Published by Copernicus Publications on behalf of the European Geosciences Union. 484M.-J. Gaillard et al.: Holocene land-cover reconstructions for studies on land cover-climate feedbacks Abstract. The major objectives of this paper are: (1) to review the pros and cons of the scenarios of past anthropogenic land cover change (ALCC) developed during the last ten years, (2) to discuss issues related to pollen-based reconstruction of the past land-cover and introduce a new method, REVEALS (Regional Estimates of VEgetation Abundance from Large Sites), to infer long-term records of past landcover from pollen data, (3) to present a new project (LAND-CLIM: LAND cover -CLIMate interactions in NW Europe during the Holocene) currently underway, and show preliminary results of REVEALS reconstructions of the regional land-cover in the Czech Republic for five selected time windows of the Holocene, and (4) to discuss the implications and future directions in climate and vegetation/land-cover modeling, and in the assessment of the effects of human-induced changes in land-cover on the regional climate through altered feedbacks. The existing ALCC scenarios show large discrepancies between them, and few cover time periods older than AD 800. When these scenarios are used to assess the impact of human land-use on climate, contrasting results are obtained. It emphasizes the need for methods such as the REVEALS model-based land-cover reconstructions. They might help to fine-tune descriptions of past landcover and lead to a better understanding of how long-term changes in ALCC might have influenced climate. The RE-VEALS model is demonstrated to provide better estimates of the regional vegetation/land-cover changes than the traditional use of pollen percentages. This will achieve a robust assessment of land cover at regional-to continental-spatial scale throughout the Holocene. We present maps of RE-VEALS estimates for the percentage cover of 10 plant functional types (PFTs) at 200 BP and 6000 BP, and of the two open-land PFTs "grassland" and "agricultural land" at five time-windows from 6000 BP to recent time. The LAND-CLIM results are expected to provide crucial data to reassess ALCC estimates for a better understanding of the land suface-atmosphere interactions.

spectroscopy at an alpine lake (Sjuodjijaure) in northern SwedenHolocene climatic change reconstructed from diatoms, chironomids, pollen and near-infrared http://hol.sagepub.com/cgi/content/abstract/11/5/551The online version of this article can be found at: Abstract:The results of a multiproxy study reconstructing the climate history of the last 9300 years in northern Sweden are presented. It is based on diatom, chironomid and pollen analyses, as well as near-infrared spectroscopy (NIRS), of a radiocarbon dated sediment core from Sjuodjijaure (67°22ЈN, 18°04ЈE), situated 100 m above tree-line in the Scandes mountains. Mean July air temperature was reconstructed using transfer functions established for the region. The biological proxies show significant changes in composition during the Holocene and the inferred temperatures all follow the same general trend. For the period between about 9300 to 7300 cal. BP the reconstructions should be interpreted with caution due to the lack of convincing modern analogues in the training set. However the reconstruction suggest that July temperature was on average about the same as today, with several rapid short-term cold and warm periods. Cold periods were dated to about 8500, 8200 and 7600 cal. years BP and a warm period to about 7700 cal. BP. About 7300 cal. BP, a major shift to a warmer climate occurred. Pine migrated into the area, which was previously covered with birch forest. From the mid-Holocene until today the sediment record suggests a descending tree-limit and a gradual lowering of July temperature.

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Lateglacial and early Holocene macrofossils of Norway spruce (Picea abies) found in the Swedish Scandes have challenged the prevailing theory, based on pollen analyses, that spruce arrived rather late (c. 3500 yr cal. BP) to Sweden. The aim of this study was to investigate whether the early-Holocene spruce establishment could be effectively assessed by pollen analysis. Four pollen analyses were carried out on peat mires in a river valley in the southern Swedish Scandes, where spruce has been present since the lateglacial. One site was analysed for the occurrence of macrofossil wood remains. The pollen diagrams display the local vegetation history for the last c. 10 000 years, and reveal the rst occurrence of spruce pollen c. 9000 yr cal. BP. Spruce apparently became established in the northern part of the valley around 9000 BP, and thereafter spread southwards. The results are discussed in terms of the background pollen signal for spruce, i.e., local versus regional pollen, the presence or absence of forest on the sites during the Holocene, and the selection of study sites in relation to the aim of the investigation. Pollen analysis, as applied in this study, is shown to be a relevant method for the study of tree immigration in the early Holocene, at both a local and a landscape level.

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Analysis of pollen and charcoal in peat cores together with age-structure data of a swamp- forest site in the western part of central Sweden show the regional vegetation succession and the disturbance patterns over the last 9000 years. Five major vegetation sequences are identified: 1) Betula- Pinus period (c. 7000 to c. 6000 cal. BC); 2) wetland development (c. 6000 cal. BC to c. cal. AD 300); 3) Picea swamp-forest establishment ( c. cal. AD 300-1000); 4) human exploitation (c. cal. AD 1000-1900); and 5) cessation of human impact ( c. cal. AD 1900- present). Between c. 7000 cal. BC and c. cal. AD 1000, 17 fires were recorded in the peat. During the last 900 years, the area has been under the influence of human impact, mainly by animal grazing and trampling, together with deliberate flooding. These activities have affected the structure and dynamic of the swamp-forest by suppressing the regeneration of Picea and thereby creating an open Picea stand. During the last hundred years, a gradual cessation of human activities has led to increased Picea establishment and a denser swamp-forest. Despite these prolonged anthropogenic disturbances, the swamp-forest has qualities that make it unique in the Swedish forest landscape: 1) it has been forested for about 1700 years, during the last c. 900 years of which fire has been of little or no importance; 2) there are no visual signs of logging; and 3) dynamic processes, with trees continuously establishing, ageing and reaching senescence, have produced a forest with a high abundance of dead wood. The results show that the vegetation has been highly dynamic in response to both anthropogenic and 'natural' disturbance, and to the immigration of Picea. The present high biodiversity, and subsequent conservation interest does not result from long-term stability or absence of fire and other disturbance agencies. Conservation policies should therefore, in addition to species preservation, work to create a mosaic-like landscape where many different forest types are represented, containing structures, substrates and processes that are important for many different species. This provides the species the freedom of movement necessary for survival within the forest landscape in a longer perspective.

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