Vegetation analysis and plant diversity in Pinus Jantho Forest ( PJF ) nature reserve , Aceh Besar

Pinus Jantho Forest (PJF) Nature Reserve has unique characteristics and a distinctive ecosystem that plays an important role in the preservation of germplasm and the protection of natural resources. The sustainability of PJF Nature Reserve is strongly determined by vegetative species. Therefore, strategies are needed to correctly support its management. One such strategy is characterizing the diversity of plants that make up the community in PJF Nature Reserve. This research analyzes the vegetation and diversity of plant species in PJF Nature Reserve. Data collection and sampling were done using multiple squares, in which plots were laid out by systematic sampling. PJF Nature Reserve is composed of 111 species from 46 families. Seedling and understorey levels have the highest number of individuals (1028 in total). There are 240 individuals at the sapling level, 108 individuals at the pole level, and 72 individuals at the tree level. The Euphorbiaceae family has the largest number of species (11 species). The highest Important Value Index (IVI) for seedlings and understorey, saplings and poles, and trees respectively were Chloranthus elatior (11.09%), Piper aduncum (21.90% and 19.32%), and Pinus merkusii (25.52%). The diversity index indicates a high level of plant species diversity (3.25-3.63).


INTRODUCTION
Sumatran forests have a greater wealth of plant communities than other regions in the world [1]. Of five major islands in Indonesia, Sumatra is the third largest island based on endemic species [2]. This rich environment is evidenced by various types of lowland and mountainous ecosystems [3]. However, Sumatra has been categorized as one of 200 critical-status ecoregions, making it a global conservation priority [4] [5]. In the northern part of Sumatra is the province of Aceh. Aceh has many forest areas that need to be protected and conserved for their biodiversity. One such forest is Pinus Jantho Forest (PJF) Nature Reserve. Pinus Jantho Forest Nature Reserve has both typical and unique characteristics of a tropical rainforest ecosystem [6]. This region has become the natural habitat of Aceh-specific Pinus merkusii trees, as well as other plants and animals endemic to the region. Thus it plays an important role in the preservation of germplasm and protections of natural resources and catchment areas [7].
The function of PJF Nature Reserve as a conservation area for biodiversity is highly determined by its vegetative community. At present, the PJF Nature Reserve is under threat, since many forest areas have been disturbed due to illegal human activity, such as logging, forest burning, and land conversion for various purposes. In this regard, the sustainability of the forest ecosystem requires proper management systems. One such management strategy is characterizing plant diversity in the PJF Nature Reserve Area. *Corresponding Author: saida_rasnovi@unsyiah.ac.id

METHODOLOGY
This research was conducted from December 2018 to December 2019 in Pinus Jantho Forest Nature Reserve, Aceh Besar, It is located at 5°6' -5°16.2' North latitude and 95°37.2' -95°45' East longitude. Data and samples were collected by exploratory survey using multiple plots. Pathway and sample observation plots were determined perpendicularly from the edge to the inside. The observation sample plots were placed by systematic sampling on each path. Four lines were made with a distance of ± 400 m. Each path was divided into 5 observation sample plots with a 50 m distance between each sample plot. The observation sample plots were 20 x 20 m, and sub-plots were made in each plot of 10 x 10 m, 5 x 5 m and 2 x 2 m, respectively. Vegetation measured and observed included understorey, seedlings, saplings, poles and trees.
The understorey and seedlings (< 1.5 m) were observed in 2 x 2 m plots, saplings (> 1.5 m height with <10cm diameter) were observed in 5 x 5 m plots, poles (saplings with 10-20 cm in diameter) were observed in 10 x 10 m plots, and trees (mature trees with > 20 cm in diameter) were measured in 20 x 20 m plots. Each plant species was observed at various growth levels (understorey, seedlings, saplings, poles and trees). All samples were then made into herbarium specimens for further identification.

Data Analysis 1. Important Value Index (IVI)
Vegetative composition to determine the dominant species was calculated by the Importance Value Index (IVI). The Importance Value Index for tree and pole growth rates is obtained by the formula IVI = RD+ RF + RD, while for saplings, seedlings, and understorey, it is obtained using formula IVI = RD + RF [8]. The Shannon-Wiener Diversity Index is interpreted as follows: a. H'>3 shows that the species diversity in a place is high. b. 1≥H'≤3 shows that the species diversity in a place is medium. c. H'<1 shows that the species diversity in a place is low [9].  [14]. There are differences in the number of species in each region due to variations in environmental conditions. Different environmental characteristics will create different compositions of vegetation [15].  [20].

