Trees and Drought
Identification and Management
Trees require four resources to live: 1) sunlight 2) carbon dioxide 3) nutrients 4) water. Water drives all the processes within a tree from photosynthesis to root growth and nutrient uptake. As trees grow they invest energy in creating a root system that will support them in times when water is a scarce commodity. In urban landscapes we often create situations where the trees’ natural drought resistance is damaged or is circumvented. In these situations trees can be irreparably damaged by a lack of water.
Conditions that create drought susceptible trees:
- Construction that disrupts an established root system
- Soil compaction that damages an established root system
- Soil compaction that prevents new root proliferation
- Removal of organic materials that shade and retain soil moisture
- Irrigation that over waters trees, inhibiting tree root production
- Reducing watering schedules during drought periods
- Planting turfgrass and/or perennials immediately adjacent to trees
- Cold winters without adequate snow cover
In Minnesota drought conditions tend to occur in three and four year cycles. While trees can survive initial drought conditions, prolonged periods of drought will stress trees making them susceptible to insects and diseases.
Insects that attack drought stressed trees:
- Bronze birch borer on all birch species
- Two-lined chestnut borer on all oak species
- Flatheaded apple tree borer on flowering crabapples and pears
- Conifer bark beetles on pine, larch, and spruce
- Ash and lilac borer on all lilac and ash trees
Management of Trees for Drought Conditions
As with most tree problems, the best management strategy is to prevent trees from becoming susceptible to drought. Roots will grow where resources are plentiful. Water at the drip-line of the tree to increase root proliferation and drought tolerance.
Newly Planted Trees:It is important to reduce compaction of the soils and create an opportunity for roots to grow beyond the planting hole and root ball. It is also important to reduce the competition for water with other plants, primarily turfgrasses.
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Mature Trees:It is important not to disrupt the root system that has been established by the tree. If construction damage or root damage is inevitable, everything possible must be done to preserve the remaining roots. Protective programs should be used to promote the continued growth of these roots and to minimize damage of drought stress.
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An integrated approach
When caring for urban trees it is important to make a complete evaluation of all environmental conditions to accurately diagnose all stress factors and prescribe care based on specific circumstances. This prescriptive care will help your tree meet its full potential.
