Impact of Vegetation Shift from Coniferous and Broadleaf Mixed Forest to Eucalyptus Plantation on the Microclimate

For better understanding the impact of forest vegetation shift on the beneath microclimate and its ecological effects,3～4-year old eucalyptus plantation(planted in 2008,08EU)and coniferous broadleaf mixed forest(MF)were selected.Microclimatic conditions including air temperature,soil temperature and air relative humidity inside the two stands were monitored for 1year.The results showed that:(1)no difference in mean daily air temperature,mean daily relative humidity or daily max relative humidity was observed between the two stands;(2)annual average of surface soil temperature,daily max air temperature,daily air temperature range and coefficient of air temperature variation in eucalyptus were 1.5℃,1.4℃,2.2℃ and 40% higher than that inside mixed forest,respectively,but daily minimum air temperature was 0.8℃ lower than that in MF.There was 6.7% decrease of annual minimum air relative humidity in 08EU comparing with that in MF,but 16.4% of daily air relative humidity range and 22.0% coefficient of air humidity variation in 08EU higher than that in MF,respectively;(3)the range of daily air temperature and relative humidity were significantly positively or negatively related to the mean or minimum daily value,respectively,but no significant relation with max value,the largest different of microclimate condition between 08EU with MF was observed in autumn and winter seasons;(4)minimum air temperature and minimum humidity appearance times in eucalyptus plantation were 51 and 45minutes earlier than that in mixed forest,respectively.The changes of microclimate conditions beneath eucalyptus plantation would increase the rates of soil water evaporation and organic matter decomposition.