Gunung Leuser National Park forest in Bukit Lawang section is the main habitat of Sumatran Orangutan (Pongo abelii) in Sub-district of Bahorok. The condition of wildlife habitat in the region has been fragmented by various human activities which is the major threat to the wildlife survival including Sumatran Orangutan (Pongo abelii). This study was conducted by overlaid some spatial data of the year 2008 and 2018 to obtain data of vegetation density changes and the range of the Normalized Difference Vegetation Index (NDVI) in Section of Bukit Lawang and District of Bahorok. Vegetation analysis was carried out in forest, rubber plantation and mix plantation in District of Bahorok as supporting data. The purposes of this study are to Get vegetation density value and analysing the changes of vegetation density of Sumatran Orangutan (P. abelii) habitat in Bukit Lawang and Sub-district of Bahorok year of 2018. The research shows that the largest vegetation density changes was decreased of high dense class which is 47,040.02 hectare or 49.9%. The largest increased was occurred in the highest dense of 43, 304.1 hectare or 46.05%.

Forests in Indonesia that have high biodiversity, including one of them is the type of fern. The characteristic of Indonesian tropical rainforests is that they have high rainfall so that they strongly support the existence of this type of fern. In general, ferns like humid habitat conditions. The purpose of this study was to determine the types of ferns around the campus Sumatera Utara. The method of this research is by roaming, namely exploring each location that can represent the location where there is the most vegetation. The number of types of ferns found on the campus of the Universitas Sumatera Utara is 20 types. There are 9 families in the research location, including the polypodiaceae family as much as 35%, Pteridaceae (20%), Thelypteridaceae (15%), Nephrolepidaceae (10%), Aspleniaceae (10%), Athyriaceae (5%), Dryopteridaceae (5 %) and Blechnaceae (5%). There are 13 types that grow epiphytic and 7 that live terrestrially. The host trees for epiphytic ferns include Swietenia mahagoni, Elaeis guineensis, Gmelina arborea, Samanea saman and Paraserianthes falcataria.

Abstract. Zaitunah A, Samsuri, Ras S. 2021. Vegetation structure of Sumatran Orangutan (Pongo abelii) habitat in North Sumatra, Indonesia. Biodiversitas 22: 635-641. Gunung Leuser National Park forest in the Bukit Lawang section is the habitat of Sumatran Orangutan (Pongo abelii). There have been reports of the orangutans visiting the village. As some tree species are required for their sustenance to provide nests and food, there is a need to study species diversity availability in their habitat. Thus, the aim of the research was to analyze the composition and structure of the area's vegetation-this was done for the forestand mixed plantation. The sampling for the measurement of tree parameters was conducted using the line strip method. The strips (width 50 m, length 250 m) were constituted by a sub-plot measuring for seedling, pole, sapling, and trees. Within the sampling area, 181 species were found. Species within Dipterocarpaceae showed higher important value index (IVI) compared to other species in all layers. Shorea parviflora and Shorea ovalis were among the species with higher IVI in all the layers. The presence of species of Dipterocarpaceae and other species preferred by orangutans will support their quality of life. Therefore, orangutans prefer staying in the forest to entering the garden. Thus, it is concluded that their entry into the mixed gardens is related to the garden's proximity to the forest. Conservation efforts are needed to minimize the conflict between man and orangutan in the surrounding area.