tca reference manual: bad tree practices

Minnesota Tree Care Advisors

http://www.mntca.org/resources/reference/reso_ref_03_bad01.html[11/30/2010 7:31:50 AM]

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PHOTOS COURTESYGARY JOHNSON

Stress on the Streets(Trees Suffer from Road Rage, Too.)

Reprinted from the Minnesota Shade Tree Advocate VOL. 2, NO. 3Summer 1999

“Hey, we didn’t hit the tree.” Street trees arefrequently put at risk, though the results may notbecome evident for some time.

Minnesota, like the rest of the United States, is becoming moreurbanized. More than 75% of us live in urban areas. The threat torural forests that are being developed in third-, fourth- and fifth-ringsubdivisions (peri-urban forests) is real and of concern. But thedanger to these areas is geographically and resource limited. Thereare only so many forests and when those areas are developed, they’regone.

A growing concern that has no limits involves construction damage topublicly-owned, urban trees—those trees that were either survivors orwere planted after development. These trees now line our streets,parking lots, schools, businesses and parks. In some communities,they may be 50 to 70 years old or more. And even though thedevelopment and construction of our communities may have takenplace decades or a century ago, construction damage continues on aregular basis and with alarming frequency.

Construction crews may not realizethe effects of compaction, soilchanges and root damage.

This tree suffered root damage onthree sides . . . including topsoilscraping. The outlook is grim.

Street trees (boulevard trees, parkway trees, tree lawn trees) aremost at risk. Streets and curbs don’t last forever. They requireperiodic resurfacing, re-grading and re-engineering of curb shapes andheights. Sidewalks crack, heave and become dangerous forpedestrians. Many streets were designed and installed decades ago,long before they became popular as arterial streets. They havebecome too narrow for modern public safety vehicles or streetmaintenance trucks, or are designated for parking on both sides.

Utilities fail or become outdated and must be replaced. New utilities orservices are developed and installed below ground—fiber opticssystems, landscape irrigation systems and invisible fences. In mostboulevards, the top eight feet of soil is laced with an incrediblenetwork of buried utilities.

When streets, curbs, sidewalks, driveways and utilities are installed,improved or expanded, trees suffer construction damage. Most peopledon’t recognize it, however, because the damage is usuallyunderground. And most people don’t realize how vulnerable streettrees are to the stresses imposed on them from root loss or soilchanges. Rarely are street trees badly wounded or scarred aboveground during these activities, and rarely are street treesexceptionally healthy before the damage.



Boulevards were originally designed as tree lawns—literally, lawns forpublic trees to grow in. Except for water and sewer lines, drivewaysand sidewalks, there were no conflicts of use.

Stressed to begin withBoulevards are far from ideal growing sites for trees. Soils range fromrocky and sandy to hard-as-concrete clay, bone-dry to bog-soggy.Occasionally you may find beautiful sandy loam soil in a boulevard,especially in some of the older neighborhoods and towns.(Occasionally you may find a $20 bill lying on the ground, too!) SoilpH is variable. In some of our boulevard research areas, the soil isclose to the native soil pH range, 5.5-6.5. A few blocks away, it mayreach 8.5 or higher! Unfortunately, the majority of trees planted inboulevards perform best in soils that are well drained, organic andwith a pH range of 6.0-7.0.

Under normal circumstances, tree roots spread in an area two to fourtimes their height. However, if a curb is three feet away from a treetrunk, that is effectively the spread of the roots on that side. Majorroots have a tendency to grow to the curb, turn and then run linearwith it. Some roots grow under curbs, streets, sidewalks anddriveways, but it’s unpredictable. The windthrows from the storms of1997-98 illustrated this perfectly and made us wonder how some ofthose towering trees stayed vertical for as long as they did.

Street tree roots don’t penetrate very deeply, rarely more than threefeet. In some areas with compacted clay, the majority of the roots arein the top 18 inches of the soil profile. Now, add deicing salts, turfChapter 3 Page 63 competition, pesticides and animal waste to the soilmatrix, acts of unintentional “vandalism” to the trees (stapling trunks,breaking branches, lawn mower wounds and tree topping), and you’lldevelop a renewed respect for any tree that even survives theseconditions, much less thrives in them.

What they can tolerate, what they can’tAlthough “construction damage” is an ambiguous term, most of thedamage to boulevard trees involves root loss. Trenching, excavatingand re-grading the surfaces of the tree lawns removes tremendouslyhigh percentages of supportive branch roots and conductive (waterand nutrients) finer roots. A relatively healthy boulevard tree canusually tolerate one-sided root loss from trenching or excavation. Itwill definitely be less stable and more vulnerable to drought, insectand disease stresses for a few years, but it can recover if givenadequate care.

Trees that suffer two-sided root loss are unstable and less likely torecover. Unhealthy Letters to the Advocate trees are more likely to diefrom two-sided root loss. Even healthy trees are likely to suffer somebranch death and require deadwood removal pruning two to fouryears after construction. Depending on the tree species, age andrelative health, however, many of these trees can recover if theyreceive immediate and proper care after the construction.

Trees that suffer three-, four- and five-sided root loss (five-sided rootloss includes four sides cut vertically and the top re-graded) makegood firewood or woodchips, depending on the age of the tree. It’sprobably not wise to save these trees if the root loss is unavoidable.Remove them, and replace them after the construction project iscompleted.



