Question

how did trees help in soil conservation

Answer 1

trees are tall usually and prevent the wind erosion
trees fix their root in soil tightly so prevent erosion by water

Answer 2

trees play an important role in soil conservation such that during transpiration trees transpiring large amount of water which counteract(रोक-थाम करना) very wet soil and binding soil to sloping lands with their roots.And also trees reduce the rate of erosion by protecting the soil from the impact of rain and wind.