Managing Trees During Drought Conditions
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This document summarizes best practices for managing trees during drought conditions. It discusses how drought impacts trees, effective irrigation strategies like hydrozoning and using drip irrigation, and other drought management techniques. It also provides recommendations for selecting drought-resilient tree species for urban landscapes, describing species from zones 4-7 that can tolerate lower water conditions. Examples of susceptible and tolerant species are given. The goal is to keep urban trees healthy during water shortages through irrigation optimization and choosing adapted plants.
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Managing Trees During Drought Conditions
- 1. ManagingTrees During Drought Conditions Dr. Heidi Kratsch University of Nevada Cooperative Extension
- 2. What we will cover… •Impact of drought on trees •Most effective irrigation strategies for trees •Other management issues for trees during drought •Selecting trees for drought-resilience
- 4. We’re killing our urban trees!
- 5. Transpiration • Transpiration starts at the leaves. • Capillary action pulls water from below. • Soil moisture is depleted. • Hot, dry air increases transpiration. • Wind blowing across leaves increases transpiration.
- 6. Tree’s response to drought: • Stomata close and photosynthesis slows. • Death of root hairs and feeder roots • Wilting, scorch, and defoliation • New leaves may be smaller than normal. • Premature fall color • Dieback of shoots • Growth in height and girth declines. • Heavier than normal seed production • Increased susceptibility to insect pests (spider mites, wood-boring insects)
- 8. Turf-based landscape • 4,850 square feet • 15% hardscape • 45% turf • 15% shrubs • 21% perennial beds • 5% ground cover plants • 12 trees • Irrigated by pop-up sprinklers Average annual water use = 72,875 gallons Rosenberg et al., 2010,Value Landscape Engineering: Identifying costs, water use, labor, and impacts to support landscape choice, Journal of the AmericanWater Resources Association
- 9. Woodland-style landscape • 4,870 square feet • 20% hardscape • 0% turf • 60% shrub beds • 20% perennial beds • 0% ground cover plants • 18 trees • Irrigated entirely by drip Average annual water use = 22,610 gallons Trees are the most valuable asset in our urban areas.
- 10. Goal of irrigation Replace the water lost from the root zone due to: •Transpiration •Evaporation •Percolation below the rooting zone.
- 11. • Up to 90 percent of the total root system length is accounted for by fine, absorbing roots. Fine, absorbing roots Sinker root
- 12. Need to wet 60% to 75% of the tree root zone.
- 13. Hydrozoning •Group plants with similar water needs and... •Irrigate zones on separate valves.
- 14. Two aspects to irrigation scheduling •Duration: How much water to apply… •Frequency: How often to apply it.
- 15. Water trees deeply Watering depth for different plants: Tree roots 18 to 24 inches Shrub roots 12 to 18 inches Herbaceous plant roots 6 to 12 inches Turfgrass roots 6 to 8 inches
- 16. Calculate estimated daily water use Gallons per plant = 0.623 x plant area x plant factor x reference evapotranspiration (ETo) per day ÷ irrigation system efficiency Based on ASCE guidelines and modified for practical use.
- 17. Plant Area = Crown diameter2 x 0.7854 Example: Crown diameter = 10 ft., so 102 (10 x 10) x 0.7854 = 78.54 sq. ft.
- 18. Plant factor for trees ranges from 0.5 to 0.8 Actualwaterloss,in/day Reference water loss (ETo) ETo: 4 -6” fescue turf, 100% Home turf: 80% Trees: 50% to 80% http://www.washoeet.dri.edu/washoeEt.html
- 19. Water trees less frequently GALLONS OF WATER PER WEEK Plant water use Plant canopy diameter in feet 1 2 3 4 5 6 8 10 12 14 Tree medium low 29 21 52 42 81 64 116 92 158 126 Shrub medium low 9 3 7 5.5 12.5 10 20 17 29 21 43 35 Perennial medium low 1.5 1 4 3 10 5 Information valid for western Nevada and other similar climates during summer.
