Effects of airborne sea salts on soil water acidification and leaching of aluminium in different forest ecosystems in Denmark

Studies on biogeochemical cycling of elements are performed in even aged forest ecosystems of Norway spruce, Sitka spruce and beech at several locations in Denmark. Episodes with high sea salt deposition and unusual low water surplus percolation caused extreme salt concentrations in the soil solutions. The changes were smallest beneath beech stands and most pronounced at the most salt-affected Sitka spruce stands. Contemporary, the pH drops and the Al³⁺ concentration increased above 20 mg L^-1 owing to cation exchange with Na⁺. The Cl^- and Al³⁺ concentrations reached levels reported as toxic for Norway spruce, but not for Sitka spruce and beech. The changes in the soil water chemistry must be considered as important factors for the reduced vitality in Norway spruce ecosystems in Denmark.     

Deposition and soil leaching in stands of Norway spruce and European Beech: Results from the Höglwald research in comparison with other European case studies

Stands of Norway spruce (Picea abies K.) and European beech (Fagus sylvatica L.) were investigated at the Höglwald research area, Southern Germany from 1985–1988 and from 1994–1997 in order to determine the effects of tree species on deposition and soil solution fluxes. The results were compared to 15 European case studies representing different deposition levels and site conditions. At the Höglwald site, which is characterised by a high nitrogen and a moderate sulphur load, throughfall deposition of nitrogen and sulphur compounds was about two-fold higher in spruce stands compared to beech stands. The differences in elemental input were clearly reflected in soil solution chemistry with a higher leaching of nitrate and sulphate in the spruce stands. The turnover of sulphur and nitrogen compounds induced a strong soil internal production of protons especially in the spruce stands. These results are in accordance with the other European case studies. Throughfall deposition and soil leaching of nitrogen and sulphur compounds was generally higher for spruce stands compared to beech stands. The species-related differences were mainly caused by dry deposition and were relatively small in remote areas. The consequences for the forest ecosystem itself and for the hydrosphere are discussed.     

The effect of femel- and small scale clear-cutting on ground dwelling spider communities in a Norway spruce forest in Southern Germany

The early effects of femel-cutting (removing 20% of the trees) and small scale clear-cutting on ground-living spiders in a Norway spruce (Picea abies (L.) Karst.) forest in Southern Germany were investigated. The study was carried out as BACIP (before and after, control-impact, many paired samplings) study: Spiders were sampled during the pre-treatment year, the year of cutting, and the year after cutting. In total 7101 individuals were sampled, of which 4530 individuals were identified, 4468 were adult and 2633 individuals were juvenile. We identified 107 species, but a single species, Coelotes terrestris, dominated the control (spruce stand) comprising up to 49% of the total identified individuals. Clear-cutting changed the species composition in the traps, while the first step in femel-cutting preserved it. The number of individuals of the families Linyphiidae, Amaurobiidae, Agelenidae and Clubionidae decreased drastically within the 2 years after the clear-cutting, while the Lycosidae became numerically dominant in the clear-cut stands. The number of individuals with the following characterisation decreased significantly after clear-cutting: Small (<3.0 mm) and large spiders (>10.5 mm), web builders, ‘forest habitat species’, species favouring hygrophilic to medium moisture conditions, and preferences to live below ground or in and on the moss layer. On the other hand, middle-sized spiders, free hunters, ‘open habitat species’, spiders favouring dry conditions or that are euryoecious, preferring patterns covered by grasses or uncovered patches, increased in number. Clear-cut habitats with dense spruce regeneration showed a delayed and less pronounced response. With femel-cutting, species composition of ground-living spider communities may be preserved during the first step of regeneration of mature forest stands.     

