Which of the following statements about secondary succession is true?
a. secondary succession occurs in ecosystems that have no vegetation.
b. secondary succession affects ecosystems that are already established.
c. ecosystems require pioneer species to undergo secondary succession.
d. secondary succession can occur in areas without soil.

Option B,  Secondary succession affects ecosystems that are already established, is the right answer.

Explanation:

There are two types of ecological succession (the primary and the Secondary succession) in the life of a plant. Here, the secondary succession is a process which starts with an event such as a hurricane, forest fire or harvesting etc. which causes a reduction in an already organised ecosystem. Therefore, in the given options, option b, is correct.

b.

developed countries have tended to improve the environment, while developing countries have tended to damage it.