Why are the tree leaves changing color? As the drought conditions worsen across Arkansas and other areas of the South, more and more trees seem to be changing color early. Species like cottonwood are turning yellow when they should be bright green. Many hardwoods have already lost their leaves. The cause of this is simple: it’s the extreme lack of moisture. Water is the most important resource for trees and forests. As the soil moisture declines, trees begin to react to the inadequate moisture. Trees have a series of strategies for reacting to drought conditions. Once the tree “senses” that there is a root water availability problem, it starts trying to adapt by increasing root production, using food storage reserves, and as the drought increases, closing down root activities and losing leaves. The change in color is a result of the tree simply shutting down photosynthesis or leaf activity. Leaf drop or foliage senescence is one of the more harmful responses to drought. It’s a way for the tree to conserve energy. If moisture becomes available later on this growing season, some trees defoliated by drought may produce another set of leaves. However, this can further stress the tree. It takes a lot of energy to produce leaves and if the tree has already used its food storage reserves, a new set of leaves could cause more damage.
In deciduous trees, like hardwoods, leaves will curl, bend, roll, become discolored, shed, and change color early. In conifers like pine, drought can cause yellowing and browning of needle tips.
Trees that have gone into early dormancy are not necessarily dead. Whether a tree survives a drought depends on a few factors such as species, site, soil volume available for rooting, and recent history. Our forests have survived cycles of drought and in fact, our native trees are fairly tolerant of drought. But this is the third growing season with severe to exceptional drought conditions. Many of our trees might not survive this last blow. Landowners should pay attention to their site conditions and plant trees native and adapted to their local conditions.