Ecosystem reconstruction through 'taungya' plantations following commercial logging of a dry, mixed deciduous forest in Darjeeling Himalaya.

摘要

In the Darjeeling Himalayas of West Bengal, after commercial logging, natural forest is converted into taungya plantations. Under the taungya system, choice species of high timber value are planted following slash-burning on clearcut forest lands, and agricultural crops are raised in the interplanting spaces for the first 2 consecutive years. Regeneration is allowed along with the growth of planted species after abandoning the crop cultivation. This study examines ecosystem recovery 35 yr after theconversion of a dry, mixed deciduous forest into a taungya plantation. Planted tree species were mainly Tectona grandis (as stumps) and Shorea robusta (as seed), with various associate species, and sometimes Michelia champaca and Mangifera indica. Agricultural crops were maize, millet and vegetables. Only 28 out of 87 species in natural forest regenerated in the ?0-cm cbh (circumference at breast height) class of individuals. The loss of species was independent of abundance in the community; not onlyrare, but also common, species of natural forest were lost in the taungya plantation. Mature forest specialists suffered the greatest loss, and open-habitat specialists increased. The introduced species Tectona grandis dominated in terms of abundance, use of vertical space, and total ground coverage. Shorea robusta was codominant due to its coppicing ability. Prospects for recovery of the lost species are poor because juvenile populations in the regeneration layer (comprising individuals <10-cm cbh and>30-cm height) are either absent or very small. The study concludes that conversion of natural forest into taungya plantations dramatically alters the landscape, interrupts recovering ecosystem structure and causes considerable loss of species.