Judul: Species Composition and Stand Potential of Private Forests  in Kostajasa, Central Java Province
Abstrak: Hutan rakyat merupakan hutan yang diusahakan di lahan yang dibebani hak milik. Hutan rakyat ditanam dengan beberapa pola tanam, seperti monokultur, campuran, dan agroforestri. Masing-masing pola tanam memiliki komposisi jenis dan potensi tegakan yang berbeda-beda. Penelitian ini bertujuan menganalisis komposisi jenis dan menghitung potensi tegakan di hutan rakyat Kostajasa. Analisis vegetasi dilakukan dengan kegiatan Inventarisasi Tegakan Sebelum Penebangan (ITSP). Metode ITSP yang digunakan adalah metode jalur berseling dengan jarak antar jalur 10 meter dan lebar jalur 10 meter. Lokasi penelitian ditetapkan di tiga hutan rakyat yang akan ditebang butuh oleh petani pemilik hutan. Pengamatan dilakukan terhadap semua tingkat pertumbuhan pohon. Variabel yang diukur meliputi jenis pohon, jumlah pohon, diameter, tinggi bebas cabang, dan tinggi total. Hasil penelitian menunjukkan bahwa kerapatan pada tingkat semai sebesar 3628 ind/ha, pancang 317 ind/ha, tiang 475 ind/ha, dan pohon 391 ind/ha. Jenis pohon yang memiliki potensi kayu tertinggi adalah mahoni (Swietenia macrophylla) dengan jumlah pohon sebesar 208 batang/ha dan volume kayu sebesar 204,48 m3/ha. Mahoni merupakan jenis dengan Indeks Nilai Penting tertinggi pada seluruh tingkat pertumbuhan pohon., Private forests are forests cultivated on land encumbered by property rights. Private forests are planted with several cropping patterns, such as monoculture, mixed cropping, and agroforestry. Each planting pattern has a different species composition and stand potential. This study aims to analyze species composition and calculate stand potential of private forests in Kostajasa. Vegetation analysis was carried out with pre-harvest inventory activities. The method used in pre-harvest inventory is the alternating path method, with a distance between paths of 10 meters and a path width of 10 meters. The research location were set in three private forests that would be cut as needed by farmers who owned the forests. Observations were made on the growth rate of trees. Variables measured included tree species, number of trees, diameter, commercial height, and total height. The study showed that the density of seedling was 3628 ind/ha, sapling 317 ind/ha, pole 475 ind/ha, and tree 391 ind/ha. The tree species with the highest timber potential is mahogany (Swietenia macrophylla), with 208 trees/ha and a timber volume of 204,48 m3/ha. Mahogany is the species with the highest Importance Value Index at all growth rate of tree.
Keyword: analisis vegetasi, hutan rakyat, komposisi jenis, potensi tegakan

Judul: Techniques, Productivity, and Costs of Tree Felling in Private Forests Kostajasa, Central Java
Abstrak: Penebangan pohon di hutan rakyat memerlukan teknik yang tepat untuk meminimalkan kerusakan yang ditimbulkan dan sesuai dengan kondisi lokal. Penelitian ini bertujuan untuk mengidentifikasi teknik-teknik penebangan pohon, menghitung produktivitas, dan biaya penebangan di hutan rakyat Kostajasa. Penelitian ini dilakukan di empat lahan hutan rakyat di Kostajasa, yang mana setiap lahan dikerjakan oleh tim penebang yang berbeda. Pengukuran waktu kerja dilakukan menggunakan metode null stop. Produktivitas dihitung dengan membagi volume pohon berdiri dengan waktu kerja. Data biaya diperoleh melalui wawancara dengan tim penebang dan data sekunder. Hasil penelitian menunjukkan bahwa teknik penebangan yang digunakan di hutan rakyat Kostajasa adalah bervariasi, yaitu teknik tebang konvensional, teknik penebangan dengan bantuan tali, dan teknik tebang dengan pemangkasan dahan. Produktivitas penebangan di lahan 1, 2, 3, dan 4 berturut-turut adalah 2,9 m3/jam; 2,5 m3/jam; 8,9 m3/jam; dan 6,8 m3/jam. Biaya penebangan per unit untuk lahan 1, 2, 3, dan 4 berturut-turut sebesar Rp 22.435/m3; Rp 28.854/m3; Rp 7.987/m3; dan Rp 10.087/m3., Forest harvesting in private forests requires appropriate techniques to minimize the damage caused and suitable with local situations. This study aims to identify tree felling techniques, calculate productivity, and costs in the Kostajasa private forest. This study was conducted in four areas of the Kostajasa private forest, each of which was worked on by different team of loggers. Working time was measured using the null-stop method. Productivity was obtained through a comparison between the volume of standing tree and time of work produced. Costs were obtained from direct interviews with the felling team on each land. The results of the study show that the logging techniques used in Kostajasa private forests are varied, namely conventional logging techniques, logging techniques with the help of ropes, and cutting techniques with pruning branches. The productivity produced on land 1, 2, 3, and 4 is, respectively, 2,9 m3 /hour; 2,5 m3 /hour; 8,9 m3 /hour; and 6,8 m3 /hour. With the cost per unit used on land 1, 2, 3, and 4, respectively, amounting to Rp 22.435/m3; Rp 28.854/m3; Rp 7.987/m3; and Rp 10.087/m3.
Keyword: cost, logging, private forests, productivity, working time

Judul: Hamiltonian formulation for linear waves motion in two layers fluid
Abstrak: The surface wave could be considered as a wave that separates two fluids, namely water and air. Based on this assumption, it is introduced the interfacial wave, a wave between two layers of fluid with different density. The formulation of interfacial waves motion begins with deriving the base equation of irrotational ideal fluid. Furthermore, according to irrotational fluid assumption, the base equation can be stated in velocity potential. In this derivation, the fluids domain is assumed to be restricted by rigid lid boundary conditions, both at the upper and lower limit. Therefore, the interfacial waves motion can be explained in a hamiltonian formulation. In the hamiltonian formulation, total energy is defined as the sum of kinetic and potential energy. The hamiltonian system is obtained from reduction of kinetic energy by using the Dirichlet Neumann Operator. The resulted kinetic energy equation is nonlinear. Therefore, this form is linearized by first part of the Taylor expansion. This linearization gives a dispersion relation of linear wave. Based on this dispersion relation, the phase speed of the linear wave depends on the density ratio of the two layers fluid.
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