Changes in soil properties after afforestation of former intensively managed soils with oak and Norway spruce

In many European countries, surplus agricultural production and ecological problems due to intensive soil cultivation have increased the interest in afforestation of arable soils. Many environmental consequences which might rise from this alternative land-use are only known from forest establishment on less intensively managed or marginal soils. The present study deals with changes in soil properties following afforestation of nutrient-rich arable soils. A chronosequence study was carried out comprising seven Norway spruce (Picea abies (Karst.) L.) and seven oak (Quercus robur L.) stands established from 1969 to 1997 on former horticultural and agricultural soils in the vicinity of Copenhagen, Denmark. For comparison, a permanent pasture and a ca. 200-year-old mixed deciduous forest were included. This paper reports on changes in pH values, base saturation (BS_eff), exchangeable calcium, soil N pools (N_min contents), and C/N ratios in the Ap-horizon (0–25 cm) and the accumulated forest floor. The results suggest that afforestation slowly modifies soil properties of former arable soils. Land-use history seems to influence soil properties more than the selected tree species. An effect of tree species was only found in the forest floor parameters. Soil acidification was the most apparent change along the chronosequence in terms of a pH decrease from 6 to 4 in the upper 5 cm soil. Forest floor pH varied only slightly around 5. Nitrogen storage in the Ap-horizon remained almost constant at 5.5 Mg N ha^–1. This was less than in the mineral soil of the ca. 200-year-old forest. In the permanent pasture, N storage was somewhat higher in 0–15 cm depth than in afforested stands of comparable age. Nitrogen storage in the forest floor of the 0–30-year-old stands increased in connection with the build-up of forest floor mass. The increase was approximately five times greater under spruce than oak. Mineral soil C/N ratios ranged from 10 to 15 in all stands and tended to increase in older stands only in 0–5 cm depth. Forest floor C/N ratios were higher in spruce stands (26.4) as compared to oak stands (22.7). All stands except the youngest within a single tree species had comparable C/N ratios.     

Experimental evidence of a deleterious soil microflora associated with Norway spruce decline in France and Germany

Norway spruce (Picea abies (L.) Karst.) seedlings were grown in a glasshouse pot experiment in soils from 11 declining and 7 healthy spruce stands from France and Germany. In soils from 9 declining stands, seedlings showed decline symptoms (needle yellowing). Soil pasteurization suppressed the symptoms, and reinoculation of the pasteurized soil with a rhizospheric extract from the corresponding stand re-induced yellowing. This suggests that a deleterious soil microflora is associated with spruce decline. The occurrence of this microflora seems to be correlated with the main chemical characteristics of the soils (low pH, low saturation of the adsorbing complex, low exchangeable Ca²⁺ and Mg²⁺, and high level of exchangeable Al). ei]R F Huettl     

Biomass, morphology and nutrient contents of fine roots in four Norway spruce stands

Fine root systems may respond to soil chemical conditions, but contrasting results have been obtained from field studies in non-manipulated forests with distinct soil chemical properties. We investigated biomass, necromass, live/dead ratios, morphology and nutrient concentrations of fine roots (<2 mm) in four mature Norway spruce (Picea abies [L.] Karst.) stands of south-east Germany, encompassing variations in soil chemical properties and climate. All stands were established on acidic soils (pH (CaCl₂) range 2.8–3.8 in the humus layer), two of the four stands had molar ratios in soil solution below 1 and one of the four stands had received a liming treatment 22 years before the study. Soil cores down to 40 cm mineral soil depth were taken in autumn and separated into four fractions: humus layer, 0–10 cm, 10–20 cm and 20–40 cm. We found no indications of negative effects of N availability on fine root properties despite large variations in inorganic N seepage fluxes (4–34 kg N ha⁻¹ yr⁻¹), suggesting that the variation in N deposition between 17 and 26 kg N ha⁻¹ yr⁻¹ does not affect the fine root system of Norway spruce. Fine root biomass was largest in the humus layer and increased with the amount of organic matter stored in the humus layer, indicating that the vertical pattern of fine roots is largely affected by the thickness of this horizon. Only two stands showed significant differences in fine root biomass of the mineral soil which can be explained by differences in soil chemical conditions. The stand with the lowest total biomass had the lowest Ca/Al ratio of 0.1 in seepage, however, Al, Ca, Mg and K concentrations of fine roots were not different among the stands. The Ca/Al ratio in seepage might be a less reliable stress parameter because another stand also had Ca/Al ratios in seepage far below the critical value of 1.0 without any signs of fine root damages. Large differences in the live/dead ratio were positively correlated with the Mn concentration of live fine roots from the mineral soil. This relationship was attributed to faster decay of dead fine roots because Mn is known as an essential element of lignin degrading enzymes. It is questionable if the live/dead ratio can be used as a vitality parameter of fine roots since both longevity of fine roots and decay of root litter may affect this parameter. Morphological properties were different in the humus layer of one stand that was limed in 1983, indicating that a single lime dose of 3–4 Mg ha⁻¹ has a long-lasting effect on fine root architecture of Norway spruce. Almost no differences were found in morphological properties in the mineral soil among the stands, but vertical patterns were apparently different. Two stands with high base saturation in the subsoil showed a vertical decrease in specific root length and specific root tip density whereas the other two stands showed an opposite pattern or no effect. Our results suggest that proliferation of fine roots increased with decreasing base saturation in the subsoil of Norway spruce stands.     

