Physical and Human factors which make arid ecosystems vulnerable

Physical:

• Harsh Climate
• Wind and water (flash flood)- They can remove unprotected soils and uproot vegetation.
• Lightning strikes can trigger fires (convection storms due to HP systems)
• Dust storms bury vegetation (high winds reduces photosynthesis as dust covers the leaves.

Human:

• Urbanisation and associated activities e.g. road building= separate out areas decreases migration for breeding.
• Water abstraction from groundwater= plants have long tap roots, lower the groundwater, the tap roots can no longer reach and the plants die.
• Grazing livestock= trampling.
• Introduction of non-native species both plant and animals= this changes the ecosystems they out compete local species.

What makes an ecosystem fragile?

1) Short and highly interconnected food webs.
2) Harsh climate
3) Proportional impact
4) Recovery rates

1. Short and highly interconnected food webs

One small change affects the whole ecosystem (knock-on).

2. Harsh Climate

• Diurnal range (freezing nights)
• Temperature range (up to 50°C)
• Less than 100mm rainfall (unreliable)
• High winds (abrasion)

3. Proportional Impact

• Arid NPP= 30-200g/m2/yr
• Biomass very low

NPP= the amount of biomass added to an ecosystem in a given time.

Biomass= the combined weight of all living matter in an ecosystem.

4. Recovery rates

Very long, even limited damage can have long-lasting impacts.