Recalibrating Best Practices, Challenges, and Limitations of Estimating Tree Transpiration Via Sap Flow

The results of sap flow continuous measurements by a tree-trunk heat balance method (THB) on beech model trees are analysed in this paper. Experimental research works were carried out in a mature mixed fir-spruce-beech stand in the research area Poľana – Hukavský grúň (j= 48o39´, l = 19o29´, H = 850 m a.s.l.) in UNESCO Biosphere Reserve on two co-dominant and one sub-dominant beech trees. A mathematical model of daily transpiration dynamics was proposed for a quantitative analysis of the daily course of sap flow intensity. The model works on a one-tree level and enables to consider the influence of the tree social position in the stand on the sap flow intensity of model beech trees and to express the dependence of sap flow intensity on the tree height and crown projection.

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Influence of tree transpiration on mass water balance of mixed mountain forests of the West Carpathians

Biologia ◽

10.2478/s11756-006-0178-6 ◽

2006 ◽

Vol 61 (19) ◽

Cited By ~ 12

Author(s):

Katarína Střelcová ◽

Jozef Minďáš ◽

Jaroslav Škvarenina

Keyword(s):

Water Balance ◽

Forest Ecosystem ◽

Sap Flow ◽

Potential Evapotranspiration ◽

Biosphere Reserve ◽

Flow Measurements ◽

Tree Transpiration ◽

Precipitation Total ◽

Beech Stand ◽

Snow Precipitation

AbstractBrief information about water balance of the Carpathian temperate forest ecosystem are presented in the paper. Experimental research was done in a mature mixed fir-spruce-beech stand in the research plot “Pol’ana-Hukavský grúň” (850 m a.s.l.) in the south-eastern part of Pol’ana Mts. in the Biosphere Reserve UNESCO in Central Slovakia. Individual parameters of water budget have been continuously monitored. The water consumption of the model beech trees, as well as approximate model beech stand transpiration was estimated on the basis of sap flow measurements and up-scaling through dendrometrical approach. Sap flow of model beech trees was estimated by direct, non-destructive and continuous measurements by tree-trunk heat balance method with internal heating and sensing of temperature. These values were compared with potential evapotranspiration according to Türc. Precipitation parameters (rain and snow precipitation, through-fall precipitation, stem-flow, fog/snow precipitation and infiltration) have been measured simultaneously. Results of mass water balance and the portion of the tree transpiration within the individual water flows are presented. Evapotranspiration of beech-fir forest ecosystem in the middle mountain region (850 m a.s.l.) includes: transpiration (35% of precipitation total), interception (21%), evaporation (8%). There are differences between tree species in mass of transpirated water. Transpiration of spruce and fir reaches two-thirds of beech transpiration. Fog precipitation contribution to the water balance of beech-fir stand is 5%. Concurrently fog precipitation lowers the interception losses of vertical precipitation.

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Comparison of two sap flow methods for the estimation of tree transpiration

Annales des Sciences Forestières ◽

10.1051/forest:19980605 ◽

1998 ◽

Vol 55 (6) ◽

pp. 707-713 ◽

Cited By ~ 8

Author(s):

Régis Tournebize ◽

Stéphane Boistard

Keyword(s):

Sap Flow ◽

Tree Transpiration

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Calibration of Granier-Type (TDP) Sap Flow Probes by a High Precision Electronic Potometer

Sensors ◽

10.3390/s19102419 ◽

2019 ◽

Vol 19 (10) ◽

pp. 2419 ◽

Cited By ~ 7

Author(s):

Gaia Pasqualotto ◽

Vinicio Carraro ◽

Roberto Menardi ◽

Tommaso Anfodillo

Keyword(s):

