Effects of Drought on Tree Growth

Dr. Jon Barry, RFAssistant Professor

Southwest Research and Extension Center

Evidence ofDrought• Death

• Less growth

• Tree rings

• Increased stress

Drought and Established Trees

• Stress leading often to pest infestation

• Decreased growth

• Decreased stocking

• Changes in vegetation

- Ecotone movement between prairie and forest

- Elimination of mesic species on xeric sites

Weather Patternfor SWREC

• Two years of record rain

• Two years of severe drought

• One year moderate drought

- Decreased root growth during wet periods - Increased top growth during wet periods

- Need more roots and less top during drought

• Result: Tree stress and pest infection

2008 Rainfall

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2009 Rainfall

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2010 Rainfall

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2011 Weather

2012 Weather

Simple Energy Balance Model

Water Flow

Effect of Droughton Photosynthesis

• Decreasing water availability decreases photosynthesis

• Decreasing production of carbohydrates

• Less growth- Less roots

• Less production of “natural pesticides”

What is Tree Stress

• Trees subject to less than ideal growing conditions.

• Strain (reduction or change in function)- Elastic Strain

- Plastic Strain Off-site

Stress and Pests

• Reduced photosynthesis and increased respiration lends to depleted energy

• Lack of energy leads to the lack of resistance to pests

• Trees succumb to repeated attacks or are not able to compartmentalize pest

• Process can last decades

Stress and Pests

• Hypoxylon canker

• Bark beetles

• Root weevils and leptographium

Managing Older Stands

• Maintain vigor

- Thin when thinning is needed

- Control competing vegetation

• Recognize financial and biological maturity

Seedlings and Drought

• How do we insure success?

• Do we plan for failure during drought years?

Seedling Quality

• All nurseries in Arkansas produce quality seedlings.

• What is a quality seedling?- Fibrous root system

- Pronounced terminal bud

- Secondary needles

- Proper caliper

- Dormant

Proper Storage

• Stored in a cooler and planted directly from the cooler

• If not kept in a cooler- Don’t leave in sun

- Don’t leave in truck

• Increasing temperatures increase respiration which decrease energy reserves

Proper PlantingConditions

• Don’t Plant with Poor Soil Moisture.

• Don’t Plant at Temperatures > 60o

• Don’t Plant at Wind Speeds > 15 mph.

Proper Handlingin Field

• One tree at a time

• NO ROOT PRUNING

Planting

• Tight and deep!

- Beyond the root collar

- As long as the terminal bud is above the ground

- Don’t be over-concerned with root deformation

- Vertical not at an angle

Strategy to ImproveSuccess• Site preparation

- Debris removal

- Tillage

• Vegetation control- More water

• Containerized seedlings- Fall planting

Poor DensityStrategy• Plant more trees

- Overstocking

Ford’s Axiom

• When environmental conditions are good, the little things matter a little.

• When environmental conditions are bad, the little things matter a lot.

Questions?