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Damage caused by Hymenoscyphus fraxineus , the causal agent of ash dieback, was genetically evaluated based on scorings made on five occasions during the years 2006–2016 at two seed orchards of ash ( Fraxinus excelsior L.) established in southern Sweden in 1992 and 1995, respectively. The studied population included grafts originating from 106 plus-tree clones selected from 27 stands in southern Sweden. The study verified previous results of (1) high genetic control of damage traits, (2) high genotypic variation in disease susceptibility and (3) that only a small proportion of the natural population are at least partly resistant. The clonal response for dieback damage was stable over the 10-year period, i.e. the least susceptible clones selected in 2006 still belong to the healthiest ones after several years of heavy infection pressure. There were no clear trends in the development of damage over time for trees being alive at each assessment. However, the proportion of trees that died was substantial (7–8% per year), but this estimation was influenced by other factors than the disease, such as wild game and sanitary cuttings. Altogether, the results are promising for initiating breeding programs to improve the dieback resistance. However, this is a heavy and costly task, since only a very small proportion of the ash trees are partially resistant to the dieback disease. Thus, a joint breeding program involving all the northern European countries is justified. [ABSTRACT FROM AUTHOR]

Abstract: A sound knowledge of the soil properties required by tree species is a prerequisite for addressing many practical and scientific issues such as forest management or the predictive mapping of tree species. To date, such knowledge has been derived mainly from laboratory experiments and from case studies in the field. The importance of soils for the distribution of tree species has, however, hardly been tested systematically with comprehensive data including climate, soil and vegetation inventories. In our study, we analysed a comprehensive database to explore how soil and topo-climatic properties relate to the abundance of regenerating and mature beech (Fagus sylvatica L.), ash (Fraxinus excelsior L.) and sycamore (Acer pseudoplatanus L.) in mature forests across Switzerland. From 806 forest plots distributed all over strong environmental gradients, we used soil and topo-climatic data as predictors and the abundances of tree species in the herb and in the tree layer as response variables. To test the explanatory power of the predictors, we conducted variation partitioning analyses with generalized linear models. Soil predictors involved nutrients, potentially toxic elements, soil aeration and water availability. The explanatory power of most soil predictors was tested in different soil layers to a depth of 1m. Ash and sycamore were much more sensitive to soil variables than beech. The most relevant soil variables for the competitive ability of the three species were C/N-ratio, humus form, aluminium content, base saturation, magnesium content, and soil aeration. Shortage of nutrients limited the distribution of ash and sycamore and excess of toxic elements the distribution of ash. For beech, no soil-induced distribution limits were detectable. Ash was absent if the C/N-ratio in the topsoil was greater than 20. On such sites, sycamore was absent too or reached heights of at most 15–20m, i.e. well below the upper canopy. Ash was absent or reached a maximum height of 15m on acidic soils including at least one soil layer with a base saturation less than 20% in the upper 1m of the soil. The soil properties relevant for the competitive ability of ash and sycamore were more apparent for mature than for regenerating trees. In most cases, the topsoil influenced tree abundances more than the subsoil did. [Copyright &y& Elsevier]

Abstract: This paper discusses determinants of the historical and current spatial extent of the floodplain forest in Leipzig as well as its tree species composition using a GIS-data based delineation model and historical forest inventories for the floodplain forest in the district of Leipzig in Germany from the 19th to the 20th century. We found that the spatial extent of the floodplain forest remained considerably stable in spite of an overall decline in the entire floodplain area from the period where the city first experienced industrialisation in the 19th century to now. However, with river regulations and the alteration of forest management from coppice-with-standards forest to high forest in the 19th century, major changes can be found in the tree species composition of the floodplain forest. Comparing these findings with references from other European floodplain forests we discuss the impact of historical and current forest management as well as the city location''s influence on the extent and tree species composition of urban floodplain forests. For urban forest management in particular there is a great need to integrate biophysical, historical and forestry knowledge when predicting future developmental trends. [Copyright &y& Elsevier]

Abstract: In Europe, remnants of formerly widespread natural mixed forests are rare. We analyzed an exceptionally tall tree stand with a very high wood volume in Hrončokovský grúň reserve, covering 55.2ha in Slovenské Rudohorie Mountains in central Slovakia (48°43′N and 19°35′E) between 730 and 1050m a.s.l. We compared our data to other natural stands to see if the growing stock and tree height were higher in Hrončokovský grúň. Fifty-four circular plots of 0.05ha each and spaced at 100m×100m distance sampled the entire reserve. Within each plot, live and dead trees were measured. Number, basal area and volume of live trees and volume of CWD were calculated. Moreover, measurements of the tallest trees were conducted in the whole reserve area. Total volume of live trees and CWD in the studied reserve was 1030m3 per hectare. It is the second highest value ever recorded in an area of several hectares or larger in European forests. The feature that makes the stand in Hrončokovský grúň a unique one is the height of trees. In the whole reserve, about 600 trees exceeded the height of 45m. Individuals of three deciduous species (Acer pseudoplatanus, Fraxinus excelsior, Ulmus glabra) are the tallest ones found in unmanaged forests in the whole Europe. Those of Fagus sylvatica reached height near the maximum value ever recorded. In Europe, stands of average total live and dead wood volume above 1000m3 ha−1 with numerous trees above 40m tall were probably very rare even several centuries ago, when virgin forests were widespread. Most likely, they were confined to rather small mountain areas, where rich soils supporting high stand productivity occurred along with wind-protected slopes, where natural disturbances were rare and stand turnover rate was low. [Copyright &y& Elsevier]

