Published online April 18, 2022
Journal of Ecology and Environment (2022) 46:11
1Central Department of Botany, Tribhuvan University, Kathmandu 44600, Nepal
2Forest Research and Training Center, Ministry of Forests and Environment, Kathmandu 44600, Nepal
3Ashok Medicinal and Aromatic Plants Center, Dabur Nepal Pvt. Ltd., Kavre 45210, Nepal
Correspondence to:Nirmala Phuyal
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Background: Zanthoxylum armatum is one of the 30 prioritized medicinal plants for economic development of Nepal with a high trade value. Understanding the ecology of individual species is important for conservation and cultivation purposes. However, relation of ecological factors on the distribution and populations of Z. armatum in Nepal remain unknown. To address this knowledge gap, an attempt has been made to study the population structure, distribution, and regeneration potentiality of Z. armatum. Vegetation sampling was conducted at six different localities of Salyan district along the elevation range of 1,000 m to 2,000 m.
Results: Altogether 50 plant species belonging to 44 genera under 34 families were found to be associated with Z. armatum. Significantly higher species richness was found at Rim (1,400–1,700 m) and Chhatreshwori (1,800–2,000 m) and lower at Kupinde (1,600–1,800 m). The highest population density of Z. armatum was at Kupinde (1,600–1,800 m) with a total of 1,100 individuals/ha. and the lowest at Chhatreshwori (1,800–2,000 m) with 740 individuals/ha. Based on the A/F value (Whitford index), it can be said that Z. armatum has random distribution in the study area. The plants were categorized into seedlings, saplings and adults based on plant height and the status of natural regeneration category determined. The regeneration potentiality of Z. armatum in the study area was fair with the average seedlings and saplings densities of 150 and 100 individuals/ha. Respectively. A Shannon–Weinner index mean value of 2.8 was obtained suggesting high species diversity in the study area.
Conclusions: The natural distribution and regeneration of Z. armatum is being affected in the recent years due to anthropogenic disturbances. Increasing market demand and unsustainable harvesting procedures are posing serious threat to Z. armatum. Thus, effective conservation and management initiatives are most important for conserving the natural population of Z. armatum in the study area.
Keywords: density, distribution, ecology, population, species diversity, regeneration
The National Conservation Strategy (1988), Master Plan for the Forestry Sector (1988), Industrial Enterprises Act (GoN 1992), Forest Act (GoN 1993) and Regulations (GoN 1995), Herbs and Non-Timber Forest Products Development Policy (DPR 2004) have emphasized on the subsequent development and commercialization of the Non-timber Forest Products including Medicinal and Aromatic Plants (MAPs) for uplifting the livelihood of the rural communities through sustainable and wise use of these valuable resources. Trade Policy in Nepal (GoN 2009) has also prioritized
There have been ample studies on the medicinal plants of Nepal regarding their botany, ecology, ethnobotany, population size, and distribution. A significant amount of research has also been carried out in Zanthoxylum in the Indian subcontinent. However, there have been very few studies in
A preliminary filed survey was carried out in April 2017 to select the study site and sampling areas, gather general information about the study species viz.
The study was mainly based on primary data collection. Necessary information was collected through extensive field observation of the area. The data was collected through physical measurement in the field and review of relevant literature on similar previous studies. Systematic random sampling design was applied in which plots were selected by a random or stratified random plan (Misra 1968). The sampling sites were selected from six localities to cover all the possible habitats and associated vegetation types of
Vegetation sampling was done along the elevation of 1,000 m to 2,000 m. In each locality, four transect lines were set up at 30–50 m in
Vegetation attributes, including frequency, density, and richness, were recorded, along with environmental coordinates such as latitude, longitude, and elevation of each sample plot using a global positioning system (Garmin model 2000) (Shaheen et al. 2011a).
The species richness in this study was obtained by counting the number of species present in each 5 m × 5 m sample plot. In this study, species richness has been defined as, the number of species per plot and expressed as species/m2.Density and abundance
Both this term refers to the number of species in a community. Abundance of any individual species is expressed as a percentage of the total number of species present in community and therefore it is a relative measure (Khan et al. 2014). In sampling the abundance of species, the individual of species is counted instead of just nothing their presence or absence was done while studying the frequency of a species.
Density (D) (plants/ha)
Relative Density (RD%)
Relative Abundance (RA%)
Occurrence of trees and shrub species within each major plots of the study area were recorded to assess their distribution pattern in
Frequency (F) (%)
Relative Frequency (RF%)
Distribution pattern (A/F ratio)
Abundance and frequency taken together are of great importance in determining the structure of a community. High frequency and low abundance indicate regular distribution whereas the converse indicates contiguous distribution. The ratio of abundance to frequency (A/F) for different species was determined for eliciting the distribution pattern. Spatial distribution of plant species was determined following Whitford index WI (Singh and Singh, 1987) as
If value is < 0.025 = regular distribution, value lies between 0.025–0.05 = random distribution and value > 0.05 = clumped distribution (Whitford 1949).
