The present study communication examines the forest Community structure and their status in Rudraprayag district of Garhwal Himalaya. On the basis of physiognomy, species composition, structure, habitat and physiography forests of the district were classified into four types viz., temperate forest, temperate mixed forest, Subtropical forest and subtropical mixed forest. The district is mostly covered by temperate forests and partially by the sub tropical forest. Temperate forests are dominant forest types of the district with a density of 1980, 1550 plant ha-1 and basal cover 40.19, 20.94 m2 ha-1 in temperate mixed and temperate forest, respectively. The subtropical forests located in the lower valleys with southern slopes and are generally sparse forest type of the district.
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Vegetation, an important dynamic characteristic of the earths surface is defined as a system of large spontaneously growing plant populations, growing in coherence with all other sites and forming an ecosystem (Whittaker, 1963). The natural vegetation of land can be grouped as forest, grassland, scrub and desert. Vegetation is complex in nature and its occurrence, structure, composition, etc, differ from place to place. Species diversity as a whole and its distribution along altitudinal gradient had been a subject of ecosystem (Hubbell et al., 1999).
The Himalayan region is well outside the tropics, therefore both climatic conditions and some of the vegetation types are close to those of more northerly (Kharkwal et al., 2005). This vast range of Himalaya plays an important role in regulating climate over most part of country. Altitudinal range, diverse topographic and climatic features make the Himalayan region rich in biodiversity. Vegetation is classified based on either vegetation itself, the environment surround it or a combination of vegetation and its environmental components (Muller-Dombois and Ellenberg, 1974). In most part of the study sites, the dominant forest types are temperate forest (Quercus leucotrichophora, Rhododendron arboreum), temperate mixed (R. arboreum, Q. glauca, Q. leucotrichophora, Alnus nepalensis, Myrica esculenta, Cinnamomum tamala, etc.) subtropical forest (P. roxburghii) and subtropical mixed forest (Lagerstroemia parviflora, Cassia glauca, Ougeinia oojeinensis, etc.).
Quantitative information on the distribution and abundance of tree species is of key significance to understand the form and structure of a community and for planning and implementation of conservation strategy of the community. On the other, a community is characterized by giving the details of those species which are accountable for its unique composition.
In recent years, several workers on different aspects of ecology including Semwal and Bhatt (1999), Bhandari (2003), Raturi and Bhatt (2004, 2006), Kumar et al. (2004) and Sharma et al. (2010) studied vegetation of Garhwal Himalaya. Effect of anthropogenic pressure viz., burning of ground vegetation for cultivation and cutting trees for fuel wood and leaf fodder caused severe damage to forest vegetation (Bargali et al., 1998; Sharma et al., 2009). Similar, phytosociology, composition and related aspects of the forest from India and abroad were studied by Rajdeep et al. (2011), Agbagwa and Ekeke (2011), Galal (2011), Kukshal et al. (2009), Jumaat et al. (2011), Valipour et al. (2009), Njunge and Mugo (2011) and Dzomeku and Enu-Kweai (2006). Present study communication was an attempt to assess the phytososiological status and distribution pattern of the forest community of district Rudraprayag.
MATERIALS AND METHODS
The Rudraprayag district of Uttarakhand state lies between the lat 30° 12' 58 "-30° 56' 47" N and long 78° 50' 07" -79° 22' 34" E. covering Survey of India toposheet No. 53J and 53N. The altitudinal range of the study area lies between 500-6940 masl. and covers two sections of the Himalaya, i.e., Lesser Himalaya and Greater Himalaya. Rudraprayag district in general comprises of the temperate zone of Western Himalaya and the forests owe their diversity due to physiognomy, altitude and climatic conditions. On the basis of physiognomy, species composition, structure, habitat and physiography and visual interpretation of IRS LISS-III Standard False Colour Composite (FCC) of November 1998, forests of the district were classified into four type viz., temperate forest, temperate mixed forest, Subtropical forest and subtropical mixed forest.
Selected forest types i.e., temperate forest, temperate mixed forest, Subtropical forest and subtropical mixed forest were sampled for the quantitative study to get an over view of the vegetation. The procedures adopted for the study included those of McIntosh (1967), Misra (1968) and Smith (1980). Quadrat was used as a sampling unit for vegetational analysis. The size and number of quadrat was determined on the basis of species-area-curve method (Oosting, 1958) and 20 quadrats of 10x10 m were placed at random to analyze forests for tree and shrub species. Circumference at breast height (DBH 1.37 m above the ground) of all the trees (with a diameter>31.5 cm) in each quadrat was measured and recorded individually for every species. Individuals with a DBH range from 10.5-31.4 cm were considered as shrubs.
The vegetation was quantitatively analyzed to compute frequency, density and abundance as described by Curtis and McIntosh (1950). Distribution pattern of species was determined by applying abundance to frequency ratio following Whitford (1949). In order to express the dominance and biological success of any species (Philips, 1959; Misra, 1968) designated IVI as a better expression, than the single absolute measure like frequency, density and total basal cover. A species which attains maximum IVI within the community, is considered as dominant species of that community.
Computation of total diversity (i.e., species richness and evenness) was used following Shannon-Wiener information index H (Shannon and Weaver, 1963) to obtain information in a group of species that have different probabilities (number of individuals). Beta diversity (β, inter community diversity) was measured following Whittaker (1972). To evaluate the degree to which dominance is focused to compare species within a community or between the communities which resemble each other in physiognomy. The two communities that resemble each other in appearance are never exactly alike. They differ in species composition due to differences in inter-specific association. Index of similarity (S) between two samples was computed following Muller-Dombois and Ellenberg (1974).
