Phytosociological study of coastal flora of Devbhoomi Dwarka district and its islands in the Gulf of Kachchh, Gujarat

The study described the diversity and phytosociological attributes of plant species (trees, shrubs and herbs) in coastal areas of Devbhoomi Dwarka District and its islands in the Gulf of Kachchh. A random sampling method was employed in this study. A total of 243 plant species were recorded of which trees and shrubs represented with 30 specieseach. Grasses & sedges were also represented by 30 species and 29 species were climbers. Among the tree and shrub species, Prosopis juliflora showed the highest density (373.51 ind. /ha), frequency (63.50.67%), relative density (30.19.7%), relative frequency (24.41%) and relative abundance (7.68%).Regarding herb species, Aristida redacta represented the highest density (3.97ind./sq.m) and frequency (39.02%). Moreover, the highest importance value index was measured in Prosopis juliflora (62.28) among trees & shrubs and Aristida redacta (31.51) among herbs. The Abundance/Frequency ratio of trees, shrubs and herb species showed contagious distribution pattern within the study area. The present study also includes α diversity (Shannon diversity index, Simpson's Index, species richness, evenness index) of the coastal terrestrial plants.


III. METHODOLOGY Study area
Devbhoomi Dwarka district of India is located on the southern coast of the GoK, in Gujarat state. It extends between 21.42° to 22.58°N Latitude and 68.58° to 70.40° E Longitude [18]. Coastal areas of the district are distributed in three Talukas which are Okhamandal, Kalyanpur and Khambhaliya. Nine Islands viz., Ajad, Beyt Dwarka, Bhaidar, Dabdaba, Dhani, Gadu, Leffa, Kalubhar and Panero have been covered in this district. The soil of Devbhoomi Dwarka district is calcareous and alkaline in nature with grain size varying from silty loam to clay [19]. The district receives average rainfall of 596 mm [20].

Field Data collection
The present work is based on the survey of vegetation occurring in coastal areas and its 9 islands of Devbhoomi Dwarka district during 2011-2015. The area was surveyed on foot and random sampling method was followed. In the coastal area,line transects of 500 m were laid perpendicular to HTL (High Tide Line to landward side) by using 5km×5km grid laid over land use/land cover maps. Distance of 5 km between two subsequent line intersects was maintained using Global Positioning System (GPS).Within each transect, quadrates were laid at an interval of 20 m, 5m ×5m for trees and shrubs and1m×1m for herbs, grasses and climbers [21,22,23]. However, to enrich the species inventory the opportunistic coastal area at each site (areas falling out side of the quadrates) were also explored and monsoon data for herbaceous plants were also recorded in the same sampling plots. The coastal areas of Devbhoomi Dwarka District and its Islands were explored by laying a total of 46 transacts comprising of 915 quadrates (1m×1m size) and 589 quadrates (5m×5m size), respectively. Within each sampling plot the number and name of all the trees, shrubs and herbs were counted and recorded. The plants were collected in the flowering and fruiting stages and were identified by using different available floristic keys [24,25,26,27,28]. Documentation was done in the form of photographs as well as plant specimen were preserved by preparing herbarium and deposited in the GEER Foundation, Gandhinagar, Gujarat for future reference.

Data Analysis:
Phytosociological characters like Density (D), relative density (RD), frequency (F), relative frequency (RF), abundance (A), relative abundance (RA) and Importance Value Index (IVI) were calculated by using different formulas [29] and abundance frequency ratio (A/F) for Tree, shrub and herb species were also calculated through distribution patterns of Whitford [30]. Plant biodiversity was calculated by using different standard equations such as Shannon-Wiener diversity index [31], Simpson's index [32], Evenness index [33] and Species richness index [34].

IV. RESULTS AND DISCUSSION Qualitative analysis
The coastal areas and 9 islands of Devbhoomi Dwarka district were found predominantly covered with shrubby and herbaceous species including grasses. A total 242 Angiosperm and 1 Gymnosperm species belonging to 177 Genera and 61 Families were recorded (  Figure 2).
During study, it was revealed that Poaceae was the largest family in Monocotyledons represented by 23 species and 20 Genera, whereas Fabaceae was the largest family among Dicotyledons represented by 20 species and 12 Genera. Out of 61 families, only 11 families were represented with more than half of the species recorded and 22 families were represented with single species. The genera Ipomoea had the highest number of species i.e. 8 followed by Cassia and Euphorbia genera both represented with 6 species. Among recorded 177 genera, 28 genera were represented by two species and 137 genera were represented with a single species (Annexure 1).
Habit wise distribution of angiosperms is illustrated in Figure 2. Among 243 recorded species, herbs were represented by the highest number of species (124), followed by trees, shrubs and grasses & sedges represented with 30 species each and climber (29 species).
Among 3 talukas, the highest species diversity was found in Khambaliya taluka (207 species) followed by Okhamandal (192 species) and Kalyanpur (169 species). Among islands, Beyt Dwarka showed the maximum species diversity (166 species) followed by Azad (120 species) and Gadu (118 species). The lowest species diversity was found in Kalubhar island with 24 species (Figure 4). High floral diversity in Beyt Dwarka may be due to its proximity to coast and human interference due to tourist influx as well as fishermen. It was observed that, the islands near to the coast have high floral diversity, which is similar to the adjoining coastal area. Human beings, winds and water current help to disperse the seeds of various species in such islands and after that great struggle for survival of the plant species acclimate to island conditions ensues. Other islands were with less floral diversity and one of the reasons may be isolation and distance from coastal area. It was reported that a total of 127 vascular plants and a species of Gymnosperm recorded from Beyt Dwarka Island [16]. In that study, the dicotyledonous plant included 45 families, 91 genera and 113 species, and the monocotyledonous plant included 3 families, 11 genera and 13 species [16].

