International Research Journal of Environment Sciences________________________________ ISSN 2319–1414Vol. 4(3), 108-114, March (2015) Int. Res. J. Environment Sci. International Science Congress Association 108 Plant Invasion Ecology of an Indo-Burma Hot spot region along the Disturbance Gradient: A case study Prabhat Kumar Rai Department of Environmental Science, Mizoram University, Aizawl, INDIA Available online at: www.isca.in, www.isca.me Received 12th January 2015, revised 17th February 2015, accepted 19th March 2015 AbstractPlant invasion is the priority threat to global biodiversity and hence deleterious to both ecology and economy of any nation. Invasive plants or weeds transmogrify the landscapes of urban forests and duly affect its phytosociology as well as diversity of native species in a complex intricate manner. Various hypotheses have been proposed to understand the basic mechanism of succession in order to device sustainable management strategy, however, no one describe it in its totality. Present case study was performed in urban forests of Aizawl, Mizoram, North East India falling under an Indo-Burma hot spot region of existing ecological relevance and pristine environment. Phytosociolology of invasive weeds and soil attributes (pH, soil moisture, soil respiration) or resources (organic matter, C, N, K) were analyzed along a disturbance gradient. Ageratum conizoides was the widest occurring invasive weed which was recorded at all the three sites along the disturbance gradient. Organic matter, soil carbon, soil moisture, soil respiration, soil nitrogen; soil pH was recorded highest at disturbed sites which may be responsible for highest diversity of weeds. Results concluded that high intensity of disturbance and plenty of soil resources may facilitate the site ripe for plant invasion.Keywords: Plant invasion, biodiversity, human health, soil attributes, disturbance. Introduction Biodiversity is extremely precious resource issue in current civilization as it is inextricably linked with sustainable development. In recent Anthropocene era, biodiversity extends to humankind multifaceted direct economic benefits and direct essential services through natural ecosystems and plays a prominent role in ecosystem function and stability1-7. Biodiversity provides a vast array of products which are intimately linked with the human health1-7. Introduction of exotic invasive species are assumed to be the major threats to the global biodiversity1,3. In current scenario, plant invasion is generally considered to be one of the ‘big five’ environmental issues of public concern1,8,9 and one of the six most serious environmental problems which may influence future economic and social development. Although there are several definitions of alien invasive species, however, the one given by GISP (2003) seems to be most relevant in totality i.e.: ‘Invasive alien species are non-native organisms that cause, or have the potential to cause, harm to the environment, economies, or human health’. Likewise, Convention on Biological Diversity held in 1992, defined invasive species as alien species whose introduction or spread threaten biological diversity. Thus, establishment and spread of these invasive species threatens landscape in terms of economy as well as environment1,10-12. Mizoram (literally-house of forest) is an important state of NE India (an Indo-Burma Hot spot) and the forests in Mizoram are classified as Tropical Wet Evergreen Forests, Tropical Semi-Evergreen Forests and Sub-Tropical Hill Forests2,-4,13. Therefore, there are varying forest types Mizoram harbouring great deal of biodiversity which are of immense values to its rural tribal people. Mizoram is the