The Role of the Intraspecific Variability of Hydraulic Traits for Modeling the Plant Water Use in Different European Forest Ecosystems.

The drought resilience of forest ecosystems is generally believed to depend on the dominant tree species' hydraulic traits. These traits define the maximum water transport capacity and the degree of vulnerability to hydraulic failure of a tree species. This work evaluates the effect of the intraspecific variability of hydraulic traits on the simulated tree water use in the Community Land Model (CLM, version 5.0). We selected two contrasting broadleaved tree species and performed a series of numerical experiments by modifying the parameters of the plant vulnerability curve and the maximum xylem hydraulic conductance accounting for the variability within each species. Our prescribed parameter sets represent vulnerable and resistant tree responses to the water deficit. At sites with an ample water supply, the resistant configuration simulates reduced water stress and increased transpiration compared to the vulnerable configuration. Meanwhile, the model results are counter‐intuitive at temporarily dry sites when water availability is the limiting factor. The numerical experiments demonstrate the emergent role of the maximum xylem conductance as a modulator of the plant water use strategy and the simulated transpiration within the model. Using the default value for maximum xylem conductance, the model tends to overestimate the early summer transpiration at drier sites, forcing the vegetation to experience unrealistic water stress later in the year. Our findings suggest that the parameterization of maximum xylem conductance is an important yet unresolved problem in the CLM and similar land surface models. Plain Language Summary: The survival of trees in drought conditions depends on their ability to adapt to water scarcity. Part of this adaptation is characterized by specific plant traits, which are an important component of Land Surface Models and largely determine the relationship between soil moisture and canopy gas exchange. Our study explores how the variability of specific plant traits of individual tree species may affect the selected model's ability to reproduce the water use observed in forest stands in Europe. For climates with a pronounced summer dry period, we found that the default model settings overestimated the vegetation water use in the early growing season, when water is abundant, resulting in severe water stress and underestimated transpiration as the dry season progressed. We specifically demonstrate that a rarely considered plant trait, representing the maximum water transport capacity, plays an essential role in controlling the magnitude of simulated water use and that adjustments to this parameter greatly help to reproduce the vegetation water use observed in seasonally dry climates. Key Points: We explore the impact of the intraspecific variability of plant hydraulic traits on the simulated transpiration by Community Land Model 5.0We find that a choice of plant hydraulic traits that reproduces observed plant transpiration also reduces simulated water stressWe demonstrate the critical role of the maximum xylem conductance in the model and its dependency on factors other than vegetation type [ABSTRACT FROM AUTHOR]

Copyright of Journal of Advances in Modeling Earth Systems is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)