1012-B1

Impact of Human Settlements on Forest Structure and Composition in Kudremukh National Park, Western Ghats, South India

R. K. Somashekar^[1], M. Bunty Raj and B.C. Nagaraja

Abstract

A study was carried out in Kudremukh National Park, Southern Western Ghats of India to assess the changes in vegetation structure and floristic composition along the tribal and non-tribal settlement areas in order to understand the impact of forest use, in comparison with the undisturbed forest in the vicinity. At three sites, a 1 ha plot was set up around the two human settlement areas and one site was demarcated in the undisturbed forest type. The sites were described by the point-centered quarter method to measure the diversity, dominance and Ramakrishnan index of stand quality (RISQ). For this purpose, only tree species of seedling, sapling and mature trees were considered to locate regeneration status of the forest. A total of 46, 49 and 45 plant species were recorded in tribal, non-tribal and undisturbed forest. Shannon-Wiener’s diversity indices for mature trees were 4.17, 4.07 and 3.74 respectively in the three areas. The tribal plots showed slightly higher indices because of concomitant disturbance.

The result is that more light-demanding species have invaded the area. Poeciloneuron indicum, Callophyllum apetalum and Elaeocarpus tuberculatus occupied the top canopy in undisturbed forest, whereas Dimocarpus longon, Holigarna arnottiana, Mimusops elengi, Persea macrantha and Aglaia annamalayana were the common forms in both tribal and non-tribal plots. Stem densities in tribal plot were higher (638 trees ha-1) than in non-tribal (601 trees ha-1). The respective value for undisturbed forest however, remained much higher (440 trees ha-1). The changes in species composition observed in the locality are largely due to transition in vegetation types influenced by extraction of green foliage, firewood, timber and other forest products for domestic use by the inhabitants of the area. Because of this, policy-makers have to think about rehabilitation of these settlements outside the park to conserve the biodiversity of the area.

1. Introduction

The rain forests of the Western Ghats mountain range have been the subject of many studies of which the most comprehensive is that of Pascal [5]. These forests are unique because of their geographical location, stable geological history, equable climate, heavy rainfall and good soil conditions that support a variety of tropical forest ecosystems. During the last few decades these forests have been subjected to various human pressures generated by human activities in agriculture, construction of hydroelectric projects, raising monoculture plantations, logging and a host of other developmental projects. Needless to add that all these activities led to a steady depletion of forest areas.

The study area ‘Karchar’ locates in the Kudrermukh National Park, in Western Ghats of South India and has been the home of ‘Gowdlu tribe’. They are living in this area for centuries, practicing shifting agriculture, hunting wildlife and gathering a wide variety of products from the wild habitats. Whereas the non-tribal communities are more dependent on forest for sustenance and have converted part of forest area into Areca plantation. As such it was felt necessary to study the impact of tribal and non-tribal settlement’s forest use patterns on forest structure and composition.

2. Study area and climate

The study area comes within Kudremukh National Park (KNP), lies in the Western Ghats of Karnataka State (South India). This has been recognised as eco-sensitive area and several conservation efforts are underway. It covers an area of 600.34 km² and lies approximately between 13°1´ to 13(29´ N latitude and 75(0´ to 75(30´ E longitude. The soils are mainly Inceptisols and Ultisols (Bourgeon [6]). The Kudremukh-Gangamoola belt of the Precambrian Dharwar Schist comprises hornblende schists, amphiboles and thick beds of magnetite-quartzites. The climate is typical tropical with an annual rainfall ranging from 600-800 cm. The average rainfall for the past two decades has exceeded 776 cm, in principle spreads over June and Sept. January to March is relatively dry. The mean monthly maximum temperature during monsoon at the nearby locality Sringeri ranged between 21((July) and 34.1°C (April) and the mean daily minimum temperature varied between 12.2°C (January) and 18.8°C (May).

