Publications

Pfeifer, Marion; Lefebvre, Veronique; Gonsamo, Alemu; Pellikka, Petri K. E.; Marchant, Rob; Denu, Dereje; Platts, Philip J. (2014). Validating and Linking the GIMMS Leaf Area Index (LAI3g) with Environmental Controls in Tropical Africa. REMOTE SENSING, 6(3), 1973-1990.

Abstract
The recent Global Inventory Modeling and Mapping Studies (GIMMS) LAI3g product provides a 30-year global times-series of remotely sensed leaf area index (LAI), an essential variable in models of ecosystem process and productivity. In this study, we use a new dataset of field-based LAI(True) to indirectly validate the GIMMS LAI3g product, LAI(avhrr), in East Africa, comparing the distribution properties of LAI(avhrr) across biomes and environmental gradients with those properties derived for LAI(True). We show that the increase in LAI with vegetation height in natural biomes is captured by both LAI(avhrr) and LAI(True), but that LAI(avhrr) overestimates LAI for all biomes except shrubland and cropland. Non-linear responses of LAI to precipitation and moisture indices, whereby leaf area peaks at intermediate values and declines thereafter, are apparent in both LAI(True) and LAI(avhrr), although LAI(True) reaches its maximum at lower values of the respective environmental driver. Socio-economic variables such as governance (protected areas) and population affect both LAI responses, although cause and effect are not always obvious: a positive relationship with human population pressure was detected, but shown to be an artefact of both LAI and human settlement covarying with precipitation. Despite these complexities, targeted field measurements, stratified according to both environmental and socio-economic gradients, could provide crucial data for improving satellite-derived LAI estimates, especially in the human-modified landscapes of tropical Africa.

DOI:
10.3390/rs6031973

ISSN:
2072-4292