Marcos Sebastián Karlin

Environmental Dynamics in Salinas Grandes, Catamarca, Argentina

Saline systems are open systems where energy and matter fluxes produce modifications in the ecosystem, especially in plant communities, defined by species abundance and plant cover. Based on these changes, it is possible to define vectors that show the tendencies of such communities to reach mature or stationary states and their modifications by natural or anthropic disturbances. Salinity and topsoil thickness dominate the system dynamics. The decrease in soil salinity and the increase in the sandy topsoil horizon thickness would allow installation of new plant populations, a higher biodiversity, ecological resilience, and productive potential. Plant and soil surveys were conducted, establishing several relationships among the studied variables. Lyapunov coefficients (L) were calculated as the Euclidean distance of each site from a reference condition, used as exergy of the system. These values were correlated with the electrical conductivity data. The presence of soluble salts in the soils generates adverse conditions for unadapted species, reducing the total amount of biomass of a plant community, and therefore its exergy. When L decreases in time, it is expected that the system goes towards a steady state. If the contrary occurs, the equilibrium is unstable and becomes less resilient. While primary succession evolves, minimum rangeland requirements increase, depending on the dynamics of the system. According to the relationship between climate, plant cover, and erosive processes, dunes development would increase total biomass and biodiversity. Anthropic degradation, through fire, deforestation, and overgrazing, can produce retrogression of primary or secondary successions through erosive processes and salinization.

Exergetic Model of Secondary Successions for Plant Communities in Arid Chaco (Argentina)

Ecosystems are open systems where energy fluxes produce modifications over plant communities. According to the state and transition model, plant formations are defined by changes in natural conditions and disturbs. Based on these changes, it is possible to define vectors that show the tendencies of the communities towards other states. Within the subregion of Arid Chaco, mature communities of Aspidosperma quebracho blanco represent the quasistable equilibrium communities or “climax,” similar to that observed in the Chancani Natural Reserve (Cordoba, Argentina). Biodiversity values and Lyapunov coefficients were calculated based on plant abundance and cover data. Lyapunov coefficients were calculated as the Euclidean distance of each site with respect to reference condition (community of Aspidosperma quebracho blanco), representing for each state the necessary exergy to reach the reference condition. When Lyapunov coefficients decrease in time, it is expected for the system to drive towards a quasistationary state; otherwise, the equilibrium is unstable and becomes less resilient. The diversity of species has a significant effect over the resistance to perturbations but equivocal for the recovery rate. Lyapunov coefficients may be more precise succession indicators than biodiversity indexes, representing the amount of exergy needed for a vegetation state to reach the reference condition.

Tratamientos pregerminativos para la ruptura de la dormición en semillas de tres poblaciones de Ramorinoa girolae, leñosa endémica de zonas áridas en Argentina

For the conservation of species, especially those endemic or vulnerable, it is necessary to deepen the knowledge about their ecological dynamic and to find adequate techniques for multiplication. Ramorinoa girolae, “chica”, is an endemic woody species of the xerophytic flora from western Argentine arid regions, with a restricted occupation area and fragmented communities. The lack of records makes relevant the conduction of research underpinning knowledge of the species, regeneration mechanisms and multiplication techniques. The objective of this work was to study the behavior of seeds of three populations under germination conditions and the response for different pre-germinative treatments. Germination trials were made in the laboratory with different pre-germinative techniques using the seeds of three populations under a completely aleatory design. Results confirm the presence of physical dormancy in seeds restricting the imbibing process for their rapid germination. The treatments, hot water scarification and mechanical scarification with sandpaper, increase significantly the germination percentages. The best treatment is mechanical scarification with sandpaper, reaching values of 92 % of germination at five days from the beginning of the treatment. The uneven response of germination of the different populations confirms the different behavior of local populations and results interesting for ecosystem studies and future lines of investigation and management of this species. These technical aspects appear as relevant for the application of reforestation and environmental restoration programs.

Soil-Plant Relationships in the Sabkhat of America

In Sabkhat, plant ecology will depend on the soil characteristics, according to the type and dynamics of sediments and to water movement, dynamized by salt concentration and climate. Soil profile defines the ability of species to develop under its influence, according to critical variables such as soil salinity, water table depth and granulometry. Also, plant growth and development will depend on special physiological and morphological characteristics that are suited to extreme conditions in sabkhat. In America, sabkhat are the habitat of halophytic species, dwelling characteristic genera that can be found from the Columbia Basin to the Monte ecoregion. In this review soil conditions, plant characteristics and their interactions in saline basins of America will be discussed. Hydrology controls the sediment and solute chemistry, forming a dynamic cycle with halophyte vegetation. When the water table is depressed, deflation is enabled and medium-coarse particles are deposited over small hummocks, usually by the form of dunes or over tussocks, forming nabkhat. Aeolian dust may be responsible for the development and maintenance of plant communities along a salinity gradient towards the adjacent dunes in the periphery. Sabkhat hold an important pool of plant functional groups according mainly to soil salinity and water table depth. Such functional groups perform important ecological functions in the soil-plant-climate triad, such as soil formation, facilitation and zonation. These processes have a dynamic behaviour according to seasonality and climate interannual and decadal variability, assisted by anthropic impacts such as fire, overgrazing or even climatic change.

Caracterización florística de la Reserva Natural Militar Estancia La Calera

Las Sierras de Cordoba experimentan en la actualidad transformaciones causadas por el avance inmobiliario, incendios, tala, sobrepastoreo e invasion de especies exoticas. Estas transformaciones condicionan el estado de conservacion de la flora nativa. La Reserva Militar Natural La Calera, ubicada en las Sierras de Cordoba, ha mantenido gran parte de su estructura vegetal original como consecuencia de las restricciones al ingreso debido al uso militar. El presente trabajo muestra los resultados de las actividades de diagnostico floristico llevados a cabo en esta area de 14 mil hectareas durante 2012 y 2013. Se realizo una clasificacion ISO Cluster, como base para los relevamientos floristicos realizados a traves del Metodo Fitosociologico de Braun Blanquet. Se calcularon los Indices de Biodiversidad de Shannon-Weaver y se determinaron las especies caracteristicas de cada ambiente, basados en los valores de abundancia y dominancia. A traves de un analisis discriminante se determinaron las clases de vegetacion, las cuales permitieron definir las mismas en una clasificacion supervisada. Fueron identificadas 230 especies, de las cuales el 8,3% son exoticas, valor inferior a la proporcion de exoticas encontradas para el total de las Sierras de Cordoba. Estas especies exoticas se restringen a zonas riparias. El 17,0% del total de especies relevado son endemicas de la ecorregion Chaquena, lo que hace de esta Reserva un lugar de alto valor de conservacion. Seis comunidades vegetales fueron identificadas, representadas en cuatro clases de vegetacion en la clasificacion supervisada.