Dynamics of Species Richness in Understory Deciduous Teak Forest (Tectona grandis)

Teak plantation forest is a deciduous forest that sheds its leaves during the dry season. It is generally a secondary forest that is managed in a monoculture manner so that it is homogeneous. However, when teak sheds its leaves, it that may impacts the dynamics of understory species changes due to differences in environmental factors growing in the dry and wet seasons. The study observed 90 plots carried out over a year, namely two times during the dry season and 2 times during the wet season. We placed three transects around the forest edge, each (9 transects), and plotted 1 m × 1 m plots. Data collection was carried out at distances of 5, 10, 15, 20, 25, 30, 35, 40, 45 and 50 m on each transect. In each plot, the composition of the understory vegetation cover, litter cover and soil bare was observed. The research was also observed canopy openness and collected rainfall data for one year from the nearest Meteorology station. Species found were recorded for identification based on origin, life form, original habitat, and seed dispersal. The study‘s results found 57 species, 16 species only in DS, then 17 species only in WS, and 24 in both seasons. The dynamics of changes in these species are influenced by the season, which will affect the environment around the plant. Seasonal differences impact light intensity, canopy openness, leaf fall and growth, and litter thickness, which impact the understory diversity and abundance.


Introduction
Teak plantation forest (Tectona grandis) is a form of secondary forest management in Indonesia [15], generally in the form of Industrial Plantation Forests (HTI) which are intended for economic purposes with forest products in the form of wood [16,2].The management of industrial plantation forests, which are secondary forests tends to be monoculture and has homogeneous stands [29,11].Homogeneous stands from year to year impact the understory composition of species that will remain unchanged [18,20].This is certainly different from teak plants which have the characteristics of dropping leaves in the dry season (deciduous plant) and turning green during the wet season [5].This unique characteristic of the teak plant can have a direct impact on the ecosystem beneath it [19], especially due to differences in conditions due to influences entering the understory when the leaves fall and dark conditions when the leaves are dense [3].In evergreen forest types that tend to keep the ecosystem underneath always 1299 (2024) 012008 IOP Publishing doi:10.1088/1755-1315/1299/1/012008 2 shaded, the ecosystem under teak stands in the dry season tends to be unshaded and open while in the wet season it tends to be shaded and closed [30].
The difference in conditions in the dry and wet seasons will directly impact the interaction of abiotic and biotic factors under teak stands [14].The interactions that occur are thought to impact the dynamics of understorey species4.The dynamics of species change is related to the carrying capacity of the distribution of understorey species [13].The diversity of species in which vegetation varies greatly is influenced by various physical, chemical and climatic factors [13].According to Hadi et al. [7] the diversity of vegetation species is also influenced by environmental factors including climate, edaphic (soil), topography and biotic.Light and water factors affect understory species composition [28].The most visible thing from this dynamic change is the light factor, the tendency for plants to drop their leaves.These changing environmental conditions result in differences in the diversity of undergrowth species during the wet and dry seasons or during summer and winter [12].
In dry season, teak leaf litter can act as a mulch covering the lower plants.So, it has the potential to inhibit the growth of the understory.This will affect the components and structure of communities in forest ecosystems that are closely related to each other and their environment [22].Where wind animals will be able to enter the middle/core/core of the forest and spread seeds into the forest.The relationship between these factors will affect the formation of diversity in the number of each type of plant and the formation of the community structure of plants in the forest6.The formation of patterns of diversity and structure of forest vegetation types is a dynamic process, closely related to biotic and abiotic environmental conditions so that vegetation that grows naturally results from the interaction of various environmental factors [28].
One of the vegetation components that make up the forest structure is undergrowth.The understory is a type of basic vegetation found under a forest stand except for forest tree rejuvenation, which includes grasses, herbs and shrubs.In tropical rainforest stratification, the undergrowth occupies stratum D, namely layers of shrubs, shrubs, and ground cover plants [21].The composition, structure and diversity of species growing in undergrowth in natural forest and plantation locations are quite different [24].The community of an ecosystem is governed by various abiotic and biotic factors which ultimately affect the overall structure of the community, resulting in variations in population dynamics.An inventory of vegetation structure includes composition, stratification, and community type, while diversity provides key information about species richness, distribution, and rate of change in species composition [10].The ecological function of undergrowth on the forest floor can serve as a barrier to rainwater blows and runoff thereby minimizing the danger of erosion.In addition, understorey vegetation plays an important role in forest ecosystems and determines the microclimate [9].
In this study, we see the importance of looking at the dynamics of changes in species richness of the undergrowth found in teak forests as a deciduous plant, which have the character of dropping leaves during the dry season and having dense leaves during the wet season.The hypothesis is that there are dynamics in the undergrowth composition species because of teak dropping leaf mechanism due to seasonal changes.