site of particular ecological relevance as it falls under an Indo-Burma hot spot region (figure-1). In Mizoram, land use change through shifting cultivation is very frequent which may exacerbate the problem of biological invasions13. In Aizawl, which is capital city of Mizoram, shifting cultivation transmogrify the landscapes of urban forests ripe for plant invasions. Land-use change is projected to have the largest global impact on biodiversity by the year 2100, followed by climate change, nitrogen deposition, species introductions and changing concentrations of atmospheric CO1-3,8. Land-use change is expected to be of particular importance in the tropics, climatic change is likely to be important at high latitudes, and a multitude of interacting causes will affect other biomes. Various hypotheses have been proposed to understand the basic mechanism of succession, however, no one describe it in its totality. However, one of the prime threats to biodiversity of indigenous/native diversity in Mizoram is plant invasion or introduction of exotic or alien plant species. Despite the large documented threats from invasive species to native biodiversity in several ecosystems of North East India, invasive species have rarely been considered as a significant threat to the diversity of tropical forests, and while invasions have been the subject of intensive ecological research during the last two decades, this research has largely ignored tropical forests confined particularly to urban areas. Henceforth, present study is an initial attempt to identify the prime invasive plants of Aizawl, International Research Journal of Environment Sciences______________________________________________ ISSN 2319–1414 Vol. 4(3), 108-114, March (2015) Int. Res. J. Environment Sci. International Science Congress Association 109 Mizoram, North East India at sites of varying disturbance i.e. low (Vety Tlang), moderate (Kendriya Vidayalaya site located at Tanhril campus of Mizoram University) and high disturbance (Roadside site at Ramrikawn). Further, the present study investigated the selected soil characteristics at these three sites along a disturbance gradient. Lantana camara, Mikania micrantha and Ageratum conizoides were phyto-sociologically dominant invasive weeds at disturbed sites. Material and Methods The phyto-sociological studies were performed at three sites in Aizawl, Mizoram, North East India during the month of November to December, 2011 while the soil attributes as well as nutrients were analysed during the month of April, 2012. It is worth to mention that sites were selected in accordance with varying disturbance intensity. To perform phyto-sociological studies at different sites 5 quadrats of 10m×10m in size has been randomly used. Quantitative/phyto-sociological parameters such as % frequency, density, abundance and total basal cover of each species present in quadrats has been recorded and analysed as per the methods of Kershaw14 and Misra15. Part of the moist soil samples is air-dried and sieved to obtain fine soil samples (2 mm). Soil pH has been measured with soil water (1:5) slurry using a pH glass electrode. Organic carbon has been determined according to the Walkley and Black method and total nitrogen with Kjeldahl method. All other analyses are conducted as per the methodology described elsewhere16. Results and Discussion Table 1-12 document the results obtained pertaining to diversity of invasive plants and soil attributes along a disturbance gradient. Maximum number of weeds12 were recorded during the month of November and December, 2011 at site of high disturbance (Roadside site at Ramrikawn) followed by site of moderate disturbance (Kendriya Vidayalaya site