Comparative Study of Understory Between Exotic Monoculture Plantation (Acacia Sp.) and Adjacent Natural Sal (Shorea Robusta) Forest

To achieve forest management goal it is important to maintain biodiversity. This paper compares understory plant species diversity between exotic monoculture plantation (Acacia auriculiformis) and adjacent natural sal (Shorea robusta) forest. A total of 35 sample plots were taken by random sampling from six patches of adjacent natural sal forest and exotic monoculture plantation. Shannon-Wiener diversity index, species richness and evenness were calculated and compared. Result revealed that, a total of 2,218 plants of 42 species were recorded in natural sal (Shorea robusta) forest. Dominant families were Apocynaceae and Verbanaceae, having three species in each family. Shannon-Wiener diversity index was 2.1 and mean species richness was 14.4. On the contrary, 2,827 plants were found from 15 species in exotic monoculture (Acacia auriculiformis) plantation study area. Dominant family was Leguminosae family. Three species were found under Leguminosae family. Shannon-Wiener diversity index was 0.86 and mean species richness was 4.47. Therefore, Shannon diversity index and richness were significantly higher in natural sal forest as compared to exotic monoculture plantation. Species evenness of natural sal forest was 0.8 and 0.6 for monoculture plantation which indicates less equitable distribution of understory vegetation in monoculture than adjacent natural sal forest. With regard to herb species, evenness was significantly lower in monoculture plantation (0.03) as compared to natural sal forest (0.52). There was no equitable distribution for the herb species under monoculture plantation. Jaccard’s similarity index showed that 36% shrub species and 30% of herb species were same in exotic monoculture plantation area and adjacent natural sal forest.