Methods of suppressing colonizing sedge to help to establish tree seedlings in a natural forest

Abstract

Dense bamboo grasses have delayed the growth of tree seedlings after the wind damage in a natural coniferous forest in deep mountains of Kiso District, Central Japan. After suppression treatment of the bamboo grass, a native sedge Carex oxyandra replaced them and made the growth of tree seedlings worse. The technique to suppress colonized Carex oxyandra is unknown, since this sedge has not ever been a harmful weed to be controlled. Thus, we established first experimental plots for suppressing Carex oxyandra by a herbicide, glyphosate potassium salt solution (Roundup Max load) by normal levels of dilution (control without herbicide, diluted to ×25, ×50 and ×100 volume with water) in May 2010. Next experimental plots with above-normal levels (diluted to ×100, ×200, ×400, ×800, ×1,600 and ×3,200) were established in June 2011. Coverage percentage, plant height of Carex oxyandra and tree seedlings were measured in each plot in autumn up to 2015. As a result, coverage and plant height of Carex oxyandra decreased obviously after a half year in all dilution levels, and the suppressing effect continued during 2 years in the lower dilution from ×25 to ×400. However, withered leaves formed a carpet-like thick mat, which remained several years and was suspected to restrict the germination and growth of tree seedlings. Consequently, the herbicide proved out effective to the sedge for 2 years, but some additional treatment is needed to secure the foundation space for tree seedlings within the mat of withered leaves.