Impact of invasive alien Plants on understorey vegetation in Tholpetty range of Wayanad Wildlife Sanctuary

Abstract

A study titled “Impact of invasive alien plants (IAP) on understorey vegetation in Tholpetty Range of Wayanad Wildlife Sanctuary” was undertaken to understand the distribution characteristics of selected invasive alien plant species (IAPS) viz., Lantana camara L., Senna spectabilis (DC.) H.S. Irwin and R.C. Barneby and Chromolaena odorata (L.) R.M. King & H. Robin in the three vegetation types (Plantation, NF, and Vayal) of WS I part of the WWLS. The additional objective was to assess the impact of these IAPS on the native plant communities in these vegetation types. In the WS I area, L. camara invasion was rampant, except in the southern regions. Higher invasion was seen in the Kaimaram and Thirulkunnu forest sections. C. odorata invaded all the four sections viz. Kaimaram, Dasanghatta, Thirulkunnu and Bavali. S. spectabilis invasion was heavy in the Kaimaram section near the boundary of Thirunelli RF, and in the boundaries between Nagarhole TR and Kaimaram section. In all the three vegetation types, the density of Chromolaena was high, while it was lowest for Senna. The density of Chromolaena in NF, Plantation and Vayal was respectively 3734.11 ± 5.65, 8457.64 ± 27.52 and 7761.17 ± 9.74 stems/ha. The density of Lantana in NF, plantation and Vayal was respectively 1061.17 ± 2.75,334.11 ± 1.02and 215.29 ± 0.50stems/ha. The density of Senna in NF, plantation and Vayal was 414.11 ± 1.55, 589 ± 2.67 and 34.11 ± 0.21stems/ha respectively. In the Vayals, Senna invasion, though minimal, could be noticed. Chromolaena had the highest percentage cover in both plantation (24.58 ± 3.06) and Vayal (46.19 ± 4.03). In NF, Lantana (19.46± 3.43) had the highest percentage cover. In all the three vegetation types, Chromolaena had the highest frequency and abundance. Out of the total 140 plant species identified from the WS I region, number of species recorded in each weed category types like L, C, S, LC, CS, LS, LCS and Control were 67, 96, 20, 64, 9, 7, 14 and 113 respectively. Vis-a-vis the impacts of IAPS in NF, highest MSR (Mean Species Richness) was seen in Control (weed-free area), followed by L (Lantana invaded) and C (Chromolaena invaded) regions. The lowest MSR was in LCS (Lantana, Chromolaena, and Senna invaded) and LS (Lantana and Senna invaded) regions. In plantation, highest MSR was seen in Control (weed-free area) and the lowest in L (Lantana invaded) area. In Vayal too, highest MSR was observed in control, followed by C (Chromolaena invaded) and lowest in LC (Lantana and Chromolaena invaded) areas. All three IAPS negatively influenced the native species richness, although no specific declining trend in species richness could be observed. Among the three IAPS, C. odorata had the biggest impact on the species richness of native species in both NF and Vayal. In the plantations, L.camara had the biggest impact on species richness. Canopy openness and percentage cover of IAPS were found to be positively correlated. In NF and Vayal, Lantana showed highest correlation with canopy openness, while in plantation, Chromolaena showed highest correlation with canopy openness. In plots where Senna and Lantana occurred together, plant species richness decreased from 67 to 7. Similarly, when Senna and Chromolaena came together, species richness dropped from 96 to 9. This probably indicates a dominating interference of Senna on the recruitment of native species which needs research attention. Left unmanaged, Senna will soon become a major “biological pollutant” of Wayanad WLS.