of Tanhril campus of Mizoram University) and lowest weeds were recorded during the month of December, 2011 at Vety Tlang site of low disturbance (table-1 to 6). The results revealed that number of weeds increased as the intensity of disturbance along the sites increased. Lantana camara, Mikania micrantha and Ageratum conizoides were phyto-sociologically dominant invasive weeds at disturbed sites (table-2 to 6). Mikania micrantha is a many-branched perennial vine of the family Asteraceae that can reproduce easily through both sexual as well as vegetative reproduction. Particularly, during the winter season, this invasive weed virtually covers the upper canopy of most of the angiosperm plants in Aizawl, producing the shade effect which may hamper the plant photosynthesis. Figure-1 Map of the Study Area (Aizawl) Mizoram, North-East India (An Indo-Burma hot spot) International Research Journal of Environment Sciences______________________________________________ ISSN 2319–1414 Vol. 4(3), 108-114, March (2015) Int. Res. J. Environment Sci. International Science Congress Association 110 This vine can produce a large number of seeds. Lantana camara is a member of the family Verbenaceae and is apantropical invasive weed affecting urban forests, pastures and native forests in60 countries worldwide. Ageratum conizoides was the widest occurring invasive weed which was recorded at all the three sites along the disturbance gradient (table-1 to 6). It is worth to mention that organic matter, soil carbon, soil moisture, soil respiration, soil nitrogen; soil pH was recorded highest at disturbed sites which may be responsible for highest diversity of weeds (table-7 to 12). Thus soil attributes and resources may alter the invasion success drastically. Generally, the soil with higher nutrients favored the invasive plants in present case study Only the potassium content of the soil was lowest at the disturbed site while higher values were recorded at the site of low disturbance (table-12).Table-1 List of invasive weeds- Site 1: Vety Tlang (Low Disturbance site); November, 2011 Name of Species Q1 Q2 Q3 Q4 Q5 No. of Individuals Density Freq. Abundance Basal Area Basal Cover Relative Density Relative Frequency Relative Abundance IVI Ageratum conizoides + + + + + 140 28 100 28 7.06 197.68 35.80563 16.12903 56.48 108.4147 Spilanthes oleracea + + + + + 90 18 100 18 3.14 56.52 23.0179 16.12903 16.14857 55.2955 Stellaria media + + + + + 44 8.8 100 8.8 0.19 1.672 11.2532 16.12903 0.477714 27.85994 Galinsoga parviflora - + - + + 31 6.2 60 10.3 3.14 19.468 7.928389 9.677419 5.562286 23.16809 Cyrtococcum accrescens - + + - + 23 4.6 60 7.6 1.76 8.096 5.882353 9.677419 2.313143 17.87292 Comellina sikkimensis - - + - + 8 1.6 40 4 0.78 1.248 2.046036 6.451613 0.356571 8.85422 Kyllingia brevifolia - - + + + 30 6 60 10 0.78 4.68 7.672634 9.677419 1.337143 18.6872 Mikana micrantha - + - - + 18 3.6 60 6 7.06 25.416 4.603581 9.677419 7.261714 21.54271 Dicrocephala latifolia - - - - + 5 1 20 5 3.8 3.8 1.278772 3.225806 1.085714 5.590292 Clerodendron infortunatum - - - - + 2 0.4 20 2 78.55 31.42 0.511509 3.225806 8.977143 12.71446 Table-2 List of invasive weeds Site 1: Vety Tlang (Low Disturbance site); December, 2011 Name of Species Q1 Q2 Q3 Q4 Q5 No. of Individuals Density Freq. Abundance Basal Area Basal Cover Relative Density Relative Frequency Relative Abundance IVI Ageratum conizoides + + + + + 114 22.8 100 22.8 7.06 160.968 28.00983 14.70588 50.29464 93.01035 Spilanthes oleracea + + + + + 87 17.4 100 17.4 3.14 54.636 21.37592 14.70588 17.07108 53.15288 Stellaria media + + + + + 61 12.2 100 12.2 0.19 2.318 14.98771 14.70588 0.724262 30.41785 Cyrtococcum accrescens + + + + + 42 8.4 100 8.4 