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Questions: Can herbaceous above-ground net primary production (ANPP) be estimated from remote sensing when woody and herbaceous plants are intermingled? How does herbaceous ANPP change in space and time in an ecosystem dominated by woody species? What are the main controls of herbaceous ANPP to paddock scale?. Location: Native plant communities and buffelgrass roller chopped pastures of the Arid Chaco, western Argentina (28–32° S, 64–67° W; area: 100 000 km2). Methods: We decomposed normalized difference vegetation index (NDVI) data from MODIS (pixel size: 250 m × 250 m) into woody (W) and herbaceous (H) components. We calibrated the relationship between field estimates of herbaceous ANPP and the H component of NDVI using linear regression. The regression model fitted was applied to a 10-yr MODIS database for four paddocks to estimate herbaceous ANPP. We analysed the relationship between herbaceous ANPP and watering point distance and growing season precipitation. Results: The annual integral of NDVI × proportion of the herbaceous component [H/(H + W)] explained 71% and 91% of herbaceous ANPP variation in native plant communities and buffelgrass roller chopped pastures, respectively. The regression model fitted, however, differed (P

Questions: (1) Can above-ground net primary production (ANPP) of Patagonian meadows be estimated from remote sensing? (2) How does ANPP of Patagonian meadows change in space and time? Location: Northwestern Patagonia, meadows embedded in a steppe matrix (39–43°S, 70–72oW; area: 85 000 km 2 ). Methods: For the first question, we contrasted field ANPP measurements with MODIS high-spatial resolution (pixel size: 0.0625 km 2 ) data and developed a model that estimates radiation use efficiency. For the second question, we applied the model to a 6-year MODIS record for 14 meadows whose physiognomic heterogeneity was known from previous work. Results: Up to 77% of the field-based ANPP variation was accounted for by the absorbed photosynthetic radiation, based on a linear transformation of the normalized difference vegetation index derived from MODIS data. Mean radiation use efficiency was 0.54 g dry matter MJ � 1 . ANPP ranged between 610 and 1060 g m � 2 year � 1 , which represents three to 5.3 times the ANPP of the surrounding arid and semi-arid steppes. The inter-annual coefficient of variation of ANPP was 10%, which is higher than other systems of similar productivity, but much lower than the surrounding steppes (33%). At the level of management units (paddock), ANPP spatial variations were mainly related to the proportion of Prairies, a proxy for low topographic position in the landscape, and longitude, a proxy for precipitation. ANPP inter-annual variation was most related to latitude, a proxy for temperature. Conclusion: The model developed and tested can be used to infer ANPP from remote sensing data at a spatial resolution that allows one to detect variability within meadows and management units. Variations at both the physiognomic unit and paddock level were associated with geographic patterns and topography. Meadows were three to five times more productive and less fluctuating than nearby steppes. When compared with other ecosystems, their productivity was high, but more variable inter-annually, likely due to exceptionally high variability of precipitation in Patagonia.

Question: Do species traits explain differences in productivity in grazed and ungrazed plots?

Question: Are trait differences between grasses along a gradient related to climatic variables and/or photosynthetic pathway? Location: Temperate grassland areas of South and North America. Methods: In a common garden experiment, we cultivated C3 and C4 grasses from grasslands under different climatic conditions, and we measured a set of 12 plant traits related to size and resource capture and utilization. We described (1) interspecific plant trait differences along a climatic gradient defined by the precipitation and temperature at the location where each species is dominant and (2) the association between those plant trait differences and the photosynthetic pathway of the species. Results: Trait differences between grasses were related to the precipitation at the area where each species is dominant, and to the photosynthetic pathway of the species. Leaf length, leaf width, plant height, leaf area per tiller, specific leaf area, leaf δ13C ratio, and nitrogen resorption efficiency increased while...