Reversing borealization as a means to restore biodiversity in Central-European mountainforests – an example from the Krkonoše Mountains, Czech Republic

Forestry in the Central-European mountains is confronted with a severe forest decline, which is attributed to the combined effects of 'borealization', brought about by large scale continued spruce (mainly Picea abies) monocultures, and atmospheric deposition. Borealization is defined as enhanced soil acidification and litter accumulation, retarded nutrient cycling and changed forest climate in such planted coniferous forest ecosystems. An additional effect of borealization is a major decline in biodiversity of the stands. Based on a comparative study of Norway spruce and European beech stands in the Krkonoe National Park (Czech Republic), it is concluded that traditional management should be abandoned and that management should instead focus on regeneration towards broad-leaved or mixed forest stands, to enhance the stability of forest ecosystems and their biodiversity, and to reverse borealization in lower montane zones. Available surveys of forest typology were evaluated for their suitability in regeneration management and were found to be unsuitable, since they reflect the effects of borealization rather than true site conditions. The two main pioneer tree species, birch (Betula pendula) and mountain ash (Sorbus aucuparia), were found to improve soil conditions and reverse borealization. Furthermore, trends in natural vegetation and soil development in declined forests and clear-cuts, and their relevance for forest restoration management were studied, focusing on borealization and plant species diversity. It is concluded that this natural development offers very good possibilities for a more passive, low-cost restoration management.     

Effects of elevated soil solution Al concentrations on fine roots in a middle-aged Norway spruce (Picea abies (L.) Karst.) stand

Aluminium (Al), mobilized by acidic deposition, has been claimed to be a major threat to forest vitality. Fine root mortality, decreased root growth and reduced nutrient uptake have been observed in controlled laboratory experiments where roots of tree seedlings were exposed to elevated concentrations of Al. Yet, evidence for Al-induced root damage from forest stands is scarcely reported. Nevertheless, Al dissolved in soil water has received a key role in the critical load concept for forests. Here, we present effects of artificially elevated concentrations of Al in the soil solution on fine roots in a middle-aged stand of Norway spruce (Picea abies (L.) Karst.). Although the inorganic Al concentrations about 200 µM and Ca:Al ratio about 0.7 that were established in the soil solution within this experiment have been associated with reduction of root growth and root mortality for spruce seedlings in hydroponic studies, no acute damage on fine roots was observed. Three years of treatment did not cause visual root damage, nor were effects on fine root necromass observed. Fine root necromass made up about 10% of fine root biomass for all treatments. However, significantly lower molar Ca:Al and Mg:Al ratios in living and dead fine roots were found in the plots where Al concentrations were highest and ratios of Ca to Al in the soil solution were lowest. The lack of response on fine root biomass suggests that forest stands tolerate higher Al levels than results from laboratory experiments indicate. We conclude that effect studies in the laboratory have limited value for field conditions. The key role of Al toxicity, expressed as the Ca/Al ratio, in critical load calculations for forests may have to be reconsidered.     

