Living in Central Oregon, we’re fortunate to be surrounded by many beautiful, mature ponderosa pine trees (Pinus ponderosa). These towering giants are a hallmark of our landscape, providing shade in the summer heat, visual appeal, habitat for wildlife, and so many other ecosystem benefits. Stands of large old pines in Drake Park in Bend, and Creekside Park in Sisters typify Central Oregon landscapes where large old trees have been preserved.

However, not all ponderosa pines are created equal, and some may pose significant hazards when not managed and inspected regularly–-particularly trees with co-dominant, or competing, tops. Understanding the risks of co-dominant tops can help homeowners make informed decisions about the safety of their trees.

What Are Co-dominant Tops?

Co-dominant tops occur when two or more main trunks grow from the same point on a tree, typically forming a "V" or "Y" shape and creating a structural weakness. This growth pattern is common in ponderosa pines. Unlike a single, dominant trunk, co-dominant tops compete for resources and often grow at the same rate, leading to an equal-sized but potentially unstable tree structure.

The Risks of Co-dominant Ponderosa Pines

1. Increased Risk of Splitting
   The junction where co-dominant tops meet is inherently weak. As the tree grows and the stems thicken, the pressure at this junction increases. External factors such as wind, heavy snow, or ice can exacerbate this stress, leading to a higher likelihood of splitting. A split tree can cause significant damage to property and pose serious safety risks to residents.

2. Susceptibility to Disease and Pests
   The structural weakness of co-dominant tops makes these trees more susceptible to diseases and pests. Cracks and splits in the bark can become entry points for insects and pathogens, which can further weaken the tree and accelerate decay. In Central Oregon, common pests like bark beetles can quickly infest and kill stressed trees, turning them into potential hazards.

3. Reduced Longevity and Stability
   Trees with co-dominant tops often have a reduced lifespan compared to their single-stem counterparts. The competition between stems for sunlight, water, and nutrients can lead to overall poor health. Additionally, as these trees age, their structural integrity diminishes, making them more prone to falling during storms or high winds, leaving behind large wounds and cavities.

4. Potential Liability Issues
   Homeowners have a responsibility to maintain their trees and ensure they do not pose a risk to others. A failing co-dominant ponderosa pine can cause significant damage to neighboring properties or public areas, potentially leading to legal and financial repercussions. Proactively managing these trees can help mitigate such risks.

Mitigation and Management Strategies

1. Regular Inspections
   Regular inspections by a certified arborist can help identify co-dominant tops and assess their risk. Early detection of potential problems allows for timely intervention, reducing the likelihood of catastrophic failure.

2. Selective Pruning
   Pruning can help reduce the weight and wind resistance of co-dominant tops, decreasing the chances of splitting. If caught early in a tree's life, co-dominant tops can be “prevented” through subordination pruning. Proper pruning techniques can also improve the overall health and structure of the tree.

3. Subordination Pruning
   Subordinating one of the co-dominant tops involves pruning it back to slow its growth, allowing the other stem to become dominant. This can improve the tree's structural integrity over time by reducing competition between the stems.

4. Installing Dynamic Cables
   Dynamic cables, or non-rigid cables, can be installed to provide flexible support to co-dominant tops. These cables allow for natural movement while reducing the risk of splitting. This method is less invasive than rigid cabling and helps maintain the tree's aesthetic and structural balance.

5. Tree Removal
   In situations where a co-dominant ponderosa pine poses a significant risk and cannot be effectively mitigated, removal may be the best option. While this is often a last resort, it is sometimes necessary to ensure the safety of your property and loved ones.

Actionable Steps for Homeowners

1. Schedule Regular Inspections
   Contact a certified arborist to perform regular inspections of your ponderosa pines. Early detection of co-dominant tops and other structural issues can prevent future hazards.

2. Implement Pruning and Subordination
   Work with your arborist to create a pruning plan that includes subordinating one of the co-dominant tops. This will help improve the tree’s structural stability over time.

3. Consider Dynamic Cabling
   If your arborist recommends it, install dynamic cables to provide additional support to the tree. Ensure the cables are checked and maintained regularly.

4. Evaluate Tree Health and Stability
   Continually monitor the health and stability of your trees. If a co-dominant tree shows signs of significant decline or poses an immediate threat, consider tree removal.

5. Stay Informed
   Keep yourself updated on best practices for tree care and management. Access resources from reputable sources to make informed decisions about your trees.

Resources for Further Reading

International Society of Arboriculture (ISA):

ISA's information on codominant stems and tree risk assessment

University of California Agriculture and Natural Resources:

Tree Failure Reports and resources from UC Agriculture and Natural Resources

ISA's Guide to Pruning Codominant Leaders:

This article from the International Society of Arboriculture provides guidance on identifying and pruning codominant leaders to reduce risks: ISA - Pruning Codominant Leaders

USDA Forest Service - Managing Codominant Trees:

Explore this publication from the USDA Forest Service that discusses strategies for managing codominant trees to improve tree health and reduce risks: USDA Forest Service - Managing Codominant Trees

Arbor Day Foundation - Tree Care Tips:

The Arbor Day Foundation offers tips and techniques for managing tree health, including strategies for addressing codominant stems: Arbor Day Foundation - Tree Care Tips

TCIA - Proper Pruning Techniques:

This article from the Tree Care Industry Association covers proper pruning techniques, including considerations for managing codominant tree tops: TCIA - Proper Pruning Techniques

Purdue Extension - Tree Pruning and Maintenance:

Purdue University Extension provides resources on tree pruning and maintenance practices, including guidance on managing structural issues like codominant stems: Purdue Extension - Tree Pruning and Maintenance

Spar Tree

At Spar Tree, we specialize in a variety of tree services in Central Oregon, including Bend, Redmond, Sisters, and Camp Sherman. Our services range from tree removal and trimming to hazard tree assessment and preservation. Our team of arborists is dedicated to preserving the health and safety of your trees and beauty of your landscape. Contact us about your tree work needs, including co-dominant tree management and pine tree care.

Spar Tree: good for trees, good to people.