ABSTRACT Background: Atmospheric methane (CH 4) is responsible for approximately 20% of global warming since the preindustrial era. Forests are land ecosystems whose role is crucial for mitigating the greenhouse effect due to their capacity to capture and store C and preserve other processes such as CH 4 oxidation in the soil. On the other hand, in the particular case of afforestation, there are contradictory results about the magnitude of CH 4 uptake variation due to changes in methanotrophic bacteria activity and its relationship with micro-environmental conditions. Results: The average potential CH 4 oxidation rate in the laboratory (MOL) of afforested soil was 186% greater than that of the grassland, which could be marginally attributed to differences in soil physicochemical parameters like bulk density, pH and organic matter. A seasonal pattern in MOL was observed in both land uses, with the highest values at the warm and rainy season. MOL magnitude increased with soil depth up to 10-15 cm, which corresponds with the mineral layer. Conclusion: Pine afforestation would improve the biological soil attributes linked to methane oxidising bacteria compared to the grassland systems.

ABSTRACT Stand density management diagrams (SDMD) provide a guide for forest density management taking into account stands attributes such as trees´ diameter or volume. One of the most common species planted in Pampean plains of Argentina is Eucalyptus viminalis for multiple objectives: solid wood use or firewood in local markets, pulp for cellulose industry and to provide services for agriculture and cattle raising (windbreaks or cattle refuge). The objective of this study was to gather the available production information /inventory data and to develop a first SDMD for estimating standing volume, biomass and canopy cover of E. viminalis as a tool for forest managers aiming at different plantation purposes. Data to develop the SDMD were obtained from 161 plots, distributed along a climate and soil gradient. We also generated two predictive equations capable of estimating dominant height from the diameter of the trees as well as canopy cover from stand basal area. As an example of application, the SDMD was used to estimate the wood production of three alternative systems: a) an unmanaged plantation (simulating a common practice in the region), b) a mixed production system such as an agroforestry system, and c) a plantation that maximizes wood biomass or volume production.

The objective of this paper was to design sequential sampling plans for the spotted alfalfa aphid (Therioaphis trifolii Monell) with fixed precision level, for density estimation and decision making. The study of spatial pattern based on Taylor's Power Law and Iwao's regression, showed different degrees of clumping of T. trifolii populations in alfalfa crops, depending on the developmental stage of aphids. The sequential sampling plan for decision making was calculated using two economic thresholds based on the height of the crop. The sequential sampling models developed by Kuno and by Green, were used to calculate stop lines. Green's model is recommended because Taylor's Power Law's regression yielded higher determination coefficients than Iwao's method.

El objetivo de este trabajo fue construir planes secuenciales de muestreo para el pulgón manchado de la alfalfa, Therioaphis trifolii Monell (Homoptera: Aphididae), con niveles fijos de precisión para estimar su densidad en función de toma de decisiones. El estudio de la disposición espacial basado en la Ley de Potencia de Taylor y regresión de Iwao, indicó que esta especie se distribuye de manera agregada en el cultivo de alfalfa, aunque con diferentes grados de agregación según el estado de desarrollo de los áfidos. Para el cálculo del plan secuencial de muestreo se usaron dos umbrales económicos según la altura del cultivo. Para el cálculo de las líneas críticas se utilizaron los modelos secuenciales de muestreo desarrollados por Kuno y por Green. Se recomienda el modelo de Green debido a que la Ley de Potencia de Taylor mostró los mayores coeficientes de determinación.

Eriopis connexa (Germar) is an important aphidophagous coccinelid, widely distributed in several South American countries. The influence of different feeding and temperature conditions on biological features of the immature and adult stages, were studied. Cohorts of cocinelids larvae were reared on the combinations of four constant temperatures (9, 15, 19 and 27ºC) and six diets based on Acyrthosiphon pisum Harris and Schizaphis graminum (Rondani) aphid species with, respectively, four and two different initial numbers and increasing rates. Tested temperatures above 15ºC did not affect the number of eggs/cluster and their viability. Incubation time varied from 2.5 days and a 92% of hatched eggs at 27ºC, to 13 days with a 71% of viability at 15ºC. At 9ºC, neither oviposition nor births were observed, although development until adult stage could be achieved at four experimental temperatures. The combination of food supply and temperature affected both aphid ingestion and immature developmental times, but not adult sizes. The number of A. pisum and S. graminum consumed varied approximately from 57 to 256 and from 104 to 641, respectively. Developmental times, from larval to adult stage, ranged from ca. 84 days at 9ºC to ca. 12 days at 27ºC. Larger adult sizes were observed at 19ºC. Body weight of adults increased when they were offered greater numbers of aphids. Pronotum widths and femur lengths were slightly influenced by prey species but these dimensions were independent on larvae ingestion of food.

Eriopis connexa (Germar) es un importante coccinélido afidófago distribuido en varios países de Sudamérica. Se estudió el impacto de la temperatura y alimentación sobre parámetros biológicos de sus estados inmaduros e imagos resultantes. Cohortes de larvas del coccinélido fueron criadas en una combinación de cuatro temperaturas constantes (9, 15, 19 y 27ºC) y 6 dietas de áfidos de las especies Acyrthosiphon pisum Harris y Schizaphis graminum (Rondani) con, respectivamente, cuatro y dos cantidades iniciales y tasas de incremento diarios. Las cantidades de huevos/postura y su viabilidad no fueron afectadas por las temperaturas superiores a 15ºC evaluadas. Los tiempos de incubación fueron desde 2,5 días y 92% de eclosión a 27ºC, hasta 13 días con una viabilidad del 71% a 15ºC. A 9ºC no se registraron oviposturas ni nacimientos aunque el desarrollo hasta adulto pudo ser completado en las cuatro temperaturas experimentales. La combinación de oferta de alimento y temperatura afectó tanto la ingesta de áfidos como los tiempos de desarrollo inmaduro, pero no las dimensiones de los adultos. Las cantidades totales de pulgones consumidos oscilaron aproximadamente entre 57 y 256 ninfas de A. pisum y desde 104 a 641 áfidos de la especie S. graminum. Los tiempos para el desarrollo, desde larva hasta adulto, fueron cercanos a 83,7 días a 9ºC hasta 11,8 días a 27ºC. Las mayores dimensiones de imagos se registraron a 19°C. El aumento del número de pulgones ofrecidos causó un incremento del peso corporal del adulto. El ancho del pronoto y la longitud del fémur del adulto fueron levemente influenciados por la especie presa pero sería relativamente independiente de la cantidad ingerida por las larvas.