Studies on wood litter decomposition sometimes show conflicting results. While low temperatures and humidity during winter in temperate climates are reported to halt the activity of decomposing agents, in the warmest and wettest tropical regions of the Far East, peat accumulates on the forest floor, indicating that the decomposition process is not proceeding well. In this study, we compared the inter-seasonal and inter-forest communities decomposition rate constant (k) of jabon (Anthocephalus macrophyllus (Roxb.) Havil.) and tusam (Pinus merkusii Jungh. & de Vriese) woods in three forest communities (Karst, Lowland, and Pine) on the Indonesian island of Sulawesi. We placed 1,200 wooden planks (600 jabon logs and 600 tusam logs) measuring 10cm×10cm×1.5cm on the ground in each forest community during different seasons: dry season and wet season. k was observed seasonally. We also observed the decomposing agent diversity, soil properties, and chemical content of the wood sample to examine factors affecting k values. The results showed the tendency of jabon wood k to be higher in the dry season than in the wet season, and the opposite trend was noted for tusam wood. k of both wood samples was highest in Karst, followed by Lowland and Pine forests. However, except for bacterial diversity and abundance of Odontotermes sp., there was no clear correlation between k and the diversity and abundance of decomposing agents. The k values varied distinctly, even among samples within the same forest community in the same season, causing the data not to be normally distributed. These findings indicate that decomposition processes in tropical forests vary at the microsite scale due to the high diversity of decomposing agents and their complex reciprocal association.

Due to the absence of topsoil, low pH, and contamination by various heavy metals, revegetation of post-nickel mining land, which is generally carried out by planting economically valuable species, is usually unsuccessful. This study aims to identify tree species suitable for revegetation on post-nickel mining land in Kolaka Regency, Indonesia. Nine plots measuring 20 m x 20 m were distributed in the revegetated post-nickel mining land at three different age categories (1, 5, and 10 years) to observe the growth of revegetation trees, which are introduced species and native tree species that naturally invade the revegetation area. In total, there were 24 tree species found in the revegetated post-nickel mining land consisting of 9 introduced revegetation species and the other 15 tree species were native tree species that invaded the revegetated area. The older the age of the revegetation, the more native plant species are found. In line with the increasing age of revegetation, the density of revegetation plants decreases while the density of native plants increases. The population structure of revegetation trees does not indicate that the species can regenerate, while the inverted shape of the population structure of native plants indicates excellent regeneration potential. Thus, the results of this study recommend making native species, including Buchanania arborescens, Alstonia macrophylla, Ficus sp. Syzygium sp. Colona scabra, Litsea sp., and Metrosideros cf. petiolata as revegetation plants in former nickel mining areas.

Putra PS, Achmad A, Yamada T, Ngakan PO. 2023. Seasonal litter production patterns in three tropical forests in Sulawesi, Indonesia: Implications for managing secondary forests. Biodiversitas 24: 852-860. We studied the seasonal patterns of litter production in three tropical forests (Karst, Lowland, and Pine) on the Indonesian island of Sulawesi and measured environmental factors related to litter production from June 2019 to May 2020. Permanent plots of 0.4 ha to 1.0 ha were established in each forest to analyze forest structure and species composition. Thirty-six traps with a surface area of 1 m2 were installed to collect litterfall. The results showed the highest species diversity in the Karst forest, the highest tree density in the Lowland forest, and the largest basal area in the Pine forest. The most excellent litter production was in the Lowland forest (1,607.21 g/m2/year), followed by the Pine forest (1,288.24 g/m2/year) and Karst forest (1,099.83 g/m2/year). Litter production was more significant in the dry season in Karst and Pine forests, but there was no inter-seasonal difference in Lowland forest. Rainfall was the only environmental factor that differed between seasons. Differences in phenological adaptation between pioneer and climax species that comprise each forest likely account for the observed differences in litter production patterns.

Mas’ud W, Maulany RI, Putra PS, Ngakan PO. 2023. Impacts of edge effects on the invasion of alien plant species in Bantimurung Bulusaraung National Park, Indonesia. Biodiversitas 24: 6160-6168. Invasive Alien Plant Species (IAPS) are a threat to biodiversity and natural ecosystems. Factors influencing the IAPS distribution are well-known, but the impact of edge effects on the distribution is rarely discussed. This study aims to reveal the effect of differences in physical environmental factors along the edge effect gradient on the distribution of IAPS in Bantimurung Bulusaraung National Park, South Sulawesi, Indonesia. Twenty-five line transects were established where 125 plots (20m x 20m) were systematically located to analyze the density, dominance, and distribution of IAPS on the edge bordering natural forest ecosystems and anthropogenically disturbed areas. Of the 21 IAPS found, 95.2% were distributed in clumps and 4.8% at random. As the light intensity decreases significantly (r = 0.042; p = 0.029) with the increasing distance from the edge to the forest interior, the IAPS density decreases significantly (r = -0.512; p = 0.0001). Species of IAPS that experienced a decrease in individuals were those with a habitus of herbs and shrubs. Considering that the seedlings were found to spread outside their mother tree stands, Swietenia macrophylla King. and Maesopsis eminii Engl. are suspected to be long-lived IAPS that have the potential to spread to natural karst forest ecosystems, so they need to be monitored continuously.

Climatic elements are limiting factors for plants; therefore, climate change can impact the phenology of plants. This study aims to determine the impact of climate change on the reproductive phenology of four local mango cultivars on Sulawesi Island, Indonesia. Data were collected during 2013 and 2014 by observing and recording the production of vegetative shoots, generative shoots, and fruits from the trees of each mango cultivar weekly. To assess the impact of seasonal change on fruit quality, the weight and sugar level of the ripe fruits in each cultivar were measured. Climate data were obtained from the National Centers for Environmental Prediction and the Indonesian Agency for Meteorology, Climatology, and Geophysics Region IV, Makassar. Results show that from 1979 until 2014, the climate in the study site changed from type D to type C according to the Schmidt-Ferguson Climate Classification method, indicating that the wet season became longer. Following climate change, the reproductive phenology of the four mango cultivars also changed from once to twice annually, whereby the flush of vegetative and reproductive shoots that appeared during the first period in March did not successfully develop into mature fruit but developed following the second period in July. The change of season also impacted the quality of the mangoes, as fruit produced during the longer dry season had higher sugar levels than those produced during the shorter dry season.