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ABSTRAK Penggunaan kayu jati muda merupakan solusi alternatif terhadap terbatasnya ketersediaan bahan baku yang dihadapi oleh industri mebel. Kayu muda cenderung memiliki kayu berkualitas rendah. Salah satu pengukur kualitas kayu adalah sifat struktur makroskopik. Penelitian bertujuan untuk mengetahui pengaruh umur pohon, bonita dan posisi aksial batang terhadap struktur makroskopis kayu dan kualitas kayu. Tiga puluh enam pohon jati muda ditebang dari kawasan hutan KPH Kendal, Provinsi Jawa Tengah. Tiga cakram berketebalan 3 cm diambil dari masing-masing posisi aksial batang, yaitu bagian pangkal, tengah dan ujung. Pengukuran proporsi kayu teras dan dimensi lingkaran tahun dilakukan berdasarkan perbedaan warna alami dan dengan menggunakan lembaran plastik transparan bergambar pola milimeter. Data dianalisis dengan analisis varians dalam rancangan acak lengkap berblok yang disusun secara faktorial. Pengujian lanjutan dilakukan dengan uji HSD Duncan. Kualitas kayu ditentukan dengan analisis determinan berdasarkan kurva normal Z. Hasil penelitian menunjukkan bahwa interaksi tiga faktor tidak berpengaruh terhadap proporsi kayu teras, dan dimensi lingkaran tahun. Interaksi kelas umur dan bonita pengaruh nyata terhadap proporsi kayu teras dan dimensi lingkarah tahun. Posisi aksial batang berpengaruh secara nyata terhadap proporsi kayu teras dan berpengaruh sangat nyata terhadap dimensi lingkaran tahun. Semakin mendekat pada posisi pangkal batang, semakin tinggi proporsi kayu teras dan dimensi lingkaran tahun. Interaksi tiga faktor yaitu kelas umur V, bonita 4 dan posisi tengah batang menghasilkan kualitas kayu tertinggi, yaitu kelas 2, dan interaksi kelas umur V, bonita 3 dan bagian ujung batang menghasilkan kualitas terendah, yaitu kelas 4. Penggunaan kayu berbasis kualitas akan memaksimalkan nilai guna dan meningkatkan umur pakai produk, sehingga mengurangi intensitas penebangan hutan dan lebih ramah lingkungan hidup. ABSTRACT Young teak utilization is an alternative solution of limited raw materials faced by furniture industry. Young wood tends to have a low-quality wood. One element for measuring wood quality is wood macroscopic structure properties. This study was aimed to determine the effect of tree age, site quality index and axial stem position on wood structures and wood quality. Thirty-six young teak trees were harvested on forest areas of Kendal Forest District, Central Java Province. Three disks were taken from each trunk, namely from the butt, middle and upper parts. Heartwood proportion and annual ring dimensions were measured based on natural color difference by using millimeter grid apparatus. Data were analyzed by using variance analysis arranged in blocked factorial and further testing were performed by using HSD Duncan. Wood quality was analyzed using determinant method which elaborated based on Z norm curve. Results showed that interaction of three factors did not affect on heart-wood proportion and growth ring dimensions. Interaction of age classes and site quality index influence significantly on heart-wood proportion and growth ring dimensions. Stem axial position significantly affects on heart-wood proportion and very significantly effect on growth ring dimensions. The lower wood position, the higher heart-wood proportion and the wider growth ring dimensions. Interaction of three factors namely class age V, site quality index 4 and middle trunk position has a highest wood quality, namely class 2, but interaction of age class V, site quality index 3 and top trunk has the lowest one, namely class 4. The use of wood-based quality will maximize the value and increase the product lifespan, thereby reducing the intensity of logging and become more environmental friendly.