1.76 14.784 10.31941 14.70588 4.619278 29.64457 Kyllingia brevifolia + + + + + 67 13.4 100 13.4 0.78 10.452 16.46192 14.70588 3.26574 34.43354 Mikania micrantha - + + - + 21 4.2 60 7 7.06 29.652 5.159705 8.823529 9.264802 23.24804 Galinsoga parvviflora - - + + + 10 2 60 3.3 3.14 6.28 2.457002 8.823529 1.962193 13.24272 Gynura bicolor - - + + - 3 0.6 40 1.5 15.9 9.54 0.737101 5.882353 2.980784 9.600238 Clerodendron infortunatum - - - - + 2 0.4 20 2 78.55 31.42 0.4914 2.941176 9.817216 13.24979 International Research Journal of Environment Sciences______________________________________________ ISSN 2319–1414 Vol. 4(3), 108-114, March (2015) Int. Res. J. Environment Sci. International Science Congress Association 111 Table-3 List of invasive weeds; Site-2: Kendriya Vidayalaya site (moderately disturbed site), November 2011 Name of Species Q1 Q2 Q3 Q4 Q5 No. of Individuals Density Freq. Abundance Basal Area Basal Cover Relative Density Relative Frequency Relative Abundance IVI Ageratum conizoides + + + + + 59 11.8 100 11.8 7.06 83.308 11.21673 12.19512 10.69137 34.10322 Spilanthes oleracea + + + + + 85 17 100 17 3.14 53.38 16.1597 12.19512 6.850546 35.20537 Mikania micrantha + + + + + 74 14.8 100 14.8 7.06 104.488 11.59696 12.19512 13.40951 37.20159 Biden biternata + + + + + 61 12.2 100 12.2 19.63 239.486 13.68821 12.19512 30.73454 56.61787 Stellaria media + + + + + 72 14.4 100 14.4 0.19 2.736 20.15209 12.19512 0.351126 32.69834 Kyllingia brevifolia + + + + + 106 21.2 100 21.2 0.78 16.536 7.794677 12.19512 2.122155 22.11195 Par yellow (local name) + + + + + 41 8.2 100 8.2 3.14 25.748 3.231939 12.19512 3.304381 18.73144 Sida acuta - + - + + 17 3.4 60 5.6 63.62 216.308 0.570342 7.317073 27.75998 35.6474 Merremia umbellatum - + - - - 3 0.6 20 3 19.63 11.778 1.520913 2.439024 1.511535 5.471472 Gynura bicolor - - - + + 8 1.6 40 4 15.9 25.44 14.06844 4.878049 3.264854 22.21134 Table-4 Invasive weeds Site-2 Kendriya Vidayalaya site (moderately disturbed site), December 2011 Name of Species Q1 Q2 Q3 Q4 Q5 No. of Individuals Density Freq. Abundance Basal Area Basal Cover Relative Density Relative Frequency Relative Abundance IVI Ageratum conizoides + + + + + 45 9 100 9 7.06 317.7 11.22195 13.88889 8.977822 34.08866 Spilanthes oleracea + + + + + 51 10.2 100 10.2 3.14 160.14 12.7182 13.88889 4.525365 31.13246 Mikania micrantha + - + + + 61 12.2 80 15.2 7.06 430.66 15.21197 11.11111 12.16994 38.49302 Biden biternata + + + + + 58 11.6 100 11.6 19.63 1138.54 14.46384 13.88889 32.17378 60.52651 Stellaria media + + + - - 44 8.8 60 14.6 0.19 8.36 10.97257 8.333333 0.236244 19.54215 Kyllingia brevifolia + + + + + 79 15.8 100 15.8 0.78 61.62 19.70075 13.88889 1.741308 35.33095 Par yellow (local name) + - + - + 33 6.6 60 11 3.14 103.62 8.229426 8.333333 2.928177 19.49094 Sida acuta - + - + + 17 3.4 60 5.6 63.62 1081.54 4.239401 8.333333 30.56303 43.13576 Merremia umbellatum - - - + + 8 1.6 40 4 19.63 157.04 1.995012 5.555556 4.437763 11.98833 Gynura bicolor + - - - - 5 1 20 1 15.9 79.5 1.246883 2.777778 2.246575 6.271236 Anthropogenic perturbations are causing a biodiversity crisis in the form of invasive plants1,15 as revealed in the present study. The results indicated that increase in the intensity of disturbance and soil nutrients may facilitate the mechanism of plant invasion as supported by multifaceted hypothesis described elsewhere. References 1.Rai P.K., Plant invasion ecology: Impacts and Sustainable management, Nova Science Publisher, New York, 196 (2013)2.Rai P.K., Land Use Changes in North Eastern Himalayan Region (an Indo-Burma Hot spot) and its Impact on Human Health, In Biodiversity and Sustainable Development(Ed. K.N. Tiwari and S. Lata), Prasanna Prakashan, Bhopal, 