The forests of the world play vital role in maintaining and balancing natural eco-system. These forest resources fulfill human demands by providing renewable raw materials and energy, maintain biodiversity and protect land and water resources. These resources are under degradation extensively due to increasing population pressure, agricultural and urban expansion, industrialization, infrastructure development and other disturbances.

In global scenario, Nepal allows many habitats and tremendous biodiversity and ecosystems representing 29% of forest resources. It holds less than 0.03% of earth surface which blessed with 1.3% (22,000 species) species of plants and animals embracing 49th position in the Worlds Biodiversity Index [1] . For richness of flowering plant species, Nepal represents 27th position in the world and 10th in Asia. At present, subsequent growing developmental activities and continuous pressures on forest resources cause rapid depletion and degradation of the resources. Forest and vegetation of particular ecosystem generally influenced by the external factors especially the man made development activities.

According to Clements, 1916 [2] , Braun-Banquet, 1932 [3] and Odum, 1971 [4] , vegetation is composed of certain distinct and fairly discrete plant communities. Odum 1971, further elaborate that the communities have a degree of internal organization which jointly modifies the environment with sharp delimitation from other communities.

The external environmental factors of disturbance suddenly change the composition of plant structures. The present vegetation composition of a particular ecosystem reflects the site conditions and disturbances over the time. To estimate environmental change at a given site with reference to different current vegetation comprising pristine or potential natural vegetation, a hemeroby concept was developed [5] -[8] . Because of the complex and nonlinear nature of ecosystems and unique ecological histories, that method is flawed as one cannot detect a pristine ecosystem in this changing world. Therefore, Reif, 2000 [9] suggested that the vegetation completely “natural” and pristine as well “potential natural” is only hypothetical.

Furthermore, as the species number found depends on the plot size studied (i.e. species-area relationship); the method cannot be used for cross scale evaluation. According to Karki, 1991 [10] , Chaudhary and Kunwar, 2002 [11] , human impact is the major cause leading varying degrees of biodiversity reduction in most of the forested areas in Nepal. For the effective conservation of such disturbed forest, it is important to understand the composition of the particular forest, effects of past disturbances, and the present impact of neighboring land use [12] ). It is essential to study the phytosociological structure of such disturbed Himalayan forests to understand the distribution pattern of individual plant species with various girth classes, associations among other species, patterns of dispersion and various indices of diversity [13] .

Several global vegetation mapping systems use temperature and moisture relations as predictors for vegetation types occurring in different areas [14] [15] . Similarly, based on temperature, moisture and rainfall, Nepal’s forest and vegetation is classified into tropical, subtropical, temperate, sub alpine and alpine [16] [17] .

Humankind development activities entail a change in land use, biodiversity and habitats, running the risk of potential destruction, degradation and fragmentation of natural habitats. Potential repercussions that could occur during construction activities can have temporary or permanent negative impacts on biodiversity and habitats with different intensity, magnitude and size depending on location, ecosystem, location and site size. The potential impact is largely depending on specific habitat conditions, species and the level of awareness of the people surrounding the natural environment. To protect and restore forest resources an integrated assessment tool is necessary to support decision making towards human impacts on forest biodiversity and their use [18] . To ensure that potential adverse impact of developments have been anticipated, addressed and integrated into decision making process so that the mitigation hierarchy be rightly applied [19] .

Government of Nepal has applied EIA since 1993 with formulation of Environmental Impact Assessment Guideline and formally after endorsement of Environmental Protection Act and its Regulation 1997. Accordingly, EIA study suggested implementation of mitigation measures for impact area of upper bhotekoshi hydropower project. The comparison of data since 1995 feasibility study, 1997 EIA study and EIA monitoring period from 1998-2002 to this study analyzed variation in species composition and distribution. The existing forests of the study areas fulfill daily demand of firewood, litter, fodder and timber to support the livelihoods of rural communities, but similar other activities face pressure like clearance for agriculture, browsing by livestock, human-set fires, timber logging, and fuel wood extraction. The temperate forest and vegetation of the study area comprised with lower temperate mixed broad-leaved forest, riverine forests with association of Tona, Albizzia and Bombax and upper temperate mixed broad-leaved forest (Quercus-Rhododendron-Tsuga forest). Later on the study site was selected for planned development activities in and around of the forest areas. Previous studies experiencing high rates of forest loss and degradation as a result of over-exploitation and conversion of forest to other land uses in many developing countries [20] -[22] .

