Spring floods are a normal occurrence in native pecan groves. Yesterday, 4 1/2 inches of rain fell over a period of about 36 hours causing flash flooding on many small streams in the area. As Fly Creek ran over its banks, the native trees pictured above became flooded. Pecan trees can withstand a moderate level of flooding, however floods that last more than 2 weeks will reduce tree vigor. In addition, flooding during the growing season (when trees are in full leaf) is more stressful to pecan trees than if the flooding event occurs during the dormant season.
In flooded soils, soil oxygen reserves become depleted causing two major problems. Without oxygen, tree roots can't respire (breath) and they stop taking up water and nutrients. During extended flooding events, trees will actually suffer from a lack of water being transported up to the leaves.
The lack of oxygen in flooded soils also causes microorganisms in the soil to steal the oxygen from nitrate molecules causing soil nitrogen to become depleted in a process called denitrification. I have seen pecan leaves yellow during flooding events due to a lack of nitrogen.
There is not much we can do about flooding in areas where native pecans grow--it is going to happen. What we can do is ensure that the water moves off the field a quickly as possible by improving the surface drainage within our groves.
There is one more observation I've made about flooding and pecans. On a section of my own farm I have allowed native pecan seedlings to sprout up where they wish. What's interesting to me is the distribution of the seedlings across the field follows the flooding patterns I see every time we receive heavy rains. Even though the entire field is located in the Neosho River flood plain, seedling trees seem to be clustered in areas that have a little better drainage (photo at right). The "wet" spot in this field has few or no seedlings volunteering to become a part of my future pecan grove. So it seems that pecans can tolerate floods but don't thrive in soils that are excessively wet.