Long-term changes in radial growth of seven tree species in the mixed broadleaf-Korean pine forest in Northeast China:Are deciduous trees favored by climate change?

The role of the temperate mixed broadleaf-Korean pine forest(BKF)in global biogeochemical cycles will depend on how the tree species community responds to climate;however,species-specific responses and vulner-abilities of common trees in BKF to extreme climates are poorly understood.Here we used dendrochronological meth-ods to assess radial growth of seven main tree species(Pinus koraiensis,Picea jezoensis,Abies nephrolepis,Fraxinus mandshurica,Phellodendron amurense,Quercus mongolica,and Ulmus davidiana)in an old-growth BKF in response to climate changes in the Xiaoxing’an Mountains and to improve predictions of changes in the tree species compo-sition.Temperature in most months and winter precipita-tion significantly negatively affected growth of P.jezoensis and A.nephrolepis,but positively impacted growth of P.koraiensis and the broadleaf species,especially F.mandshu-rica and U.davidiana.Precipitation and relative humidity in June significantly positively impacted the growth of most tree species.The positive effect of the temperature during the previous non-growing season(PNG)on growth of F.mandshurica and Q.mongolica strengthened significantly with rapid warming around 1981,while the impact of PNG temperature on the growth of P.jezoensis and A.nephrolepis changed from significantly negative to weakly negative or positive at this time.The negative response of radial growth of P.jezoensis and A.nephrolepis to precipitation during the growing season gradually weakened,and the negative response to PNG precipitation was enhanced.Among the studied species,P.koraiensis was the most resistant to drought,and U.davidiana recovered the best after extreme drought.Ulmus davidiana,P.jezoensis and A.nephrolepis were more resistant to extreme cold than the other species.Climate warming generally exacerbated the opposite growth patterns of conifer(decline)and broadleaf(increase)spe-cies.Deciduous broadleaf tree species in the old-growth BKF probably will gradually become dominant as warming continues.Species-specific growth-climate relationships should be considered in future models of biogeochemical cycles and in forestry management practices.

Correlation Between Phase Stability and Tensile Properties of the Ni-Based Superalloy MAR-M247

Phase stability and its effect on tensile properties of MAR-M247 alloy have been investigated during thermal exposure at 800–900°C for up to 10,000 h.Detailed investigations reveal that the larger secondaryγ′phase has no obvious growth,but the smaller tertiaryγ′phase obviously coarsens and the coalescence occurs during thermal exposure at 850°C and below.γ′coarsening behavior is consistent with the description of Ostwald ripening theory beforeγ′coalescence.Hf-rich blocky MC carbide shows excellent thermal stability,but Ta-rich script-type MC carbide gradually degenerates via reaction,MC+γ→M_(23)C_(6)+γ′and finally formsγ film around MC and M_(23)C_(6) carbides.With increasing thermal exposure time,the tensile strength decreases.The ductility first increases and then decreases during exposure at 800°C,but it decreases continuously at 900°C.In addition,the ductility keeps almost constant when the exposure time is longer than 5000 h.