The abundance of soil fauna in Gunung Halimun Salak National Park at altitude: 1100 – 1300 masl

As a bioindicator of soil quality and controller of soil dynamic (fertility), soil fauna is influenced by various environmental factors like climate and edaphic elements. This research aimed to examine the abundance of soil fauna in a lower montane forest ecosystem at different elevations and analysed how the environment affects their abudance. The study used purposive sampling in Gunung Halimun Salak National Park, specifically at altitude of 1,100 masl; 1,200 masl; 1,300 masl; and an open area (1,230 masl) as a control. LSD test revealed a significant difference on soil fauna abundance between the 1,100 masl elevation and the control group. However, there was no significant difference of soil fauna abundance between altitude of 1,200 masl and 1,300 masl. The highest abundance of soil fauna was found at 1,100 masl, with 156 individual/m2. Conversely, the lowest abundance of soil fauna was recorded in the open area at 1,230 masl, with 3 individual/m2. The Pearson correlation analysis showed that soil fauna had positive correlation with light intensity and air temperature, and negative correlation with air humidity. Furthermore, Soil fauna abundance had also positive correlation with edaphic parameters (CEC, C-org., litter weight, soil respiration, porosity, and soil temperature, except soil pH and bulk density.


Introduction
Soil fauna paly important role on the various processes according to biogeochemical cycle within the forest and land ecosystem.Soil fauna can play a strategic role as a connector among elements in the environment, as well as supporting on the material and energy cycle through the food chain and food web within an ecosystem [1].Soil fauna have an important role on organic matter decomposition [2].Even, they contribute up to ± 30% of the total net nitrogen mineralization in the ecosystem [3], [4].Soil fauna refers to addressing the group of animals (organisms) that spend a part or whole of their life cycle in the soil as habitat.
The presence of soil fauna can potentially lead the dynamic processes on the soil habitat, then improve or give impact to other soil properties as well as soil fertility.Based on the body size, soil fauna can be divided into three groups, such as microfauna (20 -200 μm), mesofauna (200 μm -1 cm), and macrofauna (> 1 cm) [5].As a part of soil biology component, soil fauna have also special function as a bioindicator to indicate soil quality [6].In a forest ecosystem, soil fauna plays a role in the process of litter decomposition on the forest floor, support the soil nutrition cycle, and allowing the nutrient content in the litter to be absorbed by plants.The presence of soil fauna can be influenced by the abundance and quality of litter on the forest floor, soil acidity (soil pH), and soil moisture [7].
Therefore, as a conservation area, GHSNP play important role as a natural habitat for numerous species of flora and fauna, including the soil fauna.Besides, conservation area has also important function as a buffer zone for life (e.g.: water and soil conservation, erosion control, micro-climate control, carbon sequestration, etc.).Forest is a natural habitat for soil fauna, which is having a principal role in maintaining of forest ecosystem stability [13].Forest soil is an abiotic component within forest ecosystems that has great influences on forest stability and productivity.There will be nothing on forest stands growth, decomposition and soil nutrient cycling, soil fertility development, as well as ecosystem services of forest without the existence of soil fauna within the forest ecosystem.
Soil fauna biodiversity is one of key elements that can support stability of forest ecosystems (forest's condition and function), due to it special function as a connector among elements or material and/or energy cycle, as well as the surveillance of soil quality (fertility) in the forest ecosystem.Hence, knowledge about soil fauna biodiversity and their relationship with ambient factors are important toward sustainable forest management.This research aimed to analyse the abundance of soil fauna (mesofauna and macrofauna) in lower montane forest ecosystem at altitude of 1,100 -1,300 masl in the GHSNP and to analyse the influence of the environmental factors (edaphic and climatic) in lower montane forest ecosystem at altitude of 1,100 -1,300 masl in the GHSNP to the abundance of soil fauna.

Plot Establishment
We collected data related to this study in Cikaniki Resort, GHSNP in several altitudes of forested area, such as 1,100 masl; 1,200 masl; and 1,300 masl.We also developed the observation plot in an open area at 1,230 masl as a control plot.The 20 x 20 m square single plot was established in each altitude.Furthermore, there were three subplots with 1 x 1 m in size within the main plot (20 x 20 m).The observation plots in this study were placed with purposive sampling method [1], according to specific ambient characteristic (forested area and open area) as well as the altitude.Figure 1 showed the observation plot design of this study.Soil and soil fauna sample were taken and observed on 1 x 1 m subplot.We used the composite soil sample (disturbed soil sample) and undisturbed soil sample (by using soil sample ring) from five points respectively, in the 1 x 1 m subplot.The composite soil sample was used to analysing several soil parameters, such as soil acidity (soil pH), cation exchange capacity (CEC), C-organic, and soil respiration.In other hand, the undisturbed soil sample was used to analysing bulk density and soil porosity.

