Influences of soil properties and stem density on the growth and inner bark biomass of paper mulberry (Broussonetia papyrifera) in natural stands, Thailand

Abstract

Natural stands of paper mulberry are the main source of raw material for paper mulberry manufacturing. Stand improvement is needed for proper growth and high yield. Three 5×10 m sample plots (50 m²) of different tree and stem density (low, medium and high density as Plot A, B and C, respectively) were set on Mae Charim district, Nan province, and Wang chin district, Phrae province, Thailand, which are famous for paper mulberry production. Within all plots, soil properties, crown closure, growth and biomass were investigated. In this study, stem density correlated to inner bark biomass; soil fertility and light intensity also contributed to growth enhancement. As for soil nutrients, available phosphorus showed a significant correlation to paper mulberry growth. Although paper mulberry in the Wang chin site had a higher average stem density after the first harvesting than paper mulberry in the Mae Charim site, the former site resulted in a lower inner bark yield that may have been caused by low soil fertility and smaller number of stems in the 1.5 - 3.5 cm DBH class (economical stems) than those in the Mae Charim site, except in plot C.. In both study sites and the two annual harvesting periods, inner bark biomass in Plot C was the highest followed by those in Plot B and then A. . Therefore, among sites with similar soil fertility (site quality), increasing stem density resulted in higher inner bark yield. Applying fertilizer and maintaining 2 - 3 stems m^-2 is recommended for paper mulberry stands in Thailand.