Managing Trees During Drought Conditions
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Managing Trees During Drought Conditions Webinar by Heidi Kratsch
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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.