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Demographic Study of Nepenthes Species (Nepenthaceae) Recorded along the Trail to the Summit of Mount Kinabalu in Sabah, Malaysia



Jumaat H. Adam
 
ABSTRACT

A total of 1255 pitcher plants belonging to two species were recorded from 11 plots set between 2610 m to 2970 m altitude on Mount Kinabalu, each with an area of 0.01 hectare. Of these plants, 1180 (94%) belonged to Nepenthes villosa, followed by N. kinabaluensis contained 75 (6%) plants. The density of N. villosa and N. kinabaluensis ranged from 0 to 260 and 0 to 65 plants respectively. Nepenthes villosa was recorded absent in P5, whereas N. kinabaluensis was recorded in P2, P3 and P11. Differences in density of both species between the study plots is influenced by combination of factors, which include topography, soil, habitat, different light intensities reaching the forest floor and water deficient due to exposure to wind and light intensities at higher altitudes. The Id values were greater than 1 for both species in all plots showing contagious dispersion pattern. Size class distribution and population structure varied for both species between plots. Generally there were more seedlings and juveniles than mature plants of both species at different elevations indicating regenerating populations. In mature plants there were more male than female plants in both species.

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Jumaat H. Adam , 2002. Demographic Study of Nepenthes Species (Nepenthaceae) Recorded along the Trail to the Summit of Mount Kinabalu in Sabah, Malaysia. Pakistan Journal of Biological Sciences, 5: 419-426.

DOI: 10.3923/pjbs.2002.419.426

URL: https://scialert.net/abstract/?doi=pjbs.2002.419.426

Introduction

Nepenthes plant can regenerate either by vegetative shoots or seeds. The seedling has a rosette of leaves and each leaf normally bears a pitcher at its tip. Secondary rosettes also form on the stem and from the base of the stems. These rosette stage may persist for two or three years (Green, 1974); only when the stem produces leaves of full size does it begin to grow rapidly in length (Holttum, 1954) and in most species the internodes gradually lengthen with increasing age attaining 20-30 cm in length when the plant is upright. At this stage the plants only produce ground pitchers and no inflorescence. Later, the stem elongates continuously and, with the support of strong curled tendrils, it may climb up trees and begin to produce aerial pitchers which depending on species are similar or different in shape to the lower pitchers. Species capable of growing in both closed, tall canopy forest and in open habitats or in secondary vegetation, for example, Nepenthes ampullaria, N. bicalcarata, N. macrovulgaris, N. gracilis and N. rafflesiana may climb to more than 10 m tall and equal the length of the tree canopy. In open habitats, species, such as N. ampullaria, N. bicalcarata, may flower when a few meters tall whereas it is capable of growing to 30 m tall in dipterocarp forest. If the stem fails to find the support, for example, in N. ampullaria and N. gracilis, the stem lies on the ground, rooting abundantly at the nodes, and producing short lateral branches with dense clusters of leaves with reduced laminas and large pitchers (Macfarlane, 1908). The switch from the lower to upper pitcher type appears usually to coincide with the onset of flowering (Juniper et al., 1989).

The main objectives of my study were to identify the species composition and density of Nepenthes recorded from the study plots, and, secondly, to determine the dispersion pattern, size class distribution and population structure of each of Nepenthes species recorded.

Materials and Methods

In order to accomplish the objectives of this study, a total of eleven plots, all of uniform sizes, each measuring 10 x 10 m2, was set up along the summit trail of Mount Kinabalu from 2610-2970 m altitude. Each of the plot was subdivided into twenty five subplots, each measuring 2 x 2 m2. The division of larger plot was necessary to determine the spatial pattern of arrangement of individuals in the population also known as the dispersion or population distribution (Brower and Zar, 1977).

In this study, all individual plants of Nepenthes in each plot were identified to species in the field and mapped to scale on graph paper. Every pitcher plant mapped was numbered using a plastic tag. Stem length, number of leaves and number of pitchers were measured for each plant. The life stage of each plant was recorded (Table 2) namely the seeding stage (SC1), the juvenile stage, the upright plant capable of producing only ground pitchers (SC2-SC3), the mature sterile plant which produce both upper and lower pitchers but is not reproductive (SC4-SC8), and the mature fertile male and female plant. This arbitrary classification was necessary to avoid confusion and to ease the enumeration of plants found within the study plots.

