Ecological effects of selected invasive plants and their nature based management approaches
Ngondya, Issakwisa Bernard
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Biological invasions are one of the major threats to most ecosystems as they often suppress native plant species. This suppressive effect is usually costly and irreversible hence calling for effective management strategies that are ecologically safe and appropriate at local level. This research work aimed at assessing the ecological effects of the invasive weeds Tagetes minuta and Gutenbergia cordifolia on native vascular plants and development of the nature-based management solutions for the two invasives. To understand if T. minuta and G. cordifolia have any effects on native plant communities and soil chemistry, the study compared native vascular plant species abundance, richness, cover, height and soil chemistry of the Ngorongoro ecosystem by sampling systematically along a continuum of invasion gradient from uninvaded to highly invaded areas in the Ngorongoro crater. It further identified the most dominant co-existing native vascular plant in the field (Cynodon dactylon) that can be facilitated to out-compete the two weeds. The results indicated that the two invasive weeds decreased native species abundance, ground cover and richness while increasing native vegetation height. Soil available Phosphorus, Nitrogen, and Cation Exchange Capacity levels were also influenced by invasions of either and/or both T. minuta and G. cordifolia. The competitive effects of the observed most dominant native vascular plant (Cynodon dactylon) on the growth and development of the two weeds was tested experimentally in both screen house and field plots using a completely randomized and randomized block design respectively in order to identify the most suppressive C. dactylon density. It was observed that increasing densities of C. dactylon strongly reduced the growth and development of T. minuta and G. cordifolia. The allelopathic experiments were done in both laboratory and screen house to identify the effective Desmodium root/ leaf extract concentration that can impair the growth and germination of T. minuta and G. cordifolia as a second management approach. Generally, seedlings treated with higher D. uncinatum leaf extracts (≥62.5%) were half as tall, had one-third the weight and half the leaf chlorophyll content compared to those treated with lower concentrations. Based on the field, screen house and laboratory experiments, the suppressive effects of the two invasives are evident hence necessitating their management. Although needs to be scaled up in the field, this study has devised and tested two novel nature-based management approaches that have proven to be functional.