Variations in Anarthrophyllum rigidum radial growth, NDVI and ecosystem productivity in the Patagonian shrubby steppes

SRUR, ANA M.; VILLALBA, RICARDO; BALDI, GERMÁN

PLANT ECOLOGY

SPRINGER

Año: 2011 vol. 212 p. 1841 - 1854

1385-0237

The lack of long-term records of productivityis a critical limitation to the study of ecosystemdynamics. Annual rings, a measure of growth inwoody species, are a useful tool to documentecosystem dynamics. Time series of the NormalizedDifference Vegetation Index (NDVI) provide estimatesof ecosystem productivity through satellitederiveddata on the fraction of photosynthetic activeradiation absorbed by vegetation. In the Patagoniansteppes, we relate changes in NDVI to interannualvariations in the radial growth of the shrub Anarthrophyllumrigidum. A widely distributed network of15 ring-width chronologies of A. rigidum was used toestimate changes in NDVI across the Patagoniasteppe (35–50S). In most sites, interannual variationsin shrub growth and NDVI are regulated bywinter precipitation. The water accumulated in thesoil during winter is used by A. rigidum during thegrowing season, concurrent with the maximum NDVIvalues. At 10 from the 15 selected sites, variations inthe radial growth of A. rigidum explained between 23and 62% of the total variance in seasonal NDVI, suggesting that the A. rigidum growth at some sitesprovides good estimates of productivity in thePatagonian shrubby steppes during the growingseason. However, we were unable to determine clearrelationships between radial growth and NDVI athigh-elevation mountainous sites or where intensivegrazing by sheep masked the effect of climatevariability on shrub growth. We conclude thatdendrochronological methods can complement otherestimates to reconstruct variations of productivity,supplementing and extending the few short recordsavailable in the Patagonian steppe.