Four thousand years of vegetation and fire history in the spruce forests of northern Kyrgyzstan (Kungey Alatau, Central Asia)

Analyses of pollen, macrofossils and microscopic charcoal in the sediment of a small sub-alpine lake (Karakol, Kyrgyzstan) provide new data to reconstruct the vegetation history of the Kungey Alatau spruce forest during the late-Holocene, i.e. the past 4,000 years. The pollen data suggest that Picea schrenkiana F. and M. was the dominant tree in this region from the beginning of the record. The pollen record of pronounced die-backs of the forests, along with lithostratigraphical evidence, points to possible climatic cooling (and/or drying) around 3,800 cal year B.P., and between 3,350 and 2,520 cal year B.P., with a culmination at 2,800-2,600 cal B.P., although stable climatic conditions are reported for this region for the past 3,000-4,000 years in previous studies. From 2,500 to 190 cal year B.P. high pollen values of P. schrenkiana suggest rather closed and dense forests under the environmental conditions of that time. A marked decline in spruce forests occurred with the onset of modern human activities in the region from 190 cal year B.P. These results show that the present forests are anthropogenically reduced and represent only about half of their potential natural extent. As P. schrenkiana is a species endemic to the western Tien Shan, it is most likely that its refugium was confined to this region. However, our palaeoecological record is too recent to address this hypothesis thoroughly.

Accumulation of the pathogenic fungus Batrachochytrium dendrobatidis on the regressing tail of midwife toads Alytes obstetricans undergoing metamorphosis

Batrachochytrium dendrobatidis (Bd) is a fungus infecting the skin of amphibians. On metamorphosing animals the infection is difficult to detect because of the limited information concerning the location of Bd on the animals during this stage. Histological investigation revealed that Bd accumulated on the reabsorbing tail of metamorphosing animals. This observation may facilitate the detection of Bd in metamorphosing amphibians.

Holocene climate, fire and vegetation dynamics at the treeline in the Northwestern Swiss Alps

Treelines are expected to rise to higher elevations with climate warming; the rate and extent however are still largely unknown. Here we present the first multi-proxy palaeoecological study from the treeline in the Northwestern Swiss Alps that covers the entire Holocene. We reconstructed climate, fire and vegetation dynamics at Iffigsee, an alpine lake at 2,065 m a.s.l., by using seismic sedimentary surveys, loss on ignition, visible spectrum reflectance spectroscopy, pollen, spore, macrofossil and charcoal analyses. Afforestation with Larix decidua and tree Betula (probably B. pendula) started at ~9,800 cal. b.p., more than 1,000 years later than at similar elevations in the Central and Southern Alps, indicating cooler temperatures and/or a high seasonality. Highest biomass production and forest position of ~2,100–2,300 m a.s.l. are inferred during the Holocene Thermal Maximum from 7,000 to 5,000 cal. b.p. With the onset of pastoralism and transhumance at 6,800–6,500 cal. b.p., human impact became an important factor in the vegetation dynamics at Iffigsee. This early evidence of pastoralism is documented by the presence of grazing indicators (pollen, spores), as well as a wealth of archaeological finds at the nearby mountain pass of Schnidejoch. Human and fire impact during the Neolithic and Bronze Ages led to the establishment of pastures and facilitated the expansion of Picea abies and Alnus viridis. We expect that in mountain areas with land abandonment, the treeline will react quickly to future climate warming by shifting to higher elevations, causing drastic changes in species distribution and composition as well as severe biodiversity losses.

Fire in ice: two millennia of boreal forest fire history from the Greenland NEEM ice core

Biomass burning is a major source of greenhouse gases and influences regional to global climate. Pre-industrial fire-history records from black carbon, charcoal and other proxies provide baseline estimates of biomass burning at local to global scales spanning millennia, and are thus useful to examine the role of fire in the carbon cycle and climate system. Here we use the specific biomarker levoglucosan together with black carbon and ammonium concentrations from the North Greenland Eemian (NEEM) ice cores (77.49° N, 51.2° W; 2480 m a.s.l) over the past 2000 years to infer changes in boreal fire activity. Increases in boreal fire activity over the periods 1000–1300 CE and decreases during 700–900 CE coincide with high-latitude NH temperature changes. Levoglucosan concentrations in the NEEM ice cores peak between 1500 and 1700 CE, and most levoglucosan spikes coincide with the most extensive central and northern Asian droughts of the past millennium. Many of these multi-annual droughts are caused by Asian monsoon failures, thus suggesting a connection between low- and high-latitude climate processes. North America is a primary source of biomass burning aerosols due to its relative proximity to the Greenland Ice Cap. During major fire events, however, isotopic analyses of dust, back trajectories and links with levoglucosan peaks and regional drought reconstructions suggest that Siberia is also an important source of pyrogenic aerosols to Greenland.

The role of human-induced fire and sweet chestnut (Castanea sativa Mill.) cultivation on the long-term landscape dynamics of the southern Swiss Alps

Changes in fire occurrence during the last decades in the southern Swiss Alps make knowledge on fire history essential to understand future evolution of the ecosystem composition and functioning. In this context, palaeoecology provides useful insights into processes operating at decadal-to-millennial time scales, such as the response of plant communities to intensified fire disturbances during periods of cultural change. We provide a high-resolution macroscopic charcoal and pollen series from Guèr, a well-dated peat sequence at mid-elevation (832 m.a.s.l.) in southern Switzerland, where the presence of local settlements is documented since the late Bronze Age and the Iron Age. Quantitative fire reconstruction shows that fire activity sharply increased from the Neolithic period (1–3 episodes/1000 year) to the late Bronze and Iron Age (7–9 episodes/1000 year), leading to extensive clearance of the former mixed deciduous forest (Alnus glutinosa, Betula, deciduous Quercus). The increase in anthropogenic pollen indicators (e.g. Cerealia-type, Plantago lanceolata) together with macroscopic charcoal suggests anthropogenic rather than climatic forcing as the main cause of the observed vegetation shift. Fire and controlled burning were extensively used during the late Roman Times and early Middle Ages to promote the introduction and establishment of chestnut (Castanea sativa) stands, which provided an important wood and food supply. Fire occurrence declined markedly (from 9 to 5–6 episodes/1000 year) during late Middle Ages because of fire suppression, biomass removal by human population, and landscape fragmentation. Land-abandonment during the last decades allowed forest to partly re-expand (mainly Alnus glutinosa, Betula) and fire frequency to increase.