Diversity of undergrowth types in frankincense stands in Humbang Hasundutan Regency

Understory plants are one of Indonesia’s biodiversity. The presence of undergrowth has an important role in the ecosystem and economy of the surrounding community. Research on the diversity of understory plants in the Frankincense forest has never been carried out. This research aims to determine the diversit y of understory plants in incense stands in Humbang Hasundutan Regency. Sampling was carried out using understory vegetation analysis plots. Analysis of the distribution pattern of incense using the standardized Morisita’s index. Based on the results of vegetation analysis at the understory level, 27 types of understory plants were found in community forests, with the most dominant type found being the fern (Diplazium esculentum) with an IVI value of 25.90%. In the protected forest, 16 types of understory plants were found with the most dominant type being Etlingera elatior with an IVI value of 31.48%. Species diversity in community forests (2.76) is in the medium category and in protected forests (2.48) is in the medium category. Species richness (R) in Community Forests is 4.34 in the medium category and in protected forests is low (2.36).


Introduction
Indonesia is a country that has vast tropical rainforests with a high level of biodiversity.Biodiversity is all forms of life on earth, from flora, fauna, microorganisms to the genetic material they contain and the environment in which they live [1].Understory plants are one of Indonesia's biodiversity.Understory plants are vegetation found on the ground surface under tree stands, including grasses, herbs and shrubs [2].In stratification, the understory plants occupy stratum D, namely the shrub layer, bushes, and the ground cover plant layer in stratum E [3].
Undergrowth has an important role in the ecosystem.The presence of undergrowth on the forest floor can function to block the impact of rainwater and surface runoff, thereby minimizing the danger of erosion.Undergrowth is also often used as an indicator of soil fertility and as a litter producer in increasing soil fertility and as a producer in the food chain [4].The presence of understory plants will also increase biomass which will increase soil fertility [5].Different understory vegetation with different carbon and nitrogen stocks can change soil microbes, properties, structure as well as soil temperature and water content which in the end can have a big influence on soil carbon and nitrogen [6].Apart from that, understory plants also act as pioneer plants on post-burning land [7].Undergrowth plants have potential as traditional medicinal ingredients, their use has been carried out for generations.The use of understory plants as medicinal ingredients has a close relationship with the community, namely as a 1302 (2024) 012046 IOP Publishing doi:10.1088/1755-1315/1302/1/012046 2 source of livelihood and business opportunities for the surrounding community [8].Apart from being a medicinal ingredient, undergrowth also has the potential to be an ornamental plant which has high economic value because of its beauty [9].
The presence of understory plants in the ecosystem has many roles.However, the existence of these understory plants is still not given enough attention because so far it is considered that variations in their use are still limited [10].Apart from that, it is not uncommon for undergrowth to become a weed that inhibits the growth of tree regeneration, especially in cultivated monoculture plants, so it is often destroyed because it is considered a pest [11].The lack of public knowledge regarding the potential of understory plants results in less than optimal utilization.For this reason, further information is needed regarding the potential diversity of understory plant species in an ecosystem.Understory plants are closely related to each other and their environment, one of which is the frankincense forest.However, research on the diversity of understory plants in Frankincense forests has never been carried out.This research aims to determine the diversity of understory plants in incense stands in Humbang Hasundutan Regency.

Methodology
The research was carried out in 2022 in Protected Forests and Community Forests in Aek Nauli Village, Pollung District, Humbanghasundutan Regency.Understory vegetation analysis plot

Data analysis
Vegetation analysis uses the calculation of the Important Value Index (IVI), Similarity Index, Diversity Index, Richness Index and Evenness Index.

− 𝐷𝑒𝑛𝑠𝑖𝑡𝑦 = Number of individuals of type i
The total area of the sample plot Species diversity is determined by the Shannon-Wiener Diversity Index formula: Information: E = Species Evenness Index H' = Species Diversity Index S = Number of types Analysis of the distribution pattern of incense uses the standardized Morisita's index.The index is calculated using the equation:

Understory vegetation composition
The results of the understory vegetation analysis level showed that the number of species identified was 27 plant species.Of the 27 types, the one with the highest Importance Value Index (IVI), namely Fern (Diplazium esculentum) belongs to the Athyriaceae family with a value of 25.90% and the lowest value is Lasianthus constrictus with a value of 0.92%, which can be seen in Table 1a and Table 1b.

Analysis of understory vegetation in protected forests
The results of the vegetation analysis at the understory level showed that the number of species identified was 16 types of understory plants.The type of understory that dominates at the understory level is the Etlingera elatior type which belongs to the Zingiberaceae family.Etlingera elatior is a traditional plant.This plant in North Sumatra is usually called Rias (Medan) and kincung (Berastagi) [13].The results of vegetation analysis at the understory level, the dominant understory type at the research location is the Etlingera elatior type with an IVI value of 31.48%.The results of vegetation analysis at the understory level can be seen in Table 2a and 2b.Species richness in the Aek Nauli Village Community Forest at the understory level is 4.34 in the medium category and the R value in protected forests is low (2.36).The species richness index is to determine the number of species (species) in a community.The more species found, the greater the richness index.Usually, a community/ecosystem that has many species will have a small number of individuals in each species.If the R value is less than 3.5, it indicates low species richness, and if R is 2.5-5.0, it indicates high species richness [15].Index Richness, Evenness of Species, and Morisita Index can be seen in Table 3.The Species Evenness Index (E) in the Aek Nauli Village Community Forest shows a low species evenness index and stable community (0.83) and the E value in the protected forest is high evenness, stable community (0.88).The evenness index (J) is an index that shows the level of species distribution in an observation area/plot.The evenness index shows the degree of evenness of individual abundance between each species [16].At the understory level in community forests, the distribution pattern category is random (0), while the Morishita index value in protected forests is 4.12, including the clustered category.

Conclusions
The results of vegetation analysis at the understory level found 27 types of understory plants in community forests and in the protected forest, 16 types of understory.Species diversity at the lower plant level in community forests (2.76) is in the medium category and in protected forests (2.48) is in the medium category.Species richness (R) at the understory level in Community Forests is 4.34 in the medium category and in protected forests is considered low (2.36).The Species Evenness Index (E) at the understory level in Community Forests shows a small species evenness index and the community is stable (0.83) in protected forests including stable (0.88).The Morisita Dispersion Index in community

H
Shannon-Wiener Diversity Index ni = The number of individuals of the n th type N = The value of H' is as follows: H'<1 = low level of species diversity H'1-3 = moderate level of species diversity 3 H'>3 = high level of species diversity The richness of vegetation types was determined using the Richness Index [12] Richness Index S = Number of types N = Total Number of IndividualsThe evenness of vegetation types is determined using the Evenness Index[12]

Information
= Morisita dispersion index n = Number of plots x = Number of individuals found in each plot

Table 1a .
Composition of understory vegetation under frankincense stands in community forests.

Table 1b .
Composition of understory vegetation under frankincense stands in community forests.

Table 2a .
Composition of understory vegetation under frankincense stands in protected forests.

Table 2b .
Composition of understory vegetation under frankincense stands in protected forests.Index richness, evenness of species, and morisita Index Based on the data from this research, it shows that the level of species diversity at the understory level in community forests (2.76) is in the medium category and the H' index value in protected forests (2.48) is in the medium category.The Shannon-Wienner Index (H') in[14]defines the magnitude of the diversity index if the value of H > 3 indicates that species diversity is highly abundant, the value 1 ≤ H ≤ 3 indicates that species diversity is moderately abundant, and the value of H < 1 indicates that species diversity low or little.

Table 3 .
Index richness, evenness of species, and morisita index