Ernesto F. Viglizzo

Ecological lessons and applications from one century of low external-input farming in the pampas of Argentina

Ecology may benefit from long term, large scale experiments on low intensity farming to test theoretical principles and convert them into practical lessons. One century of land conversion in the Argentine pampas, and its effect on critical ecological properties, were analysed and discussed. Land transformation has resulted in significant changes of land use, land cover, energy flow, nutrient dynamics, hydrology, and the trade-offs between productivity, stability and sustainability. The analytical procedure involved the complementary utilisation of different data sources and approaches. The study was focused on large geographical scales: the entire pampas and its five ecoregions. Results were interpreted under the theoretical framework of succession in ecology. The historical conversion of natural grasslands into cultivated grasslands and croplands was not homogeneous, determining a variety of land use and land cover patterns. Due to its higher productivity, much more energy, nutrients and water were mobilised in the rolling pampas than in the other ecoregions. This study provides lessons about how the energy flow, the nutrient dynamics and the hydrological process are modified by land transformation under low external-input conditions. Technical coefficients to be applied in emerging fields of environment administration such as ecological-monitoring, environmental accounting and auditing, agro-ecological certification, land evaluation and allocation, and land management, can also be supplied by this kind of studies.

Climate and land-use change in field-crop ecosystems of Argentina

In line with a worldwide trend, statistical records in the Argentine Pampas show that cultivated lands increased greatly in the last century at the expense of natural areas. However, very little is known about the factors causing this. Our hypothesis was that climate was the main factor associated with land-use change in a high time-space scale, but factors other than climate would have to be considered in a scaling down analysis. The purposes of this work were (a) to study the dynamics of climate and land-use in the last century and across the Pampas plain, (b) to quantify the impact of climate on land-use change, and (c) to discuss the applicability of the results to guide adaptive land-use strategies. A broad transect was displayed along the underlying rainfall gradient to make a long-term analysis in different agroecological environments across the study region. Different statistical and research data sources were utilised, and simple regression analysis using linear and nonlinear models were applied. The results suggested that the original hypothesis had to be revised. In humid environments, the degree of association between climate and land-use change along the time axis was high, but this association declined in the transition from the humid to the semiarid zones. This suggested that factors other than climate, such as technology, could also explain a considerable part of land-use variability. On the other hand, the association between climate and land-use was very low across a wide geographic scale within a specific period of time. Thus, this association seems to be a site-specific and a time-dependent function, specially for the humid zones, and suggests that our former hypothesis can be accepted only in part. These results are necessary to guide land-use adaptive strategies in response to potential changes in the climate scenario.

Scale-dependent controls on ecological functions in agroecosystems of Argentina

Agricultural managers that operate at different levels (plot, farm, landscape, region) need to understand how ecological functions (energy, nutrients and water flows and cycles) are controlled by scale-dependent factors. Using cross-level data from the Argentine pampas, analyzed by simple and multiple regression analysis, we demonstrate that controls differ from one spatio-temporal level to the other, but they can be altered by humans. In the Argentine pampas, environmental controls (climate, landform, soil quality) seem to have a strong top-down influence on lower levels. But the bottom-up aggregated effect of anthropogenic controls seems to scale-up to upper levels and counteract such influence. Thus, the more intense use of land and technology in small units, the larger the up-scaling human influence on ecological functions. We suggest that a discrimination among farming intensity levels is useful and necessary to understand and predict human controls on ecological functions across scales.

On trade-offs in low-input agroecosystems

Abstract More fundamental knowledge on critical trade-offs is potentially important to improve the performance of low-input agroecosystems. Productivity, stability and sustainability are expressions of performance, and their trade-offs are a cause of scientific debate. Our results show that articulation and storage within the system play an important role in the trade-offs between productivity and stability, and between productivity and sustainability. Both articulation and storage involve complex structures that have a high maintenance cost, and consequently depress the overall ecosystem productivity. However, they are important to smooth the effect of external perturbations. The inverse relationship between productivity and stability and productivity and sustainability cannot be easily reverted unless external inputs are added. But some structural arrangements in the agroecosystem that produce anomalies and deviations from those inverse trends look promising as a means to reconcile opposite effects in a low-input scheme.

