Autecology of Nepenthes spp. in Peat Swamp and Heath Forest Pematang Gadung, West Kalimantan

Nepenthes occur in various habitat types in West Kalimantan. But some species are categorized as vulnerable on the IUCN red list. Autecological studies of Nepenthes spp. are required for species management and conservation. The study aimed to analyze species diversity, distribution pattern, association, and environmental factors that correlated with Nepenthes spp. at peat swamp and heath forest in Pematang Gadung. Data was collected in September 2021 by purposive sampling on 60 plots measuring 3m x 3m in each habitat type. Species diversity was analyzed based on the presence and abundance of species in the plots. The distribution pattern was determined using a standardized Morisita index (Ip). Meanwhile, the association type was determined based on the Jaccard index (JI). Environmental data were analyzed by Canonical Correspondence Analysis (CCA) using Past Version 4.03. This study found six wild species in a peat swamp and four species in a heath forest. The population of Nepenthes spp. has clumped distribution pattern with Ip>0. Nepenthes spp. are associated with plants such as Barringtonia racemosa , Syzygium sp., Nephrolepis biserrata , and Campnosperma auriculatum . The result of CCA revealed that environmental factors in both habitat types affected the presence of each Nepenthes species. The air temperature, humidity, soil moisture, and light intensity show different influences on different species.

penthes provides ecological advantages such as climate indicator in areas with high annual rainfall, humid, and low soil nutrients (Mansur 2006), absorbing carbon dioxide (CO 2 ) in the atmosphere (Mansur 2012), supplying nitrogen and phosphorus elements to the soil (Kissinger et al. 2015) and providing food sources for insects (Bauer et al. 2016).
Pematang Gadung Village Forest has a unique ecosystem because it is a swamp forest surrounded by a heath forest. Exploring these habitat types can potentially find endemic and new species of Nepenthes. Botanically, the island of Borneo is relatively well-explored in the north (Sabah, Sarawak and Brunei) (Danč ák et al. 2022). In contrast, research about Nepenthes diversity, especially in peat swamps and heath forests in West Kalimantan, is rarely reported.
An autecological study in Pematang Gadung Village needs to be conducted. Many Nepenthes species are threatened due to illegal gold mining activities in this village. This study aimed to analyze Nepenthes spp. diversity, distribution pattern, association, and environmental factors that influence the presence of Nepenthes spp. in peat swamps and heath forests in Pematang Gadung.

Data Collection
This study was conducted in September 2021. The presence of Nepenthes spp. was selected through survey and exploration during the study. Sixty plots of 3m x3m were purposively placed in peat swamps and heath forests. Purposive sampling was chosen for an in-depth investigation to define characteristics for a purpose relevant to the study. Purposive sampling provides a sample that can logically assume to represent the population (Palinkas et al. 2015). The number of Nepenthes counted as one individual if more than half of the plant was in the plot. Nepenthes were identified using literatures (Cheek & Jebb 2001;Mansur 2006). Meanwhile, the associated plants were observed and identified using (Soepadmo et al. 1995) and websites (https://powo.science.kew.org/ and https://www.asianplant.net/). Abiotic data collection, including air temperature, humidity, light intensity, and wind speed, was measured using a handheld 4-in-1 environment meter. Soil samples were collected in 1 kg from 10 points of each habitat type at 10-20 cm depth using a sample ring. Then prepared by removing litter residues and plant root debris for physical and chemical analysis.

Data Analysis
The composition of the Nepenthes species and the Important value index (IVI) are calculated using the formula (Mueller-Dombois & Ellenberg 1974) as follows: Relative Frequency (RF) = Important value index (IVI) = RD + RF The Shannon-Wiener formula calculates the diversity index species (H') (Shannon 1948), dominance index (D) is calculated to determine the degree of species dominance (Odum 1993). The evenness index (e) estimates the distribution of individual species within a community (Krebs 1989). The formulas used were as follows: Where: ni is the number of individual species, N represents the number of individuals of the whole species, and S represents the number of species.
The distribution pattern of Nepenthes was analyzed using a Standardized Morisita Index (Ip) (Krebs 1989). Using the formulas: Where: Id is the Morisita index, n is the number of observation plots, x is the number of Nepenthes individuals in plots, Mu is the uniformity index, χ 2 0.975 is the chi-square table with a confidence interval of 97.5%, Mc is the clumping index, χ 2 0.0025 is the chi-square table with a confidence interval of 2.5%.
Association analysis was determined using a 2x2 contingency table, and the degree of association was calculated using the Jaccard index (JI) (Mueller-Dombois & Ellenberg 1974). Using the formula: Where a: a is the number of plots found Nepenthes and others species, b is the number of plots found Nepenthes, c is the number of plots found others species.
Canonical Correspondence Analysis (CCA) using Past software version 4.03 was used to examine the correlation between environmental conditions and the existence of Nepenthes (Hammer et al. 2001).

