Plants Profile of Sultan Khail Valley, Hindukush Range of Pakistan: Floristic Composition, Biological Spectrum and Its Seasonal Variation

1. Introduction

Flora is an assembled checklist of all plant species growing in a particular geo-graphical region [1]. The floristic composition of a region represents the type, number, composition, population size, and distribution of plant species. For the study of biodiversity and understanding the prevailing climate, the knowledge of the flora of any area is important [2] and offers an effective starting point for more systematic studies [3]. A Floristic inventory is a taxonomic analysis of a major division of flora in a given area [4]. Floristic diversity describes physiognomy and ecological relations in a variety of environments [5]. The life form of the plant is defined as the form that the vegetative body of the plant takes as a result of all life processes affected by the climate, whereas the biological spectrum is the proportion of various life form classes combined [6]. The life form reflects the adaptation of plant species to particular ecological conditions. Species that have identical morphological characteristics are grouped under the same life form in response to environmental factors [7]. Life form and leaf size spectra are the key physiognomic features that indicate the micro and macroclimatic state and association of plants, as well as the anthropogenic disturbance in a specific region [8]. Comprehensive life form research gives an idea of the physiological processes of plant communities [9]. The leaf size spectrum also provides an understanding of the floristic version, which is useful for exploring plant relationships about dominant climatic features and for studying flora at the local level [10]. The physiognomic properties of plants, such as life form and leaf size spectra, have been frequently used in vegetation research [7]. The life form represents climate adaptability and, therefore, the entire vegetation will be an indication of the dominant climate in particular [11]. However, biotic impacts such as overgrazing, agricultural operations, trampling, and deforestation may alter the percentage of different life forms [12]. Various researchers have investigated the floristic and biological spectrum in Pakistan and abroad [6,11,13,14,15,16,17,18,19,20]. However, no such work has been conducted in the Sultan Khail valley, Dir Upper, Pakistan. The present study aimed to explore the floristic inventory, ecological characteristics, and biological spectrum of vegetation in the Sultan Khail valley and Hindu Kush range of Pakistan. Such information is scanty, and so no such study is conducted in the target area. This study provides baseline information on the flora of the area and will be helpful for further research in the fields of forestry, taxonomy, ecology, ethnobotany, and conservation of vegetation.

2. Materials and Methods

2.1. Description of Study Area

The beautiful Sultan Khail valley is situated in Dir Upper, Khyber Pakhtunkhwa, Pakistan. It lies in Pakistan's subtropical dry temperate zone [21]. It lies between 34°59’339", 35°59’870" North latitude and 71°00’176", 72°00’036"East longitude. The area is mostly dominated by hills and mountains that are a part of the Hindu Kush range of Pakistan. The altitude of the area varies from 1015 meters to 3230 meters. The highest peak in the valley is Shekly Top. The valley is bordered by the rivers Panjkoro and Nehag Dara in the East, Dir Lower (Maidan) in the West, Jelar Valley in the South, and Kair Dara in the North (Figure 1). The climate of the study area is influenced by various topographic and ecological variables. Spring, summer, autumn, and winter are the four distinct seasons of the year in the area. The winter season is very cold and severe and starts in the middle of November when the temperature falls abruptly. The summer season in the valley is typically moderate, with June and July being the hottest months of the year. The average maximum temperature reaches 35.5 C to 35.9 C in June and July, while in January the mean minimum temperature falls below zero (-1.3) degrees centigrade. The relative humidity is moderately high throughout the year. The area receives maximum rainfall in February (6.7mm), March (8.2mm), and August (8.6mm). Snow usually begins to fall in the upper parts of the valley in December and gradually descends as the temperature decreases in January and February. Depending on elevation, snowmelt starts in the valley in March and continues into April [22].

2.2. Data Collection and Analysis

From 2017 to 2019, regular trips were arranged in different seasons of the year to conduct data for the preparation of a floristic checklist of Sultan Khail valley, Dir Upper, Pakistan. The collected specimens of plant species were preserved and identified with the help of the flora of Pakistan, compiled in alphabetical order, and deposited at the Herbarium, Department of Botany, Islamia College, and Peshawar, Pakistan. The collected plant species were divided into different life form classes [23,24] using the formulas:

Plant species were also classified based on their habitat [16].

