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  • 1
    In: Journal of Ecology, Wiley, Vol. 109, No. 7 ( 2021-07), p. 2678-2691
    Abstract: Mixed‐species forests often enhance the provision of ecosystem functions, both above‐ and below‐ground. Several of these effects are mediated by the amount and spatial distribution of tree tissues. However, previous studies on tree diversity effects on fine‐root biomass (FRB) have returned inconsistent results and did not distinguish between absorptive and transport fine roots. Furthermore, owing to the lack of species‐specific data, it is not well understood whether complementarity or selection effects contribute more to these mixing effects. Here, we analysed tree species mixing effects on fine‐root traits while considering the respective tree species contributions and root functional types. Specifically, we tested whether tree species mixing increases FRB and root length density (RLD) and results in vertical root stratification. We quantified FRB and RLD in 30‐cm deep soil profiles for 13 tree species in mixed and pure stands across four widespread European forest types. The differentiation of different fine‐root species in mixtures allowed us to disentangle complementarity and selection effects. Across all sites, mixtures supported on average less FRB than pure stands, which was reflected in negative complementarity and selection effects. RLD of absorptive fine roots did not change across the soil profile and even increased in the topsoil, which was associated with positive complementarity effects. There was no evidence for vertical root stratification. Conifer proportion, which was mainly associated with selection effects, dampened net diversity effects. Root functional type further influenced tree species mixing effects. Synthesis . Despite the underyielding of FRB in mixtures, overall soil occupation by absorptive fine roots (RLD) did not decrease in mixtures, pointing to morphological root trait adaptations associated with higher resource‐use efficiency. Increased RLD in the most nutrient‐rich layer in mixtures further indicates complementary interactions among species and a greater resource uptake capacity. This work illustrates that considering only one aspect of trait‐functioning relationships, for example, root biomass, may not capture the full effect of plant diversity on ecosystem functioning. The integration of a larger range of relevant traits is required. Moreover, traditional classification of fine roots based on the 2‐mm diameter cut‐off may obscure responses of roots to environmental changes.
    Type of Medium: Online Resource
    ISSN: 0022-0477 , 1365-2745
    URL: Issue
    Language: English
    Publisher: Wiley
    Publication Date: 2021
    detail.hit.zdb_id: 3023-5
    detail.hit.zdb_id: 2004136-6
    SSG: 12
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  • 2
    In: Journal of Ecology, Wiley, Vol. 109, No. 7 ( 2021-07), p. 2649-2661
    Abstract: In den letzten Jahrzehnten haben die Wälder der gemäßigten Zone Europas wiederholt unter schweren Dürreperioden gelitten. Durch Trockenheit geschwächte Wälder sind oft anfälliger für Befall mit Schädlingen wie z.B. Borkenkäfer geworden. Es wird erwartet, dass Baumartenvielfalt die Resistenz gegen Trockenheit und Schädlinge erhöht, aber bisher gibt es nur wenige Hinweise dafür, dass Baumdiversität den Befall mit Insektenschädlingen reduziert. In dieser Studie haben wir die Auswirkungen der Baumdiversität und der biogeographischen Herkunft der Baumarten auf den Borkenkäferbefall in einem großen, jungen Baumdiversitätsexperiment mit sechs Laub‐ und sechs Nadelbaumarten aus Europa und Nordamerika getestet. Nach einer starken Trockenheit im Sommer 2018 wurden die Nadelbäume vom Kupferstecher Pityogenes chalcographus befallen. Bohrlöcher durch den Borkenkäfer wurden im Winter 2018/2019 an allen Nadelbaumarten festgestellt. Ein geringeres Befallsrisiko wurde für die exotischen Baumarten in jedem Gattungspaar (Fichte, Lärche und Kiefer) und für Mischungen mit höherem Artenreichtum und höherem Laubbaumanteil erwartet. Die Gemeine Fichte Picea abies und Europäische Lärche Larix decidua waren die am stärksten befallenen Arten und galten somit als Hauptwirte des Borkenkäfers. Für diese beiden Arten nahm die Befallswahrscheinlichkeit mit zunehmender Baumdiversität ab (obwohl dies nur für Larix signifikant war). Im Gegensatz dazu waren Pinus , die insgesamt weniger befallen waren, in Parzellen mit hoher Baumdiversität häufiger befallen. Exotische Bäume waren tendenziell weniger befallen, wobei der deutlichste Beleg dafür auf der Ebene der Befallsintensität bei reinen Nadelbaumbeständen gefunden wurde. Insgesamt waren die Effekte der Baumvielfalt und der Baumartenherkunft nicht so stark wie der Effekt der Position innerhalb der Versuchsfläche, wo am Rand höhere Befallsraten als in der Mitte beobachtet wurden. Synthese . Eine zunehmende Baumvielfalt kann das Risiko eines Borkenkäferbefalls für Gattungen, die für hohe Befallsraten anfällig sind ( Picea und Larix ), verringern, aber das Risiko für weniger bevorzugte Gattungen ( Pinus und bis zu einem gewissen Grad die exotischen Baumarten) kann mit der Baumvielfalt aufgrund von spill‐over von bevorzugten Wirten zunehmen. In Mischwäldern kann das Befallsrisiko, selbst durch relativ spezialisierte Schadinsekten, eher auf die Baumarten umverteilt als für alle reduziert werden.
