Most of the biodiversity is concentrated and protected in the Western Ghats. Three quarters of the land area of Kerala was under thick forest up to 18th century. s of 2004[ [update]], over 25% of India's 15,000 plant species are in Kerala. Out of the 4,000 flowering plant species; 1,272 of which are endemic to Kerala, 900 are medicinal, and 159 are threatened.: Its 9,400 km2 of forests include tropical wet evergreen and semi-evergreen forests (lower and middle elevations—3,470 km2), tropical moist and dry deciduous forests (mid-elevations—4,100 km2 and 100 km2, respectively), and montane subtropical and temperate (shola) forests (highest elevations—100 km2). Altogether, 24% of Kerala is forested.: Three of the world's Ramsar Convention listed wetlands—Lake Sasthamkotta, Ashtamudi Lake and the Vembanad-Kol wetlands—are in Kerala, as well as 1455.4 km2 of the vast Nilgiri Biosphere Reserve. Subjected to extensive clearing for cultivation in the 20th century,: much of the remaining forest cover is now protected from clearfelling. Eastern Kerala's windward mountains shelter tropical moist forests and tropical dry forests, which are common in the Western Ghats. The world's oldest teak plantation 'Conolly's Plot' is in Nilambur.