4a. By 40-60 years after farm fields had been abandoned, the amount of herbaceous plants decreased. Give one reason why the amount of herbaceous plants decreased as the amount of trees

increased.

See the answer below

Explanation:

The amount of herbaceous plants in an abandoned farm field will keep decreasing with time and the amount of trees would be increasing instead due to successional forces.

Succession refers to the gradual change in the species structure of a community with time. Early successional species usually colonize new habitats and with time, they are replaced with late successional species until a relatively stable community, climax community, is established.

Herbaceous species on abandoned farmland represent early successional species and as time goes on, they will be replaced by mid to late successional species in the form of shrubs and trees until a relatively stable community is formed. Hence, herbs would be decreasing while trees would be increasing.

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