USDA Northeastern AreaForest Service State and Private Forestry

NA-TP-02-01

Patterns of Storm Injuryand Tree Response

by Kevin T. Smith, Walter C. Shortle and Kenneth R. Dudzik

USDA Forest ServiceNortheastern Research Station

www.fs.fed.us/ne www.na.fs.fed.us

This publication is based on research conducted by the Northeastern Research Station and funded by theNortheastern Area, State and Private Forestry. We also thank the White Mountain National Forest, the Stateof Vermont, the Mead Paper Company, and the Cooperative Forestry Research Unit at theUniversity of Maine for providing research locations. We thank Helen Thompson and Debbie Muccio(Northeastern Area, State and Private Forestry) for their help.

Red maple

White ash American

Paper birch

YellowYellow birchAmerican beech

Edge trees two years after storm injury

The ice storm of January 1998 in thenortheastern US and adjacent Canada was anextreme example of severe weather that injurestrees every year. Broken branches, split branchforks, and snapped stems are all examples ofstorm injury.

Immediately following the storm, broken stemsand hanging branches presented a safetyhazard. In addition to safety, landowners andforesters were concerned about the amount ofdamage—defined as the loss of economic valueof wood products—that would result fromstorm injury. In response to this concern abouthardwood quality, we began a five-yearresearch program to identify patterns of storminjury and tree response to wounding.

During the first two years of research, wemethodically dissected forty hardwood treesthat had been injured in the 1998 and earlierstorms. Particular attention was given to wooddiscoloration and decay that would reduce thevalue of wood products. Because future stormsare sure to occur, we hope these observations ofinjury and damage can help predict the effect offuture storms on trees and wood quality.

Patterns of tree shape and position

In northeastern forests, the spreading branchesof hardwood trees like maple, birch, and ashmake them much more vulnerable to injurythan softwoods such as spruce, fir, andhemlock. Tree crowns at the edge of openings,in recently thinned stands, or those that areexposed above the adjacent forest canopy arehit especially hard.

Patterns of injury and damage

Wood discoloration and decay is the largestsource of lost economic value of hardwood.Discoloration and decay are processes initiatedby wounding and involve the injured tree,microorganisms, and the environment.

Any wound or break that exposes wood causesa defensive reaction in the tree and provides anopportunity for infection by microorganisms.Trees resist the spread of injury and infectionthrough the process of compartmentalization.The details of compartmentalization varyamong tree species. In all wounded trees,effective compartmentalization leads torelatively little loss of function and smallamounts of discolored and decaying wood.

Broken branches are the most common form ofstorm-related injury. Branches that are brokenhigh in the tree crown are not likely to initiatediscoloration and decay in the main stem.

Injured ash

Healthy spruce

3

Discoloration that does spread into the bolefrom broken branches will tend to be in thecentral core of the tree, the least valuableportion for products. Extensive branchbreakage in the outer crown can result in thesignificant loss of foliage and reduced growth.

Split forks occur whenone member of a twinor multiple stem ispulled and broken awayfrom the remainingstem. Split forks canresult in large woundsand extensive loss offoliage. Discolored anddecayed woodassociated with splitforks is usuallysuperficial, extendingbeyond the edge of thewound up to an inch ortwo along the length ofthe stem after twoyears.

Stem snaps occur when the entire trunk breaksin two. Stem snaps can cause a large wound tothe remaining stem, often with extensive areasof torn bark and exposed wood.

After two years, discolored and decayed woodin sugar and red maple, white ash, andAmerican beech extend from a few inches toless than a foot along the main stem, beyondthe base of the wound. Stem snaps in yellowand paper birch produce columns ofdiscoloration and decay that extend several feetdown the stem. These columns frequently joincolumns of discoloration initiated fromprevious injuries.

Indicators of damage severity

Similar wounds on different trees of a givenspecies can produce widely different amountsof damage, estimated as loss of value of woodproducts.

Stem snap on paper birch

Split fork on sugar maple

Logging wound on yellow birch

Small broken branches, limited defect

4

New sprouts in ash

Armillaria root disease on yellow birch

After the ice storm, the most severe damagewas to trees with previous injuries to the lowertrunk. Such injuries frequently result fromlogging or roadbuilding. Similarly, trees withprevious root and butt infections such asArmillaria root disease were severely damaged.

Changes in tree form

New sprouts may formnear branch and stembreaks, producing a tuftedappearance that frequentlyconceals wounds. Newsprouts may also growalong the tree stem. Overseveral years, the potentialadded value from furthergrowth may be reduced bychanges in wood grainpatterns caused by theseepicormic branches.

Variation in tree injury and response

In surviving trees, all broken branches andstems are compartmentalized with varyingdegrees of effectiveness. The least effectivecompartmentalization and the greatest amountof wood discoloration are in paper and yellowbirch, with intermediate amounts found in redmaple, and the least amounts of wooddiscoloration in sugar maple and white ash.

The greatest damage is in trees with previousinjuries such as those caused by logging.

Compartmentalization is most effective forwounds located adjacent to a vigorous, healthybranch. Healthy branches supply energy toresist the spread of discoloration and infection.

In most cases, the progress of wooddiscoloration and decay in surviving trees is aslow process.

Damage (reduced product value of wood)depends on forest stand characteristics (species,tree density) and prior disturbance history (treeinjury from machinery, root and butt disease,recent defoliation) as well as storm severity.Assessments of injury and predictions ofdamage require examining the whole tree, theremaining crown, and previous stem injuriesand infections.

In conclusion, storm injury is a recurringfeature in northeastern forests. Survivalstrategies of injured trees include sprouting toreplace foliage and compartmentalization toresist the spread of infection. In surviving trees,reductions in wood quality and value frequentlytakes years to develop. Trees at greatest risk forreduced value are those that have beenpreviously injured, especially by wounding ofthe lower trunk.

This electronic version was prepared January 9, 2006.

Recovery of injured trees