1 Model Pendugaan Biomassa Diatas Permukaan Tanah Jenis Eucalyptus urophylla Pada Hutan Tanaman Marulam MT Simarmata 1 Jan Ricky Tambunan 2 1 Dosen Fakultas Pertanian USI 2 Alumni Fakultas Pertanian USI E-mail : simarmatamarulam@yahoo.com Abstract Although global climate changes issue after which talked a few times ago but world concern seriously after Earth High Confrence in Rio de Janeirio Brazil on 1992. Ones alternatives in controlling the carbon concentration is through development of sink program, in which organic carbon resulted from fotosyntesis is fixed in biomass of forest vegetation or woody trees. Indonesia is very potential to develop carbon sink program because have third largest areas of tropical rain forest after Brazil and Zaire. The most indicator to estimating forest potency for sink carbon is biomass. Biomass study is very important to studied forest ecosystem characteristic, expecially to analysis management system of sustainable principles. This research aim explain to ; 1) Now about above ground biomass component of eucalyptus urophylla (trunk, branch and twigs) from industrial forest plantations of PT. Toba Pulp Lestari; 2) to pile up allometric similarity for estimate above ground biomass from industrial forest plantations of TP. Toba Pulp Lestari. Data of this research is collected with inventory of 21 trees sample from 7 age class. The trees sample is taken with purposive sampling and cut down. The biomass estimating which used in this research is non destructive models with pile up allometric similarity, to find fault correlation trees dimency with biomass. Choosing the best allometric similarity based on criterias determination correlation (R 2 ), Mean Square Error (MSE) and Predicted Residual Sum of Square (PRESS) by Drapper et al, (1996). The result from this research that; 1) Above ground biomass can be enhanced more by riding age class; 2) Trunck has been the largest biomass proporcy without the biomass proporcy of branch and twigs; 3) The moisture contents can be enhanced by riding age class and 4) Dimencion of trees (dbh and h) is the best parameters for estimate about above ground biomass. ------------------------------------------------------------------------------------------------------------ Key words : Eucalyptus urophylla, biomass, carbon, estimating, forest plantations. PENDAHULUAN Perubahan fungsi lahan seperti konversi hutan merupakan salah satu penyebab penting perubahan iklim global, disamping peningkatan polusi udara di Indonesia, perubahan iklim global telah mempengaruhi ekosistem teresterial yaitu terjadinya peruba- han suhu, ketersediaan air dan meningkatnya akumulasi karbon di atmosfir. Indikator penting untuk menghitung potensi hutan sebagai sequester karbon adalah biomassa karena sebagian besar karbon