Habitat Characteristics of Nepenthes
Peat swamp forest is characterized by relatively dense canopy cover, wet soils, low light intensity, and rich leaf litter on the forest floor. Peat swamp is naturally often waterlogged and the water surface and peat surface are highly acidic (Page et al. 1999;Tanjung et al. 2020). The Pematang Gadung Village Forest area is a coastal peat dome located between the Pawan and Pesaguhan Rivers. The floral composition of the peat swamp forest consists of Aglaia rubiginosa (Hiern) Pannell, Baccaurea sp., Combretocarpus rotundatus (Miq.) Danser, Cratoxylum glaucum Korth., Diospyros spp., Pandanus spp., and Syzygium spp. In this area, Gonystylus bancanus (Miq.) Kurz was also found. This species is a peat swamp endemic plant, categorized as an endangered species.
In contrast, heath forest has low canopy cover with high light intensity, located close to illegal gold mining sites. The forest floor is covered with white quartz sand; trees have small trunk sizes with tight branches (Whitten et al. 1987). The trees commonly found in this area include Baeckea frutescens L., Cratoxylum glaucum Korth., Melaleuca cajuputi Maton & Sm. ex R. Powell, Rhodomyrtus tomentosa (Aiton) Hassk, and Tristaniopsis obovata Benn. Ferns and Cyperaceae species are also found, such as Dicranopteris linearis (Burm.f.) Underw. and Scleria biflora Roxb.
Nepenthes thrive in peat swamps and heath forests, growing in the ground or climbing a host tree. Generally, Nepenthes are vines or subscandent scrubs that grow and attach to adjacent trees using looped tendrils. We did not find differences in Nepenthes habits in either peat swamp or heath forest.

Species Richness
We recorded four species from the heath forest, Nepenthes ampullaria Jack, Nepenthes gracilis Korth., Nepenthes mirabilis (Lour.) Druce, and Nepenthes rafflesiana Jack. These species are also found in peat swamp forest and we recorded two other species from this forest, Nepenthes bicalcarata Hook.f. and Nepenthes x hookeriana Lindl. (Figure 2). N. bicalcarata is an endemic species to Borneo. The latest species is a hybrid of N. ampullaria and N. rafflesiana (Clarke 2001). N. bicalcarata has never been reported to be found in Ketapang Regency (Sunardi & Mansur 2021), so it is the first report of N. bicalcarata from Ketapang Regency. N. reinwardtiana Miq. can be found in a peat swamp and heath forests (Rantau et al. 2019;Wulandari et al. 2020) but has not been found in this study. N. reinwardtiana prefers to grow in open areas (Hariyadi 2013). Nevertheless, degradation in the heath forest due to illegal gold mining may cause this species to be absent at the study site. The most common species found in the peat swamp forest Pematang Gadung Village are N. ampullaria. This species, with a density value of 3,370 ind/ha, is predominant since it has the highest (IVI 115.13%) in the peat swamp forest (Table 1). Generally, N. ampullaria is abundant in humid conditions, with high water availability and shaded areas (Moran et al. 2003;Nurhadi et al. 2018). This kind of condition is found in Pematang Gadung Village Forest.
Furthermore, a community of Nepenthes in the heath forest was dominated by N. gracilis, (4,241 ind/ha, IVI 170.36%) ( Table 1). This species thrives in heath forest probably because heath forest in Pematang Gadung has lower canopy cover and higher light intensity (479-1987 lux) than in peat swamp forest. N. gracilis prefers to grow in conditions with high light intensity. According to Armanda, et al. (2020), N. gracilis dominates in heath forests because this species is often more adaptable than others.
N. ampullaria and N. rafflesiana prefer to thrive in shaded habitats with high soil moisture. We found these species more abundant in the peat swamp forest compared to the heath forest. In this study, we reported that N. bicalcarata was found in peat swamps. The density of N. bicalcarata in peat swamp forests is poor (148 ind/ha). In contrast, N. bicalcarata is not found in heath forests, probably due to high temperatures. N. bicalcarata grow optimally at 18−29℃ (Mansur 2006). N.
x hookeriana was rarely found in the peat swamp forest (74 ind/ ha, IVI 3.05%) and absent in the heath forest. This species is usually found in limited quantities among the parent species. N. mirabilis in the heath forest has the lowest density (37 ind/ha); it might be due to competition with the other species, primarily the dominant species, N. gracilis.
Diversity of Nepenthes in the peat swamp forest of Pematang Gadung is slightly higher compared with the heath forest. The diversity of Nepenthes is categorized as medium (H'= 1.04) in the peat swamp forest and low (H'= 0.39) in the heath forest ( Figure 3a). This data is supported by the values of the dominance and evenness index (Figure 3b, 3c). High diversity, evenness, and density of species in the community indicate the availability of niches, so it is important to maintain their sustainability (Benayas et al. 1999). To avoid their extinction and ensure the availability of genetic material for development efforts, ex-situ conservation and cultivation are necessary.
High dominance index (0.81) makes Nepenthes diversity low in heath forests (Figure 3b). A high dominance value indicates that the habitat has low species diversity with an uneven number of species distribution. However, the dominant species with a high IVI score need conserving to maintain species composition. Decreasing species diversity will reduce competition between species and increase competition for each species. Nepenthes in peat swamp and heath forest is categorized as having an uneven distribution of the number of species with a value of (e) ≤ 0.50 (Figure 3c). Diversity and low evenness in the community caused by species dominance may indicate competition for resources and limited niches to occupy (Wilsey & Polley 2004).
Nepenthes spp. have a clumped distribution pattern (Ip >0) in both peat swamp and heath forest of Pematang Gadung (Table 2). These results are in line with reports from previous studies elsewhere (Payung et al. 2021;Apriyanto et al. 2021). Nepenthes tends to be clumped and thrive in forests with acidic soils that are nutrient-poor and seasonally wet (Damit et al. 2017 Clumped distribution occurs due to generative reproduction supported by environmental conditions. When released and carried by the wind, Nepenthes seeds that are thread-shaped with thin wings will fall not far from the Nepenthes parent. It is because trees near the Nepenthes can restrict the movement of their seeds. Vegetative reproduction in Nepenthes also caused clumped distribution patterns. Vegetative reproduction in Nepenthes with developing basal shoots that arise from axillary buds along stems at ground level (Lam et al. 2020).

