Human Ecology & its Impact on Biodiversity

The Western Ghats first came under human influences during the palaeolithic or old stoneage some 12,000 years ago (see Table 1). Stone tools used by palaeolithic people have been excavated in the river valleys of Palakkad, Mallapuram and Dakshina Kannada districts in the Western Ghats. Elsewhere, palaeolithic artifacts have been found in and around Mysore, Chickmagalur and Shimoga districts of western Karnataka.

Table 1: Chronology of human ecological events in the Western Ghats

Years before present Era Ecological Events
> 12,000
12,000-5,000
Palaeolithic
Mesolithic
Hunting and gathering
Hunting-gathering, use of fire, forest decline and increase in savanna.
5,000-3,000 Neolithic Agri-pastoralism in the Deccan, vegetation change in the Nilgiris, coastal deforestation, use of iron, Harappan and Deccan immigrants into the Western Ghats.
3,000-1,000 Megalithic Agri-pastoralism, Western Ghats neoliths, shifting cultivation, decline in primary forests, sacred groves, extraction of spices and timber.
1,000-200

200-100

100 -
Historical European trade, extraction of timber for ship building, increase in spice trade, organised agriculture, shifting cultivation continues
Increase timber harvest, state forestry begins, shifting cultivation regulated, natural teak depleted, Plantation initiated,
Timber harvest intensified, timber stocks depleted, Conservation by state, mines, dams, townships.

Mesolithic sites (12,000-5000 ybp) have been discovered around the river Mandovi in Goa. Charcoal beds dating back to 5000 ybp in Tenmalai (southern Western Ghats) suggest that humans burnt forests around this time. During the new stoneage (5000-3000 ybp) there were domesticated cattle, sheep and goats in and around the Western Ghats. Whereas rainfed crops including millets and horse gram were cultivated, in Maharashtra the Jorwe people cultivated wet rice. Shifting cultivation was apparently the form of agriculture that predominated the Western Ghats till recently. Crops such as Eleucine coracana, Cajanus cajan, Ricinus communis, Panicum sumatrense, etc were mainly cultivated in this traditional system of agriculture.

Human influences have had varied impacts on the biodiversity of the Western Ghats. History of species extinctions in the Western Ghats was certainly coincident with the climatic and human histories. Extended arid periods and human interference starting 12,000 years before present, led to slow but extensive transformation of habitats in and around the Western Ghats. Unique landscape elements such as the Myristica swamps gave way to cultivation of rice. Along with the swamps, trees such as Myristica fatua var magnifica, Gymnacranthera carnatica, Semecarpus auriculata and the palm Pinanga dicksonii, disappeared locally.

The use of fire to clear forests for cultivation has had a major influence on the forests of the Western Ghats. The spread of bamboo and deciduous trees in the region would have been aided by this human practice. Widespread occurrence of fire tolerant trees such as Acacia catechu, Careya arborea, Dalbergia latifolia, Dillenia pentagyna, Schleichera oleosa, Tectona grandis, Terminalia spp and Xylia xylocarpa suggests this.

Hill agroecosystems in the Western Ghats are today dominated by estates - chiefly of tea, coffee, rubber and monocultures of various tree species, including the oil palm, that was introduced lately. Available estimates indicate that above an altitude of 1500 m in the Western Ghats, there are 750 sq km of tea plantations. A total of not less that 1500 sq km are under coffee and 825 sq km under cardamom. It has also been highlighted that the Nilgiri district with a total area of 2549 sq km has around 1000 sq km under various forms of cultivation.

Casuarina plantations first appeared in Uttara Kannada district between 1868 and 1869. Till then the forest plantations were of native species. Teak was first raised as monocultures in 1840. The first teak plantation in Kerala was established in Nilambur in 1844. Over the years, eucalypts, cinchona, wattle, rubber, clove, etc, have displaced extensive patches of natural forests throughout the Western Ghats.

The impact of monocultures on the biodiversity of the Western Ghats has been little understood. In the Uttara Kannada district, monocultures were found to support as diverse a community of birds as natural forests. The bird assemblage may however include a greater number of generalist species than the natural forests. As mentioned above, teak when raised as a monoculture fails to attract hole-nesting birds.

Apart from the introduction of commercially important plants, there have been invasions by a number of aggressive alien plant species. The British Colonists spread over most of the Western Ghats in the late seventeen hundreds and early eighteen hundreds. The Nilgiris were colonised only in 1813 almost 2000 years after the Todas did. Much of the exotic flora, especially those of temperate origin, came in after this. A large number of ornamental plants of temperate origin have since run wild in the higher elevations of the Western Ghats. For instance, in Palani Hills alone there are 600 such species especially, around Kodaikanal. Similarly, 400-500 introduced species of plants have been reported from the Nilgiris.

Important amongst these are Lantana camara (var aculeata), Eupatorium odoratum, Mikania cordata, Parthenium hysterophorus, etc. Wattle (Acacia sp) once introduced for the extraction of tannin in the higher hills is today a major threat to the sholas and grasslands at these altitudes. The impact of these exotic plants has been reason for a lot of debate. Contrary to general predictions, the presence of Lantana camara has not been detrimental to woody plant species diversity in the BR Hills.

In selectively logged evergreen forests, the woody plant species diversity has declined. This has been accompanied by the selective loss of certain plant species of greater economic value and an overall reduction in forest biomass. Other organisms have responded to human disturbance rather differently. Selective logging (consequently lower tree and canopy density) has locally increased the diversity of butterflies, lizards and birds in the Western Ghats. To balance the impacts of human interests with the long-term conservation of biodiversity in the Western Ghats is the greatest future challenge.