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Higher tree species richness often increases the diversity of other taxonomic groups and is promoted in many managed forest systems. The reason for the higher diversity is due to, for example, inter‐specific differences in resource filtering of the trees. Resource filtering also depends on the total density of the tree layer, but the interaction between tree species composition and density is, so far, unexplored. Likewise, few studies have addressed whether mixtures of tree species host higher diversity, or support higher productivity, of other taxa than monocultures of the same tree species. We use a gradient in overstory tree species composition, ranging from pure Norway spruce (Picea abies) to pure Birch (Betula sp.), combined with a gradient from open to closed forest, to assess the joint effects of tree species mixture and forest density on the understory vegetation. The cover and species richness of understory vascular plants increased with an increasing proportion of birch and decreased with increasing forest density, while the cover of bryophytes decreased with an increasing proportion of birch and increasing forest density. There were clear interactions between tree species composition and forest density; the decrease in vascular plants with forest density was stronger in forest dominated by spruce than in forests dominated by birch, and the positive effect of an increasing proportion of birch was smaller in dense than in open forests. There were no indications of mixed forests supporting a higher species richness or plant cover than any of the two monocultures. Additionally, few species (10%) showed tendencies toward a higher probability of occurrence in mixed forests, and most of these also occurred in open pure stands. Our results indicate a potential conflict between goals for diversified forests and increased biomass production, as the positive effects for understory vegetation from mixtures may be lost to concomitant increases in forest density. Furthermore, the limited number of species benefiting from mixtures per se indicates that similar biodiversity benefits for understory vegetation may be obtained at landscape levels from the increased use of broadleaf and lower‐density production stands, as from mixtures.

The Black Death (1347-1352 CE) is the most renowned pandemic in human history, believed by many to have killed half of Europe's population. However, despite advances in ancient DNA research that conclusively identified the pandemic's causative agent (bacterium Yersinia pestis), our knowledge of the Black Death remains limited, based primarily on qualitative remarks in medieval written sources available for some areas of Western Europe. Here, we remedy this situation by applying a pioneering new approach, 'big data palaeoecology', which, starting from palynological data, evaluates the scale of the Black Death's mortality on a regional scale across Europe. We collected pollen data on landscape change from 261 radiocarbon-dated coring sites (lakes and wetlands) located across 19 modern-day European countries. We used two independent methods of analysis to evaluate whether the changes we see in the landscape at the time of the Black Death agree with the hypothesis that a large portion of the population, upwards of half, died within a few years in the 21 historical regions we studied. While we can confirm that the Black Death had a devastating impact in some regions, we found that it had negligible or no impact in others. These inter-regional differences in the Black Death's mortality across Europe demonstrate the significance of cultural, ecological, economic, societal and climatic factors that mediated the dissemination and impact of the disease. The complex interplay of these factors, along with the historical ecology of plague, should be a focus of future research on historical pandemics.

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 land-cover from pollen data, (3) to present a new project (LANDCLIM: 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 land-cover and lead to a better understanding of how long-term changes in ALCC might have influenced climate. The REVEALS 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 REVEALS 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 LANDCLIM results are expected to provide crucial data to reassess ALCC estimates for a better understanding of the land suface-atmosphere interactions.

Palaeoecological studies are yielding fresh insights into slow forest ecosystem processes that are rarely observed using standard ecological methods, yet have major impacts on ecosystem function. Regional pollen data describe the broad features of the regional spread of trees but yield few insights into the processes of stand invasion and the facilitating role of disturbance. Pollen and charcoal data from small forest hollows are used to complement regional data in the study of the spread of Picea abies and Fagus sylvatica into southern Scandinavia during the last 4000 years. P. abies spread as a migrating front and preferentially invaded successional Betula stands, which had become particularly widespread in the region during the last 1000 years as a result of human activity. The spread of P. abies also closely tracked the changing area of suitable regional climate. The spread of F. sylvatica was more directly linked to anthropogenic activities and disturbance by fire prior to stand establishment. F. sylvatica preferentially invaded rich deciduous stand types that had declined in abundance during the last 2000 years. A recent range reduction of F. sylvatica can also be ascribed to human activity. The stand-scale palaeoecological data show how site conditions and disturbance are more important rate-limiting factors for F. sylvatica than for P. abies and help explain why F. sylvatica spread shows a patchy dynamic rather than the smoother migrating front of P. abies.

