Studies On Water Consumption Of Three Main Afforestation Tree Species In Yunmou Dry-hot Valley Of Southwest China

Abstract:The thermal dissipation probes(TDP) were applied to measure the sap flow of main afforestation tree species:Albizia kalkora、Azadirachta Indica and Acacia auriculaeformis, in Yunmou dry-hot valley of Southwest China, from2011July to2012June.Soil moisture and meteorological factors such as photosynthetic active radiation, air temperature, relative humidity, water vapor pressure deficit(VPD) and wind speed were measured at the same time. Seasonal and Diurnal change of stem sap flow of Albizia kalkora, Azadirachta Indica and Acacia auriculaeformis was analyzed.And the influence of meteorological factors and soil factors on the stem sap flow was explained. Simulation equation between meteorological factors and the sap flow rate was obtained. Then forest water consumption was reckoned by using the relationship model of water consumption along the diameter variation.The results showed:(1)The diurnal variation of sap flow of Albizzia kalkora and Acacia auriculaeformis displayed a typical peaked curve during the wet and dry seasons. The diurnal variation of sap flow of Azadirachta Indica is same as the sap flow of Albizzia kalkora and Acacia auriculaeformis in the wet season.however,in the dry seasin,especially in January、 February and March, the starting time of sap flow in the wet season was later than in the wet season,it’s at14:30pm.And the highest values of sap flow velocity also delay from day to night. The diurnal variation of sap flow of Azadirachta Indica is displayed a curve which was higher value at night and was lower value in the day.Under different weather conditions and different positions, there are obvious differences. The mean and highest value of sap flow velocities in a sunny day was higher than those in rainy and cloudy day.By comparing with the mean sap flow rate and water consumption of Albizia kalkora, Azadirachta Indica and Acacia auriculaeformis, in the typical months of dry and wet season, the mean value of sap flow velocities and water consumption in the wet season(July,August) were higher than those in the dry season(January, February and March). Besides, the mean sap flow rate and water consumption of Albizia kalkora were higher than those of Azadirachta Indica and Acacia auriculaeformis.And the curves of three main afforestation tree species have same trend, under different weather conditions. (2)Sap-flow velocity of Albizia kalkora and Acacia auriculaeformis was significantly correlated with PAR, air temperature,VPD and wind speed,and was negatively correlated with atmospheric relative humidity, in the dry and wet season. However, sap-flow velocity of Azadirachta Indica was significantly correlated with VPD, atmospheric relative humidity and wind speed, and was negatively correlated with PAR and air temperature. The ranking of correlation coefficients was PAR>VPD>air temperature>relative humidity> wind speed.(3) The stem sap flow of the three tree species was significantly correlated with the radiation (PAR) and vapor pressure deficit (VPD), and the stem sap flow was lagged behind PAR but ahead of VPD. The time lags were10-20min, between stem sap flow of the three tree species and PAR. While the time lags were90-120min, between stem sap flow of the three tree species and VPD.There was a small difference among the time lags of the three tree species and PAR. And the diurnal sap flow was more dependent on PAR than on VPD.The time lag between the stem sap flow and PAR/VPD was not correlated with the tree features, such as DBH, tree heigh, canopy area, sapwood area and the nocturnal water recharge.(4) A significant correlation between sapwood area and diameter at breast height (DBH) was found. The prediction model is well fitted by linear model. The equation of Azadirachta Indica is:y=6.5655x-20.204; The equation of Acacia auriculaeformis:y=6.3876x-16.101.Water consumption is mainly concentrated in the May to August, while the other months remain relatively low level. By building up the relationship model of single tree water consumption along the diameter change, it was realized that the prediction and estimation of water consumption of different diameter sizes of Azadirachta Indica and Acacia auriculaeformis. The diurnal accumulated flux of Acacia auriculaeformis and Azadirachta Indica forest was just0.11m3in January and0.51m3in July.