Development activities cause impacts in the ecological processes, both at the landscape scale and the scale of individual forest patches which influence species composition and habitat characteristics at different scales. Restoration of such disturbed ecosystem can be achieved through establishment of native tree species including artificial establishment and/or encouragement of natural regeneration, in a wide range of site conditions (Newton et al. 2009). These restoration practices of forests take a great deal of time to recover following disturbance. Whereas, total stem number, basal area, or leaf area index rapidly recover the structural characteristics and late- successional species composition or the number of large trees for variables characterizing old-growth conditions require a timescale of centuries to re-establish [23] -[26] .

This study relates the impacts and changing pattern of forest and vegetation during the implementation and operation of the development activities. The collected ecological data in phased wise manner and different time period are valuable for reconstructing early environmental and vegetation community conditions and examination of changes towards vegetation communities and disturbance regimes. The data’s collected and experimentally calculated over decadal and longer temporal scales were free from error.

The study area lies between 27˚54'87"N latitude and 85˚55'51"E longitude along the Botekoshi River within the Tatopani and Phulpingkatti Villages Development Committees (VCDs) of Sindhupalchowlk district, Nepal (Figure 1). The Bhotekoshi River originates from the Tibet Autonomous region of China and set steep across the high Himalayan zone with extreme steeps slopes, unique vegetation cover and narrow valleys. Along the run of the river Bhotekoshi, dam and powerhouse sites of upper bhotekoshi hydropower Project (35 MW) are located within an elevation range of 1440 m and 1285 m asl. However, in the closer surrounding areas of the Bhotekoshi project site, altitude varies from about 1250 m to 3500 m. In the study area and its surroundings, air temperature rises usually during the pre-monsoon period from February to May and decreases during post monsoon period from October to January, respectively. The mean annual precipitation in the study site and its surrounding area vary from 3000 mm to 3500 mm, of which 2500 mm to 3000 mm occur during monsoon.

The proposed study area Botekoshi River basin was described rich forest and vegetation except on steep slope east to Larcha, across the River (EIA study of Botekoshi hydropower project, IUCN 1995 [27] ). The study identified total 11,345 ha forest area was recorded of two VDCs (6407 ha in Phulpingkatti, and 4938 ha in Tatopani VDC) of project influence area. The grasslands comprise 725 ha at Phulpingcutti VDC and 1762 ha at Tatopani VDC respectively. During EIA study Larcha forest up along the Bhairabkunda khola recorded high species diversity, followed by Pansherpu forests. The Larcha and Pansherpu forests are on north slopes, and moist indicate higher number of species. However, Khajilung community forest located within the steep west facing slope reported lower number of species.

The lower temperate mixed broad-leaved forest along the Bhotekoshi river basin recorded dominant evergreen laurels comprising species of Actinodaphne anguistifolia, Persea ghamblei, Litsea elongeta, Neolitsea spp, Cinnamomoum spp and Dodecadenia spp with other associated species in the forest species of Macarange, Leucosceptrum, Michillia spp, Acer, Dynplocos, Caryoteris and Measa sps. Along the Bairabkunda Khola, above Larcha comprised degraded riverine forests. This forest dominated by the species of Albiizzia, Bombex, Macarange and Alnus spp towards the lower part. As one ascends the Bairabkunda Khola, again the lower temperature mixed broad leaved forest with evergreen laurels were reported. Species of Wendlandia, Enelhardia, Michelia, Caryoptries and Measa were reported as major associate species in this forest. These characteristics features of forest and vegetation studied in pre and post periods of EIA surroundings of upper Bhotekoshi hydropower project area.

