せき悪地に造成したスギ林の生産力と施肥効果解析の一例

Abstract

極めてせき悪な場所に造成された28年生スギ林の生産力, 生産物質配分および施肥効果を調べた。その結果, 次の諸点が明らかとなった。1) この林分の葉量は3. 7t/haで, この葉が生産する地上部生産量は0. 74t/ha・yrと推定され, 一般のスギ林に比べると生産力も生産能率も著しく低い値であった。2) この林分の地上部生産量の55％が葉の生産に使われ, 幹41％, 枝4％の配分比であった。3) 林地施肥により, その後4年間にわたり, 幹の生産速度は著しく促進された。4) 幹の材積生長速度は, 施肥後の4年間だけでなく, その後も7年間以上にわたり, 高い水準に維持された。その効果も, 施肥効果のひとつであると推測された。

To examine the forest productivity corresponding to sterile soil conditions, the production rate of the above ground parts (Pn*) and the response in stem growth to forest fertilizer were investigated in a 28-year-old poor forest (Cryptomeria japonica D. Don) at Shirahama-chō of Wakayama Pref. The annual stem and branch production was estimated by the usual allometric method, and the leaf production rate was estimated by the method of cutting the new part. The leaf biomass (YL), net production (Pn*) and leaf efficiency (Pn*/YL) of this stand were very low due to the sterile condition (Table 2, Fig. 1, A). On the other hand, the allotment ratio of leaf production to the Pn* was very high, about 55 percent (Fig. 1, C), and the rotation rate of leaf (ΔYL/YL) was maintained constant (Fig. 1, B). These features seemed to be characteristics of the forest productivity on sterile soil conditions. Because the growth response to fertilization represented by diameter, cross-sectional and volume growth differ (Fig. 4), changes in volume growth of sample stems were examined from stem sections 0.3m above the ground. The duration of rapid growth directly after fertilization was very short, about 4 years in this poor forest (Fig. 5). The response to fertilization continued for more than 7 years after the prompt-growth.