Environmental variables vis-a-vis distribution of herbaceous tracheophytes on northern sub-slopes in Western Himalayan ecotone
In the northern hemisphere, the north face of the mountains has a high diversity of species which is attributed to the moist and shady conditions at the north face. Other environmental variables may also influence the species diversity on the northern faces of the mountain and therefore needs to be studied in detail. The northern slopes represent three different sub-slopes—north, north east, and north west. During the current investigation of Pir-Panjal and Dauladhar ranges in Bhadarwah valley, fine-scale studies on the relationship between vegetation and four variables (soil pH, moisture content, electrical conductivity, and steepness) were conducted. The study determined the role of these variables on the vegetation of three different sub-slopes. The sampling was done at the confluence of two communities (forest and grassland) at three sites on the northern sub-slopes of the lesser stratum in western Himalayan.
The result revealed that rich herbaceous diversity prevails on the lesser Himalayan stratum (Bhadarwah valley). As many as 65.8% species differ from site to site, whereas species commonality among the sites is minimum. The role of environmental variables on the species composition at different sub-slopes of the north mountain face is deduced through canonical correspondence analysis (CCA).
The availability of solar light increases air and soil temperature on the north east–facing slope. All the environmental variables (soil pH, moisture, electrical conductivity, and mountain steepness) are insignificant at pure north face for the species composition. Therefore, it can be concluded that some other environmental variables may influence the species composition which are needed to be further investigated.
KeywordsNorth face Environmental variables Species heterogeneity Treeline ecotone Species turnover Canonical correspondence analysis
Budh Ro Kut
Canonical correspondence analysis
Khanitop grassland north
Steepness of the mountain
Soil moisture content
The particular mountain face composes a unique habitat for a specific type of plant community (Nowak et al. 2014). Each mountain face shows contrasting characteristics with respect to insolation, light intensity, soil moisture, pH of the soil, humidity, etc. (Pook and Moore 1966; Gupta and Arora 2017). These facets are also closely associated with the vegetation composition and community structure (Gilliam et al. 2014; Kumar et al. 2018). The north-facing slopes retain moisture and are more cold and humid than the south-facing slopes; consequently, they support moisture-loving plants (Erdos et al. 2012). The north slopes offer a better habitat for plant growth and help in adequate regeneration of species (Maren et al. 2015). The north-facing slopes are characterized by higher species diversity than the south-facing slope (Gong et al. 2008; Ucles et al. 2015). These slopes are efficient ecosystems for maintaining a specific microhabitat (Mehrabi et al. 2014). The microhabitat parameters (soil pH, moisture, electrical conductivity, etc.) influence the species richness/heterogeneity on the north-facing slopes (Härdtle et al. 2003; Maren et al. 2015).
Ecosystem being a cybernetic system maintains a specific species composition and richness using various environmental variables (Odland and Birks 1999). Among various environmental variables, altitudinal and latitudinal gradients also contribute to the maintenance of species diversity (Murray 1997; Bhattarai 2017). In this regard, the altitudinal gradients along with geographical coordinates are evaluated for their pivotal role in the distribution of vegetation (Juarez et al. 2007; Kazakis et al. 2007). In recent years, new approaches to quantify changes in species diversity across environmental gradients and boundary regions are also developed (Wilson and Shmida 1984; Koleff et al. 2003; Mena and Domı’nguez 2005). Beta-diversity or species turnover is recognized as a simple modus operandi for comparing the diversity of two landscapes or communities or ecosystems (Wilson and Shmida 1984).
Transition zone also called ecotone has become a central topic in landscape ecology and nature conservation because of high floral and faunal diversity. Therefore, the study of ecotone is one of the most rampant research fields nowadays (Cadenass et al. 2003; Ries et al. 2004; Yarrow and Marin 2007, Erdos et al. 2014). Apart from maximum biodiversity, transition zones are differentiated from their nearby communities because these zones are known for maximum transfer of materials, energy, genotypes, and other environmental variables (Austin 2005; Kumar et al. 2017; Guerin et al. 2019). Ecotone delimits the spatial heterogeneity of a landscape and forms an ideal ecosystem (Fagan et al. 2003; Hou and Walz 2016).