3. Methods

3.1. Phytosociological analysis of tree species

Two plots were selected that represented the tribal and non-tribal settlements. One plot, selected 6km away from the settlements had served as a benchmark. Quantitative sampling of vegetation was carried out separately among the categories of trees, saplings and seedlings adopting Point-centered quarter method of Cottam and Curtis [7]. Fifty-one points at more than 10m intervals were randomly located along the three experimental forest plots. At each point, in each of the four quadrants around (NE, SE, SW and NW), the nearest plant of each categories were located, identified; their distances from the point on ground, girth at breast height (for trees, greater than 30.1cm, and for saplings, between 10.1cm and 30.0cm, both at 1.37m above ground level or at 2-2.5m in case of buttressed individuals), and collar diameter (for seedlings, girth below 10cm) were recorded. The data on vegetation were analysed for relative frequency, density and dominance, and their sum represented importance value index (IVI) of the species (Kershaw [8]).

3.2. Determination of Stand Quality

Using the available literature, (Gamble [11], Chandrashekaran [12], Rai[13], Rai and Procter[14], Pascal [5], Chandrashekara and Ramakrishnan [15]) species encountered in the three plots were categorized into three groups, each group is assigned with a numerical value, viz., Pioneer index 1 (primary species) for the group requiring a small gap for regeneration; Pioneer index 2 (early secondary) for the species whose seedlings established in small gaps but need small to medium sized gaps to grow; and Pioneer index 3 (late secondary) for the group of strong light demanders. The procedure described by Whitmore[16] and modified by Chandrashekara [17] was adopted for this purpose: RISQ = S {(n_i x pioneer index)/N}

4. Results

Total species in Tribal plot was 46; with Lophopetalum wightianum (85.79 IVI) as the dominant forms at mature tree stage. Total species in Non-tribal plot was 49; with dominance of Aglaia anamallayana (47.67 IVI). Poeciloneuron indicum was abundant in undisturbed forest at all stages (Table 1). The diversity indexes value of mature tree (gbh > 30.1cm) was more in tribal and non-tribal forest (Table 2).

Table 1 Pioneer index (PI) and importance value index of tree species (mature tree phage only) in Kudremudh National Park.

On the other hand, in respect of seedlings, higher values were recorded in undisturbed forest. The average value of Simpson’s Index is more in undisturbed forest followed by tribal and non-tribal plots (Table 2). Besides value for stem density of sapling stage in tribal and non-tribal were significantly low. Also values for seedling density in tribal and non-tribal were significantly high. The per cent of primary species (shade bearer) were more in undisturbed forest in both sapling and seedling stage (Table 3), while per cent of light demanding tree species were more in tribal and non-tribal forest.

In undisturbed forest primary tree species accounted for 81.86% and occupied a basal area of 86.83%, while such trends did not exist in tribal forest. Here primary tree species accounted for 49.5% and occupies a basal area of 84.63%.

RISQ value for mature trees, saplings and seedlings stages ranged between 1.163 and 1.191 revealing a low value. In all the categories, RISQ values in tribal and non-tribal forest ranged between 1.406 and 2.221 with highest value in sapling stage of non-tribal forest.

Discussion

The influence of human activities on natural forest has been profound particularly on the biodiversity of forest ecosystem (Sayer and Whitmore [18]). This in turn changes the quality of stand, microclimate, nutrient cycling and composition of forest species (Kouki [19], Kappelle et al [20]).

One of the characteristic features of the humid tropical forest ecosystem is its high species richness (Parsons and Cameron [21]). Korning, et. al., [22] found about 105 species of about 200 trees sampled by the point-centered quarter method in Ecuador forest. In general, the number is known to vary between 22-223/ha in tropical evergreen forest (Whitemore [23]). The number recorded during the course of present study (46-49 species) is comparable to that of Swamy and Proctor report [24] in the surrounding forest. The range of stem density in the low and Mid elevation evergreen forest of Western Ghats of India, at sapling and mature trees phase together varied from 663 ha^-1 to 3341 ha^-1 (Pascal [5], Chandraskekara and Ramakrishnan [15]). The stem density values in our studies also fell within this range. A lower canopy cover causes a higher light transmittance, which stimulates germination and rapid growth of pioneer species (Wales [25]; Levenson, [26]; Ranney et al., [27]; Lopez de Casenave et al., [28]; Jose et al., [29]). A similar situation existed in both tribal and non-tribal plots.

