Robust Estimation for Linear Panel Data Models

In different fields of applications including, but not limited to, behavioral, environmental, medical sciences and econometrics, the use of panel data regression models has become increasingly popular as a general framework for making meaningful statistical inferences. However, when the ordinary least squares (OLS) method is used to estimate the model parameters, presence of outliers may significantly alter the adequacy of such models by producing biased and inefficient estimates. In this work we propose a new, weighted likelihood based robust estimation procedure for linear panel data models with fixed and random effects. The finite sample performances of the proposed estimators have been illustrated through an extensive simulation study as well as with an application to blood pressure data set. Our thorough study demonstrates that the proposed estimators show significantly better performances over the traditional methods in the presence of outliers and produce competitive results to the OLS based estimates when no outliers are present in the data set

Vegetation trend after roller chopping and native grass seeding in La Rioja

In La Rioja plains, roller chopping and buffelgrass seeding is a widespread strategy for forage rec uperation of deg raded rangelands. Native grass species seeding arises a s apossible alternative strategy. The purpose of this study was to evaluate the medium time impacts of roller chopping and roller chopping + native species seeding on grass forage yield, cover and density and woody cover in degraded sites of critic environments of the mentioned region. Four treatments were evaluated, T0=control, T1=Roller chopping, T2= Roller chopping+Trichloris crinite (Lag.) Parodi seeding and T3= Roller chopping+Trichloris crinite (Lag.) Parodi and Pappophorum vaginatum Phil. seeding on three degraded environments. T1, T2 y T3 produced important increments (p<0.05) on grass forage grass, total perennial grass cover and density respect to T0. Initial impacts of roller chopping with and without seeding produced 68±13% diminution of woody cover with an annual recuperation rate of 7±2%. Results of this study suggest that, especially roller chopping + native grass seeding would be a promising alternative strategy for rapid recuperation of grass forage capacity of degraded areas at La Rioja plains.En Los Llanos de La Rioja, el rolado y siembra de buffel (Cenchrus ciliaris L.) es una estrategia difundida para recuperar la p roductividad de aéreas altamente degradadas. La siembra de especies nativas surge como una posible estrategia alternativa. El objetivo de este estudio fue evaluar el impacto a mediano plazo del rolado y rolado + siembra de especies nativas sobre la producción de forraje, eficiencia de uso de las precipitaciones, densidad y cobertura de gramíneas y cobertura de leñosas en sitios degradados de ambientes críticos de la región. Se evaluaron 4 tratamientos T0=testigo, T1=Rolado, T2= Rolado+ siembra de Trichloris crinita (Lag.) Parodi y T3=Rolado+siembra de Tricholris crinita y Pappophorum vaginatum Phil. en tres ambientes degradados. T1, T2 y T3 produjeron importantes incrementos (p<0,05) en la producción de forraje, la densidad y cobertura de gramíneas perennes respecto a T0. El impacto del rolado con o sin siembra produjo una disminución inicial del 68±13% de la cobertura de leñosas, y una posterior tasa de recuperación anual del 7±2%. Los resultados de este estudio sugieren que especialmente el rolado+siembra de especies nativas sería una estrategia alternativa promisoria para recuperar rápidamente la capacidad forrajera del estrato herbáceo en áreas degradas de ambientes críticos de Los Llanos de La Rioja

Efecto del rolado y siembra de buffel sobre la evolución del estrato graminoso en un arbustal degradado del Chaco árido

