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Plant diversity components of agroforestry in Tanjung Botung, Village, Barumun District, Padang Lawas Regency, North Sumatra

Agroforestry is a land-use pattern that combines crops in one land with spatial and temporal arrangements. This study aims (1) to identify the species components of agroforestry, (2) to analysis the species diversity in agroforestry, and (3) to calculate the benefits of species in agroforestry for the community around Tanjung Botung Village. Based on the results in this research, it is known that there are 33 species of plants found in agroforestry land which consists of 19 families. To determine the type that dominates the growth rate, it is seen from the value of the Important Value Index. The highest IVI level was in the shurbs level namely Elaeis guineensis (56.67), in the seedling level namely Hevea brasiliensis (83.57), in the sapling level namely Durio zibethinus (38.37), in the pole level namely Hevea brasiliensis (68.04) and in tree level namely Hevea brasiliensis (99.69). To find out the level of species diversity was calculated using the Shannon-Wiener Index (H’). From the results of the study, it was concluded that the value of species diversity ranged from 1.63 to 2.35, meaning that the value of species diversity (H’) for all growth levels was categorized as moderate.


Introduction
Agroforestry is a land-use system and technology in which long-lived trees and short-lived crops are cultivated on the same land in time and space settings [1,2]. The component of agroforestry is in the form of food plants that are needed by the community daily. According to [3] states that food plants are everything that grows, lives, has stems, roots, leaves, and can be eaten or consumed by humans. Foodstuffs that come from plants in the forest are in the form of fruits, leaves, and seeds.
The application of agroforestry patterns has been carried out since ancient times in various regions in Indonesia. The agroforestry pattern contains various types of plants (tree-based) that are grown and treated with a forest-like cropping pattern and ecosystem. This system is covered by various components such as trees, shrubs, annual plants and grasses in large quantities [4,5]. Because the types of plants vary so the products produced will vary as well. In addition to the dual benefits, it also has a high ecological function because it consists of several canopy stars.
One of the challenges of land management in the community in North Sumatera is the conversion of land to monoculture plantations such as oil palm plantations. Tanjung Botung is one of the villages that still has agroforestry land which is still being developed by the community. The existence of Agroforestry in Tanjung Botung Village is expected to continue to be maintained by the community.  (1) to identify the species components of agroforestry, (2) to analysis the species diversity in agroforestry, and (3) to calculate the benefits of species in agroforestry for the community around Tanjung Botung Village.

Study location and method
This research was conducted from January to March 2021 in Tanjung Botung Village, Barumun District, North Padang Lawas Regency, North Sumatera Province. The research method was carried out by analysis of vegetation on 20 plots of agroforestry land. The plots were laid out intentionally on community lands that applied agroforestry patterns. Vegetation analysis was carried out at each growth level, namely understorey and seedlings with a subplot size of 2 x 2 m, saplings with a size of 5 x 5 m, poles 10 x 10 m and trees with a plot size of 20 x 20 m.
Compared to the results [8] in Jurit Village Agroforestry, there were 15 species of understorey, 11 species of seedling level, 19 species of sapling level, 22 species of pole level and 22 species of tree level. The difference in the number of species is caused by differences in cropping patterns. Based on [9]

Important Value Index of Understorey
The understorey is all vegetation that is not a tree species and cannot grow to a tree level. The presence of understorey in forest plantations, apart from being a source of biodiversity, also plays a role in protecting the soil and soil organisms, helping to create a microclimate on the forest floor, protecting the soil from erosion, and maintaining soil fertility [6]. The presence of a plant species in an area indicates the ability adaptation to habitat and wide tolerance to environmental conditions [10,11]. The higher the IVI value of a species shows the higher level of control over the community. The dominant species is the species that has the highest IVI value in a forest vegetation [12]. A species can be said to play a role if the IVI value for the seedling and sapling level is 10% and for the pole and tree level it has an IVI value 15%. The IVI value of each understorey species in detail can be seen in Table 2. The highest IVI at the understorey level was Elaeis guineensis (56.67), followed by Saccharum officinarum (42.92), and Mimosa pudica (31.81). Based on the IVI value, the highest of IVI values was found in oil palm plants, which was 56.67, meaning that the type of oil palm was the dominant species at the understorey level. Elaeis guinensis is a plantation commodity that has recently been in great demand because it has a promising economic value.

Important Value Index of Seedling
The results showed that the highest IVI at the seedling level was Hevea brasiliensis (83.57), followed by Coffea sp (29.14), Theobroma cacao (25.75) and then Durio zibethinus (21.28). Hevea brasiliensis was the dominant species in the growth rate of seedlings. While the lowest IVI were Archidendron pauciflorum, Cinnamomum verum, and Syzygium aromaticum. Values of Relative Density, Relative Frequency and Important Value Index for the seedling level can be seen in Table 3.

Important Value Index of Sapling
The highest growth rate of saplings IVI was Durio zibethinus (38.37), then Coffea sp (32.94) and Theobroma cacao (28.27). At the sapling growth rate, Durio zibethinus had the highest number compared to other species, meaning that Durio zibethinus was the dominant species. Durio zibethinus is a type of fruit plant that is deliberately planted to produce fruit.

Important Value Index of Pole
The highest growth rate of pole IVI was Hevea brasiliensis (68.04), Theobroma cacao (37.00) then Coffea sp (30.56). Based on the IVI value, each species has a value more than 10. The highest IVI value is Hevea brasiliensis, this indicates that this species dominates the growth of agroforestry at the pole level. Hevea brasiliensis is a type of plant that is deliberately cultivated to produce sap.  [13,14] also revealed that H. brasiliensis can dominate community lands around riverbanks. H. brasiliensis is a type of wood that is deliberately planted to produce sap.

Shannon-Wiener Index (H')
To see the level of plant diversity is calculated using the Shannon-Wiener Index (H'). The H' value at the understorey level is 1.72, at the seedling level is 1.63, at the sapling level is 2.35, at the pole level is 2.09 and tree level of 1.77. From the results of the study, it was concluded that the value of species diversity ranged from 1.63 to 2.35, meaning that the value of species diversity (H') for all growth levels was categorized as moderate.