Nepenthes spp. Association with other Plants
Associations influence the occurrence of each species in its habitat. Nepenthes spp. in peat swamps and heath forests may have a positive association with a plant species and negative association with the other (Table  3). Positive associations between species indicate differences in resource use and non-competitive interactions between species, while negative associations occur due to competition that can inhibit the presence and abundance of other species (Maire et al. 2012;Sritharan et al. 2021). The positive association between Nepenthes species and other plants indicates that these plants can be a climbing tool for Nepenthes. In addition, other plants also contribute litter to the pitchers of N. ampullaria, which is a semi-detritivorous species.
N. mirabilis tends to coexist with Barringtonia racemosa in peat swamp forests (JI 0.60). N. mirabilis also associates with other species in peat swamp forests, such as Poikilospermum suaveolens. This species was found in plots with low canopy cover, where light can reach the forest floor. In this study, N. mirabilis often occupied open areas close to river, whereas N. ampullaria did not thrive in these niches. Habitat specification occurs to avoid competition with dominant species (Calatayud et al. 2020). Therefore, associations in species with low abundance suggest that the species may not compete with dominant species for the same resources.
The endemic species, N. bicalcarata is positively associated with Antidesma coriaceum. Antidesma coriaceum is often found in plots where N.   bicalcarata thrive. This species was also found to be used as a climbing tool for N. bicalcarata. This report supports previous information on N. bicalcarata in West Kalimantan (Sunardi & Mansur 2021). Nepenthes spp. exhibited negative associations with some plants. Cratoxylum glaucum is a common tree in a peat swamp and heath forest, which has negative associations with N. ampullaria and N. gracilis. We assume that the dominant species compete for the same resources in these niches. Negative associations in forest communities are found in the most common species with a wide distribution and low habitat specificity (Sritharan et al. 2021). N. rafflesiana and C. glaucum tends to be found in the same plot, suggesting no competition between both species. In addition, N. rafflesiana is not a dominant species in peat swamp forests, so it is unlikely to compete with C. glaucum. Nepenthes abundance and vegetation composition influence the associations that occur within habitats. N. ampullaria in heath forest associated with Syzygium sp. This species grows on the forest floor under the shade of Syzygium sp. Meanwhile, N. mirabilis is associated with Nephrolepis biserrata and Scleria biflora. This result is aligned with the report from Hidayat et al. (2018) that N. mirabilis is often found growing together with Cyperaceae and ferns.
Dominant species of Nepenthes are negatively associated with some other Nepenthes. It indicates that the dominant species found in peat swamp (N. ampullaria) and heath (N. gracilis) tend to compete for nutrients and insect prey. Therefore, different Nepenthes species were rarely found in the same plot at the research location.  Air temperature and air humidity are essential factors for Nepenthes' growth. The measurements of environmental factor in peat swamp forest show that the average air temperature is 24.8 °C with an average air humidity of 81.3%. Meanwhile, the average air temperature in the heath forest is higher at 29.8 °C with an air humidity of 73.8%. Nepenthes growth in air temperature ranges from 23°C-31°C (Mansur 2006), with air humidity ranging from 67−90% (Nainggolan et al. 2020). Precipitation is one of the environmental factors affecting the existence of Nepenthes. Nepenthes is predominantly found in the rainfall range between 3500-4000 mm/year (Sartika et al. 2017). Ketapang Regency rainfall for 2020-2021 ranges from 3871.2-4352 mm/year. Heavy rainfall also supports the availability of water in both habitat types, which can support the growth of Nepenthes.
Based on CCA analysis, environmental factors correlate with the presence of Nepenthes spp. in peat swamps ( Figure 4a) and heath forests (Figure 4b). In peat swamp forest, showed a positive correlation between N. mirabilis and N. gracilis to light intensity. Both species in the study site are often found in open canopy cover with the light intensity reaching to forest floor. The existence of N. rafflesiana is influenced by the air temperature. N. ampullaria and N. bicalcarata are affected by air humidity. Meanwhile, N. x hookeriana had a low correlation with air humidity.