Little is known about the paleoecological histories of the three spruce species (white spruce, Picea glauca; black spruce, P. mariana; and red spruce P. rubens) in eastern North America, largely because of the difficulty of separating the three species in the pollen record. We describe a novel and effective classification method of distinguishing pollen grains on the basis of quantitative analysis of grain attributes. The method is illustrated by an analysis of a large sample of modern pollen grains (522 grains from 38 collections) of the three Picea species, collected from the region where the three species co-occur today. For each species X we computed a binary regression tree that classified each grain either as X or as not-X; these three determinations for each grain were then combined as Hamming codes in an error/uncertainty detection procedure. The use of Hamming codes to link multiple binary trees for error detection allowed identification and exclusion of problematic specimens, with correspondingly greater classification certainty among the remaining grains. We measured 13 attributes of 419 reference grains of the three species to construct the regression trees and classified 103 other reference grains by testing. Species-specific accuracies among the reliably classified grains were 100, 77, and 76% for P. glauca, P. mariana, and P. rubens, respectively, and 21, 30, and 22% of the grains by species, respectively, were problematic. The method is applicable to any multi-species classification problem for which a large reference sample is available.

Pollen analyses were carried out at two sites with contrasting land‐use histories (in‐field and out‐land) within a single estate. The aim was to distinguish the relative importance of natural processes and cultural influence on the development of vegetation and biodiversity. The estate lies in the boreo‐nemoral zone of southern Sweden, and attention is focused on the distribution of coniferous and deciduous trees. The in‐fields. which lie close to the estate buildings, are currently dominated by deciduous trees, and have a documented history as fields and hay meadows. The more distant out‐lands were primarily used as grazing land in the past, and support coniferous forest at present. The study covers the last 4000 yr, 2000–1000 BC: the out‐lands site supported natural, dense forests consisting of Quercus, Betula, Tilia, Alnus and Corylus. 1000 BC–AD 1100: several events are best interpreted as an increased cultural activity in the area. Agriculture was based on animal husbandry and the recorded cereals probably originate from a kind of shifting cultivation. AD 1000–1800: agriculture intensified on the in‐fields with cereal cultivation of increased importance, while the out‐fields were used for slash‐and‐burn agriculture and forest grazing. The forests became more open in structure but the composition remained unchanged. An increase in Colluna was a possible consequence of over‐exploitation, AD 1800 onwards: the out‐field deciduous forests were rapidly replaced by Picea‐Pinus coniferous forests during the l800's. The in‐fields retained deciduous forest with a continuity of Quercus and other species. There is a close, positive relationship between floristic diversity and cultural influence during the last 4000 yr. A comparison is made with a similar investigation on another estate in the region, revealing small differences between the estates, but striking similarities in the effects of land‐use types on the development of vegetation. The significance of former in‐fields for nature conservation is discussed, particularly as a potential source for increasing the deciduous component in commercial forestry practice.

