1. Autumn phenology of mountain birch at the sub-arctic treeline in comparison with silver birch in the cold and mild temperate zonePaolo Zuccarini, Friederike Gehrmann, Manuela Balzarolo, Omar Flores, Jožica Gričar, Bertold Mariën, Matteo Campioli, 2025, original scientific article Abstract: Lack of knowledge on autumn phenology of deciduous trees still exists for high-latitude regions. We studied the leaf and wood growth autumn phenology of mountain birch in a sub-arctic climate (northern Sweden) and compared them with the same dynamics for silver birch in a temperate climate (southern Norway and Belgium). The first autumn phenophase for mountain birch was the decline of the remotely sensed Terrestrial Chlorophyll Index (TCI) at the end of July. This was followed by wood growth cessation, onset of chlorophyll degradation and of loss of canopy greenness, and the latter accompanied by onset of anthocyanin production and flavonoids degradation. The earlier timing of TCI decline than chlorophyll degradation was probably due to the different scales of measurements (ecosystem level vs. tree leaves, respectively). In 2020, the decline in canopy greenness started in the same period at the three studied sites, showing an unexpected early timing for Belgium, likely due to the very warm late summer conditions and drought stress or intraseasonal legacy effects. Accordingly, wood growth cessation also occurred unexpectedly earlier in Belgium than in Norway. The end of senescence was inversely related to latitude. Our study presents, for the first time, the autumn timeline of a deciduous species at the northern treeline, and indicates that the timing of autumn phenology of birch populations does not consistently follow the latitudinal gradient but varies according to the phenophase, the scale of measurements and the current year meteorological conditions.
Keywords: Betula pendula, Betula pubescens, deciduous trees, leaf senescence, terrestrial chlorophyll index, wood phenology
Published in DiRROS: 19.12.2024; Views: 928; Downloads: 400
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2. Timeline of autumn phenology in temperate deciduous treesInge Dox, Jožica Gričar, Lorène Julia Marchand, Sebastien Leys, Paolo Zuccarini, Charly Geron, Peter Prislan, Bertold Mariën, Patrick Fonti, Holger Lange, Josep Peñuelas, Jan Van den Bulcke, Matteo Campioli, 2020, original scientific article Abstract: Cessation of xylem formation or wood growth (CWG) and onset of foliar senescence (OFS) are key autumn phenological events in temperate deciduous trees. Their timing is fundamental for development and survival of trees, ecosystem nutrient cycling, the seasonal exchange of matter and energy between the biosphere and atmosphere and affect the impact and feedback of forests to global change. A large-scale experimental effort and improved observational methods have allowed us to compare the timing of CWG and OFS for different deciduous tree species in Western Europe, in particularly silver birch, a pioneer species, and European beech, a late-succession species, at stands of different latitudes, of different levels of site fertility, and for two years with contrasting meteorological and drought conditions i.e., the low-moderately dry 2017 and the extremely dry 2018. Specifically, we tested whether foliar senescence started before, after or concurrently with CWG. OFS and CWG occurred generally between late September and early November, with larger differences across species and sites for OFS. Foliar senescence started concurrently with CWG in most cases, except for the drier 2018 and, for beech, at the coldest site, where OFS occurred significantly later than CWG. Behavior of beech in Spain, the southern edge of its European distribution, was unclear, with no CWG, but very low wood growth at the time of OFS. Our study suggests that OFS is generally triggered by the same drivers of CWG or when wood growth decreases in late summer, indicating an overarching mechanism of sink limitation as a possible regulator of the timing of foliar senescence.
Keywords: autumn phenology, xylem formation, foliar senescence, cambium, chlorophyll, radial growth, wood, decidiuous trees, common aspen, common beech, pedunculate oak, silver birch
Published in DiRROS: 10.06.2020; Views: 2998; Downloads: 1955
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