RESULTS AND DISCUSSION
The dominance of Euphorbiaceae in several forest areas is closely related to its effective reproductive strategy of spreading fruit and seeds by birds and mammals. As a dominant species in most tropical forests, Euphorbiaceae has a year-round flowering and fruiting period with high adaptability to various environmental conditions [21]. Importance Value Index (IVI) is a quantitative parameter used to express the degree of dominance (level of control) of species in a plant community. That means that the most dominant species has the greatest Importance Value Index [20]. The Importance Value Index (IVI) of plants in the PJF Nature Reserve shows that Chloranthus elatior has the highest dominance at the seedling and understorey levels (11.09%). In contrast, the sapling and pole levels are dominated by Piper aduncum (21.90% and 19.32%), while the tree level is dominated by Pinus merkusii (25.52%) ( Table  2).
The dominance of Chloranthus elatior in seedling and understorey growth rates is evidenced by its individual density and high frequency in several research plots. The abundance of this species is supported by the ideal environmental conditions for its growth. The PJF Nature Reserve forest area has a temperature of 27-34.3 o C, a humidity of 65-98%, and a soil pH of 4.5-6.5 (Table 1). Chloranthus elatior can grow well in shaded areas at 21-27 o C, 86.8% humidity, and 6.0 pH [22]. Species with higher IVI values have a better survival rate for growth or adaptation compared to other species [11]. Naturally, forests maintain balance by improving diversity and fertility Piper aduncum was found to grow predominantly in several observation plots with high light intensity, such as on the edges and in forests with gaps (gap canopy). However, it can also be found in shaded forest areas. Its dominant presence is supported by its excellent physiological and ecological characteristics. Piper aduncum has light-loving (photoblastic) seeds, making it able to germinate optimally in an environment with sufficient light. In addition, it has a high sexual and vegetative reproductive capacity since animals help in its dispersion, allowing it to adapt to various environmental conditions [23][24] [25].  The dominance of Pinus merkusii at the tree level is supported by environmental conditions in the PJF Nature Reserve. Pinus merkusii can grow optimally between 19 to 28 o C and 400-1500 m above sea level, but it can also grow well in low lands (± 90 above sea level) and mountains (± 2000 m above sea level). It competes well against other species due to allelopathy compounds that can inhibit the growth of nearby individuals of other species. Such compounds can inhibit the growth of other species that grow close together. Its ability to produce allelopathic compounds helps them fight competitors for nutrients, allowing pinus merkusii to survive longer and develop more effectively [11]. It is endemic to the PJF Nature Reserve and must be conserved and protected. Based on the results of IVI, pine poles, saplings and seedlings are less healthy. There is a possibility that pine regeneration will be hampered in the future. They may be replaced by other plants, particularly P. aduncum, which is found predominantly at the pole and sapling level. This study finds that P.aduncum has the highest IVI in the pole and sapling classes . As the most invasive plant species in the world, Piper aduncum in PJF Nature Reserve could pose a serious threat to the protected plant community in PJF Nature Reserve. Thus, Piper aduncum might become the most dominant species in the PJF Nature Reserve Area, Aceh Besar in a few years.
The Shannon-Wiener species diversity index (H ') shows that the level of plant diversity in the PJF Nature Reserve is high. This can be seen from the index value which is greater than three (H '> 3) for each growth rate (Table 3). A high diversity index indicates a stable forest community. The higher the diversity index value, the higher the species diversity, ecosystem productivity, pressure on the ecosystem, and ecosystem stability [26]. High diversity index also indicates the PJF Nature Reserve is in the succession stage. Forests that are nearing the climax succession stage tend to have a higher diversity of species than forests in the early succession stage. In climax succession, there are high levels of species interaction and complexity, whereas in the early succession stage, interactions between species are few [14][27] [28]. The number of old trees found in the PJF Nature Reserve Area is also an indicator that the forest has almost reached climax succession. Old trees have a diameter (DBH) of more than 60 cm, such as P. merkusii (DBH = 89.1 cm), Bouea oppositifolia (DBH = 115.9 cm), Shorea lepidota (DBH = 87.8 cm), Dipterocarpus grandiflorus (DBH = 74.2 cm) and several other species. The existence of the Dipterocarpaceae family also indicates a forest near the climax stage, since the species from this group have a large trunk and canopy size [14].

CONCLUSION
The vegetation in PJF Nature Reserve is composed of 111 species of plants from 46 families. The family with the highest number of species is Euphorbiaceae. The species with highest level of dominance at the seedling and understorey levels is Chloranthus elatior, sapling and pole levels is Piper aduncum, and at tree level is Pinus merkusii. Pinus merkusii is endemic to PJF and must be conserved and protected. However, based on the results of IVI, pines are less abundant at the pole, sapling, and seedling levels. This suggests that future pine regeneration will be inhibited and the species will be replaced with other plants, particularly by Piper aduncum. This species is the most abundant species found at the pole and sapling level. The dominance of Piper aduncum in PJF Nature Reserve could pose a serious threat to the preservation of plant diversity, indicating the need for special attention to the current PJF Nature Reserve area. The diversity index is high and indicates stable forest conditions.