Grasslands are globally extensive, but the processes governing their ecology and evolution remain unclear. The role of fire for the expansion of ancestral C
grasslands is particularly poorly ...understood. Here we present the first biomass combustion record based on late Miocene to Pleistocene (~10-1.9 Ma) charcoal morphologies (grass, herbs, wood) from the Black Sea, and test the extent of fire events and their role in the rise of open grassy habitats in eastern Eurasia. We show that a mixed regime of surface and crown fires under progressively colder and, at times, drier climates from the late Miocene to Pliocene (8.5-4.6 Ma) accelerated the forest to open woodland transition and sustained a more flammable ecosystem. A tipping point in the fire regime occurred at 4.3 Ma (mid-Pliocene), when increasingly cold and dry conditions led to the dominance of grasslands, and surface, litter fires of low intensity. We provide alternative mechanisms of C
plant evolution by highlighting that fire has been a significant ecological agent for Eurasian grasslands. This study opens a new direction of research into grassland evolutionary histories that can be tested with fossil records of fire alongside climate and vegetation as well as with dynamic vegetation modells.
Long-term ecological studies can provide useful information on forest ecosystem resilience against past climatic change and human caused disturbances. Here, we present a high-resolution ...2200-year-long record of forest development in north-eastern Poland, Suwalki region, using paleobotanical proxies (pollen, plant macrofossils, and charcoal). We show that the pollen abundance of deciduous trees was higher than that of coniferous trees, indicating a near pristine state until 900 AD and a semi-natural forest state until 1500 AD. After 1500 AD, the proportion of coniferous tree taxa surpassed that of deciduous trees and have since remained the dominant forest component. The 17th century experienced massive deforestation coupled with a new phase of human colonization in the area that led to the continued and significant decline of deciduous tree cover, for example, Carpinus, Quercus, and Tilia. Cooling associated with the Little Ice Age may have played a role in Picea’s expansion in this area after 1450 AD. Despite significant climatic shifts associated with the warmer Roman Period or Medieval Climate Anomaly and colder Migration Period, as well as a more sustained human impact, Quercus remained a stable forest component until 1500 AD. The stability of Quercus is an important aspect for forest management strategies as future projections suggest warmer conditions and increased frequency of climate extremes will impact forest composition and structure. Our long-term data suggest that forests in the Suwałki region should contain more abundant deciduous tree species, that is, Quercus, whereas conifer cover should be reduced. We also show clear regional differences in the forest development in the Suwałki region, highlighting the importance of local hydrology, geomorphology, and degrees of human activity on the forest composition.
Wildfires in Siberia are documented to have increased in frequency and severity over recent decades. However, in the absence of long-term records, it is unclear how far and why this trend deviates ...from centennial to millennial scale variability. Here we reconstruct past patterns of fire frequency and fire type, and explore how the fire-related traits of boreal species and plant functional types (PFTs) determine ecosystem responses to changing fire regimes. We use charcoal-based reconstructions of the fire regime in combination with a pollen-based assessment of vegetation composition in two boreal forest peat profiles from Plotnikovo Mire in western Siberia that span the last 2400 and 5000 years. We found moderate levels of biomass burning between 5000 and 4000 cal yr BP. Biomass burning and fire severity i.e., more biomass burning per fire episode, increased over the last 1500 cal yr BP associated with the dominance of fire invaders (Betula). Conversely, between 4000 and 1500 cal yr BP lower biomass burning, with perhaps fire types affecting mostly litter and understorey vegetation, coincided with the dominance of fire resisters (e.g., Pinus sylvestris, P. sibirica, Larix) intermixed with a considerable number of fire avoiders (e.g., Abies sibirica and Picea obovata). This long-term perspective shows that the current fire regime commenced 1500 years ago and deviates from the trends observed over the last 5000 years. This deviation is linked to a combination of climate conditions conducive to fire, the amount and composition of woody fuels, and land use changes. Although pines reacted more sensitively to increased fire severity, the fire avoider Picea obovata appears to be much more vulnerable to both frequent, severe fires than Abies sibirica. We anticipate that climatically driven changes in fire weather, with frequent warm and dry spells, and anthropogenic land use intensification will heighten fire severity and their impact, driving vegetation composition towards Betula species to the detriment of Picea obovata. This study also shows that charcoal morphotypes can provide useful information on fuel and fire type, and that, although all macro-charcoal size classes reliably indicate local-scale fires, the larger fraction (>300–500 μm) allows the identification of on-site fire episodes. We recommend multi-site palaeo-fire reconstructions in boreal peatlands to adequately reflect the influence of localised peat moisture content, and vegetation composition and structure variability on the small-scale heterogeneity of fire type and spread. This will ensure that trends in fire regime dynamics are representative and not limited to the local scale. We also propose future directions in fire research that can be tested using fossil records of fire, climate and vegetation ideally in an interdisciplinary approach.