Other variablesThe width of the boulevard plays an important role in the survival andhealth of the trees after construction, provided that the trees arecentered between the curb and sidewalk. Trees growing in boulevards10 feet or wider have a much better chance of tolerating the rootlosses compared to trees growing in three- to five- foot wide lawns.There’s simply more room for a higher percentage of the trees’ rootsystems to grow in and avoid damage.

Age or size of the tree. Younger or smaller trees recover faster fromroot loss than older and bigger trees. There are less wood and leafChapter 3 Page 64 surface areas for their roots to supply water andnutrients to, and there are more actively growing tissues in a youngertree.

Relatively healthy trees survive root loss better than highly stressedtrees. Severely stressed trees are living on the edge, so to speak. Theadded stress of root loss, soil compaction or pH changes caneffectively push them over the edge.

Tree species vary in their tolerance to root and soil changes. Somespecies—silver maple, hackberry, green ash and bur oak—are moretolerant of root loss and soil changes. Other more sensitive species—ironwood, white oak, black walnut and blue beech—quake and shakeat the sight of a bulldozer.

Most of the damage to boulevard treesinvolves root loss.

Some logical steps to reduce the damage and loss

1. Seek variances. Not all streets need to be widened. If yourcommunity values the boulevard trees more than acres ofconcrete, let your city know. You pay the bills and they workfor you. Create reasonable compromises that protect the besttrees by avoiding root loss. Keep streets the same width. Allowcurves in the street to avoid damaging trees. Compromise byrestricting parking to one side or no sides of the street ratherthan both sides. This will negate the necessity for landing-stripstreet widths.

2. Combine utility trenches whenever possible. Not every utilityneeds its own separate trench. Simply combining just twoutilities to a common trench eliminates one trench, and mayreduce the damage from two-sided to one-sided.

3. Save the best; chip the rest. Don’t save trees that areunhealthy, too tall for the root space they’ll be confined to,hazardous or of a very sensitive species – if the damage isunavoidable.

4. Insist that foresters and arborists make the evaluations anddecisions regarding trees. These significant investmentsdeserve the attention of knowledgeable professionals.

5. Do not allow construction activities on boulevards that compactor pollute the soil. Allow no parking of vehicles or equipment,no storage of construction materials or excess soil, no cleaningof concrete truck chutes or equipment.



Keeping trees wellwatered at all times isthe single most effectivetreatment for helpingthem recover fromdamage.

6. Whenever possible, insist that tunnels be drilled under theroots for utilities near trees rather than trenches being dugthrough the root systems.

7. If new curbs will replace old ones, hand-form the curbs nearthe roots, using forms that “slip” in between the existing curband roots. Avoid curb excavation that cuts roots.

8. Assume some ownership and responsibility for the health of thetrees. Don’t let them become stressed before, during and afterthe construction process. Keeping the trees well watered at alltimes before, during and after construction is the single mosteffective treatment you can do to help them recover fromdamage.

9. Nurture the trees’ remaining roots forever. Think beyond thebox! Boulevards don’t absolutely need to be covered withmown turf. Mulch the root systems with wood chips.

10. Plant a “blooming boulevard” in the mulched area withperennials, shrubs and/or ornamental grasses, but not—formaintenance efficiency— annual flowers like petunias.

11. Replant with logic. If the remaining boulevard is only three feetwide, don’t replant with a tree, especially a big tree. Considercreating “green easements” within your community - replantingthe trees on the property owner’s side of the sidewalk. Selecttrees that are adapted to the unique soil and spacecharacteristics of your boulevard. For information on treesadapted to specific sites, refer to these publications: “The RightTree” brochure, available from Minnesota Power Association at1-800-228-4966 or the University of Minnesota ExtensionService Distribution Center at 612/625- 8173.

Soil compaction from trucks andother vehicles is often worse thanbulldozer compaction, especiallywhen the soil is a wet clay.

Depending on the tree species, ageand relative health, many trees canrecover if they receive immediateand proper care after theconstruction.

Root damage and soil pollution —adeadly prescription if not remedied.

That’s not black dirt - waste asphaltat the base of a tree...



Also available from the Distribution Center are these University ofMinnesota Extension Service Publications:

Recommended Trees for Southeastern Minnesota

Recommended Trees for Southwestern Minnesota

Recommended Trees for Tallgrass Prairie

Recommended Trees for North Central Minnesota

These steps will initially cost the residents of a community more thancarte blanche removal of trees and roots, and uninterrupted trenching.But long-term costs will be reduced through fewer tree replacements,increased property values and less damage to the gray infrastructure(sidewalks, curbs, streets). It’s worth the investment.



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Accepting 30- 50%forest loss duringdevelopment ignores thebiological principle thatthe system has beendisrupted and will falter.

The character ofMinnesota is changing,courtesy of urbanization,development and

It’s More Than Wrapping SnowFence Around Tree TrunksReprinted from the Minnesota Shade Tree Advocate VOL. 2, NO. 3Summer 1999

Trees and forests are biological systems—systems that operatebeautifully and for a long time when all their parts are present andworking. Take away one part and the system skips a beat, maybefaltering just slightly. Remove another part or two and the systemfalters more noticeably.

