0699-B2

Biodiversity of Tropical dry deciduous forest ecosystem

B R Pandit ¹

ABSTRACT

The Gir Forest, famous as the abode of Asiatic lions is situated in the Saurashtra region of Peninsular Gujarat (20⁰ 41' N and 21⁰ 50' N, 70⁰ 50' E and 71⁰ 50' E). The total forest area is 1412 km². The area is hilly terrain elevation varies from 152 to 531 m above msl.

The climate is very hot and dry. The rains are highly erratic, both in intensity and frequency; with average annual rainfall is 700 mm. The climate is supporting typically dry deciduous forest ecosystem. The forest is enriched with a faunal diversity including 31 species of mammals and comprising the floral diversity of 431 species of plants.

The present study enumerated 431 species, which belonged to 294 genera and 94 families of flowering plants, out of which, Dicotyledons contributed 371 plant species belonging to 246 genera and 80 families, which is quite higher than that of Monocotyledons. The Monocotyledons contributed only 60 species belonging to 48 genera and 14 families. Leaving Poaceae and Cyperaceae, Monocotyledons are poorly represented. Proportion of the Monocotyledons to Dicotyledons was recorded 1:5.71 of families, 1:5.12 of genera and 1:6.18 of species. The ratio of the total number of genera to species was recorded 1:1.46. 42 families were found monotypic and 49 families with one genus (monogeneric). Among the various habits, herbs contributed more than 50 % of plant species (53.59 %).

The plant diversity study of the Gir forest is claim to be the first of its kind. The diversity indices viz Simpson's index (D=0.361), Simpson's index of diversity (1-D= 0.639), Simpson's reciprocal index (1/D = 2.77), Shannon-wiener index (H= 1.194) and Evenness index (E= 0.861) were calculated.

The biological spectrum of the flora of Gir forest falls under the category of therophytic type of phyto-climate, which indicates hot and dry climate in the region, which is congenial for the growth of annuals and perennial herbs.

INTRODUCTION

The loss of natural habitat and species extinctions around the world have served to focus intense international attention on the issue of biodiversity, culminating in the negotiation of the United Nations Conservation on Biological Diversity. It is widely recognized that the path to sustainable development requires the conservation and wise use of the world's biodiversity. Indeed, measuring and monitoring biodiversity must be the first step towards effective conservation and sustainable development. However, because of the overwhelming variety of life on earth and spanning, as it does. The complete range of biological organization form genes to landscapes, measurement of biodiversity poses some serious problems.

The Gir forest is situated in the Saurashtra region of Peninsular Gujarat between 20041'N and 21051'N latitude and 700051'E and 71050'E longitude. The total area of Gir forest occupies approximately 1412.13 km², adjoining Junagadh and Amreli districts.

The entire part of the tract is hilly and elevation varies form 152 to 513 meters above mean sea level. There are few notable plains in Gir forest especially near Jesadhar. Similar plains also occur at Timberva region. In the river system, Hiren, Machhundri and Singwada are important rivers.

The soil of this forest is formed partly form sedimentary rocks and partly form igneous rocks. The soil layer is very thin, black-cotton soil is generally found in the valleys and low lands and the red soils in the uplands. The red soil is light and porous. Soil is moderately fertile and usually mixed up with good proportions of stones.

A year can be divided into three distinct seasons. The winter (Maximum 19⁰ C, Minimum 10⁰ C) from November to February is followed by the summer (Maximum 40⁰ C, Minimum 34⁰ C) from March to May. The monsoon from June to October contributes to the Southwest monsoon (the average annual rainfall is 700 mm). The rains during monsoon are highly erratic, both in intensity and intervals between two successive rains.

MATERIALS AND METHODS

Several field trips of duration ranging from 2 to 10 days were made at regular intervals to various parts of Gir forest extending over a period of more than three years, and made intensive and extensive collection of plants. For collection and preservation the procedures given by Jain and Rao(1977) and Balgooy (1987) were generally followed. The trips were arranged in such a way so as cover all the six localities and collect most of the plants in flowering or fruiting stages. All the specimens collected were serially numbered. The field notes were taken regularly, included habitat, color of the flowers, association and other pertinent features. Efforts were made to identify the plants from the fresh material; those that could not be satisfactorily identified in the field were brought to the laboratory and identified by checking it with monographs, herbarium specimens and other available literature.