For this study, two types of forest, natural and planted or regenerated forest and vegetation (disturbed slopes by the projects) were selected. The natural forest comprises community forest determined as influence zone of the project in EIA study. The planted forests are the disturbed slope of the study area with adoption of the mitigation

measures. To enumerate and identify floristic composition, community sampling units were established. Quadrate, transect and point sampling methods were used with the size of 10 × 10 m² for regeneration or planted area and 20 × 20 m² for natural forest areas. Several blocks or squares (quadrates) with definite size were established in the natural and project disturbed area to identify total number of trees, shape and size as described by Mueller-Dombois and Ellenberg, 1974 [28] . The Spatial data layers like boundary, drainage pattern, contours (altitude, slope and aspect), and vegetation types were extracted from topo sheet of the project area, at the scale of 1:50,000 (Figure 1).

Suunto Hypsometer was used for measuring height of the trees. Likewise, for measuring diameter and circumferences, instruments like Caliper, Finnish Caliper and measuring tape were employed. For McHarg overlays, Geographical Information Systems (GIS), GPS was used. The diameter was measured at 1.30 m aboveground. In case of normal trees, measurement was done horizontally and strait across the stem for leaning trees. Likewise for forking trees, forks above 1.30 m were taken into account as two trees.

The transect stands of an area of 100 m² size (0.01 hectare), having 10 m length and breadth each, were fixed by measuring tape. Planted area was estimated dividing the reforested area in 10 ha blocks (200 × 500 m). Planted area less than 10 ha was divided in 1 ha block (100 m × 100 m). Similarly, in natural forests around at dame site, adit a, adit b, and powerhouse area, 20 × 20 m² quadrate was established. Trees with girth exceeding 10 cm diameter at breast height (dbh, at 1.37 m above the ground) were measured. The height of standing trees was measured by means of clinometers. Finally, vegetation analysis was done by adopting releve analysis approach (M. Dombosis and Ellenberg, 1974). The plant species of all growth forms within each quadrate were enumerated by using a simple matrix. The diameter at breast height and height of each trees including cut stumps, having more than 10 cm circumference were measured by using measuring tape and calibrated 1 m long pole, respectively.

Density, frequency, basal area and their relative values of tree species were calculated following Mueller-Dombois and Ellenberg, 1974. Botanical name and author citation were written as per Department of Plant Resources 2000 [29] . In addition to qualitative data regarding community forests, interviews and group discussions were conducted. In order to assess the general condition and vegetation structure of the forest, a density-diameter histogram was developed.

The species area curve of each community forests was calculated by randomly adding up the number of tree species in each quadrate. “S”, or species richness, was determined following Whittaker, 1976 [30] by tabulating the number of woody species in each plot. Shannon-Weiner’s diversity index “H” (Shannon and Weiner [31] ), concentration of dominance “D” (Simpson [32] ) and Hill diversity numbers N₀, N₁ and N₂ (Hill [33] ) were computed.

Simpson’s index “D” was calculated using the formula

where, is the relative density.

Shannon-Weiner’s diversity index “H” was calculated using the formula

where, represents the proportional abundance of the species in the community.

Hill diversity indices were calculated using the following formulae:

Number 0: N₀ = S, where S is the total number of species

Number 1: N₁ = eH, where “H” is the Shannon’s index (3)

Number 2: N₂ = 1/D, where “D” is Simpson’s index

Composition and distribution pattern of vegetation and forest types and change of environmental gradients in the project area was studied with extensive literature [34] and collection/measurement of field data’s. The density of tree per ha, basal area and volume estimation of trees were calculated by using the following formulas [35] .

where, V = Volume, BA = Basal Area (m²), h = Height (m).

Species area curve estimate

The plots of the studied area were examined estimating Species Area Curve with cumulative sampling area (x-axis) versus the total number of species found in the quadrate samplings (y-axis). The species area curve was used as a log-log relationship [36] .

where; S = Number of species (= species richness); A = Area sampled; a = y-intercept of the regression.

The environmental impacts in the study area observed at range of spatial and temporal scales. Temporal fluctuations of environmental factors change biodiversity constantly over different scales. Natural population and communities of taxa turnover means origination and extinction predominantly in global scales, and colonization and disappearance at local to continental scale [38] .

Source: EIA Study 1995, IUCN Nepal.