- 20. Micro-irrigation (Drip) •Slow application •Measured in GPH rather than GPM •Less loss to evaporation •Reduces runoff and leaching •System efficiency of 80% to 90% (sprinklers < 75%)
- 21. Micro-irrigation emission devices (low pressure 10-30 psi) • Drip emitters – for shrubs and small trees (0.5–6 gph) • Bubblers – best for new trees with a berm or trees in wells (2–20 gph) • Micro-spray emitters – for medium to large trees (3–30 gph) The main difference is the mode of water dispersal.
- 22. Micro-spray emitters • External emitters connected to the lateral distribution line using spaghetti tubing • Fewer heads needed to cover large areas. • Visible to easily check for damage.
- 23. Example: How long should I water? Size Drip Emitters Microspray Emitters Large trees (canopy 14+ feet) 20 2-gph emitters for 4 hours once a week Eight 20-gph emitters for 1 hour once a week Medium trees (canopy 10-12 feet) 14 2-gph emitters for 3 to 4 hours once a week Six 14-gph emitters for 1 to 1.5 hours once a week Small trees/large shrubs (canopy 6-8 feet) 10 2-gph emitters for 1.5 to 2.5 hours once a week Five 11-gph emitters for 0.5 to 1 hour once a week Based on gallons of water needed per tree.
- 24. CLAYSILTSAND The spread of the wetting front depends on soil texture.
- 25. Emitter arrangement for young trees • Wet as much of the root ball as possible. • Irrigation line should not be up against the trunk. • Emitters should be placed within and beyond the spread of the root ball to encourage root growth into native soil. Roots don’t seek water – they follow water.
- 26. Result of inadequate early water distribution Roots won’t spread into dry soil.
- 27. Emitter arrangement for mature trees Southern Nevada Water Authority New Mexico State University The depth and distribution of water application will determine the architecture of the root system.
- 28. How will the architecture of this tree’s root system look?
- 29. Remember where the roots are.
- 32. Irrigation of trees surrounded by turfgrass
- 33. What’s going on with this tree?
- 34. Other strategies for managing trees during drought • Mulch at least out to the drip line, further if possible. • Do not fertilize trees during drought conditions. • Limit pruning to removal of dead wood or crossing branches.
- 35. Urban tree selection for drought resilience
- 36. Water is lost through leaf stomata (pores). What our eyes see What our eyes can’t see
- 37. Plant adaptations to arid conditions • Leaf size • Leaf color • Leaf orientation • Extensive root system Rocky Mountain Juniper Common Hackberry Gambel OakFremont barberry
- 38. Some species susceptible to secondary infestation by bark beetles and borers •Ash •Some birches •Elm •Fir •Locust •Pine •Spruce
- 39. Many native trees are not drought-tolerant: •Aspen, Quaking •Birch, River •Cottonwood, Fremont •Douglas-fir •Fir: Subalpine,White •Pine, Ponderosa •Pine,White •Willow Ponderosa pine in an urban area
- 40. Trees that do surprisingly well with less water (in zones 4 – 7) • Baldcypress • Coffeetree, Kentucky • Corktree, Amur • Cyprus, Leyland • Ginkgo • Goldenraintree • Hackberry: Common, Douglas, Netleaf • Hawthorn: Cockspur, Green, Lavalle, Washington • Honeylocust • Juniper, Rocky Mountain • Maple: Amur, Sycamore,Tatarian, Trident • Mulberry: Red, White • Oak: Bur, Chinkapin, Gambel, Shumard,Turkey • Osage-orange • Pine: Bristlecone, Jeffrey, Limber, Mugo • Sycamore, American • Zelkova, Japanese
- 41. Contact: Heidi Kratsch University of Nevada Cooperative Extension Phone: 775-784-4848 Email: KratschH@unce.unr.edu Questions? This presentation was brought to you by the Nevada Extension IPM Program and funded by USDA-NIFA.