Soil Fauna Extraction and Identification
The extraction of soil fauna (including mesofauna and macrofauna) was conducted by using two methods, such as: (1).The Sorting method or Hand Capture method that was done in the 1 x 1 m subplots with 5 -10 cm depth from the ground surface, and (2).The Barlesse-Tullgren Funnel method was conducted in the Lab. of Forest Influence and Lab. of Forest Entomology, Department of Silviculture, IPB University.The soil fauna sample was observed by using a stereomicroscope.Moreover, soil fauna identification process was carried out by using the identification key or identification book by several references, such as Jocque and Dippenaar-Schoeman (2006), Plowes and Patrock (2000), as well as Borror et al. (1989).

Edaphic factor
Soil acidity (soil pH) and cation exchange capacity (CEC).Soil acidity and CEC determination had been done toward the composite soil sample.Soil sample and distilled water (1:3) were added and homogenously mixed for 5 minutes, into a bottle sample.Then, we used digital pH meter for soil acidity assessment by dipping the digital pH meter's indicator into the soil solution for 3 -5 second.Afterwards, we read the pH value that appeared on the pH meter screen.Soil CEC parameter analysis was conducted in the Testing Laboratory by using Titration method.
Soil temperature and litter weight.Soil temperature measurement by using digital soil thermometer was measured directly in the field, within 1 x 1 m subplot with five points of observation.Furthermore, the litter was collected from the 1 x 1 m subplot, then the wet weight was determined by using digital weighing scale.
Bulk density and porosity.Bulk density and porosity were determined by using gravimetry method.Undisturbed soil sample within soil sample ring (DWsr) was oven-dried on 105 o C for 24 hours, then it was weighted by using digital weighing scale.Hereafter the bulk density and soil porosity were determined by using the following formula [14]: C-organic.C-organic parameter was determined through Dry-Ashing method on 550 -600 o C.This procedure could have an impact on the loss of organic matter of the soil sample, which converted into CO2.Afterwards, C-organic value was able to be determined by using the following formula [15] : Ash content (%) = (W2 / W) x Cf x 100 Organic matter content (%) = (W -W2) / W x Cfw x Cfc x 100 C-organic content (%) = Organic matter content x 0.58 Where: W2 : ash weight after 500-600 o C dried-oven (g) W : soil sample weight after 105 o C dried-oven (g) Cfw : correction factor of water content = 100 / (100 -% water content) Cfc : correction factor of co-material content = (100 -% co-material content) / 100 0.58 : conversion factor of organic matter to C Soil respiration.Soil respiration of soil sample was determined by using modified Vestraete method.Furthermore, the amount of CO2 production of soil sample was measured using the following formula [2]: Where: a : volume of HCl titration for soil sample (ml) b : volume of HCl titration for control (ml) t : HCl normality (0.1 N) n : incubation period 2.3.2.Climatic factor.The parameters of climatic factor ware directly observed and measured in the field within observation plot (1 x 1 m subplot).Ambient temperature and humidity were measured in every subplot by using digital thermo-hygrometer with 3 repetitions in every 30 minutes.Beside that, the light intensity was measured by using luxmeter regarding to the wind direction in every subplot.

Data Analysis
Data processing was conducted to analyse and identify the soil fauna biodiversity, such as species diversity index (H') [16], species richness index (DMg) [17], species evenness index (E) [18], and soil fauna abundance [19].In other hand, we also conducted the statistical analysis by using R-Studio, included the Least Significant Difference (LSD) Test to investigate the disparities in soil fauna abundance across different elevations as well as the Pearson Correlation Test to analyse the relationship between soil fauna existence with environmental factor (edaphic and climatic factor).

