Effects of experimental warming at the microhabitat scale on oak leaf traits and insect herbivory across a contrasting environmental gradient

Forest microclimatic variation can result in substantial temperature differences at local scales with concomitant impacts on plant defences and herbivory. Such microclimatic effects, however, may differ across abiotically contrasting sites depending on background environmental differences. To test these cross-scale effects shaping species ecological and evolutionary responses, we experimentally tested the effects of aboveground microhabitat warming on insect leaf herbivory and leaf defences (toughness, phenolic compounds) for saplings of sessile oak Quercus petraea across two abiotically contrasting sites spanning 9(degrees) latitude. We found higher levels of herbivory at the low-latitude site, but leaf traits showed mixed patterns across sites. Toughness and condensed tannins were higher at the high-latitude site, whereas hydrolysable tannins and hydroxycinnamic acids were higher at the low-latitude site. At the microhabitat scale, experimental warming increased herbivory, but did not affect any of the measured leaf traits. Condensed tannins were negatively correlated with herbivory, suggesting that they drive variation in leaf damage at both scales. Moreover, the effects of microhabitat warming on herbivory and leaf traits were consistent across sites, i.e. effects at the microhabitat scale play out similarly despite variation in factors acting at broader scales. These findings together suggest that herbivory responds to both microhabitat (warming) and broad-scale environmental factors, whereas leaf traits appear to respond more to environmental factors operating at broad scales (e.g. macroclimatic factors) than to warming at the microhabitat scale. In turn, leaf secondary chemistry (tannins) appears to drive both broad-scale and microhabitat-scale variation in herbivory. Further studies are needed using reciprocal transplants with more populations across a greater number of sites to tease apart plant plasticity from genetic differences contributing to leaf trait and associated herbivory responses across scales and, in doing so, better understand the potential for dynamics such as local adaptation and range expansion or contraction under shifting climatic regimes

