An area that has undergone secondary succession doesn't start from bare rock like in primary succession. Thus, without beginning from the "starting stage", secondary succession will reach climax community faster because it doesn't need to start developing on bare rock. Instead, it already has soil or other natural materials.
Primary succession is a gradual introduction of a species in an area where no soil or previous life was. Secondary succession is the gradual change in the species of an area after a disturbance. So, Primary succession will take longer than Secondary succession because Primary succession has nothing (soil, leftover plants, ect.) to start from.