Method
The research was carried out in the production forest area of Perum Perhutani under the Kalipare Forest Management Resort (RPH), Malang Regency, East Java.The teak was planted at 1997 (25 years old).The coordinates of the research location are at 8°11'37.0"S 112°26'57.4"Ewith an elevation of 298 meters above sea level.The research location had annual rainfall between 1.794-2.407mm per year, with average daily temperature at 23 o C.
Data was collected using a field survey method at the research location.The survey was conducted 4 times a year, namely in February (Wet Season 1), June (Dry Season 1), August (Dry Season 2), and November (Wet Season 2).We placed three transects around the forest edge, each (9 transects), and plotted 1 m × 1 m plots.Data was collected at distances of 5,10,15,20,25,30,35,40,45 and 50 m on each transect.On each transect (line) 3 repetitions were carried out so that there were 90 quadrats.In each observation plot, measurements were made of the land cover composition.The land cover composition in question includes understory vegetation cover (%), bare ground and leaf litter cover (%).Then the soil surface of each plot is determined visually, and the light factor (Sky Factor, canopy openness) is measured for each square.For SF measurements, hemispherical photos were taken at the centre of each plot (1 m above ground level) using a fisheye lens (Samsung Gear 360).SF was calculated by processing hemispherical photographs using GLA 2.0 (gap light analyser).The types of vegetation species found were recorded to determine the diversity of species distribution.Clustering of the vegetation found was carried out based on origins, original habitat, seed dispersal and functional group25.Then the number of species per plot and canopy openness found analysed by Kruskal-Wallis to see the differences between wet season and dry season.

Result
From Figure 1 it is known that there are a total of 57 species in the teak forest, there are differences in the number of species found in each season.The highest number is in DS1 with 33 species, it is 26.9% higher than those in the DS2.Based on the original habitat (figure 5), the number of species in the wetland is an indication that the influence of the wet season has resulted in the emergence of species capable of living in high humidity conditions.Then the occurrence of woodland species was higher during the dry season than the wet season with an average of 10.5 and 8.5.

