Growth Increment and Slenderness of 15-Year-Old Ulin (Eusideroxylon zwageri T. et B.) Plants in the Ex-situ Conservation Area of the State Agricultural Polytechnic of Samarinda

This research was motivated by the lack of information regarding growth dynamics, increment rates, and the slenderness ratio of Ulin (Eusideroxylon zwageri T. et B.) at the juvenile stage in an ex-situ conservation area. Ulin is an endemic tree species of Bornean tropical rainforests that is categorized as rare and protected, making conservation efforts and growth evaluation essential. The purpose of this study was to determine the diameter increment, height increment, and slenderness ratio of 15 year old Ulin plants. The research was conducted in the Ex-situ Conservation Area of the State Agricultural Polytechnic of Samarinda by measuring 68 individual plant samples. The observed parameters included stem diameter, total height, annual increment, and the slenderness ratio (H/D). The results showed that the average diameter of the 15 year old Ulin plants reached 9.78 cm, and the average total height reached 10.24 m. The average annual increments were recorded at 0.65 cm/year for diameter and 0.68 m/year for height. Meanwhile, the stand slenderness ratio ranged from 72.23 to 143.33 with an average value of 108.70, indicating that the trees grew under relatively intense growing space competition.