175-192, (2011)3.Rai P.K., Assessment of Multifaceted Environmental Issues and Model Development of an Indo- Burma Hot Spot Region, Environmental Monitoring and Assessment184,113–131 (2012) 4.Rai P.K. and Lalramnghinglova H., Threatened and less known ethnomedicinal plants of an Indo-Burma hotspot region: conservation implications, Environmental Monitoring and Assessment,178, 53–62 (2011) International Research Journal of Environment Sciences______________________________________________ ISSN 2319–1414 Vol. 4(3), 108-114, March (2015) Int. Res. J. Environment Sci. International Science Congress Association 112 Table-5 Invasive weeds- Site 3: Roadside (disturbed-Ramrikawn site); November 2011 Name of Species Q1 Q2 Q3 Q4 Q5 No. of Individuals Density Freq. Abundance Basal Area Basal Cover Relative Density Relative Frequency Relative Abundance IVI Lantana camara + + - + + 20 4 80 5 78.55 314.2 4.950495 8.510638 34.25957 47.7207 Ageratum conizoides + + + + + 65 13 100 13 7.06 91.78 16.08911 10.6383 10.00746 36.73487 Spilanthes oleracea + + + + + 70 14 100 14 3.14 43.96 17.32673 10.6383 4.793287 32.75832 Biden biternata + + - + + 32 6.4 80 8 19.63 125.632 7.920792 8.510638 13.69859 30.13002 Spilanthes sp. - - + - + 14 2.8 40 7 4.9 13.72 3.465347 4.255319 1.495994 9.21666 Mikania micrantha + + + + + 31 6.2 100 6.2 7.06 43.772 7.673267 10.6383 4.772788 23.08436 Clerodendron infortunatum + + - - - 8 1.6 40 4 78.55 125.68 1.980198 4.255319 13.70383 19.93935 Imperata cylindrica + + + + + 42 8.4 100 8.4 4.9 41.16 10.39604 10.6383 4.487982 25.52232 Par eng (local name) + + + - - 19 3.8 60 6.3 3.14 11.932 4.70297 6.382979 1.301035 12.38698 Merremia umbellatum + + + - + 22 4.4 80 5.5 19.63 86.372 5.445545 8.510638 9.417784 23.37397 Panicum conjugatum + + + - + 32 6.4 80 8 1.76 11.264 7.920792 8.510638 1.228198 17.65963 Kyllingia brevifolia + - + + + 49 9.8 80 12.2 0.78 7.644 12.12871 8.510638 0.833482 21.47283 Table-6 Invasive weeds- Site 3: Roadside (disturbed-Ramrikawn site); December, 2011 Name of Species Q1 Q2 Q3 Q4 Q5 No. of Individuals Density Freq. Abundan ce Basal Area Basal Cover Relative Density Relative Frequency Relative Abundance IVI Lantana camara + + - + + 18 3.6 80 4.5 78.55 282.78 4.825737 9.302326 34.87933 49.00739 Ageratum conizoides + + + + + 56 11.2 100 11.2 7.06 79.072 15.0134 11.62791 9.753089 36.3944 Spilanthes oleracea + + + + + 61 12.2 100 12.2 3.14 38.308 16.35389 11.62791 4.725078 32.70688 Biden biternata + - + - + 28 5.6 60 9.3 19.63 109.928 7.506702 6.976744 13.559 28.04245 Spilanthes sp. - + + + + 39 7.8 80 9.7 4.9 38.22 10.45576 9.302326 4.714223 24.47231 Mikania micrantha + + + + + 25 5 100 5 7.06 35.3 6.702413 11.62791 4.354058 22.68438 Clerodendron infortunatum + + - - - 7 1.4 40 3.5 78.55 109.97 1.876676 4.651163 13.56418 20.09202 Imperata cylindrica - + + + + 38 7.6 80 9.5 4.9 37.24 10.18767 9.302326 4.593346 24.08334 Par eng (local name) - + + - - 10 2 40 5 3.14 6.28 2.680965 4.651163 0.774603 8.106731 Merremia umbellatum + + + + - 14 2.8 80 3.5 19.63 54.964 3.753351 9.302326 6.779502 19.83518 Panicum conjugatum + + - - + 34 6.8 60 17 1.76 11.968 9.115282 6.976744 1.476186 17.56821 Kyllingia brevifolia + - + - - 43 8.6 40 21.5 0.78 6.708 11.52815 4.651163 0.827394 17.00671 International Research Journal of Environment Sciences______________________________________________ ISSN 2319–1414 Vol. 4(3), 108-114, March (2015) Int. Res. J. Environment Sci. International Science Congress Association 113 Table-7 Organic carbon and organic content at different sites (April, 2012) Soil samples Replicates Burette Readings Means Organic Carbon Contents Blank Reading Organic Matter Content Initial Final SITE 1 (Low Dist.) R1 0 17.4 18.1 1.3 23.1 