Managing ash woodlands with emerald ash borer

Woodland owners need to understand their own goals and specific site conditions before making decisions about timber harvesting and regeneration. Foresters and other natural resource professionals can conduct a woodland inventory and help prepare a management plan.

Measurements for a woodland inventory: 

• Tree measurements such as diameter, height, species, age and volume.

• Stand measurements such as volume and stocking.

• Site measurements such as depth to water table and site quality.

• The proportion of trees that are ash versus non-ash species.

• The number of existing seedlings of non-ash species on the site.

These variables help in understanding the potential of the forest. The same measurements can also help to determine wildlife habitat and placement of recreational trails. 

Once the inventory is done, management methods should be applied on time to lessen or eliminate the effects of EAB. 

• Try to harvest healthy trees before an attack from EAB. 

• Limit the number of ash trees in the woodland to control the spread of EAB.

Choosing a specific timber harvesting and regeneration method depends on the quality and quantity of timber produced by the forest. Higher quality woodlands on well-drained soils with faster-growing ash trees have more management options compared to lower quality sites.

• The focus of timber harvesting is to remove mature trees and prepare a stand to be regenerated by new trees. 

• The type of timber harvest and regeneration method chosen is collectively called a silvicultural system. 

• The way trees are removed has an effect on the future of the woodland. 

Ash is often found in lowland areas in Minnesota. In woodlands with more ash, harvest activities should be carried out only when the ground is frozen or dry. 

• Consider how the water table will be affected before choosing an appropriate harvesting method. 

• Wetter sites have a greater chance of the water table rising after harvesting and have a higher risk of “swamping.”

Clearcut

• Harvest all trees in a stand, without considering the species or marketability. This method can cause a large disturbance.

• Avoid this method on wet sites due to the risk of increased water table rise.

• Clearcutting in strips that are harvested over two or three cuts may minimize water table rise and deter browse from white-tailed deer on non-ash species.

Seed tree

• Retain mature trees at low densities during harvesting as seed sources.
• Consider on wet sites if other non-ash species are present in the canopy.

Shelterwood

• Harvest all trees over two or three cuts to encourage advanced regeneration before a final clearcut.

• Consider for wet sites if:

  • Other non-ash species are present in the canopy.

  • Existing seedlings are abundant and healthy.

  • Implementing a shelterwood in strips.

Single-tree selection

• Individual trees of all sizes and ages are periodically removed to form an uneven-aged stand.
• Consider using in floodplains or mesic hardwood forests on dry or frozen ground.

Group selection

• Trees are removed in small groups up to 1/2 acre in size to form an uneven-aged stand.

• Consider for wet sites to minimize water table rise and transition to non-ash species.

• Consider using in floodplains or mesic hardwood forests on dry or frozen ground.

Timber harvesting and regeneration are interconnected. Due to the spread of EAB across Minnesota’s woodlands, it is recommended to regenerate non-ash species. 

Regeneration is the process of replacing trees in a woodland with new trees. A woodland can be regenerated in three ways:

1. Natural seeding
2. Stump sprouting
3. Planting new seeds or seedlings

Natural seeding

• Natural seeding from nearby trees is an example of natural regeneration.
• If you want to encourage natural regeneration of non-ash species, it is important to be familiar with the seeding strategies of ash as well as the replacement trees.

• Seeding process in ash:

  • Ash seeds are an important seed source for game birds, songbirds and small animals.

  • Seeds of ash trees (called “samaras”) mature in the fall and can live through the winter.

  • Ash seeds can be dispersed by wind to over 300 feet from the parent tree. 

  • Ash seed banks can survive in the soil for up to eight years. 

Stump sprouting

• Stump sprouting is also an example of natural regeneration.
• Ash, oak, maple and birch trees are some tree species that can reproduce naturally through stump sprouting.
• Stump sprouts grow from exposed stumps and are genetically identical to the parent tree. 
• It is important to note that black ash trees produce several stump sprouts after harvest.

Planting new seeds or seedlings

• Planting new seeds or seedlings are examples of artificial regeneration. 

• Artificial regeneration is more expensive than regeneration from natural seeding. 

• The advantage is that a woodland owner can select the appropriate tree species, genetic characteristics and tree spacing by planting. 

Replacement trees can be selected depending on site characteristics and the native plant community of the woodland.