Relationship between the Floristic Composition and Soil Characteristics of a Tropical Rainforest (TRF)

Abstract

Hutan Rimba Alam (HRA), Putrajaya is an urban forest which is the habitat for various tropical rainforest species. A field survey was undertaken to state the floristic composition, investigate the soil characteristics and identify the relationship between the recorded plant communities and soil characteristics. Six plots sized 10 × 10 m square were established in a lowland area of which 93 individual trees were identified. Moreover, the floristic composition revealed vascular tree communities consisting of 10 botanical families, 15 genera, and 27 species with Dipterocarpaceae as being predominant. Based on the important value index (IVI), Mangifera odorata (Anacardiaceae) was the highest (IVI = 68.80%). Furthermore, large trees such as Koompassia excelsa (Becc.) Taub. (Fabaceae) and Sandoricum koetjape (Burm.f.) Merr. (Meliaceae), with heights ranging from 17 m to 24 m, indicated that HRA is on the way to becoming a mature forest. The soil pH in all plots showed acidic properties, with a mean pH of 4.69 that is considered normal for tropical rainforests. The pH of the soils in HRA, Putrajaya had a positive correlation with the CEC and with nitrogen, but the value was low; however, the correlation was negative with C and P. The CEC had a relatively low correlation with C, N and P. Carbon had a very high correlation with N but low with P. Meanwhile, nitrogen had a very negatively low correlation with P. Extractable phosphorus exhibited a mean of 2.22 mg/kg which is normally used in plants for fruits, roots, and flower development. The present study revealed that plant communities in the urban forest in Putrajaya, meaning the diversity of the plant species belonging to a wide range of families, were established on acid soil, matching with the overall characteristics of tropical forest soils. With regard to the climate change context, which is leading to many altered ecosystems, the authors expect that the outputs of this research will be valued by decision makers for a better management of the forest.