Stability in the patterns of long‐term development and growth of the Canadian spruce–moss forest

Aim The spruce–moss forest is the main forest ecosystem of the North American boreal forest. We used stand structure and fire data to examine the long‐term development and growth of the spruce–moss ecosystem. We evaluate the stability of the forest with time and the conditions needed for the continuing regeneration, growth and re‐establishment of black spruce (Picea mariana) trees. Location The study area occurs in Québec, Canada, and extends from 70°00′ to 72°00′ W and 47°30′ to 56°00′ N. Methods A spatial inventory of spruce–moss forest stands was performed along 34 transects. Nineteen spruce–moss forests were selected. A 500 m² quadrat at each site was used for radiocarbon and tree‐ring dating of time since last fire (TSLF). Size structure and tree regeneration in each stand were described based on diameter distribution of the dominant and co‐dominant tree species [black spruce and balsam fir (Abies balsamea)]. Results The TSLF of the studied forests ranges from 118 to 4870 cal. yr bp . Forests < 325 cal. yr bp are dominated by trees of the first post‐fire cohort and are not yet at equilibrium, whereas older forests show a reverse‐J diameter distribution typical of mature, old‐growth stands. The younger forests display faster height and radial growth‐rate patterns than the older forests, due to factors associated with long‐term forest development. Each of the stands examined established after severe fires that consumed all the soil organic material. Main conclusions Spruce–moss forests are able to self‐regenerate after fires that consume the organic layer, thus allowing seed regeneration at the soil surface. In the absence of fire the forests can remain in an equilibrium state. Once the forests mature, tree productivity eventually levels off and becomes stable. Further proof of the enduring stability of these forests, in between fire periods, lies in the ages of the stands. Stands with a TSLF of 325–4870 cal. yr bp all exhibited the same stand structure, tree growth rates and species characteristics. In the absence of fire, the spruce–moss forests are able to maintain themselves for thousands of years with no apparent degradation or change in forest type.     

The role of planted forests in the provision of habitat: an Irish perspective

The continued decline of natural forests globally has increased interest in the potential of planted forests to support biodiversity. Here, we examine the potential conservation benefits of plantation forests from an Irish perspective, a country where remaining natural forests are fragmented and degraded, and the majority of the forest area is comprised of non-native Sitka spruce (Picea sitchensis (Bong.) Carr.) and Norway spruce (Picea abies (L.) Karst.) plantations. We examine the true value of Irish plantation forests to native biodiversity, relative to remaining natural forest fragments, and to prior and alternative land use to afforestation. We find that plantation forests provide a suitable surrogate habitat primarily for generalist species, as well as providing habitat for certain species of conservation concern. However, we find that plantation forests provide poor habitat for native forest specialists, and examine potential management strategies which may be employed to improve habitat provision services for this group.     

Nesting Ecology of Boreal Forest Birds Following a Massive Outbreak of Spruce Beetles

Abstract: We studied breeding dark-eyed juncos (Junco hyemalis), yellow-rumped warblers (Dendroica coronata), and spruce-nesting birds from 1997 to 1998 among forests with different levels of spruce (Picea spp.) mortality following an outbreak of spruce beetles (Dendroctonus rufipennis) in Alaska, USA. We identified species using live and beetle-killed spruce for nest sites and monitored nests to determine how the outbreak influenced avian habitat selection and reproduction. We tested predictions that 1) nesting success of ground-nesting juncos would increase with spruce mortality due to proliferation of understory vegetation available to conceal nests from predators, 2) nesting success of canopy-nesting warblers would decrease with spruce mortality due to fewer live spruce in which to conceal nests, and 3) both species would alter nest-site selection in response to disturbance. Juncos did not benefit from changes in understory vegetation; nesting success in highly disturbed stands (46%) was comparable to that in undisturbed habitats throughout their range. In stands with low spruce mortality, nesting success of juncos was low (5%) and corresponded with high densities of red squirrels (Tamiasciurus hudsonicus). Yellow-rumped warblers nested exclusively in spruce, but success did not vary with spruce mortality. As disturbance increased, nesting warblers switched from selecting forest patches with high densities of live white spruce (Picea glauca) to patches with beetle-killed spruce. Warblers also placed nests in large-diameter live or beetle-killed spruce, depending on which was more abundant in the stand, with no differences in nesting success. Five of the 12 other species of spruce-nesting birds also used beetle-killed spruce as nest sites. Because beetle-killed spruce can remain standing for >50 years, even highly disturbed stands provide an important breeding resource for boreal forest birds. We recommend that boreal forest managers preserve uncut blocks of infested forest within managed forest landscapes and practice partial harvest of beetle-killed spruce rather than commercial clear-cutting of infested stands in order to sustain breeding bird populations until natural reforestation occurs. Because breeding densities do not always reflect fitness, assessing impacts of a massive natural disturbance should include measuring impacts of changes in vegetation on both reproductive success and predator-prey dynamics.     