Indian Himalayan Region (IHR), including the Tibetan Plateau, is a unique physico-geographical region with an average elevation of 4000 m above msl (Zheng et al. 1981; Ding et al. 2014). The western Himalayan montane and subalpine vegetation on north slopes primarily consist of coniferous species comprising stands of Abies pindrow (Royle ex D. Don) Royle, Pinus wallichiana A. B. Jacks., Picea smithiana (Wall.) Boiss., and Cedrus deodara (Roxb. ex D. Don) G. Don). At few places, individuals of birch (Betula utilis D. Don) also grow in the upper subalpine belt. These individuals of birch finally turn into a narrow band of more or less pure birch stands (Schickhoff et al. 2015). These stands are followed by the grasslands and pastures at high elevation at various mountain faces. Out of the four major mountain faces (north (N), south (S), east (E), and west (W)), north face is not always known for high densities of mesic temperate species and south face predominate by paleotropical xeric biota (Erdos et al. 2012; Nevo 2001). Moreover, the north and east faces of the mountains are evaluated as more productive slopes (Maren et al. 2015). Therefore, the number of studies on vertical transects has been conducted to understand the ecology and species distribution.
Along the elevational gradient (vertical transect), species richness may decrease with the increase in altitudes on the north face (Grytnes 2003). However, such studies on horizontal plane for sub-slopes of the north face like pure N, north east (NE), and north west (NW) are wanted in the science. Moreover, the role of environmental variables on vegetation at specific sub-face of the north is also not fully tacited by the ecologists. During the current study, sampling sites were selected on the transition zone between forest-grassland communities, because of structural composition and functional value of these ecosystems. Data has been collected to understand the role of environmental variables on herbaceous species diversity at various sub-slopes of the north.
Material and methods
Arrangement of plots and sampling
Details of study sites in Lesser Himalayan stratum
Elevation (meters above msl)
32° 56.282′ N-75° 46.109′ E
North west (NW)
32° 55.269′ N-75° 47.416′ E
North east (NE)
32° 54.008′ N-75° 45.184′ E
32° 56.326′ N-75° 45.878′ E
Data for 4 environmental variables namely, pH, electrical conductivity (EC), moisture contents of soil (SM), and steepness in the mountain slope (MS) were collected in situ using portable pH meter (EuTech), field conductivity meter (ME Max digital conductivity meter), soil moisture meter (ELICO DM-33), and inclinometer (BOSCH DNM 60 L), respectively. The reason for in situ analysis was longer sampling durations, and in order to maintain the accuracy of parameters the analysis was done under in situ conditions.
Data on environmental variables and individuals of plant species were arranged on Microsoft Excel. Correct names of the species were authenticated using a web-based database (www.theplantlist.org) and taken as the biotic parameter. Canonical correspondence analysis (CCA) is a multivariate method to elucidate the relationships between biological assemblages of species and their environmental variables (Hejcmanovā-Nežerková and Hejcman 2006). The CCA was performed using PAST v. 3.21 software.
