Productive performance of alternative land covers along aridity gradients: Ecological, agronomic and economic perspectives

MURRAY, FRANCISCO; BALDI, GERMÁN; VON VERNARD, TAMARA; VIGLIZZO, ERNESTO; JOBBÁGY, ESTEBAN G.

AGRICULTURAL SYSTEMS

ELSEVIER SCI LTD

Lugar: Amsterdam; Año: 2016 vol. 149 p. 20 - 29

0308-521X

The replacement of natural vegetation by pastures and extensive crops is generally driven by economic incentives and supported by technology improvements and multiple subsidies. Towards areas of increasing aridity, however, the ecological, agronomic and economic performance of this replacement may decline, due to intrinsic differences in the structural and physiological adjustment of natural and cultivated vegetation to increasingly reduced and fluctuating water availability. Here we compare tree-dominated natural vegetation, perennial pastures and annual crops (maize, soybean and wheat) along a gradient of decreasing water availability (900-500 mm of mean annual precipitation) within the Chaco and Espinal regions of South America. We assess (i) aboveground net primary productivity (ANPP) and its inter-annual variability, (ii) agronomic yields in terms of product dry mass and edible energy and protein outputs and, (iii) economic performance captured by gross margins and return of investment (ROI). We linked climatic data with yield data from national statistics, field trials, empiric models and satellite information, together with productive parameters and market prices obtained from local technical reports and economic bulletins. Maize achieved the highest ANPP of all vegetation covers (+42% in average compared to the rest) along the entire water availability gradient, while the rest of the crops were very similar to natural vegetation. Pastures approached the ANPP of natural vegetation in the humid range, but had a poorer performance below 700 mm (-13%). ANPP interannual variability, as captured by remote sensing greenness indexes, was higher in crops and pastures than in natural vegetation (0.15 and 0.13 vs. 0.08 of average NDVI and EVI CV). Along the entire gradient, goods dry mass and edible energy and protein yields were higher for crops compared to natural vegetation and pastures (2,677 vs. 449 kg, 10,101 vs. 140 Mcal and 436 vs. 8 kg ha-1 year-1 for crops vs. average of the rest, respectively). Soybean had the highest gross benefits per hectare (+149%) and total capital ROI (+159%), while pasture had the highest working capital ROI (+230%) because its lower operative costs and higher product prices. Hence, we revealed the decisive influence of crop choice, rather than land cover type, defining a key ecological attribute such as ANPP. Even with lower agronomic yields than annual crops, pastures offered the highest financial returns, explaining their relevance at the onset of the natural vegetation replacement process, when land prices are still low and capital is limiting, and the gradual prevalence of crops when land becomes more limiting than capital. Although there are strong agronomic and economical incentives for natural vegetation replacement, their ecological consequences are highly dependent on the trajectory of these transformations, which in turn are highly influenced by land and capital costs, infrastructure, and territorial regulations, among others.