The IVI was calculated to understand the species’ share in the community (Curtis and Cottam 1956). Species with the highest importance value are the leading dominant species of the specified vegetation (Shibru and Balcha 2004). This considers density, frequency, and abundance of the species present in the community. For each species, the relative density, relative frequency, and relative abundance were calculated and summed. It gives the overall importance of each species in the community structure. The IVI for all the species was calculated by adding the sum of relative values of density, frequency and abundance. It was calculated following Bhadra and Pattanayak (2016) as
Importance Value Index (IVI) = Relative Density + Relative Frequency + Relative Abundance.
Population structure of naturally emerged seedlings of
Regeneration status was totally based on population size of seedlings and saplings (Khan et al. 1987; Saha et al. 2016). Good regeneration if seedlings > saplings > adults; fair regeneration, if seedlings > or ≤ saplings ≤ adults; poor regeneration, if the species survives only in sapling stage, but no seedlings (saplings may be or = adults). If a species is present only in an adult form it is considered as not regenerating. The status of natural regeneration was determined based on the values as shown in Table 2 (Bhuyan et al. 2003; Khumbongmayum et al. 2006).
As shown in the above table, ‘good regeneration’ is defined as the condition in which an ample or adequate number of seedlings and saplings contribute to the mature population, while ‘fair regeneration’ is defined as the condition in which there were a fair number of seedlings, but the percentage of saplings was either lower than or close to that of the mature trees. ‘Poor regeneration’ is the condition in which individuals were found at either the seedling or sapling stage only, in greater numbers than the mature trees. The fourth regeneration status is termed as ‘no regeneration,’ in which a species presented only at the mature stage and did not occur in either seedling or sapling stages.
Diversity in species refers to the combined effect of richness and evenness in species. While richness pertains to the number of species in each sampling unit, evenness implies to the distribution of individuals among the species. Species richness is a biologically appropriate measure of diversity and the total number of species in any ecological community, landscape, or region relative to the total number of all individuals in that community.
A diversity index can reveal the structure of biological community in terms of numerical value. It gives more information on community composition than simply species richness. Further, it offers insights into rarity and commonness of species in a community, thereby diversity index acts as important tool for biologists in the understanding of community structure (Muthulingam and Thangavel 2012). Several indices are used to quantify the species diversity of which Simpson’s index (Simpson 1949) and Shannon-Wiener’s index are the most commonly used. Shannon’s diversity index (H) and Simpson’s Index (1 − D) in terms of density for each plot were calculated using the following indices:
Where, pi = (n/N),
n = density of individual species in a plot
N = Total density of all species in a plot
ln = Natural logarithm values
The Shannon diversity index ranges typically from 1.5 to 3.5 and rarely reaches 4.5 (Gaines et al. 1999). The Simpson’s Index values range from 0 to 1. The closer the value of Simpson’s Index to 0, the more diverse the plot will be. A plot with only one species would have a Simpson’s Index value of 1. Trends are opposite to those found for Shannon Weaver values since Simpson’s Index values decrease with increased diversity (Reich et al. 2001). In practice, the values below 0.5 indicates a relatively even community, while high values are indicative of communities dominated by one or a few species.
Soil samples were collected from the four corners and center of each sample plot from the depth of 5–10 cm. The subsamples were mixed thoroughly, and about 100 g soil were collected, air dried in shade (Yadav et al. 1987), kept in zipper plastic bags, properly labeled, and brought to the Laboratory for the analysis of pH, soil organic carbon, total nitrogen, available phosphorus, and soil potassium. Soil organic carbon was determined by following Walkley and Black (1934), total nitrogen (N) by Kjeldahl method (Tsuji and Ohnishi 2001), available phosphorous (P) by a modified Olsen’s method following Gupta (2000), soil potassium (Flame photometer method following Trivedy and Goel 1986 and pH using a digital pH meter with 1:5 soil water ratio (Gupta 2000).
All the analyses were carried out in R platform (R Core Team 2020). The normality (Shapiro–Wilk test) for all the parameters were tested prior to choosing a parametric or non-parametric tool to analyze. All the parameters were tested by Analysis of Variance (ANOVA), Tukey’s test for normal data, and non-parametric Kruskal–Wallis one-way ANOVA, Duncan multiple comparison test for non-normal data.