Characteristics of the study area
Environmental variables at different sites among three communities
pH of the soil
Moisture contents of soil (in %)
Electrical conductivity of soil (in simens/m)
Steepness of the mountain (in angle)
Relationship of environmental variables and biological assemblage
Both north and south slopes of Lesser Himalayan mountain abode coniferous forest at low and grassland communities at high altitudes. Behavior of the mountain’s north face coupled with the environmental variables toward herbaceous tracheophytes has been elucidated by dividing the north slopes into three sub-slopes (pure north, north east, and north west). NE and NW faces are observed as the paramount habitat for the growth of herbaceous tracheophytes. Data collection on the number of species on vertical belt transects from forest to grassland communities intersecting perpendicularly transition zone helped in the identification of 3 communities namely forest, ecotone, and grassland. Presence or absence of individual species indicated that the transition zone is characterized by the maximum number of species and their individuals. Climate, topography, aspect, inclination of slope, soil type, and land use pattern are recognized as the major contributor to vegetation type (Maren et al. 2015). Furthermore, insolation and light intensity also put down a range of microclimates at the multifaceted landscape. These factors are responsible for the diverse type of vegetation at different mountain aspects (Gillingham 2010). Variation in vegetation between two contrasting aspects (mountain faces) is the result of the difference in reception of solar radiation (Ghimire et al. 2010; Paudel and Vetaas 2014). On the northern hemisphere, south-facing slopes receive more sunlight and become more xeric and warmer. Therefore, such slopes support drought-resistant vegetation and are less favorable for tree growth. However, north-facing slopes hold moisture and remain cold as well as humid, thus supporting moisture-loving plants (Nevo 2001; Maren et al. 2015). It has also been implicated that south-facing slopes receive six times higher solar radiation than north-facing slopes. Therefore, the microclimatic conditions on both slopes differ considerably and uphold different levels of biodiversity (Auslander et al. 2003). Ecotones are described as dynamic zones and play several important roles in ecosystem functioning (Pandita and Dutt 2016). Himalayan treeline ecotones show considerable differences in altitudinal position, physiognomy, and species composition (Schickhoff 2005). Detection of ecotones can be done using field data gathered along transects (one dimension) or across a grid (two dimensions). During the current study, data collection on one dimension reveals that the species composition at ecotone varies drastically from site to site. This indicates that beside species interaction other factors also play imperative role in ecotones. Few species act as ecotonal specialists; therefore, the strongest process for species richness in Lesser Himalaya can be additive blending. Additive blending may be because of an intermediate type of microhabitat with respect to pH, moisture content, EC, and steepness of the mountain at ecotone (Table 2).
Out of studied communities, ecotone is a well-studied community because of its unique characteristic features (Erdos et al. 2012). Mohd-Aizat et al. (2014) while working on soils of Ayer Hitam Forest Reserve reported a pH range of 3.12 to 5.28 which is lower compared with the present work. Ashraf et al. (2012) reported a range of pH 5.90 to 6.23, moisture content 13.3 to 19.3%, and EC 207 to 239 μS/cm in grassland soils of Yusmarg Hill Resort. Fauze et al. (2015) in their confirmation on soils of Yamuna Biodiversity Park, Delhi, found that pH varied from 6.82 to 7.90; EC, 96 to 1679 μS/cm; and moisture content, 8.7 to 29.7%, and corroborate with the current findings.
The present work showed that species have very less similarity (ca. 6%) among different sites, indicating that each mountainous habitat is characterized by high species diversity at a coarse scale. EC-pH of the soil on NE-facing slopes and SM-MS are vital variables on NW-facing slopes. The insolation and period of solar energy are also dependent on the position of the slope. The north east slopes receive maximum insolation, since the studied area is placed on the northern hemisphere. The availability of solar light increases air and soil temperature on the north east–facing slope. All the environmental variables (soil pH, moisture, EC, and mountain steepness) are insignificant at pure north face for the species composition. Therefore, it can be concluded that some other environmental variables may influence the species composition which are needed to be further discovered.
The authors are thankful to Head, Department of Botany, University of Jammu, Jammu, for providing the herbarium and other equipment facilities to conduct the study. Authors are also thankful to Prof. Rahul Gupta, Department of Statistics, University of Jammu, Jammu, for helping in the application of statistical tool during the study. A trial version of StyleWriter 4 is also acknowledged for punctuation and English language proofreading.
SP and HCD designed and analyzed the samples. SP wrote the initial draft of the paper. VK and HCD help in finalizing the paper. All authors read and approved the final manuscript.
Ethics approval and consent to participate
Consent for publication
The authors declare that they have no competing interests.
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