Ash - a native genus facing a foreign threat
By Martin Streit, R.P.F. (OMNR Stewardship Coordinator – Grenville County) and Lynn Farintosh (OMNR Project Forester, North Bay)

Ash is getting a lot of media buzz these days because of the threat of the emerald ash borer.   How does this relate to your job as a tree marker?

Ash in Ontario

There are five native species of ash in Ontario.  They are:  white, red (often called green), black, pumpkin, and blue.  In Ontario, pumpkin (Fraxinus profunda Bush) and blue ash (Fraxinus quadrangulata Michx.) are rare and are limited to the southwest of the province.  Black ash, (Fraxinus nigra Marsh.) is usually found in swampy areas from the southern most portions of Ontario up into the boreal forest (Farrar, 1995).  Red ash (Fraxinus pennsylvanica Marsh) is often called green ash, but green ash is actually a hairless variety of red ash (Farrar, 1995 and Peattie, 1991) that likely originated in the mid-western prairie portion of the species’ range (Waldron, 1997).  Red ash grows throughout the Great Lakes-St. Lawrence Forest Regions, usually along river banks and lake shores and can also be found in uplands sites, if the competition isn’t too great (Burns et al, 1990).

Green ash (Fraxinus pennsylvannia var. subintegerrima (Vahl) Fern.) is often used as an ornamental tree on city streets and parks (Farrar, 1995). It is commonly found in woodlots, fencerows and regenerating in plantations of south eastern Ontario, where it can move into abandoned farmland and form near pure stands.   White ash, Fraxinus americana L., is the most widely distributed of the ashes in Ontario.  It grows throughout most of the Deciduous and Great Lakes-St. Lawrence Forest Regions.  It grows best on deep, moist, well drained soils (Farrar 1995 and Burns et al, 1990).  White and green ash are both mid-tolerant of shade and are usually found in early successional forest stages or where gaps occur in mature forest. 

Green and white ash wood products are marketed together.  Both woods are valued for their durability and are used for flooring, sporting goods, tools, and furniture.  The value of high quality ash can appreciate substantially, if managed properly, as shown in the example below (2006 prices).

The Emerald Ash Borer

The emerald ash borer, Agrilus planipennis Fairmaire, (EAB) is an invasive beetle that was first identified in North America in 2002.   It attacks and kills all native species of ash and has already killed millions of ash trees in southwestern Ontario, Michigan and surrounding states.   It poses a major economic and environmental threat to urban and forested areas (CFIA, 2011).  Despite substantial research and some control efforts, the beetle has continued to spread to new areas.  Some of this spread has been natural dispersal, but long distance spread has been helped by people, primarily through the movement of infested firewood and also possibly on nursery stock.

Symptoms of ash being attacked by the EAB are often very similar to those of other causes of decline.  In fact, many ash in Ontario have been showing signs of decline and general poor health over quite a number of years in many areas.  When identifying a tree under attack from the EAB look for: tiny (<0.5 cm) D-shaped exit holes anywhere on the trunk or roots, 7-10 cm bark cracks on young trees and larvae galleries on trees that were attacked 1-2 years previous.  Headless adults are sometimes found in exit holes and increased woodpecker activity is a good indicator of EAB.  An ash under attack may have dieback in the top half to third of the crown in the first year, followed by epicormic branching along the bole.  Foliage may turn yellow or wilt during the growing season.

Research into controlling the EAB is taking a number of approaches.  Both breeding native ash that show some resistance and hybridizing native ash with ash species native to the area where the EAB originated show promise (species of ash native to China, where the EAB originated, are resistant unless stressed by another factor).  Also showing success are studies using parasites that occur naturally in the native region of the EAB. The parasites attack at various stages of the EAB’s lifecycle: three promising ones have been found.   As well, the effectiveness of predators and diseases that are native to the area of the outbreaks in North America are being investigated. There is also ongoing work into monitoring the spread of the EAB by using coloured traps and even a wasp predator.  An application to Health Canada has been made for registration of a chemical insecticide that has shown good efficacy for urban trees (International Society of Arborists newsletter, 2010).