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•Increased biomass burning and fire severity over the last 1500 years.•Frequent fires shifted vegetation cover towards fire-adapted Betula forest.•Pinus sensitive to increased fire severity, Picea obovata to both frequency and severity .•Charcoal morphotypes signal fuel type and fire severity.•Multi-site reconstructions recommended in boreal peatland to be representative beyond local scale.
•Stable mean fire rotation (mFRI) of ∼200–300yr occurred throughout the Holocene.•P. abies favoured by low to moderate fire severity/area burned.•Disturbance by fire facilitated the establishment of ...F. sylvatica.•F. sylvatica negatively affected by severe/larger size fires.•Humans lengthen FRI and increased charcoal peak magnitude.
Fire frequency and severity are key parameters in evaluating fire-mediated changes in ecosystems, but these metrics are rarely reconstructed at extensive temporal scales. Notably our understanding of the role of fire regime dynamics in the functioning and biodiversity of Central Eastern European temperate forests is limited because investigation of the effect of fire has been neglected. To fill this gap in knowledge, we applied a multi-proxy approach (macrocharcoal, charred remains, pollen, plant macrofossils) to two sedimentary sequences spanning stands of closed canopy Picea abies to the P. abies treeline located in the northern Carpathians, Romania. We found that climate exerts a broad-scale influence, whereas vegetation feedbacks strongly modulate this fire-climate relationship. Fire has been almost continuously present throughout the Holocene with a remarkably stable mean fire rotation (∼250yr) with fires of mostly low to mid severity and/or small to medium size. Humans have shifted the fire regime during the last 2800years to slightly longer fire return intervals (mean 300yr) and more biomass consumption per fire. We found that P. abies was favoured by low to moderate fire severity/area burned. The establishment of late-successional, shade tolerant Fagus sylvatica was facilitated by fire disturbances, but its expansion coincided with major gaps in fire events. This highlights the key role of fire in the expansion of F. sylvatica that seems only possible in a low/small to mixed severity/size fire regime with a sufficiently long fire return interval. High magnitude charcoal peaks negatively affected F. sylvatica. We found more diverse pollen assemblages, especially taxa linked to anthropogenic impact, at times of moderate fire disturbance corroborating the intermediate disturbance hypothesis. In terms of forest management, our results show that, contrary to current understanding, fire is a natural and important driver of vegetation change in this region. The anticipated increase in fire activity with the climate warming and/or augmented fuel accumulation may threaten the dominant forest ecosystems, given that these are adapted to low frequency and severity fires. We advise forestry to consider the effects of fire as part of climate-change conservation strategies. Diversifying the forest tree mixture with more fire-resistant native species is desirable in order to mitigate the effects of increased fire occurrence and severity.
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•Multi-proxy long-term ecological studies are important tool to indicate peatland state.•Climate change and land cover in the catchment impact development of spring-fed fen.•Mollusc ...populations are sensitive to hydrological disturbances.•Restoring spring-fed ecosystems may also require catchment restoration.