Question: What are the changes in vegetation structure, soil attributes and mesofauna associated with grazing in mesic grasslands? Location: Southern Campos of the Rio de la Plata grasslands, in south-central Uruguay. Methods: We surveyed seven continuously grazed and ungrazed paired plots. Plant and litter cover were recorded on three 5-m interception lines placed parallel to the fence in each plot. We extracted soil fauna from a 10 cm deep composite sample and analysed the oribatids. Soil attributes included bulk density, water content, organic carbon (in particulate and mineral associated organic matter) and nitrogen content and root biomass at different depths. Changes in floristic, Plant Functional Types and mesofauna composition were analysed by Non-metric Multidimensional Scaling. Results: Species number was lower in ungrazed than in grazed plots. Of 105 species in grazed plots only three were exotics. Shrub and litter cover were significantly higher inside the exclosures, while the cover of Cyperaceae-Juncaceae was lower. Grazing treatments differed significantly in plant and oribatid species composition.. Grazing exclusion significantly reduced soil bulk density and increased soil water content. Carbon content in particulate organic matter was lower in the upper soil of ungrazed sites, but deeper in the profile, grazing exclosures had 8% more carbon in the mineral associated organic matter. Conclusions: Our results generally agree with previous studies but deviate from the results of previous analyses in (1) the increase of shrub cover in ungrazed sites; (2) the redistribution of the soil organic carbon in the profile and (3) the low invasibility of the prairies regardless of grazing regime.

We studied floristic and diversity patterns and their environmental controls in two landscapes of contrasting to- pography in the Patagonian steppe. The analyses were focused on the effects of water availability gradients and landscape configuration on plant species distribution and coexistence. Floristic variation was investigated using Correspondence Analysis. The relationship between floristic and environmen- tal variation was analyzed using Canonical Correspondence Analysis and correlation tests. We explored diversity patterns by relating spatial distance to floristic dissimilarities. The floristic gradient was determined by shrub and grass species and was related to precipitation in the flat area, and to precipi- tation, elevation and potential radiation in the mountain area. Site species richness increased with water availability in both areas. Mean site species richness and species turnover in space was higher in the mountain than in the flat area. Landscape species richness and floristic gradients were more concen- trated in the mountain than in the flat area. In contrast to shrubs

Grass cover along a grazing intensity gradient in Patagonia decreases, whereas bare soil and shrub cover increases. Our objective was to study the effect of a change in the dominant plant functional type on soil water balance, primary production, herbivore biomass, roughness, and albedo. Using a soil water balance model, we found increases in evaporation and deep drainage, and a decrease in total transpiration along the grazing intensity gradient. Above-ground primary production, estimated from transpiration, decreased along the grazing intensity gradient because shrubs did not fully compensate for the decrease in grass production. Using a statistical model, we calculated herbivore biomass from estimates of above-ground primary production. Estimated herbivore biomass was lowest in the shrub-dominated extreme of the grazing gradient. Roughness increased from the grass-dominated to the shrub-dominated community. Albedo had a maximum at an intermediate position along the gradient. Our results suggest that changes in plant functional type composition, independent of changes in biomass, affect ecosystem functioning and the exchange of energy and material with the atmosphere. Grasses and shrubs proved to be appropriate plant functional types to link structure and function of ecosystems.

Variation in vegetation in extra-Andean Patagonia (Argentina) was analyzed using spectral data derived from AVHRR/NOAA satellite. The study of seasonal dynamics of the Normalized Difference Vegetation Index (NDVI, i.e. a combined index of the reflection in the red and infrared bands) highlighted similarities in functional aspects between regional vegetation units which are dissimilar in a geographical, physiognomical and/or floristical way, and also suggested that gross primary production is correlated with mean annual rainfall. The first axis in a Principal Component Analysis of NDVI data was correlated (r2 = 0.90) with NDVI as integrated for the study period. The second axis was correlated (r2 = 0.50) with the differences in NDVI during the growing season, reflecting seasonality. Mean annual rainfall accounted for 60% of integrated NDVI variability among vegetation units. Much of the residual variance (62%) was accounted for by the inverse of the distance to the Atlantic Ocean, which is interpreted as an ocean effect on vegetation functioning in the extra-Andean Patagonia.