A modified Jarvis model to improve the expressing of stomatal response in a beech forest

Abstract

The Jarvis‐type model, which incorporates stress functions, is commonly used to describe the physiological behaviour of stomatal response in various vegetation species. However, the model has been criticized for its empirically formulated multiplicative equation, which may not accurately capture the mutual impact of intercorrelated stress factors, for example, vapour pressure deficit (VPD) and air temperature (Ta). This study proposed a modified Jarvis model that introduces reduction factors in the stress functions of VPD and Ta to provide the description of canopy conductance. We used sap flow data from a beech forest in the mid‐latitude region of Centre Europe to inversely estimate the canopy conductance with optimized stress functions. Our findings reveal that two recommended parameterization strategies for general deciduous broadleaf forest (DBF) significantly overestimated the transpiration rate, with a maximum value of ~2 mm/day on rainless days. This suggested that the beech forest exhibited a distinct stomatal response compared to the general DBF category. By applying boundary line analysis to fit the parameters, both the unmodified and modified Jarvis models provided better simulations of transpiration, with relatively high Nash‐Sutcliffe Efficiency (NSE) values of 0.75 and 0.77, respectively. These results indicated that modelling transpiration can be improved by refining the parameterization of canopy conductance, particularly for vegetation species with unique stomatal behaviours that deviated from the characteristics of their general vegetation type. The modified Jarvis model offers a more accurate description of canopy conductance and enhances the modelling of transpiration in vegetated areas, especially under dry environment conditions with relatively high VPD.

Evidence of field‐scale shifts in transpiration dynamics following bark beetle infestation: Stomatal conductance responses

“…Stomatal conductance is a key parameter governing the exchange of water and CO 2 between stomata and the atmosphere (Baca Cabrera et al, 2021;Damour et al, 2010;Henry et al, 2019;Lin et al, 2015). Various stomatal conductance models have been proposed based on different conceptualizations of stomatal behaviour in response to environmental conditions (Buckley & Mott, 2013;Lamour et al, 2022;Shao et al, 2023). Jarvis et al (1976) developed a stomatal conductance model formulated with multiple stress factors, including light density, leaf temperature, vapour pressure deficit (VPD), CO 2 concentration, and soil water potential.…”