The dispersion pattern of Nepenthes population was computed using Morista ‘s Index of Dispersion (Id), and the departure of an observed dispersion pattern from randomness was assessed statistically using Chi-square (χ2) test (Brower and Zar, 1977).

Results and Discussion

Population density: A total of 1255 pitcher plants representing two different species were enumerated from eleven study plots (2610-2970 m) on the summit trail of Mount Kinabalu (Tables 1 and 2). Two of these species were Nepenthes villosa and N. kinabaluensis. The altitude range of these two species differed. N. villosa occupied a wider altitudinal zone (2610-2970 m), whereas N. kinabaluensis was found in a narrow altitudinal zone (2645-2790 m).

The population of N. villosa is larger than that of N. kinabaluensis with total of 1180 (94%) plants compared with 75 (6%) of N. kinabaluensis. Nepenthes villosa was present in 10 of the 11 plots sampled. Both species were absent in plot 5 at 2750 m altitude. The number and percentage of N. villosa plant present in each plot varied considerably from 156 (13.2%) to 260 (22.1%) in P3, P4, P6, P7 and P8, to less than 10 (8.5%) plants in P1, P2, P9, P10 and P11, and it was absent in P5 (Table 1). On the other hand, N. kinabaluensis with a narrow altitudinal distribution range was found only in P2, P3 and P11 with 65 plants (86.5%) of the population in P11 and only 6 and 4 plants in P2 and P3 respectively. Principal component analysis (PCA) showed that P5 (2750 m) set on Mount Kinabalu has higher tree species diversity, no moss cover, steeper slope, no exposed rocked faces, the tallest tree, a higher tree basal area and deeper soil (Fig. 13a-f). The forest above and below P5 has lower tree species diversity, often mossy, shallow slopes, sometimes rocky, tree shorter with low basal area, shallow soil depth and abundance of N. villosa and N. kinabaluensis.

Table 1:
The Id, χ2 goodness of fit test, density and dispersion pattern of N. villosa and N. kinabaluensis in 11 sampling plots from Summit Trail, Mount Kinabalu in Sabah
*Plot: Size of all plot sampled was 10 x 10 m2; SP= All plots were divided into 25 subplots, each with 2 x 2 m2 in size; D = Density; DP = Dispersion pattern.

Table 2: Size class distribution of N. villosa and N. kinabaluensis for 11 sampling plots on Summit Trail of Mount Kinabalu
P-  Plot; Sp.- Species; STR- Sterile plant; MP- Male plant; FP- Female plant; SC- Size class; SC1:10.1-20 cm (seedling); SC2: 20.1-40cm (Juvenile); SC3: 40.1-60 cm (Juvenile); SC4: 60.1-100 cm (mature sterile); SC5: 100.1-140 cm (mature sterile); SC6: 140.1-180 cm (mature sterile); SC7: 180-250 cm (mature sterile); SC8: >250 cm (mature sterile); No.- Number of plants; %- percentage; AP – Total number of plants recorded from all sampling plots; NV- N. villosa; NK – N. kinabaluensis

Table 3: Summary of characteristics of 11 sampling plots on the summit trail of Mount Kinabalu
RF- Exposed rocked faces; GC- Undergrowth cover; MC- Moss cover; MH- Mean tree height; BA- Basal area of tree; SH – Soil horizon; HM- Humus; BS- Black soil; BRS – Brown soil; P- plot.

Fig. 1: CDP of NV in P1 (2610 m) on MK

Fig. 2:
CDP of NV (filled circle) and NK in P2 (2645 M) on MK.

Fig. 3: CDP of NV in P9 (2940 m) on MK.

The highland pitcher plants are more conspicuous in mossy forest (Smythies, 1965) and mountain ericaceous forest (Smythies, 1965). Nepenthes villosa and N. kinabaluensis are confined to forests on ultrabasic soils and results of this study confirm the earlier studies (Adam et al., 1989, 1992, 1994; Adam and Wilcock, 1996; Kurata, 1976; Phillipps and Lamb, 1988). Pitcher plants are rare or absent in oak forest or in closed canopy, deeply shaded forests at high elevations.

Fig. 4: CDP of NV in P10 (2970 m) on MK.

Fig. 5: CDP of NV in P4 (2710) on MK.

Fig. 6: CDP of NV in P6 (2830 m) on MK.

Adam (1997) demonstrated that pitcher plants growing in the infertile soil supplement nutrients by trapping animals especially insects. The absence or rare occurrence of pitcher plants in closed canopy forest at higher elevation is due to light and soil factors (Smythies, 1965; Adam et al., 1994; Adam, 1995).

