Model Dinamika Struktur Tegakan Hutan Alam Bekas Tebangan di Provinsi Kalimantan Tengah, Kalimantan Barat, dan Kalimantan Selatan

Abstract

Most of the natural forest areas in Indonesia are logged over areas, in which their stand structures are different from those of primary forests. The phenomenon of stand structure dynamics includes recruitment, upgrowth, and mortality. The sustainability of productive forests depends on, among others, forest growth capability, environmental characteristics and proper forest management techniques in accordance with the ability of forest dynamic process. The objective of this study was to obtain dynamic models for the stand structures of logged over natural forests for each diameter classes and tree species groups, and then used them to predict stand structures for the next few years by using a stand structure projection method. This study used periodical measurement data from 44 permanent sample plots (PSP), which were established in the logged over areas of 5 HPH (timber concession companies) in West Kalimantan, 1 HPH in South Kalimantan, and 12 HPH in Central Kalimantan Provinces. Each PSP was one hectare in size, and it had various logging times and measurement periods. Data processing was carried out in the four stages : 1) analyzing the stand growth of each PSP in a 3-year period ; 2) species grouping (i.e. Dipterocarp and Non-Dipterocarp) and diameter grouping into 11 diameter classes (starting from 10-14,99 cm up to 60 cm up; 3) calculating the number and basal area of trees for each species group at each PSP; and 4) analyzing the data by using regression analysis to derive prediction models for projecting the dynamic of stand structures. Results showed that the upgrowth models for Dipterocarpaceae had coefficients of determination (R2) ranging from 14.8% to 70.4%, while those for Non-Dipeterocarpaceae ranging from 12.0% to 92.2%. The fixed models had R2 ranging from 5.4% to 73.0% (for Dipterocarpaceae) and from 5.6% to 82.3% (for Non-Dipeterocarpaceae). For diameter classes with non significant relationships or R2 < 50%, the mean of proportions was used to calculate the probabilities of upgrowth and stay on such diameter classes. The projection result of stand structure dynamics up to 51 years showed that the number of trees was increase. However, the projected stand structures tended to not follow the common “inverse J” curve of stand structure. Therefore, the projected stand structures were only recommended for no more than 12 years, which was also the maximum limit of the after logging period as used for constructing the models.