Nutrient Status of Different Ages on Cryptomeria japonica Plantations (Study at Ehime University Forest)

Abstract

C. japonica has been planted throughout Japan and covers 44% of all Japanese plantation forests. Afforestation involve development in stand structures and environment conditions at differents ages. Stand development patterns can be inferred by studying stands of different ages within the same geographic, edaphic and physiographic conditions. The effect of age on nutrient dynamics of plantation was important, since nutrients play fundamental roles in the primary production of plantations. Studies describing nutrient trend in plantation development, especially those providing information on the amounts of nutrient in soils, forest floor and vegetation, which influenced management decisions were important. Therefore there is a need to carry out study on nutrient status in sugi plantation of different ages. The objectives of this research were to describe the effect of ages on the trend of (i) diameter at breast heigh (dbh) (ii) leaf C, N and C/N ratio (iii) FF biomass, C, N and C/N ratio (v) soil C, N, C/N ratio and exchangeable cations of sugi plantation To assess long-term changes on nutrient dynamics, samples were collected on 7 plots of sugi plantations (0, 5, 10, 20 30, 50 and 100 year old) in the Ehime University Forest. FF, soil and leaf were sampled with five replications in each plot. Also dbh of 10 trees in each plot of sugi plantations were measured. Soil sampling was confined to the upper 10 cm of soils. FF was collected on 25 x 25 cm 2 in each plot. Total C and N of soil, FF and leaf of sugi were analysed by dry combustion method with C and N analyzer MT -700 II type. The exchangeable cations were extracted by ammonium acetate pH 7 1N, then quantified using atomic absorption spectrophotomoter (AAS). Dbh of sugi plantation increased with ages. The dbh increase rate of sugi was high until 50 years old, then relatively steady from 50 to 100 years old, indicates the harvest time of sugi plantation in Ehime University Forest can be done with 50 year rotation. The similar trend was also showed on FF biomass of sugi. Leaf C and C/N ratio contents of sugi plantation were relatively steady from 0 to 100 years old. Foliar and branch FF C and foliar FF C/N ratio content was increase with age, indicates C accumulation on FF. Leaf N contents of sugi plantation decreased from 0 to 30 years old, then increased from 30 to 100 years old. The similar trend was also showed on foliar FF N content. The trend of age effect on soil C and N content of sugi plantation was an increase from 0 to 30 years old and a decrease from 30 to 100 years old. This indicated higher C and N input from FF decomposition at early stages of sugi plantation development than at mature stages of sugi plantation. To increase FF decomposition of sugi plantation, three alternatives can possibly be done: (1) Establishment of mixed species plantation of sugi with another species of Japanese plantation forest (2) Regular thinning practices on sugi plantation. (3) Minimize soil disturbance. An increase of FF decomposition rate until later stage of sugi plantation development will increase soil C and N. This will improve productivity and ecological sustainability