| The ecological effects of eucalyptus have always been the focus of academic attention.In recent years,due to a series of problems brought by extreme climate,such as extreme drought and extreme precipitation,how to effectively manage large-scale plantations and their water allocation has become a top priority.Eucalyptus was widely introduced into my country in the 1980s due to its fast-growing properties.So far,there are different opinions about its high water consumption and"water pump".The theory of"water pump"stems from the general belief that eucalyptus has a large demand for water,which leads to a decrease in soil water content in the region.However,it is biased to study the water ecological effect of eucalyptus only from the perspective of water consumption,and it is difficult to fully and systematically understand the water ecological effect of eucalyptus.Based on this,in order to objectively understand the balance relationship between eucalyptus and water,this study explores the water ecological effects of eucalyptus plantations from the dual perspectives of tree species water consumption and stand water holding.The water ecological effect of eucalyptus plantation was comprehensively evaluated by the method of field real-time observation and the fuzzy comprehensive evaluation method.Based on the above research background,this study attempted to comprehensively evaluate the water ecological effects of eucalyptus plantations from the perspectives of tree species water consumption and stand water holding.In this study,the Haikou Forest Farm in Kunming was selected as the research area,and the three plantations were overmatured Eucalyptus benthamii plantation(OEB plantation)(34 years old),medium-aged E.benthamii plantation(MEB plantation)(9 years old),and overmatured Pinus armandii plantation(OPB plantation)(61 years old)were the research objects(the latter two were experimental controls).Synchronous observation for one year(2020.05-2021.04).Based on synchronous observation data,a fuzzy comprehensive evaluation method was introduced to comprehensively evaluate the water ecological effects of three plantations.The main findings are as follows:(1)The sap flow rates of the tree species did not differ significantly between the rainy season(2020.05-2020.10)and the dry season(2020.11-2021.04),and the average daily sap flow rate of OEB(0.037 m L/cm~2·min)was smaller than that of OPA(0.041 m L/cm~2·min)and MEB(0.046 m L/cm~2·min).The effects of surface soil moisture,photosynthetically active radiation,solar radiation,atmospheric temperature,saturated water vapour pressure difference,wind direction,gusts and wind speed were all positively correlated,while atmospheric pressure,soil temperature and relative humidity were negatively correlated for the sap flow rate in the trunks of the three tree species.(2)The average daily water consumption per tree during the study period was5.97 L/d,5.69 L/d and 9.44 L/d for OEB,MEB and OPA,respectively;at the stand scale,the daily water consumption was 1.19 mm,0.78 mm and 0.79 mm for OEB,MEB and OPA,respectively.The total water consumption of OEB,MEB and OPA during the study period was 436.10 mm,285.31 mm and 286.94 mm respectively,which accounted for 51.25%,39.25%and 39.20%of the total rainfall respectively.The total water consumption of OEB,MEB and OPA during the study period was436.10 mm,285.31 mm and 286.94 mm respectively,accounting for 51.25%,39.77%and 38.04%of the total rainfall respectively.(3)Canopy interception,trunk runoff,and throughfall varied with rainfall intensity.There was no significant difference in the total rainfall of OEB,MEB and OPA.The penetration rainfall of OEB and MEB was significantly higher than that of OPA.The trunk runoff of OEB was higher than that of MEB and higher than that of OPA.The canopy interception of OPA was significantly higher than that of OEB and MEB.There was no significant difference in the maximum water holding capacity of vegetation between OEB and MEB,but it was significantly larger than that of OPA;the maximum water holding capacity of litter in OPA was significantly greater than that of OEB and MEB.(4)The net increase of soil water storage in the rainy season(135.19 mm)of OEB was greater than that of MEB(88.23 mm)and OPA(87.14 mm),and its soil water loss in dry season(72.79 mm)was greater than that of MEB(22.64 mm)and OPA(40.72 mm),the relatively large amount of soil moisture loss in the dry season can leave more water storage space in the next rainy season.The difference between the net gain in soil water storage in the wet season and the loss of water in the dry season was 62.40 mm,65.59 mm and 46.42 mm for OEB,MEB and OPA respectively.The soil water surplus in both eucalyptus plantations was higher than that in OPA,which shows that the eucalyptus plantations did not cause soil water scarcity during the study period.The main factors affecting soil moisture content in the stands were rainfall,soil temperature,solar radiation,soil bulk density and soil capillary porosity.(5)The water ecological effect of the OEB is evaluated as medium(III),the water ecological effect of the MEB is evaluated as high(I)and the water ecological effect of the OPA is evaluated as high(I),indicating that the water ecological effect of the OEB is worse than that of the OPA and the MEB at the same age and lower age. |
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