Topographic and edaphic factors determining <i>Chromolaena odorata</i> and <i>Hyptis suaveolens</i> invasion of grassland in the Guineo-Congolian / Sudanian transition zone (Benin)

Abstract

Objectives: Soil properties-invasive vegetation relationships remains uninvestigated. This study aimed at analyzing the main ecological factors, which explain the spatial distribution of two invasive species: Chromolaena odorata (Siam weed) and Hyptis suaveolens (Tea-bush). Methodology and Results:The Data were collected in 33 plots installed randomly according to the phytosociological method. These data were submitted to the Canonical Analysis of Correspondence. The, wet grasslands contamined were distinguished from grasslands of dry plateaus. A difference was also made between establishment and invasion from the step of contamination of both plants. The relevant edaphic main factors related to grasslands on dry plateau were sandy rate, pH, potassium and carbon rate. Wet grasslands of floodplains were located on soils with a high concentration of clay and silt, phosphorus, calcium and magnesium, as well as a high cation exchange capacity. Conclusions and application of findings: It could be concluded that the texture-moisture of the soil is the main factor, which explained the invasion intensity and the floristic composition of the investigated savannah. Dry plateau soil and oligotrophe induced the development of these alien plants. Therefore, it was suggested planning activities to prevent the expansion of these species on dry plateau grasslands.

Mapping actual distribution of invasive species siam weed and its abundance across biogeographical zones in Benin (West Africa)

“…This could be one of the raisons there was the highest level of infestation in the sudano-guinean zone compared to the guinean one. These results further corroborate with those of Aboh et al (2017) who demonstrated that high infestations of C. odorata are only observed on soils with pH values around 7.12.…”

“…However, it was noted that the sudanian zone located in the northern part of the country is almost free of the invasion apart from the beginning of infestation reported at its southwestern parts. The extent of occurrence of the species was within latitudes 6°30' and not favor the invasion of C. odorata (Aboh et al, 2017). The minimum annual rainfall requirement for C. odorata is over 1,000 mm even though considerable lower limits have been recorded in some studies, and this may be a limiting factor to its occurrence in the far north as the annual rainfall over there is under 1,000 mm (Gnanglè et al, 2011).…”

“…Low: 2 Soils in Center Benin are indeed classified as neutral to weakly acidic since their pH ranges from 6.6 to 7.2; while soils of southern Benin with pH from 4.9 to 6 are classified as very strongly to moderately acid (Igue et al, 2013). Siam weed grows best on soils with the potential hydrogen (pH) value near to neutral (Aboh et al, 2017). This could be one of the raisons there was the highest level of infestation in the sudano-guinean zone compared to the guinean one.…”

“…These findings are consistent with previous studies on the species distribution ecology in Sub-Saharan African region and elsewhere. Indeed, while Fandohan et al (2015) reported high contribution of rainfall to the species occurrence in West Africa, Aboh et al (2017) reported that the higher the soil pH, the higher C. odorata abundance, and Nath et al ( 2019) reported C. odorata gradually distributed along altitude in Terai grasslands in India.…”

Predicting the distribution of the invasive species Hyptis suaveolens in Nigeria

“…This may enable it to thrive in new environments such as Benue, Kogi, Niger, Kaduna and Bauchi States, in the future. Similarly, H. suaveolens thrives in sandy soil with a high pH, low fertility and is well-drained (Aboh et al 2017), which with climate change could result in it invading new habitats (Padalia et al 2015).…”