Can forest management based on natural disturbances maintain ecological resilience?

Given the increasingly global stresses on forests, many ecologists argue that managers must maintain ecological resilience: the capacity of ecosystems to absorb disturbances without undergoing fundamental change. In this review we ask: Can the emerging paradigm of natural-disturbance-based management (NDBM) maintain ecological resilience in managed forests? Applying resilience theory requires careful articulation of the ecosystem state under consideration, the disturbances and stresses that affect the persistence of possible alternative states, and the spatial and temporal scales of management relevance. Implementing NDBM while maintaining resilience means recognizing that (i) biodiversity is important for long-term ecosystem persistence, (ii) natural disturbances play a critical role as a generator of structural and compositional heterogeneity at multiple scales, and (iii) traditional management tends to produce forests more homogeneous than those disturbed naturally and increases the likelihood of unexpected catastrophic change by constraining variation of key environmental processes. NDBM may maintain resilience if silvicultural strategies retain the structures and processes that perpetuate desired states while reducing those that enhance resilience of undesirable states. Such strategies require an understanding of harvesting impacts on slow ecosystem processes, such as seed-bank or nutrient dynamics, which in the long term can lead to ecological surprises by altering the forest's capacity to reorganize after disturbance

Agricultural Landscape Dynamics and Its Response in Seasonal Vegetation Activities in the Loess Plateau, Northern Shaanxi, China

Part 1: GIS, GPS, RS and Precision FarmingInternational audienceThe ecological and environmental conditions in semiarid areas are closely linked to landscape dynamics. This study examined the seasonal vegetation activities of landscape classes and dynamics in the Loess Plateau in North Shaanxi Province, China. Landscape dynamics were studied by comparing Landsat images in 1987 and 2007, and classified as landscape transitions, landscape variations and unchanged landscape. The characteristics of seasonal vegetation activities, such as dates for onset-of-greenness, peaks, and onset-of-senescence for landscapes were determined using Moderate Resolution Imaging Spectroradiometer (MODIS) 10-day vegetation index composite products (2002–2009). The landscape dynamics showed that some sloping croplands were converted to woodlands and grasslands. Vegetation activities responded diversely and seasonally to landscape classes and dynamics. Temporal analysis of the Normalized Difference Vegetation Index (NDVI) showed that the time of onset-of-greenness and onset-of-senescence were similar for all major landscape classes, while the time of peak vegetation activity was longer for tree than grass species. The analysis of seasonal vegetation activities and landscape dynamics indicated that seasonal vegetation activities were not only relative to landscape classes, but also affected by landscape dynamics