Discussion
We recorded the dynamics of species change in teak forests due to changes in the dry and wet seasons.We found 57 Species which were species in DS 16, then WS 17 species, and 24 in both.This is due to differences in the condition of the humidity factor and changes in the structure of the teak canopy.According to Saha [17] differences in environmental condition affect the vegetation composition and structure, which in this research is happen due to seasonal changes.Also, in Soto et al. [22] shows the decrease in rainfall drastically affects the understory pattern.Likewise in this study, we saw a change in vegetation due to dry conditions to wet conditions or vice versa.The trend of rainfall data decreasing towards the dry season and rising again during the wet season shows a relationship with the number of species, leaf litter, vegetation cover and bare ground (Figure 6).The average number of species in the dry season is higher than the wet season, it can be seen that a decrease follows the trend of decreasing rainfall in the average number of species.This shows a consistent relationship between rainfall and the number of species that appear, only a few species can live in high-humidity conditions.The same trend also occurs in vegetation cover, where there is a decrease in the percentage during the dry season.This is due to the high production of litter in the dry season which inhibits the growth of the undergrowth.Therefore, the forest floor will be covered more by litter than undergrowth.Meanwhile, the opposite trend occurs in bare ground and leaf litter.As rainfall decreases, leaf litter and bare ground will increase.It can be seen in the graph that the leaf litter increases towards the end of the dry season and then decreases at the beginning of the wet season.At the beginning of the dry season, the largest percentage of bare ground is due to reduced plants covering the ground and less litter from fallen leaves.Whereas at the end of the dry season, there was a decrease in bare ground percentage, leaf litter was the highest from all observations.At the end of the dry season, leaf litter is highest when environmental conditions become very dry [25].
Figure 7. Cover percent between vegetation, leaf litter and bare ground during the wet and dry season.Teak is a deciduous plant that sheds its leaves during the dry season.So that teak leaves act as mulch which has the potential to inhibit the growth of lower plants.However, we see that there is an interaction between the condition of the amount of vegetation cover, leaf litter and bare ground.From these figures the vegetation cover during wet season is higher than bare ground and vice versa during the dry season.
The relationship between the number of species and the amount of intensity that enters through Canopy openness also shows a positive correlation.The number of species increases when the openness of the canopy is greater.So that the light that enters the forest floor is getting bigger to support the growth of the undergrowth, this certainly can describe changes in the dynamics of different species richness during the dry and wet seasons.Vroh [27] research shows different plant richness in different teak age, it will affect the intensity of light can reach the forest floor.In a study conducted by Helbach et al. [8] it is known that the number of species varies due to the light factor.Adam's [1] research, also shows an interaction between light and soil pH that affects the richness of the undergrowth.The characteristics of deciduous plants related to the conditions of the different seasons result in different types of plants being observed in each season.However, a negative correlation occurs at the end of the dry season, where the correlation should be even greater due to the increasingly open canopy.This is possible due to the increasing number of litters that covers the undergrowth and prevents the undergrowth from getting light.The difference in the proportions between vegetation, leaf litter and ground illustrate how teak responds and results in different proportions during the dry and wet seasons.Dry season conditions give rise to a phenomenon where Forbs plants decrease during the dry season and are high during the wet season.On the other hand, tolerance to light causes the number of shrub plants to be higher during the dry season than during the wet season.Interestingly, native plant species are higher than exotics during the dry and wet seasons due to their adaptive ability and life cycle of native plants which are more able to survive in conditions covered with litter and dry conditions with high light intensity.The type of vegetation that is distributed during the dry season is much higher than during the wet season, where during the dry season the leaves start to fall so that animals can enter further into the forest core due to open conditions.
The emergence of species with original wetland habitat occurs at the end of the wet season.High water and humidity levels at the end of the wet season and a little inundation in several locations trigger species' growth in these original habitats.Conversely, during the dry season, there is an increase in species with original woodland habitat.The dynamics also occur in various types of seed dispersal plants that appear, be it wind, water, animals, or generalists.This indicates that the change of seasons followed by changes in environmental conditions has resulted in the dynamics of various types of seed dispersal methods for growing plants.

Conclusion
This research shows that the influence of the season causes dynamics in the composition of the understory observed.Changes in environmental conditions in the form of rainfall and the response of teak in dropping its leaves result in changes in the composition of the understorey on the forest floor.The appearance of species originating from the wetlands at the end of the wet season and an increase in woodland species during the dry season indicate a response to the composition of the understory that lives under the stands.There were also changes in the composition of the plot cover between vegetation, leaf litter and bare ground between the dry season and the wet season due to changes in environmental conditions.

Figure 1 .
Figure 1.Number of species between the wet and dry season.

Figure 2 .
Figure 2. Number of species based on origins between the wet and dry season.

4 Figure 3
Figure3shows the number of species based on seed dispersal, the figure shows that in WS 1, DS 1, DS 2 and WS 2 as many as 9, 13, 14 and 11 species were generalists respectively, then 13, 11, 5 and 11 species is by animal and 8, 4, 4 and 6 are types of plants whose seeds are spread by the wind.Then the emergence of plant species that were not identified only in DS 1 and DS 2 a number of 4 and 2 species.

Figure 3 .
Figure 3. Number of species based on seed dispersal between the wet and dry season.

Figure 4 .
Figure 4. Number of species based on life forms between the wet and dry season.

Figure 5 .
Figure 5. Number of species based on original habitat between the wet and dry season.

Figure 6 .
Figure 6.Trend of rainfall data and the changes of number of species, leaf litter, vegetation cover and bare ground.

1st 7 Figure 8 .
Figure 8.The differences canopy openness during the wet season and dry season.Different letters on the boxes indicate a significant difference (Kruskal-Wallis one-way analysis of variance, p<0.05).

Figure 9 .
Figure 9.The differences in number of species/m 2 between wet season and dry season.Different letters on the boxes indicate a significant difference (Kruskal-Wallis one-way analysis of variance, p<0.05).