RESULT AND DISCUSSION
Champion used the term temperate for those forest that occur on mountains either in south or in the Himalaya (above 1700 m) (Puri et al., 1989). In the present study the temperate and temperate mixed forests are generally localized in mid to high altitude and are characterized by cold and moist climate. These forests have extensive branching and boles are often covered over with mosses while undergrowth is mostly shrubby with deciduous species. Subtropical forest and subtropical mixed forests are localized in the lower altitude and warmer climate.
The observation from 4 forest types based on above parameters revealed interesting results. Considering Importance Value Index (IVI) as a measure of dominance the four-forest type differed in their dominant and co-dominant tree and shrub species. Quercus leucotrichophora emerged as a dominant tree species of temperate forest while Rhododendron arboreum, Pinus roxburghii and Lagerstroemia parviflora were found to be dominant elements of temperate mixed forest, subtropical forests and subtropical mixed forests, respectively. Similarly, in the shrub stratum Berberis asiatica was the dominant and most successful shrub species of subtropical forests. Carissa opaca was identified to be the dominant shrub of temperate mixed forest as well as subtropical mixed forest. Hypericum cernuum emerged as dominant shrub of temperate forests (Table 1).
Vegetation of the research area is mostly temperate with high density values. The temperate mixed forest exhibited highest density (1980 plant ha-1) while subtropical forest had minimum density (1090 plant ha-1). The shrub density in these forests ranged between 720-860 shrub ha-1. Similarly the total basal area were maximum for Pinus roxburghii (43.62 m2 ha-1) in subtropical mixed forest and minimum for Q. glauca (3.182 m2 ha-1) in temperate forest. These observations are in conformity with the findings from other regions of Garhwal and Kumaun Himalaya (Ralhan et al., 1982; Kusumlata and Bisht, 1991; Semwal and Bhatt, 1994; Baduni and Sharma, 2001).
There is great variation in the range of basal cover in the species and site (Table 1). Trees with higher basal cover indicate good performance of the species while lower basal area either demarcates the chance of occurrence or the biotic disturbance in the past (Saxena et al., 1978; Prasad, 2002; Pandey, 2003).
Species diversity (H) ranged between 0.78-3.45 for top (tree) stratum (Table 2). Maximum diversity (3.45) was recorded for temperate mixed forest and minimum diversity for subtropical forest (0.78). Species diversity for second (shrub) stratum was lowest for temperate forest (2.08) and maximum for subtropical mixed forest (2.74). The higher elevation promotes greater diversity due to availability of more atmospheric humidity (Rikhari et al., 1989). The second story in these forest types was comparatively poor as Whittaker (1972) suggested that the dominance of one stratum affect the diversity of other stratum.
The species richness or alpha (α) diversity felled between 2-13 for trees and shrubs were well within the range of reported values (2-13) in similar forest type in Central Himalaya (Ghildiyal et al., 1998; Dhannai et al., 2000). The values for beta (β) diversity oscillated between 0.40-16.90 and were similar to those reported by Kumar et al. (2004) for different forest type ranging between 1.75-15.24. Thus there seems to be uniformity in vegetation pattern throughout the Central Himalayan region with slight fluctuations.
Diversity is the combination of two factors, the species richness and distribution among species, referred as equitability. Equitability (Ec) was accounted between 4.88 (for both trees in temperate mixed forest and for shrubs in sub tropical mixed forest) to 1.41 (for shrub in temperate forest) and 0.49 (for trees in subtropical forest).
|Table 1:||Vegetational structure in different forest types|
|Table 2:||Diversity indices of forest vegetation of Rudraprayag district|
|H: Shannon- Wiener information index, D: Diversity, α: alpha, β: beta, Cd: Index of dominance and Ec = equitability|
|Table 3:||Distribution pattern (%) of species in different forest types|
|*: No. of species|
|Fig. 1:||Dominance-diversity curve for tree species. SF: Subtropical forest, TF: Temperate forest, SMF: Subtropical mixed forest and TMF: Temperate mixed forest|
|Fig. 2:||Dominance-diversity curve for shrub species. SF: Subtropical forest, TF: Temperate forest, SMF: Subtropical mixed forest and TMF: Temperate mixed forest|
These observations indicate that the maximum of species in temperate mixed forest for tree and in subtropical mixed forest for shrubs have more or less equal number of individuals as compared to other forests with respect to tree and shrub layers. The concentration of dominance (Cd) was recorded to be highest for subtropical forest being 0.63 and lowest (0.09) for temperate mixed forest for trees. Minimum and maximum concentration of dominance was recorded to be 0.16 and 0.25 for the shrub stratum of subtropical mixed forest and temperate forest, respectively. These values fall within the range reported for other Central Himalayan forests (Saxena and Singh, 1982; Kumar et al., 2004).
Dominance-diversity curve for the tree and shrub layers approached geometric series for all forest type constructed on the basis of IVI. The log normal distribution of the forest layer was due to highly mixed nature of vegetation (Fig. 1, 2). The geometric series for both the layers confirmed the niche preemption hypothesis of Whittaker (1975).
The ratio of abundance to frequency for tree stratum indicated 57.89% random while shrub layer of forest had an A/F ratio of 44.44% revealing random and regular distribution pattern for both (Table 3). Sharma and Kumar (1992), Singh and Singh (1992) and Semwal and Bhatt (1994, 1997) reported similar results for Central Himalayan forests.
It is clear from the results that temperate and temperate mixed forests are dominant forest types of Rudraprayag district. The subtropical forests on the other hand are narrow forest types in the district. Species diversity in subtropical forest was least among all forest types while, the concentration of dominance was greater than the mixed forest. This is probably because these forest types are located in the area with easy access than those of mixed forests.
Authors are thankful to the Department of Science and Technology (DST) for the financial assistance.
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