    Type of Medium: Online Resource
    ISSN: 0022-0477 , 1365-2745
    URL: Issue
    Language: English
    Publisher: Wiley
    Publication Date: 2021
    detail.hit.zdb_id: 3023-5
    detail.hit.zdb_id: 2004136-6
    SSG: 12
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  • 3
    In: Global Change Biology, Wiley, Vol. 28, No. 10 ( 2022-05), p. 3365-3378
    Abstract: Unprecedented tree dieback across Central Europe caused by recent global change‐type drought events highlights the need for a better mechanistic understanding of drought‐induced tree mortality. Although numerous physiological risk factors have been identified, the importance of two principal mechanisms, hydraulic failure and carbon starvation, is still debated. It further remains largely unresolved how the local neighborhood composition affects individual mortality risk. We studied 9435 young trees of 12 temperate species planted in a diversity experiment in 2013 to assess how hydraulic traits, carbon dynamics, pest infestation, tree height and neighborhood competition influence individual mortality risk. Following the most extreme global change‐type drought since record in 2018, one third of these trees died. Across species, hydraulic safety margins (HSMs) were negatively and a shift towards a higher sugar fraction in the non‐structural carbohydrate (NSC) pool positively associated with mortality risk. Moreover, trees infested by bark beetles had a higher mortality risk, and taller trees a lower mortality risk. Most neighborhood interactions were beneficial, although neighborhood effects were highly species‐specific. Species that suffered more from drought, especially Larix spp. and Betula spp., tended to increase the survival probability of their neighbors and vice versa. While severe tissue dehydration marks the final stage of drought‐induced tree mortality, we show that hydraulic failure is interrelated with a series of other, mutually inclusive processes. These include shifts in NSC pools driven by osmotic adjustment and/or starch depletion as well as pest infestation and are modulated by the size and species identity of a tree and its neighbors. A more holistic view that accounts for multiple causes of drought‐induced tree mortality is required to improve predictions of trends in global forest dynamics and to identify mutually beneficial species combinations.
    Type of Medium: Online Resource
    ISSN: 1354-1013 , 1365-2486
    URL: Issue
    Language: English
    Publisher: Wiley
    Publication Date: 2022
    detail.hit.zdb_id: 2020313-5
    SSG: 12
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  • 4
    In: Diversity and Distributions, Wiley, Vol. 26, No. 12 ( 2020-12), p. 1646-1662
    Abstract: Primary forests are critical for forest biodiversity and provide key ecosystem services. In Europe, these forests are particularly scarce and it is unclear whether they are sufficiently protected. Here we aim to: (a) understand whether extant primary forests are representative of the range of naturally occurring forest types, (b) identify forest types which host enough primary forest under strict protection to meet conservation targets and (c) highlight areas where restoration is needed and feasible. Location Europe. Methods We combined a unique geodatabase of primary forests with maps of forest cover, potential natural vegetation, biogeographic regions and protected areas to quantify the proportion of extant primary forest across Europe's forest types and to identify gaps in protection. Using spatial predictions of primary forest locations to account for underreporting of primary forests, we then highlighted areas where restoration could complement protection. Results We found a substantial bias in primary forest distribution across forest types. Of the 54 forest types we assessed, six had no primary forest at all, and in two‐thirds of forest types, less than 1% of forest was primary. Even if generally protected, only ten forest types had more than half of their primary forests strictly protected. Protecting all documented primary forests requires expanding the protected area networks by 1,132 km 2 (19,194 km 2 when including also predicted primary forests). Encouragingly, large areas of non‐primary forest existed inside protected areas for most types, thus presenting restoration opportunities. Main conclusion Europe's primary forests are in a perilous state, as also acknowledged by EU's “Biodiversity Strategy for 2030.” Yet, there are considerable opportunities for ensuring better protection and restoring primary forest structure, composition and functioning, at least partially. We advocate integrated policy reforms that explicitly account for the irreplaceable nature of primary forests and ramp up protection and restoration efforts alike.
