Why does primary ecological succession on a freshly exposed sand dune or newly cooled volcanic lava require hundreds to thousands of years to reach a stable climax community?

Answer and explanation

Correct answer: C. Starts on sterile substrate devoid of soil and requires pioneer lichens to weather rock

  1. Step 1: Primary succession begins on newly formed, sterile substrate where no life previously existed and where there is zero preexisting soil (e.g., cooled lava flow, bare rock, newly formed sand dune).
  2. Step 2: The establishment of a mature plant community requires fertile organic soil containing nitrogen, phosphorus, and moisture.
  3. Step 3: Soil pedogenesis is an exceedingly slow process: rock weathering by pioneer lichens and mosses, accumulation of detritus, and microbial humification take hundreds to thousands of years.
  4. Step 4: In contrast, secondary succession occurs where vegetation was destroyed (by fire or clearing) but topsoil and seed banks remain, progressing much more rapidly (decades).
Answer
Because primary succession starts in an area completely devoid of organic soil, requiring prolonged physical and biological weathering to create topsoil
Why not the others: 'Because seeds are physically incapable of germinating...' is false; once organic soil forms, seeds germinate readily; 'Because primary succession occurs only in freezing arctic environments...' is false, as volcanic lava and sand dunes occur across tropical and temperate zones; 'Because climax tree species must evolve new genetic codes...' is biologically nonsensical.

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