The response of low-input agricultural systems to environmental variability. A theoretical approach

Abstract The aims of this paper are: (a) to analyze the response of low-input agricultural systems to environmental variability; and (b) to suggest a theoretical framework to explain such behavior. Available evidence suggests that low-input systems are, in general, more sensitive than high-input systems to changes in the climatic environment. However, on the one hand this is not necessarily the case with respect to the economic environment, but, on the other hand, low-input systems of any region can differ in their response to similar environmental changes. Thus, when different levels of productivity and degrees of environmental sensitivity are combined, different patterns of performance can arise. A theoretical approach is presented in which the variations in system performance are related to system structure. It is suggested that a key feature is the degree of linkage between the system components. The ‘articulation hypothesis’ proposed here associates different patterns of articulation among essential components of the system with its performance. It is argued that, sensitivity in systems shows a negative relationship with the degree of internal articulations among different farming activities. The hypothesis also suggests that, the higher the internal articulation, the higher the maintenance cost, and hence, the lower the productivity of the system. Articulation appears to be a powerful risk-dissipative structural feature, reducing sensitivity at the price of lower productivity. In principle, the hypothesis could be successfully tested in marginal environments, but not in non-limiting or very extreme conditions.

Agroecosystems' performance in the semi-arid pampas of Argentina and their interactions with the environment

Abstract The main objectives of this work were to identify systems which showed different biological and economic performance, to elucidate their interactions with the biophysical and socio-economic environments, and to study some variables associated with varying system performance. Data from 34 farms in the semi-arid pampas of Argentina were analysed by cluster and linear correlation analysis. Farms were classified into two major groups: (1) the cattle production systems in the areas of lower rainfall; and (2) the cattle—crop systems associated with higher rainfall regimes. The procedures adopte were successful in identifying systems of different performance, and in selecting variables with a high degree of association with performance. Ten biological and 14 economic variables were selected to test their degree of association with systems productivity and their sensitivity to variations in the environment. Variables were then grouped into three sets concerned with environmental, ecological and managerial factors, and their relative impacts on systems performance were estimated. Results showed that: (1) systems did not necessarily coincide in terms of biological and economic performance; (2) the level of technology employed was a common factor associated with both biological and economic performance; and (3) the administrative ability farmers appeared to have high degree of association with the economic performance of the systems. A generalised model was proposed to describe the behaviour of systems with different performance, and their interactions with the environment. No clear relationship between sensitivity of systems to the environment and the selected variables was found.

Partition of some key regulating services in terrestrial ecosystems: Meta-analysis and review

Our knowledge about the functional foundations of ecosystem service (ES) provision is still limited and more research is needed to elucidate key functional mechanisms. Using a simplified eco-hydrological scheme, in this work we analyzed how land-use decisions modify the partition of some essential regulatory ES by altering basic relationships between biomass stocks and water flows. A comprehensive meta-analysis and review was conducted based on global, regional and local data from peer-reviewed publications. We analyzed five datasets comprising 1348 studies and 3948 records on precipitation (PPT), aboveground biomass (AGB), AGB change, evapotranspiration (ET), water yield (WY), WY change, runoff (R) and infiltration (I). The conceptual framework was focused on ES that are associated with the ecological functions (e.g., intermediate ES) of ET, WY, R and I. ES included soil protection, carbon sequestration, local climate regulation, water-flow regulation and water recharge. To address the problem of data normality, the analysis included both parametric and non-parametric regression analysis. Results demonstrate that PPT is a first-order biophysical factor that controls ES release at the broader scales. At decreasing scales, ES are partitioned as result of PPT interactions with other biophysical and anthropogenic factors. At intermediate scales, land-use change interacts with PPT modifying ES partition as it the case of afforestation in dry regions, where ET and climate regulation may be enhanced at the expense of R and water-flow regulation. At smaller scales, site-specific conditions such as topography interact with PPT and AGB displaying different ES partition formats. The probable implications of future land-use and climate change on some key ES production and partition are discussed.