Ecological Consequences of Invasive Weeds: Zimbabwean Experience: A Review

Invasive weeds may be defined as troublesome or unsightly plants growing in abundance in both upland and aquatic situations where they are not wanted. The establishment of invasive species cause elevated destruction of waterways, disrupted fire regimes, and the loss of biodiversity in many natural and agrarian ecosystems. <i>Tithonia diversifolia</i> is one of the largest, aggressive colonizers especially in sun-exposed abandoned sites. The impact of this weed result in economic loss through controlling and abandonment of agrarian land. The menace of <i>Tithonia diversifolia</i> is reaching alarming proportions in many parts of the world, especially in Zimbabwe where they have led to serious ecological and economic losses. Invasion of both upland and aquatic ecosystem by weeds, has undergone serious ecological changes including over-exploitation of its natural resources and land degradation of both agrarian and natural ecosystem, and invasion by <i>Tithonia diversifolia</i> among others. <i>Tithonia diversifolia</i> The presence of the invasive weed was viewed as a universal threat to crop farming and ranching enterprises because invasive weeds alter forage quantity or quality for livestock and therefore reduce net revenue. The invasive nature of <i>T diversifolia</i>, its ability to produce a large biomass and possession of an extensive root system has made it a good candidate for remediation of polluted environments. This invasive weed has been implicated in allelopathy as it produces a myriad of phytochemicals such as alkaloids, flavonoids, phenols, saponins, tannins and terpenoids there by creating its novel niche. <i>Tithonia diversifolia</i> after Invasive weeds have the potential for exploitation animal feed, human food, soil additives, fuel production, wastewater treatment, source of raw materials and habitat to many organisms. This paper reviews the ecological consequences of invasive weeds with examples from some selected fields and special reference to <i>Tithonia diversifolia</i>.