Kajian kualitas tapak hutan tanaman industri hibrid Eucalyptus urograndis sebagai bahan baku industri pulp dalam pengelolaan hutan lestari (Studi Kasus di PT Toba Pulp Lestari, Simalungun, Sumatera Utara )

Abstract

Eucalyptus urograndis (E. urophylla x E. grandis) is a hybrid resulting from cross mating between species E. urophylla S.T. Blake and species E. grandis W.Hill ex Maid and constitutes one of the fast growing species being used as pulp industry raw materials in Sector of Aek Nauli, PT Toba Pulp Lestari, North Sumatra. With the progressive decrease in length of cutting rotation, it is feared that there would be negative impacts on site quality which will ultimately influence productivity, if there is no proper management. The objective of this research was studying site quality of industrial plantation forests of E. urograndis hybrid. This research used survey method by collecting field data in first and second rotation (stand ages of 1, 2, 3, 4 and 5 years). Research results showed that up to age of 5 years, stand growth of E. urograndis hybrid at first rotation reached utilizable volume of 159.89 m3/ha, whereas at second rotation the volume acquired 142.49 m3, so there was volume decrease by 10.8 %. Rotation of maximum volume for first rotation occurred at age of 5.4 years with average volume increment of around 31.85 m3/ha/year, and that of second rotation occurred at age of 6 years with average volume increment of 28.80 m3/ha/ year. There was biomass decrease by 6.3 % for stems with diameter ≥ 5 cm between first and second rotation. There was decrease in site quality from first to second rotation as reflected by decrease in nutrient content in soil, up to depth of 40 cm by 24% for N, 16% for K, 6% for Ca and 16% for Mg. Nutrient elements P and Ca in soils had positive correlation with dominant height of E. urograndis hybrid. On the basis of results of leaf analysis, it could be shown that nutrient N was highly deficient, whereas nutrients Ca and Mg were categorized as deficient so they constituted the limiting factors for growth of E. urograndis hybrid which were planted in Inceptisol soils. Dynamics of nutrient balance with cutting rotation of 5 years was predicted to have negative balance, since the end of first rotation, up to rotation 5. At cutting rotation of 6 years, nutrient balance of N, K and Ca were positive, only at the end of rotation 1, whereas nutrient balances of P and Mg were still positive up to rotation 2. At cutting rotation of 7 years, nutrient balances of N, K and Ca had been negative since the end of rotation 1, except the nutrient balances of P and Mg which were still positive at the end of rotation 1. Quality of site with rotation of 5 years decreased more rapidly as compared with those with cutting rotation of 6 and 7 years. Fertilizer application and several silvicultural techniques are required for recovery of sites and nutrient balance. On the basis of maximum volume rotation, it could be suggested that the optimum rotation for hybrid of E. urograndis in Inceptisol soils is 6 years.