森林立地学会誌 森林立地37(2), 1995, pp, 67〜76
論 文
幼齢林の養分動態に及ぼす雑草木と下刈りの影響
高 橋 輝 昌・生 原 喜久雄・相 場 芳 憲
戸 田 浩 人・福 田 誠
雑草木と下刈りが幼齢林の養分循環に及ぼす影響を明らかにする目的で，スギとヒノキの幼齢林において，雑草木量と雑草木中の養分量の変化，下草通過雨の水質，下草通過雨に含まれる養分量と下刈りで林地に供給された有機物の分解を調査した。また，下草通過雨の水質を生態的に安定した壮齢林の林内雨と比較するために，隣接するスギとヒノキの壮齢林（85年生）で調査した。3〜5年生時の雑草木量は3〜5t・ha-1であり,雑草木中の養分含有量は壮齢林での年間の吸収量に相当した。幼齢林では植栽木の養分吸収量が少なく，幼齢林の地上部への養分吸収の多くは雑草木によって行われていた。下草通過雨量は林外雨量の約90％であり，壮齢林の林内雨量の70％よりも多かった。下草通過雨のpH（5〜7）は，林外雨や壮齢林の林内雨のpH（4〜5）よりも高かった。また，落葉期にはN以外の溶存元素濃度が著しく増加した。このように雑草木はスギやヒノキの壮齢林に比べて元素が溶脱しやすかった。下刈りで土壌に供給された粗大有機物は急激に分解され減少した。下刈り後の累積地温と有機物の残存率の関係は指数曲線で近似できた。土壌への養分供給量は下刈りを行った方が，下刈りを行わなかった場合に比べて多かった。しかし，下刈り直後に多量の養分が土壌に供給され，養分吸収量の少ない植栽木には利用されにくいと考えられた。下刈りを行わなかった場合には雑草木から土壌への養分供給は比較的安定していた。
Terumasa
TAKAHASHI, Kikuo HAIBARA, Yoshinori AIBA, Hiroto TODA, Makoto FUKUDA: Effects of weeds and weeding on nutrients
dynamics in young stands: Jpn. J. For. Environment 37, 67-76, 1995
Changes in weed cover, weed nutrient
contents, water chemistry of throughfall and the decomposition process of
organic matter after weeding were investigated in stands of young Japanese
cedar (Cryptomeria japonica D. Don)
and Japanese cypress (Chamaecyparis
obtusa Endl.) to study the effects of weeds and weeding on the nutrient
dynamics of young stands. Nutrient contents of throughfall in established
Japanese cedar and Japanese cypress stands adjacent to the young stands was
investigated for comparison with that of young stands. Weed cover amounted to 3〜5 t・ha-1 in 3〜5-yr-old stands and the nutrient contents of weeds
equaled the amount of uptake by established stands. The weeds took more
nutrients from the soil than did the young trees. The throughfall in the young
stands was approximately 90% of the precipitation and was more than the
throughfall of the established stands. The pH values of the weed throughfall (5〜7) were higher than those of the
precipitation and the throughfall (4〜5) in the established stands. In the defoliate
period, significant increases in the dissolved element concentrations except N
were observed in the weed throughfall, because weeds easily leached mineral
nutrients. The relationships between the accumulated surface soil temperature
after weeding and the residual organic matter satisfied an exponential curve.
Great amounts of nutrients were supplied to the soil by the weeding, but most
of the nutrients supplied by the decomposition of weeded organic matter could
not be used by the young stands, because there was little nutrient uptake by
planted trees. Therefore, nonweeding can provide a constant nutrient supply in
young stands. The complete weeding is not advantage for maintaining soil
productivity and effective biological utilization of nutrient in young stand.