Judul: Komposisi Vegetasi dan Keanekaragaman Tumbuhan Obat di Arboretum PT Arara Abadi Provinsi Riau
Abstrak: One of potency natural resources in PT. Arara Abadi’s Arboretum is medicinal plants. A study on vegetation composition and diversity of medicinal plants in the area of PT. Arara Abadi’s Arboretum was conducted during October-November 2009. The data that were collected during the study consisted of primary and secondary data. The primary data consisted of medicinal plants species that were collected through vegetation analysis. The secondary data were general condition of study location consisted of wide and geographically location, climate, hydrological data, flora and fauna. The vegetation analysis used combination of strip and quadrate sampling techniques. The sampling plots were (20 x 50) of meter square width that consisted of 4 strips. The sampling plot was allocated systematically at every 100 m far from each strip. Line is again divided into (20 x 20) of meter plots for trees, (10 x 10) of meter for the pole, (5 x 5) of meter for the stake, and (2 x 2) for seedlings. The result of the vegetation composition in PT. Arara Abadi’s arboretum consisted of 102 species from 47 families. Based on Important Value Index (IVI) the tree level was dominated by Meranti (Shorea smithiana) (48.06 %), the sapling level was dominated by Meranti (Shorea smithiana) (41.43%), the pole level was dominated by Medang (Litsea odoreifera) (34.68%), the seedling level was dominated by Kelat (Syzygium) (20.60%). The biodiversity of plants species that have potency as medicinal plants were 38 species from 25 families, those were 37% from the total plants species found in PT. Arara Abadi’s Arboretum.
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Judul: Komposisi Jenis dan Struktur Tegakan Arboretum Fakultas Kehutanan dan Lingkungan IPB
Abstrak: Ekosistem hutan terdiri dari komunitas pohon dan sumber hayati lainnya yang saling terhubung satu sama lain dan dengan lingkungannya. Hubungan ini dapat dilihat melalui jumlah variasi jenis tumbuhan dan struktur tumbuhan tersebut. Tujuan dari penelitian ini adalah mendeskripsikan komposisi jenis tumbuhan dan menganalisis struktur tegakan di Arboretum Fakultas Kehutanan dan Lingkungan IPB. Metode yang digunakan adalah metode kuadrat (petak). Analisis data meliputi analisis vegetasi, dan analisis nilai Indeks Nilai Penting (INP). Hasil penelitian menunjukkan bahwa komposisi jenis pada tegakan hutan Arboretum Fakultas Kehutanan dan Lingkungan IPB didominasi oleh jenis Arthropyllum diversifolium, Calophyllum soulattri, Maesopsis eminii, Khaya anthotheca pada tingkat pohon dan permudaannya dan, Piper aduncum, dan Dracaena Fragrans pada tingkat tumbuhan bawah. Jumlah jenis pohon berikut permudaannya dan tumbuhan bawah berjumlah sebanyak 48 jenis. Stratifikasi tajuk tegakan Arboretum Fakultas Kehutanan dan Lingkungan IPB didominasi oleh stratum C dengan struktur tegakannya berbentuk huruf J terbalik., Forest ecosystems consist of communities of trees and other biological resources that are interconnected with each other and with their environment. This relationship can be seen through the number of variations in plant species and plant structure. The purpose of this study was to describe the composition of plant species and to analyze the structure of the stands in the Arboretum of the Faculty of Forestry and Environment, IPB. The method used is the quadratic method (plots). Data analysis includes analysis of vegetation, and analysis of Important Value Index (INP) values. The results showed that the species composition of the Arboretum forest stands of the Faculty of Forestry and Environment IPB was dominated by the species Arthropyllum diversifolium, Calophyllum soulattri, Maesopsis eminii and, Khaya anthotheca at trees with their regeneration, Piper aduncum, and Dracaena Fragrans at undergrowth. The total number of species for trees with their regeneration and undergrowth is 48 species. The canopy stratification of the Arboretum of Faculty of Forestry and Environment of IPB is dominated by stratum C with an iverted J shaped stand structure.
Keyword: arboretum, type composition, stratum, structure

Judul: Bifurkasi Hopf pada Model Siklus Bisnis Kaldor Kalecki tanpa dan dengan Waktu Tunda
Abstrak: Business cycle model is one of dynamical system models in economic. One of the business cycles model is Kaldor-Kalecki model. Kaldor-Kalecki business cycle model that is written in delayed defferential equations, is a business cycle model that involves gross product and capital stock of a company. In this paper Kaldor-Kalecki business cycle model is analyzed using both nondelay and delay in time of capital stock. By Taylor expansion for the time delayed model, an analysis of stability around the fixed points has been done. Furthermore, by using Hopf bifurcation theorem, it can be shown that there exists periodic orbits and limit cycle. In the nondelayed model, changing the parameter of goods market could lead to the occurrence of Hopf bifurcation and the existence of limit cycle. Similarly, for the delayed model, it has been shown that changing the time delay parameter may result in the occurrence of Hopf bifurcation and limit cycle.
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