3. Results

3.1. Floristic Diversity

The flora of Sultan Khail Valley is found to be diverse and home to 332 species belonging to 234 genera and 96 families (Table S1). Gymnosperms (8 species, 3 families) and pteridophytes (22 species, 6 families) were less prevalent in the area. Angiosperms were represented by 302 species belonging to 215 genera and 87 families, including dicots (275 species, 76 families) and monocots (27 species, 11 families). Asteraceae was the dominant family in the area (32 species, 9.7%), followed by Rosaceae (28 species, 8.5%), Lamiaceae (21 species, 6.4%), Fabaceae, and Poaceae (12 species, 3.6%) (Figure 2). In gymnosperms, Pinaceae was the leading dominant family while Dryopteridaceae was the richest family of Pteridophytes (Table 1). The herbaceous flora was dominant (220 species, 66.3%), followed by shrubs (54 species, 16.3%), and trees (48 species, 14.5%) (Table 1).

3.1. Subsection

3.2. Raunkiaer Life Form and Leaf Size Classification of Vegetation

In the present study area, therophytes (126 species, 38.0%) were found dominant, followed by phanerophytes (104 species, 31.3%) and hemicryptophytes (58 species, 17.5%) (Table 2), indicating that the phytoclimate of the area is of the thero-phanerophytic type. The results of leaf size spectrum of vegetation revealed that the area was dominated by microphylls (107 species, 32.2%), while megaphylls and aphyllous were the least abundant leaf size classes (Table 2).

3.2.1. Seasonal Variation in Life Form and Leaf Size Spectra of Vegetation

Seasonal variation in life form reveals that Phanerophytes (104 species, 41.4%) dominated the spring flora, followed by Therophytes (80 species, 31.9%), and Hemicryptophytes (38 species, 15.1%). In summer, therophytes (109 species, 35.4%) were the most abundant life form class, while in autumn and winter, phanerophytes were dominant (Figure 3). Seasonal variation in leaf size spectra shows that microphylls were dominant in the spring (34.3%) and summer (31.2%) seasons, while in autumn and winter, nanophylls were dominant (Figure 4).

3.3. Habitat Types

The plants species were also classified on their habitat. The results revealed that the maximum number of species (92 species) was found in dry places, followed by forests (83 species), and moist places (78 species) (Figure 5).

4. Discussion

The total number of wild and cultivated plants species found in any geographical area is called the floristic composition. Floristic study provides baseline information for further detailed taxonomical and ecological research and planning for sustainable management and conservation of plants resources [25]. The flora of Sultan Khail valley is found to be diverse as compared to other areas [16,17,26,27] and homed to 332 species belonging to 234 genera and 96 families. Gymnosperms and pteridophytes were less predominant in the area. Asteraceae was the dominant family in the area with 32 species (9.7%) followed by Rosaceae, Lamiaceae, Fabaceae and Poaceae. A similar study was conducted by [11] in the Riyadh region Saudia Arabia and Asteraceae (17.4%) was reported as the most widespread family, followed by Poaceae, Brassicaceae and Fabaceae, while [18] reported 154 plant species from Karkhasa (Baluchistan) with Asteraceae being the predominant family, followed by Poaceae. [17], explored the flora of Takht Bhai and listed 140 species, 63 families. Asteraceae was found to be the dominant family in the area, followed by Poaceae and Solanaceae, while [28] conducted similar research in Lajbouk (Dir Lower). [16] reported 250 species within 77 families, in which Asteraceae and Lamiaceae were the leading dominant families. Our findings strongly coincide with those of [6], who found Asteraceae as a dominant family followed by Rosaceae, Lamiaceae, and Poaceae in Jammu and Kashmir. Similarly, [29] also found Rosaceae, the largest family, followed by Asteraceae and Lamiaceae in the Keran Valley, in the northwestern Himalaya. The dominance of Asteraceae families in the target area as well as in the world represents its wide range of ecological amplitude [11,30,31]. In the present study area herbaceous flora was dominant, followed by shrubs and trees. The dominance of herbaceous flora is due to the overexploitation of trees and shrubs species by the inhabitants of the valley, due to which the population of trees and shrub species is decreasing day by day. Similar findings were also reported by [3] while exploring the flora of Swat Ranizai, [32] from district Nowshera, [33] from Ghalegay Hills, Swat, [34] from Karak, [35] from darra Adam Khel, [36] from Miandam, Swat, [16] from Jelar Valley, and [18] from Baluchistan.