2.2 R2 0 18.8 R3 0 18.1 SITE 2 (Moderate Dist.) R1 0 19.5 19 1.06 1.8 R2 0 18.6 R3 0 18.9 SITE 3 (High Dist.) R1 0 18.7 16.8 1.63 2.8 R2 0 15.4 R3 0 16.4 Table-8 Soil respiration at different sites (April, 2012) Soil samples Replicates Burette Readings Means Blank Reading Soil Respiration Initial Final Site 1 (Low Dist.) R1 0 39.8 38.5 41.3 6.16 R2 0 37.5 R3 0 38.4 Site 2 (Moderate Dist.) R1 0 40.5 40.5 1.76 R2 0 40.8 R3 0 40.2 Site 3 (High Dist.) R1 0 35.2 34.7 14.5 R2 0 34.2 R3 0 34.8 Table-9 Soil moisture at different sites (April, 2012) Soil Samples Replicates Wt. of soil samples Means Of Soil B Soil moistures (a-b) Before drying (A) in g After drying (B) in g Site 1 (Low Dist.) R1 10 8.5 8.6 1.4 R2 10 8.6 R3 10 8.8 Site 2 (Moderate Dist.) R1 10 8 7.8 2.2 R2 10 7.7 R3 10 7.9 Site 3 (High Dist.) R1 10 8.2 8.1 1.9 R2 10 8.3 R3 10 8 Table-10 pH of soil samples at different sites (April, 2012)Soil samples Replicates pH Readings Mean pH Site 1 (Low Dist.) R1 6.21 6.2 R2 6.25 R3 6.24 Site 2 (Moderate Dist.) R1 6.61 6.8 R2 6.92 R3 6 .89 Site 3 (High Dist.) R1 6.42 6.3 R2 6.28 R3 6.32 International Research Journal of Environment Sciences______________________________________________ ISSN 2319–1414 Vol. 4(3), 108-114, March (2015) Int. Res. J. Environment Sci. International Science Congress Association 114 Table-11 Soil Nitrogen at different sites (April, 2012) Soil Samples Replicates Burette Readings Means % of Total Nitrogen Initial Final Site 1 (Low Dist.) R1 0 5.4 5.2 0.14 R2 0 5 R3 0 5.1 Site 2 (Moderate Dist.) R1 0 6.9 6.3 0.17 R2 0 6 R3 0 6.2 Site 3 (High Dist.) R1 0 7.6 7.6 0.21 R2 0 7.7 R3 0 7.5 Table-12 Soil potassium (K) content at different sites (April, 2012) Soil samples Replicates Burette Readings Means Potassium Contents Initial Final Site 1 (Low Dist.) R1 0 22 22 0.85 R2 0 22 R3 0 23 Site 2 (Moderate Dist.) R1 0 17 16 0.68 R2 0 16 R3 0 15 Site 3 (High Dist.) R1 0 13 13 0.5 R2 0 13 R3 0 14 5.Rai P.K. and Panda L.S., Dust capturing potential and air pollution tolerance index (APTI) of some roadside tree vegetation in Aizawl, Mizoram, India: An Indo-Burma hot spot region, Air quality, Atmosphere and Health,7(1), 193-101 (2014a) 6.Rai P.K. and Panda L.S., Leaf dust deposition and its impact on biochemical aspect of some roadside plants in Aizawl, Mizoram, North-East India, International Research Journal of Environmental Sciences,3(11), 14-19 (2014b) 7.Rai P.K. and Chutia B.M., Assessment of Ambient air quality status Before and after shifting cultivation in an Indo-Burma hot spot region, International Research Journal of Environmental Sciences,3(11), 1-5 (2014) 8.Sala O.E. et al., Global biodiversity scenarios for the year 2100, Science, 287, 1770-1774 (2000) 9.Didham R.K., Tylianakis J.M., Hutchison M.A., Ewers, R.M. and Gemmell N.J., Are invasive species the drivers of ecological change? Trends in Ecology and Evolution,20(9), 470-474 (2005) 10.GISP, The IAS problem, The Global Invasive Species Programme, (2003) 11.Sharma G.P., Raghubanshi A.S. and Singh J.S., Lantana invasion: An overview, Weed Biology and Management , 157–165 (2005) 12.Davis A.M., Invasion Biology, Oxford University Press, 244 (2009) 13.Rai, P.K., Comparative Assessment of Soil Properties after Bamboo Flowering and Death in a Tropical Forest of Indo-Burma Hot spot, Ambio: A Journal on Human Environment,38(2), 118-120 (2009) 14.Kershaw R.A., Quantitative and dynamic plant ecology, London: Edward Arnold Ltd, (1973) 15.Mishra R.,Ecology work book, New Delhi: Oxford and IBH Publishing Co., (1968)16.Jackson M.L., Soil chemical analysis, Prentice-Hall Inc., Englewood Cliffs, NJ (1958)17.Brooker R.W., Plant–plant interactions and environmental change, New Phytologist,171, 271–284 (2006)