In Argentinean Chaco Arid region, rolling and buffelgrass seeding is widespread. In this region, information related to its short and medium time effects on vegetation attributes is available. The purpose of this study was to evaluate the long time impacts (10 years) of roller chopping and buffelgrass seeding on grass yield, precipitation use efficiency and cover in a degraded site of the mentioned region. The treatments were: T0 = No roller chopping-seeding (Control) and T1= Roller chopping+buffelgrass seeding. Forage grass yield and precipitation use efficiency tended to be higher in T1 than in T0 during the evaluation period. Forage grass yield increment in T1 was highly associated to increment in total perennial grass cover (R2=91%), mainly due to buffelgrass cover (R2=76%). In T1, native perennial grass cover showed a negative lineal tendency in relation to years. Annual native grass, perennial native grass, total perennial grass and buffelgras covers followed a quadratic tendency related to years. Results of this study suggest that roller chopping and simultaneous buffelgrass seeding is, from a point of view of animal production, an efficient strategy for rapid restoration of grass cover and grazing capacity of degraded areas and that its effects maintains in the long time.En el Chaco Árido, el rolado y siembra de buffel (Cenchrus ciliaris var. Texas 4464) está ampliamente difundido, contándose solo con información de los efectos a corto y mediano plazo de la aplicación de esta técnica sobre atributos de vegetación. El objetivo fue evaluar el impacto a largo plazo (10 años) del rolado y siembra de buffel sobre la producción de materia seca acumulada, eficiencia del uso de la precipitación y cobertura de gramíneas en un ambiente degradado de la región. Los tratamientos fueron: T0 = Sin rolado ni siembra (Testigo) y T1= Rolado + siembra simultanea de buffel. La producción de forraje y la eficiencia de uso de la precipitación tendieron a ser mayores en T1 respecto a T0, en todo el período evaluado. El incremento de la producción en T1 estuvo altamente relacionado al incremento en la cobertura de pastos perennes totales (R2=91%), principalmente a la cobertura de buffel (R2=76%). En T1, la cobertura de pastos nativos perennes tendió a disminuir en el tiempo, mientras que la cobertura de pastos nativos anuales, la de pastos perennes totales y la de buffel, presentaron una tendencia cuadrática. Estos resultados sugieren que el rolado y siembra de buffel, desde un punto de vista de la producción animal, es una eficiente estrategia para recuperar la capacidad de forrajera de sitios degradados del Chaco Árido

Contrasting CO2 and water vapour fluxes in dry forest and pasture sites of central Argentina

The dry forests of South America are a key player of the global carbon cycle and the regional water cycle, but they are being intensively deforested. We used eddy covariance measurements to compare the temporal patterns of CO2 and water vapour fluxes and their relationships with environmental variables in dry forest and pastures sites of central Argentina. Ecosystem fluxes showed clear contrasts in magnitude, timing and response to environmental controls between ecosystems. The dry forest displayed higher daily gross primary productivity (GPP, 10.6 vs. 7.8 g CO2 m−2 d−1) and ecosystem respiration (Reco, 9.1 vs. 7.0 g CO2 m−2 d−1) and lower net ecosystem exchange (NEE, −1.5 vs. −0.7 g CO2 m−2 d−1) than the pasture. These differences were explained by a lower tolerance of the pasture to cool temperatures and drought. The lowest NEE rates were observed between 26°C and 34°C in the pasture, but below this range, NEE increased sharply, switching to a carbon source with temperatures <20°C. By contrast, the dry forest remained as a strong carbon sink down to 18°C. The pasture also showed a stronger drop of GPP with drought compared with the dry forest, becoming a carbon source with soil wetness <25% of soil available water. Rainfall was strongly coupled with GPP in both ecosystems, but the dry forest responded to longer rainfall integration periods. This study helps to understand how ecosystems can respond to climate change, improve global scale modelling and increase the productivity and resilience of rangelands.Fil: Nosetto, Marcelo Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Luis. Instituto de Matemática Aplicada de San Luis "Prof. Ezio Marchi". Universidad Nacional de San Luis. Facultad de Ciencias Físico, Matemáticas y Naturales. Instituto de Matemática Aplicada de San Luis "Prof. Ezio Marchi"; ArgentinaFil: Luna Toledo, Emanuel Santiago. Instituto Nacional de Tecnología Agropecuaria; Argentina. Universidad Nacional de Chilecito; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Magliano, Patricio Nicolás. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Luis. Instituto de Matemática Aplicada de San Luis "Prof. Ezio Marchi". Universidad Nacional de San Luis. Facultad de Ciencias Físico, Matemáticas y Naturales. Instituto de Matemática Aplicada de San Luis "Prof. Ezio Marchi"; ArgentinaFil: Figuerola, Patricia Irene. Universidad Nacional de Chilecito; ArgentinaFil: Blanco, Lisandro Javier. Instituto Nacional de Tecnología Agropecuaria; ArgentinaFil: Jobbagy Gampel, Esteban Gabriel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Luis. Instituto de Matemática Aplicada de San Luis "Prof. Ezio Marchi". Universidad Nacional de San Luis. Facultad de Ciencias Físico, Matemáticas y Naturales. Instituto de Matemática Aplicada de San Luis "Prof. Ezio Marchi"; Argentin

The evolution and storage of primitive melts in the Eastern Volcanic Zone of Iceland: the 10 ka Grímsvötn tephra series (i.e. the Saksunarvatn ash)