With continued faltering, remaining parts begin to suffer as theburden of the whole weighs heavier on them. In time this once-healthy system becomes vulnerable. What may once have beenrelatively tolerable stresses might now mean a forest at risk. Onesummer of drought, one defoliation by insects or diseases or oneunusually generous winter serving of deicing salt can mean disaster.

Some parts of a forest’s system are obvious— vegetation that includestrees, shrubs and groundcovers. Just as important are the lessobvious parts—soil, water, soil microorganisms, ambient temperaturesand humidity. Success or failure of the system depends on the healthof the sum of all the parts.

Individual trees are systems, too. The major parts – canopies, stemsand roots – are in turn linked to soil, water, air and soilmicroorganism quality. Damage to one part of a tree’s system affectseverything else. If a significant amount of the root system is lost ordamaged during construction, the whole system is affected andsometimes fails.

As root systems decline, photosynthesis is reduced as well as waterand nutrient transport to the stem, branches and leaves. Branches“shut down” and fail (die). Energy reserves that contain(compartmentalize) the decaying, dead branches are not as plentifuland the containment weakens as decay becomes more aggressive.

A summer-long drought comes along. The tree becomes morestressed; opportunistic insects like borers move in and finish it off.And it probably all started with someone thinking, “What’s the worstthat could happen if I cut off these roots?”

Construction damage at the landscape level is insidious, and the causeand effect relationship often escapes even the trained eye. Relativelysmall pockets cut into a forest for a home-site seem almostinconsequential. But then roads and driveways are cut for access tothe site, and utilities are trenched in for 20th Century conveniences.It’s likely that more than one building pad will be cut in so severalsites can be served by the roads and utility trenches.

Wherever two or more people settle, it seems a convenience storesoon follows. Gas pumps, liquor stores and pizza parlors spring up. As



construction damage toforest and tree systems.

the area develops, it attracts more commuters seeking the solitudeand freedom of living in the country. Roads are expanded andimproved to accommodate the increased traffic, and voila!—urbansprawl inches forward once more.

What’s happening to the forest system? The formerly solid, continuousforest is becoming “fragmented,” – cut up into smaller, separate orloosely connected units. Even if individual trees are labeled“significant” and carefully protected, more edges of the forest areexposed to drying sun and wind, more chainsaws collect dead (or live)wood for the fireplace and deicing salts drift off those new andimproved roads.

Forest edges get “tidied up,” ridding the visual park of unsightly leafand branch litter. Lawns are established, and petrochemical products(pesticides, fertilizers) are used to support the newly planted and thedeclining remnant forest trees. “New and improved, fast-growing”plants like tallhedge buckthorn, honeysuckle and Amur maple areplanted. The biological character of the original forest slowly changesto the character of the 20th Century residential landscape.

Urbanization is characteristically a slow, deliberate degradation of thenatural system. Soil temperatures and moisture contents fluctuatemore than before. Soil chemistry (usually pH) becomes altered, andnative soil microorganisms shift in character. Individual trees along thenew edges begin failing; other interior trees become the new edgetrees. Natural, forward, forest succession (the natural replacement ofone group of plants by another) often screeches to a halt.

The character of Minnesota is changing, courtesy of urbanization,development and construction damage to forest and tree systems. Inour lifetime, we’ll never see century-old oak savannas, sugar mapleand basswood forests or red oak and hornbeam forests regenerate ifthey are chopped up for subdivisions. And our grandchildren will neversee them either if the forest floor is stripped, compacted, sodded andpaved.

Now is the moment to intervene. Act to protect connected forestsystems from urbanization. Encourage your community and developersto subdivide in open spaces or at the edge of forests, rather thanwithin them. Cluster new homes, rather than spreading them out.Build up rather than out. Reconnect fragmented forests such as theGreening the Great River Project is attempting to do. Contact JeanMoulle at Metro DNR Forestry and get information on the drafted“Conserving Wooded Areas in Developing Communities: BestManagement Practices in Minnesota.” (Web reference)

Protecting individual trees during construction is good. But accepting30- 50% forest loss during development ignores the biologicalprinciple that the system has been disrupted and will falter. Believingthat protecting half of the forest system will ensure a healthy remnantforest is about as (bio) logical as believing that wrapping snow fencearound a tree trunk will protect it from construction damage.



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Tree Preservation DuringConstruction: A Guide toEstimating Costsby Gary R. Johnson

Contractors took some fairly simple measures to protect this 165-year-old bur oak during construction of a large concrete sculpture andseating area. The original plan to cut and fill the grade within the rootzone was altered to preserve the tree roots, and 11 concrete pierswere sunk into the ground to eliminate the need for grade changes.The build-able area was fenced off to allow only foot traffic.Mechanized equipment was restricted from the critical root zone;concrete was pumped in from a truck parked a safe distance away. Astrategically placed sign explained the tree preservation effort.

Hoffman Homes, Inc., took extraordinary steps to preserve this buroak in an Eagan, Minnesota, development. The original plan for thefoundation was altered to preserve more roots, a retaining wall wasconstructed to avoid filling soil over much of the root system, and thetree was professionally braced, cabled, and pruned. This photo, takenin mid-spring one year after construction, illustrates the importance ofthe tree to the home site.