Abstract: Low intensity grazing with large herbivores is increasingly used to steer the development of mosaic landscapes (including wood-pastures) and woodland expansion on former agricultural land. We studied the establishment and early growth pattern of woody species in grasslands (formerly used for high intensity summer cattle grazing) in which a low intensity-grazing regime was set up between 4 and 11 years ago. We tested whether the developing vegetation patches, consisting of tall herbs and scrub, influenced this pattern. Further, we investigated if increased susceptibility to trampling disturbance by large herbivores on wet soils in floodplains influenced sapling establishment. Formerly intensively used grasslands were studied at six sites, four in floodplains and two in interfluvial zones on nutrient rich, heavy soils. In total, we sampled 141 plots with grassland, tall herb or scrub vegetation and recorded individuals of established tree and shrub species, their height, diameter, browsing damage and distance to potential seed sources. In the floodplains, we recorded soil disturbance by large herbivores (hoofprints) in wet and moist soils. Sapling frequencies, with Fraxinus excelsior as the most common species (>50% of all individuals), were two to three times higher in tall herb and scrub patches compared to grassland. Only the spiny Crataegus monogyna established in higher frequencies in grassland plots. In floodplains, we found two to three times more established woody saplings in wet tall herb plots, compared to moist and wet grassland plots and moist tall herb plots. Browsing reduced sapling height in grassland and tall herb patches. Only in scrub patches did average height (±2.5m) reach above the browse line. We found 30–70% less browsing damage to saplings in scrub compared to damage in grassland and tall herb plots. In particular, damage to the apical shoot was strongly reduced. Our findings show that tree establishment occurs in spatial association with non-grassland patches that offer protection against browsing. Fast growing spiny shrubs like Rubus sp. offer protection for palatable saplings, allowing establishment and growing out beyond the browse line. Alternatively, increased establishment occurs in wet tall herb patches, where soil disturbance by moderate trampling favours germination and, subsequently, saplings are protected at least temporarily against browsing by unpalatable tall herbs. [Copyright &y& Elsevier]

Abstract: Under natural conditions the zonation of woody species in floodplains is to a large extent determined by hydrological conditions. Flood survival varies even among closely related species of the same genus. Most studies that quantify flood survival of seedlings and saplings of European floodplain species focus on species of the genera Salix and Populus, while few studies on saplings of Quercus robur, Fraxinus excelsior, Crataegus monogyna have been carried out, and even less on comparing these species groups. We performed a comparative observational study on the presence of saplings (<150cm) of Quercus robur, Fraxinus excelsior, Crataegus monogyna (hardwood species), Salix alba, Salix viminalis and Populus nigra (softwood species) in nature reserves along the Lower Rhine in the Netherlands. For each plot (n =1178) the duration, frequency and depth of inundation was determined. This was done for both the entire year (January–December) and the growing season (March–October). We found that the presence of the hardwoods decreased with increasing inundation duration and even more so if the inundation occurred during the growing season. Contrary to what is generally assumed, the negative effects of flooding were stronger for F. excelsior than for Q. robur. For the hardwood group the total annual inundation duration was the best explanatory variable. The presence of the softwood species increased with increasing inundation duration and more so if the inundation occurred during the growing season. The average duration per inundation event was the best explanatory variable for this group, especially for both Salix species. The presence of P. nigra was best explained by the average inundation depth. A canonical correspondence analysis on species composition was consistent with these findings. Overall, our results agree with the general perspective of tree zonation along rivers. This is the first study that shows the singular and combined effects of several flooding characteristics on both presence, and species composition, of softwood and hardwood species from riparian woodlands. We outline an approach indicating how the results can be used for the selection of sections in retention areas suitable for the recruitment of the studied tree species. [Copyright &y& Elsevier]

