Why does secondary session occur faster them primary secession

During secondary succession, the soil isn't damaged hence there is no need for pioneering species such as lichens to dissolve the damaged soil into organic ones that can sustain more complex plants.

Explanation:

Secondary succession, type of ecological succession (the evolution of a biological community’s ecological structure) in which plants and animals recolonize a habitatafter a major disturbance—such as a devastating flood, wildfire, landslide, lavaflow, or human activity (e.g., farming or road or building construction)—significantly alters an area but has not rendered it completely lifeless. Secondary succession is distinguished from primary succession, in which a biological community develops where no life had existed

Secondary succession, type of ecological succession (the evolution of a biological community’s ecological structure) in which plants and animals recolonize a habitatafter a major disturbance—such as a devastating flood, wildfire, landslide, lavaflow, or human activity (e.g., farming or road or building construction)—significantly alters an area but has not rendered it completely lifeless. Secondary succession is distinguished from primary succession, in which a biological community develops where no life had existed previously.

Secondary succession follows a major disturbance, such as a fire or a flood. The stages of secondary succession are similar to those of primary succession; however, primary succession always begins on a barren surface, whereas secondary succession begins in environments that already possess soil. In addition, through a process called old-field succession, farmland that has been abandoned may undergo secondary succession.

Secondary succession takes place where a disturbance did not eliminate all life and nutrients from the environment. Although fire, flooding, and other disturbances may bring visible ruin to a landscape, drive out many plants and animals, and set back the biological community to an earlier stage, the habitat is not lifeless, because the soil retains nutrients and seeds that were set down before the disturbance occurred. Buried seeds can sprout shortly after the effects of the disturbance pass, and some may have greater success from reduced competition and reduced shading. Some species may be adapted to the frequent passage of a particular disturbance. For example, the jack pine (Pinus banksiana), a tree species common in the northeastern U.S. and Canada, requires heat from a wildfire to open its cones (strobili) before seeds can be spread for new growth.

a time line cause it goes from 685 to 978

the answer is true when observing or determining population size, a direct observation is use, in which each organism is counted in a population or in an area. one benefit of this measure is that you get the exact population count but it will take a long time to  determine  the  size  of a  population.