Causes of regional change—land cover

Anthropogenic land-cover change (ALCC) is one of the few climate forcings for which the net direction of the climate response over the last two centuries is still not known. The uncertainty is due to the often counteracting temperature responses to the many biogeophysical effects and to the biogeochemical versus biogeophysical effects. Palaeoecological studies show that the major transformation of the landscape by anthropogenic activities in the southern zone of the Baltic Sea basin occurred between 6000 and 3000/2500 cal year BP. The only modelling study of the biogeophysical effects of past ALCCs on regional climate in north-western Europe suggests that deforestation between 6000 and 200 cal year BP may have caused significant change in winter and summer temperature. There is no indication that deforestation in the Baltic Sea area since AD 1850 would have been a major cause of the recent climate warming in the region through a positive biogeochemical feedback. Several model studies suggest that boreal reforestation might not be an effective climate warming mitigation tool as it might lead to increased warming through biogeophysical processes

Europe's lost forests: a pollen-based synthesis for the last 11,000 years

8000 years ago, prior to Neolithic agriculture, Europe was mostly a wooded continent. Since then, its forest cover has been progressively fragmented, so that today it covers less than half of Europe’s land area, in many cases having been cleared to make way for fields and pasture-land. Establishing the origin of Europe’s current, more open land-cover mosaic requires a long-term perspective, for which pollen analysis offers a key tool. In this study we utilise and compare three numerical approaches to transforming pollen data into past forest cover, drawing on >1000 14C-dated site records. All reconstructions highlight the different histories of the mixed temperate and the northern boreal forests, with the former declining progressively since ~6000 years ago, linked to forest clearance for agriculture in later prehistory (especially in northwest Europe) and early historic times (e.g. in north central Europe). In contrast, extensive human impact on the needle-leaf forests of northern Europe only becomes detectable in the last two millennia and has left a larger area of forest in place. Forest loss has been a dominant feature of Europe’s landscape ecology in the second half of the current interglacial, with consequences for carbon cycling, ecosystem functioning and biodiversity

Pollen-based quantitative reconstructions of Holocene regional vegetation cover (plant-functional types and land-cover types) in Europe suitable for climate modelling

We present quantitative reconstructions of regional vegetation cover in north-western Europe, western Europe north of the Alps, and eastern Europe for five time windows in the Holocene [around 6k, 3k, 0.5k, 0.2k, and 0.05k calendar years before present (bp)] at a 1 degrees x1 degrees spatial scale with the objective of producing vegetation descriptions suitable for climate modelling. The REVEALS model was applied on 636 pollen records from lakes and bogs to reconstruct the past cover of 25 plant taxa grouped into 10 plant-functional types and three land-cover types [evergreen trees, summer-green (deciduous) trees, and open land]. The model corrects for some of the biases in pollen percentages by using pollen productivity estimates and fall speeds of pollen, and by applying simple but robust models of pollen dispersal and deposition. The emerging patterns of tree migration and deforestation between 6k bp and modern time in the REVEALS estimates agree with our general understanding of the vegetation history of Europe based on pollen percentages. However, the degree of anthropogenic deforestation (i.e. cover of cultivated and grazing land) at 3k, 0.5k, and 0.2k bp is significantly higher than deduced from pollen percentages. This is also the case at 6k in some parts of Europe, in particular Britain and Ireland. Furthermore, the relationship between summer-green and evergreen trees, and between individual tree taxa, differs significantly when expressed as pollen percentages or as REVEALS estimates of tree cover. For instance, when Pinus is dominant over Picea as pollen percentages, Picea is dominant over Pinus as REVEALS estimates. These differences play a major role in the reconstruction of European landscapes and for the study of land cover-climate interactions, biodiversity and human resources.Peer reviewe