Quantitative analysis of trees and Shrubs:
During the quadrate sampling, a total of 17 species of trees and shrub were recorded.   Distribution of species is one of the important aspects of ecological studies, which has previously attracted attention of a number of ecologists [30,35,36,37]. A value of abundance and frequency ratio below 0.025 was considered as regular distribution, between 0.025 to 0.050 as random and more than 0.050 as contagious distribution pattern [38]. In the present study, A/F values for different tree and shrub species revealed that all the species had contagious distribution pattern in the district (Table 2). It has been stated that the A/F ratio as a measure of contagiousness among plant population was widely accepted [30].
Important Value Index determines the extent of dominance of a species in the structure of a forest stand [39]. It is said that species with the greatest importance value are the leading dominant of the particular vegetation. Accordingly the leading dominant tree and shrub species of coastal areas of Devbhoomi Dwarka district was Prosopis juliflora (62.28) followed by Capparis deciduas (27.93) and Zizyphus nummularia (26.24). On the other hand, the least dominant species was Acacia Senegal (5.82) ( Table 2).

Quantitative analysis of Herbs:
With respect to the herb species, a total of 93 species were enumerated during quadrate study. The highest density was measured in Aristida redacta ( in Bangladesh which showed contagious distribution [40]. The present work reveals that, the study area was not completely uniform because several species showed contagious distribution [41] (Table 3). As a general rule, higher frequency and lower abundance indicates regular distribution pattern whereas the reverse indicates the contagious distribution. In general, regular distribution occurs where severe competition exists between individuals; random distribution is found in very uniform environment and contagious distribution is common in nature [41]. Contagious distribution depends on local habitat, seasonal weather changes and reproductive processes.

Plant Species Diversity:
Measurement of biodiversity concentrates on the species level and species diversity is one of the most important indices which are used for the evaluation of ecosystems at different scales [42]. The Shannon-Wiener Index (H') and Simpson's index (c) were used to determine which community is more diverse. A large value of H'Index indicates rich ecosystem with high species diversity, whereas a low value of H'Index represents an ecosystem with little diversity [43]. An ecosystem with H' value greater than 2 has been regarded as medium to high diverse in terms of species [44]. The probability that two individuals chosen at random will be the same species is measured by The Simpson's Index. Because of this, the range for the Simpson's Index (c) is from Zero to One. Zero is the least diverse and one is the highest level of diversity attainable with this index [43]. In the present study Shannon-Wiener diversity (H') index and Simpson's index (c) was 3.113 and 0.916, respectively. Thus the coastal area of Devbhoomi Dwarka District and its islands has rationally high species diversity.
The study came with index of dominance of 1.190 for the coastal area of Devbhoomi Dwarka District and its islands. The greater value of index of dominance exhibits the lower species diversity and vice versa in the scale of 0 to 1 [45].
Species richness and evenness are the two separate ideas of heterogeneity− it is only natural to try to measure the evenness component separately. In 1964, Lloyd and Ghelardi [46] were the first who came with idea to measure the evenness component of diversity separately [47]. Evenness describes how equally individuals are distributed amongst the species. Pielou's evenness index (e) was 0.794 and Margalef species richness index (d) was 10.87 in the study area.

V. CONCLUSION
Floristic diversity assessment at local and regional levels is required to understand the present status and to make effective management strategies for conservation. The results in the present study clearly show that, the Coastal areas of Devbhoomi Dwarka district and its islands are rich in phytodiversity. A record of 243 species during the study period reflects that the coastal areas of Devbhoomi Dwarka district and its islands have the potential to harbour rich species diversity with various ecological services. The present finding provides an assessment on floral diversity, density, frequency and important value index which will be helpful for preparing a sustainable management plan. Moreover the study results will serve as a primary input towards monitoring and sustaining the phytodiversity of the coastal areas of Devbhoomi Dwarka district and its islands in the Gulf of Kachchh.