Stress

• Trees exhibit signs of stress during floods and droughts. The more both occur the more severe the consequences. Stressed trees lose foliage. In some cases, the leaves yellow or grow to smaller than normal size. The tree may only lose or not grow leaves at the crown. Slightly stressed trees lose their leaves early in the fall and the leaves turn brown instead of red, yellow and orange.
  
  

Diseases and Insects

• During or after the drought or flood, trees succumb to diseases and insects. Their weakened state causes increased susceptibility. Insects include the pine bark beetle chestnut borer, bronze birch borer and hickory bark beetle. Diseases include nectria canker, diplodia tip blight, rhizosphaera needlecast, verticillium and cytospora canker. In particular, all pines, oaks, hybrid poplars, birches and hickories are at greater risk for infection and infestation following a drought or flood.
  
  

Roots

• While floods and droughts affect the roots, each disaster damages the roots in different ways. With frequent floods, the roots grow shallow and lose mass, making it more likely to get infections in the root system. For young saplings, floods can damage the trunk and the root system. Droughts kill off the tree's delicate short water-uptake roots, hurting the tree's ability to get enough water. Newly planted or transplanted trees already have limited roots, making it difficult for these trees to survive a prolonged drought.
  
  

Floods

• Floods impact the soil more than droughts. Flooding removes acids and minerals, like iron, from the soil. It also erodes the top soil, exposing roots. It limits the release of oxygen from the roots.
  
  

Droughts

• Short-term droughts usually just stress the tree. It's long-term drought that can kill a tree. All trees need water to live. Of course, some species tolerate droughts more than others and consequences of droughts vary heavily by species.