Research On Applicability Of Thermal Dissipation Probe Method In Sap Flow Measurement Of Diffuse-porous Wood

Thermal dissipation probe based on thermal technology is one of the most widely used methods in the study of forest water consumption.In order to verify the applicability of this method to the determination of trunk sap flow in diffuse-porous wood.In this paper,Populus tomentosa,Platanus orientalis,and Salix matsudana,the main diffuse-porous wood in the north,are selected as the research objects.Set up three heating modes(continuous heating,heating for 10 min and 50 min intermittently,heating for 30 min and 30 min intermittent)to measure the trunk sap flow.At the same time,the whole tree container weighing method was used as the water consumption benchmark to evaluate the error of Granier’s formula for calculating the sap flow of the three kinds of diffuse-porous woods.Error correction was performed according to the evaluation results,and a corrected Granier formula was established.To improve the accuracy of forest water consumption measurement.The results are as follows:1.The trunk sap flow of the three diffuse-porous wood all showed obvious"single-peak" diurnal changes,which were consistent with the changes in micrometeorological factors,reflecting the normal growth and development of forest trees.Based on the measured value of the whole tree container weighing method,there is a large error in the trunk sap flow rate measured by TDP and calculated by the Granier formula.The error rates of Populus tomentosa,Platanus orientalis,and Salix matsudana are-67.74%,-84.28%,-62.99%.2.The species-specific correction formulas of Populus tomentosa,Platanus orientalis,and Salix matsudana have been established,and the combined correction formula of diffuse-porous wood are:Fd=0.0135K0.6952(R2=0.767),Fd=0.078K1.213(R2=0.822),Fd=0.0243K0.9936(R2=0.805),Fd=0.0172K0.7558(R2=0.751),the fitting effect is better.3.It is verified that the species-specific Granier correction formula of a single tree species works well.Verification index D>0.9,determination coefficient R2>0.8,RMSE=0.0218～0.0477,MAE and MBE are closer to 0,and the calculated flow rate error is only-3.39%～-12.53%compared with the reference value.4.The error rate of sap flow rate and transpiration rate of Populus tomentosa,Platanus orientalis,and Salix matsudana Calculated by the combined correction formula for diffuse-porous woods is in the range of-10.24%～-23.12%.The verification index between transpiration is D>0.8,the determination coefficient is R2>0.8,RMSE=0.0318～0.0644,MAE and MBE are close to 0.5.The diurnal variation trend of temperature difference between the two cyclic heating modes and continuous heating mode set for Populus tomentosa,Platanus orientalis,and Salix matsudana was basically consistent.In 10 min/50 min cyclic heating mode,the formulas of the correction sap flow rate of Populus tomentosa,Platanus orientalis,and Salix matsudana are Fd=0.0187K0.8529(R2=0.621),Fd=0.045K1.0067(R2=0.472),and Fd=0.1014K1.6547(R2=0.653),combined correction formula Fd=0.0209K0.8259(R2=0.578).The correction flow rate formulas of Populus tomentosa,Platanus orientalis,and Salix matsudana under the 30 min/30 min cyclic heating mode are Fd=0.0123K0.5765(R2=0.864),Fd=0.0621K0.953(R2=0.730),and Fd=0.0286K0.7687(R2=0.827),the combined correction formula is Fd=0.0166K0.5917(R2=0.708).The 30min/30min cyclic heating mode fits better.6.The error range of the sap flow rate and transpiration rate of the single tree species calculated by the 10 min/50 min correction formula is-6.79%～38.16%.The consistency index of the verification index between the sap flow and transpiration amount calculated by the 10min/50min correction formula is 0.7,determination coefficient R2>0.5,RMSE=0.0388～0.1103;The error range between the sap flow rate and the transpiration rate calculated by the 30 min/30 min correction formula is-4.27%～10.22%.The verification index D>0.9 is between the sap flow rate and the transpiration amount calculated by the 30min/30min correction formula.The measurement coefficient R2>0.8,RMSE=0.0300～0.0377.7.The 30 min/30 min combination correction formula for diffuse-porous wood is in the range of-12.02%～16.74%when calculating the flow rate and transpiration rate of Populus tomentosa,Platanus orientalis,and Salix matsudana D>0.8,and the determination coefficient R2>0.8,RMSE=0.0357～0.0428,MAE and MBE are closer to 0.Granite’s original formula based on TDP was used to calculate the sap flow rate of diffuse-porous wood,which was significantly lower than the reference value.The true transpiration rate could not be expressed,which caused a large error.The specific correction formula of tree species and the combined correction formula of diffuse-porous wood and the correction formula of 30 min/30 min can better reflect the relationship between K value and flow rate.Able to express real sap flow.Therefore,in practical applications,the correction formula can more accurately reflect the sap flow rate of diffuse-porous wood.