Vegetation changes over the past two decades in a West African savanna ecosystem

Abstract

Questions: West African savanna ecosystems are affected by increasing land use intensity (e.g., agriculture and livestock herds) due to a growing human population. To understand the impact of land use intensification on savanna vegetation, we aim to answer the following questions: How do savanna species composition, diversity and structure change with increasing land use pressure? Are the impacts of land use change different in the woody and the herbaceous layers? Do the effects of land use change differ between vegetation types? Location: Southeastern Burkina Faso, West Africa. Methods: Vegetation plots from the early 1990s representing vegetation types occurring in fallows of different age and in uncultivated pasturing zones were resurveyed. We distinguished between woody (tree and shrub layer) and herbaceous vegetation types. Species composition changes were analyzed using ordination techniques (detrended correspondence analysis, DCA) and indicator species analysis (IndVal). Species turnover and plant diversity as represented by species richness and evenness were compared between the baseline survey and the resurvey. Results:In most woody vegetation types, we found no change in species composition and richness over the past two decades. However, some highly valued woody species decreased in abundance. In contrast, in most herbaceous vegetation types, species composition changed considerably and species richness increased. The proportion of wide-ranging, ruderal herbaceous species increased, indicating a homogenization of herbaceous vegetation types, while preferred fodder herbaceous species decreased. We assume that the increased grazing intensity over the past two decades is the driver of these changes in the herbaceous layer. Conclusions:Our results show different reactions of vegetation types and layers to land use intensification and reinforce the need for studies on the basis of vegetation type that incorporate both the herbaceous and the woody layers.

The role of landscape composition and heterogeneity on the taxonomical and functional diversity of Mediterranean plant communities in agricultural landscapes

“…Therefore, the gradient of area dedicated to agricultural activies not only results in changes in plant richness but also in changes in species composition by affecting the proportion of ruderal species. These results agree with those of Leßmeister et al [ 78 ], who reported a change in species composition and an overall increase in species richness derived from an increase in the proportion of ruderal and segetal species in modified landscapes of West African savanna. Despite the effect of percentage of crops in the landscape on plant richness, we did not find any effect of this variable on the Shannon’s diversity of plant species.…”

The role of fallowing in the restoration of woody species in the Woodlands of Northern Uganda

“…The findings therefore show that abandonment of crop field as fallow can result into establishment of early successional species (pioneer) especially Annona senegalensis and Piliostigma thonningi (Ahmed, 1983; Donfack et al, 1995; Leßmeister et al, 2019; Oke & Jamala, 2013) in the first six years and if the fallow length is extended, late successional species such as Combretum collinum can be established without displacing the early successional species. This is reflected by occurrence of early successional species in old fallow albeit at relatively lower density.…”

Detecting phenological changes in plant functional types over West African savannah dominated landscape

“…insect attacks and wildfire), herbivory and land use (e.g. grazing and agriculture) (Belsky 1992;Leßmeister et al 2019). The current study, therefore, investigated the presence of abrupt changes in the NDVI time series and further assessed how PFTs are affected in terms of positive or negative magnitude changes (Figures 8(a, e), 10(a, b), Table 3).…”

“…They are also more resistant to fire and can recover more easily after a fire once they have grown to a certain height and escaped the 'fire trap' de Bie et al 1998). A recent study by Leßmeister et al (2019) who studied vegetation changes over the past two decades in a West African savannah ecosystem found no change in woody species composition and richness over the past two decade studies while grass species have changed and species richness has increased.…”

“…Even though climate, soil, species diversity, and habitat type are some of the important driving factors influencing the savannah vegetation changes (Hill et al 2011;Cho et al 2012;Higgins et al 2011), human management and land use have been identified as a major contributing factor in West Africa (Ibrahim, Balzter, and Kaduk 2018;Leßmeister et al 2019). Generally, anthropogenic factors were found to have serious negative consequences for vegetation productivity and overall climate (Valentini et al 2014).…”