The biological spectrum is an indicator of the physiognomy of flora, vegetation and their relation to the prevailing climatic conditions of the region [37,38,39]. In the present study area, therophytes were found dominant, followed by phanerophytes (Table 3.2), indicating that the phytoclimate of the area is thero phanerophytic type. Normally therophytes are the indicators of arid phytoclimate [40], hemicryptophytes of temperate region [6] while, chamaephytes are the indicator of high altitudinal zones and arctic regions [41] while Phanerophytes are the indicators of moist regions [42]. The dominance of therophytes in the area reflects that the flora is under heavy biotic pressure such as deforestation, overgrazing, and overexploitation [26] of the plants species for fuel, timber, medicinal purposes, and agricultural practices [43]. [11] conducted a similar study, and therophytes and chamaephytes were reported dominant. [44], conducted similar research and found therophytes dominant, followed by phanerophytes, and stated that the environmental condition of the area is dry and hot. Similar results were also reported from Koont [45], Gadoon, Swabi by [46]. The present findings are strongly supported by [16,28,29] who reported the dominance of therophytes in the area and stated that the flora is under heavy biotic pressure such as deforestation, overgrazing, and overexploitation of the plants species for fuel, timber, and medicinal purposes.

Leaf size is also an important physiognomic trait that influences different functions of plants, such as photosynthesis and transpiration. The knowledge of leaf size among plants species may help to know about the physiological processes of plants and their communities [9]. The results revealed that the vegetation of Sultan Khail valley is dominated by microphylls, while megaphylls and aphyllous were least contributed leaf size classes in the area (Table 3.4). The present findings are in line with [34,47] who also reported microphylls and nanophylls as the dominant leaf size classes. Our results are strongly supported by [16] who reported microphylls as dominant, followed by nanophylls and mesophylls, in Jelar Valley. The present findings are also in line with [43,48], who reported the same leaf size classes dominant in Kashmir and Quetta. Seasonal variation in leaf size spectra shows that in the spring and summer seasons, microphylls were dominant, while in the autumn and winter seasons, nanophylls were dominant.

Seasonal variation in life forms shows that phanerophytes dominated the spring flora. In summer, therophytes were the most abundant life form class, while in the autumn and winter seasons, phanerophytes were dominant. The seasonal variation in life forms is due to the presence of short-lived species. The present findings are line with [12,35,37], [16,28,49]. The difference in seasonal variation of leaf size classes is due to the presence of geophytes and short lived therophyte species; however, altitude also plays an important role in the distribution of leaf size classes, as reported by [16,28,48,50]. The habitat condition of the area is mostly dry as maximum numbers of species were found in dry habitat followed by forests. Various researchers such as [16,51,52] also conducted similar studies. They classified plants species based on habitat types. Therefore, our findings are in correlation with them.

5. Conclusions

From the present study, it is concluded that the flora of the Sultan Khail valley is diverse. The phytoclimate of the area is of the therophytic type. The vegetation of the investigated area is under heavy biotic pressure in the form of grazing, fuel wood collection, medicinal plant collection, timber smuggling to other areas, and some natural phenomena such as soil erosion and land sliding, due to which the vegetation of the area is decreasing day by day and needs proper conservation. The habitat condition of the area is mostly dry, as the maximum numbers of species were found in dry habitats. This study provides baseline information on the flora of the Sultan Khail valley, and further studies will be needed to assess the conservation status of wild flora and obtain quantitative information on vegetation.