Burying the bottom of a full-grown tree under 2 feet of dirt can potentially harm the tree. Trees are adapted to specific soil conditions, and altering these conditions can affect their health. Here are some potential issues:

1. Root Suffocation: Tree roots require oxygen to function properly. Adding extra soil can compact the existing soil and reduce the amount of oxygen available to the roots, leading to suffocation.

2. Water Drainage: Excess soil can alter the drainage pattern around the tree. Poor drainage can lead to waterlogged conditions, which may cause root rot or other fungal diseases.

3. Trunk Decay: Burying the trunk can increase moisture around it, promoting decay and attracting pests or diseases that thrive in damp conditions.

4. Nutrient Imbalance: The additional soil layer might change the nutrient availability, affecting the tree’s ability to absorb essential nutrients.

5. Stress: Any significant change in the environment can stress a tree, making it more susceptible to disease and reducing its overall vitality.

If you need to change the landscape around a tree, it’s best to consult with an arborist or tree care professional to ensure the tree’s health is not compromised. They can provide guidance on how to manage soil levels without harming the tree.