Structuring of the forest communities is influence by the disturbance, as an important factor [39] and different types and level of disturbances have a differential impact on forest communities [40] . Human pressures with development activities and other biotic components are detrimental for the vegetation structure of forests. The upper Bhotekoshi hydropower project area has recorded high species diversity before the project construction but this study shows that the decreasing trend of species composition and diversity of plant species over long temporal scales (Table 13). The study area was modified by the hydropower development activities which might become a greater cause of species extinction and direct habitat destruction.

According to the pervious study, (EIA of UBHP, 1995), Alnus nepalensis was recorded with the highest relative dominance followed by Pinus roxburgii and Litsea chartacea on the basis of the basal area. Pinus wallichiana was recorded with the highest importance value which may be attributed to its pure stand in a localized area. Likewise, importance value of Alnus nepalensis and Quercus leucotrichophora were also shown exceeding the value of 26, while Lyonia ovlifolia had the lowest importance value. 41.57 m³ of total standing volume was calculated for all species in the sample plots. In terms of species, Alnus nepalensis reported covering 9m³ followed by Pinus roxburgii (6 m³). The sample plot 3 (Forest North to Larcha) reported with the highest timber volume (nearly 13 m³) followed by plot 1 (forest below Panserpu village).

In this study, highest basal area (5.27 m²) and volume (62.01 m³) of Pinus wallichiana was found in plot 4 (Thulo Ban CF) followed by Schima wallichii in plot 3 (Khajilung CF). Likewise, Litsea elongeta in plot 2 (Bhairabkunda) calculated basal area of 4.63 m² and timber volume of 16.77 m³ which is followed by Actinodaphne anguistifolia, Toona cialita and Rhus javanica in plot 1 (Panserpu forest). The plot 2 has shown the lowest calculated BA and timber volume however 1995 showed the highest timber volume. Thus, the study concludes that the Larcha forest is the most disturbed forest of the project area.

According to EIA monitoring report, 150 trees at headwork and a tree of Michelia champaca at audit were cleared and Artemisia vulgaris, Arundinaria intermedia and Alnus nepalensis proposed as a compensatory measures for reforestation. However, the present study assessed abundant number of regenerated and planted individuals the species composition is found in decreasing trend in natural forests. Besides that, the regenerated area is found dominated by unwanted species of herbs and shrubs like Eupatorium adennophorum, Cyathula capitata and Artimesia valguris.

Beier et al., 2008 [41] , found no consistent diversity overall pattern of climate change-induced decline across climate drivers, scales, or ecosystem types. Dullinger et al., 2012 [42] argue that the reduction in diversity, often caused by range contractions driving long-term extinctions due to significant climatic effect. As the study area belongs to the temperate region, an exception to this pattern is expected at high elevations, where temperature limits to many species [43] , so diversity should respond favorably to warming [44] .

Floristic composition and species diversity in pervious and this study revealed changes on species, genera and family at the ratio of 2:1:2. Similarly, Simpsons index (D), Shannon’s Diversity (H) and Species equitability (E) are also found decreasing at the ratio of −0.014:40.0419:007 (Figure 4).

The study concludes that the species diversity in the study area is in declining trend with decreased species composition in both natural and regenerated forests due to intensive pressure. Abundance of Alnus nepalensis with high relative dominance followed by Pinus roxburgii and Litsea chartacea in 1995 is replaced by Litsea elongeta followed by Actinodaphne anguistifolia, Toona cialita and Rhus javanica in this study which is the result of long-term interactions between the vegetation and site factors over time and space.

The disturbed forest slopes were found with low species diversity and abundance of single species. Moreover, growth of unwanted or alien species found spreading over the regenerated area. An ineffective implementation of policies, slight overlook of the impacts and prediction methods, absence of major changes in policy and human behavior, effects on the environment will continue to alter biodiversity, change land-use and increase atmospheric CO₂. Thus, effective management of forest with intensive control on human disturbance could protect the natural integrity of forest ecosystem.

RameshPrasad Bhatt,SaralaBhatt, (2016) Floristic Composition and Change in Species Diversity over Long Temporal Scales in Upper Bhotekoshi Hydropower Project Area in Nepal. American Journal of Plant Sciences,07,28-47. doi: 10.4236/ajps.2016.71004