森林立地学会誌　森林立地45(2),2003,93〜98

Jpn.J.For.Environment 45(2), 93-98 2003

 

苗畑土壌における植林後の土壌炭素・窒素蓄積量の変化

 

酒井寿夫^＊＊・稲垣昌宏^＊＊＊・高橋正通^＊＊＊＊・野口享太郎^＊＊＊＊・田中　格^{＊＊＊＊＊}

^＊＊森林総合研究所北海道支所・^＊＊＊国際農林水産業研究センター・^＊＊＊＊森林総合研究所

^{＊＊＊＊＊}山梨県森林総合研究所　　

 

　新規植林に伴う土壌炭素・窒素蓄積増加を明らかにするため，苗畑において若い林分を含む４林分から土壌と堆積有機物を採取し，A₀層を含めた土壌有機物の蓄積速度を求めた。

　各林分の土壌0-5cmの炭素・窒素蓄積増加速度はスギ幼齢林（2年生）では60.3gC m^-2yr^-1，4.66gN m^-2yr^-1，広葉樹混交林（6年生）では47.3gC m^-2yr^-1，2.57gN m^-2yr^-1，ヒメコマツ林（18年生）では14.0gC m^-2yr^-1，0.70gN m^-2yr^-1，スギ林（33年生）では19.0gC m^-2yr^-1，1.01gN m^-2yr^-1で，若い林分で蓄積増加速度が速い傾向にあった。

　A₀層中の炭素・窒素蓄積増加量は，林齢との相関が見られなかったが，土壌0-5cmの蓄積量は炭素，窒素ともに植栽年数とともに増加した。炭素と窒素の平均的な蓄積増加速度はそれぞれ18.7gC m^-2yr^-1と0.99gN m^-2yr^-1であった。

　土壌における蓄積速度の推定については土壌深5-10cmにおける炭素・窒素密度を植栽初期の値と仮定して計算したため，林齢の高い林分で蓄積増加量を低めに見積もった可能性があったが，新規植林後は林齢の増加とともに土壌中の有機物は明らかに増加していた。

 

　Hisao Sakai, Masahiro Inagaki, Masamichi Takahashi, Kyotarou Noguchi and Tadashi Tanaka : Changes in carbon and nitrogen accumulation in the soil after afforestation on nursery soils

  To determine the accumulation rates of soil carbon and nitrogen after afforestation practice, we investigated surface soil and organic layer in different aged four nurseries, from a two years-old stand to a 33 years-old stand.

  The accumulation rate of carbon and nitrogen in the soil of 0-5cm depth were 60.3gC m^-2yr^-1, 4.66gN m^-2yr^-1 in 2 years-old stand (Cryptomeria japonica), 47.3gC m^-2yr^-1, 2.57gN m^-2yr^-1 in 6 years-old stand (deciduous tree), 14.0gC m^-2yr^-1, 0.70gN m^-2yr^-1, in 18 years-old stand (Pinus parviflora), 19.0gC m^-2yr^-1, 1.01gN m^-2yr^-1 in 33 years-old stand (Crytomeria japonica). The accumulation rate of carbon and nitrogen in soil tended to be faster in younger stand.

  Althrough the accumulations of carbon and nitrogen in the organic layer were not correlated with stand ages, the accumulations of carbon and nitrogen in the soil of 0-5cm depth were linearly correlated with stand ages. The mean accumulation rate of carbon and nitrogen in soil was estimated at 18.7gC m^-2yr^-1 and 0.99gN m^-2yr^-1, respectively.

  Since the reference layer (5-10cm depth) was used in order to estimate the accumulation rates of soil carbon and nitrogen, the accumulation rates may have been estimated to be low. But, carbon and nitrogen in the soil of 0-5cm depth were clearly increased after afforestation. 

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