Tree Species Diversity and Population Structure in the Tropical Forests of North Central Eastern Ghats , India

The tree species diversity and population structure were studied in four stands of the tropical forests in the north-central Eastern Ghats, based on tree inventories conducted on four 1-ha plots. In the four independent plots, two 5 x 1000 m transects were established and all trees with ≥ 15 cm girth at breast height were enumerated. The density, frequency, basal area and IVI along with diversity indices viz. Shannon index, species richness, equitability and species dominance were computed to see the variation in tree community. A total of 92 species representing 73 genera under 40 families of angiosperms were recorded. Tree species richness was as low as 34 species per hectare plot in Geddapalli to as high as 48 species in Koruturu. Tree density ranged from 360 stems per hectare in plot Geddapalli to 526 stems in plot Chintapalli and that of total basal area from 16.31 m ha in Koruturu to 31.15 m ha in Chintapalli. The number of species and stems decreased from the smaller to the largest girth classes. The tree inventories of the study area when compared to those of the other tropical forests showed great differences in density and basal area. This may probably be due to differences in geography and annual rainfall patterns. The information on tree species structure and function can provide baseline information for conservation of the biodiversity.


Introduction
Tropical forests are the most complex of all the terrestrial ecosystems.They provide many goods and ecosystem services, such as prevention of soil erosion and preservation of habitats for plants and animals (Anbarashan and Parthasarathy, 2013).Although tropical forests occupy only 7% of the earth's land surface (Wilson, 1988), they harbors about two thirds of all biological populations (Hughes et al., 1997).Phytogeographically, these forests are characterized by a large biological diversity and enriched with economically important species (Hare et al., 1997).On a global basis, 52% of total forests are tropical and over 42% of tropical forests have been classified as dry forests (Holdridge, 1967) and these currently are disappearing at an alarming rate, ranging between 0.8-2% per year (May and Stumpf, 2000;Sagar et al., 2003).Many tropical forests are under great anthropogenic pressure and require management interventions to maintain the overall biodiversity, productivity and sustainability (Kumar et al., 2006).Trees from the major structural and functional basis of tropical forest ecosystems can serve as robust indicators of changes and stresses at the landscape scale (Sahu et al., 2012b).Plant diversity inventories in tropical forests have mostly been concentrated on tree species than other life forms, because tree species diversity is an important aspect of forest ecosystem diversity and also fundamental to total tropical forest biodiversity (Rennols and Laumonier, 2000).They provide resources and habitat structure for almost all other species and form the major biotic component in the forest ecosystem.
Eastern Ghats are a long chain of broken hills and elevated plateaus, running along the east coast of India in the states of Orissa, Andhra Pradesh, Tamil Nadu and Karnataka.The topography and varied climate promoted luxurious growth of plants and diverse forests with a number of invaluable medicinal plant species (Rawat, 1997;Sahu et al., 2012a).Certain wild crop relatives have been reported from these tracts, giving these landscapes special conservation value as sources of novel genes for future crops.This rich biodiversity is being utilized by the inhabitants of the region for medicine, food (wild edible), fodder, fuel, timber, making agricultural tools, religious and other purposes.As the Eastern Ghats constitute important catchments of the peninsula and natural resource, they are threatened due to anthropogenic disturbances, such as indiscriminate collection of fodder, fuel species, extraction of timber and minerals from the forests besides the shifting cultivation (Reddy et al., 2008).Several authors have studied the flora and stressed the need for better conservation of the Eastern Ghats.
In peninsular India, quantitative phytodiversity related inventories from the forests of Eastern Ghats are very few.Some studies related to Eastern Ghats of Tamil Nadu (Kadavul and Parthasarathy, 1999a, b;Jayakumar et al., 2002;Natarajan et al., 2004;Pitchairamu et al., 2008;Pragasan and Parthasarathy, 2010); Orissa (Reddy et al., 2007;Sahu et al., 2012a, b;Sahu et al., 2007;Dash et al., 2009), Andhra Pradesh (Rawat, 1997;Reddy et al., 2008;Reddy and Ugle, 2008;Rao et al., 2011) are available.Such studies about Eastern Ghats are very few in the state of Andhra Pradesh, though it has major tracts of Eastern Ghats.Therefore, the present study was conceived to compare the species diversity, density and stand structure of the four plots of north-central Eastern Ghats, in the West Godavari district of Andhra Pradesh.

Study area
The study was carried out in four forest stands in the tropical dry deciduous forests (Champion and Seth, 1968) located in West Godavari district, Andhra Pradesh and the plots are 330 km south-west of Visakhapatnam city.They include Chintapalli (CP), Puliramudugudem (PG), Koruturu (KT) and Geddapalli (GP).The West Godavari district is located between the northern latitudes of 16°-15' and 17°-30' and eastern longitudes of 80°-50' and 81°-55' bound on the north by Khammam district, on the south by Bay of Bengal and a small part of Krishna district, on the east by the river Godavari and on the west by Krishna district.The elevation measures about 450 m above the mean sea level.Geological formation of the region consists in chiefly crystalline metamorphic rocks.Soil of north central Eastern Ghats is loamy, black, lateritic and alluvial.Lateritic soils are the common type along the deciduous forests in the area.There are three distinct seasons in a year: winter (November to February), summer (March to June) and rainy season (July to October).The maximum temperature ranges between 28.0 -46.2 °C and minimum temperature ranges between 12.9 -27.0 °C.The maximum rainfall is 1300 mm per annum during south-west monsoon period.Similar pattern of temperature and rainfall prevails throughout the year for all the four studied plots.The relative humidity varied between 70 -88%.