Results and Discussion
3.1.The Abundance of Soil Fauna in several Altitude of Lower Montane Forest in GHSNP Soil fauna abundance can be indicated by the number of soil fauna in a community.The presence of soil fauna is influenced by various factors.The abundance of soil fauna is affected by climatic factors such as rainfall, temperature, humidity, and soil factors such as aeration, soil temperature, litter, soil moisture, acidity, nutrient content, as well as vegetation cover factors such as forests, grasslands, shrubs, and agriculture [20].LSD test, which was presented on Tabel 1 showed that soil fauna abundance was significantly different in every elevation (altitude) at the 95% confidence level.The highest of soil fauna abundance was found at the altitude of 1,100 masl in lower montane forest ecosystem.In other hand, the open area (non-forested area) with 1,230 masl altitude had the lowest on soil fauna abundance.The abundance of soil fauna could be affected by the microclimate, namely temperature and soil moisture.The air temperature will decrease by 0.6 o C for every 100 m increase in altitude [21].The number (mean value) followed by the same letter was not significantly different according to LSD test on 95% confidence level.
Elevation is a climate-controlling factor that strongly influences air temperature [22].Air temperature is a limiting factor for the activity of soil fauna.Air temperature tends to decrease with increasing elevation.Moreover, humidity is a factor affecting the metabolic activity and reproduction of soil fauna, which increases with rising elevation.As the elevation increases, the density tends to disperse, creating empty spaces, resulting in reduced vegetation [23].Soil fauna abundance is also influenced by vegetation conditions.Denser vegetation provides a greater amount of litter, leading to a proliferation of soil fauna in areas rich in organic resources.
Table 2 showed that soil fauna at each elevation had different compositions.The lower montane forest area at an elevation of 1,100 masl was the location with the highest abundance of soil fauna, with 156 individual/m 2 comprised of 11 orders and 25 families.On the other hand, the open area land was the location with the lowest occurrence of soil fauna, with only 3 individual/m 2 and a composition of 1 order.The greatest number of soil fauna which was found in this study belongs to the family Formicidae (Figure 2).The lower montane forest area at an elevation of 1,100 masl the location with the highest number of Formicidae individuals, totalling 80.
Formicidae is a macrofauna that lives socially by forming colonies.Functionally, Formicidae falls into the group of engineering ecosystem species, which means their role is to engineer the ecosystem by forming soil formations that promote good soil aggregation [24].Formicidae is classified as an ecosystem engineering group because their activities involve building nests both within and beneath the soil, creating tunnels and empty spaces [25].This group could influence the physical, chemical, and biological conditions of the soil.Physically, Formicidae nests were ables to improve soil structure, increase soil porosity, reduce bulk density, and enhance water infiltration, consequently affecting soil moisture and temperature.Chemically, they could transform acidic pH into neutral conditions through the decomposition of organic matter, thus increasing the total organic carbon content.Additionally, Formicidae also had a role in soil biology by producing CO2 and serving as a hotspot of metabolic activity within the ecosystem through respiration processes.
Collembola was a soil mesofauna commonly found at an altitude of 1,300 masl.There were four families in the Collembola order that had been discovered, namely Isotomidae, Paronelidae, Onychiuridae, and Entomobrydae.Family of Onychiuridae was only found at an altitude of 1,300 masl, while family of Entomobryidae was exclusively found at 1,200 masl.Furthermore, familiy of Paronellidae was only found at 1,100 masl.Isotomidae was the most frequently encountered family in the Collembola order.Collembola plays a role in decomposing organic matter and also contribute to soil respiration [24].The abundance of Collembola is influenced by both biotic and abiotic factors [26].Biotic factors refer to the presence of other soil fauna, such as predators like Formicidae.Collembola  Tabel 3 showed the biodiversity of soil fauna on lower montane forest ecosystem in GHSNP at several altitudes.The species richness of soil fauna was found in altitude of 1,100 masl and 1,300 masl with value of 4.75 and 3.98, consecutively.Nonetheless, the soil fauna species richness in 1,200 masl appeared the lower value (2.29) than 1,100 masl and 1,300 masl elevations.In addition, the lowest species richness of soil fauna was found in 1,230 masl as an open area land (ecosystem), due to only one family (Achatinidae) which was found in this ecosystem type.This phenomenon was probably caused by the absence of vegetation in open area land (ecosystem).As we knew that vegetation as a plant's community was assembly of various plant species, where they had a principal role as a producer within the forest ecosystem.Therefore, it could probably affect the species richness of soil fauna in open area location.The diversity index (H') of soil fauna related to the abundance of species within an ecosystem.The calculated diversity index revealed that all plots, except for the open land plot, exhibit high diversity.Specifically, the H' values for each altitude were 2.08, 1.86, and 2.38, respectively.Notably, the observation plot at 1,300 masl showed a high diversity, potentially influenced by a high ratio of the number of families to the number of individuals in that plot.
The evenness index (E) could be used to describe the species distribution level toward other species in an ecosystem.The evenness index was categorized into three criteria: low evenness (E ≤ 0.31), moderate evenness (0.31 < E ≤ 1), and high evenness (E > 1) [27].The observation plot at 1,300 masl demonstrated the highest evenness index (E = 0.84).In contrast, the open area ecosystem showed a lowest of evenness index (E = 0), where indicated the uniform distribution of soil fauna which was dominated by a single species.