Structure and stand development in three subalpine Norway spruce (Picea abies (L.) Karst.) stands in Paneveggio (Trento, Italy)

1. Three permanent plots (100×0 m) were established in the subalpine Norway spruce (Picea abies (L.) Karst.) forest of Paneveggio in the spring of 1993, to begin a long-term forest ecosystem research project. The main purpose of these plots was to provide information about subalpine Norway spruce stand dynamics and to provide suggestions for close-to-nature silviculture. 2. The three stands were selected to represent the most common forest structures in the Paneveggio forest. The first stand is close to forestry roads, has a relatively regular and continuous canopy, and thinning and cutting operations only ended in the 1980s; the second stand is far from forest roads and has developed without anthropogenic influence for several decades; the third one is located at the present upper limit of the pure spruce forest and, apparently, was heavily used in the past as a pasture. 3. The first step in the investigation was to describe the structure and to study the history of the three stands using both written evidence from manage- ment plans and biological archives from tree rings. 4. The stands in plots 1 and 2 began to establish after a disturbance that removed part of the previous stands according to dendroecological studies, which are partially supported by written evidence. The remaining parts of these stands were eliminated by two major disturbances that occurred during the following decades. Written records about the use of the forest lead us to assume that the initial disturbances that occurred in the two stands were logging activities as a part of a group shelterwood system. The stand in plot 2 has developed without significant human interference for about half a century as confirmed by the presence of many dead trees. The stand in plot 3 consists of old trees that were part of an open stand and a secondary population that established after cessation of grazing. 5. The study has confirmed that dendroecological techniques can be used to identify occurrence and intensity of previous disturbance in forests stands, although at Paneveggio it is difficult to distinguish between natural and anthropogenic disturbances in the tree ring record. The presence of human activity necessitates investigation of multiple lines of evidence. 6. Paneveggio's forest management plans were useful in the interpretation of the data obtained through dendroecological analysis, although events did not always correspond because data from the management plans (yearly thinning, felling, wind-throw damage) never gave stand-level details, but applied to areas of several hectares. Despite these limitations, the information included in the management plans is of crucial importance in studying stand history and only by using all these sources of information is it possible to delineate the most important features of the history and disturbance that affected the origin and subsequent growth of the forest stands.     

Belowground ectomycorrhizal communities in three Norway spruce stands with different degrees of decline in the Czech Republic

