Tree plantations are areas where trees are planted for a particular purpose. Some tree plantations increase the supply of wood for construction and fuel. In many plantations, fast-growing, alien tree species are planted. Undergrowth is found in and around plantations, increasing plant biodiversity. Undergrowth is mainly made up of indigenous (native) small plants and shrubs. [Figure 1.1] shows part of a plantation of eucalyptus trees. Bangladesh has many tree plantations as part of a national tree-planting programme. Two fast-growing, alien tree species planted in Bangladesh are acacia, Acacia auriculiformis, and eucalyptus, Eucalyptus camaldulensis. Acacia and eucalyptus are considered to be invasive species as they outcompete indigenous tree species such as sal tree, Shorea robusta, and mango, Mangifera indica. Scientists carried out an investigation into the biodiversity of plant species in the undergrowth in plantations of alien trees compared with the undergrowth in plantations of indigenous trees. The hypothesis that the scientists tested was stated as: The undergrowth in plantations of alien tree species will have a lower biodiversity of plant species than the undergrowth in plantations of indigenous tree species.