PG Thesis
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Item Impact of invasive alien plants on understorey vegetation in Wayanad wildlife sanctuary(Department of Natural Resource Management, Vellanikkara, 2018) Vishnu Chandran, M; Gopakumar, SThe present study “Impact of invasive alien plants (IAP) on understorey vegetation in Wayanad Wildlife Sanctuary” was conducted in three vegetation types (Plantation, NF and Vayal) of WS II part of the sanctuary. The distribution characteristics of selected invasive alien species (IAPS) viz. Lantana camara L., Senna spectabilis (DC.) H.S. Irwin and R.C. Barneby and Chromolaena odorata (L.) R.M. King & H. Rob and the impact of these invasive alien species on the regeneration of other plant communities were studied and compared. L. camara and C. odorata invaded all areas of the sanctuary except in the borders of Kurichiat and Sulthan bathery forest ranges. Lantana invasion was high in the Kurichiat RF (Reserve forest) and Rampur RF. Chromolaena invasion was found to be high in Mavinahalla and Kurichiat RF. In WS II part of the sanctuary, S. spectabilis was mainly distributed along the boundaries of Sulthan bathery and Muthanga ranges. In Muthanga, Senna invasion was extended up to “Kakkapadam” (2.5 km from Muthanga station). Among the IAPS, Chromolaena showed the highest density in all the three vegetation types, while the density of Senna was lowest in all the three vegetation types in WS II area. The density of Chromolaena in plantation and NF was 4943.52 ± 1079.07 and 4996.47 ± 1484.42 respectively. The density of Lantana in plantation and NF was 322.35 ± 88.18 and 85.42 ± 29.55 respectively. The density of Senna in plantation and NF was 63.5 ± 31.66 and 49.74 ± 23.93 respectively. Senna invasion was absent in vayal. Vayal showed highest density of Chromolaena (5810.59 ± 1262.43). Chromolaena had the highest percentage cover in both plantation and vayal. In NF, Lantana has (14.2 ± 2.8) the highest percentage cover. In all the three vegetation types, Chromolaena had the highest frequency and abundance. Among the seven weed category areas identified from the study area, highest MSR (Mean Species Richness) was seen in Control (weed free area), followed by L (Lantana invaded) and LC (Lantana and Chromolaena invaded)regions. The lowest MSR was obtained in S (Senna invaded) and CS (Chromolaena and Senna invaded) regions. All the three IAPS negatively influenced the native species richness. But no specific declining trend in species richness was observed during regression analysis. Results of regression analysis showed that, among the three IAPS, C. odorata had the biggest impact on the species richness of native species. It was followed by L. camara and S. spectabilis. Species richness of each growth form (herb & shrub) declined significantly with increasing Lantana, Chromolaena and Senna cover. In the current study, trees and climbers did not show any significant variation with increasing percentage covers of IAPS. For every 10% increase in percentage cover of C. odorata, two native herb species were observed being removed from the study area. At the same time only one shrub species was removed at every 10% increase in Chromolaena cover. For every 10% increase in Lantana cover, one native herb species was removed from the study area of the sanctuary. The species richness of shrubs also declined due to Lantana invasion. On plotting herb species richness against Senna percentage cover, only four herb species were obtained at 50% Senna cover. On further increase in percentage cover of Senna the herb species richness declined linearly and it was decreased to one at 100% Senna cover. It was also found during the study that, in plots where Senna and Chromolaena occured together, the species richness decreased from 86 to 4. Similarly in plots where Senna occured with Lantana and Chromolaena, species richness declined. This probably indicates a dominating interference of Senna on the recruitment of native species and could be because of the impacts of its larger size, big and wider canopy, competitive reproductive ability, allelopathy and a broad, deeper root system. Out of the 125 plant species identified from the sanctuary, only thirteen were observed from Senna invaded region. But during regression analysis it was found that, among the three IAPS Senna has the least impact on native species richness. This may be due to the fact that compared with Lantana and Chromolaena, the invasion of Senna is restricted to only a small portion of Wayanad WLS. But left uncontrolled Senna will soon become a major threat in Wayanad WLS in the near future.Item Impact of invasive alien Plants on understorey vegetation in Tholpetty range of Wayanad Wildlife Sanctuary(Department of Natural Resource Management, College of Forestry, Vellanikkara, 2019) Harilal, K; Gopakumar, SA 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.