Drought impacts, Tree windbreak damage needs evaluated
The 2012 drought has taken its toll on many tree windbreaks. Producers may want to spend some time surveying their trees to identify not only trees that are dead but ones that are suffering from drought and water stress.
According to Southwestern Nebraska District Forester Rachel Allison, trees that have turned brown or are turning brown are dead.
“After having an open, dry winter in 2011 and then 80 degrees in March, followed by a hot, dry summer with virtually no precipitation, all types of trees were affected by the drought in 2012. We had people call who couldn’t understand why trees that were 30 to 40 years old were dying,” she explained. “This drought affected everything from newly established trees to old trees and all types of trees.”
Allison said some pine trees have had their tops turn brown from lack of water.
“What happens is there isn’t enough moisture available in the soil for the roots to get moisture and pull it all the way to the top of the tree,” she said. “In some cases, it can only go part way or half up the tree.”
The results of the drought vary depending upon moisture deprivation and type of tree, she said.
Broadleaf trees may have brown leaf margins and irregular browning in the veins. They may also show brown scorching on the leaves.
Spruce trees may show some purpling from lack of water.
Trees like pines may have shorter tip growth. Allison showed one instance where the tips had grown five inches in a good year and only an inch during the drought.
These trees may also suffer more damage from winter freeze and burning, since they are already drought stressed.
“People may notice some white tips on the pine trees. This is uniform needle dieback, which is mainly caused by lack of water,” she said. “If it was caused by insects or disease, the white tips would be more sporadic than uniform.”
Allison said producers should make time to assess damage to their tree windbreaks.
One of the first things to evaluate is the soil moisture, which can be determined with a screwdriver, soil probe or a rod or dowel.
“Producers should be able to push the rod in at least down to 12 inches,” Allison said. “Eighteen inches is even better.”
If the trees are lacking water, Allison recommends watering them through a dripline, water wagon or hose.
“Trees do better with infrequent rainfall events and normally survive fairly well in years with average rainfall,” she said. “In windbreaks with a drip system that can be turned on as needed, water the trees at least once or twice a summer.”
“Run the water until the moisture in the soil is down several inches,” she recommended. “Typically, we think of watering right along the top, but this way water is only put on temporarily. We actually need to get the water down to a depth of two feet. That is where the adequate soil moisture is required for root growth and so the tree can absorb nutrients.”
Moisture needs can also vary depending upon the tree species, soil type and the amount of compaction. The trees also need moisture in an area that extends to the edge of the tree’s canopy, Allison noted.
Trees should be watered for 12 to 24 hours at each location and until the end of the line is reached.
“Water them again in three to four weeks if the weather is still hot, and there has been no rainfall,” she added. “Watering frequency can also depend on the type of trees in the windbreak, if they are evergreen or deciduous, the size and age of the trees, whether the ground is shaded or open and the presence of cool season grasses, like brome.”
The windbreak setting can also be a factor, she continued. Producers should ask themselves questions, such as, is the windbreak exposed to a lot of wind, and is it next to a lawn or pivot?
“Trees can take a while to show drought stress,” Allison concluded.
Some signs are subtle like thinning of the crown, fewer leaves and shorter new growth each year.
“The previous droughts in 2001-02 and 2006-07 reduced the mass of the tree’s root system, which limits the amount of water and nutrients the tree can take in,” she explained. “This can make any age of tree susceptible to drought.”