A modified Jarvis model to improve the expressing of stomatal response
in a beech forest
Abstract
Jarvis-type model with a flexible parameterization of stress functions
can improve the descriptions of physiological behaviour for specific
vegetation species. However, it is criticized for the empirically
formulated multiplicative equation that can deviate from the mutual
impact of intercorrelated stress factors, e.g., vapor pressure deficit
(VPD) and air temperature ( Ta). This study
proposed a modified Jarvis model by adding reduction factors in the
stress functions of VPD and Ta to provide a
better description of stomatal conductance. The sap flow data of
transpiration rate in a beech forest in the mid-latitude of Centre
Europe was used to inversely estimate the stomatal conductance, which
facilitated the formulation of stress functions. Taking two recommended
parameterization strategies for general deciduous broadleaf forest (DBF)
led to severe overestimation of transpiration rate with a maximum value
of ~2 mm/day in rainless days, which suggested that the
beech forest had rather different stomatal response. With the
parameterization using boundary analysis, the unmodified and modified
Jarvis model provided the better simulation of transpiration with NSE
values of 0.75 and 0.77. The results suggested that modelling
transpiration can be improved through a more specific parameterization
of stomatal conductance, especially for a vegetation species featuring
its own stomatal behaviour that differed from its belonged general
vegetation type. Particularly, the modified Jarvis model can further
improve the description of stomatal conductance and modelling of
transpiration in vegetated areas, especially under dry environment
conditions with relatively high VPD.