Ecophysiological and dendroecological data from a temperate sessile oak (Quercus petraea (Matt.) Liebl.) stand in Belgium were used to develop and parameterize a dendroecological process-based model. The purpose of this model is to serve as a tool for exploring the relationship between climate variability and tree growth based on dendro ecological data. When parameterized, the model was able to correctly simulate measurements of bud-burst date, through fall (r(2) = 0.95), soil water content (r(2) = 0.81), transpiration (r(2) = 0.80), and ring-width series from 1960 to 1999 (r(2) = 0.46). Model sensitivity analysis showed that atmospheric vapor pressure deficit is the major controlling factor of transpiration in this type of ecosystem. The model shows that bole increment is principally controlled by temperature because it affects the phenological process of bud burst and thus the growing season length. Precipitation variability does not affect variation of transpiration rate and bole increment because calculated soil water stress is negligible during the simulation period. Discrepancies between observed and simulated bole increment may be a consequence of stand density variations and worm defoliation in the spring. The MAIDEN model is particularly suited for dendreocological analysis because it takes simple species, site condition, and climatic variables as input.

A process-based model (MAIDEN, modeling and analysis in dendroecology) is compared with statistical response functions to analyze the climate-growth relationship for two different species (sessile oak (Quercus petraea (Matt.) Liebl.) and Aleppo pine (Pinus halepensis Mill.)) growing in contrasting climates (temperate and Mediterranean). Growth data were obtained using dendroecological sampling procedures. Results obtained with both methods are consistent, but the MAIDEN model provides a more explanatory analysis than classical statistical tools. Analyses with MAIDEN indicate that oak stomatal conductance is sensitive to atmospheric vapor deficit, whereas precipitation and soil water deficit are not limiting factors in the study area. In contrast, the soil water regime is the major controlling factor of bole growth variability for Aleppo pine. The model shows that remobilization of the carbohydrate reserves in spring is of major importance for leaf and root expansion, and it affects the subsequent bole increment of oak. Because the amount of carbon that can be mobilized in spring is linked to carbon stored the previous year, these processes explain how the growth of oak trees is linked in this way from one year to the next. In contrast, the MAIDEN model shows that carbohydrate-reserve dynamics, phenology, and bole growth are less connected for Aleppo pine trees.

We tested, compared and modified three models of stomatal conductance at the leaf level in a forest ecosystem where drought stress is a major factor controlling forest productivity. The models were tested against 2 years (1999 and 2000) of leaf-level measurements on ponderosa pine (Pinus ponderosa Dougl. ex Laws.) growing in the Mediterranean climate of California, USA. The Ball, Woodrow and Berry (1987) (BWB) model was modified to account for soil water stress. Among the models, results of the modified BWB model were in the closest agreement with observations (r(2) = 0.71). The Jarvis (1976) model showed systematic simulation errors related to vapor pressure deficit (r(2) = 0.65). Results of the Williams, Rastetter, Fernandes et at. (1996) (SPA) model showed the poorest correlation with empirical data, but this model has only one calibration parameter (r(2) = 0.60). Sensitivity analyses showed that, in all three models, predictions of stomatal conductance were most responsive to photosynthetically active radiation and soil water content. Stomatal conductance showed little sensitivity to vapor pressure deficit in the Jarvis model, whereas in both the BWB and SPA models, vapor pressure deficit (or relative humidity) was the third most important variable. Parameterization of the SPA model was in accordance with the parameterization of the modified BWB model, although the two models differ greatly. Measured and modeled results indicate that stomatal behavior is not water conservative during spring; however, during summer, when soil water content is low and vapor pressure deficit is high, stomatal conductance decreases and, according to the models, intrinsic water-use efficiency increases.