Прегледај по Аутор "Ammer, Christian"

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    Emerging stability of forest productivity by mixing two species buffers temperature destabilizing effect
    (Wiley, 2022) del Río, Miren; Pretzsch, Hans; Ruiz-Peinad, Ricardo; Jactel, Hervé; Coll, Lluís; Löf, Magnus; Aldea, Jorge; Ammer, Christian; Avdagić, Admir; Barbeito, Ignacio; Bielak, Kamil; Bravo, Felipe; Brazaitis, Gediminas; Cerný, Jakub; Collet, Catherine; Condés, Sonia; Drössler, Lars; Fabrika, Marek; Heym, Michael; Holm, Stig-Olof; Hylen, Gro; Jansons, Aris; Kurylyak, Viktor; Lombardi, Fabio; Matović, Bratislav; Metslaid, Marek; Motta, Renzo; Nord-Larsen, Thomas; Nothdurft, Arne; den Ouden, Jan; Pach, Maciej; Pardos,Marta; Poeydebat, Charlotte; Ponette, Quentin; Pérot, Tomas; Reventlow, Ditlev Otto Juel; Sitko, Roman; Sramek, Vit; Steckel, Mathias; Svoboda, Miroslav; Verheyen, Kris; Vospernik, Sonja; Wolff, Barbara; Zlatanov, Tzvetan; Bravo-Oviedo, Andrés
    1. The increasing disturbances in monocultures around the world are testimony to their instability under global change. Many studies have claimed that temporal stability of productivity increases with species richness, although the ecological fundamentals have mainly been investigated through diversity experiments. To adequately manage forest ecosystems, it is necessary to have a comprehensive understanding of the effect of mixing species on the temporal stability of productivity and the way in which it is influenced by climate conditions across large geographical areas. 2. Here, we used a unique dataset of 261 stands combining pure and two-species mixtures of four relevant tree species over a wide range of climate conditions in Europe to examine the effect of species mixing on the level and temporal stability of productivity. Structural equation modelling was employed to further explore the direct and indirect influence of climate, overyielding, species asynchrony and additive effect (i.e. temporal stability expected from the species growth in monospecific stands) on temporal stability in mixed forests. 3. We showed that by adding only one tree species to monocultures, the level (overyielding:+6%) and stability (temporal stability: +12%) of stand growth increased significantly. We identified the key effect of temperature on destabilizing stand growth, which may be mitigated by mixing species. We further confirmed asynchrony as the main driver of temporal stability in mixed stands, through both the additive effect and species interactions, which modify between-species asynchrony in mixtures in comparison to monocultures. 4. Synthesis and applications. This study highlights the emergent properties associated with mixing two species, which result in resource efficient and temporally stable production systems. We reveal the negative impact of mean temperature on temporal stability of forest productivity and how the stabilizing effect of mixing two species can counterbalance this impact. The overyielding and temporal stability of growth addressed in this paper are essential for ecosystem services closely linked with the level and rhythm of forest growth. Our results underline that mixing two species can be a realistic and effective nature-based climate solution, which could contribute towards meeting EU climate target policies.
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    With increasing site quality asymmetric competition and mortality reduces Scots pine (Pinus sylvestris L.) stand structuring across Europe
    (Elsevier, 2022) Pretzsch, Hans; Bravo-Oviedo, Andr´es; Hilmers, Torben; Ruiz-Peinado, Ricardo; Coll, Lluís; L¨of, Magnus; Ahmed, Shamim; Aldea, Jorge; Ammer, Christian; Avdagić, Admir; Barbeito, Ignacio; Bielak, Kamil; Bravo, Felipe; Brazaitis, Gediminas; Cerný, Jakub; Collet, Catherine; Dr¨ossler, Lars; Fabrika, Marek; Heym, Michael; Holm, Stig-Olof; Hylen, Gro; Jansons, Aris; Kurylyak, Viktor; Lombardi, Fabio; Matović, Bratislav; Metslaid, Marek; Motta, Renzo; Nord-Larsen, Thomas; Nothdurft, Arne; Ord´o˜nez, Crist´obal; Ouden, Jan den; Pach, Maciej; Pardos, Marta; Ponette, Quentin; P´erot, Tomas; Reventlow, Ditlev Otto Juel; Sitko, Roman; Sramek, Vit; Steckel, Mathias; Svoboda, Miroslav; Uhl, Enno; Verheyen, Kris; Vospernik, Sonja; Wolff, Barbara; Zlatanov, Tzvetan; del Río, Miren
    Heterogeneity of structure can increase mechanical stability, stress resistance and resilience, biodiversity and many other functions and services of forest stands. That is why many silvicultural measures aim at enhancing structural diversity. However, the effectiveness and potential of structuring may depend on the site conditions. Here, we revealed how the stand structure is determined by site quality and results from site-dependent partitioning of growth and mortality among the trees. We based our study on 90 mature, even-aged, fully stocked monocultures of Scots pine (Pinus sylvestris L.) sampled in 21 countries along a productivity gradient across Europe. A mini-simulation study further analyzed the site-dependency of the interplay between growth and mortality and the resulting stand structure. The overarching hypothesis was that the stand structure changes with site quality and results from the site-dependent asymmetry of competition and mortality. First, we show that Scots pine stands structure across Europe become more homogeneous with increasing site quality. The coefficient of variation and Gini coefficient of stem diameter and tree height continuously decreased, whereas Stand Density Index and stand basal area increased with site index. Second, we reveal a site-dependency of the growth distribution among the trees and the mortality. With increasing site index, the asymmetry of both competition and growth distribution increased and suggested, at first glance, an increase in stand heterogeneity. However, with increasing site index, mortality eliminates mainly small instead of all-sized trees, cancels the size variation and reduces the structural heterogeneity. Third, we modelled the site-dependent interplay between growth partitioning and mortality. By scenario runs for different site conditions, we can show how the site-dependent structure at the stand level emerges from the asymmetric competition and mortality at the tree level and how the interplay changes with increasing site quality across Europe. Our most interesting finding was that the growth partitioning became more asymmetric and structuring with increasing site quality, but that the mortality eliminated predominantly small trees, reduced their size variation and thus reversed the impact of site quality on the structure. Finally, the reverse effects of mode of growth partitioning and mortality on the stand structure resulted in the highest size variation on poor sites and decreased structural heterogeneity with increasing site quality. Since our results indicate where heterogeneous structures need silviculture interventions and where they emerge naturally, we conclude that these findings may improve system understanding and modelling and guide forest management aiming at structurally rich forests.