Collected plants were properly processed, numbered and prepared for herbarium. The herbarium specimens were labeled and deposited in Herbarium Section of the Department of Life Sciences, Bhavnagar University, Bhavnagar.
For species diversity various diversity indices were calculated

Floristic and vegetational studies

Flowering plants of Gujarat had been studied earlier by Cooke (1908), Saxton and Sedgwick (1918), Sutaria (1958), Gandhi (1958), Chavan (1961), Oza (1962), Jain (1963), Vaidya and Vora (1964), Santapau and Janardhanan (1966), Sabnis (1967), Bedi (1968), Inamdar (1968), Bhatt (1969), Bhatt and Sabnis (1974), Parabia (1974) and Shah (1978); published a `Flora of Gujarat State' in two volumes.

Cooke (1901-1908) and Talbot (1902) recorded plants of Saurashtra. The floristic studies on different parts of Saurashtra have been made by Borgeson (1929), Rao (1941), Rhizada and Santapau (1955) and Thaker (1966). Santapau (1953) published a preliminary list of 980 plant species from Saurashtra region. The first volume of "The Flora of Saurashtra" was published by Santapau (1962). Bhatt and Imandar (1971) made some more additions to the flora of Saurashtra. The vegetation of Bhavnagar was worked out by Murthy (1957) and reported 378 plant species from the area including cultivated plants. Vora et al. (1981) reported 341 flowering plants of Ghoghamahal of Bhavnagar district. The floristic and ecological study of Bhavnagar and its surroundings has been studied by Oza (1991), and reported 528 flowering plant the area. Desai (1992) has recorded five new taxa from Bansda forest, for the first times, which are new additions to the flora of Gujarat State.

An assessment of floristic studies

The present work is based on the result of three years of intensive and extensive study of the plants of this area. The analysis of the total plant species found are presented in the following way:

The present study enumerated 431 species, which belonged to 294 genera and 94 families of flowering plants (table-1). Out of which, Dicotyledons contributed 371 plant species belonging to 246 genera and 80 families, which is quite higher than that of Monocotyledons. The Monocotyledons contributed only 60 species belonging to 48 genera and 14 families. Leaving Poaceae and Cyperaceae, Monocotyledons are poorly represented. Proportion of the Monocotyledons to Dicotyledons was recorded 1:5.71 of families, 1:5.12 of genera and 1:6.18 of species (table-2). The ratio of the total number of genera to species was recorded 1:1.46, which is rather low in comparison to a corresponding ratio for whole India (1:7), but it more or less in conformity with the ratio of Delhi state (1:1.63), as reported by Maheshwari (1963) and W. Rajasthan (1:1.9), reported by Bhandari (1978).

A comparison of the present study with other regions of Gujarat State gives very interesting results. The ten dominant families, which were found in the Gir forest, have been compared with other regions of Gujarat viz., Ghoghamahal (Vora et al., 1981); Victoria Park reserved forest (Patel, 1982); South Gujarat (Yadav, 1979); Saurashtra region (Santapau and Janardhan, 1966) and Gujarat State (Shah, 1978)(table-6).

It is evident form this table that that most of the dominant families in the present study, have been reported earlier form different regions of Gujarat State, but the order of dominance is different. However, the legumes and grasses occupy the first and second place in all these regions of Gujarat, except South Gujarat, where grasses occupied the first position. Table-3 shows the number and percentage of genera and species of the ten dominant families found in the present study.

The floristic composition analysed critically and it showed that 42 families were monotypic, 49 families were monogeneric, 14 with two genera, ten with three genera, four with four genera, four with five genera, four with six genera, three with seven genera, one with eight genera, one with nine genera, and five with ten or more then ten genera. Monotypic genera contributed only 14.28 % in the Gir forest region, which was less when compared with South Gujarat (29.8 %), but was more or less in conformity with Bhavnagar (12.63 %), as reported by Oza (1991). The other families which showed their remarkable percentage were as follows: families with one genera, two genera, three genera and four genera were 52.68 %, 15.05 %, 10.75 % and 4.30 % respectively. Families with five to nine genera are in the range of 1.30 to 4.30 % and the families with more than ten genera were little high (5.37 %).

