Written by: August Hoppe (Certified Arborist WI-0477A)
Southeastern Wisconsin is experiencing a drought that started last summer and has continued through this winter. This is notable because it can affect our trees and shrubs this upcoming growing season.
In a typical year, autumn rains provide moisture that tree roots need to use before the ground freezes for the winter. However, this last fall was dry, and many trees were unable to obtain adequate moisture. This, coupled with a dry winter and a lack of insulating snow cover, has created some tough challenges for trees.
The Importance of Snow for Tree Health
Trees in our region rely heavily on snow not just for hydration, but also as an insulating layer. Snow cover protects tree roots from freezing temperatures, allowing moisture to remain more accessible throughout the season. Research shows that a snow cover depth of about 12 inches is ideal for protecting roots. However, without adequate snowfall, soil can freeze quickly, putting stress on root systems.
Moreover, as temperatures change, snow slowly melts providing essential moisture that trees need. According to studies, trees can absorb up to 60% of the moisture from melted snow. When snow is sparse, trees struggle to find the water they need during the growing season, which can lead to long-term health issues.
Winter Burn on Evergreens
Evergreens are more susceptible to winter burn than deciduous trees because they retain their needles throughout the year. This means that they continue to lose moisture through transpiration even when the ground is frozen, making it difficult for their roots to replenish that water. This can lead to desiccation (drying out) in harsh winter conditions like cold temperatures and drying winds. This coupled with freezing and thawing cycles in early spring can push a stressed evergreen over the edge. An example was in 2019 when we had a polar vortex winter. Come spring many yews and arborvitae bushes rapidly turned brown and died back. That year we also saw many Japanese Maple trees succumb to winter dieback as well.
Drought Stress and Root Health
Drought stress becomes a critical concern when trees cannot obtain enough water. This stress weakens root systems, making trees more prone to environmental changes and diseases. In southeastern Wisconsin, increasing drought conditions could lead to a rise in issues related to root health.
Healthy roots are vital for stability, nutrient uptake, and overall growth. When conditions become dry, trees may enter a stress state where they conserve resources. This can result in halted new growth and premature leaf shedding. For instance, stressed trees may shed up to 25% of their leaves earlier than normal, reducing their energy storage for spring. Such conditions directly affect blooming, leaf production, and fruiting.
Increased Pest and Disease Susceptibility
Drought-stressed trees are more likely to face pest challenges and diseases. When trees are under stress, their natural defenses weaken, making them attractive to insects and pathogens. For example, bark beetles often target stressed trees, with infestations reported to increase by over 40% in drought conditions. Insects such as bronze birch borer find it much easier to prey upon drought-stressed paper birch trees than healthy birches. Oak trees are also affected by an opportunistic insect, the 2-lined chestnut borer. This insect attacks moisture-stressed white oak trees.
Effect on Growth Patterns
A lack of moisture in winter directly affects tree growth patterns. Winter is vital for energy conservation, root development, and hydration. Without sufficient snow or rain, trees may experience stunted growth, producing fewer leaves, flowers, and fruits in the upcoming seasons.
Moreover, erratic moisture levels can lead to irregular growth patterns, creating structural weak points within the tree. These weak areas increase vulnerability during storms or high winds, raising the risk of branches breaking, or even tree failure.
Signs to Look Out For
As we move through winter and the drought persists, keeping an eye on your trees for signs of stress is crucial. Here are indicators to watch for:
Wilting or curling leaves: If leaves curl or wilt prematurely it indicates the tree is struggling to retain moisture. Keep an eye on this once leaves emerge, and give Hoppe a call to have a Certified Arborist take a look at your trees.
Yellowing leaves: This occurs when stressed root systems are not able to pull up adequate amounts of micronutrients from the soil.
Bark damage: Cracks or peeling bark can signal internal stress.
Early leaf drop: Trees dropping leaves unexpectedly can be a distress signal.
Unusual growth patterns: Look for signs of stunted growth or an uneven canopy.
If you observe any of these signs, it's important to seek professional assistance to help your trees recover.
How Hoppe Tree Service Can Help
Overall wellness for your trees is the first place to start. Proper watering (approximately 1” of water per week during the growing season) can make a big difference. Also applying 2-3” of mulch around the base of the tree can help retain moisture, insulate the root system, and provide nutrients to the plant over time.
Fertilization programs and soil amendments can help build up the root system and increase the amount of water-absorbing fine roots.
Protect Your Landscape Investment
With the support of professionals like Hoppe Tree Service, you can take steps to ensure your trees not only endure this challenging winter but also thrive in the seasons to come. Give Hoppe Tree Service a call at 414-257-2111 or request an appointment for one of our Certified Arborists to review your trees to ensure they are ready for spring.