Summary The population dynamics of Eupatorium adenophorum Spreng. and E. riparium Regel was studied in the field for 2 years, in relation to burning, by following the fate of individuals in permanent quadrats at short and regular time intervals. Both species showed increased population density and longevity of individuals on the burnt site. Adult and seedling populations of both species showed greater survival in the burnt plot. Eupatorium riparium survived better than E. adenophorum adults after burning. In the unburnt plot, however, the seedling survival of both species was nil. The heavy juvenile mortality of both species in the unburnt situation is attributed to the accumulation of a thick layer of pine needles and the growth of herbaceous vegetation. Moisture stress and low temperature in winter months also seem involved in the regulation of seedling population of these two weeds.

Summary The data on seed population dynamics of three weedy species of Eupatorium, viz. E. adenophwrum Spreng., E. riparium Regel and E. odoratum L. have been presented and discussed in the paper. The seed production and seed populations in soil seed bank were estimated, and the fate of buried seeds in soil was followed over a 2‐year period. All the three species of Eupatorium produced a large number of seeds. The seed production of E. riparium per unit area was higher than that of the other two species because of its high population density. In all the three species most of the seeds were found to be present in the top 2 cm of the soil. The viable seed population of the three species of Eupatorium declined exponentially alter their burial in soil showing almost similar mortality patterns. A large proportion of seeds of all the Eupatorium spp. remained under enforced dormancy during their burial in soil with only a small fraction exhibiting induced dormancy. The longevity of the buried seeds increased on account of the dormancy imposed on them. The loss of seeds through degeneration and/or decomposition was rather low.

This chapter covers the reproductive potential, population ecology (competitive interaction, allelopathic interaction, and effects of soil moisture, light intensity, and soil nitrogen on population density), origin, geographical distribution, invasion and management (physical, biological and chemical control methods) of E. odoratum [Chromolaena odorata], E. riparium and E. adenophorum [E. trapezoideum].

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This chapter describes the geographical distribution (including Asia, and Central and South America), morphology, reproductive potential, growth, flowering, chemical composition, allelopathic effects, ecological impact, and management (biological and chemical methods) of M. micrantha.