On the autumn phenology of Fagus sylvatica, Quercus robur, Betula pendula and Populus tremula

Ondertitel:timing leaf senescence and fine-root growth

Korte inhoud:Knowing the leaf senescence and fine-root phenology of deciduous trees is important to understand forest ecosystems and their feedback on the climate. To improve our knowledge on the phenology of deciduous trees a paradigm was suggested: the LEAF-FALL paradigm. This paradigm proposed that the onset of leaf senescence is not directly impacted by changes in the photoperiod and other environmental drivers (e.g. the temperature, and the light intensity and spectral quality) but rather indirectly through the impact of environmental drivers on tree growth, including fine-root growth. The cessation of the wood growth and the photoperiod would then act as the trigger of leaf senescence at the end of summer in favorable and unfavorable conditions, respectively. This work addresses here just two aspects: (I) determining the timing of the leaf senescence and (II) determining the fine-root phenology throughout the year to investigate a possible coupling between the phenology of the leaves and fine-roots. The objectives were investigated through observations of the below- and aboveground phenology in mature deciduous trees (Fagus sylvatica L., Quercus robur L., Betula pendula Roth. and Populus tremula L.) in Belgium. Additional leaf senescence data from the same species in Norway and Spain were also used. The leaf senescene and fine-root growth have been investigated mostly through measurements of the chlorophyll content index in leaves and through observations of fine-roots using a minirhizotron. Consequently, substantial attention has also been given to detecting phenological transition dates in longitudinal data of the chlorophyll content index and fine-roots. Especially the use of generalized additive models (GAMs) and generalized additive models for location, scale and shape (GAMLSS) has been explored in relation to the detection of phenological transition dates. The results show that the global radiation, temperature and vapor pressure deficit affected the timing of the onset of leaf senescence in all species. In Fagus sylvatica, unlike in Quercus robur and Betula pendula, the timing of the onset of leaf senescence was conservative (i.e. not varying much). A significant inter-annual trend in the onset of leaf senescence could not be established in any of the species. The seasonal trend in the fine-root growth was also inconsistent among species and years, although species with the same life strategy did show similar phenological trends and similar fine-root lifespan and turnover rate estimations. Our results about the two researched aspects do not provide immediate support for the LEAF-FALL paradigm.

Jaar van publicatie:2022

Trefwoorden:Doctoral thesis

Toegankelijkheid:Open