Fig. 7: CDP of NV and NK in P3 (2680 m) on MK.

Fig. 8: CDP of NV in P4 (2710 m) on MK.

Fig. 9: CDP of NV in P6 (2830 m) on MK.

Fig. 10: CDP of NV and NK in P11 (2790 m) on MK

Fig. 11: CDP of NV in P7 (2875 m) on MK.

Fig. 12: CDP of NV in P8 (2910 m) on MK.

Fig. 13a: PCA ordination showing relationship between altitude (alt) of plots (P) and species number (S) on MK.

Fig. 13b: PCA ordination showing relationship between alt. Of P and % ground cover (G) and moss cover (M) on Mt. Kinabalu.

Differences in the density of N. villosa and N. kinabaluensis in the 11 study plots on Mount Kinabalu are influenced by a combination of factors, which include topography, soil, habitat and different light intensities reaching the forest floor due to the density and forest canopy height and water deficient particular for plots located on exposed ridge, due to both the high rate water loss from the soil, constant exposure to wind from the western part of the island, and high light intensities at high altitudes.

Fig. 13c: PCA ordination showing relationship between alt. Of P and slope © and % of rock faces on MK.

Fig. 13d: PCA ordination between alt., tree height, basal area (B) (m2) on MK.

The absence of these two species in P5 is related to very high tree basal area (BA=52 m2) and, the plot is located below the ridge thus the area is not exposed to wind and high light intensity. The tree species in the plot are tall with a dense canopy that permits little light to reach the forest floor thus may deter the germination of seeds of these two species or their growth (Som, 1988).

Fig. 13e:
PCA ordination showing relationship between altitudes and density of N. villosa (V) and N. Kinabaluensis (K) in plots on Mt. Kinabalu.

Fig. 13f:
PCA ordination showing relationship between observed ecological factors and altitude on Mt. Kinabalu

Factors such as shallow soil and exposed rock, lack of forest floor vegetation create unfavorable dry conditions for the growth of N. villosa in P9 and vice versa in P3, P4, P11, P7 and P8 where plants show a strong tendency to grow well in parts of the plot with a gentle terrain, deep soil profile, presence of floor vegetation cover and moss cover, which create moist conditions at ground level, thin forest canopy that allows a certain amount of light to reach the forest floor, required for germination and growth of pitcher plants (Table 3). Nepenthes villosa was totally absent in parts of the plots with very dense undergrowth cover, and a dense canopy. The observations clearly show that lights is one of the important factors required for the establishment of Nepenthes villosa.

Som (1988) reported that the high humidity and moist conditions are the two factors, favoring growth of Nepenthes species. In P1, N. villosa population comprised mostly of small plants (Fig. 1). Factors that may deter or slow down the growth and account for the low density of these plants include steep slopes, active erosion, shallow soils and a high percentage of barren rock faces (Fig. 2). In this plot, N. villosa grew in the limited area of land on well developed soil. The poor establishment of N. villosa and N. kinabaluensis in P2 were due to water deficiency due to the constant wind exposure and high light intensity on the summit of exposed ridge (Fig. 2). In P3, fewer N. villosa was recorded from the shaded and steep section of the plot, but was commonly on the gentle section (Fig. 7). The influence of topography on the establishment of N. villosa plants was evident in P4 (Fig. 8), P6 (Fig. 9), P7 (Fig. 11), P10 (Fig. 4), and P11 (Fig. 9), where plants tend to grow on the gentle section of the plot with forest opening. It was absent from steep slopes (34o) and shallow gullies. In these areas of the plot, erosion was active thus preventing the development of the soil and the establishment of pitcher plants. The ultrabasic endemics are characterized by being able to obtain calcium even at low concentration, being the characteristic of these sites; the heavy metal ion concentration may serve to exclude competitors, rather than providing a specific need for endemic (Kruckenberg, 1954). Brooks (1987) explained the unusual floristic composition and poor species composition of forest on ultrabasic formation as attributable to the “serpentine factor” which includes chromium, nickel and magnesium toxicity, and low calcium content and other nutrient deficiencies. This study shows that N. kinabaluensis, particularly N. villosa which are found on ultrabasic soil, associated with Leptospermum recurvum. It is known that L. scoparium recorded from ultrabasic area in New Zealand has a high calcium content (Lyon et al., 1971) that reduces chromic ion toxicity ( Brooks, 1987; Proctor, 1971). This may explain its tolerance to serpentine soils (Brook, 1987). A similar explanation may be applicable but research is needed to explain the successful establishment of N. villosa, N. kinabaluensis and L. recurvum on Mt. Kinabalu.