We investigated the ectomycorrhizal communities on the roots of adult trees and seedlings associated with three Norway spruce stands in the Czech Republic using morphological and molecular tools. The stands had different degrees of forest decline due to air pollution. The aims of the study were to obtain information about the belowground ectomycorrhizal community in a heavily damaged spruce forest and to assess whether missing ectomycorrhizal fungal partners could be one of the reasons for the observed lack of regeneration. The ectomycorrhizal species richness on the roots of adult trees was significantly lower in the heavily damaged site Mumlavska hora than in the other two, but less drastically so than that found in a fruitbody survey. The roots of adult trees and seedlings were fully mycorrhizal at this site although they were less species-rich. The most abundant ectomycorrhizal species on the root system of adult trees in all three forest stands was Tylospora fibrillosa, a member of the athelioid clade. It made up over 60% of root tips in Mumlavska hora and its proportion was at least twice that in the other two sites. This species was also an efficient colonizer of roots from seedlings, in particular, in the most damaged site. The different soil properties in this site may have caused the observed differences in the ectomycorrhizal species richness and composition. For example, cation exchange capacity and soil base saturation were lower and the soil more often saturated. However, the number of living trees and their defoliation status may well directly impact the ectomycorrhizal species composition by presumably affecting the amount of carbon delivered to the symbiotic fungal partners. Athelioids and thelephoroids are an important component of the belowground ectomycorrhizal community in most temperate and boreal forests, but the role they play might even be more crucial in stressed forest ecosystems. Based on our results, we suggest that factors other than missing ectomycorrhizal inoculum constrain natural regeneration in the heavily damaged site Mumlavska hora.     

Community structure of soil oribatida (acari) two years after windthrow in the high tatra mountains

In November 2004 a catastrophic windstorm destroyed a large part of the spruce forest in the Tatra National Park (Slovakia). The majority of the windthrown area was cleared; only a small part was left uncleared, thereby allowing regeneration by natural succession. The aim of the present study was to assess the impact of the different forestry practices on soil Oribatida. Three different stands were selected for the study, where sampling took place in June and October 2006: control forest stands (REF), windthrown stands left for natural development (NEX) and clear-cut windthrown stands (EXT). The mean abundance of Oribatida recorded in REF and NEX stands was significantly higher than in EXT stands. Kruskal-Wallis test of mean abundance of adults as well as juveniles confirmed significant influence of treatment and date. The highest abundance of adults was found in control forest stands (REF). Post hoc multiple comparison proved significantly lower abundance of adults in clear-cut stands (EXT) compared with REF. The mean abundance of adults and juveniles was several times higher in stands left for natural development (NEX) than in EXT stands. The highest species richness was observed in REF, followed by NEX and EXT stands. Ordination method showed differences in species composition between studied treatments. Furthermore, a much lower abundance of Hermannia gibba, a dweller of leaf litter and upper soil layers, was recorded in cleared stands compared to the other stands. Indeed, windthrown stands had an obvious lower species richness than control stands. The ordination method used demonstrated a significant influence of both treatment and sampling date on the abundance and species richness of Oribatida. The present study showed that clear-cutting of wind-damaged spruce forest markedly decreases the abundance of soil Oribatida compared with windthrown forest stands left to natural succession.     

Silver fir stand productivity is enhanced when mixed with Norway spruce: evidence based on large‐scale inventory data and a generic modelling approach

Questions: How to evaluate the mixture effect on basal area increment in two‐species forest stands? Is a mixed Norway spruce–silver fir stand more productive than pure adjacent stands of either species? How to develop generic modelling approaches to assess mixture effects in forest stands? Location: In addition to a case study on Norway spruce–silver fir stands in French mountain forests, the generic approach used goes beyond local applications. Methods: We took advantage of National Forest Inventory data to develop a unique stand basal‐area‐increment model for pure and mixed stands of Norway spruce and silver fir that responds to ecological site conditions. The database was made up of 284 pure Norway spruce stands, 196 pure silver fir stands, and 323 mixed stands of these species. Results: Pure silver fir basal area increment is strongly influenced by spring climatic conditions, whereas pure Norway spruce is more influenced by soil conditions. The mixture of these species has a positive effect on silver fir, which decreases as the proportion of fir increases. In contrast, the mixture has no noticeable effect on Norway spruce. Conclusion: We developed a stand basal‐area‐increment model evidencing an advantage of the mixture on silver fir basal area increment, but not on Norway spruce. The mathematical formulation of the model developed is generic and can be used in all two‐species mixture situations. It also makes it possible to compare different mixture situations with each other.     