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Enhancing Diversity in the Woodlot

Ash occurs as a minor species in most hardwood stands throughout its range.   However, ash can form a substantial component of many woodlots and forested areas in southern Ontario.  The EAB could have a devastating impact on these stands.  Poor to imperfectly drained clay and clay-loam soils that were previously farmed are typical of stands that now have a high ash component.  These early successional forests are primarily composed of green ash, soft maple, elm, poplar and/or cedar but may contain a minor component of many other tree species.  Well stocked stands of this forest type have basal areas of 35 to 40 m²/ha.  A harvest cut can reduce the overall percentage of ash in the overstory while creating conditions for regeneration of other tree species.  Increasing species diversity can help to mitigate the impact of the EAB threat and tree markers can play a significant role in achieving this aim.  

A few basic principles can be incorporated into tree marking prescriptions to diversify a woodlot to better withstand an emerald ash borer outbreak.

1. Thin stands lightly and regularly using a shorter cutting cycle (e.g., 15 years), particularly if ash comprises > 30% of total basal area.  This will favour the regeneration and development of other mid-tolerant tree species.  In ash-dominated stands over-harvest may lead to:
   
   a. a proliferation of ash regeneration,
   b. an increase in undesirable or exotic species,
   c. a conversion to non-forest cover and/or,
   d. elevated water tables with increased risk of windthrow.
   
   
2. For selection management, stick with the 1/3 basal area removal rule, or use lighter more frequent thinnings if ash content is > 30%, as in point 1) above.
   
   
3. For uniform shelterwood management in even-aged stands, the target canopy closure for the regeneration cut should be 70%.  Marking will focus on thinning from below, although AGS non-ash species which are developing in the understory should be considered for retention as part of the next forest.
   
   
4. Priority tree species to consider for retention as a seed source for regeneration in an ash-dominated stand include red, silver and Freeman maple, bur oak, white pine, shagbark and bitternut hickory, yellow birch, hemlock, and white spruce.  Other less shade tolerant minor species may also occur sporadically as regeneration, including red oak, black cherry, and butternut.
   
   
5. White and red elm are also common associates in younger ash stands.  Although prone to Dutch elm disease and eventual mortality, AGS elm trees are also candidates for retention by tree markers.   They may prove to be resistant and any seed they provide may be resistant as well.
   
   
6. Consistent with the marking target, remove Unacceptable Growing Stock (UGS) ash stems by thinning in all diameter classes. 
   
   
7. When comparing trees of similar quality, favour retention of non-ash species.
   
   
8. 8. Consider the retention of Acceptable Growing Stock (AGS) stems of non-traditional species, including poplar, to maintain the stocking target.

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Here are some management suggestions based on EAB threat levels:

• Keep in mind that much is still unknown about the potential impact of this insect.  Natural balances may still take effect, along with prospective mitigation measures.  A considerable amount of research is being conducted on potential controls. 
  
  
• Where the threat is not imminent, prescriptions that recommend pre-emptive ash salvage are not recommended: i.e., recommending preferential removal of AGS ash where the closest EAB infestation is more than 24 km away is not encouraged. Rather, promote diversity and healthy woodlots, while maintaining a wide range of all species, sizes, and ages. 
  
  
• Salvage is recommended if a woodlot is infested, but retention of potentially resistant ash trees is suggested – EAB resistance will obviously be difficult to detect, so until early indicators of resistance are identified this may mean simply retaining survivors in an already infested area. 
  
  
• If the nearest EAB infestation is less than 24 km away, then pre-salvage of some ash trees may be a consideration.  Regenerating non-ash species (i.e., through single-tree selection or uniform shelterwood) is encouraged, but avoid opening the stand too much.  This could encourage more ash regeneration, and potentially an increase in undesirable or exotic species.  Local expert advice is strongly recommended before a pre-salvage operation is undertaken. 
  
