Latin America in general and the Rio de la Plata Grasslands (RPG) in particular, are one of the regions in the world with the highest rates of change in land use/land cover (LULC) in recent times. ...Despite the magnitude of this change process, LULC descriptions in the RPG are far from being complete, even more those that evaluate LULC change through time. In this work we described LULC and its changes over time for the first 14 years of the 21st century and for the entire grassland biome of the Rio de la Plata, one of the most extensive grassland regions in the world. We performed simple but exhaustive classifications at regional level based on vegetation phenology, using extensive LULC field database, time series of MODIS NDVI satellite images and decision trees classifiers, generating an annual map for all RPG. The used technique achieved very good levels of accuracy at the regional (94.3%–95.5%) and sub-regional (78.2%–97.6%) scales, with commission and omission errors generally low (Min = 0.6, Max = 10.3, Median = 5.7, and Min = 0, Max = 41.8, Median = 6.8 for regional and sub regional classification respectively) and evenly distributed, but fails when LULC classifications are generated in years when the climate is very different from those used to generate spectral signatures and train decision trees, or when the NDVI time series accumulates large volumes of lost data. Our results show that the RPG are immersed in a strong process of land use change, mainly due to the advance of the agricultural frontier and at the expense of loss of grassland areas. The agricultural area increased 23% in the analyzed period, adding over than 50,000 Km2 of new crops. Most agricultural expansion, and therefore the greatest losses of grassland, concentrates on both sides of Uruguay river (Mesopotamic Pampa and the western portion of Southern and Northern Campos) and the western portion of Inland Pampa. The generated maps open the door for more detailed and spatially explicit modeling of many important aspects of ecosystem functioning, for quantification in the provision of ecosystem services and for more efficient management of natural resources.
Questions: Does the magnitude of grazing-induced changes in species composition vary with habitat productivity? How does the sign and magnitude of grazing effects on species richness and ...beta-diversity change with increasing productivity? Do major life forms exhibit consistent responses to grazing along productivity gradients? Location: Steppes and grasslands of southern South America in Argentina and Uruguay. Methods: We evaluated grazing effects on plant composition, species richness, beta-diversity and life-form abundances along a ten-fold, regional productivity gradient and within subregions of contrasting productivity, using a common sampling protocol for 23 paired grazed vs ungrazed plots. The annual integral of the normalized difference vegetation index was used as a surrogate for above-ground net primary productivity. Results: Compositional dissimilarity between grazed and ungrazed plots, as well as grazing-induced differences in plant richness and beta-diversity all increased with habitat productivity. Grazing decreased species richness in low-productive steppes but enhanced the richness of high-productive grasslands. On average, grazing reduced beta-diversity in high-productive sites but not in low-productive sites. Dominant species were more strongly suppressed by grazing towards productive grasslands. Grazing generally decreased shrub species cover, whereas graminoid and forb cover did not consistently change with grazing through the productivity gradient. Conclusions: Our results indicate that the overall grazing effects on vegetation structure increased along a regional productivity gradient. Yet the sign of grazing impacts on species richness and beta-diversity shifted with habitat productivity, in agreement with models of herbivore-mediated co-existence and species colonization in productive systems. Further, we found that narrowing the spatial extent of analysis to the subregion generally obscured grazing–productivity relationships. Biodiversity conservation programmes should carefully weigh the varied impacts of livestock grazing across productivity gradients.
Background and aims Grazing can affect the stock and flow of C between above and below-ground vegetation layers. Components of below-ground stratum are one of the less studied. The goals of this ...research were: 1) to characterize and estimate the vertical distribution of below-ground biomass in grazed and ungrazed areas during a growing season, and 2) to evaluate grazing effects on below-ground net primary production (BNPP). Methods Below-ground biomass was cored four times to 100 cm depth during a growing season on three paired grazed-ungrazed areas in South-central Uruguayan grasslands. BNPP was estimated using both field data and CENTURY model. Results On average, below-ground biomass was higher in grazed (1417 gm−2) than in ungrazed areas (945 gm−2) and showed a marked reduction in relation with soil depth. Turnover rates were 0.40 and 0.37 years−1 in grazed and ungrazed areas respectively. Field data and CENTURY simulation showed higher BNPP in grazed areas (1.86; 0.77 gm−2days−1 respectively) than in ungrazed areas (1.07; 0.67 gm−2days−1 respectively). Conclusions Grazed areas showed higher below-ground biomass, BNPP and turnover that ungrazed areas. Grazing has an important role in regulating both stock and dynamics of C in grassland ecosystems.
