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No.61 (2014/12) >

Title :沖縄県におけるフクギの樹齢推定に関する調査研究
Title alternative :Age Estimation of Fukugi Trees in Okinawa Prefecture
Authors :仲間, 勇栄
柴田, 昌和
陳, 碧霞
Authors alternative :Nakama, Yuei
Shibata, Masakazu
Chen, Bixia
Issue Date :27-Dec-2014
Abstract :The tree age estimation formula developed by Hirata (2006) is not suitable for all regions in Okinawa Prefecture because its calculation was based on a small number of samples from only a few areas. This study aimed to revise the Hirata method by considering environmental factors. Samples for analysis were collected from a wide range of areas in Okinawa Prefecture. Following this, the growth rings were counted in samples and compared with the results obtained using the Hirata method. In total, 14 samples were collected from Mainland Okinawa, Tarama Island in Miyako Island City, and Ibaruma in Ishigaki City. In the present study, two methods were developed to determine the age of Fukugi trees grown in a general environment: 1) Estimated age (year) = [3.4908 x diameter (cm) at the height of 20-30 cm above ground level] - 11.538 2) Estimated age (year) = [diameter (cm) at the height of 20-30 cm above ground level] )/2 x 6.2 The age estimate using the Hirata method by multiplying the diameter at 20-30 cm above ground level instead of multiplying the diameter at breast height is applicable to trees with a diameter lesser than 10 cm or greater than 70 cm. Therefore, it showed approximately 10-year error. However, the deviation from the calculation result using the Hirata method is large for trees with a diameter ranging from 10-70 cm measured at 20-30 cm above ground level. This error in the age estimate is attributed to the rapid growth rate in this age range. On average, approximately 6.2 growth rings were counted for every centimeter of a diameter. We obtained an average error of 9.2 years by calculating the estimated age according to the Hirata method by multiplying the radius (cm) at the height of 20-30 cm above ground level by 6.2. In particular, this exhibited a good fit for the samples with a diameter lesser than 40 cm. Therefore, we conclude that the second method can be applicable to estimate the tree age. From the variance of increment in growth rings among the three samples from Tarama Island in Miyako Island City, a Tarama-specific method was proposed as follows: 3) Estimated age (years) in Tarama Island = [6.317 x radius (cm) at the height of 20-30 cm above ground level] + 1.152 A correlation between the growth ring increments and annual precipitation was found.
平田(2006)によりDBHを利用したフクギの樹齢推定式が提案されたが、平田式の算出に用いたサンプル数は少なく採取地も限定しているため、沖縄全域のフクギに対応する確証は得られていない。そこで本研究では、平田式の改良や環境に対応したフクギの樹齢推定式の検討を目的とした。調査方法として、沖縄県の複数地域からフクギの円板サンプルを採集し、得られたサンプルの推定樹齢と平田式による計算値との比較を行った。沖縄本島、多良間村、石垣市伊原間から合計14本のサンプルが採集できた。今回得られたサンプルから、一般的な樹齢推定式として、次の2つの式が算出できた。推定樹齢(年)=[3.4908×採取高20~30cmの直径(cm)]-11.538 推定樹齢(年)=[採取高20~30cmの直径(cm)÷2]×6.2 (本) 平田式に関しては、胸高直径ではなく採取高20~30cmの直径を用いた場合は、採取高直径10cm以下及び70cm以上のものに対しては、誤差10年以内で、有効であると推測された。採取高直径10~70cm の範囲の推定樹齢と平田式計算値との差は大きかった。その理由はその範囲内では肥大生長が盛んになるためと考られる。全サンプルの1cm当たりの平均年輪数は6.2本であるため、平田式に則り「採取高の半径×6.2」で樹齢を推定して平田式計算値との比較を行った。その結果、平均9.6年の差で収まり、特に直径約40cm以内のものとすることが可能だと考えられる。多良間村で採取された3つのサンプルの年輪幅累加値の変動から、多良間村独自の次式が導き出された。年輪幅累加値は年間降水量の変動と相関関係、があると推測された。推定樹齢(年)=[6.317×地上高20~30cmの半径(cm)]+1.152
Type Local :紀要論文
ISSN :0370-4246
Publisher :琉球大学農学部
URI :http://hdl.handle.net/20.500.12000/31694
Appears in Collections:No.61 (2014/12)

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