Pollen signals of ground flora in managed woodlands

This paper explores the vegetation signals contained in the non-arboreal pollen and spore (NAPS) components of pollen assemblages from Tauber traps placed in woodlands subject to rotational cutting (coppicing) in lowland England. Sets of three Tauber traps were placed in compartments of different ages at multiple locations within each woodland for 1 year, and pollen assemblages recorded along with a vegetation survey using a modified pin-frame method in an area of 10 m radius around each trap array. Cluster analysis suggests that, as expected, the ground layer vegetation broadly reflects the different environmental conditions in the three woods, with the main subdivisions within woods apparently driven by changes in ground cover between the early and late stages of the coppice cycle. Non-arboreal pollen and spores (NAPS) assemblages group according to woodland of origin, with subdivisions which relate to pollen abundance but lack a simple relationship with years since cutting. Indices of Association between NAPS records and plant presence in the area around each array were calculated using presence–absence data for multiple distances of vegetation survey. All values tend towards an asymptote, which is interpreted as implying an effective source area for the single taxon presence–absence indicator values of ground flora taxa in coppiced woodlands on the order of a 10 m radius. Only four taxa, Poaceae, Ranunculus acris-type, Cyperaceae, and Scilla-type, have an Index of Association (A) greater than 0.5, implying that the presence of pollen can be interpreted in terms of the local presence of the relevant plant taxon with some confidence. Estimates of Pollen Productivity relative to Poaceae are presented for five taxa: Apiaceae, Asteraceae (Cardueae), Cyperaceae, Mercurialis perennis, and Scilla-type. Years since cutting does affect the ground vegetation and NAPS assemblage trapped in these woods, but that the effect is more clearly seen at an assemblage level in the vegetation than in the pollen assemblages. The interpretative significance of NAPS taxa does not seem to be in providing information about the local conditions around the sampling point, but in reflecting the ground flora of the wider woodland

Mid-Holocene European climate revisited: new high-resolution regional climate model simulations using pollen-based land-cover

International audienceLand-cover changes have a clear impact on local climates via biophysical effects. European land cover has been affected by human activities for at least 6000 years, but possibly longer. It is thus highly probable that humans altered climate before the industrial revolution (AD1750e1850). In this study, climate and vegetation 6000 years (6 ka) ago is investigated using one global climate model, two regional climate models, one dynamical vegetation model, pollen-based reconstruction of past vegetation cover using a model of the pollen-vegetation relationship and a statistical model for spatial interpolation of the reconstructed land cover. This approach enables us to study 6 ka climate with potential natural and reconstructed land cover, and to determine how differences in land cover impact upon simulated climate. The use of two regional climate models enables us to discuss the robustness of the results. This is the first experiment with two regional climate models of simulated palaeo-climate based on regional climate models. Different estimates of 6 ka vegetation are constructed: simulated potential vegetation and recon- structed vegetation. Potential vegetation is the natural climate-induced vegetation as simulated by a dynamical vegetation model driven by climate conditions from a climate model. Bayesian spatial model interpolated point estimates of pollen-based plant abundances combined with estimates of climate- induced potential un-vegetated land cover were used for reconstructed vegetation. The simulated potential vegetation is heavily dominated by forests: evergreen coniferous forests dominate in northern and eastern Europe, while deciduous broadleaved forests dominate central and western Europe. In contrast, the reconstructed vegetation cover has a large component of open land in most of Europe. The simulated 6 ka climate using reconstructed vegetation was 0-5° C warmer than the pre-industrial (PI) climate, depending on season and region. The largest differences are seen in north-eastern Europe in winter with about 4e6 C, and the smallest differences (close to zero) in southwestern Europe in winter. The simulated 6 ka climate had 10-20% more precipitation than PI climate in northern Europe and 10 -20% less precipitation in southern Europe in summer. The results are in reasonable agreement with proxy-based climate reconstructions and previous similar climate modelling studies. As expected, the global model and regional models indicate relatively similar climates albeit with regional differences indicating that, models response to land-cover changes differently

Testing the Effect of Relative Pollen Productivity on the REVEALS Model: A Validated Reconstruction of Europe-Wide Holocene Vegetation

Reliable quantitative vegetation reconstructions for Europe during the Holocene are crucial to improving our understanding of landscape dynamics, making it possible to assess the past effects of environmental variables and land-use change on ecosystems and biodiversity, and mitigating their effects in the future. We present here the most spatially extensive and temporally continuous pollen-based reconstructions of plant cover in Europe (at a spatial resolution of 1° × 1°) over the Holocene (last 11.7 ka BP) using the ‘Regional Estimates of VEgetation Abundance from Large Sites’ (REVEALS) model. This study has three main aims. First, to present the most accurate and reliable generation of REVEALS reconstructions across Europe so far. This has been achieved by including a larger number of pollen records compared to former analyses, in particular from the Mediterranean area. Second, to discuss methodological issues in the quantification of past land cover by using alternative datasets of relative pollen productivities (RPPs), one of the key input parameters of REVEALS, to test model sensitivity. Finally, to validate our reconstructions with the global forest change dataset. The results suggest that the RPPs.st1 (31 taxa) dataset is best suited to producing regional vegetation cover estimates for Europe. These reconstructions offer a long-term perspective providing unique possibilities to explore spatial-temporal changes in past land cover and biodiversit

