Vegetation. None of Goa's original vegetation remains untouched. The mangrove forests of the tidal marshes have been steadily eroded by the need to drain land for agriculture, while the estuarine waters have been increasingly polluted by mining activity. The most important mangroves are found today in the Mandovi-Zuari estuary, with minor forests remaining along the Chapora, Talpona, Galgibag and Tiracol estuaries.
Inland, the tropical rain forests which once covered both the Ghats and the lowland have been steadily reduced by clearance for farming and by cutting for timber. Two types of deciduous tree were once particularly common across peninsular India and even today they remain important. Sal (Shorea robusla), now found mainly in eastern India, and teak (Tectona grandis). Most teak today has been planted. Both are resistant to burning, which helped to protect them where man used fire as a means of clearing the forest, common along the Western Ghat ranges from north to south.
The most striking vegetation contrasts are provided by the regular succession of laterite plateaus and riverine valleys. The valley sides are still densely covered in cultivated trees - the tall and usually gently curving coconut palms and the equally tall but slender and arrow-straight areca palms, interspersed by a dense and rich cover of valuable nut and fruit trees.
The most widespread - and economically the most important - is the shiny-leaved cashew, introduced originally from South America, with its distinctive almost pear-shaped fruit and highly valued nut. These drought-tolerant trees sprawl across the thin soils of the laterite pavements and down into the richer more fertile soils of the valleys, giving Goa one of its most important sources of income.