The calcareous substrate of spring-fed fens makes them unique islands of biodiversity, hosting endangered, vulnerable, and protected vascular plants. Hence, spring-fed fens ecosystems require special conservation attention because many of them are destroyed (e.g. drained, forested) and it is extremely difficult or even impossible to restore the unique hydrogeological and geochemical conditions enabling their function. The long-term perspective of paleoecological studies allows indication of former wetland ecosystem states and provides understanding of their development over millennia. To examine the late Holocene dynamics of a calcareous spring-fed fen (Raganu Mire) ecosystem on the Baltic Sea coast (Latvia) in relation to environmental changes, substrate and human activity, we have undertaken high-resolution analyses of plant macrofossils, pollen, mollusc, stable carbon (δ13C) and oxygen (δ18O) isotopes combined with radiocarbon dating (AMS) in three coring locations. Our study revealed that peat deposits began accumulating ca. 7000 cal. yr BP and calcareous deposits (tufa) from 1450 cal. yr BP, coinciding with regional hydrological changes. Several fire events occurred between 4000 and 1600 cal. yr BP, which appeared to have had a limited effect on local vegetation. The most significant changes in the forest and peatland ecosystems were at 3200 cal. yr BP associated with a dry climate stage and high fire activity, and then between 1400 and 500 cal. yr BP potentially associated with temperature changes during the Medieval Climate Anomaly (MCA) and Little Ice Age. Hydrological disturbances in the peatland catchment from 1400 cal. yr BP were most likely strengthened by human activity (deforestation) in this region. The relationship between the development of this peatland and changes in its catchment area, such as land cover changes or fluctuations in groundwater levels, suggest that protection and restoration of spring-fed fen ecosystems should also include the surrounding catchment. The presence of calcareous sediments, as well as appropriate temperature and local hydrological conditions appear to be the most crucial factors controlling Cladium marisus populations in our site - currently at the eastern limit of its distribution in Europe.
We conducted multi-proxy analyses in two subalpine lakes, Lake Gropile, in the Rodna Mountains and Lake Vinderelu in the Maramureș Mountains, the Eastern Carpathians, Romania, to investigate the ...effect of different land-use practices on landscape composition, diversity and slope erosion. In the case of Lake Gropile, results evidenced a more extended tree and shrub cover and high fire activity between 6400 and 2800 cal yr BP, accompanied by reduced soil erosion, which appeared more strongly regulated by climatic conditions. Anthropogenic impact became evident 2800 years ago, when landscape openness, pasturing, and disturbance of soil cover increased and intensified over the last four centuries. In the case of Lake Vinderelu, intensified burning was followed by grazing around 1200–1100 cal yr BP and continued throughout the last millennium. Results also highlight the site-specific effects of land-use on vegetation composition and landscape diversity. For Lake Vinderelu, a combined effect of local burning and grazing in removing shrub cover appear to be the main drivers of changes in landscape diversity and structure. At Lake Gropile, fire was more connected to shrub cover changes while grazing to herbaceous cover diversity. Moderate to low grazing appeared to benefit both subalpine ecosystems, creating rich grassland-shrub mosaic communities, while overgrazing reduced landscape diversity and exacerbated erosion. Our findings document the millennial-scale legacy of land-use practices on the subalpine landscapes in this region. We propose that these semi-natural ecosystems hold important ecological and cultural value, and recommend their maintenance through controlled, low intensity pasturing and/or burning.
Faster-than-expected post-glacial migration rates of trees have puzzled ecologists for a long time. In Europe, post-glacial migration is assumed to have started from the three southern European ...peninsulas (southern refugia), where large areas remained free of permafrost and ice at the peak of the last glaciation. However, increasing palaeobotanical evidence for the presence of isolated tree populations in more northerly microrefugia has started to change this perception. Here we use the Northern Eurasian Plant Macrofossil Database and palaeoecological literature to show that post-glacial migration rates for trees may have been substantially lower (60-260 m yr(-1)) than those estimated by assuming migration from southern refugia only (115-550 m yr(-1)), and that early-successional trees migrated faster than mid- and late-successional trees. Post-glacial migration rates are in good agreement with those recently projected for the future with a population dynamical forest succession and dispersal model, mainly for early-successional trees and under optimal conditions. Although migration estimates presented here may be conservative because of our assumption of uniform dispersal, tree migration-rates clearly need reconsideration. We suggest that small outlier populations may be a key factor in understanding past migration rates and in predicting potential future range-shifts. The importance of outlier populations in the past may have an analogy in the future, as many tree species have been planted beyond their natural ranges, with a more beneficial microclimate than their regional surroundings. Therefore, climate-change-induced range-shifts in the future might well be influenced by such microrefugia.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Peatlands cover 3% of the land, occur in 169 countries, and have—by sequestering 600 Gt of carbon—cooled the global climate by 0.6 °C. After a general review about peatlands worldwide, this paper ...describes the importance of the Great Vasyugan Mire and presents suggestions about its protection and future research. The World’s largest peatland, the Great Vasyugan Mire in West-Siberia, forms the border between the Taiga and the Forest-Steppe biomes and harbours rare species and mire types and globally unique self-organizing patterns. Current oil and gas exploitation may arguably be largely phased out by 2050, which will pave the way for a stronger focus on the mire’s role in buffering climate change, maintaining ecosystem diversity, and providing other ecosystem services. Relevant new research lines will benefit from the extensive data sets that earlier studies have gathered for other purposes. Its globally unique character as the ‘largest life form on land’ qualifies the Great Vasyugan Mire in its entirety to be designated as a UNESCO World Heritage Site and a Ramsar Wetland of International Importance.