Abstract: In northern temperate climates, broad-spectrum contact acting herbicides could be used in the dormant season to remove established herbaceous weeds, and release trees from competition. Unfortunately, there is little published information on broadleaved tree tolerance. In an experiment on open-grown 2-year-old planting stock, 1.1kga.i.ha−1 paraquat was found to be generally safe to spray over dormant oak (Quercus robur), ash (Fraxinus excelsior), sycamore (Acer pseudoplatanus), cherry (Prunus avium), birch (Betula pendula), alder (Alnus glutinosa), and sweet chestnut (Castanea sativa), provided no immature buds, bark, or leaves were present. Survival of these species was unaffected, although there were occasional reductions in subsequent growth. Poplar (Populus sp.) and willow (Salix sp.) were severely damaged. Growth and survival of dormant beech (Fagus sylvatica) transplants were also apparently unaffected. Previous work has suggested that younger seedlings may respond differently than older, larger transplant stock, particularly where seedlings have grown amongst dense weed cover and are less dormant. Hence in a further experiment on 1-year-old container grown ash seedlings kept outdoors, glyphosate and paraquat were applied at two doses as an overall spray in January and before bud-burst in March. None of the treatments had any apparent adverse effects. In a field experiment, plots of ash seedlings were kept weed-free or grown with a natural population of weeds for one season, then paraquat sprayed at five doses (0.4–2.0kga.i.ha−1) in late March over the dormant seedlings. Paraquat had no apparent effect on either plant type. First-year weed competition reduced height increment but not survival, although growth recovered once weeds were removed. Seedlings grown in unweeded conditions flushed earlier than those grown in weed-free conditions, potentially making them more susceptible to early spring frosts. This work suggests applications of up to 1.1kga.i.ha−1 paraquat may be tolerated by dormant ash seedlings grown in open conditions, and this could be a useful treatment for controlling over-wintering weeds in direct sown woodlands, forest nurseries and in natural regeneration situations, where an overstorey of trees is not present. [Copyright &y& Elsevier]

This paper reviews site factors that influence early growth of ash (Fraxinus excelsior L.). Sites where ash will grow well can now be described in terms of the ecological site classification of Pyatt et al. (2001) [An ecological site classification for forestry in Great Britain. Forestry Commission Bulletin 124. Forestry Commission, Edinburgh]. Good sites are where the climate is ‘warm’ (>1376 day-degrees>5.6 °C), soil moisture is ‘fresh’ to ‘very moist’ (generally meaning that depth to the winter water table is between 40 and 100 cm) and soil nutrient status is ‘rich’ and ‘very rich’ (generally soil pH in the range of 5.0–7.5). These preferences are explored with reference to more detailed information concerning the influence of water, nutrients, light and patterns of shoot and root growth. [Copyright &y& Elsevier]

The effect of soil type and light availability on a natural regeneration community comprising of several shade tolerant species was studied in 120-year-old managed, beech-dominated, forest in the Czech Republic. Full inventory of natural regeneration was conducted and a light climate (canopy openness, DSF, ISF, TSF) determined from hemispherical photographs on 81 sampling plots (3.14 m2 each) belonging to two distinctly different soil types (Calcaric regosol and Calcaric cambisol). The effect of light and soil on basal diameter and height of nine naturally regenerated tree species was examined. The mean density of natural regeneration was about 160 000 ind./ha, which is several times higher than recommended afforestation rates. Density of natural regeneration was independent of soil type and negatively regressed to canopy openness, probably as a result of increased competition with herbal vegetation in open spots. Mean height of natural regeneration was significantly related to soil type and available light. Although species composition of the regeneration community was similar on both soil types, the partitioning of species differed greatly. Influence of soil and light availability on seedling diameter and height differed among species. Soil had significant effect on height of elm and sycamore maple and on basal diameter of elm. Light climate had significant effect on height of beech and diameter of beech and Norway maple. Browsing by deer was found to be an important factor determining natural regeneration community development. Ash, maple and elm were the most preferred with up to 100% of individuals being browsed while less than 15% of beech seedlings were damaged. [Copyright &y& Elsevier]

• Tree-ring chronologies of four temperate broad-leaved tree species were studied. • Growth always responded negatively to high summer temperatures and climatic aridity. • Climate sensitivity of growth decreased in the period 1967–2016. • Larger growth reduction during severe drought in diffuse- than ring-porous species. • Minor timber species deserve broader consideration in silvicultural concepts. Climate warming and a rise in evaporative demand expose forests to increasing stress, challenging silvicultural planning in many temperate forest regions. As some major timber species are drought susceptible, the choice of native broadleaf minor timbers with assumed higher drought tolerance is a promising alternative option. However, their growth performance and vitality in a warmer and drier climate are not well known. We studied tree-ring chronologies of the Central European minor timbers Acer platanoides L. , Fraxinus excelsior L., and Tilia cordata Mill. in comparison to the widely planted Quercus petraea Matt. Liebl in different mixed stands along a precipitation gradient in Central Germany and analyzed the sensitivity of radial growth to climatic drivers and severe drought events with the aim to compare the species' drought tolerance. While growth responded in all four species positively to summer (or spring) precipitation and negatively to higher summer temperature and climatic aridity, climate sensitivity of growth decreased in the period 1967–2016, proving non-stationarity. Superposed epoch analysis revealed larger growth reduction during severe drought in the diffuse-porous species (A. platanoides, T. cordata) than the ring-porous species (Q. petraea, F. excelsior), but resilience was high in all species. Moreover, none of the species showed negative growth trends with recent climate warming, and drought sensitivity was not higher at drier sites, suggesting a considerable acclimation and adaptation potential to increasing drought stress. As all four species proved to be fairly drought tolerant, they deserve broader consideration in silvicultural concepts targeted at adapting production forests to climate warming. [ABSTRACT FROM AUTHOR]