Attitudes towards protection of biodiversity in forests

The focus of nature protection through area protection in Swedish forests has for a long time been on boreal, subalpine and alpine areas. Large areas have of this reason been protected in northern Sweden, while the protection of forest in southern Sweden, and especially in the temperate zone, have been almost neglected. Only 2,5 per cent of the land area in the southernmost county in Sweden, the county of Skåne, has some kind of protection today and considerably less of the forest is protected. Some possible reasons for this distorted balance of share of protected forest between northern and southern Sweden are: * The large share of state-owned forest in northern Sweden has facilitated the work with area protection. * The large share of forest owned by non-industrial private forest owners in southern Sweden and the relatively small estates in southern Sweden has been a hindrance in the implementation of area protections. * The long history of land use in southern Sweden has made it difficult to find areas with high nature values for protection, and these areas are very often scattered in the landscape. The need of protection of biodiversity in the forests of southern Sweden is largely due to the long history of land use. Southern Sweden has much more threatened species than northern Sweden, not only due to the land use history, but also due to the generally higher number of species in the south. The area of protected forest has however increased much in Skåne during recent years and many private forest owners have been involved in this process. The County Forestry Board of Södra Götaland has been the most active authority in the number of concerned estates and thereby influenced forest owners. The County Board of Skåne and the Swedish Environmental Protection Agency have implemented some new nature reserves and national parks. These areas are usually of larger size but concern in relation to their size fewer estates and thereby there are less forest owners influenced. The encroachment of these forms of protection is however most often to be considered of larger magnitude than the habitat protection and nature conservation agreements that are implemented by the County Forestry Board. This is not only due to the larger size of the areas but also due to differences in the forms of agreements. A large number of private forest owners have been influenced by the implementation of area protection of forest, and there is a lack of knowledge how the forest owners perceive these processes, even though some studies have been performed in the field. This study is a part of a joint Nordic project with the task "to study effects of various policy instruments and develop proposals concerning the development of policies within the field". A questionnaire, consisting of a set of questions in common for the joint project with some adjustments for regional differences and completed with a set of questions specific for this study, was sent to 241 addressees in Skåne. The addressees were private forest owners or previous private forest owners who had been involved in a process with the objective of an area protection of forest in the form of one or more of the protection types below: * National park * Nature reserve * Habitat protection * Nature conservation agreement The real response rate was 53 per cent and for another ten per cent the reason for absence of answers is known. The average age of the respondents was 58 years and 78 per cent were men. Most respondents had purchased their estate, often in combination with inheritance and gift. The respondents were rather independent of their income from the forestry on the estate. The average share of income from the forestry on the estate was 15 per cent while the median was much lower with five per cent. Still most of the respondents valued commercial wood the highest among the goods from their forest. Another important good was recreation. The change in share of income from the forestry on the estate after the area protection was implemented was small. The largest loss of income had the respondents with the 25 per cent highest shares of income from the forest. These respondents had on average ten per cent less of their income from the forestry on the estate after the area protection was implemented. Most respondents associated the concept biodiversity with species and ecosystems and/or with conservation of nature. A majority had the opinion that the owner of the land also is owner of the biodiversity, while they did not consider this ownership to imply an economical responsibility of preserving it. Most respondents thought that the state should have the main economical responsibility of the protection of forest. Many were satisfied with how large share of the forest that was protected in the Swedish private forest, and many more wanted the area of protected forest to increase than wanted it to decrease. However, they were not willing to protect forest without compensation. The type of compensation that was preferred by most respondents was a yearly compensation, only 31 per cent wanted a once-and-for-all payment. The once-and-for-all payment is the today most common way of compensating the landowners for the encroachment of an area protection and 82 per cent of the respondents for whom the protection process was completed had also gotten this kind of compensation. Many also wanted new land in exchange, which was only realised in one case, and is maybe often less feasible due to small size of the area. The respondents preferred agreements with the authorities were they remained owner of the land and the rights following it. Also this is in contrast to what is most common, the authorities usually buy the land or the right to use the land. They also wanted to be involved in the management of the protected areas, the only form of agreement that today involves the landowner in the management is the nature conservation agreements. The respondents that had been involved in the protection process to a large extent were in general more satisfied with it. Among the respondents that had been involved to a very or rather large extent there were 86 and 72 per cent, respectively, satisfied with the process, while the corresponding figure among the ones that had been involved to a very small extent was 8 per cent. The County Forestry Board had succeeded better than the County Board and the Environmental Protection Agency in involving the forest owner into the process. Thereby there were also more of the respondents satisfied with the process among the ones that had their main contact with the County Forestry Board. An underlying cause of this can be that the County Forestry Board's work usually concerns smaller areas, but it can also be so due to that the County Forestry Board has a long tradition and experience of contact with and education of forest owners. A majority of the respondents did not consider the compensation they had received to cover the economic losses of forest production due to the protection. Many of the respondents who considered themselves to be self-active in their forestry, did not consider the compensation to cover the loss of employment. Just a few of the respondents had made some changes in the management of the remaining part of their forest due to the implementation of the area protection. Neither changes positive to biodiversity nor changes negative to biodiversity were made at any considerable extent. The addressees were given 17 statements to which they were going to respond, to what extent they agreed with the statements. The statements concerned protection of biodiversity in general, protection of biodiversity in forest, and protection of biodiversity in the respondent's forest. There was no significant difference in attitude of the respondents due to which of the categories the statement belonged. The respondents were positive to nature protection, independent of what level it concerned. But it has to be mentioned that the statements concerning protection of biodiversity on the respondents own estate included the condition that the respondent was fully compensated for the encroachment. However, when the answers were analysed in relation to different characteristics of the respondents there were some differences found. Which sex the respondent belonged to was of importance for the level of agreement when the statement concerned protection of biodiversity in general. Women were more positive towards protection of biodiversity in general than men. No difference of this kind was found when the statement concerned protection of biodiversity on the estate of the respondent. The characteristics most important for how the forest owner responded to the statements concerning protection of biodiversity on his or her estate were: * General education * Membership of an environmental organisation * Size of forest * Income from the forestry on the estate * Share of own work on the estate * Felling per hectare Some characteristics were correlated with the size of the forest. Sex, income from the forestry on the estate and share of own work on the estate showed a correlation with the size of forest. The most important characteristics for the respondents' attitudes towards protection of biodiversity were characteristics closely connected with the intensity of the management of the forest on the estate. Many of these characteristics were also correlated with the size of the forest.Tyngdpunkten i det svenska naturskyddet har länge legat i de boreala, subalpina och alpina delarna av Sverige. Stora områden har därmed skyddats i norra Sverige, medan skyddet av skog i södra Sverige till stor del har förbisetts. Bara 2,5 procent av landarealen och en betydligt mindre del av skogen i Skåne är idag skyddad. Några anledningar till snedvridningen av skyddad skog mellan södra och norra Sverige är: - Den stora andelen av statligt ägd skog i norra Sverige har underlättat processen med naturskydd där. - Den stora andelen skog som ägs av privata enskilda skogsägare och den relativt stora ägosplittringen i södra Sverige har varit ett hinder i reservatsbildning och naturskyddsarbetet. - Markanvändningen i södra Sverige har pågått under längre tid än i de norra delarna av landet. Detta har försvårat arbetet med att finna områden lämpliga för reservatsbildning. Ett frågeformulär skickades till 241 adressater i Skåne. Adressaterna var enskilda privata skogsägare som hade varit berörda av en process med målsättningen att en eller flera av nedanstående skyddsformer skulle införas på deras mark. Frågeformuläret bestod av en bas av frågor som var gemensamma för det Nordiska projektet. Dessa anpassades dock till regionala förhållanden och kompletterades med ytterligare ett antal frågor av relevans för denna studie. De skyddsformer som var aktuella var: - Nationalpark - Naturreservat - Biotopskydd - Naturvårdsavta

