Structure and Phenology of Herbaceous Stratum in the Sahelian Rangelands of Senegal

Abstract

This study describes the structure and phenology of Sahelian rangelands during the rainy season. It was undertaken on a grazed plot and a fenced plot. Measurements were taken every 10 days over two rainy seasons between July and October 2018 and between August and October 2019. The measurements included the phenological stage, the vegetative and flowering height, the coverage, and the phytomass. The results showed that phytomass did not systematically differ between grazed and fenced plots. Flowering started as early as mid-July, but most of the plants flowered in early October. Flowering and fruiting occurred earlier (based on the number of days after the first rain) in the late rainy season (2019) than in the early one (2018). These stages reached their peak in October; senescence began in October. Vegetative height, reproductive height, and coverage were similar between the two years. Height peaks were similar, but they were reached earlier (based on the number of days after the first rain) in the late rainy season than in the early one. Coverage peaks were similar (59.8% in the early rainy season vs. 65.8% in the late one). Vegetative height (around 30 cm), reproductive height (around 36 cm), and coverage (around 60%) reached their maximum in October, but reproductive height was greater than vegetative height. These parameters were lower at the grazed site compared to the fenced site, and flowering started earlier at the grazed site. The pasture had a negative impact on coverage, height, and early flowering. Structure and phenology were more sensitive than to changes in rainfall between years. Phenology results will help determine the best time to harvest the phytomass (phytomass stock), as the nutritional quality of the forage is known to decrease after fruiting.

Estimating herbaceous aboveground biomass in Sahelian rangelands using Structure from Motion data collected on the ground and by UAV

“…Trees also influence the herbaceous layers and management of the different plots (free grazing, enclosure, and dense Senegalia senegalensis planting). Here, SfM tools can be used to test the impact of these factors on the herbaceous layers (Diatta et al, 2021), especially with a focus on the temporal aspect (within or between growing seasons). For more applied and operational usage, operations on a landscape scale should be considered in relation to the management type and size involved.…”

“…In 2019, images were collected close to the Dahra research center office, and in 2020 they were collected around the Dahra flux tower site (Tagesson, Fensholt, Cropley, et al, 2015). Both years, the images were collected along two perpendicular 1 km transects (Diatta et al, 2021). Every 10 days, measurements were taken 1 m to the north of the last measurements (10 days earlier).…”

“…Both years, the images were collected along two perpendicular 1 km transects (Diatta et al, 2021). Every 10 days, measurements were taken 1 m to the north of the last measurements (10 days earlier).…”