Crecimiento de renuevos y expansión de copas en claros del dosel de bosques de Nothofagus pumilio (lenga) en Chubut, Patagonia, Argentina

In the province of Chubut in Patagonia, Argentina, Nothofagus pumilio forests (locally known as lenga), are managed through selective cuts, which imply the opening of canopy gaps. This management scheme is carried out without taking into consideration the sapling requirements changes through neither a cutting cycle nor the precipitation gradient in which these forests thrive. To analyze these changes, we inferred the facilitation-competition balance between the canopy and regeneration studying the effects of precipitation levels, gap size and gap age on saplings growth in height on 45 canopy gaps artificially created between 1960 and 1993. Results shown that during the first 20 years since the gap opening, the regeneration growth is determined by light availability in mesic sites and by water availability in dry sites. However, the difference due to the precipitation levels gradually decreases over time. Moreover, in the period between 20 and 35 years after gap opening, in both mesic and xeric sites, light is the limiting factor to growth. This means that in xeric sites, saplings shift from a water-dependent to a light-dependent growth. The average closing rate of gaps due to lateral growth of trees bordering the gap is high enough so that within the proposed gap size range, the gap healing can occur before regeneration reaches the upper stratum. Consequently, in mesic sites the gap opening can be done by a single operation that generates gaps with diameters of approximately twice the average height of the canopy (D/H). While in xeric environments, lenga seedling establishment and initial growth require the cover of small gaps, but advanced regeneration requires bigger gaps to reach the canopy. For this reason, gaps should be opened in two stages: the first gaps should be opened with a D/H between 0.8 and 1, and after a cutting cycle of 35 years, these openings should be enlarged to a D/H between 1.5 and 2. The close relationship is maintained between the new cohort and the upper strata require special considerations regarding the evolution of the balance between positive and negative interactions during development. Our work highlights the need to adjust management practices to these spatial and temporal variations so as to achieve an optimal growth along the entire production cycle.En la provincia del Chubut, Patagonia Argentina, los bosques de Nothofagus pumilio (lenga) son manejados mediante cortas de selección, que implican la apertura de claros en el dosel. Este esquema de manejo es implementado sin tener en cuenta los requerimientos de los renuevos a lo largo de todo el ciclo de cortas ni el gradiente de precipitaciones presente en su distribución. Para analizar estos aspectos estimamos el balance facilitación-competencia entre el dosel y la regeneración, considerando los efectos de los niveles de precipitación, el tamaño de los claros y la antigüedad de los mismos, en 45 claros creados artificialmente entre los años 1960 y 1993. Los resultados muestran que durante los primeros 20 años desde la apertura del claro, el crecimiento de la regeneración está determinado por la disponibilidad de luz en los sitios mésicos y por la disponibilidad de agua en los sitios xéricos. Sin embargo, la diferencias entre los distintos niveles de precipitación decrece gradualmente a lo largo del tiempo y entre los 20 a 35 años luego de la apertura de los claros, tanto en los sitios mésicos como xéricos el factor limitante es la luz. Esto implica que en los sitios xéricos el crecimiento de los renuevos pasa de ser dependiente del agua a dependiente de la luz. Por otro lado, la tasa de cierre de los claros debida al crecimiento lateral de la copa de los árboles límite es lo suficientemente grande como para que pueda ocurrir el cierre antes de que los renuevos alcancen el estrato superior. Por lo tanto, en los sitios mésicos la apertura de los claros puede realizarse en una única operación que genere claros con un diámetro de aproximadamente el doble de la altura dominante del bosque (D/H ≈ 2). Por el contrario, en los sitios xéricos, el establecimiento y crecimiento inicial de los renuevos requiere la apertura de claros pequeños (D/H entre 0,8 y 1) que luego deberán ser ampliados para maximizar el crecimiento avanzado (D/H entre 1,5 y 2). La estrecha relación entre la regeneración y el dosel del bosque requiere la consideración de los posibles cambios en el balance entre los apsectos positivos y negativos de la misma a lo largo de todo su desarrollo. Nuestro trabajo resalta la necesidad de ajustar las prácticas de manejo a estas variaciones espaciales y temporales para alcanzar un desarrollo óptimo a lo largo del todo el ciclo productivo

Implementación de middleware publicador/subscriptor para aplicaciones web de monitoreo

En la actualidad, millones de clientes se conectan a la nube utilizando el protocolo HTTP (Protocolo de Transferencia de Hipertexto). Históricamente, el estudio de los sistemas distribuidos ha propuesto diversas técnicas de optimización de acceso; como ser Sun RPC, CORBA, SOAP. Sin embargo, en el ámbito de las aplicaciones web una tendencia muy generalizada es la abstención a este tipo de middlewares, en favor de principios arquitectónicos propuestos como REST (Representational State Transfer). Uno de los problemas que presenta esta mecánica de comunicación, es la imposibilidad que un cliente reciba actualizaciones de un recurso remoto sin iniciar un requerimiento. Una técnica actual para mitigar el problema consiste en la utilización de WebSockets. Paralelamente, las bases de datos relacionales han ganado capacidades de notificación a través de canales asincrónicos. Estas pueden ser aprovechadas para recuperar cambios en los datos de tiempo real. En este trabajo se presenta el desarrollo de una aplicación web con requerimientos de actualizaciones de estado en tiempo real. Inicialmente se plantea su diseño exponiendo recursos bajo REST, para luego abordar un enfoque Publicador Subscriptor sobre los mismos recursos utilizando middleware basado en WebSockets.Eje: Arquitectura, Redes y Sistemas Operativos.Red de Universidades con Carreras en Informática (RedUNCI