High altitude environments are experiencing more rapid changes in temperature than the global average with the risk of losing essential ecosystem services in mountain environments. The Carpathians ...Mountains are regarded as hosting Europe's most pristine mountain ecosystems, yet the paucity of past environmental records limits our understanding of their sensitivity to the various drivers of change. A multi-proxy palaeoecological approach (plant macro-remains, pollen, charcoal) applied to three Holocene sediment sequences (between 1540 and 1810 m a.s.l.) in the Rodna Mountains documents past treeline and timberline shifts in response to climate change and human impact to anticipate the likely future responses. Our results indicate that forest reacted sensitively to past climate conditions. The timberline had exceeded an elevation of 1540 m a.s.l. by 10,200 cal. yr BP, when summers were warmer than today. The treeline remained below 1810 m a.s.l. at this time and reached its maximum elevation after 8500 cal. yr BP, when winter temperatures became milder. Cool summer conditions probably caused a lowering of the timberline and an extension of the treeline ecotone from 4900 cal. yr BP, a process accentuated by human impact from the Bronze Age (3500 cal. yr BP) onwards. The anticipated upslope tree movements as a consequence ongoing global warming are not yet clearly visible in our records, but will more probably take place in abandoned agricultural areas and be counter-balanced by re-enforced anthropogenic pressure elsewhere. Pinus sylvestris was the dominant tree species in the timberline under a warm and dry climate, when fires were frequent, during the early Holocene (11,250–10,200 cal. yr BP), while Picea abies became dominant in the timberline and Pinus mugo in the treeline ecotone, respectively from 10,200 cal. yr BP to the present. Abies alba became a significant component of the timber over the last four millennia. The anticipated future warmer and moister climatic conditions will favour the persistence of P. abies as well as A. alba. However, A. alba is more sensitive to anthropogenic disturbance, which implies that in places with continuing farmland pressure, A. alba may be less prevalent than P. abies in the future. Anthropogenic pressure is expected to increase the proportion of tree species characteristic of more disturbed forests and consequently threaten biodiversity with important implications for mountain ecosystem services.
•The timberline had exceeded 1540 m by 10,200 cal. yr BP when summers were warmer.•The treeline reached its maximum after 8500 cal. yr BP under milder winter conditions.•Cool summers led to a lowering of the timberline and treeline from 4900 cal. yr BP.•Since the Bronze Age (3500 cal. yr BP) human impact has accentuated treeline depression.•Future upslope tree movements will favour abandoned agricultural areas.
The Black Sea basin is the sink for some of the largest European rivers and has acted as such, since it was part of the Eastern Paratethys. The late Miocene-to-Pliocene sedimentary record of the ...Black Sea documents several phases of strongly evaporitic conditions associated with extreme changes in regional hydrology. Here, we present the first combined record of continental temperature, soil type, and biomass burning in the circum–Black Sea region from the late Miocene to the transition into Pliocene (~ 10.0 to 5.0 Ma). We use branched glycerol dialkyl glycerol tetraethers (brGDGT) to reconstruct mean annual air temperature (MAT) and soil pH within the catchment of the Black Sea basin and complement these data with evidence from charcoal morphology as a proxy for burned biomass. The brGDGT data reveal generally decreasing temperatures and acidic soils between ~ 10 and 8.5 Ma, overlapping with increase in herbaceous cover in the Black Sea region. The Pontian flooding at 6.12 Ma is characterized by large quantities of organic debris and charcoal fragments in the basin and is followed by cooling starting at 5.97 Ma, event that is superimposed on the TG 20 and TG 22 glacial peaks (at 5.8 Ma). Between 5.8 and 5.0 Ma, the brGDGTs seem to be primarily derived from a cold steppe environment. Enhanced fire activity coinciding with generally cooler temperatures and a higher proportion of herbaceous plants are indicative of increased continentality between 5.8 and 5.0 Ma in the Black Sea region.
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