Patterns of vegetation greenness during flood, rain and dry resource states in a large, unconfined floodplain landscape

Abstract

Floodplains are multi-state systems in which vegetation distribution is associated with the presence or absence of water as a resource. Less is known about the associations between the presence and absence of water and vegetation productivity. We examined patterns of vegetation productivity in a large (10 519 km²) unconfined floodplain during flood, rain and dry resource states. Mosaics of vegetation greenness were derived at two scales using the Normalized Difference Vegetation Index: a whole-of-landscape scale and a geomorphic unit scale with a riparian and floodplain unit. The NDVI was also calculated within a-priori vegetation community types within the floodplain. In all resource states over 50% of the floodplain showed no discernible vegetation greenness. When water is added as rain or flooding vegetation greenness increases, but the highest greenness occurs in the flood state. Trees situated in the riparian geomorphic unit maintain greenness during the dry resource state, whereas grasses situated in the floodplain contribute greenness during rain and flood resource states, with the highest greenness in the flood resource state. Aligned with views that dryland floodplains are boom-bust ecosystems, we suggest that flooding is a fundamental driver of vegetation productivity in this unconfined floodplain, contributing functional heterogeneity to the landscape.