Comparison of four methods of grassland productivity assessment based on Festuca pallescens phytomass data

The relative utility of 4 methods for grasslands above-ground net primary productivity (ANPP) assessment were evaluated. These methods, applied to a set of phytomass and litter data collected at about bimonthly intervals for 2 years in a Festuca pallescens (St. Yves) Parodi grassland steppe of southwestern Chubut, Argentina, were: (1) summation of positive increments of green (live) biomass between harvests, (2) summation of positive increments of total phytomass between harvests, (3) summation of positive increments of green biomass between harvests plus correction factors which accounted for the concomitant increases in dry, old dead, and litter, respectively, and (4) mathematical model of simultaneous differential equations which fitted the values of phytomass data obtained in the field. Method 1 gave consistently (p less than or equal to 0.05) the lowest ANPP values in both years. Productivity values obtained with methods 2, 3, and 4 were highly correlated and did not differ significantly (p less than or equal to 0.05) with each other. Their estimates varied from 94.9 to 105.3 g of dry matter per m2 for the first year and from 73.0 to 149.4 g of dry matter per m2 for the second year. These values are within the range of productivity given for other climatologically and physiognomically similar semiarid grasslands of North America. Each method except 1 provided reliable estimations of ANPP for the grassland studied. Methods 2, 3, and 4 can also be used to assess ANPP in any other grassland with similar characteristics. Each one, however, might have particular applications according to the specific objectives pursued.This material was digitized as part of a cooperative project between the Society for Range Management and the University of Arizona Libraries.The Journal of Range Management archives are made available by the Society for Range Management and the University of Arizona Libraries. Contact [email protected] for further information.Migrated from OJS platform August 202

Seedlings dynamics of Festuca spp. in a grassland of Patagonia, Argentina, as affected by competition, microsites, and grazing

The effects of competition, grazing, and microsites on seedling dynamics of Festuca spp. were investigated in a semiarid steppe of Patagonia, Argentina. In an exclosure and an adjacent grazed area, the level of root competition for seedlings was controlled through root exclusion tubes (0.1 m diameter, 0.4 m long) installed adjacent to 7 similarly-sized Festuca pallescens plants and in the interspace between F. pallescens plants. Seedling dynamics at the phenological stages of a) recently emerged and up to 4 leaves and b) 5 leaves and up to 1 tiller were followed inside the tube area (no competition) and in paired circles (competition) for approximately 3 growing seasons. Peak density of Festuca spp. seedlings occurred in fall and early spring, when water content in the first 0 to 5 cm of the soil was above 8%. Seedling densities of Festuca spp. at the 2 phenological stages were significantly reduced by grazing. At the phenological stage of 1 to 4 leaves, seedlings were not affected by root competition, although their densities were significantly higher for seedlings adjacent to F. pallescens plants than in the interspace between plants. This was due to higher soil water content in these areas throughout the season in the 0 to 5 cm of the soil. Seedling densities at the phenological stage of 5 leaves and up to 1 tiller were significantly higher when there was no competition from neighboring grass plants as compared to seedlings exposed to competition. In regard to microsite differences, seedling density was significantly greater in the interspaces than adjacent to mature plants. These results suggest that although higher seedling densities can be obtained by excluding the area from grazing, intraspecific competition for soil water during the summer drought period can act as a barrier for further Festuca spp. seedling establishment.The Journal of Range Management archives are made available by the Society for Range Management and the University of Arizona Libraries. Contact [email protected] for further information.Migrated from OJS platform August 202

Above-ground phytomass dynamics in a grassland steppe of Patagonia, Argentina

Aerial phytomass and litter dynamics of a grassland steppe in Patagonia, Argentina, were studied at either monthly or bimonthly intervals for 2 years. This area is characterized by a cold and wet winter (June to September) and a warm and dry summer (December to March). The growing season extends from September to April, with moist spring and fall periods interrupted by a midsummer drought. Festuca pallescens (St. Yves) Parodi produced about 95% of the total annual phytomass. Peaks of green phytomass were recorded in spring-summer of the first growing season (33.6 +/- 2.9 g m-2) and in early spring (35.0 +/- 2.4 g m-2) and fall (32.7 +/- 2.7 g m-2) of the second growing season. Less abundant forage grasses were Poa ligularis Nees ap Steudel, Bromus setifolius Presl., Hordeum comosum Presl., and Rytidosperma virescens (Desvaux) Nicors. Shrubs and forbs represented less than 2% of the total annual phytomass of this grassland. The relationships between phytomass production of the main species and some environmental variables are discussed. These results contribute to the knowledge of above-ground phytomass dynamics and forage availability throughout seasons of this grassland in Patagonia, and are part of the data necessary for proper range management planning. This information will permit the designing of appropriate grazing schedules by balancing the number of grazing animals to the forage resources available.This material was digitized as part of a cooperative project between the Society for Range Management and the University of Arizona Libraries.The Journal of Range Management archives are made available by the Society for Range Management and the University of Arizona Libraries. Contact [email protected] for further information.Migrated from OJS platform August 202