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As the forest growth slowly, the change in it’s condition is relatively small. The mentioned change will be clearer if it is observed periodically with an interval of several years. A continuous aerial photographs is one of the tool can be applied for this purpose. In relation to this, an interpretation of several fixed observation points on a continuous aerial photographs has been conducted to explain the change in forest environmental condition. The observation object is Kyushu University Forests in Kasuya District with an area of 486.19ha. A serial of continuous aerial photographs taken in 1963, 1974, 1981 and 1986 has been applied in this study (Refer to Fig.1, Table 1 and Fig.2). Kasuya University Forests has been devided into 5 block namely A, B, C, D, and E. The observation point on aerial photographs has been plotted systematically with an interval of d=√<A/N>×100=√<486.19/316>×100=124.04≒120m, where A and n are forest area and the number of compartment in Kasuya University Forests, respectively. Accordingly, there are 308 observation point has been plotted on every set of aerial photographs (Refer to Table 2).Further, several classification has been made as the standard for interpretation of every observation point on aerial photographs as follows; (1) Species: Cryptomeria japonica(Sugi=S), Chamaecyparis obtusa (Hinoki =H), Pinus (Matsu=M), broadleaved (L), (2)Crown density dense (D_1), medium (D_2), sparse (D_3), (3) Crown diameter: small (C_1) medium (C_2), large (C_3), (4) Tree height: small (H_1), medium (H_2), high (H_3), and (5) Stand ages: juvenile (A_1), medium (A_2) and old (H_3), as presented in Table 3. The interpretation result for 4 sets of continuous aerial photographs are presented in Table 4. Regarding the factors that can not be clearly interpreted on aerial photographs, field observations have been conducted From the interpretation result was found that the corresponding occupied area of every observation point, α is equal to 1.44ha. The estimation of corresponding area for every factor on observation point was conducted and the actual area was observed plantation statistic data and forest survey statistic data (the expection for the corresponding area of photographs taken in 1963 where available data were not found). Then, t-test has been conducted to clearity the difference between estimated area and actual area for every species and age class (Refer to Table 5). As the result, the estimated area and actual area were not differ significantly. This mean that the estimated area to be fitted well to the actual area Further, crown density (D), crown diameter (C), tree height (H), and stand age (A) in every observation point were also interpreted and the interpretation result is presented in percentage (Refer to Table 8). Also, the relationship between interpreted and measured factors in every block are presented in graph. As the result, it was found that there is as mall variation in every block. However, in overall, there is a constant rate of forest to be preserved, especialy in the whole of observed area, the development of forest from the juvenile and medium to the old one is clearly observable. This mean that the original social function of forest expressed by forest environmental condition is being prevented well. Fig.3 shows the resultant figure of block A, B, C, D and E.
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生長が緩慢で変化の少ない森林も,数年単位でみるとそれなりに変化や推移が認められる.その度合や傾向を測定する方法の一つとして経年空中写真上での定点観測による判読測定を行ない,これにより森林環境の推移の状態を把握するテストを試みた.測定は九州大学粕屋演習林(面積486.19ha)を対象とした.また経年空中写真は1963年,1974年,1981年,および1986年に撮影された4組の空中写真を使用した(Fig.1,Tab,11eFig.2参照).まず,粕屋演習林全域をA,B,C,D,およびEの5ブロックに分けた.また森林環境の変化の最小単位は小班にあるとみなし小班当たり1点の定点観測点を空中写真上に設定することとした.粕屋演習林の小班数は全体で316個である.したがって316点を全域に対し一定間隔に設定することとし,設定間隔d=√<A/n>×100=√<486.19/316>×100=124.04≒120mを求めた.空中写真上への実際の測定点の設点は308点となった(Table2参照).この308点の測定点を4組の各空中写真上にそれぞれ対応させて設定した.次に,各測定点に対する空中写真の判読測定の基準を,①樹種:ヒノキ(H),スギ(S),マツ(M),広葉樹(L),②林齢:幼(A_1),中(A_2),壮(A_3),③疎密度:密(D_1),中(D_2),疎(D_3),④樹冠直径:小(C_1),中(C_2),大(C_3),および⑤樹高:低(H_1),中(H_2),高(H_3)とした(Table3参照).これにもとづいて行なった4組の経年空中写真に対する判読測定の結果はTable4に示すとおりである.なお,空中写真上で不明確な判読要因については現地チェックを行なった.以上の判読測定の結果から,まず,測定点1点当たりの占有面積aをd=120mからa=1.44haと計上し,各要因別写真判読面積を推定した.また造林台帳・森林調査簿から実面積を求めた(写真-1は資料がないため除外した).そしてa.樹種,およびb.齢階別の面積を対応させ(Table5参照),両者の対応性についてt検定を行なった.その結果,写真判読面積と実面積の間にはすべて有意差はなかった(Table6参照).すなわち写真判読の結果は実際の林分によく対応していることが確められた.次に,林齢(A),樹冠疎密度(D),樹冠直径(C),および樹高(H)の各測定要因があらわれる頻度つまり測定点にもとづく判読測定要因の出現数を百分率で求めた(Table8参照).また各ブロック毎,判読要因別に各測定要因を経年毎にグラフ上にプロットし,その推移の状態をグラフ上でチェックした.その結果はそれぞれの要因間ではA,B,C,D,およびEの各ブロックとも若干の変動はみられるものの,全体的にはほぼ一定の森林率が保たれていることが確められた.とくに対象地全域としては幼・中齢林の壮齢林化がすすんでいるという結果がみられた.すなわち森林の公益的機能の素因をなす森林環境はプラスの形で維持されているとみることができる.Fig.3はこれをA,B,C,D,およびEの各ブロックについて示したものである.
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