The growth of willows and aspens increased due to reduction of herbivorous animals such as deer in the park.
After wolf reintroduction into Yellowstone National Park in 1995, it was observed that the growth of willows and aspens increased because the wolves control and reduce the population in the normal range.
So we can conclude that the growth of willows and aspens increased due to reduction of herbivorous animals such as deer in the park.
Learn more about reintroduction here: https://brainly.com/question/25958333