RÉSUMÉ
The ecological functioning of dryland ecosystems is closely related to the spatial pattern of the vegetation, which is typically structured in patches. Ground arthropods mediate key soil functions and ecological processes, yet little is known about the influence of dryland vegetation pattern on their abundance and diversity. Here, we investigate how patch size and cover, and distance between patches relate to the abundance and diversity of meso-and microarthropods in semi-arid steppes. We found that species richness and abundance of ground arthropods exponentially increase with vegetation cover, patch size, and patch closeness. The communities under vegetation patches mainly respond to patch size, while the communities in the bare-soil interpatches are mostly controlled by the average distance between patches, independently of the concurrent changes in vegetation cover. Large patches seem to play a critical role as reserve and source of ground arthropod diversity. Our results suggest that decreasing vegetation cover and/or changes in vegetation pattern towards small and over-dispersed vegetation patches can fast lead to a significant loss of ground arthropods diversity in drylands.
RÉSUMÉ
The Brazilian savanna (Cerrado) has been extensively converted to croplands, pastures and forestry plantations, and the deforestation frontier continues expanding. Land conversion may cause critical changes in soil functioning, yet very little is still known about the impact of Cerrado conversion on nutrient cycling and soil fertility. Here, we addressed this knowledge gap by investigating the effects of the woodland cerrado (cerradão) conversion into pastures and Eucalyptus plantations on nitrogen availability and mineralization potential, considering a wide range of spatial and temporal variability due to soil depth, site conditions, and seasonal variation. For three sites in São Paulo state and each of the target land cover types, we assessed the total N and inorganic N (NH4-N and NO3-N) pools, potentially mineralizable nitrogen (PMN) and soil urease activity in the first 2 m of the soil profile. Cerrado conversion to either pastures or Eucalyptus plantations significantly reduced NH4-N, while NO3-N showed similar values in Cerrado and Eucalyptus and lower values in pastures. We found a consistent pattern of lower N mineralization in the uppermost soil layers associated to Cerrado conversion, with decreases in PMN rate and urease activity. The soil below 30 cm depth showed no relevant changes. Considering the first 30 cm of the soil profile, the reduction in the stocks of inorganic N (NH4-N + NO3-N) ranged from ~14% for the conversion to Eucalyptus to â½20% for the conversion to pasture. The impact of land conversion on N cycling surpassed the influence of the spatial (between-site) and seasonal variation. Overall, the results indicate a decline in available N and overall soil fertility due to Cerrado conversion, which could further increase N limitation in the Cerrado region, increase fertilization needs for future exploitation, and compromise the recovery of Cerrado in case of land abandonment or restoration.
Sujet(s)
Agriculture , Conservation des ressources naturelles , Écosystème , Surveillance de l'environnement , Eucalyptus , Azote/analyse , Brésil , Science forêt , Forêts , Prairie , SolRÉSUMÉ
se presenta la metodologia diseñada para elaborar una propuesta de gestion sustentable de los recursos hidricos,para ser aplicada en el estado de Zulia, Venezuela, tomando las cuencas como unidades integradas de gestion y definiendo las competencias en materia ambiental de los organismos a nivel nacional, regional y local, asi como las estrategias y funciones que rigen la Entidad de Cuenca
Sujet(s)
Bassins Géographiques et Hydrographiques , Administration Environnementale , Politique de l'environnement , Ressources en eauRÉSUMÉ
se presenta la metodologia diseñada para elaborar una propuesta de gestion sustentable de los recursos hidricos,para ser aplicada en el estado de Zulia, Venezuela, tomando las cuencas como unidades integradas de gestion y definiendo las competencias en materia ambiental de los organismos a nivel nacional, regional y local, asi como las estrategias y funciones que rigen la Entidad de Cuenca