Invasive Prosopis juliflora replacing the Native Floral Community over three decades: a case study of a World Heritage Site, Keoladeo National Park, India

A biodiversity assessment of any region is a fundamental necessity towards implementing an efficient conservation action plan. The alteration of habitat and vegetation composition through the successful invasion of non-indigenous species can be a serious management issue. The most prominent threat resulting in a rapid decline of native plant communities is the competition and indirect effects of alien plant species. In this study, we aim to assess the spread of invasive Prosopis juliflora and its consequences on the native flora over a span of three decades in Keoladeo National Park, India. The community structure was assessed by gridding the entire park with quadrates laid systematically. We recorded a total of 7179 individual plants, of which 3667 individuals were woody trees representing 26 species and 3512 individuals were shrubs belonging to 25 species. The invasive P. juliflora represented a maximum number of individuals among both trees (n = 957) and shrubs (n = 1560), and appears to be the dominant shrub species (IVI-74.96; SDI-0.14). The spatial comparison of species dominance (1985–2015) showed a significant increase in the dominance of P. juliflora (Z = 5.14, p < 0.00), replacing the dominant native species, including Acacia nilotica, Mitragyna parvifolia, Prosopis cineraria, Salvadora oleoides, Salvadora persica and Ziziphus mauritiana. The classified images also confirm an increase in spatial extent of both pure stands of invasive P. juliflora (from 4.02 to 16.46%) and open scrub dominant with P. juliflora thickets (from 2.16 to 50.94%). The article also discusses possible reasons of the high invasibility of P. juliflora, particularly its high allelopathic (inhibition) effect and highlights conservation management issues in the region. These issues deserve careful consideration to help safeguard the entire ecosystem of this world heritage site.