Field methods
For determination of biodiversity, the methodology prescribed by the National Bioresource Development Board, Department of Biotechnology, Government of India was followed.In all the four study plots, two belts transects of size 5 x 1000 m (totaling 1 ha) were randomly laid during the calendar years 2007 -2009 and all live trees with ≥15 cm girth at breast height (gbh) were enumerated.The height of trees was measured using a clinometer.Depending 449 on the shape of the forest stand, these transects were subdivided into fifty 5 x 20 m quadrats.The representative taxa were collected and identified with the help of regional floras (Gamble andFischer, 1915-1935;Rao et al., 1986) and preserved into herbarium.The voucher specimens were deposited in the Botany Department Herbarium (BDH), Department of Botany, Andhra University, Visakhapatnam.

Data analysis
Based on the individuals recorded in the discrete plot samples, vegetation data were quantitatively analysed for basal area, relative density, relative frequency and relative dominance.
The importance value index of tree species was determined as the sum of relative frequency, relative density and relative dominance (Curtis and McIntosh, 1950).
The data collected were also used to compute community indices like species diversity (H') of different tree species; it was calculated using the Shannon-Weiner Index (Shannon and Weiner, 1963): where, Pi = ni/N, which denotes the importance probability of each species in a population, ni= importance of value of species and N is the total number of individuals of all species in that vegetation type.
Species dominance (Cd) was calculated following Simpson (Simpson, 1949): where, ni and N are the same as those for Shannon-Weiner information function.
Equitability of evenness refers to the degree of relative dominance of each species in that area.It was calculated according to Pielou (1966) as: Evenness (e) = H'/log S where, H'= Shannon index, S = number of species.Species richness was determined by Margalef index (1968) as: where, S is the number of species and N is the number of individuals.
Structural composition was analysed by comparing the distribution of tree height and diameter classes.The mean tree density is 447 stems for 1 ha and density ranges from 360 -526 stem ha -1 .The stand density is more for plot CP and less for plot GP.Basal area ranged between 16.32 m 2 ha -1 -31.16 m 2 ha -1 and mean basal area was 22 m 2 ha -1 .Basal area is more voluminous in plot CP and less voluminous in plot GP.

Floristic composition and species richness
Tree girth class-wise density is more for 31-60 cm gbh class interval, with 32.9%, while the class interval <30 cm accounted for 20%, girth interval between 91-120 cm accounted 15.09% and less abundance is for class interval >120 cm, with 12.5%.The stand structure based on girth frequency of species has a greater number of trees in lower size class particularly in plot CP and plot KT compared to plot PG and plot GP (Tab.2).Stem density across girth classes in all the study plots decreased from the smallest to the largest trees, except in first girth class (<30 girth class).Tree girth class-wise basal area is more for >120 cm class represents 51 m 2 ha -1 and less for <30 cm girth intervals with 1.64% m 2 ha -1 .
The mean tree height is 18.5 m with the high ranging between 2-20 m.Tree distribution by height intervals shows that around 22% of individuals are in <5 m, about 60% of individuals fall in 5-10 m height interval and only 14% of individuals are contributed by 11-15 m interval, while >15 m tree species are very few and constitute about 2.9% of total individuals (Tab.3).