Altogether fifty plant species (trees and shrubs) belonging to 44 genera under 34 families were found to be associated with
The species richness for each plot was the number of species per plot. Significantly higher species richness (
The mean population density of
Among all the species,
The mean frequency and relative frequency of
The most frequently occurring associates (with > 70% of occurrence) at different localities were
The abundance of
Based on IVI values,
Natural regeneration of
The distribution pattern of
Diversity values according to the Shannon and Simpson indices were higher at Rim and lower at Kupinde. The mean Shannon-Weaver diversity index (H’) which measures the diversity of Z. armatum along with its associates ranged from 2.5 to 3.08. Among the six study sites the highest species diversity (H’ = 3.08) was recorded from Chhatreshwori whereas the lowest species diversity (H’ = 2.5) was recorded at Kupinde. The mean Simpson’s diversity index (1 − D) value ranged from 0.92 to 0.95 (Fig. 9).
Soil nutrient analysis showed that soil organic carbon, soil nitrogen, and soil phosphorus were highest at Chhatreshwori than other localities (Table 5).
Species composition and species richness are important indicators for assessing the biodiversity (Husch et al. 2002) and may strongly depend and/or be influenced by the applied management practices. The listing of 50 shrub and tree species in the area shows the forest is rich in diversity (Table 3). This is comparable to other studies carried out in similar forest types of Bhutan, India, and Nepal. Wangda and Ohsawa (2006) listed 78 tree species in west central part of Bhutan and Buffum et al. (2008) reported 39 tree species from the eastern part of Bhutan. Sundriyal and Sharma (1996) recorded 81 tree species in the temperate forest in Sikkim, and Shrestha et al. (2013) recorded 31 and 37 plant species in the two sites within the elevation range of 2,650–2,800 m asl in Nepal.
The lower number of species recorded at Baghchaur (1,400–1,600 m) and Kupinde (1,600–1,800 m) (Fig. 3) is because of the the nearby settlement and agriculture zones as compared to the other sites. Bhuyan et al. (2003) reported only 16 species in highly disturbed site as compared to 47 species in the least disturbed site in the eastern part of India. Sunil et al. (2011) observed 34 tree species in the low disturbed sites against tree species of 14 in the highly disturbed sites in the southern part of India. The lowest was found in plantation forests, with only 9 species in Nepal (Webb and Sah 2003). All these studies attribute the differences in the results to the degree of disturbances caused by anthropogenic activities.
There is generally a linear relationship between vegetation attributes like species richness, diversity, and ecological factors like altitude, aspect, and distance of the site from disturbance stimuli (Schuster and Diekmann 2005). A monotonic decline in the number of species with increasing elevation has often been considered a general pattern (Brown 1988; Stevens 1992). Inverse correlation between altitude and species richness in Himalayan alpines have also been established in several studies (Kala and Mathur 2002; Panthi et al. 2007; Vetaas 2000). However, the present study did not follow the similar pattern; maximum number of species was recorded at 1,400–1,700 m and 1,800–2,000 m. The high species richness may be attributed to less anthropogenic activities, higher soil moisture and greater topographic variations in habitat conditions.
Several factors as lower elevation, moist habitat, resource availability, disturbance levels, moderate fragmentation together with climatic variability, fluctuations to resources and dispersal limitation may influence the population structure (Shaheen et al. 2011a). The variation in the densities along the elevation gradient at different localities might be the result of the variations in the soil nutrients and other abiotic as well as climatic factors. A study in Indonesia showed that fully opened habitat with full sun exposure during daytime may not be the suitable habitat for the natural population of
The density and frequency values of
The average seedlings and saplings densities of
Regeneration status of any species is determined by the number of saplings and seedlings (Dhar et al. 1997; Singh and Singh 1992). The seedlings and saplings densities of
Natural regeneration is a key process for the continued existence of a species in a community. The three major components of successful regeneration are the ability of species to initiate new seedlings, their survival and growth (Saikia and Khan 2013). Presence of sufficient number of seedlings, saplings and young trees in a given population indicates successful regeneration (Saxena and Singh 1984), which is frequently influenced by the biotic interactions and anthropogenic disturbances. The future composition of the forests depends on the potential regenerative status of tree species within a forest stand in space and time (Henle et al. 2004). Generally, regeneration of a species is usually affected by anthropogenic and natural factors. Seed germination rate in
Regeneration of any species is confined to a peculiar range of habitat conditions and the extent of those conditions is a major determinant of its geographic distribution (Grubb 1977) and the presence of saplings under the canopies of adult trees also indicates the future composition of a community (Pokhriyal et al. 2010). The natural regeneration of
The reason behind less density, frequency, abundance and regeneration at Chhatreshwori might be due to the overexploitation by the local people as they collect bigger trees for their own consumption and extra income.
