URBAN & COMMUNITY FORESTRY
  • Drought is defined by a relatively long duration with substantially below-normal precipitation, usually occurring over a large area, and Texas is no stranger to drought. According to the US Drought Monitor, during our most recent significant drought in 2011 more than 80% of Texas experienced exceptional drought conditions. This drought killed an estimated 300 million trees, 5.6 million being urban shade trees.

    Read drought and trees – explained here.

     + Caring for Trees During Drought

    Prolonged drought can cause decline and death in young and mature trees alike. Fortunately, there are things you can do to minimize the effects of drought on your trees, specifically as it relates to watering and soil management. Trees need less frequent irrigation than turf grass, but they need to be water long and slow allowing the water to soak deep into the soil. You can use a screwdriver to determine if it's time to water; simply try to push it into the ground. If the ground is dry, you won't be able to. If the ground is wet, you will. If you can't get your screwdriver to easily go at least 6 to 8 inches into the ground, it's time to water. The specifics for watering vary depending on whether the trees are young or mature (see below); however, for all trees it is important to minimize water contact with the trunk and lower leaves of the tree as water droplets can act as vectors for bacteria and other harmful diseases. 

    Mature Trees 

    Mature trees should be watered at least every two weeks while experiencing drought. These mature trees with established roots can be watered through various methods, but water should be applied to the entire area within the dripline under the crown of the tree. During periods of prolonged drought, apply water to all soil under the canopy while remaining compliant with any local water restrictions.  


    Younger Trees  

    Younger trees will need more frequent waterings until they become established at roughly two years after planting.It is recommended to water newly planted trees 2-3 times a week with at least one gallon of water per caliper inch of trunk diameter. Watering should be focused primarily on and immediatelyadjacent to the original root ball as these trees have not yet developed long ranging roots. Water should be applied slowly allowing it to soak deep into the soil rather than run off. Another way to help care for trees, whether young or mature, during times of drought is with the use of mulch. Hardwood mulch is beneficial to conserving a tree’s water and retaining moisture in the soil. Mulch helps to improve water percolation into the soil and keeps that root system underneath cooler than surrounding areas. This reduces water lost to evaporation and provides the tree with less stress for any water or nutrient exchange. Mulch also protects from herbaceous competition and generally improves overall tree health. Mulch should be applied no more than three inches thick over as much of the root system as possible, but not in direct contact with the tree trunk. 

     + Assessing Damage to Trees from Drought
    Assessing trees damaged or killed by drought can be tricky, but grouping trees into one of three categories – definitely dead, likely to live and questionable – can help with the task.

    Definitely Dead – It is easier to make this call for pines, Ashe junipers (cedars) and other needle-bearing, coniferous trees. The determination can be more difficult for hardwoods, which are more commonly thought of as shade trees. In most cases, a red pine is a dead pine, and the same can be said for cedars with red needles. Once all or most of the foliage of a pine or cedar tree turns red or brown, the tree is incapable of recovering.

    Pine trees in this stage probably are already infested with tree-killing bark beetles and will eventually harbor wood-boring insects, termites and other critters. These trees should be cut down and removed, particularly if they are likely to fall on homes, buildings or power lines.

    Shade trees, such as oaks, that have lost all their foliage and are beginning to drop limbs or lose large patches of bark are most likely already dead and should be removed. Hypoxylon canker, a fungus that appears as gray or brown patches on the trunk of the tree, is another sign of a dead shade tree.



    Likely to live - This category includes shade trees with at least some green or yellow leaves still attached to the limbs. In fact, even those that have dropped all their leaves may still be alive. Some native shade trees, such as post oaks and live oaks, are more drought resistant than others like water oaks or elms.

    You can use a scratch test to determine if the tree is dead or just dormant. If you scrape the bark off a small branch or limb and find green, moist tissue underneath, the tree is still hanging on, waiting for the next rain. That means you may need to wait until the following spring to see if the tree makes a recovery — unless the tree starts to show other signs of being definitely dead. If the scratch test doesn’t reveal any green, moist tissue, the tree is likely dead.

    An exception is the baldcypress. This tree is a conifer, but unlike pines and cedars, its foliage generally turns red and drops in the fall or during periods of drought stress. Baldypress trees usually will re-sprout in the spring. If in doubt, apply the scratch test or wait until spring to be sure.

    Pines with a few yellow or red needles scattered throughout an otherwise green canopy have a good chance at survival. Pine trees typically shed a large portion of their older needles every year as winter approaches, and then put on new needles in the spring.

    Though it’s not as feasible to water your forest, any yard trees that show signs of life (green inner tissues or green foliage) should be watered deeply to reduce lingering drought stress.



    Questionable - Questionable trees are those that appear to fit somewhere between the Definitely Dead and Likely to Live categories.

    A pine that is topped with brown or red needles but still has green foliage in its lower branches is alive, but likely will eventually die. That’s because bark beetles will eventually invade the lower trunk, killing the tree in stages.

    When inspecting a questionable pine tree, look for popcorn-sized masses of resin (pitch tubes) or brown dust in the bark fissures. These are early signs of attacks by pine bark beetles. The foliage of the infested pine may still be green, but the tree is ultimately doomed. This is particularly true if you find bark beetle galleries or trails beneath the bark. Pines with these signs of bark beetle attack should be removed as soon as possible.

    In the case of shade trees, those that have many dead or dying limbs or mostly bare branches may or may not survive.  A few green, yellow or red leaves may remain for a while as the tree slowly dies, or it may partially recover when rains return, although likely with quite a few dead branches scattered through the canopy that will need to be addressed through proper pruning. 



    Deciding whether to remove a questionable tree can be a tough decision for both property owners and professional tree care experts. Removal should be considered if a severely drought-stressed or fire-damaged tree is close to a house or other structure on which it might fall. If it is away from such areas, it may be more feasible to wait and see if the tree makes a comeback. 
     
     + Landscape Effects of Drought
    Forests across the Southeast are experiencing warmer, drier climates leading to increased mortality from phenomena such as drought. The predicted tree mortality in traditional forest landscapes is expected to have wide-ranging, long-term impacts. Forests, much like people, go through natural life cycles. Unlike people, these life cycles span hundreds of years at a time. Forest life cycles see generational changes as overstory species naturally age out of the canopy and are replaced by younger ones. This is an important process for a forest's biodiversity. However, due to drought conditions in an already warmer climate, mature trees in that overstory are experiencing increased stressors and are dying at an above average rate than they have historically. These increased stressors can invite other unwanted invasive pests and diseases into the forest and further contribute to increased tree mortality. Forest compositions are reliant on this timing to allow the slower growing species to better compete with undesirable or invasive species like Chinese tallow. Given today’s conditions, if our forests experience prolonged drought, we can expect less biodiversity, larger and more frequent insect and diseases outbreaks, and impacts to our carbon market as our mature trees are replaced with smaller, faster growing species less conducive to carbon sequestration.
     + Rural Forestland

    Final survey shows 301 million trees in rural areas killed by drought (September 2012)

    Commercial timber losses reach $669 million—East Texas Drought Update (March 2012)
        Report
    East Texas Forest Recovery - Damage estimates from the 2011 drought and wildfire season
     + Watering Your Trees