Question: How well does the use of NDVI predict secondary productivity at landscape scales? What is the influence of vegetation quality and phenology over secondary productivity?

Location: Magellanic steppe in Tierra del Fuego, Argentina. (52°45′ to 54° S, 68°15′ to 67°30′ W).

Methods: Monthly and yearly integrated NDVI (NDVI-I) were calculated from AVHRR/NOAA 14, as estimators of phenology and aerial net primary productivity respectively. From a vegetation map we obtained the proportional cover of different physiognomic types and calculated the palatable fraction (forage) productivity that were used as estimators of vegetation quality. Data were analysed through correlations and regressions.

Results: NDVI-I was not related with secondary productivity indices, while December and annual maximum NDVI, proportion of lawns and tussock grasslands and forage productivity were positively related with secondary productivity. A negative relationship was found between the proportion of heathlands and secondary productivity, but a positive relationship between heathland's proportion and NDVI-I was found.

Conclusions: NDVI-I is not a good predictor of secondary productivity at the scale of our study. These results could be due to: (1) NDVI-I is not related to primary productivity and (2) primary productivity is not related to secondary productivity.

Abbreviations: ANPP = Above-ground net primary productivity; aPAR = Absorbed photosynthetic active radiation; AVHRR = Advanced very high resolution radiometer; NDVI = Normalized difference vegetation index; NDVI-I = Integrated normalized difference vegetation index; NOAA = National Oceanic and Atmospheric Administration.