The habit approach revealed that out of 431 flowering plants, herbs contributed more than 50 % of plant species i.e. 53.59, followed by trees, shrubs and climber or twiners which were 19.03 %, 14.39 % and 12.99 % respectively (table-4). These results were in close agreement with earlier reports of Pandya (1972) and Oza (1991).

The higher percentage of herbs in the area could be attributed to edaphic and peculiar climatic conditions like mager rainfall and high temperature. During summer, when the temperature become severe and the soil become intolerable to plants, as a result only short living plants like annual herbs are only favored. Because, herbs can complete their life cycle before the commencement of the dry season and set seed during the summer. Hence the proper utilization of climate and edaphic factors are often responsible for such type of distribution pattern. While studying the temperate and tropical forest types, Smith (1973) reported that an increased structural integrity of the forest will lead to the proper utilization of climatic and edaphic conditions.

The plant species are presented in the Appendix-1 with reference to their name of the family, genera and species; and also their vernacular name, habit, flowering and fruiting period, Life forms of Raunkiaer (1934), Life forms of Numata (1954), Life forms of Numata and Asano (1969) and Rare or Common.

The biological spectrum presented in Table-5 showed the highest percentage (54.98 %) of Therophytes. Other groups of life forms in order of importance are given as follow: Phanerophytes (34.81 %), Chamaephytes (5.34 %), Hemicryptophytes (3.48 %) and Cryptophytes or Geophytes (1.39 %). Hence, the area falls under the category of stherophytic type of phytoclimate, which indicates hot and dry climate in the region, which is congenial for the growth of annuals and perennial herbs.

A comperation of the biological spectrum of the flora of Gir forest with different regions of Gujarat (table-7) reveals that among all life forms, therophytes contributed the highest percentage in all the region of Gujarat including the present study. According to Danserau (1957) the predominance of therophytes indicates warm climate. Bharucha and Dave (1944), Pandeya (1964), Yadav and Singh (1977) and Agrawal (1984) attributed the preponderances of therophytes to the influence of heavy grazing or biotic interferences. However, Meher- Homji (1964) and Daubenmire (1968) attributed the occurrence of therophytes to aridity factor.

Increase in the percentage of therophytes and decrease in that of phanerophytes and hemi cryptophytes in the flora of Gir forest was caused by deforestation, intensive utilization of land for cultivation and grazing by livestocks. The result of the present study is in conformity with the conclusion drawn by Meher-Homji (1981).

Plant Diversity Indices

It is a measured by a number of diversity indices. There has been a lot of development and proliferation of diversity indices over the years. These indices are mathematical expressions that combine three components of community structure, i.e. richness (number of species present), evenness( the distribution of individuals among species), and abundance( total number of plants present).

The plant diversity studies of the Gir forest (Table-8) is claimed to be the first of its kind. The diversity indices, Simpson's index (D=0.361): Simpson's index is a dominance measure as refer by Magurran (1988) and a probability measure as refered by Sai and Mishra (1986). The higher value at Gir forest could mean the high dominance of the occurring species. There were herbs with Pi² = 0.287 indicating they that were in higher number than all others. Herbs were followed by trees Pi²= 0.036, trees were followed by shrubs with Pi²= 0.021 and lastly climbers with Pi²= 0.017. Index of similarity (0.639) showing high diversity. Reciprocal index was 2.77. Shannon-wiener index was 1.194 indicating low diversity. This is lower than the range 1.5 to 3.5 as mentioned by Margalef(1972). Finally Evenness index was 0.861 indicates that abundance of different species are similar in proportion to all species.

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Table: 1. Number and percentage of families, genera and species of each class

Table: 2. Ratio between Monocotyledons and Dicotyledons

Table: 3. Number and percentage of genera and species of the dominant families

Table: 4. Number and percentage of species belonging to the different habits

Table: 5. Biological spectrum

Table: 6. Comparison of ten dominant families of Gir forest with different regions of Gujarat State.

Table: 7. Comparison of biological spectrum of Gir forest with different regions of Gujarat

Table: 8. Plant Diversity Indices

¹ Department of Life Sciences,
Bhavnagar University, Bhavnagar-364 002