Vegetation responses to pathogen-induced tree loss: Swedish elm and ash forests revisited after 32 years

Invasive fungal pathogens are an increasing problem globally and can cause strong effects on forest ecosystems. In this study, we contrast vegetation surveys in eutrophic elm (Ulmus glabra) and ash (Fraxinus excelsior) forests in southern Sweden, conducted just prior to the arrival of Dutch elm disease (DED) in 1989, and then again in 2021, several years after ash dieback (ADB) began. At the sample plot scale, species richness (& alpha;-diversity) of the upper tree layer strongly decreased from 1989 to 2021, and the mean cover of elm decreased from 27 to 1% and of ash from 29 to 13%. In the lower tree and shrub layers, elm and ash were replaced by other, mainly shade-tolerant, tree species. The cover and richness of the shrub layer increased in previously elm-dominated stands but not in ash-dominated stands. The extensive loss of canopy cover in elm stands caused a larger change in upper tree layer species composition and increased compositional variability (& beta;-diversity) between plots when compared to the ash stands. The direction of the changes in tree layer composition between the surveys varied with soil moisture and nutrient availability. While beech increased in less eutrophic plots, more nutrient-rich plots changed toward hornbeam or small-leaved lime, and wetter plots turned toward alder and bird cherry. Hence, our results indicate increased compositional diversity and alternative successional pathways for community reorganization following DED and ADB. Future research will reveal if these pathways will later merge or further split

Effects of fertilization on soil CH4 and N2O fluxes in young Norway spruce stands

Climate change mitigation strategies have increased the demand for wood products, resulting in an urgent need to increase wood production. One approach is to fertilize forest land, but this can influence greenhouse gas (GHG) fluxes within the ecosystem. The aim of this study was to examine the effects of forest N fertilization on soil CH4 and N2O fluxes in young Norway spruce (Picea abies (L.) Karst.) stands in southern Sweden. The gas fluxes were measured using flow-through non-steady-state dark chambers. In the first, long-term, experiment, half of the stand was fertilized twice (once in 2014 and once in 2016) with 150 kg ha(-1) of N, and gas flux measurements were taken throughout 2014-2017. In the second, dose, experiment, 0, 150, 300, or 450 kg ha(-1) of N was added to the stand in April 2016, and gas flux measurements were taken during April-December 2016. The dose experiment showed that the sink strength of CH4 decreased with increasing amounts of N; the long-term experiment indicated that repeated fertilization decreased the CH4 sink strength over time. Additionally, the long-term experiment indicated that, while significantly higher N2O emissions were recorded in the fertilization years, this was not detected in subsequent years, suggesting the effect to be short-lived. In the dose experiment, fertilization tended to increase the N2O emissions relative to the amount of fertilizer. However, despite the significant effects of fertilization on these GHGs, the summed fluxes were a fraction of the net uptake of C at the sites, as recorded in another study. These findings suggest that fertilizing forest land with commercial NP or NPK fertilizers corresponding to 150 kg ha(-1) of N, the level used in operational forestry in Sweden today, can be conducted without changing CH4 and N2O fluxes to any great extent

Broadleaf retention benefits to bird diversity in mid-rotation conifer production stands

Retention forestry involves saving important forest structures for flora and fauna during the final felling of a stand, including dead wood and variable amounts of living trees, i.e. green tree retention (GTR). Here we evaluate the long-term effects on avian diversity from GTR by surveying forest birds in 32 mid-rotation stands in southern Sweden, in which broadleaf GTR was present or absent. Complementing the many studies that have assessed GTR in clear-cuts, our results indicated that bird assemblages can also benefit from broadleaf GTR several decades after final felling in conifer dominated production stands. The GTR stands harboured a higher bird abundance and species richness than the control stands without GTR, and also appears to have benefited several important guilds, such as broadleaf-associated birds and cavity nesters. However, variation in the number trees retained, the species composition of retained trees, and their environmental context within the stand (e.g. density and proximity of surrounding production trees), limited our capacity to detect threshold requirements for GTR. In summary, our study provides a "glimpse into the future" as mid-rotation production stands with such old and large retained trees are unusual in today's landscape, but are expected to become more common in the decades to come, in Sweden and many other nations. Our study thereby provides provisional support for the continued and future use of this practice, and indicates that the biodiversity contribution of retention trees continues to occur several decades into the stand's rotation