Importance value index (IVI) and diversity
The IVI values of the 92 species varied considerably (Tab.4).The IVI of the top ten tree species contributed by 76.5%, 48%, 44.4% and 51.7% of total IVI values respectively for plots CP, PG, KT and GP.Cleistanthus collinus is the dominant species in plot CP (IVI 105.34)In plot PG, Dalbergia paniculata was the dominant species (IVI 24.15) which contributed with 8% of total IVI.Tamarindus indica was the co-domonant species (IVI 20.11) accounting for 6.7% of total IVI.The other species with IVI greater than 10 include Haldinia cordifolia, Anogeissus acuinata, Terminalia alata, Chloroxylon swietenia, Lannea coromandelica and Strychnos nux-vomica, which accounted for 4 -6% of the total IVI.
In the plot KT, Cleistanthus collinus, Dalbergia paniculata, Terminalia alata, Schleichera oleosa, Anogeissus latifolia and Albizia odoratissima had IVI values greater than 10.Cleistanthus collinus had the largest IVI, with a value of 21.52, accounting for 7.1% of total IVI, followed by Dalbergia paniculata with IVI -18.9 accounting for 6.3% of the total IVI.The IVI of the other four species ranged between 10.67-17.21,accounting for 3.5 -5.7% of total IVI.
Diversity of tree species in the study plots calculated using the Shannon-Weiner diversity index (H') showed values of 3. 55, 3.47, 3.48 and 3.32 for the plots of CP, PG, KT and GP respectively.The values for Simpson's index were 0.96, 0.97, 0.95 and 0.96 for the plots of CP, PG, KT and GP respectively.Pielou's evenness index of tree communities at CP, PG, KT and GP plots showed values of 0.76, 0.71, 0.68 and 0.81 respectively.The Margalef species study plots are compared with that of tropical dry deciduous forests of Eastern Ghats, southern Andhra Pradesh, which represents 18 -86 tree species in 3 ha (Reddy et al., 2008), Niyamgiri hill ranges of Orissa with 22-29 species in 0.6 ha (Sahu et al., 2012b), Similipal Biosphere Reserve harbouring 76-121 species in 8.48 ha (Reddy et al., 2007), Khokham Wildlife Sanctuary comprising 11-17 tree species in 2 ha (Pant and Samant, 2012), inland forests and coastal forests of peninsular India with 19-35 and 21-28 tree species respectively in 5 ha each (Mani and Parthasarathy, 2006), tropical dry evergreen forests of Coromandel coast of India harbouring 18-27 species in 4 ha (Anbarashan and Parthasarathy, 2013), tropical dry deciduous forests of western India contributed 18-37 species in 3 ha (Kumar et al., 2010), Kaan forests in the central Westrn Ghats harbouring 28-53 species in 3 ha (Ganuga et al., 2013).
Girth class-wise frequency population structure of trees in four study plots are in conformity with other forest stands in tropical forests such as Shervarayan hills (Kadavul and Parthasarathy, 1999a), Kalarayan hills (Kadavul and Parthasarathy, 1999b), sacred groves of the Jaintia hills (Upadhaya et al., 2003), Malayagiri hill ranges of Eastern Ghats (Sahu et al., 2012a) and Cerros de Amotape Cordillera, Peru (Palomino and Alvarez, 2005).Species richness and density decreased with the increasing tree size classes in all four plots, as the middle class stems 61-90 cm contributed with 33% of total density, whereas the largest size >120 cm comprised 12.5%.The trend of decreasing diversity with increasing girth class is similar to that observed by Paijmans (1970) in New Guinea.
The basal area is used as one of the important aspects for studying the forest vegetation structure in most of the studies (Mani and Parthasarathy, 2006).The mean basal area obtained in the present study is 22 m 2 ha 1 , as it ranges between 16.32-31.16m 2 ha -1 ; with this value, is greater than the one for tropical forests of Hainan Island, with 17.04-21.11m 2 ha -1 (Meng et al., 2011), Niyamgiri hill range of Eastern Ghats constituted 3.16-10.04m 2 ha -1 (Sahu et al., 2012a), Cerros de Amotape Cordillera, Peru comprised 2.31-22.79m 2 ha -1 (Palomino and Alvarez, 2005), tropical forests of southern Eastern Ghats harboring 5.6-24.4m 2 ha - 1 (Pragasan and Parthasarathy, 2010).This value is closer of near reserved forests of southern Eastern Ghats of Andhra Pradesh has 10.5-31.7 (Rao et al., 2011) richness index is 7.18, 7.37, 7.68 and 5.61 for plots of CP, PG, KT and GP respectively (Tab.1).

Discussion
The tree species richness varied among the four plots.There are 92 species enumerated in the 4 ha of the north central Eastern Ghats.Species richness ranges between 34-48 stems ha -1 .Species richness is higher for plot CP, with 48 species, while GP has least diversity, with 34 species.These Pradesh with 8.55-34.39m 2 ha -1 (Reddy et al., 2008), but lower than that of 61.32-70.93m 2 ha -1 for Niyamgiri hill ranges of Orissa (Dash et al., 2009), sacred groves of Jaintia hills contributed 57.46-77.44m 2 ha -1 (Upadhaya et al., 2003), fan-palm dominated forests of east coast peninsular Malaysia with 25.3-48.6m 2 ha -1 (Nizam et al., 2013).The basal area and vertical structure of a forest is difficult to summarize as these depend heavily upon climate and prevailing edaphic factors.

Conclusion
Tropical dry deciduous forests are a critical repository of India's biodiversity and are threatened due to wide spread of habitat destruction.Plant diversity inventories in tropical forests have mostly been concentrated on tree species than other life-forms, because tree species diversity is an important aspect of forest ecosystem diversity and also fundamental for total tropical forest biodiversity.The present quantitative inventory of tree species diversity revealed considerable variation in the composition of dominant species and stand density in various forest areas.The IVI values have helped to understand the ecological significance of the tree species in community structure.The present study clearly established the fact that the tree diversity in tropical forests of Eastern Ghats varied greatly from location to location, mainly due to variation in biogeography and habitat disturbance.Most of the species present in these communities are used for fuel, fodder, making agricultural tools, house building and miscellaneous purposes.During the surveys, it has been observed that use-pressure on species along with heavy grazing is responsible for habitat degradation, poor regeneration and population depletion of the tree species.
, tropical dry deciduous forests of Eastern Ghats, Southern AndhraTab.4. Top ten IVI of the tree species in four 1-ha plots