Major, trace and volatile elements were measured in a suite of primitive macrocrysts and melt inclusions from the thickest layer of the 10 ka Grímsvötn tephra series (i.e. Saksunarvatn ash) at Lake Hvítárvatn in central Iceland. In the absence of primitive tholeiitic eruptions (MgO > 7 wt.%) within the Eastern Volcanic Zone (EVZ) of Iceland, these crystal and inclusion compositions provide an important insight into magmatic processes in this volcanically productive region. Matrix glass compositions show strong similarities with glass compositions from the AD 1783–84 Laki eruption, confirming the affinity of the tephra series with the Grímsvötn volcanic system. Macrocrysts can be divided into a primitive assemblage of zoned macrocryst cores (An_78–An_92, Mg#_cpx = 82–87, Fo_79.5–Fo_87) and an evolved assemblage consisting of unzoned macrocrysts and the rims of zoned macrocrysts (An_60–An_68, Mg#_cpx = 71–78, Fo_70–Fo_76). Although the evolved assemblage is close to being in equilibrium with the matrix glass, trace element disequilibrium between primitive and evolved assemblages indicates that they were derived from different distributions of mantle melt compositions. Juxtaposition of disequilibrium assemblages probably occurred during disaggregation of incompatible trace element-depleted mushes (mean La/Yb_melt = 2.1) into aphyric and incompatible trace element-enriched liquids (La/Yb_melt = 3.6) shortly before the growth of the evolved macrocryst assemblage. Post-entrapment modification of plagioclase-hosted melt inclusions has been minimal and high-Mg# inclusions record differentiation and mixing of compositionally variable mantle melts that are amongst the most primitive liquids known from the EVZ. Coupled high field strength element (HFSE) depletion and incompatible trace element enrichment in a subset of primitive plagioclase-hosted melt inclusions can be accounted for by inclusion formation following plagioclase dissolution driven by interaction with plagioclase-undersaturated melts. Thermobarometric calculations indicate that final crystal-melt equilibration within the evolved assemblage occurred at ~1140°C and 0.0–1.5 kbar. Considering the large volume of the erupted tephra and textural evidence for rapid crystallisation of the evolved assemblage, 0.0–1.5 kbar is considered unlikely to represent a pressure of long-term magma accumulation and storage. Multiple thermometers indicate that the primitive assemblage crystallised at high temperatures of 1240–1300°C. Different barometers, however, return markedly different crystallisation depth estimates. Raw clinopyroxene-melt pressures of 5.5–7.5 kbar conflict with apparent melt inclusion entrapment pressures of 1.4 kbar. After applying a correction derived from published experimental data, clinopyroxene-melt equilibria return mid-crustal pressures of 4±1.5 kbar, which are consistent with pressures estimated from the major element content of primitive melt inclusions. Long-term storage of primitive magmas in the mid-crust implies that low CO_2 concentrations measured in primitive plagioclase-hosted inclusions (262–800 ppm) result from post-entrapment CO_2 loss during transport through the shallow crust. In order to reconstruct basaltic plumbing system geometries from petrological data with greater confidence, mineral-melt equilibrium models require refinement at pressures of magma storage in Iceland. Further basalt phase equilibria experiments are thus needed within the crucial 1–7 kbar range.D.A.N. was supported by a Natural Environment Research Council studentship (NE/1528277/1) at the start of this project. SIMS analyses were supported by Natural Environment Research Council Ion Microprobe Facility award (IMF508/1013).This is the final version of the article. It first appeared from Springer via http://dx.doi.org/10.1007/s00410-015-1170-

Long-Term Vegetation Change in Central Africa: The Need for an Integrated Management Framework for Forests and Savannas

peer reviewedTropical forests and savannas are the main biomes in sub-Saharan Africa, covering most of the continent. Collectively they offer important habitat for biodiversity and provide multiple ecosystem services. Considering their global importance and the multiple sustainability challenges they face in the era of the Anthropocene, this chapter undertakes a comprehensive analysis of the past, present, and future vegetation patterns in central African forests and savannas. Past changes in climate, vegetation, land use, and human activity have affected the distribution of forests and savannas across central Africa. Currently, forests form a continuous block across the wet and moist areas of central Africa, and are characterized by high tree cover (>90% tree cover). Savannas and woodlands have lower tree cover (<40% tree cover), are found in drier sites in the north and south of the region, and are maintained by frequent fires. Recent tree cover loss (2000–2015) has been more important for forests than for savannas, which, however, reportedly experienced woody encroachment. Future cropland expansion is expected to have a strong impact on savannas, while the extent of climatic impacts depends on the actual scenario. We finally identify some of the policy implications for restoring ecosystems, expanding protected areas, and designing sustainable ecosystem management approaches in the region

Cours d'institutes et d'histoiredu droit romain

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