A Comparative Study On Ecosystem-atmosphere Fluxes Of Tropical Seasonal Deciduous And Evergreen Forests In Thailand

The tropical forest vegetation canopy is tall and complex,the tree species are rich and diverse,and rich carbon is stored,which plays a very important role in global carbon balance,water cycle and energy budget.The torrid zone are mostly underdeveloped areas,and the research strength is weak.Coupled with the research on tropical forests,there are many new challenges to the technical requirements.Therefore,our understanding of tropical forests is still very insufficient.In Thailand,which is 18 degrees north latitude,some areas have annual rainfall of up to 1600 mm,but seasonal deciduous forests are widely spread.In some areas with lower annual rainfall?1300-1400 mm?,the forest can maintain evergreen throughout the year.How this difference in canopy phenology affects the material and energy exchange fluxes between the ecosystem and the atmosphere,and how these exchange fluxes can be used to reveal the causes of different canopy phenology in forests,is a scientific question worth eploring.In order to answer this scientific question,we carried out a systematic comparative analysis based on two long-term positioning stations,based on years of flux monitoring data,and combined with remote sensing vegetation index.The main results are:?1?There is a significant difference in the changes in LAI and NDVI at the MKL and SKR.In the past 20 years,the NDVI values of both have increased slightly.?2?The diurnal changes of net radiation?Rn?,latent heat flux?LE?,sensible heat flux?H?and soil heat flux?G?are consistent,all of which are obvious unimodal,and all are peak at noon.The annual average closure of MKL deciduous forest is 0.46,and the average annual closure of SKR evergreen forest is 0.91.?3?There is no significant difference in the radiant fluxes at the two observation points of MKL and SKR.On the seasonal scale,there are extremely significant differences in total solar radiation and surface reflection radiation in the dry and rainy seasons about MKL?P<0.01?,and there is no significant difference in total solar radiation and surface reflection radiation in the dry and rainy seasons about SKR.However,there were extremely significant differences in atmospheric long-wave radiation between the MKL and SKR observation points during the dry and rainy seasons?P<0.01?.There was no significant difference in the surface reflection radiation and net radiation between the MKL and SKR observation points during the dry and rainy seasons.The daily changes of the land surface albedo of MKL and SKR show a“U”-shaped trend.Generally,the land surface albedo of SKR observation points is larger than MKL.?4?The diurnal variation of CO₂flux at the MKL presents an asymmetric“U”-shaped change trend.The CO₂flux is related to the sensible heat flux?H?,latent heat flux?LE?,net radiation?Rn?,relative humidity?Rh?and soil heat flux?G?showed a very significant correlation?P<0.01?.?5?The daily change trends of WUE at MKL and SKR show different patterns.The value of WUE at MKL is 1.75 times that of SKR.Both observation points WUE are strongly correlated with temperature?Ta?,air relative humidity?Rh?,and water vapor pressure?VPD?.