Dispersion pattern: Table 1 summarizes the results on density and dispersion pattern of N. villosa and N. kinabaluensis enumerated from 11 plots using Morista’s Index of Dispersion (Id) and Chi-square test (χ2 ). The actual dispersion pattern of these species is illustrated in Fig. 1-12.

The Id values N. villosa in 10 of the 11 plots were all greater than 1, ranging from 1.08 (P4; 2710 m) to 9.00 (P10, 2940 m). Id values greater than 1 indicate the contagious dispersion pattern of N. villosa populations (Brower and Zar, 1977). The χ2 for N. villosa in all plots ranged from 37.60 (P4) to 229.3(P7), and χ2 values of all plots were greater than X20.05, 24=36.4. These results show the dispersion pattern of N. villosa in the study plots was significantly different from random. Since their Id values were greater than 1, the dispersion pattern of N. villosa in these plots is therefore contagious (Fig. 1-12). Following the same argument, the dispersion pattern for N. kinabaluensis populations recorded in P3 (2680 m), P11 (2790 m) and P2 (2645 m). Factors influencing the contagious pattern of distribution of N. villosa and N. kinabaluensis include gentle terrain, deep soil profile, low tree basal area, low tree height which allow enough light to reach the forest floor, presence of undergrowth and moss cover that create a wet and humid soil environment.

Size class distribution (SCD): The stem length of two species present in the plots were grouped into eight size classes (Table 2).

In a regenerating population, larger number of plants fall within the small size classes, with increasing size representing successive mortality as the plants grow older. The SCD of N. villosa and N. kinabaluensis on the summit trail on Mount Kinabalu were similar (Table 2). Both show a general decline in number with increasing size. Populations with few seedlings could be interpreted as being in decline.

Population structure: Nepenthes populations comprise of individual plants of different ages or life stages. In this study, four life stages were recognized namely seedlings (SC1), juvenile (SC3-SC4), mature sterile (SC4-SC8), matured fertile (Table 2). Pitcher plants are dioecious, male and female flowers are borne on different plants.

Populations of N. villosa and N. kinabaluensis had relatively larger number of seedlings and juvenile plants compared to mature sterile. Thus the populations of these two species at different elevations on this mountain are regenerating. The mature sterile have low number of fertile plants. There are more male than female plants in N. villosa and N. kinabaluensis with a ratio of 5:3 and 12:1. The higher number of male plants than the female plants may possibly be a reproductive strategy of both species as to ensure the ample pollens produced by the hundreds of male flowers in each inflorescence successfully pollinate the thousands of ovules in the flowers on female inflorescence. Large number of female plants are not vital since each female inflorescence is capable of producing thousands of seeds.

Nepenthes villosa and N. kinabaluensis were recorded in plots from altitude 2610-2970m and 2645-2790 m respectively located on ultrabasic rock formation on Mount Kinabalu. The population density of these two species varied considerably between plots. These differences may be attributed to a combination of local factors which include light intensity, soil, topography, slope inclination, erosion processes due to steep slopes, rock faces, and lack of vegetation cover. The dispersion pattern of both species in the plots studied was significantly contagious. The SCD of stems showed considerable variation between species; generally larger number of plants fell into small size class with a decline with increasing size, indicating regenerating population. Population structure generally comprised a low number of fertile plants with more male plants than female and a larger number of seedlings and juvenile plants compared to matures plants.

Acknowledgments

The author is grateful to University Kebangsaan Malaysia, University of Aberdeen, Sabah Parks, Malaysian Government Research and Grant 4-07-03-042 & 56, FSSA Biodiversity Fund; I wish to thank Sabah Parks, Datuk Lamri Alisaputra (Sabah Parks Director) for giving permission to carry out the work within the park area; Dr. Ramlan Omar for his technical assistance; Mr. Julaihi Adam, Mr. Aliosman Mahdi and technical staff of Sabah Parks for helping me in the field; Dr. C. C. Wilcock and Dr. M. D. Swaine of University of Aberdeen for commenting this manuscript; and to those people in government or private agencies in Sabah for contributing directly or indirectly to the successful completion of this project

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