Questions: Do the effects of grazing components on vegetation structure differ in their relative importance? Do components interact in their effect on vegetation? Location: San Jose department, ...Southern Campos, Uruguay. Methods: In a manipulative field experiment we simulated three different grazing components: trampling, defoliation and urine deposition, over 3 yr in a natural grassland. Defoliation was analysed through two intensity levels and two procedures: uniform and selective cutting. We evaluated the effects of grazing components on species diversity and composition, and frequency of plant functional types. Results: All simulated grazing components had at least some effect on vegetation structure. Additionally, both individual and interactive effects on vegetation attributes were detected. Our study indicates that the relative influence of each grazing component varied according to the attribute considered. N addition was the only treatment that affected plant diversity. Plant functional type composition, in turn, was affected mainly by trampling. N addition and trampling were the component that affected the frequency of the largest number of species. Defoliation selectivity showed effects both in terms of plant functional type and species composition. Exclosure treatment and defoliation intensity had slight effects on grassland structure. Conclusions: This study provides insight on the underlying mechanisms of some observed patterns of grazing on the Campos grasslands. Our results lead us to conclude that all grazing components have to be taken into account to understand vegetation dynamics subjected to grazing. Prevention of woody encroachment by grazing can be attributed to direct and indirect effects of trampling. Trampling should be taken into account to explain increaser species responses. However, mechanisms responsible for other general patterns remain less clear. The importance of selective defoliation in species replacement induced by grazing in these grasslands has yet to be clarified.
Latin America, and particularly, the Rio de la Plata Grasslands (RPG), are one of the regions with the highest rates of land use change worldwide. These changes drastically alter ecosystems energy ...flows, affecting biodiversity, atmospheric composition, and the ecosystem capacity to provide services. In this work we evaluated the impact of these changes on Net Primary Production (NPP), one of the most important and integrative ecosystem attributes, through the calculation of Human Appropriation of NPP (HANPP), a very complete indicator of human impact on ecosystems. Our results provide a comprehensive and fine grained description of HANPP patterns over an entire biogeographycal region for two periods that encompass a strong agricultural intensification process. We used medium resolution land use maps and NPP estimates from sub-national level agricultural statistics and remotely sensed data modeling. Results show that the human impact on the energy flow in RPG ecosystems reached very high levels compared to other regions of the world. The average appropriation of was 42% of the potential vegetation NPP in 2001/2002 and it increased 4.5% during the last years due to an intense land use changes. Most of the HANPP was explained by harvest rather than by land use changes, mainly in the last period due to crops yield increase and the expansion of double crop system as a common agronomic practice. High HANPP values found were associated to a set of environmental impacts that affect ecosystems sustainability and their ability to provide ecosystem services.
A common and simple approach to evaluate models is to regress predicted vs. observed values (or vice versa) and compare slope and intercept parameters against the 1:1 line. However, based on a review ...of the literature it seems to be no consensus on which variable (predicted or observed) should be placed in each axis. Although some researchers think that it is identical, probably because
r
2 is the same for both regressions, the intercept and the slope of each regression differ and, in turn, may change the result of the model evaluation. We present mathematical evidence showing that the regression of predicted (in the
y-axis) vs. observed data (in the
x-axis) (PO) to evaluate models is incorrect and should lead to an erroneous estimate of the slope and intercept. In other words, a spurious effect is added to the regression parameters when regressing PO values and comparing them against the 1:1 line. Observed (in the
y-axis) vs. predicted (in the
x-axis) (OP) regressions should be used instead. We also show in an example from the literature that both approaches produce significantly different results that may change the conclusions of the model evaluation.
Grazing modifies the structure and function of ecosystems, affecting soil organic carbon (SOC) storage. Although grazing effects on some ecosystem attributes have been thoroughly reviewed, current ...literature on grazing effects on SOC needs to be synthesized. Our objective was to synthesize the effects of grazing on SOC stocks in grasslands, establishing the major mechanistic pathways involved. Additionally, and because of its importance for carbon (C) biogeochemistry, we discuss the controls of soil organic nitrogen (N) stocks. We reviewed articles analyzing grazing effects on soil organic matter (SOM) stocks by comparing grazed vs. ungrazed sites, including 67 paired comparisons. SOC increased, decreased, or remained unchanged under contrasting grazing conditions across temperature and precipitation gradients, which suggests that grazing influences the factors that control SOC accumulation in a complex way. However, our review also revealed some general patterns such as 1) root contents (a primary control of SOC formation) were higher in grazed than in their ungrazed counterparts at the driest and wettest sites, but were lower at sites with intermediate precipitation (∼400 mm to 850 mm); 2) SOM C∶N ratios frequently increased under grazing conditions, which suggests potential N limitations for SOM formation under grazing; and 3) bulk density either increased or did not change in grazed sites. Nearly all sites located in the intermediate precipitation range showed decreases or no changes in SOC. We grouped previously proposed mechanisms of grazing control over SOC into three major pathways that can operate simultaneously: 1) changes in net primary production (NPP pathway), 2) changes in nitrogen stocks (nitrogen pathway), and 3) changes in organic matter decomposition (decomposition pathway). The relative importance of the three pathways may generate variable responses of SOC to grazing. Our conceptual model suggests that rangeland productivity and soil carbon sequestration can be simultaneously increased by management practices aimed at increasing N retention at the landscape level.
