Floristic Composition, Diversity and Status of Threatened Medicinal Plants in Tropical Forests of Malyagiri Hill Ranges, Eastern Ghats, India

Tropical and subtropical forests harbour maximum diversity of plant species found on the earth (WCMC, 1992). These forests are rich in medicinal and economically important plants. Exploitation of these forests has resulted in rapid loss of tropical forests and it is recognized as one of the serious environmental and economic problems all over the world (Hare et al., 1997). A study on floristic composition and species diversity of threatened medicinal plants of tropical forests is ecologically significant besides its usefulness in forest management.

Tropical Forests 204 Saxena, 1990;Patra & Choudhury, 1989;Saxena & Dutta, 1975;Saxena et al., 1991), no quantitative study analyzing the vegetation structure of the forest has been undertaken.Therefore, a detailed study was undertaken to analyze the diversity, distribution and population structure of tree species in these forests.

Field sampling and data analysis
Vegetation analysis was carried out during March 2007 to December 2009 by laying 60 quadrants for each element of vegetation.For all trees ≥15 cm girth at breast height (GBH) were sampled through 20 x 20 m quadrants with sampling intensity of 0.001% based on random sampling methods in tropical dry deciduous forest stand of 2.4 ha area.Individuals with less than 15cm GBH were considered as saplings.The shrubs were sampled through 5 x 5 m and herbs, climbers and saplings were sampled by laying 1 x 1 m quadrants.Herbarium specimens were prepared and the species were identified with the help of regional flora (Gamble & Fischer, 1915-1935;Saxena & Brahmam, 1996).The specimens were deposited in the herbarium (RRL-B) at Institute of Minerals and Materials Technology, Bhubaneswar.The vegetation data were analyzed for 57 tree species.Abundance (A), Frequency (F), Relative frequency (RF), Density (D), Relative density (RD), Basal Area (BA), Relative Basal Area (RBA), Importance Value Index (IVI), Shannon -Wiener index (Shannon and Weaver, 1963) and Simpson's index (Simpson, 1949) were calculated using the quadrant data and following the methods of Misra (1968).IVI of each species was calculated by summing the RF, RD and RBA following the methods of Curtis (1959).Abundance to Frequency (A/F) ratio of each species was calculated to study the dispersion pattern.The range of values for determining dispersion pattern were: regular (< 0.025), random (0.025-0.05) and contiguous (> 0.05) (Curtis and Cottam, 1956).Population structure of tree species was analyzed across the five girth classes.The status and degree of threat to medicinal plants in their natural habitat has been indicated by classifying them according to Red Data Book categories, as defined by the IUCN (Maheswari, 1977;Melville, 1970-71).Shannon and Weiner's Index (1963) was calculated as follows: Where, p i = n i /N n i = Importance value for species "i" N = Total of importance value Concentration of dominance was calculated following Simpson (1949): Where p i is same as the Shannon-Wiener Index.

Results and discussion
The dominant forest type of Malyagiri hill range is tropical dry deciduous forest (Champion and Seth, 1968) Out of 57 tree species, five species were randomly distributed and 52 species were contiguously distributed.The study reveals prevalent clumping nature of tree species in the tropical forest of Malyagiri hill ranges.Odum (1971) stated that contiguous distribution is the commonest pattern of plant distribution in nature.Kumar and Bhatt (2006) also reported that most species follow contiguous distribution pattern in foot-hills forests of Garhwal Himalaya and Rao et al. (1990) had similar findings for tree species of a subtropical forest of north-east India.The Shannon-Wiener index (H') was 3.38 and Simpson's index was 1.0.These values indicate that tropical deciduous forests are species diverse systems.The diversity value (H') of 3.38 falls within the range of 0.83-4.1 reported by earlier workers for Sal forest (Rasingam & Parathasarathy, 2009;Shukla, 2009;Singh et al., 1985;Tripathi & Singh, 2009;Visalakshi, 1995).
The mean tree density of the forest was 443 ha -1 .The mean stand density of the forest is well within the range of 276-905 stems ha -1 reported for trees ≥15 cm GBH in other tropical forests (Bhadra et al., 2010;Nirmal Kumar et al., 2010;Sahu et al., 2007).The value obtained for basal area in the present study is comparable to the Indian tropical forests (Visalakshi, 1995).
The mean tree height was 10 m with a height range of 1 to 35 m.Tree distribution by height class intervals shows that 39.1% of individuals were in the height class of 5-10 m, followed by 24.3% in the height class of 10-15 m and 20.4% in the height class of 0-5m (Fig. 2).Only 5.73% of individuals were in the height class of >20 m.The tallest trees were Shorea robusta (35 m), Mangifera indica (33 m), Terminalia bellirica (32 m), Syzygium cumini (32 m), Diospyros malabarica (27).
The data on species/genus (S/G) ratio helps to compare the rate of species development because high ratio indicates recent diversification.Tropical areas have low species/genus ratio, indicating that the tropical species have emerged over a long period of time (Ricklefs www.intechopen.com Tropical Forests 208 and Miller, 2000).In the present study, all the study sites show lower S/G ratio in the tree layer (1.18), thus showing conformity with the findings of Ricklefs and Miller (2000).The invasive, exotic species were also found, which can be a serious threat to the forest ecosystem in the future.Important among them are Ageratum conyzoides L., Chromolaena odorata (L.) R. King & H. Robins., Crotalaria pallida Ait., Hyptis suaveolens (L.) Poit., Lantana camara L., Mimosa pudica L., Parthenium hysterophorus L. and Triumfetta rhomboidea Jacq.
Girth class frequency showed J-shaped population structure of trees exhibited in the study sites are in conformity with many other forest stands in Eastern and Western Ghats such as Shervarayan hills (Kadavul and Parathasarthy, 1999a); Kalrayan hills (Kadavul and Parthasarathy, 1999b); Kakachi (Ganesh et al., 1996); Andaman Islands (Rasingam & Parathasarathy, 2009)

Conclusion
Reverse J-shaped population structure of trees denotes an evolving or expanding population, which needs to be maintained.The unsustainable collection of medicinal plants such as the bark of Oroxylum indicum (L.) Vent.and whole plant of Gloriosa superba L. and Uraria picta (Jacq.)Desv.exDC., need to be checked to maintain the favourable population structure.Study on floristic composition and diversity will be useful to the conservation researchers and scientists and also to the forest managers for effective management of the forest ecosystem.The present investigation highlights the presence of threatened medicinal www.intechopen.com

Table 2 .
. List of Threatened Medicinal plants in Malyagiri hills, Odisha