Why does secondary succession occur faster than primary succession?

answer from e2020

Soil with nutrients is already present.

Seeds are present from earlier occupants, brought in by wind, and/or germinate after fire.

Due to remains of primary succession, secondary succession occur faster

Explanation:

The secondary succession usually takes place in the ecosystem after the primary succession has taken place and got disrupted somehow leaving behind some of its traces. A secondary succession is faster than a primary succession due to the following reasons –

a)Soil is readily available

b)The remains of trees such as seeds, roots and other vegetative organs of plant  

hypoxemia refers to a below usual concentration of oxygen in the blood, mainly in the arteries. hypoxemia is an indication of an issue associated with circulation or breathing and may lead to various symptoms like shortness of breath.  

the condition is identified by determining the level of oxygen in the blood sample obtained from an artery. it can also be predicted by determining the oxygen saturation of the blood with the application of a pulse oximeter.  

the normal arterial oxygen is about 75 to 100 mm hg. the values underneath 60 mm hg is generally considered with the requirement for supplemental oxygen. the normal pulse oximeter readings generally range between 95 to 100 percent. the values under 90 percent are regarded as low.  

in the given case, the oxygen saturation is measured at 93 percent, hence, there is no need to administer oxygen, that is, one should withhold oxygen.