The Structure, Composition, and Health of Remnant Forest Vegetation of West Timor, Indonesia

Aims: The forest of West Timor has been cleared for different purposes for decades, leaving only small patches of remnant forest vegetation. Understanding tree-shrub composition and structure of this remnant forest vegetation is a vital instrument in assessing the sustainability of forest, species conservation, and management of forest ecosystems. This research was therefore conducted to investigate the current structure and composition pattern of tree-shrub species in such remnant forest vegetation.

Study Design: This research project was designed using a vegetation survey employing the Point Centered Quarter Method.

Place and Duration of Study: The research project was conducted in five sample stands of remnant forest vegetation, namely Oliana, Tablolong, Fatukoa, Oenesu, and Alak, the District of Kupang, West Timor, Indonesia, between April to July 2020.

Methodology: In each sample stand, the tree-shrub vegetation was surveyed using Point Centered Quarter Method by placing three 100-m-long transects. The first transect was placed at random and the second and third transects were placed parallel to the first, with a distance of 100 m between two transects. Sample points were then determined in an interval of 10 m along each transect to construct four quarters. In each quarter, the nearest tree or shrub (≥ 1 m height) to the sample point was identified and the distance measured. For each tree or shrub species, number of individual, dominance, frequency, Importance Value Index (IVI), stem diameter at 0.5 m height, and average value of plant height for each species were determined. Index Similarity (IS) between stands were also calculated using Sørensen Coefficient.

Results: Of the 600 invidual tree and shrub measured in a total of about 1,500-m-long line transect, about 28 tree-shrub species of 16 families were identified. The number of plant/hectare was 833 and the mean number of species/stand was 9.60 (sd = 1.94). Generally, the number of species and families found in the remnant vegetation community was relatively low compared to that of commonly found in rain forests. The IS between stand was 28.21 (sd = 14.40)%. The highest IS were between stand 1-2 (IS 55.56%) and between stand 1-4 (IS 47.62%). The lowest IS were between stand 3-4 and 3-5 (IS 10.53%). Based on the number of species, the five stands of remnant vegetation was dominated by families of Fabaceae, Arecaceae, and Anacardiaceae, but based on the IVI, they were dominated by families of Lamiaceae, Fabaceae, and Sapindaceae. On the basis of plant height, about 6.15% of the total individual was within the category of small plant (≤2 m) and 3.32% was of big tree (>14 m). However, on the basis of stem diameter, about 27.86% of the total individual was on the category of small plant (≤10 cm) and about 2.99% was of big tree (>130 cm). Most existing species were within the category of small and very small IVI, only about 14.26% of the existing species were within the category of very high IVI (>20%) and 71.43 were within the category of low and very low IVI (<10%). Four most prominent species, namely Tectona grandis Linn., Schleichera oleosa (Lour.), Vachellia nilotica (L.) P.J.H.Hurter & Mabb., and Spondias pinnata (L.f.) Kurz contributed to more than 50% IVI in the five stands of remnant vegetation. Among all species found, Leucaena leucocephala (Lam.) de Wit, Caesalpinia pulcherrima (L.) Sw., Sesbania grandiflora (L.) Poiret, Syzygium cumini (L.), Pterocarpus indicus Willd., Pinus mercusii Jungh. & de Vriese, and Acacia auriculiformis A.Cunn. ex Benth. were present in very small IVI. In general, the contribution of invasive species in the stands of remnant vegetation was relatively high (total IVI 56.96%), about a quarter of which were invasive weedy shrub species.

Conclusion: Based on this result it can be concluded that the five stands of remnant forest were in the state of poor health as indicated by the low number of species and families, the low species diversity, the heterogeneous floristic composition as most of species present were in the category of low occurrence, and the dominance of invasive non-native tree and shrub species. Therefore, the forest needs immediate intervention by taking conservation and restoration action to prevent further destruction.