    Type of Medium: Online Resource
    ISSN: 1366-9516 , 1472-4642
    URL: Issue
    Language: English
    Publisher: Wiley
    Publication Date: 2020
    detail.hit.zdb_id: 2020139-4
    detail.hit.zdb_id: 1443181-6
    SSG: 12
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  • 5
    In: Ecology and Evolution, Wiley, Vol. 10, No. 3 ( 2020-02), p. 1489-1509
    Abstract: Retention forestry, which retains a portion of the original stand at the time of harvesting to maintain continuity of structural and compositional diversity, has been originally developed to mitigate the impacts of clear‐cutting. Retention of habitat trees and deadwood has since become common practice also in continuous‐cover forests of Central Europe. While the use of retention in these forests is plausible, the evidence base for its application is lacking, trade‐offs have not been quantified, it is not clear what support it receives from forest owners and other stakeholders and how it is best integrated into forest management practices. The Research Training Group ConFoBi (Conservation of Forest Biodiversity in Multiple‐use Landscapes of Central Europe) focusses on the effectiveness of retention forestry, combining ecological studies on forest biodiversity with social and economic studies of biodiversity conservation across multiple spatial scales. The aim of ConFoBi is to assess whether and how structural retention measures are appropriate for the conservation of forest biodiversity in uneven‐aged and selectively harvested continuous‐cover forests of temperate Europe. The study design is based on a pool of 135 plots (1 ha) distributed along gradients of forest connectivity and structure. The main objectives are (a) to investigate the effects of structural elements and landscape context on multiple taxa, including different trophic and functional groups, to evaluate the effectiveness of retention practices for biodiversity conservation; (b) to analyze how forest biodiversity conservation is perceived and practiced, and what costs and benefits it creates; and (c) to identify how biodiversity conservation can be effectively integrated in multi‐functional forest management. ConFoBi will quantify retention levels required across the landscape, as well as the socio‐economic prerequisites for their implementation by forest owners and managers. ConFoBi's research results will provide an evidence base for integrating biodiversity conservation into forest management in temperate forests.
    Type of Medium: Online Resource
    ISSN: 2045-7758 , 2045-7758
    URL: Issue
    Language: English
    Publisher: Wiley
    Publication Date: 2020
    detail.hit.zdb_id: 2635675-2
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  • 6
    In: Ecology, Wiley, Vol. 104, No. 7 ( 2023-07)
    Abstract: It is commonly expected that exotic plants experience reduced herbivory, but experimental evidence for such enemy release is still controversial. One reason for conflicting results might be that community context has rarely been accounted for, although the surrounding plant diversity may moderate enemy release. Here, we tested the effects of focal tree origin and surrounding tree diversity on herbivore abundance and leaf damage in a cross‐Atlantic tree‐diversity experiment in Canada and Germany. We evaluated six European tree species paired with six North American congeners in both their native and exotic range, expecting lower herbivory for the exotic tree species in each pair at each site. Such reciprocal experiments have long been called for, but have not been realized thus far. In addition to a thorough evaluation of overall enemy release effects, we tested whether enemy release effects changed with the surrounding tree diversity. Herbivore abundance was indeed consistently lower on exotics across all six tree genera (12 comparisons). This effect of exotic status was independent of the continent, phylogenetic relatedness, and surrounding tree diversity. In contrast, leaf damage associated with generalist leaf chewers was consistently higher on North American tree species. Interestingly, several species of European weevils were the most abundant leaf chewers on both continents and the dominant herbivores at the Canadian site. Thus, most observed leaf damage is likely to reflect the effect of generalist herbivores that feed heavily on plant species with which they have not evolved. At the German site, sap suckers were the dominant herbivores and showed a pattern consistent with enemy release. Taken together, the consistently lower herbivory on exotics on both continents is not purely a pattern of enemy release in the strictest sense, but to some degree additionally reflects the susceptibility of native plants to invasive herbivores. In conclusion, our cross‐Atlantic study is consistent with the idea that nonnative trees have generally reduced herbivory, regardless of tree community diversity and species identity, but for different reasons depending on the dominant herbivore guild.