Introduction Builders and developers are increasingly being called upon byordinance or consumer demand to protect selected trees duringconstruction. This guide helps you estimate the costs of doing so. Treepreservation requirements vary considerably from one community tothe next. So do actual costs, due to regional variations in labor (andto a lesser extent, materials) costs. Therefore, "costs" are listed inthis guide as labor hours, equipment hours, and materials for a rangeof tree preservation activities. You can customize these tables byselecting the activities that apply to your situation and multiplying thefigures given by dollar values appropriate for your area. In mostinstances, hours and supplies are listed as ranges. These allow forvariables such as experience level of labor, weather, and soilconditions. If you have an inexperienced labor force working on asevere slope in the muddy season of the year, it would be logical touse the high-end estimate. As the name implies, this is a guide, notan absolute. You'll find it particularly valuable if you are performingtree preservation tasks for the first time. As you gain experience, itmay simply become a reminder of the steps involved. If you record



your actual labor hours, quantities, and volumes in the 'your notes'columns, you'll have a handy, customized reference for future jobs.

Sample Ordinance Requirements and Language This section reviewsand clarifies common requirements and defines some terms oftenused in tree preservation ordinances.

aeration A process in which holes are drilled into the soil within the critical rootzone to provide relief from compaction. Holes typically are 8 to 10inches deep and 1.5 feet to 4 feet on center (o.c.).

balled-and-burlapped nursery stock Trees that have been either hand-dug or tree-spade-dug with a soilball enclosing the roots. The soil ball is wrapped in burlap and may ormay not be enclosed in a wire basket.

bare-root nursery stock Trees that are dug and shipped during dormant (leafless) seasons andhave no soil harvested with the roots.

caliper inch (stem caliper) The diameter of a tree trunk measured 6 inches above the ground fortrees less than or equal to 4 inches and at 12 inches for stems greaterthan 4 inches. This measure is used for nursery stock.

certified nursery stock Nursery-grown trees that have been inspected by a state'sdepartment of agriculture and certified free of pests and diseases.condition The general health and structural integrity of a tree, asevaluated by a qualified professional.

container nursery stockTrees that have been either grown their entire lives in containers orfieldpotted into containers.

critical root zone A way to define the protection zone for an individual tree. It iscommonly calculated as the roots and soil within 1) the dripline, or 2)an area defined by a circle with a diameter 24 to 36 times the d.b.h.of the tree (1 to 1.5 feet of radius for each inch of d.b.h.).

crown The section of a tree containing most of the branches and leaves.

d.b.h. Literally, diameter at breast height. The d.b.h. is measured 4.5 feetfrom the ground on the uphill side of a tree.

deadwood pruning The removal of only deadwood from a tree's crown by a tree careprofessional.

deciduous tree A tree that normally drops its leaves in winter.

dripline The land area within a circle defined by the extent of the farthestgrowing branches of a tree.

evergreen tree



A tree that normally has green foliage during all seasons.

forest restoration plan (reforestation plan, landscape plan) A plan prepared by a qualified professional for the ordinance authoritythat specifies replacement tree locations and restoration of othervegetation and disturbed land.

inventory At minimum, a list of all significant trees and their d.b.h. sizes. Someordinances also require that inventories indicate tree condition.Inventory requirements usually can be satisfied by locating significanttrees on a site map and coding them with a number or acronym thatcorresponds to the map legend. Many ordinances require thatsignificant trees be marked with a metal or plastic tag with thecorresponding legend code until construction and inspection arecompleted. Most ordinances require that the inventory be prepared bya qualified professional.

land disturbance permit A permit granted by the ordinance authority for removal/loss ofsignificant vegetation and/or changes in site grade and soil.

protection zone (preservation area) The part of a parcel outside the build-able area.

qualified professional A tree specialist qualified to prepare inventories, tree removal plans,tree protection plans, and reforestation/ landscape plans. Qualifiedprofessionals include (but are not necessarily limited to): certifiedregistered land surveyors, landscape architects, foresters, arborists(tree care professionals), nursery and landscape professionals, andInternational Society of Arboriculture certified arborists.

radial trenching The process of improving tree condition by digging trenches in a radialfashion, starting approximately 3 feet from a tree's trunk andextending to the perimeter of the critical root zone, then backfillingwith amended soil, organic matter, and/or fertilizer. There are nostandards for depth and width, but trenches normally areapproximately 12 inches wide and 12 inches deep. There are nostandards for number of trenches per tree since they may only beplaced where the trenching operation will not damage primary treeroots.

removal/loss Definition varies substantially among ordinances. For individual trees,removal/ loss may include soil changes within the critical root zone,root loss from trenching within the critical root area, and mechanicalwounds on tree trunks. For wooded land parcels, it may includeexcavating, grading, filling, or other earth exchanges, as well asactual clearing. Limits may be defined by volume (soil), land area(grade changes), or percentages of total vegetation cover(tree/vegetation loss).

removal plan A site plan with proposed build-able areas and significant trees to beremoved that is submitted to the ordinance authority.

replacement trees Trees planted as compensation for significant trees lost or removed



during construction. Many ordinances specify species, minimum andmaximum sizes, and type of nursery stock (e.g., bare-root, containerstock, or balledand- burlapped). Some ordinances allow thebuilder/developer to plant replacement trees on other sites within thesame development (e.g., boulevards).

