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Simulation of stand transpiration based on a xylem water flow model for individual trees

Hentschel, Rainer ; Bittner, Sebastian ; Janott, Michael ; Biernath, Christian ; Holst, Jutta LU ; Ferrio, Juan Pedro ; Gessler, Arthur and Priesack, Eckart (2013) In Agricultural and Forest Meteorology 182. p.31-42
Abstract
Quantifying the water exchange between a forest stand and the atmosphere is of major interest for the prediction of future growth conditions and the planning of silvicultural treatments. In the present study, we address (i) the uncertainties of sap flow estimations at the tree level and (ii) the performance of the simulation of stand transpiration. Terrestrial laser scan images (TLS) of a mature beech stand (Fagus sylvatica L) in Southwestern Germany serve as input data for a representation of the aboveground tree architecture of the study stand. In the single-tree xylem water flow model (XWF) used here, 98 beech trees are represented by 3D graphs of connected cylinders with explicit orientation and size. Beech-specific hydraulic... (More)
Quantifying the water exchange between a forest stand and the atmosphere is of major interest for the prediction of future growth conditions and the planning of silvicultural treatments. In the present study, we address (i) the uncertainties of sap flow estimations at the tree level and (ii) the performance of the simulation of stand transpiration. Terrestrial laser scan images (TLS) of a mature beech stand (Fagus sylvatica L) in Southwestern Germany serve as input data for a representation of the aboveground tree architecture of the study stand. In the single-tree xylem water flow model (XWF) used here, 98 beech trees are represented by 3D graphs of connected cylinders with explicit orientation and size. Beech-specific hydraulic parameters and physical properties of individual trees determine the physiological response of the tree model to environmental conditions. The XWF simulations are performed without further calibration to sap flow measurements. The simulations reliably match up with sap flow estimates derived from sap flow density measurements. The density measurements strongly depend on individual sapwood area estimates and the characterization of radial sap flow density gradients with xylem depth. Although the observed pure beech stand is even-aged, we observe a high variability in sap flow rates among the individual trees. Simulations of the individual sap flow rates show a corresponding variability due to the distribution of the crown projection area in the canopy and the different proportions of sapwood area. Stand transpiration is obtained by taking the sum of 98 single-tree simulations and the corresponding sap flow estimations, which are then compared with the stand-level root water uptake model (RWU model) simulation. Using the RWU model results in a 35% higher simulation of seasonal stand transpiration relative to the XWF model. These findings demonstrate the importance of individual tree dimensions and stand heterogeneity assessments in estimating stand water use. As a consequence of species-specific model parameterization and precise TLS-based stand characterization, the XWF model is applicable to various sites and tree species and is a promising tool for predicting the possible water supply limitations of pure and mixed forest stands. (C) 2013 Elsevier B.V. All rights reserved. (Less)
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organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
Stand transpiration, Sap flow density, Fagus sylvatica, Terrestrial, laser scan, Hydrodynamics model
in
Agricultural and Forest Meteorology
volume
182
pages
31 - 42
publisher
Elsevier
external identifiers
  • wos:000327000200004
  • scopus:84883773476
ISSN
1873-2240
DOI
10.1016/j.agrformet.2013.08.002
language
English
LU publication?
yes
id
51f23832-e4f3-456b-84d3-e2e4cc724456 (old id 4273278)
date added to LUP
2016-04-01 14:02:02
date last changed
2020-01-12 14:31:52
@article{51f23832-e4f3-456b-84d3-e2e4cc724456,
  abstract     = {Quantifying the water exchange between a forest stand and the atmosphere is of major interest for the prediction of future growth conditions and the planning of silvicultural treatments. In the present study, we address (i) the uncertainties of sap flow estimations at the tree level and (ii) the performance of the simulation of stand transpiration. Terrestrial laser scan images (TLS) of a mature beech stand (Fagus sylvatica L) in Southwestern Germany serve as input data for a representation of the aboveground tree architecture of the study stand. In the single-tree xylem water flow model (XWF) used here, 98 beech trees are represented by 3D graphs of connected cylinders with explicit orientation and size. Beech-specific hydraulic parameters and physical properties of individual trees determine the physiological response of the tree model to environmental conditions. The XWF simulations are performed without further calibration to sap flow measurements. The simulations reliably match up with sap flow estimates derived from sap flow density measurements. The density measurements strongly depend on individual sapwood area estimates and the characterization of radial sap flow density gradients with xylem depth. Although the observed pure beech stand is even-aged, we observe a high variability in sap flow rates among the individual trees. Simulations of the individual sap flow rates show a corresponding variability due to the distribution of the crown projection area in the canopy and the different proportions of sapwood area. Stand transpiration is obtained by taking the sum of 98 single-tree simulations and the corresponding sap flow estimations, which are then compared with the stand-level root water uptake model (RWU model) simulation. Using the RWU model results in a 35% higher simulation of seasonal stand transpiration relative to the XWF model. These findings demonstrate the importance of individual tree dimensions and stand heterogeneity assessments in estimating stand water use. As a consequence of species-specific model parameterization and precise TLS-based stand characterization, the XWF model is applicable to various sites and tree species and is a promising tool for predicting the possible water supply limitations of pure and mixed forest stands. (C) 2013 Elsevier B.V. All rights reserved.},
  author       = {Hentschel, Rainer and Bittner, Sebastian and Janott, Michael and Biernath, Christian and Holst, Jutta and Ferrio, Juan Pedro and Gessler, Arthur and Priesack, Eckart},
  issn         = {1873-2240},
  language     = {eng},
  pages        = {31--42},
  publisher    = {Elsevier},
  series       = {Agricultural and Forest Meteorology},
  title        = {Simulation of stand transpiration based on a xylem water flow model for individual trees},
  url          = {http://dx.doi.org/10.1016/j.agrformet.2013.08.002},
  doi          = {10.1016/j.agrformet.2013.08.002},
  volume       = {182},
  year         = {2013},
}