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: Estimating Stand Volume of the Community Forests at the Taman Wijaya Rasa Cooperative (Kostajasa) Kebumen Regency Using Plot Sampling
Abstrak: Metode inventarisasi hutan yang efisien diperlukan untuk mendukung pengelolaan hutan rakyat. Namun, masih sedikit penelitian tentang ukuran plot contoh lingkaran yang sesuai untuk memperkirakan volume tegakan hutan rakyat. Penelitian ini bertujuan menentukan ukuran plot contoh lingkaran yang optimal untuk menduga volume tegakan hutan rakyat Kostajasa. Pendugaan volume tegakan dilakukan dengan menggunakan 81 plot contoh dengan lima ukuran yaitu 0,01 ha, 0,02 ha, 0,03 ha, 0,04 ha, dan 0,05 ha yang ditempatkan di lapangan dengan menggunakan metode pengambilan contoh acak sederhana. Data yang diukur pada setiap plot contoh adalah jenis pohon, diameter setinggi dada, dan tinggi pohon. Hasil penelitian menunjukkan bahwa ukuran plot yang paling optimal untuk menduga volume tegakan di hutan rakyat adalah 0,05 ha dengan sampling error 9,24%., An efficient forest inventory method is required to support community forest management. However, there is still few studies on the appropriate size of a circular sample plot for estimating stand volume of community forests. This study aimed to determine an optimal size of the circular sample plot for estimating the stand volume of Kostajasa’s community forests. The stand volume estimation was carried out using 81 sample plots with five sizes, namely 0,01 ha, 0,02 ha, 0,03 ha, 0,04 ha, and 0,05 ha, which were established in the field using the simple random sampling method. The data measured in each sample plot were tree species, diameter at breast height, and tree height. This study showed that the most optimal plot size for estimating stand volume in community forests is 0,05 ha with a sampling error of 9,24%.
Keyword: community forest, sample plot, volume

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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