Rubber tapping is not damaging to the forest, as it does not require the tree to be cut down in order for the latex to be extracted. Jungle rubber is essentially old secondary forest, strongly resembling the primary forest. Its species' richness is about half that of the primary forest. Michon and de Foresta (1994) found that sample jungle rubber sites contained 92 tree species, 97 lianas, and 28 epiphytes compared with 171, 89, and 63, respectively, in the primary forest, and compared with 1, 1, and 2 in monoculture estates. Thiollay (1995) estimated that jungle rubber supports about 137 bird species, against 241 in the primary forest itself. Jungle rubber is expected to resemble primary forest in its hydrological functions. Mono culture rubber tree plantations have far less of an environmental impact than other crops, such as coffee or especially oil palm.