Impact of invasive alien plants Gutenbergia cordifolia and Tagetes minuta on native taxa in the Ngorongoro crater, Tanzania

Abstract

Understanding the ecological impacts of invasive plant species on the native communities and identifying native plant species that co-exist with invasive plants are important for planning the effective control and restoration of invaded rangelands. Systematic random sampling technique was applied to assess the effect of the two invasive plants (Gutenbergia cordifolia and Tagetes minuta) on native vascular plant species’ cover and diversity as well as identification of native grasses that co-exist well with the two invasive plants in the Ngorongoro crater, Tanzania. Native species ground cover in lowly invaded quadrats doubled that of medium and highly invaded quadrats. The mean height of native plants in highly invaded areas doubled the height of native plants in lowly invaded areas. While species richness was higher in both G. cordifolia and T. minuta lowly invaded quadrats compared to quadrats that were under medium and high invasion similarly, lowly invaded quadrats had higher species evenness than both medium and highly invaded quadrats. Cynodon dactylon was the most co-existing native grass with both G. cordifolia and T. minuta followed by Chloris pycnothrix. The results highlights how invasive plants G. cordifolia and T. minuta drastically changed the abundance and richness of the native vascular plant community within the Ngorongoro crater. It also highlighted on presence of native grasses that are capable of co-existing with the two invasive plants. This study further generated a baseline information for long term research to elucidate mechanisms associated with the two invasive plants interactions, while at the same time informing the management authorities on the threats to native plant species associated with invasive plants G. cordifolia and T. minuta.