  
• Check CFIA news for restrictions / quarantines <http://www.inspection.gc.ca/english/plaveg/pestrava/agrpla/regrestrice.shtml> and <http://www.inspection.gc.ca/english/plaveg/pestrava/agrpla/regmate.shtl>. 
  
  
• In all cases, keep an eye out for signs of decline. If you think you have found the pest in Canada you are asked to call 1-866-463-6017.
  

An international Canada/US website with the latest information on the EAB is at <http://emeraldashborer.info/index.cfm>.

This is a dynamic situation and directions outlined above should be considered preliminary.  Be aware that recommendations may change as we learn more about the spread and impact of the Emerald Ash Borer.  It is up to all of us to keep informed and up-to-date on this potentially devastating infestation.  It is always advisable to consult a professional before taking any action.

Additional reading

Additional information can be found online.  The MNR website has photos and text to help ID the EAB in all its stages, information its lifecycle, and what its damage looks like. 

Check out the MNR’s Forest Health Alert webpage at <http://www.mnr.gov.on.ca/en/Business/Forests/2ColumnSubPage/STEL02_166994.html> for excellent information on and photos of emerald ash borer.  It also tells you what to do if you suspect you have found an infestation. 

The Canadian Food Inspection Agency has a website with links to news releases of the latest outbreaks of the EAB.  You can find it at <http://www.inspection.gc.ca/english/plaveg/pestrava/agrpla/agrplae.shtml> there are more good photos there too.

Also, the Regional Forest Health Network at <http://www.foca.on.ca/xinha/plugins/ExtendedFileManager/demo_images/Forest_Health_Update_June_2010.pdf> has information, starting on page 5, on special surveys being conducting in Ontario to locate the EAB.

There’s an excellent article on research studies being conducted to control the EAB in the Ontario Chapter of The International Society of Arboriculture newsletter.  Find it here
http://www.isaontario.com/pages/Resources/spec_focus/2010Nov_EAB3.php>.

The Wisconsin Department of Natural Resources has a website with information all many aspect of the EAB including symptoms and signs of the EAB and how to identify pests to ash trees other than the EAB. <http://dnr.wi.gov/forestry/fh/ash/>.

References cited

Burns, Russell M., and Barbara H. Honkala, tech. coords.  1990.  Silvics of North America: 2. Hardwoods. Agriculture Handbook 654.  U.S. Department of Agriculture, Forest Service, Washington, DC. vol.2, 877 p.

Farrar, J.L.  1995.  Trees in Canada.  Fitzhenry and Whiteside Ltd. and the Canadian Forest Service.  502pp.

Streit,Martin. 2011. Stewardship Coordinator, Leeds-Grenville Stewardship Council, Brockville, Ontario.  Emerald Ash Borer: Planning Ahead, a power point presentation.

Peattie, Donald Culross, 1991.  A Natural History of Trees of Eastern and Central North America.  Houghton Mifflin Co., Boston, MA.  606pp.

Perkey,Arlyn W. and Brenda L. Wilkins, 2001.  Crop Tree Field Guide.  U.S. Department of Agriculture, Forest Service, Washington, DC.   97pp.

Waldron, Gerry E.  1997.  The Tree Book, Tree Species and Restoration Guide for the Windsor-Essex Region.  Project Green Incorporated. Windsor, ON.  219pp.

Acknowledgement – this article is re-printed with permission from The Ontario Tree Marker (Spring 2011 edition) newsletter.  Information about the Ontario Tree Marking Program is available on the web site <http://www.ontariotreemarkers.ca>.}

This article was featured in a past edition of the S&W Report, the newsletter of the Ontario Woodlot Association. 

© Ontario Woodlot Association, 2011

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