Trapped Water in Wooded Areas
Amy: Previously, Randy and I had discussed the detrimental aspects associated with the long-term flooding along the Mississippi River will possibly have on various hardwoods species. Today, we want to continue that discussion but focus more on water that might still be unable to drain or become trapped. Randy, can you give us a little further insight into this specific problem?
Randy: No problem, like you mentioned our last discussion focused on the general aspects of what type and conditions of flooding may affect tree growth and survival. Within that discussion we talked about how in the backwater areas water can become trapped leaving a situation where the trees remain in a flooded situation until the environment actually causes enough evaporation to eliminate the situation. This condition is the most common way that the trees will starve from a lack of root oxygen which would result in tree death.
Amy: How does the water become trapped?
Randy: As the river rises, the water seeks the area of the least amount of resistance, forcing the water up into smaller rivers and streams; firstinto the lowest areas and then into higher areas. At the same time if rain continues then you have those smaller streams moving their drainage water toward the larger rivers but since it has no place to drain these areas continue to back up and pushing into areas that would not usually have standing water. It is these areas that the majority of the hardwood species are not well adapted to standing water. As the time and temperatures begin to increase so does the possible damage that the tree will incur. When the water reaches its highest point and then stagnates the resulting higher temperatures and decaying biomass begins to rob the water of available oxygen thus creating an environment where there would be little if any oxygen that the tree roots could uptake. Therefore, I think that it is very important that as the water recedes you really need to begin to look for areas where the water may have become trapped and the how much is trapped in terms of area and depth.
Amy: How can we find these trapped water areas and once found water what can be done about it?
Randy: The first thing you will be looking for is discoloration of the leaves in the crown or top portion of the trees, often this discoloration is chlorotic or yellowish looking, but you might also see dying branches or what we call branch dieback. However, this does not indicate that the tree will die but is the visual aspect or a symptom that the tree exhibits while it is trying to recover. The change in leaf color and branch dieback is the tree’s mechanism to begin shutting down parts of the anatomy during a stressed condition so that it can recover in future years. Even if you see trees that appear to be dead, you should look around and see if there are other trees exhibiting the same level of damage. The reason for this is that a single or scattered individuals maybe dying these trees may have entered into the flooded situation as a stressed individual or individuals and the flooding only sped up the decline and resulted in mortality while the other non-stressed individuals of the same species may fully recover.
If trapped water is the reason for not only a single tree but rather a group of trees then you have to determine what if anything can be done to relieve the trees of the stress. If the drainage is blocked by debris that floated in a settle in the drainage causing a blockage or too slow then hopefully it can be easily removed. If the blockage has been formed by animals, such as beavers there may be a way to get someone in there to remove the blockage as well as getting rid of the beavers. There will be some areas that may be too difficult to drain and will result in trees dying. The size and species lost in these areas should be noted so that changes as to what might work better in that area in the future. As any living thing, healthy young trees have a better chance of a full recovery than older stressed trees. The key factor is the stress of the tree prior to the flood regardless of age.
I fully caution everyone not to jump to any conclusions as time has a way of indicating what should be done as the damage may not be as severe as you thing following the flood. A healthy forest are typically very resilient and can recover in a relatively short period of time.