The Influence of Climatic factors on Soil Fauna
Tabel 4 showed the result of correlation analysis between soil fauna abundance and climatic elements (humidity, temperature, and light intensity) on lower montane forest ecosystem in GHSNP.The correlation test results indicated that humidity negatively correlated with the abundance of soil fauna with a strong category (-0.62).It showed that when the air humidity of environment increased, so the soil fauna abundance was able to decrease.On the other hand, the air temperature and the light intensity showed a positively correlation with soil fauna abundance, with a moderate and low category, respectively.Excessively high humidity has critical effects on organisms and effects on nitrification, but higher humidity is more favourable for soil fauna compared to excessively low humidity [28].Temperature restricts organisms when humidity is too low or high [28].An increase in environmental temperature indirectly reduces the contribution of soil fauna due to higher temperature leading to increased C/N and soil fauna density [29].The correlation between soil fauna and light intensity falls into the low category.Light intensity influences the activity of soil fauna [30].Decrease in the number of soil fauna with increasing light intensity indicates that soil fauna are not fond of light, especially at high intensities [31].

The Influence of Edaphic Factors on Soil Fauna Abundance
Edaphic factors were elements related to the soil included the physical properties of the soil, chemical properties of the soil, and biological properties of the soil.Tabel 6 showed the result of correlation analysis between soil fauna abundance and edaphic elements (pH, CEC, C-org., litter weight, soil respiration, bulk density, porosity, and soil temperature) on lower montane forest ecosystem in GHSNP.
Correlation test results indicated a very strong correlation between litter wet weight and soil respiration with soil fauna abundance.Additionally, cation exchange capacity (CEC) showed a strong correlation with soil fauna abundance.The correlation between litter weight and soil fauna abundance could be attributed to the fact that litter weight serves as an energy source for soil fauna who stated that Soil fauna is highly sensitive to the availability of energy sources, such as organic matter [19], [32], [33].Furthermore, the litter, particularly the litter on the forest floor probably had influence toward the ambient factors, such as temperature, humidity, light intensity protection, and soil temperature and humidity which were able to give effect to the soil fauna life.Based on the study results, it was known that the abundance of soil fauna had positively correlation with several parameters of edaphic elements, such as CEC, litter weight, C-organic, soil respiration, porosity, and soil temperature.Litter may influence toward the humus characteristics which is important for soil fauna [35].CEC was influenced by the availability of organic matter [36].Soil respiration and CEC could also correlate with soil fauna due to the influence of fauna activities in the soil.CEC indicated the availability of nutrients in the soil.Soil fauna indirectly influenced the CEC through their activities in breaking down organic materials.The activities of soil fauna also implicated on soil respiration by producing CO2 and becoming hotspots of metabolic activity within the ecosystem [37].
In contrast, soil fauna abundance appeared a negatively correlation between soil acidity (soil pH) and bulk density.Soil fauna can live optimally in the soil with pH of 6.5 -7 [36].Moreover, hight bulk density implied to the soil porosity reduction, where it could be influenced by the low of soil fauna abundance [38].

Conclusion and Recomendation
The highest soil fauna abundance was found at an altitude of 1,100 masl with 156 individual/m² consisting of 11 orders and 25 families.At an altitude of 1,200 masl, the soil fauna abundance was 51 individual/m², comprising 9 orders and 10 families.At 1,300 masl, the soil fauna abundance was 72 individual/m², consisting of 11 orders and 18 families.In the open area, the soil fauna abundance was only 3 individual/m², belonging to 1 order and 1 family.The correlation analysis indicated that abiotic factors influence soil fauna abundance.Climatic factors correlated with soil fauna are air temperature (0.54) and humidity (-0.62).Edaphic factors correlated with soil fauna abundance include litter weight (0.89), respiration (0.83), cation exchange capacity (0.81), and organic carbon content (0.78).Further research is needed to study soil fauna at the species level.Additionally, in-depth and comprehensive research could be conducted to investigate the influence of soil physical, chemical, and biological properties on soil fauna, leading to more precise management practices.

Figure 1 .
Figure 1.Observation plot for soil fauna sampling and environmental variables measurement

Table 1 .
The result of LSD test of soil fauna abundance on several altitudes in lower montane forest

Table 2 .
Composition of soil fauna (mesofauna and macrofauna) at various elevations in lower montane forest ecosystem in GHSNP

Table 3 .
Soil fauna biodiversity on lower montane forest ecosystem in GHSNP at several altitudes

Table 5 .
The result of climatic parameters (temperature, humidity, and light intensity) measurement