Resilience and Other Properties of Ecological Mosaics

Mosaics are composed of patches of different type, size, and shape. Theses differences on one hand create problems of isolation, fragmentation, and edges for many species, but on the other hand reduce connectivity for the spread of diseases, species invasion, and disturbances.

A patch per se can benefit from fragmentation and isolation depending on whether it is a population patch, a community patch, or a process patch.

Patchiness increases the difficulty for prey patches to be intercepted by predators, and reduces the risk to interception by a disturbance like fire, a wind storm, or simply by a local tree fall. On the other hand, fragmentation increases the number of ecological traps and can be very attractive for many species that assume the character of population sinks.

This resilience is a property of many systems and can be defined as the capacity to incorporate disturbance. Every system has resilient properties, but such properties can be reduced by stresses like pollution or climatic changes.

Resilience means the capacity to recover after disturbance. This attribute of the majority of environmental systems operates differently in a mosaic than in an ecosystem. A mosaic can be described as a spatial system in which a set of organisms self-organize complex systems around every discontinuity. The self-organization requires a low level of heterogeneity in order not to consider such heterogeneity as a stressor per se on the mechanisms responsible for the self-organization. A mosaic can be considered a real system in which patches represent parts of the entirety. For instance, the upland prairies of the northern Apennines, above the tree level, for their relatively simple vegetational structure are wonderful laboratories to experiment with mosaics.

A hierarchy of stressors of shaping factors is responsible for such a mosaic. The highest rank is dominated by the montane climate (oro-Mediterranean). Second are the aspect and steepness that in turn control light, temperature, wind effect, snow cover, rain distribution, and fire risk. In third position are the soil properties which are linked to the geology.

The fourth system is determined by water content in the soil which increases moving from top to bottom. The fifth component is represented by livestock disturbance which is concentrated on the southern aspects and also all around the top of the mountain. Every factor acts at a different spatio-temporal scale. At local scale (micro-site) the neighbor effect around the center plant occurs to determine the fate of individual plants.

Habitat patchiness assures resilience to human-modified systems, as pointed out by Scoone (1995) in dryland Zimbabwe for livestock living in heterogeneous habitats. The phenology of resources allows livestock to find different resources in different periods of the year.

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