Tree phenology modelling in the boreal and temperate climate zones : Timing of spring and autumn events

Author

Summary, in English

Plant phenology in the boreal and temperate climate zones is synchronised with seasonal changes in temperature and photoperiod. For deciduous trees, timing of budburst and leaf colouring define the growing season length and express adaptations to trade-offs in growth and risks. An extended growing season due to climate warming will likely increase forest productivity, however these potential benefits may be outweighed by an increase in risks such as frost damage.

In order to estimate the impact of climate change on forest phenology, the reliability of phenology models needs to be assessed. In this thesis, the ability of phenology models to capture inter-annual and spatial variation in budburst and leaf colouring were evaluated for five tree species that are important in Swedish forest management; birch, beech, oak, Norway spruce and Scots pine. Model simulations were assessed in relation to model structure, the models representation of tree physiology processes and the calibration -, temperature - and phenology data used. The novelty of the thesis is that simulations were carried out across large regions using extensive phenological datasets which consist of observations of more than 1000 trees, with up to 60 observation-years per tree.

The results indicate that the model structure influence the models sensitivity to calibration data and to temperature conditions. Spatial differences in trees response to environmental cues is not well represented in the models. The models do not consider differences in provenance-specific requirements and therefore was the accuracy of the simulations influenced by the models being tuned to the average phenological response of the calibration data. Overall, the budburst models overestimated the temperature effect. In colder regions where budburst usually occurs later, budburst was simulated to occur too late, and in warmer regions where budburst occurs earlier, budburst was simulated to occur too early. The more accurate budburst models were in general structurally simple. They considered the effect of warm spring temperatures, thereby assuming full dormancy release without considering winter conditions. Leaf colouring was better estimated by average day of leaf colouring than by the model simulations.

In conclusion, the results indicate that the models do not capture the phenology across large regions well enough to be considered reliable for climate change assessments, emphasising the lack of mechanistic understanding of phenological processes.

Topic

  • Physical Geography

Status

Published

ISBN/ISSN/Other

  • ISBN: 978-91-85793-43-3

Defence date

14 November 2014

Defence time

10:00

Defence place

Pangea auditorium