36
Baselines, patterns and process
Figure 3.2 A hierarchy of processes determine tree density in savannas through their effects on tree dispersal, germination,
recruitment and mortality. Lower tiers in the hierarchy emerge from the processes which dominate at each spatial scale.
Higher - level systems constrain lower - level processes, while lower - level sub - systems provide the mechanisms and constituent
parts from which higher - level systems emerge. Modifi ed from Gillson (2004b) .
Macro–scale
The limits of the savanna biome are defined
by broad-scale climatic patterns
Climatic change, fire and arboriculture can all
modify the extent of the savanna biome
Regional–Landscape Scale
Within the savanna biome, the type of
savanna depends on:
Topography, hydrology, geology and rainfall
Regional changes in herbivore abundance
(e.g. because of Rinderpest, hunting for ivory)
Local–scale
Within savanna landscapes, patchiness is
determined by:
Local variations in soil and hydrology
Disturbance e.g. fire, herbivores
Micro–scale
Within patches tree density depends on
micro-climate, selective herbivory and
micro-disturbance
Plant–plant interactions such as competition
and facilitation (represented by arrows) also
occur at this scale
Desert
Savanna
Forest
Baselines, patterns and process
Figure 3.2 A hierarchy of processes determine tree density in savannas through their effects on tree dispersal, germination,
recruitment and mortality. Lower tiers in the hierarchy emerge from the processes which dominate at each spatial scale.
Higher - level systems constrain lower - level processes, while lower - level sub - systems provide the mechanisms and constituent
parts from which higher - level systems emerge. Modifi ed from Gillson (2004b) .
Macro–scale
The limits of the savanna biome are defined
by broad-scale climatic patterns
Climatic change, fire and arboriculture can all
modify the extent of the savanna biome
Regional–Landscape Scale
Within the savanna biome, the type of
savanna depends on:
Topography, hydrology, geology and rainfall
Regional changes in herbivore abundance
(e.g. because of Rinderpest, hunting for ivory)
Local–scale
Within savanna landscapes, patchiness is
determined by:
Local variations in soil and hydrology
Disturbance e.g. fire, herbivores
Micro–scale
Within patches tree density depends on
micro-climate, selective herbivory and
micro-disturbance
Plant–plant interactions such as competition
and facilitation (represented by arrows) also
occur at this scale
Desert
Savanna
Forest