Spatial variability of above-ground net primary production in Uruguayan grasslands: a remote sensing approach

BAEZA, S.; LEZAMA, F.; PIÑEIRO, G.; ALTESOR, A.; PARUELO J. M.

APPLIED VEGETATION SCIENCE

WILEY-BLACKWELL PUBLISHING, INC

Año: 2009 vol. 13 p. 72 - 88

1402-2001

Question: How does above-ground net primary production(ANPP) differ (estimated from remotely sensed data)among vegetation units in sub-humid temperate grasslands?Q2 Location: Centre-north Uruguay.Methods: A vegetation map of the study area was generatedfrom LANDSAT imagery and the landscapeconfiguration described. The functional heterogeneity ofmapping units was analysed in terms of photosyntheticallyactive radiation absorbed by green vegetation (fPAR),calculated from the normalized difference vegetation index(NDVI) images provided by the moderate resolutionimaging spectroradiometer (MODIS) sensor. Finally, theANPP of each grassland class was estimated using NDVIand climatic data.Results: Supervised classification presented a good overallaccuracy and moderate to good average accuracy forgrassland classes. Meso-xerophytic grasslands occupied45% of the area, Meso-hydrophytic grasslands 43% andLithophytic steppes 6%. The landscape was shaped by amatrix of large, unfragmented patches of Meso-xerophyticand Meso-hydrophytic grasslands. The regionpresented the lowest anthropic fragmentation degree reportedfor the Rio de la Plata grasslands. All grasslandunits showed bimodal annual fPAR seasonality, withspring and autumn peaks. Meso-hydrophytic grasslandsshowed a radiation interception 10% higher than theother units. On an annual basis, Meso-hydrophytic grasslandsproduced 3800 kg dry matter (DM) ha1 yr1 andMeso-xerophytic grasslands and Lithophytic steppesaround 3400 kg DM ha1  yr1. Meso-xerophyticgrasslands had the largest spatial variation during most of the year. The ANPP temporal variation was higherthan the fPAR variability.Conclusions: Our results provide valuable information forgrazing management (identifying spatial and temporalvariations of ANPP) and grassland conservation (identifyingthe spatial distribution of vegetation units).