Approaches to quantitative reconstruction of woody vegetation in managed woodlands from pollen records

There has been increasing interest in developing quantitative methods for reconstructing the dynamics of cultural landscapes over the last 15 years. This paper adds to this literature by using various approaches to reconstruct the vegetation of two woodlands subject to rotational coppicing (the periodic cutting of broadleaved trees and shrubs for wood products). Pollen deposition at ground level was determined at both sites using ‘Tauber’ traps placed near to the centre of 14 compartments of differing age in the coppice rotation. For the main woody taxa, Relative Pollen Productivity (RPP) estimates were derived using linear regression for pollen influx data and Extended R-value analysis for percentage data. The vegetation around three ponds was reconstructed by applying four methods (inverting the two RPP estimate approaches, the modern analogue technique and correction for pollen productivity using the linear regression estimated RPP values) to pollen data obtained from the uppermost sample of sediment from the ponds. To determine whether these methods gave better estimates of the vegetation composition than the original pollen proportions, the results were compared with the surveyed vegetation around each pond using the Bray–Curtis Index. Linear regression of pollen influx produced RPP values which are comparable with previous European studies, whilst for some taxa the Extended R-value analysis produced estimates which are orders of magnitude different both from values derived from the linear regression and previous work. No single approach performed equally well at reconstructing the vegetation around the ponds, and at two of the three locations the uncorrected pollen proportions were most similar to the surveyed vegetation.We conclude that applying quantitative reconstruction methods to individual small sites is, currently, not likely to be useful in complex cultural landscapes. In the context of coppiced woodland, deficiencies in our understanding of pollen taphonomy and the impact of the practice on pollen production first need to be rectified, and we identify strategies to address this situation

Long-term land-cover/use change in a traditional farming landscape in Romania inferred from pollen data, historical maps and satellite images

Traditional farming landscapes in the temperate zone that have persisted for millennia can be exceptionally species-rich and are therefore key conservation targets. In contrast to Europe’s West, Eastern Europe harbours widespread traditional farming landscapes, but drastic socio-economic and political changes in the twentieth century are likely to have impacted these landscapes profoundly. We reconstructed long-term land-use/cover and biodiversity changes over the last 150 years in a traditional farming landscape of outstanding species diversity in Transylvania. We used the Regional Estimates of Vegetation Abundance from Large Sites model applied to a pollen record from the Transylvanian Plain and a suite of historical and satellite-based maps. We documented widespread changes in the extent and location of grassland and cropland, a loss of wood pastures as well as a gradual increase in forest extent. Land management in the socialist period (1947–1989) led to grassland expansion, but grassland diversity decreased due to intensive production. Land-use intensity has declined since the collapse of socialism in 1989, resulting in widespread cropland abandonment and conversion to grassland. However, these trends may be temporary due to both ongoing woody encroachment as well as grassland management intensification in productive areas. Remarkably, only 8% of all grasslands existed throughout the entire time period (1860–2010), highlighting the importance of land-use history when identifying target areas for conservation, given that old-growth grasslands are most valuable in terms of biodiversity. Combining datasets from different disciplines can yield important additional insights into dynamic landscape and biodiversity changes, informing conservation actions to maintain these species-rich landscapes in the longer term

Quantifying the effects of land use and climate on Holocene vegetation in Europe

publisher: Elsevier articletitle: Quantifying the effects of land use and climate on Holocene vegetation in Europe journaltitle: Quaternary Science Reviews articlelink: http://dx.doi.org/10.1016/j.quascirev.2017.07.001 content_type: article copyright: © 2017 Elsevier Ltd. All rights reserved

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This book draws from a rich history of scholarship about the relations between music and cities, and the global flows between music and urban experience