    Type of Medium: Online Resource
    ISSN: 0012-9658 , 1939-9170
    URL: Issue
    RVK:
    Language: English
    Publisher: Wiley
    Publication Date: 2023
    detail.hit.zdb_id: 1797-8
    detail.hit.zdb_id: 2010140-5
    SSG: 12
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  • 7
    In: Functional Ecology, Wiley, Vol. 35, No. 9 ( 2021-09), p. 1886-1902
    Abstract: Mixed‐species forests have often been shown to enhance above‐ground ecosystem properties and processes. Despite the significance of fine roots for tree and ecosystem functioning, the role of tree species diversity for below‐ground processes driven by fine roots remains largely unknown. Previously, an underyielding of fine‐root biomass (FRB) in tree mixtures across four major European forest types has been reported. To explain this phenomenon, we tested here the effect of tree species mixing on fine‐root traits related to soil exploitation efficiency, including biotic feedbacks from ectomycorrhizal fungi (EcM), and assessed the role of root trait dissimilarity. We analysed morphological and chemical traits as well as ectomycorrhizal colonisation intensity of absorptive fine roots (i.e. first three most distal orders) in soil samples from 315 mixed and mono‐specific tree neighbourhoods in mainly mature, semi‐natural forest stands across Europe. Additionally, we quantified mycorrhizal abundance and diversity in soil samples from the same stands. At the community level, fine roots in tree mixtures were characterised by higher specific root lengths and root nitrogen concentrations, lower diameters and root tissue densities indicating a faster resource acquisition strategy compared to mono‐specific stands. The higher root EcM colonisation intensity and soil EcM diversity in mixtures compared to mono‐specific stands may further provide evidence for positive biotic feedbacks. Moreover, the diversity of fine‐root traits influenced FRB, as mixtures characterised by a higher trait dissimilarity were linked to a lower reduction in FRB. At the level of phylogenetic groups, thin‐rooted angiosperm species showed stronger responses to mixing than thick‐rooted gymnosperms, especially in terms of root morphology and EcM colonisation, indicating different strategies of response to tree mixing. Our results indicate that a lower FRB can reflect a shift in soil resource acquisition strategies, rather than a lower performance of trees in mixtures. They show that several non‐exclusive mechanisms can simultaneously explain negative net effects of mixing on FRB. This study sheds new light on the importance of using integrative approaches including both above‐ and below‐ground biomass and traits to study diversity effects on plant productivity. A free Plain Language Summary can be found within the Supporting Information of this article.
    Type of Medium: Online Resource
    ISSN: 0269-8463 , 1365-2435
    URL: Issue
    Language: English
    Publisher: Wiley
    Publication Date: 2021
    detail.hit.zdb_id: 2020307-X
    detail.hit.zdb_id: 619313-4
    SSG: 12
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  • 8
    In: Global Change Biology, Wiley, Vol. 27, No. 18 ( 2021-09), p. 4403-4419
    Abstract: Extreme droughts are expected to increase in frequency and severity in many regions of the world, threatening multiple ecosystem services provided by forests. Effective strategies to adapt forests to such droughts require comprehensive information on the effects and importance of the factors influencing forest resistance and resilience. We used a unique combination of inventory and dendrochronological data from a long‐term ( 〉 30 years) silvicultural experiment in mixed silver fir and Norway spruce mountain forests along a temperature and precipitation gradient in southwestern Germany. We aimed at examining the mechanisms and forest stand characteristics underpinning the resistance and resilience to past mild and severe droughts. We found that (i) fir benefited from mild droughts and showed higher resistance (i.e., lower growth loss during drought) and resilience (i.e., faster return to pre‐drought growth levels) than spruce to all droughts; (ii) species identity determined mild drought responses while species interactions and management‐related factors strongly influenced the responses to severe droughts; (iii) intraspecific and interspecific interactions had contrasting effects on the two species, with spruce being less resistant to severe droughts when exposed to interaction with fir and beech; (iv) higher values of residual stand basal area following thinning were associated with lower resistance and resilience to severe droughts; and (v) larger trees were resilient to mild drought events but highly vulnerable to severe droughts. Our study provides an analytical approach for examining the effects of different factors on individual tree‐ and stand‐level drought response. The forests investigated here were to a certain extent resilient to mild droughts, and even benefited from such conditions, but were strongly affected by severe droughts. Lastly, negative effects of severe droughts can be reduced through modifying species composition, tree size distribution and stand density in mixed silver fir‐Norway spruce forests.
