Prediksi Lebar Tajuk Pohon Dominan pada Pertanaman Jati Asal Kebun Benih Klon di Kesatuan Pemangkuan Hutan Ngawi, Jawa Timur

Abstract

Penelitian ini bertujuan untuk menentukan model perkembangan lebar tajuk pohon dominan jati asal Kebun Benih Klon pada tegakan berkualitas baik.Penelitian dilakukan di Kesatuan Pemangkuan Hutan Ngawi pada petak tanaman jati asal Kebun Benih Klon bertumbuhan baik pada umur 615 tahun. Petak tanaman bertumbuhan baik ditentukan berdasarkan kriteria persentase keberhasilan tanaman, rata-rata tinggi pohon dan rata-rata diameter batang serta aksesibilitasnya. Pada petak yang memenuhi syarat bertumbuhan baik dipilih sebanyak 30 sampel pohon dominan dan tiap sampel diukur radius tajuk pada empat arah mata angin. Hasil pengukuran radius tajuk digunakan untuk menghitung rata-rata radius tajuk sebagai rata-rata kuadratik 4 arah pengukuran radius tajuk dan lebar tajuk sebagai dua kali rata-rata radius tajuk. Rata-rata aritmatik dari lebar tajuk 30 pohon dominan tiap petak pengukuran digunakan sebagai variabel respons dan umur tegakan sebagai variabel prediktor. Data pengukuran selanjutnya dipilah menjadi dua bagian, yaitu sebagian besar untuk pengembangan model dan satu bagian lagi untuk validasi model. Analisis regresi non linear dengan metode kuadrat terkecil digunakan untuk memilih 4 kandidat model penduga rata-rata lebar tajuk, yaitu model Sigmoid, Power, Schumacher dan Gompertz. Pemilihan model didasarkan atas nilai koefisien determinasi tertinggi dan standard error of the estimate terkecil serta signifikansi uji F dan uji T. Akhirnya, model terbaik diuji kelayakannya dengan kriteria root mean squared error, simpangan agregatif dan simpangan relatif. Model Gompertz adalah model terbaik untuk memprediksi perkembangan rata-rata lebar tajuk pohon dominan, yang dapat dituliskan dengan persamaan:

CW = 6,585 Xe-0,705xe-0,091sage

dan dapat menjelaskan 79% variasi data. Model tersebut lolos validasi dan layak digunakan untuk memprediksi rata-rata lebar tajuk pohon dominan jati asal Kebun Benih Klon pada tegakan berkualitas baik umur 6 tahun sampai dengan umur 15 tahun di Kesatuan Pemangkuan Hutan Ngawi.

Predicting Crown-width of Dominant Trees on Teak Plantation from Clonal Seed Orchards in Ngawi Forest Management Unit, East Java

Abstract

This study aims to determine the model of crown width development of the dominant teak tree planted using seeds from clonal seed orchards. The research was carried out in Ngawi Forest Management Unit on the good quality teak compartment having stands age from 6 to 15 years old. The good quality compartments were determined based on higher stand density, taller average tree height, larger average stem diameter, and good accessibility. In a well-qualified compartment, 30 samples of the dominant tree were selected and each sample was measured for the crown radius in the four radii. The measured crown radius was used to calculate average crown radius as a quadratic mean of 4-crown radii and crown width as double of average crown radius. The arithmetic mean of the crown width of the 30 dominant trees in each measured compartment was used as the response variable and stand age as the predictor variable. The measurement data were then sorted into two parts, namely: mostly for model fitting and the remaining for model validation. Non-linear regression analysis with the least squares method was used to evaluate 4 candidate models of average crown width, namely: Sigmoid, Power, Schumacher, and Gompertz models. The model selection was based on the highest coefficient of determination and the smallest standard error of the estimate and the significance of F test and T test. The best model was eventually validated using the following criteria : root mean squared error, aggregate deviation, and relative deviation. Gompertz model was the best model to predict the average crown width development of dominant teak tree and expressed as:

CW = 6.585 Xe-0.705xe-0.091xage

and able to explain 79% variation of data. The model was passed based on statistical validation and it was feasible for predicting the average of crown width of dominant teak tree from clonal seed orchards on good quality stand aged 6 to 15 years in Ngawi Forest Management Unit.