Why are cold environments considered to be fragile?

Why is NPP low in cold environments?

• Limited insolation from sun due to curviture of the Earth, leading to low amounts of photosynthesis
• Very short days in winter due to tilt of the Earth
• High winds=High transpiration rate+plant damage due to abrasion
• Unavailable water 
• No/thin soil due to lack of weathering+low NPP meaning limited minerals and nutrients

How does this make these environments fragile?

• Limited insolation=plants are limited in photosynthesis=lack of energy available=if destroyed can't be replaced (due to low NPP and recovery rates)=leading to a high proportional impact

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.