In this paper we test the performance of the Regional Estimates of VEgetation Abundance from Large Sites (REVEALS) model using pollen records from multiple small sites. We use Holocene pollen records from large and small sites in southern Sweden to identify what is/are the most significant variable(s) affecting the REVEALS-based reconstructions, i.e. type of site (lakes and/or bogs), number of sites, site size, site location in relation to vegetation zones, and/or distance between small sites and large sites. To achieve this objective we grouped the small sites accordingto (i) the two major modern vegetation zones of the study region, and (ii) the distance between the small sites and large lakes, i.e. small sites within 50, 100, 150, or 200 km of the large lakes. The REVEALS-based reconstructions were performed using 24 pollen taxa. Redundancy analysis was performed on the results from all REVEALS-model runs using the groups within (i) and (ii) separately, and on the results from all runs using the groups within (ii) together. The explanatory power and significance of the variables were identified using forward selection and Monte Carlo permutation tests. The results show that (a) although theREVEALS model was designed for pollen data from large lakes, it also performs well with pollen data from multiple small sites in reconstructing the percentage cover of groups of plant taxa (e.g. open land taxa, summer-green trees, evergreen trees) or individual plant taxa; however, in the case of this study area, the reconstruction of the percentage cover of Calluna vulgaris,Cyperaceae, and Betula may be problematic when using small bogs; (b) standard errors of multiple small-site REVEALS estimates will generally be larger than those obtained using pollen records from large lakes, and they will decrease with increasing size of pollen counts and increasingnumber of small sites; (c) small lakes are better to use than small bogs if the total number of small sites is low; and (d) the size of small sites and the distance between them do not play a major role, but the distance between the small sites and landscape/vegetation boundaries is a determinant factor for the accuracy of the vegetation reconstructions

Pollen analyses were carried out at two sites with contrasting land‐use histories (in‐field and out‐land) within a single estate. The aim was to distinguish the relative importance of natural processes and cultural influence on the development of vegetation and biodiversity. The estate lies in the boreo‐nemoral zone of southern Sweden, and attention is focused on the distribution of coniferous and deciduous trees. The in‐fields. which lie close to the estate buildings, are currently dominated by deciduous trees, and have a documented history as fields and hay meadows. The more distant out‐lands were primarily used as grazing land in the past, and support coniferous forest at present. The study covers the last 4000 yr, 2000-1000 BC: the out‐lands site supported natural, dense forests consisting of Quercus, Betula, Tilia, Alnus and Corylus. 1000 BC-AD 1100: several events are best interpreted as an increased cultural activity in the area. Agriculture was based on animal husbandry and the recorded cereals probably originate from a kind of shifting cultivation. AD 1000-1800: agriculture intensified on the in‐fields with cereal cultivation of increased importance, while the out‐fields were used for slash‐and‐burn agriculture and forest grazing. The forests became more open in structure but the composition remained unchanged. An increase in Colluna was a possible consequence of over‐exploitation, AD 1800 onwards: the out‐field deciduous forests were rapidly replaced by Picea‐Pinus coniferous forests during the l800's. The in‐fields retained deciduous forest with a continuity of Quercus and other species. There is a close, positive relationship between floristic diversity and cultural influence during the last 4000 yr. A comparison is made with a similar investigation on another estate in the region, revealing small differences between the estates, but striking similarities in the effects of land‐use types on the development of vegetation. The significance of former in‐fields for nature conservation is discussed, particularly as a potential source for increasing the deciduous component in commercial forestry practice.

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 biodiversity.

. We reconstructed forest development and disturbance events (fire and logging) during the last 1000 yr with tree‐ring data, pollen and charcoal analysis from a semi‐natural Fagus sylvatica‐Picea abies forest (ca. 1 km2) in the hemiboreal zone. According to pollen analysis, Quercus robur together with Pinus sylvestris was abundant in the forest until the turn of the 18th/19th centuries when these species disappeared completely (Quercus) or nearly completely (Pinus) and were replaced by Fagus and Picea. The disappearance of Quercus was corroborated by the remarkable discovery of a single Quercus stump that had been cut in the 18th century and had become overgrown and preserved by a very old Picea. In total 11 fires were dated from 1555 to 1748 from fire scars in several Pinus stumps cut 100 ‐ 200 yr ago. Since the last fire in 1748, no Quercus or Pinus have regenerated in the core of the reserve apart from single pines in neighbouring managed forest (80 yr ago). During the period of documented fires Fagus was protected from fires in a refuge made up of large boulders. Picea colonized the region at the time when the fires ceased 250 yr ago. We hypothesize that most of the fires were probably of human origin because of their patchiness and high frequency compared to the natural background levels of lightning ignitions in the region. On a 300‐yr time scale, logging and fire suppression seem to strongly overshadow the effect of climate change on forest composition and dynamics.