The aim of this work was to characterize the spatial and temporal dynamics of the transformation of the natural cover in the Dry Chaco ecoregion from 1976 to 2012. Dry forests in this region have one ...of the highest deforestation rates in the world. We analyzed 44 Landsat scenes, including part of Argentina, Paraguay and Bolivia. The analysis was based on tracking individual transformed plots of the entire Dry Chaco region for over more than three decades using the same protocol. Until the end of 2012 15.8 million ha of the original habitats of the Chaco were transformed into croplands or pastures. Our study showed that the greater annual rates of transformation were observed in Paraguay, where deforestation increased dramatically in the last decade, reaching values higher than 4.0% in 2010, the highest historical value in the entire region. The size of the transformed plots increased significantly through the studied period both in Argentina and Paraguay, while in Bolivia decreased. At the landscape level, the use of several fragmentation indices showed the disruption of the continuity and connectivity of the original vegetation. The spatially explicit description of the dynamics of transformed areas is an indispensable tool for natural resources management, territorial planning and deforestation impacts assessment. The developed geo-database is available online at http://monitoreodesmonte.com.ar/ for further analyses and use.
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•We generated a geo-database of the natural cover transformation in Dry Chaco.•We analyzed the deforestation patterns at plot and landscape level.•The transformed area in Dry Chaco by the end of 2012 totalized 15.8 million ha.•Annual Rates of Transformation were intensified from 1976 to 2012 at country level.•Paraguay showed an exponential increase in the Annual Rate of Transformation.
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•An index of Ecosystem Services provision based on remotely sensed data was developed.•The index varied according changes in total C gains seasonality.•One third of temperate and ...subtropical South America presented a significant trend in the index.
We present an approach to generate estimates and to map Ecosystem Services (ES) related to C and water dynamics (Soil Carbon sequestration, evapotranspiration and groundwater recharge) and biodiversity (Avian Richness) from remotely sensed data in two ecoregions of South America: the Semiarid Chaco woodlands and the Rio de la Plata grasslands. Two attributes of the seasonal dynamics of the Normalized Difference Vegetation Index (NDVI); the annual mean (NDVI mean), an indicator of light interception and hence of total C gains and the intra-annual Coefficient of Variation of the NDVI (NDVI CV), a descriptor of seasonality; were combined into an ES provision index (ESPI=NDVImean * (1-NDVICV)). The proportion of the variance in ES provision explained by the ESPI varied from 0.484 for avian richness up to 0.662 for C sequestration. A relatively large proportion of the studied area presented changes in ES provision. A 32,4% of the Semiarid Chaco and the Rio de la Plata grasslands presented significant (p<0.01) trends. Most of the trends (30.2%) were negative, showing a decrease in ESPI. An index like the one proposed here can be used as an aggregated indicator of the status and/or trends of ES supply at large spatial scales (subcontinental in our case).
An important goal of conservation biology is the maintenance of ecosystem processes. Incorporating quantitative measurements of ecosystem functions into conservation practice is important given that ...it provides not only proxies for biodiversity patterns, but also new tools and criteria for management. In the satellite era, the translation of spectral information into ecosystem functional variables expands and complements the more traditional use of satellite imagery in conservation biology. Remote sensing scientists have generated accurate techniques to quantify ecosystem processes and properties of key importance for conservation planning such as primary production, ecosystem carbon gains, surface temperature, albedo, evapotranspiration, and precipitation use efficiency; however, these techniques are still unfamiliar to conservation biologists. In this article, we identify specific fields where a remotely-sensed characterization of ecosystem functioning may aid conservation science and practice. Such fields include the management and monitoring of species and populations of conservation concern; the assessment of ecosystem representativeness and singularity; the use of protected areas as reference sites to assess global change effects; the implementation of monitoring and warning systems to guide adaptive management; the direct evaluation of supporting ecosystem services; and the planning and monitoring of ecological restorations. The approaches presented here illustrate feasible ways to incorporate the ecosystem functioning dimension into conservation through the use of satellite-derived information.
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