    Type of Medium: Online Resource
    ISSN: 1354-1013 , 1365-2486
    URL: Issue
    Language: English
    Publisher: Wiley
    Publication Date: 2021
    detail.hit.zdb_id: 2020313-5
    SSG: 12
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  • 9
    In: Functional Ecology, Wiley, Vol. 35, No. 1 ( 2021-01), p. 67-81
    Abstract: Associational resistance theory predicts that insect herbivory decreases with increasing tree diversity in forest ecosystems. However, the generality of this effect and its underlying mechanisms are still debated, particularly since evidence has accumulated that climate may influence the direction and strength of the relationship between diversity and herbivory. We quantified insect leaf herbivory and leaf chemical defences (phenolic compounds) of silver birch Betula pendula in pure and mixed plots with different tree species composition across 12 tree diversity experiments in different climates. We investigated whether the effects of neighbouring tree species diversity on insect herbivory in birch, that is, associational effects, were dependent on the climatic context, and whether neighbour‐induced changes in birch chemical defences were involved in associational resistance to insect herbivory. We showed that herbivory on birch decreased with tree species richness (i.e. associational resistance) in colder environments but that this relationship faded as mean annual temperature increased. Birch leaf chemical defences increased with tree species richness but decreased with the phylogenetic distinctiveness of birch from its neighbours, particularly in warmer and more humid environments. Herbivory was negatively correlated with leaf chemical defences, particularly when birch was associated with closely related species. The interactive effect of tree diversity and climate on herbivory was partially mediated by changes in leaf chemical defences. Our findings confirm that tree species diversity can modify the leaf chemistry of a focal species, hence its quality for herbivores. They further stress that such neighbour‐induced changes are dependent on climate and that tree diversity effects on insect herbivory are partially mediated by these neighbour‐induced changes in chemical defences. A free Plain Language Summary can be found within the Supporting Information of this article.
    Type of Medium: Online Resource
    ISSN: 0269-8463 , 1365-2435
    URL: Issue
    Language: English
    Publisher: Wiley
    Publication Date: 2021
    detail.hit.zdb_id: 2020307-X
    detail.hit.zdb_id: 619313-4
    SSG: 12
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  • 10
    In: Insect Conservation and Diversity, Wiley, Vol. 14, No. 1 ( 2021-01), p. 144-148
    Abstract: Reports of major losses in insect biodiversity have stimulated an increasing interest in temporal population changes. Existing datasets are often limited to a small number of study sites, few points in time, a narrow range of land‐use intensities and only some taxonomic groups, or they lack standardised sampling. While new monitoring programs have been initiated, they still cover rather short time periods. Daskalova et al. 2021 (Insect Conservation and Diversity, 14, 1‐18) argue that temporal trends of insect populations derived from short time series are biased towards extreme trends, while their own analysis of an assembly of shorter‐ and longer‐term time series does not support an overall insect decline. With respect to the results of Seibold et al. 2019 (Nature, 574, 671–674) based on a 10‐year multi‐site time series, they claim that the analysis suffers from not accounting for temporal pseudoreplication. Here, we explain why the criticism of missing statistical rigour in the analysis of Seibold et al. (2019) is not warranted. Models that include ‘year’ as random effect, as suggested by Daskalova et al. (2021), fail to detect non‐linear trends and assume that consecutive years are independent samples which is questionable for insect time‐series data. We agree with Daskalova et al. (2021) that the assembly and analysis of larger datasets is urgently needed, but it will take time until such datasets are available. Thus, short‐term datasets are highly valuable, should be extended and analysed continually to provide a more detailed understanding of insect population changes under the influence of global change, and to trigger immediate conservation actions.
    Type of Medium: Online Resource
    ISSN: 1752-458X , 1752-4598
    URL: Issue
    Language: English
    Publisher: Wiley
    Publication Date: 2021
    detail.hit.zdb_id: 2404613-9
    SSG: 12
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