Table 51 Vulnerability matrix showing how different global change drivers have effects on the belowground subsystem that may be manifested at different spatial scales

Note that some drivers operate mainly at local spatial scales while others are more pervasive.

Global Change Driver Agricultural Climate Invasive

Scale

Land Use

Intensification

Change

Pollution

Organisms

Urbanization

Global

X

X

Regional

X

X

X

X

Landscape

X

X

X

X

X

Field

X

X

X

X

X

X

Patch

X

X

X

X

X

X

Single Unit

X

X

X

X

X

X

by an accumulation of surface deposits by soil invertebrates (Nye 1955). As long-term plant successional processes and pedogenesis operate, changes occur in soil organism communities and their effects on soil structure over whole watersheds and timescales of years to centuries (Bernier & Ponge 1994).

Vulnerability of ecosystem services to perturbations may be dependent on the scales at which processes and the services operate, and their comparative sizes. In theory, four different situations may occur depending on the various combination of short or large scale of either component:

1. Short scale for processes and short scale for services. In this case, the output of the process directly affects the service. This is the case for mineralization of nutrients by microbial digestion. In such a situation, any direct damage to the decomposer community or impairment of its activity has immediate consequences for the service. Vulnerability is high, although rapid reversibility may be expected as soon as processes are reinitiated.

2. Short scale for processes and large scale for services. Here, a disturbance is temporary in nature and does not impair the provision of service. This is the case for water infiltration and retention in soils. Temporary interruption of activities of those invertebrates and roots that create or rejuvenate aggregates of different sizes does not have important consequences for soil hydraulic properties (Alegre et al. 1996). Soil aggregates of biological origin, once stabilized, can be very resistant structures that last for long periods in the absence of drastic direct physical impacts. In this situation, vulnerability is minimal (Blanchart et al. 1999).

3. Large scale for processes and short scale for services. Disturbance of a large-scale process will impair the services for a long period. This is the case of salinization, in which soil translocation processes result in the migration of salts toward the soil surface (Luna Guido et al. 2000). In saline soils, biological processes are severely limited. These long-term processes, when achieved, may impair the service for long periods and even be irreversible in the order of decades. Vulnerability is high, and restoration of the service will depend on changes in biological communities by such processes as colonization or local adaptation and genetic selection, which can be very slow.

4 Large scale for processes and large scale for services. Vulnerability can now be considerable and restoration of ecosystem services is very slow. This is the case for erosion processes that may affect large portions of soils that can be restored only after a long period of soil formation through pedogenetic processes (Lal 1984). All services linked to the presence of a thick soil with well-differentiated horizons will be severely affected by such an event.

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