Impact of common European tree species and Douglas-fir (Pseudotsuga menziesii [Mirb.] Franco) on the physicochemical properties of the rhizosphere

Trees play a crucial role in nutrient cycling and ecosystem fertility, notably through rhizosphere processes. The aim of this study was to compare soil physicochemical properties between bulk soil and rhizosphere of several tree species, and to compare rhizosphere properties between fertilized and non-fertilized conditions. The soil sampling was performed in Breuil-Chenue forest (North-East of France) in seven stands: native forest (old beech (Fagus sylvatica L.) and oak (Quercus sessiliflora Smith) coppice with standards; CwS), beech, oak (Quercus petraea [Matt.] Liebl.), Douglas-fir and fertilised Douglas-fir, Norway spruce (Picea abies Karst.) and fertilised Norway spruce. Systematic soil sampling was performed at 0–3, 3–10, and 10–23 cm in 20 calibrated pits. The rhizosphere of the different species was generally enriched in C, N, Ca, Mg, and K. Interestingly, the same positive effect was observed in the fertilised plots. The rhizosphere effect varied between tree species for C, “base” cations, pH_water and cation exchange capacity. This study reveals that interactions between roots, microorganisms and soil can enrich the pool of nutrients in the rhizosphere compared to bulk soil whatever the soil fertility conditions, and that the magnitude of the rhizosphere effect depends on tree species.     

Assessment of site characteristics as predictors of the vulnerability of Norway spruce (Picea abies Karst.) stands to attack by Ips typographus L. (Col., Scolytidae)

The intensity of bark beetle Ips typographus L. (Col., Scolytidae) attack on Norway spruce (Picea abies Karst.) is known to vary greatly among stands. In a control strategy approach, previous studies investigated the relationships between the variability in intensity of I. typographus attack and site characteristics such as stand age and altitude, mean tree circumference, growth rate and nearest‐neighbour distance, soil moisture, pH in H₂O and KCl, and soil contents of C, N, K, P, Mg, Ca, Fe, Cu, Zn and Mn. The data analysis method used in these studies was mainly the multiple linear regression, with the mean number of attacks per spruce tree in a stand as variable to explain. Previous results showed that the expected vulnerability of a Norway spruce stand to attack by I. typographus can be estimated on the basis of simple information of easy access to the forester, when the data on the stand in question is used with others for fitting the regression model. Prediction of the vulnerability of a stand, without including its data in the fitting of the model, was shown to be more approximate. Therefore, the objectives of this study were: (1) to improve the performance of models predicting the vulnerability of Norway spruce stands to attack by I. typographus, based on site characteristics; (2) to assess the stability of such predictive models when these are built using a moderate number of stands; and (3) to incorporate the resulting information in a global approach to control and prevention. Published data were re‐analysed for these purposes. A jackknifed multiple linear regression procedure, in which each stand in turn is discarded when fitting the model (jackknife replication), is presented. A great variability in the models fitted, depending on the stand discarded, is observed. For instance, the number of explanatory variables retained ranges from one (i.e. soil P content, for five jackknife replications) to 10 (for one jackknife replication), for R²‐values ranging from 0.5 to 1.0 and for one influential stand (i.e. the same stand characterized by an atypically low number of insect attacks compared to other stands with similar soil P content) against many influential stands. Differences between the model finally selected here using the revisited data and the models proposed earlier are discussed. A path analysis diagram is proposed for a more comprehensive modelling of Norway spruce stand vulnerability to I. typographus attack, based on site characteristics.     

Habitat Conditions Associated With Lynx Hunting Behavior During Winter in Northern Washington

