Pseudotsuga forrestii is a relict evergreen coniferous tree species in Pinaceae endemic to China.P.forrestii tree numbers have greatly decreased due to deforestation,over-utilization and habitat degradation.Here we cl...Pseudotsuga forrestii is a relict evergreen coniferous tree species in Pinaceae endemic to China.P.forrestii tree numbers have greatly decreased due to deforestation,over-utilization and habitat degradation.Here we clarify P.forrestii community types,structure,species diversity,seedling recruitments and growth trends.We identified four P.forrestii community types:(1)Pseudotsuga forrestii-Quercus guyavifolia-Acer davidii evergreen coniferous and broad-leaved mixed forest;(2)Pseudotsuga forrestii-Pinus yunnanensis-Quercus guyavifolia evergreen coniferous and broad-leaved mixed forest;(3)Pseudotsuga forrestii evergreen coniferous forest;(4)Pseudotsuga forrestii-Abies georgei var.smithii evergreen coniferous forest.P.forrestii forests are characterized by both warm temperate and temperate affinities.Simpson diversity,Pielou evenness,Shannon-Wiener diversity indices ranged from 0.75 to 0.76,0.74-0.81,and 1.62-1.93,respectively,with no significant differences among the four forest types.The forest stratification was multilayered.The canopy layer was generally 10-25 m tall,with the emergent layer reached 25-42 m.DBH and age structures of P.forrestii showed multimodal distributions.Its maximum age P.forrestii was 570 years with a DBH of 143 cm.The growth of annual ring width of P.forrestii was slow,and generally decreased with age,whereas the basal area at the breast height increased with age.Established seedlings/saplings were mainly found in unstable micro-habitats.Regeneration of P.forrestii depends on moderate natural disturbances.Finally,we provide recommendations for P.forrestii conservation.展开更多
This research assessed empirically the quantitative analysis of some selected food imports of Nigeria (rice, wheat and sugar). Time series data were used to examine the determinant of total food imports and the trend ...This research assessed empirically the quantitative analysis of some selected food imports of Nigeria (rice, wheat and sugar). Time series data were used to examine the determinant of total food imports and the trend in the quantity of the food imported. The secondary data were obtained from institutional and national database over 1981-2010. Descriptive statistics, regression and correlation analysis were used as analytical tools. Statistical analysis shows that food deficit began in the 1970’s, when Nigeria started the importation of food to feed the country. The result of the correlation analysis shows that the postulated determinants of food imports were positively correlated with the quantity of food import. The test for the individual variables shows that;national income explains 40%, external reserves explains 38%, food production index explains 46%, population explains 58% and exchange rate explains 74% of the total variation in the quantity of food import. The over-all goodness of fit of the regression analysis result shows that, the postulated regressors namely, relative price, national income, external reserves, lagged index of domestic food production, population estimate and exchange rate explained approximately 70% of the variability in the quantity of the selected food imports for the period of study. Consequently, there is the need for Nigeria to shift base from the ideology of nationalist orientation, as well as afro centric point of view and move towards unrestrained export-led growth that seeks to develop that market as the first option with corresponding development in international trade. This is however possible by limiting the importation of foods/raw materials that can be sourced for locally, increasing the domestic production of food generally and maintaining a healthy foreign investment with developed countries as a short term measure while in the long run, diversification of the economy, massive investment in agriculture and introduction of population control measures could serve as saviours to lower the rate of increase in food import demand.展开更多
基金This study received financial support from the Science and Technology Department of Yunnan University,China(2019YNU002)Major Program for Basic Research Project of Yunnan Province,China(202101BC070002)the Special Foundation for National Science and Technology Basic Resources Investigation of China(2019FY202300).
文摘Pseudotsuga forrestii is a relict evergreen coniferous tree species in Pinaceae endemic to China.P.forrestii tree numbers have greatly decreased due to deforestation,over-utilization and habitat degradation.Here we clarify P.forrestii community types,structure,species diversity,seedling recruitments and growth trends.We identified four P.forrestii community types:(1)Pseudotsuga forrestii-Quercus guyavifolia-Acer davidii evergreen coniferous and broad-leaved mixed forest;(2)Pseudotsuga forrestii-Pinus yunnanensis-Quercus guyavifolia evergreen coniferous and broad-leaved mixed forest;(3)Pseudotsuga forrestii evergreen coniferous forest;(4)Pseudotsuga forrestii-Abies georgei var.smithii evergreen coniferous forest.P.forrestii forests are characterized by both warm temperate and temperate affinities.Simpson diversity,Pielou evenness,Shannon-Wiener diversity indices ranged from 0.75 to 0.76,0.74-0.81,and 1.62-1.93,respectively,with no significant differences among the four forest types.The forest stratification was multilayered.The canopy layer was generally 10-25 m tall,with the emergent layer reached 25-42 m.DBH and age structures of P.forrestii showed multimodal distributions.Its maximum age P.forrestii was 570 years with a DBH of 143 cm.The growth of annual ring width of P.forrestii was slow,and generally decreased with age,whereas the basal area at the breast height increased with age.Established seedlings/saplings were mainly found in unstable micro-habitats.Regeneration of P.forrestii depends on moderate natural disturbances.Finally,we provide recommendations for P.forrestii conservation.
文摘This research assessed empirically the quantitative analysis of some selected food imports of Nigeria (rice, wheat and sugar). Time series data were used to examine the determinant of total food imports and the trend in the quantity of the food imported. The secondary data were obtained from institutional and national database over 1981-2010. Descriptive statistics, regression and correlation analysis were used as analytical tools. Statistical analysis shows that food deficit began in the 1970’s, when Nigeria started the importation of food to feed the country. The result of the correlation analysis shows that the postulated determinants of food imports were positively correlated with the quantity of food import. The test for the individual variables shows that;national income explains 40%, external reserves explains 38%, food production index explains 46%, population explains 58% and exchange rate explains 74% of the total variation in the quantity of food import. The over-all goodness of fit of the regression analysis result shows that, the postulated regressors namely, relative price, national income, external reserves, lagged index of domestic food production, population estimate and exchange rate explained approximately 70% of the variability in the quantity of the selected food imports for the period of study. Consequently, there is the need for Nigeria to shift base from the ideology of nationalist orientation, as well as afro centric point of view and move towards unrestrained export-led growth that seeks to develop that market as the first option with corresponding development in international trade. This is however possible by limiting the importation of foods/raw materials that can be sourced for locally, increasing the domestic production of food generally and maintaining a healthy foreign investment with developed countries as a short term measure while in the long run, diversification of the economy, massive investment in agriculture and introduction of population control measures could serve as saviours to lower the rate of increase in food import demand.