The human inhabitants require saplings (20-30cm in gbh) for fencing (protection from wildlife), roofing, preparing agricultural implements, firewood, green foliage (for Areca and other cash crops), etc. Obviously the density of saplings was comparatively less in the tribal and non-tribal than undisturbed forest. The species that are normally used for mulching and livestock bedding are Symplocos racemosa, Nothopegia beddomii, Holigarna nigra, Syzygium gardeneri, etc.

Although light demanding early secondary seedlings are regenerating (1.2%) in undisturbed forest, they cannot establish fully as mature trees due to incessant shade. Primack et. al[30] and Silva et. al [31] opined that under such conditions the proportion of late secondary species decreases in the seedling stage and their growth is likely to decline after some years.

Values for light demanding species were more in tribal forest. This could be attributed to the vegetation changes that occurred following extensive canopy disturbance both in the past and recent past. A similar feature has been recorded in Amazonian Forest (Magnusson et al, [32]) and Kibale National Park, Uganda (Chapman and Chapman [33]), where creation of larger gap facilitated the light demanding species to colonize.

The difference in basal area between tribal and non-tribal forest to a large extent accounted for occurrence of single very large individuals of primary species such as Lophopetalum wightianum, Elaeocarpus tuberculatus, Syzygium cumini, etc, with gbh greater than 3 meters.

The mature tree species diversity index in the tribal and non-tribal is 4.15 and 4.07 respectively. These values are lower than those recorded in tropical rainforest of Barro Colorado Island (4.8; Knight [34]) and in Silent Valley, India (4.89; Singh et al., [35]), but higher than those recorded in Kerekatte forest near Sringeri area, of the neighborhood locality (3.94; Swamy and Proctor [25]). Significantly higher diversity values were observed for seedling phase in undisturbed forest, indicating an increase in regeneration phase.

The diversity indices of seedling stage were comparatively less in tribal and non-tribal forest, which indicated low regeneration phase. This could be attributed to activities like leaf litter collection, livestock grazing etc, that together disturbed the regeneration of primary forest tree species.

Values of dominance index of seedlings in tribal plots were more than non-tribal forest. This was due to the establishment of light demanding species like Aporosa lindlyana, Carallia brachiata, Caryota urenes, Mellotus phillipensis, Callicarpa tomentosa in larger canopy gaps. In undisturbed forest, these species were comparatively less abundant in all stages.

The two experimental plots showed higher disturbance index, as they are located within a gap of 1-2 km around human settlements. Higher RISQ values for saplings and seedlings than the mature trees also indicate repeated disturbance or failure of shade-bearers to establish (Chandrashekara and Sankar [36]).

Conclusions

It can be concluded that the forest ecosystem at both the settlement areas were supported higher plant diversity than undisturbed forest, with less proportion of primary forest species. It clearly indicates that human settlements nearer to evergreen forests have a direct impact on regeneration of sensitive species. However research must be expanded and strengthened to improve our understanding of biodiversity and its potential role in building sustainable human societies. At this stage we need to understand more about how, why and where human activities bring about long-term changes in biodiversity, in order to provide accurate information to decision makers. It is recommended that primary forest species like Hopea parviflora, Myristica dactyloides, Garcinia gummi-gutta etc, should be planted in the settlement. This would help forest managers to maintain stability of ecosystem in terms of regeneration and nutrient cycling.

Acknowledgement

The authors thanks the Karnataka Forest Department for granting permission to carry out work in Kudremukh National Park and their invaluable help in site selection and field data collection.

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