Aboveground Net Primary Production spatial variability of Uruguayan Grasslands: a remote sensing approach

BAEZA, SANTIAGO; LEZAMA, F.; PIÑEIRO, GERVASIO; ALTESOR, A.I.; PARUELO, JOSÉ M.

APPLIED VEGETATION SCIENCE

Wiley-Blackwell

Año: 2008

1402-2001

Abstract Question: How does ANPP differ (estimated from remotely sensed data) among vegetation units in sub-humid temperate grasslands? Location: Centre-north Uruguay. Methods: We generated a vegetation map of the study area from a supervised classification of LANDSAT TM imagery based on field data, and we described the landscape configuration. We analyzed the functional heterogeneity of mapping units in terms of the fraction of photosynthetically active radiation absorbed by green vegetation (fPAR), calculated from the Normalized Difference Vegetation Index (NDVI) images provided by the MODIS sensor. Finally, we estimated the Aboveground Net Primary Production (ANPP) of each grassland class using NDVI and climatic data. Results: Supervised classification presented an overall accuracy greater than 90%. Meso-xerophytic grasslands occupied 45% of the area, Meso-hydrophytic grasslands 43% and Lithophytic steppes 6%. The landscape was shaped by a matrix of large, unfragmented patches of Meso-xerophytic and Meso-hydrophytic grasslands. The region presented the lowest anthropic fragmentation degree reported for the Rio de la Plata grasslands. All grassland units showed bimodal annual fPAR seasonality, with spring and autumn peaks. Meso-hydrophytic grasslands showed a radiation interception 10% higher than the other units. On an annual basis, Meso-hydrophytic grasslands produced 3800 KgDM.ha-1.year-1 and Meso-xerophytic grasslands and Lithophytic steppes around 3400 KgDM.ha-1.year-1. Meso-xerophytic grasslands had the largest spatial variation during most part of the year. ANPP temporal variation was higher than the variability of fPAR. Conclusions: Our results provide valuable information for two applied issues: grazing management (identifying spatial and temporal variations of ANPP) and grassland conservation (identifying the spatial distribution of vegetation units).