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Widyati Enny,Sutiyono,Darwo,Mindawati Nina,Yulianti Mira,Prameswari Diana,Abdulah Lutfy,Yuniarti Karnita,Baral Himlal 한국산림과학회 2022 Forest Science And Technology Vol.18 No.1
To produce large volumes of biomass for implementing its green energy policy, the Government of Indonesia has issued a short rotation energy plantation program for a num- ber of tree species including Calliandra calothyrsus (Meissn.). Optimum density and prompt harvesting are needed to maximise productivity, but information regarding both factors is insufficient. This study aimed to investigate the optimum growth spacing and ideal felling age to produce the largest volumes of biomass both economically and sustainably. Experiments were arranged on one hectare of land, which was divided into four plots with different plant spacing treatments (1 1.5 m; 1.5 1.5 m; 2 1.5 m; and 2 2 m). Growth and yield observations were carried out on plants aged 12, 18, and 24 months in each plot, with 30 sample trees left for growth observations and ten sample trees cut at each of the three ages after planting. This resulted in a total of 240 samples from the 2,710 trees planted. Trees were felled at 50 cm from the soil surface, and the resulting stools were left to regrow. A year after felling, resulting coppices, were observed and cut. Growth, productiv- ity and calorific value were studied for both ‘primary’ and ‘coppiced’ wood. Study results demonstrate that competition between plants strongly determines the growth and product- ivity of ‘primary’ wood. The plot with the densest plant spacing had the lowest nutrient con- tent for almost all soil nutrients. Higher plant density showed higher competition index values, and resulted in fewer and smaller diameter stems emerging from stools, and lower biomass productivity. Competition index values, which increased with plant age, can be used as an indicator for determining harvest timing. Productivity increased by up to 15% fol- lowing development as a coppice plantation. Optimum wood productivity and greatest economy came from parent stands with plant spacing of 2 2 m, harvested at 18 months old and coppiced. This treatment yielded an average biomass/tree of primary wood 7.2 kg and coppice wood 8.22 kg, respectively, with lignin content of approximately 22%, and calor- ific value of around 18,807 kJ. These values match biomass energy requirements for feed- stock for electricity generation. Harvesting at 24 months showed no significant increases in productivity, lignin content, or calorific value.