paleoecological knowledge can be applied in nature conservation, forest management and projects for national parks.

Radiocarbon wiggle matching on laminated sediments delivers high-precision chronologies

High-resolution sediment chronologies with the best possible time control are essential for comparing palaeoecological studies with independent high-precision climatic, archaeological or historic data in order to disentangle causes and effects of past environmental, ecological and societal change. We present two varved lake sediment sequences from Moossee and Burgaschisee (Swiss Plateau) that have chronologies developed with Bayesian models and radiocarbon ( 14 C) dating of terrestrial plant macrofossils extracted from sediment samples with constant age ranges. We illustrate the potential of high-resolution 14 C dating for the construction of robust, high-precision sediment chronologies. The mean 2σ age uncertainties were reduced to±19 cal yr for Moossee and to±54 cal yr for Burgaschisee over the entire period of 3000 cal yr, while 2σ uncertainties of only±13 cal yr and±18 cal yr respectively, were achieved for shorter time intervals. These precisions are better than or comparable to those of previous varve studies. Our results imply that a sophisticated subsampling strategy and a careful selection of short-lived and well-defined terrestrial plant remains are crucial to avoid outlying 14 C ages. A direct linkage between palaeoeological studies with dendrochronologically dated, local archaeological sites as well as a precise comparison with high-resolution climate proxy data have become feasible.

Long‐term population dynamics: Theory and reality in a peatland ecosystem

Summary Population dynamics is a field rich in theory and poor in long-term observational data. Finding sources of long-term data is critical as ecosystems around the globe continue to change in ways that current theories and models have failed to predict. Here we show how long-term ecological data can improve our understanding about palaeo-population change in response to external environmental factors, antecedent conditions and community diversity. We examined a radiometrically-dated sediment core from the Didachara Mire in the mountains of south-western Georgia (Caucasus) and analysed multiple biological proxies (pollen, fern spores, non-pollen palynomorphs, charcoal, diatoms, chrysophyte cysts, midges, mites and testate amoebae). Numerical techniques, including multivariate ordination, rarefaction, independent splitting and trait analysis, were used to assess the major drivers of changes in community diversity and population stability. Integrated multi-proxy analyses are very rare in the Caucasus, making this a unique record of long-term ecological change in a global biodiversity hotspot. Synthesis. Population changes in the terrestrial community coincided primarily with external environmental changes, while populations within the peatland community were affected by both internal and external drivers at different times. In general, our observations accord with theoretical predictions that population increases lead to greater stability and declines lead to instability. Random variation and interspecific competition explain population dynamics that diverged from predictions. Population change and diversity trends were positively correlated in all taxonomic groups, suggesting that population-level instability is greater in more diverse communities, even though diverse communities are themselves more stable. There is a continuing need to confront population theory with long-term data to test the predictive success of theoretical frameworks, thereby improving their ability to predict future change. This article is protected by copyright. All rights reserved.

Das lange Gedächtnis der Moore

Moore stellen ein wichtiges Archiv vergangener Umweltbedingungen dar. Mit wissenschaftlichen Methoden kann in diesen naturlichen Geschichtsbuchern bis zum Ende der letzten Eiszeit (etwa 20000 Jahre vor heute) zuruckgeblattert werden. Diese Informationen helfen uns, den Klimawandel und seine Auswirkungen besser zu verstehen.