root collar The point of attachment of major woody roots to the tree trunk,usually at or near the ground and associated with a marked swelling ofthe tree trunk.

significant trees The units the builder or developer is charged with protecting and/orreplacing. Significant trees are the focus of most tree preservationordinances. Not all trees are significant and the definition of asignificant tree varies among ordinances, so examine the languagecarefully.

tree Any self-supporting woody plant, usually having a single, woody trunkand a potential d.b.h. of at least 2 inches. Trees may be deciduous orevergreen.

tree density The total d.b.h. of significant trees per specified land area. Ordinancesoften will simply distinguish between high and low density.

tree preservation plan An outline prepared by a qualified professional and submitted to theordinance authority that describes proposed preservation areas,buildable areas, and preservation tactics. tree replacement table Atable that specifies the number of caliper inches of replacement treesneeded to replace the lost or removed trees. The table considers 1)percent of significant tree d.b.h. inches removed, 2) tree density, and3) size of approved replacement trees. For example, an ordinance mayrequire 0.5 caliper inch in-replacement trees for each d.b.h. inch lostfrom a low treedensity land parcel where 20 to 29.9 percent of thesignificant tree d.b.h. is removed, and may require that replacementtrees have caliper measurements of 2 inches. In this case, if 100d.b.h. inches were lost, 50 caliper inches would need to be replaced,which means 25 trees would need to be planted.

trunk The part of a tree between the root collar and the first branch of thecrown.

trunk cambium The layer of trunk tissue that gives rise to the water, nutrient, andchemical energy-conducting tissues. This layer is usually founddirectly under the outer bark.

vertical mulching The addition of organic matter and/or fertilizer into holes drilled withinthe critical root zone to improve tree condition.

vibratory plowing A process that severs roots to a depth of up to 5 feet. It is sometimesrequired in areas where diseases may be transmitted through rootgrafts.

wildings



Trees that have been transplanted from natural forest habitat andhave been deemed suitable for replacement trees by the ordinanceauthority. Normally, wilding trees must have a dug root systemapproximately 30 percent larger than a similar nursery-grown tree.

Estimation TablesThe following tables will help you estimate the costs of various treeprotection measures. Figures given are common ranges for time andmaterials. Where equipment is used, estimates are for both labor andequipment hours. Notes specifying the conditions on which ranges arebased and a list of variables that affect where in the range you will fallare given after each table. You are encouraged to keep track of yourcost data for future reference by filling in the "your notes" row in eachtable.

Obtain Permit(s) (per site)

inventory parcel 2.0-6.0 hours

(your notes)

create preservationand restoration plan

1.5-4.0 hours

(your notes)

apply for permit(s) 2.0-8.0 hours

(your notes)

Comments: ranges are for a wooded, 0.2- to 0.5-acre parcel

Variables: tree density, lot size, number and types of permitsrequired, ordinance authority review process, revision of plans andapplications (can skew hours completely out of ranges)

Fell, Buck, Load Trees (per tree)

Tree Size (d.b.h.)

6" 12" 18" 24" 30"

fell/buck0.2-0.5hours

0.4-1.2hours

0.75-1.75hours

1.0-2.25hours

1.25-2.75hours

(your notes)



load0.3-0.5hours

0.5-0.75hours

0.5-0.75hours

0.75-1.2hours

1.0-1.75hours

(your notes)

Comments: includes dropping the tree, cutting it to length, andloading it into a trailer; 18-inch d.b.h. uses front-end loader; 24- and30-inch d.b.h. use boom

Variables: species, tree density, access, topography, tree size

Remove Stumps (per tree)

Tree Size (d.b.h.)

6" 12" 18" 24" 30"

remove withstump grinder

0.15-0.2hours

0.2-0.25hours

0.25-0.3hours

0.3-0.33hours

0.3-0.4hours

(your notes)

remove withbackhoe

0.1-0.2hours

0.3-0.45hours

0.5-0.7hours

0.5-1.0hours

0.75-1.5hours

(your notes)

Variables: vegetation density, access, topography, stump size

Mulch (per 1,000 square feet)

already placed including hauling

mulch 12.5 cubic yards 12.5 cubic yards

(your notes)

spread mulch by hand 2.0-3.5 hours 4.0-6.25 hours



(your notes)

spread mulch bytractor

1.75-2.5 hours not applicable

(your notes)

Comments: includes coarse wood ships spread 4 inches thick; tractorhas one-cubic-yard bucket; "already placed" indicates mulch has beendistributed in piles in strategic locations

Variables: topography, vegetation, density, access



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Buried Root Systems and TreeHealthby Gary R. Johnson

Reprinted from the Minnesota Shade Tree Advocate, Volume 3 Number4

Stem girdling roots (SGRS) are those roots that grow either partiallyor completely against and compress (girdle) stem tissues of trees.Xylem and phloem (conducting) tissues in the stems become muchsmaller in diameter at the point/s of compression, compromising thetransport of water, nutrients and photosynthates ("food"). Treesbecome stressed and more vulnerable to secondary problems(drought, insect attacks). Often, the compressed areas of the stemsare weak points and far too often are the points of failure duringwindstorms. For instance, in the catastrophic windstorms of 1998 inMinnesota, 73.3%* of the lindens that were lost actually broke atcompression points from SGRS, and most broke below ground.