High Precision ◽

Water Uptake ◽

Sap Flow ◽

Irrigation Management ◽

Thermal Dissipation ◽

Flow Density ◽

Sapwood Area ◽

Tree Transpiration ◽

New Equation ◽

Species Specific

Thermal dissipation probe (TDP) method (Granier, 1985) is widely used to estimate tree transpiration (i.e., the water evaporated from the leaves) because it is simple to build, easy to install, and relatively inexpensive. However, the universality of the original calibration has been questioned and, in many cases, proved to be inaccurate. Thus, when the TDP is used in a new species, specific tests should be carried out. Our aim was to propose a new method for improving the accuracy of TDP on trees in the field. Small hazelnut trees (diameter at breast height 5 cm) were used for the experiment. The response of TDP sensors was compared with a reference water uptake measured with an electronic potometer system provided with a high precision liquid flow meter. We equipped three stems where we measured the sap flow density, the sapwood area (by using fuchsine), the total tree water uptake (reference), and the main meteorological parameters during summer 2018. Results confirmed that the original Granier’s calibration underestimated the effective tree transpiration (relative error about −60%). We proposed a new equation for improving the measurement accuracy within an error of about 4%. The system proposed appeared an easier solution compared to potted trees and particularly suitable for orchards, thus contributing to improve the irrigation management worldwide.

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Assessing reliability of HRM sap-flow sensors under large range of vapor pressure deficit

10.5194/egusphere-egu2020-3617 ◽

2020 ◽

Author(s):

Rémy Schoppach ◽

Daniella Ekwalla Hangue ◽

Julian Klaus

Keyword(s):

Vapor Pressure ◽

Sap Flow ◽

Vapor Pressure Deficit ◽

Heat Waves ◽

Linear Trend ◽

Water Flux ◽

Gravimetric Method ◽

Flow Sensors ◽

Tree Transpiration ◽

Sap Flow Sensors

Evapotranspiration (ET) is a major water flux of ecosystems and represents globally 60-80% of the incoming precipitation lost by terrestrial environments. In forested lands, tree transpiration (TR) is the dominant component of ET, yet remains challenging to measure. Over the years, sap-flow sensors have become the standard tool for quantifying tree TR and different methods based on thermal approaches have been developed. Heat ratio methods (HRM) are considered as the most reliable and accurate method to quantify absolute flows. Leading commercial brands ensure an accurate measurement of positive flows up to 100 cm hr-1 but different studies have highlighted a saturation effect at high flows with threshold for accuracy remaining elusive[RS1]&#160;. Due to climate change, the occurrence, the severity and the duration of extreme events like heat waves and dry periods are expected to increase in future, so the potential for high TR rate periods will also increase. Therefore, it is crucial to determine the species-specific environmental conditions allowing a reliable measurement of TR in order to improve or understanding of eco-hydrological and physiological processes during high potential TR periods that can be crucial for vegetation survival. In this study, we tested the accuracy of HRM sap-flow sensors for beech (Fagus sylvatica) and oak (Quercus robur) tree species under extreme vapor pressure deficit (VPD) conditions in order to determine threshold for reliable measurements. In greenhouse conditions, we collected a complete and dense series of TR response to VPD between 0.7 to 8.3 kPa for potted beech and oak trees using three different methods: infrared gas analyser, gravimetric method, and HRM sap-flow sensors. Responses shown a linear trend at the low-canopy leaf level (41.5 and 45.1 mg H2O m-2 s-1 kPa-1 respectively for beech and oak) but a bi-linear conformation at the whole plant level (1st slope = 12.04 &#177; 0.7 mg H2O m-2 s-1 kPa-1 and break-point at 3.9 &#177; 0.07 kPa for beech trees). Sap-flow sensors using the HRM method displayed a clear inability to reliably measure flows under high VPD conditions. Thresholds of 2.25 &#177; 0.04 and 2.87 &#177; 0.14 kPa were identified as the maximum limit of method reliability for beech and oak respectively. In highly demanding environments, we suggest a bi-linear extrapolation beyond VPD threshold for better quantifying tree TR. Further experiments aiming at characterizing TR responses to VPD for a broad range of species and in different water deficit conditions are certainly needed for better understanding tree transpiration at the whole stand level.

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