Abstract Effectively managing habitat for threatened populations of Canada lynx (Lynx canadensis) requires knowledge of habitat conditions that provide for the ecological needs of lynx. We snow-tracked lynx to identify habitat conditions associated with hunting behavior and predation during winters of 2002–2003 and 2003–2004 in the northern Cascade Range in Washington state, USA. We recorded number and success of predation attempts, prey species killed, and trail sinuosity on 149 km of lynx trails. Lynx killed snowshoe hares (Lepus americanus), red squirrels (Tamiasciurus hudsonicus), and cricetids more than expected in Englemann spruce (Picea engelmannii) and subalpine fir (Abies lasiocarpa) forests, where snowshoe hare densities were highest. Lynx killed prey less than expected in Douglas-fir (Pseudotsuga menziesii) and ponderosa pine (Pinus ponderosa) forests and forest openings. We used the sinuosity of lynx trails as an index of quality of habitat hunted. Lynx trails that included predation attempts were more sinuous than trail segments without predation attempts. Lynx trails had greater sinuosity in forest stands with high hare densities dominated by Engelmann spruce and subalpine fir than in stands with low hare densities dominated by Douglas-fir and ponderosa pine or in forest openings. We encourage forest managers to maintain or create sufficient understory cover to support high densities of snowshoe hares as foraging habitat for lynx.     

Nitrate leaching from three afforestation chronosequences on former arable land in Denmark

In regions dominated by agricultural activities, nitrogen (N) is recognized as a major pollutant in aquatic environments. In north‐western Europe, afforestation of agricultural land is part of a strategy to improve water quality. In Denmark, former arable land has been afforested during the past 40–50 years. This study evaluated the effect of afforestation of former arable land on nitrate leaching, based on three afforestation chronosequences. Precipitation, canopy throughfall and soil water were collected and soil moisture was monitored at two Danish locations, Vestskoven (nutrient‐rich, medium deposition) and Gejlvang (nutrient‐poor, high deposition). Afforestation was performed using Norway spruce [Picea abies (Karst.) L.] and common oak (Quercus robur L.) at Vestskoven and Norway spruce at Gejlvang. The results suggest that afforestation of former arable land initially leads to lower nitrate leaching than that occurring under the former agricultural land use, and largely below the standard of 50 mg NO⁻₃ L⁻¹ for groundwater to be utilized as drinking water. Nitrate concentrations became almost negligible in forest stands of 5–20 years of age. However, after canopy closure (>20 years) nitrate concentrations below the root zone and nitrate leaching tended to increase. This was attributed to increased N deposition with increasing canopy development and decreased N demand once the most N‐rich biomass compartments had been built up. Nitrate leaching started to increase at a throughfall deposition level of about 10 kg N ha⁻¹ yr⁻¹. Compared with nutrient‐poor sandy soils, nutrient‐rich clayey soils appeared more vulnerable to disturbance of the N cycle and to increased N deposition, leading to N saturation and enhanced nitrate leaching. In approximately the first 35 years after afforestation, nitrate leaching below the root zone was generally higher below oak than below Norway spruce.     

Plantations of exotic tree species in Britain: irrelevant for biodiversity or novel habitat for native species?

Novel or emergent ecosystems arising from human action present both threats and opportunities for biodiversity. It has been suggested that exotic species can “facilitate” or “inhibit” native biodiversity through habitat modification. In Britain, there is a discussion over the contribution to biodiversity of plantations of exotic conifer species as these are commonly thought to have little relevancy as a habitat for native biodiversity. To address this we compared the species richness of a range of different taxonomic groups (lichens, bryophytes, fungi, vascular plants, invertebrates and songbirds) in exotic and native forest stands of differing structural stages in northern and southern Britain. In terms of overall native species-richness there was no significant difference between the exotic and the native stands. In the north, six species groups showed higher values in the exotic Sitka spruce (Picea sitchensis) stands with the remaining six showing higher values in the native Scots pine (Pinus sylvestris) stands. Most notably, lichen species richness was much lower in the exotic stands compared to the native stands, whereas bryophyte and fungal species richness was proportionately higher in the exotic stands. In the south, five species groups (all invertebrate taxa) showed higher species richness in exotic Norway spruce (Picea abies) stands compared to native oak (Quercus robur) stands. Five species groups had higher species-richness in the oak stands, in particular lichens and fungi. It is concluded that emergent ecosystems of exotic conifer species are not irrelevant to biodiversity. Where already well-established they can provide habitat for native species particularly if native woodland is scarce and biodiversity restoration is an immediate priority.