From mixtures to monocultures: Bird assemblage responses along a production forest conifer-broadleaf gradient

Increasing the prevalence of broadleaf trees in conifer-dominated production forests is a recommended means of improving habitat availability for broadleaf and mixed-forest species. The implications for biodiversity are often measured by contrasting broadleaf-conifer mixtures with conifer-dominated stands. However, few studies include broadleaf-dominated stands in these assessments. Here we contrasted the bird assemblages of even-aged production forests along a mixture gradient from Norway spruce (Picea abies) dominated, to birch (Betula spp.) dominated stands in southern Sweden. We conducted point count surveys of bird individuals exhibiting breeding behaviour within 30 stands varying from <0.5% to over 98.5% broadleaf by basal area. A total of 355 birds were detected, comprising 36 bird species, seven of which are classified as near threatened by the Swedish Red-list. Our results indicate i) a distinct shift in bird community composition linked to the percentage of broadleaf trees at stand and landscape scales, ii) significantly higher bird species richness, evenness, and abundance in stands with a higher proportion of birch, iii) higher bird abundance in birch-dominated stands than in mixtures, and iv) shifts in bird species guilds as related to stand basal area, the amount of shrubs in the understory, and quantities of dead wood. All of these results have implications for the ways in which production forest management could be altered to enhance avian diversity, and we discuss these with respect to the use of broadleaf versus mixed-species stands

From broadleaves to conifers: The effect of tree composition and density on understory microclimate across latitudes

Forest canopies buffer the macroclimate and thus play an important role in mitigating climate-warming impacts on forest ecosystems. Despite the importance of the tree layer for understory microclimate buffering, our knowledge about the effects of forest structure, composition and their interactions with macroclimate is limited, especially in mixtures of conifers and broadleaves. Here we studied five mixed forest stands along a 1800 km latitudinal gradient covering a 7 degrees C span in mean annual temperature. In each of these forests we established 40 plots (200 in total), in which air and soil temperatures were measured continuously for at least one year. The plots were located across gradients of forest density and broadleaved proportions (i.e. from open to closed canopies, and from 100% conifer to 100% broadleaved tree dominance). Air minimum, mean and maximum temperature offsets (i.e. difference between macroclimate and microclimate) and soil mean temperature offsets were calculated for the coldest and warmest months. Forest structure, and especially forest density, was the key determinant of understory temperatures. However, the absolute and relative importance of the proportion of broadleaves and forest density differed largely between response variables. Forest density ranged from being independent of, to interacting with, tree species composition. The effect of these two variables was independent of the macroclimate along our latitudinal gradient. Temperature, precipitation, snow depth and wind outside forests affected understory temperature buffering. Finally, we found that the scale at which the overstory affects soil microclimate approximated 6-7 m, whereas for air microclimate this was at least 10 m. These findings have implications for biodiversity conservation and forest management in a changing climate, as they facilitate the projection of understory temperatures in scenarios where both forest structure and macroclimate are dynamic. This is especially relevant given the global importance of ongoing forest conversion from conifers to broadleaves, and vice versa

Interactions between local and global drivers determine long-term trends in boreal forest understorey vegetation

Aim Global change effects on forest ecosystems are increasingly claimed to be context dependent, indicated by interactions between global and local environmental drivers. Most examples of such context dependencies originate from temperate systems, while limited research comes from the boreal biome. Here we set out to test if interactions between climate warming, nitrogen deposition, land-use change resulting in increasing forest density, and soil pH drive long-term changes in understorey vegetation in boreal forests. Location Sweden. Time period 1953-2012. Major taxa studied Vascular plants. Methods We used long-term (50 years) National Forest Inventory data on forest understorey vegetation in Sweden to model the combined effects of climate warming, nitrogen deposition, increase in forest density (tree basal area), and soil pH. Results Our results identify increasing temperature, nitrogen deposition and denser, shadier forest conditions as the main drivers of understorey vegetation changes during this time period. More importantly, we found that these effects varied with local conditions, that is, that the change towards a more nitrophilic understorey vegetation was more pronounced at low than high soil pH. Forest density was an important modulator of nitrogen deposition and temperature increase, with effects generally decreasing with density. Decreased cover of ericaceous dwarf shrubs was driven by both forest density and nitrogen deposition, with a stronger effect at low than at high pH. Main conclusions Our results highlight that to understand forest ecosystems' response to global change, and to make adequate management decisions to mitigate the effects of global change, we need to understand how changes in local environmental factors (forest density and soil pH) interact with global-scale drivers (nitrogen deposition and climate warming). Neglecting such interactions will lead to incorrect estimations of effects. In our case, we would for example, have underestimated the eutrophication effects on acid soils, which constitute a considerable part of the boreal biome