With California facing one of the worst droughts on record, lawns are turning brown, flowers are shriveling, and our urban leafy friends seem to me suffering with the lack of the consistent irrigation they’re used to. But, tree roots run deep and trees seemed to have had enough time to evolve to where a little drought shouldn’t hurt right? Let’s explore a bit into what the short term and long term effects of drought-stress can be, and if there is any way to help our trees through this stressful time.
Early effects of drought, or damage caused by one dry period, include wilting or discoloration of foliage, shedding of leaves or needles, and reduction in growth. Wilting, leaf ‘burn’ and shedding of needles may be the most obvious to the casual observer. Early leaf drop is another result, which is a deciduous tree’s adaptation for conserving water that it otherwise would lose through water loss through its leaves, which can occur as long as the leaves are green.
Long-term damage from drought happens over a period of years and includes stunted growth, branch die-back, and possible death of the plant. Many woody plants can take up to three years after a drought to display negative long-term effects. This happens as a result of fine feeder (fibrous) root loss, which dies if the soil remains dry. When this happens, the balance of root to canopy ratio changes and the canopy will then die back to compensate for the root loss. If the drought continues into the following growing season, then the tree may not be able to fully recover.
Pest and disease problems are another result of long-term drought to trees. There are many pests that cannot survive in a healthy tree…much like how viruses can be fought off in a healthy body. However, when a tree becomes weakened from drought, these pests invade rapidly and take advantage of the trees compromised state. Once pests invade, declining health in the tree may then be a result of these secondary killers, and not necessarily the lack of water.
Does a Drought Make my Tree More Hazardous?
Nothing so far has been linked to drought causing sudden limb failures. If the tree is suffering from long-term drought stress and limbs are dying, then these should be pruned. There is a phenomenon that happens in trees called Summer Limb Drop, but it is theorized to be due to extreme fluctuations of temperature and rapid internal moisture changes.
Can I Help my Trees During a Drought?
There are a few things you can do to help your trees through a drought:
1. Supplemental Deep-Watering
Deep watering can be accomplished by moving a hose around under the tree’s canopy during the day for a day or two at a low flow or a trickle stream, such that the water percolates into the soil, not simply run down the hill. Don’t focus the stream on or close to the trunk, but water out to the drip-line of the tree (where the tree’s canopy extends). A deep watering followed by soil drying for a month or two should not harm the tree.
Since fine-feeder roots are so close to the soil surface, they can dry-out and die when the soil loses significant moisture and becomes over heated. The removal of any turfgrass and the addition of 3 inches of wood chips or shredded bark under the drip line can have a very beneficial effect by holding in moisture and promoting healthy fine-feeder roots. Check out our other blog for more information on Mulch Matters.
3. Tree Growth Regulator (TGR) Treatment
TGR is used to extend the life of trees by keeping them at a manageable size for a longer period of time. Research shows that TGR increases drought resistance by helping the tree reduce water losses during dry, hot periods, and it increases fine root growth. The leaves of TGR treated trees tend to be greener than untreated trees and have a thicker leaf surface and denser surface hairs, which help to prevent excessive moisture loss. TGR is our #1 recommendation to combat stress in any tree. More info can be found here, or call us to schedule a treatment for you trees!
Thanks for reading…and maybe we should challenge all our trees to the Ice Bucket Challenge….I’m sure they’d appreciate it 😉
Sources: UC Berkeley Forest Research Bartlett The Tree Geek Fine Gardening
Blog written by: Arborist Sarah (Hon) Gaskin