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 Chancaní Natural Reserve (Córdoba, 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.

Soil and above-ground dead biomass are important carbon pools in drylands. They depend on local controls and patterns that should be studied. The objective of this work is to understand and quantify the influence of the vegetation canopy in the regulation of soil and dead biomass carbon stocks in woodlands of Monte region in Argentina. The hypothesis is that soil and dead biomass carbon stocks are lower in the intercanopy and higher under the canopy, independently of the type of canopy. Thirty sampling plots were selected, identifying three treatments: tree canopy, intercanopy and shrub canopy. In each sampling plot, soil and dead biomass were sampled. Four physiognomic-functional groups were identified. Prosopis woodlands accumulated about 38 Mg ha -1 of dead organic carbon (from soil, litter, and dead wood), followed by Suaeda woodlands with almost 35 Mg ha -1 . Mixed woodlands showed average values around 27 Mg ha -1 , while Bulnesia woodlands around 25 Mg ha -1 . The vegetation canopy, and consequently, litter and dead wood input affected soil organic carbon in topsoil. Shrubs such as Larrea spp. had a restricted ability to enrich soil compared to Prosopis spp. Soil, litter and dead wood are significant pools of carbon and should be included in programs on reducing emissions in arid regions. The hypothesis is accepted partially; there is a remarked contrast in carbon content between soils under the tree canopy and off the canopy. However, the effect of shrub canopy is intermediate between both treatments.

Los artículos publicados se distribuye bajo una Licencia Creative Commons Atribución 4.0 Internacional (CC BY 4.0) basada en una obra en http://www. revistas.una.ac.cr/ambientales., lo que implica la posibilidad de que los lectores puedan de forma gratuita descargar, almacenar, copiar y distribuir la versión final aprobada y publicada del artículo, siempre y cuando se mencione la fuente y autoría de la obra. Director y Editor:Dr. Sergio A. Molina-Murillo Doctor en Ciencias Agropecuarias, ingeniero agrónomo especialista en relaciones suelo-planta en zonas marginales, es profesor asistente de la

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