Why Trees Grow Where They Do. To appreciate the wide variety of trees and forests that grow in Michigan, it is important to understand the basic needs of trees as well as the natural and human forces that have shaped and influenced forest development. There are many factors that determine which trees and which forests grow in any given area. Three of the most important are the soil, moisture and climate. Soil serves as both an anchor and the source of essential nutrients for trees. The type of soil determines which nutrients are present and the quantities available. Clay and loamy soils are generally rich in nutrients. Sandy soils usually contain few nutrients. Hardwood (broad leafed) trees tend to dominate areas containing the richer loamy soils while coniferous (needle leafed) trees are more common on sandy soils. Moisture is vital to all plants. Its availability throughout the growing season helps determine which species occupy which sites.