Tree snapped at SGR compressionpoint below ground.

Above-ground stem girdling roots

Dysfunctional root system - Appletree failed in a wind storm

Poor stem condition related to stemgirdling roots and excess soil overroot system.

SGRs can and do form above ground, especially with maples andpoplars. However, they can develop on most species below groundand out of sight. How can this happen? If a tree's root system hasbeen buried too deep, the stem is subsequently buried. When rootsystems are buried too deep - with some trees, that's one inch of soilover the first, main order (first branch) roots - secondary woody rootsgrow upward, closer to the soil surface. Often, some of these rootsend up growing against the stem tissues, either partially or completelyencircling the stems.

Since 1997, the University of Minnesota Forest Resources Department



Early fall color is a sign of potentialroot problems

has randomly sampled 303 trees (ash, maple, linden). Depths of soilover the first roots ranged from 0 to 13 inches. Analysis of the datalater revealed a statistically significant relationship between depth ofsoil over the roots, condition of the trees and the frequency of stemgirdling roots. As more soil was added over the root systems of thosetrees - for whatever reason - stem conditions declined and thefrequency of stem girdling roots increased. So, deeper (planting) isnot better. In the long run, it's worse for the long-term health andstability of the trees.

*Based on the storm damage research conducted by the Department ForestResources, University of Minnesota, 1995-present.



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Rooting Around: Tree RootsBy Dave Hanson

Take a good hard look at your favorite tree. What do you see? Niceform, leaves, branches, bark, but, how many would respond – “Ohbaby! There must be some fine roots holding up this tree.”

Unfortunately for trees, not too many people respond in this fashion,the world underground does remain a mystery. What is happeningdown there? What are tree roots and for that matter where are theroots? Why and how do roots get into sewers, cause foundations tocrack and sidewalks to lift? The reason that these mysteries remain:we cannot easily see and touch tree roots, we cannot readily accessthem and typically we do not encounter them without getting out ashovel. This brief article will skim the surface, so to speak, andattempt to provide some insight and answers to these questions.

Bur oak - Support roots

So, let’s start at the beginning and address two basic questions.Question number one, what are tree roots? There are three basictypes of tree roots: Structural support, Fluid transport, and nutrient /moisture absorbers. Structural support comes in the form of larger-diameter perennial woody roots that anchor the tree to earth. Nearthe base of the tree are found the sinker or striker roots that helpstabilize the tree and help it exploit deeper soils, but they seldomextend below 1 meter deep (Harris et al.). A second group ofperennial support roots grow horizontally radiating away from the treeand also provide transport of nutrients, water and oxygen to thecanopy. In return, the canopy delivers energy back to the roots fortheir use and for storage. The last of the basic root structures todiscuss here are referred to as absorbing roots (fine root hairs andthe root tips roughly 1/16th inch diameter) that provide nutrient andmoisture absorption for the tree.

With that basic understanding, let’s move on to question number two.Where are the roots of a maturing or mature tree? Many consider thedrip-line of the tree to be the limit of the root spread; therefore, theassumption is made that this is the area to fertilize and water for the



benefit of the tree. A better mental picture to form is a wine glasspositioned on a dinner plate. In support of this mental picture sixspecies, including green ash, maple, and oak, were studied by Dr.Edward Gilman of the University of Florida. Dr. Gilman and associatesperformed root growth trials in Florida and New Jersey. The findingsclearly debunked the “drip-line” notion of tree roots. On average theyfound that tree roots extended 3 times the spread of the branchesand that more than 50% of the absorbing roots were beyond the drip-line.

Several numbers can be found in the literature concerning where thebulk of fine, absorbing roots are found in the soil profile. The stateddepths range from the top 24 inches to the top 18 inches with 50% ofthe fine roots being in the top 6 inches of the soil profile. Dr. Gilman’sresearch tightens these numbers up considerably. From the same rootgrowth trials in Florida and New Jersey Gilman states: “fine roots areconcentrated in the top 12 inches of soil with many in the top 2inches.”

Okay, so some trees have roots near the soil surface to collectnutrients and moisture. “But, I’ve never watered my tree because itstaproot gets all the water it needs from the Saint Peter sandstoneaquifer.” There are species that as seedlings produce and rely on taproots, but quite honestly, as “taprooted” species mature, tap rootsbecome insignificant in the overall root structure. The bulk of nutrientand moisture uptake is taken over by the absorbing roots near thesurface.

Tap roots and other “sinker” roots can penetrate into the soil layers,but research indicates that depth of rooting is dependant on soil-oxygen. Dr. Kim Coder from the University of Georgia states thatgood root growth requires a soil atmosphere of 15 percent oxygen. Hecontinues by saying that below 5 percent soil-oxygen, root growth willstop and below 2% roots begin to decline and die. Dr. Coderdescribes the advancing root tips existence as quite precarious andmore of a “good news / bad news” scenario. If the root progresses toodeeply, oxygen deprivation will be an issue and on the other extremeif a root progresses too shallowly, a dry spell will likely cause itsdemise. As a matter of fact, this precarious situation translates into ashort life span for an absorbing root with the root tip being replacedmany times per growing season.

