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.