Productivity Characteristics Of Chinese Fir Plantations And Its Controls In The Northern Part Of Subtropics

Chinese fir(Cunninghamia lanceolata)is an important fast-growing timber species in southern China.The productivity maintenance of Chinese fir plantation is of great significance to China’s social and economic development and timber strategic security.Soil is the main source of water and nutrients for plants.The site soil regimes has an important impact on forest productivity and are important for forest sustainable management.In this study,an investigation of Chinese fir plantations in the northern part of subtropics was conducted to reveal the growth characteristics of Chinese fir plantation in different forest ages,stand density and altitude gradient and the restriction of soil physical and chemical properties on the growth of mature Chinese fir.its productivity.The major results were as follows.(1)The biomass of Chinese fir plantation in the southern Anhui and Mt.Dabie ranged from 45.98-143.46 t/hm2 and 97.13-365.76 t/hm2,respectively.The biomass was significantly higher in Mt.Dabie than in southern Anhui,while there were not significantly different among the age classes.The annual productivity of Chinese fir plantations in Mt.Dabie and southern Anhui were 4.77-5.64 t/hm2/a and 4.98-12.86 t/hm2/a,respectively.The annual productivity of the young forests in Mt.Dabie was significantly higher than that in the southern Anhui.However,the differences were not significant between the other age classes.In general,the growth of Chinese fir plantations in Mt.Dabie was better than that in southern Anhui.This had a certain relationship with the better forest protection in Mt.Dabie.(2)The average diameter at breast height and tree height of the stands increased with the increase of stand age.The stand biomass increased with forest age,and the productivity of stand increased first and then decreased with the increase of forest age.(3)The average diameter at breast height and tree height of the stand decreased with the increase of stand density.The biomass and annual productivity of the stand increased first and then decreased with the increase of stand density,but the trend was not significant.This indicated that the growth of the diameter at breast height was more sensitive to stand density than other growth parameters.(4)The average diameter at breast height,tree height,biomass and annual productivity of the stand increased first and then decreased with the increase of altitude.Except for the average diameter at breast height,the other growth parameters were not significantly different between different altitudes.This indicates that the growth of diameter at breast height was significantly affected by the altitude than the other growth parameters.(5)Stand growth parameters were significantly correlated to soil nutrient content.Soil pH was significantly positively correlated with soil available phosphorus.The growth parameters of stand was significantly negatively correlated with soil bulk density.The bulk density over 1.20 g/cm3 was not favorable to Chinese fir plantation.(6)The fine root biomass in 0-30 cm soil layer ranged from 258.76 to 367.68 g/m2Fine root biomass was significantly positively correlated with stand biomass and stand density.The contents of N and P in fine root ranged from 4.894 to 7.609 g/kg and from 0.355 to 0.456 g/kg,respectively.The fine root N/P ratio was positively correlated with its N content and had no significant correlation with P content.The content of N and P in fine roots increased with the increase of soil N content,and increased first and then decreased with the increase of soil P content.It indicated that fine root growth was mainly controlled by soil N.Fine root biomass and N and P contents were significantly negatively correlated with soil bulk density,indicating that high soil bulk density was not favorable to fine root growth.(7)The N and P contents in the current-year foliage ranged from 11.361 to 15.371 g/kg and from 0.514 to 1.247 g/kg,respectively.The N/P ratio was significantly negatively correlated with N and P contents.The majority of foliar N/P ratio was greater than 16,indicating that the growth of the current-year foliage was mainly limited by soil P availability.The N and P contents in the current-year foliage were significantly negatively correlated with soil bulk density,suggesting that the increase in soil bulk density was not favorable to the nutrient accumulation in the current-year foliage.