The bottom line, unlike horses, roots do not smell water. Along thesame line, roots do not seek water. Instead, roots tend to grow wherethe growing is good and the growing tends to be good in the top 12inches of soil where temperature, moisture, nutrients and moreimportantly soil-oxygen are usually adequate. To underline the factthat roots are opportunistic “absorbers” – there has been a push latelyto discourage calling fine absorbing roots, “feeder roots” simplybecause the term “feeder” implies an aggressive, hunter-gathererapproach to seeking life’s necessities. Roots simply follow the moisturegradient of the surrounding soil and continue to grow where thegrowing is good. Meaning that roots tend to grow where there is agood supply of moisture, nutrients and of course soil-oxygen.



Excavated Lindens, three years intoa nine year planting depth study.These specimens had been planted10 inches too deep, note the rootsreturning to the surface.Supposition: roots were returning tozones with better soil-oxygenconcentrations.

Now is the time to step back and put this information in perspective.Tree roots require oxygen to remain viable and soil-oxygen decreasesthe deeper in the soil profile that a root penetrates. Add in soilcompaction to your thought process. By compacting a soil the porespace is reduced which in turn reduces the amount of soil-oxygen thatcan be present. Okay, one more thing – re-landscape the lawn with abobcat and add 4 inches of soil to bury the roots a little deeper. Holdon, the lawn typically means turf and that means roots from grass andcompetition for moisture, nutrients, and you guessed it soil-oxygen.The picture should be coming clearer, tree roots, all too oftenoverlooked, spread as far and as wide as they can in compacted soilsand at depths below 12 inches trying to survive. Keep in mind thatthis is biology, and the ultimate root structure depends on manyfactors below ground. Site conditions, compaction, excess fill, floodingand infrastructure have direct and indirect impacts on soil moisture,soil oxygen, soil texture and structure.

Moving on into the second round of questions: It has happened again!Another basement floods because a sewer line has been clogged bytree roots. Maybe this time it is another foundation or sidewalk beingmoved or lifted by tree roots. Are trees “perpetrators” of these acts oris it simply guilt by association. One side of the argument states thatthe tree and its roots are not at fault, but rather there is fault with thedesign or construction of the infrastructure.

Honesty is probably the best policy; trees are not as innocent in theabove scenarios as many of us would like to believe. However, whyhas the tree become the guilty party? Design error is often the onlyanswer to be arrived at whether it is the landscape design or theengineering design. Let’s face it, trees require space for rooting andresource exploitation, if a tree root happens upon a nice moist,



oxygenated resource-rich environment (a sewer line for example)where it can thrive and perform its duties – it will. In commenting ontree roots in sewers Richard Harris et al. states “the conditions ofaeration, moisture, and nutrients are so favorable that it inevitablygrows until it clogs the sewer.” The question in many minds stillremains as to how the root happens upon the sewer line.

Martin Mackenzie of the US Forest Service recently spoke to aconference audience describing the “battering-ram” root that breaksthrough even the toughest sewer lines and concrete blocks. Of coursethis statement was “tongue-in-cheek.” Roots grow quite slowly anddon’t have much chance to hurl forward with any great speed. In thecase of finding a sewer line there is both speculation and researchthat explains the encounter. Speculation from Harris et al. is that insome instances sewer line trenches are compacted to a lesser degreethan the surrounding urban soil. Thus, homeowners may unwittinglytake advantage of this and plant trees in the trench or perhaps thetree roots will encounter this less compacted environment andcontinue to grow into it unimpeded. Dr. Kim Coder researched thethermal gradients that exist between sewer lines and the surroundingsoils which allow two things to happen. One is a moisturecondensation layer on the sewer line itself. Secondly, a moisturecondensation column develops in the soil layers above the sewer line.Once a tree root encounters this moisture condensation column itgrows downward (providing adequate soil-oxygen exists) along theincreasing moisture gradient in the soil toward the sewer line. Uponencountering the sewer line, the root tips continue growing towardsmore favorable conditions, eventually a root tip may find and exploit acrack or fissure in the sewer line. Hence, back to the argumentproclaiming faulty infrastructure – “the root tip exploits a crack orfissure in the sewer line.”

Once the root tip has entered the line, the real damage to the line canbegin. The tree roots tend to form a mass of root tips that slow theflow enough to allow sediments to be trapped, thus clogging the line.Or the root may begin to develop as a woody, perennial root andexert pressures that may crush or burst the sewer line.

Larger, woody, perennial roots exert substantial radial pressure andover time can displace man-made structures. The perennial rootincreases in diameter by adding a growth layer every year.Commonly, sidewalks are lifted by this type of radial growth.Displacement of structures can be caused by horizontal roots growingunder a slab concrete floor or sidewalk or by a vertical “striker orsinker” root growing downward next to a foundation. In any case theroot growth is slow and forces can be substantial enough to displaceor otherwise damage structures.

Another mechanism by which trees cause structural damage involvesthe presence of expansive clays. Expansive clays respond to soilmoisture changes by expanding and contracting. Man-made structuresoften rely on the surrounding soils for additional support. If a tree’sroots encounter this “support soil” of expansive clay the moistureregime can be dramatically altered by the evapo-transpiration functionof the tree. The clay soil type can be dried excessively causing it tocontract, thus shrinking away from the structure it is supporting.