It was apparent that the natural distribution of this valuable species has been shrinking in the recent years due to anthropogenic disturbances, as a similar trend for other Himalayan medicinal plants as well (Vashistha et al. 2006). Increasing market demand and unsustainable harvesting are posing serious threat to the natural population of
Anthropogenic disturbances mainly harvesting from the wild without proper care and uprooting of the seedlings and saplings for transplanting them in farmyard were found to be the major cause affecting the natural distribution of
There was a huge discrimination in the harvesting pattern and collection of
The mean average species diversity (Shannon index, H) value of 2.8 recorded in the present study is comparable to the results of similar investigations in different Himalayan regions: 1.53–2.88 in the western Himalayas (Gaur and Joshi 2006; Samant et al. 1998), 2.39–4.63 in the Gharwal Himalayas (Nautiyal et al. 1999), 2.5–3.10 in the trans-Himalayan alpines of Nepal (Panthi et al. 2007) and 3.13 in the alpine pastures of Kashmir, Pakistan (Shaheen et al. 2011).
The higher value of the diversity indices is an obvious indication of high species diversity and abundance (Adekunle et al. 2013). This diversity index is comparable to that found in the tropical forest of Eastern Ghats ranging between 3.76–3.96 (Naidu and Kumar 2016). Forests with Shannon index greater than 2 are considered as medium to highly diverse in terms of species (Giliba et al. 2011). Thus from the findings of this study it can be said that the study area falls in the category of forests with high diversity.
The differences of diversity between different localities and altitudes of the study area could be because of variations in the soil type, rainfall trends, anthropogenic action, land use change, and so forth. Lowest diversity noted in Kupinde could be explained by the fact that the forest is totally degraded due to road construction and land slides. Road networks increase resource extraction and encroachment into the forest leading to a reduction in biodiversity (Hitimana et al. 2004; Sundriyal and Sharma 1996). Higher species diversity and species richness at Chhatreshwori could be because of relatively high soil nutrients. Several studies have established a direct relationship between soil nutrients and species diversity. Grime (1973), Tilman and Pacala (1993) demonstrated that soil fertility has a considerable impact on species diversity. Similarly, Loreau et al. (2001) also suggested that species diversity is usually related to soil fertility. The forest was comparatively dense and moist at Chhatreshwori. Moisture is also one of the important determinants of species richness and composition (Vetaas 2000). Soil organic matter, nutrients and moisture plays an important role in the vegetation composition of any area (Tang 1990).
There have been ample studies on the population size and distribution of other medicinal plants in Nepal. But no study has been conducted previously on the population, distribution, frequency, and abundance of this species so no comparable data is available from Nepal. However, a study from India recorded a low population size of
The market price of the fruits is very good so the extensive demand of this species has put an enormous pressure on the natural population. Though the farmers have already started commercial cultivation of
Diversity and distribution patterns of species are greatly affected by various factors, including area, latitude, precipitation, and temperature (Zhang et al. 2011). The large scale pattern in species distribution and physiognomy is also governed by the climate. Climate can be characterized by different variables which mainly determines the distribution pattern of species distribution in any area (Bakkenes et al. 2002).
Overall, due to the increase in population size and the overexploitation of forests, change of land use among other factors; negative impacts can result on the forest ecology including reduction of plant stock, disruption of regeneration, and loss of nutrients in harvested materials (Murkherjee and Chaturvedi 2017). Other factors that may affect the sustainability of plants are collection of premature plants, grazing, and soil erosion. Therefore, deliberate efforts should be taken by all stakeholders to ensure that these plants are used in a sustainable way.
Species composition, density, distribution and regeneration status can be considered important factors to judge the status of a forest.
Supplementary information accompanies this paper at https://doi.org/10.1186/jee.22.015
Table S1. Population density (in ha), frequency, abundance, and distribution of
We are thankful to Mr. Krishna Pun from District Plant Resources Office, Salyan for his help during the field work. Special thanks to Prof. Dr. Ram Kailash Prasad Yadav, Head, Central Department of Botany, Tribhuvan University for his encouragement.
NTFPs: Non-timber Forest Products
MAPs: Medicinal and Aromatic Plants
RD: Relative Density
RF: Relative Frequency
RA: Relative Abundance
IVI: Importance Value Index
SOC: Soil organic carbon
PKJ and SR conceptualized and supervised the research. NP collected and analyzed the data and wrote the manuscript. PKJ, PPR, and SR critically commented and approved the final version of the manuscript. The authors read and approved the final version of the manuscript.
This study was supported by the Dabur Nepal CSR Fellowship (Late Sri Ashok Chand Burman) 01/2016’.
All data involved in this study are available from the corresponding authors upon request.
The authors declare that they have no competing interests.