Fodder Biomass Monitoring in Sahelian Rangelands Using Phenological Metrics from FAPAR Time Series

• Published in: Remote sensing (Basel, Switzerland) Vol. 7; no. 7; pp. 9122 - 9148
• Main Authors: Diouf, Abdoul Aziz, Brandt, Martin, Verger, Aleixandre, Jarroudi, Moussa El, Djaby, Bakary, Fensholt, Rasmus, Ndione, Jacques Andre, Tychon, Bernard
• Format: Journal Article Web Resource
• Language: English
• Published: Basel MDPI AG 01.07.2015; Multidisciplinary Digital Publishing Institute (MDPI)
• Subjects: Agriculture & agronomie; Agriculture & agronomy; Biomass; Ecoregion; Ecosystems; FAPAR; Fodder biomass; Food security; Forages; Life sciences; Monitoring; Phenological metrics; Rangelands; Remote sensing; Sahel; Sciences du vivant; Seasons; Time series; Vegetation
• ISSN: 2072-4292; 2072-4292
• DOI: 10.3390/rs70709122

Timely monitoring of plant biomass is critical for the management of forage resources in Sahelian rangelands. The estimation of annual biomass production in the Sahel is based on a simple relationship between satellite annual Normalized Difference Vegetation Index (NDVI) and in situ biomass data. This study proposes a new methodology using multi-linear models between phenological metrics from the SPOT-VEGETATION time series of Fraction of Absorbed Photosynthetically Active Radiation (FAPAR) and in situ biomass. A model with three variables-large seasonal integral (LINTG), length of growing season, and end of season decreasing rate-performed best (MAE = 605 kg times DM/ha; R2 = 0.68) across Sahelian ecosystems in Senegal (data for the period 1999-2013). A model with annual maximum (PEAK) and start date of season showed similar performances (MAE = 625 kg times DM/ha; R2 = 0.64), allowing a timely estimation of forage availability. The subdivision of the study area in ecoregions increased overall accuracy (MAE = 489.21 kg times DM/ha; R2 = 0.77), indicating that a relation between metrics and ecosystem properties exists. LINTG was the main explanatory variable for woody rangelands with high leaf biomass, whereas for areas dominated by herbaceous vegetation, it was the PEAK metric. The proposed approach outperformed the established biomass NDVI-based product (MAE = 818 kg times DM/ha and R2 = 0.51) and should improve the operational monitoring of forage resources in Sahelian rangelands.