Abstract
Ozone affects adult trees significantly, but effects on stem growth are hard to prove
and difficult to correlate with the primary sites of ozone damage at the leaf level.
To simulate ozone effects in a mechanistic way, at a level relevant to forest stand
growth, we developed a simple ozone damage and repair model (CASIROZ model) that can
be implemented into mechanistic photosynthesis and growth models. The model needs
to be parameterized with cuvette measurements on net photosynthesis and dark respiration.
As the CASIROZ ozone sub-model calculates effects of the ozone flux, a reliable representation
of stomatal conductance and therefore ozone uptake is necessary to allow implementation
of the ozone sub-model. In this case study the ozone sub-model was used in the ANAFORE
forest model to simulate gas exchange, growth, and allocation. A preliminary run for
adult beech (Fagus sylvatica) under different ozone regimes at the Kranzberg forest site (Germany) was performed.
The results indicate that the model is able to represent the measured effects of ozone
adequately, and to distinguish between immediate and cumulative ozone effects. The
results further help to understand ozone effects by distinguishing defence from damage
and repair. Finally, the model can be used to extrapolate from the short-term results
of the field study to long-term effects on tree growth. The preliminary simulations
for the Kranzberg beech site show that, although ozone effects on yearly growth are
variable and therefore insignificant when measured in the field, they could become
significant at longer timescales (above 5 years, 5 % reduction in growth). The model
offers a possible explanation for the discrepancy between the significant effects
on photosynthesis (10 to 30 % reductions simulated), and the minor effects on growth.
This appears to be the result of the strong competition and slow growth of the Kranzberg
forest, and the importance of stored carbon for the adult beeches (by buffering effects
on carbon gain). We finally conclude that inclusion of ozone effects into current
forest growth and yield models can be an important improvement into their overall
performance, especially when simulating younger and less dense forests.
Key words
Beech -
Fagus sylvatica L. - forest - mechanistic model - ozone - respiration - stomatal flux
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gaby.deckmyn@ua.ac.be
Guest Editor: R. Matyssek