The CCA ordination graph in the heath forest suggests that soil temperature, air temperature, and light intensity are highly correlated with N. gracilis. This species can thrive in heath forest with high light intensity from 479-1987 lux, high air temperature of 29.8 °C and soil temperature from 27-30°C. Meanwhile, N. ampullaria is influenced by high soil moisture, similar to conditions in peat swamp forests that are often waterlogged. N. rafflesiana has a low correlation with environmental factors in the heath forest. This species is generally found in shaded areas, but some individuals are found in open areas.
The results of soil fertility analysis in the Nepenthes habitat showed that the nutrient content and pH were low, with 2.9 in the peat swamp forest and 3 in the heath forest. Nepenthes spp. in the peat swamp forest grows on soil with a silty loam texture, while in the heath forest, Nepenthes spp. grows on sandy soil. The high percentage of sand fraction in the heath forest causes the soil's capacity to bind water significantly lower. Low porosity impacts the ability of nutrients to be released from soil colloids due to infiltration. The percentage of soil texture fraction, sand, dust, and clay also affected the nutrient content.
In the peat swamp forest, the C-organic content is categorized as very high at 40.14% due to the high organic matter contained in the peat soil. Total N in peat soil is relatively high at 1.67%. However, most of it is contained in lipoproteins, so it cannot be utilized directly by plants.
Meanwhile, the C-organic content in heath forest is high at 3.3%, with a low total N content of 0.15%. Cation exchange capacity was very high at 171.32 in the peat swamp and low at 11.18 in the heath forest. Both habitats had low base saturation values of <20%.
Study results on habitat characteristics of Nepenthes are essential data in species management and necessary for conservation purposes. Nepenthes is a protected plant species under Law Number 5 of 1990 and Minister of Environment and Forestry Regulation on Permen LHK/P. 20 Year 2018. N. ampullaria, N. gracilis, N. mirabilis, and N. rafflesiana as the least concern (LC) species by IUCN. In contrast, endemic species N. bicalcarata is categorized as vulnerable (VU) (Schnell et al. 2000). Five spe-cies of Nepenthes excluding N. x hookeriana are also listed as restricted for all trade activities.
N. bicalcarata requires special attention in conservation. This species found in small quantities with a density of 142 ind/ha. Based on IUCN, the annotation of this species needs updating, and its population is considered unspecified. Consequently, further exploration and data collection of N. bicalcarata is required. The distribution of N. bicalcarata only covers the western and northern parts of Borneo (including Malaysia and Brunei Darussalam). Over the last 30 years, peat swamp forest was converted into oil palm plantations and has decimated 60% of the N. bicalcarata population in Borneo (Clarke et al. 2018).
Nepenthes spp. in the Pematang Gadung is threatened by illegal gold mining activities. In-situ conservation of Nepenthes species should be implemented in Pematang Gadung Forest Village by restricting forest clearing, illegal logging, and mining area occupation. Monitoring activities of Nepenthes spp. discovery points in study site is also crucial. Ex-situ conservation through captive breeding and cultivation techniques, both conventional and tissue culture, can be applied by considering the characteristics of the Nepenthes' habitat.

CONCLUSIONS
Based on the results of autecological studies, the population of Nepenthes in peat swamp and heath forest has clumped distribution and are often found close to other plants like Barringtonia racemosa and Syzygium sp. The factors that most influence the presence of N. gracilis include light intensity, air temperature, and soil temperature. Meanwhile, the presence of N. ampullaria is affected by high soil moisture. The Pematang Gadung Forest has a high potential for Nepenthes due to the presence of an endemic species of N. bicalcarata. Accordingly, conservation activities are very important to be carried out in this forest to maintain the existing diversity of Nepenthes.

AUTHOR CONTRIBUTION
NU, S, and NSA designed research; NU has been tasked with sampling and observing the existence of Nepenthes spp. and its autecological factors in the field, data analysis, and manuscript writing. S and NSA supervised the identification process in the laboratory, data analysis, manuscript writing, and editing