The literature identifies several tree species as “culprits” in the“aggressive” root department. The following species are on a “NotRecommended for Planting” list maintained by the MichiganDepartment of Natural Resources as those having invasive rooting



habits: silver maple (Acer saccharinum), white mulberry (Morus alba),white poplar (Populus alba), Eastern cottonwood (Populus deltoides),weeping willow (Salix alba), black willow (Salix nigra), and Americanelm (Ulmus americana). Is it necessary to “label” these trees asculprits and black list them? A better approach is to pay attention toputting “the right tree in the right place.” More and more attention isbeing paid to tree selection since it is the “key” to a trees long life.Site conditions truly need to be considered prior to starting thespecies selection process. It isn’t always successful to fall in love witha species and then try to fit it in our landscape.

In wrapping all of this together, a number of additional questionscome to mind? For instance:

What does all of this say for our notion of watering and fertilizingwithin the drip-line?

Yes, the water and fertilizer helps, but in light of root platesreaching well beyond the crown - consider expanding theapplications to a broader area.

With a tree’s absorbing roots concentrating near the soil surface,how well do the trees and turf co-exist?

Trees and turf are in a competitive battle for resources and let’sface it – turf is a tough competitor. From a trees perspective: Themore lawn that can be replaced with mulch the better.

What does this portray for trees when parking lots, sidewalks,driveways, buildings, roads and other infrastructure are placed inclose proximity to trees?

These structures almost always require a compacted base layer toprovide additional support for the impervious surface beingapplied. The needs of the tree and the reach of the root plate aretoo often ignored leaving trees with reduced stability and withreduced capacity to uptake nutrients and moisture.

There is some good news out there… Recent methods of constructingsewer lines have dramatically reduced the potential for root intrusions.Longer sections of less porous pipe are being used for constructingsewer and water lines. This helps cut down on the conflict betweentree roots and sewer lines that often results in a large, mature treebeing removed.

Researchers and trials in California are looking at composite sidewalksurfaces that flex, thus giving trees room to grow and more soil toexploit for resources.

Researchers at Cornell University have been testing and working withCU Structural Soils® for some time. These soils are compactable, yetallow tree roots to penetrate. Placing these structural soils in therooting zone under sidewalks, pavers, parking lots, roads and otherstructures allows trees to expand root plates farther.

So, next time you look at your favorite tree – give some thought tothe root structure. You may not have the, “Oh Baby!” type of reaction,but after reading this article the roots should at least be creeping intothe outer recesses of your mind.



For More Information

Bassuk, Nina. Cornell Structural Soil. Internet. Available 9/25/2001.(view cornell website)

Coder, Kim D. Tree Roots and Infrastructure Damage. Internet.Available 1/27/2007. (view tree roots website)

Coder, Kim D. “Don’t Stumble Over Surface Tree Roots” GroundsMaintenance. August 1 1998

Gilman, Edward F. Where are Tree Roots? Extension Service BulletinENH 137, Florida Cooperative

Extension Service, University of Florida, Institute of Food andAgricultural Sciences. Internet. Available (view extension website)9/25/2001.

Harris, Richard W., Clark, James R., Matheny, Nelda P., Arboriculture:Integrated Management of Landscape Trees, Shrubs, and Vines. ThirdEdition. Prentice-Hall, Inc. 1999.

Graphic, ISU Forestry Extension. Tree Roots October 2001. Internet.Available 9/25/2001.

Graphic, The Morton Arboretum, Internet. Available 9/25/2001.

Pool, Bob.“With Rubber Sidewalks, Trees Are on the Rebound,” LATimes. 14, July 2001. Internet. Available 9/25/2001. (view rubber sidewalks website)

Randrup, Thomas B, McPherson, E. Gregory, Costello, Laurence R.“Tree Root Intrusion in Sewer Systems: Review of Extent and Costs.”Journal of Infrastructure Systems, Vol 7, No. 1, pages 26-31. March2001.

Soil Compaction: Causes, Effects, and Control. 2001. Internet.Available 9/25/2001. (view compaction website)



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Protecting Trees and ShrubsAgainst Winter DamageBert T. Swanson and Richard Rideout

Copyright © 2003 Regents of the University of Minnesota. All rightsreserved.

Minnesota's harsh climate is often responsible for severe damage tolandscape plants. Winter sun, wind, and cold temperatures can bleachand desiccate evergreen foliage, damage bark, and injure or killbranches, flowerbuds, and roots. Snow and ice can break branchesand topple entire trees. Salt used for deicing streets, sidewalks, andparking lots is harmful to landscape plantings. Winter food shortagesforce rodents and deer to feed on bark, twigs, flowerbuds, and foliage,injuring and sometimes killing trees and shrubs. All is not bleak,however, as landscape plants can be protected to minimize some ofthis injury.

Cold Damage Cold temperatures can damage plants in several ways. Plants that arenot hardy in Minnesota will be killed or injured during the winterunless protected in a microclimate. Plants that normally grow inhardiness zone 3 (northern Minnesota) and hardiness zone 4 (southernMinnesota) may also be injured if winter conditions are abnormallysevere or if plants have been stressed by the environment. Injury ismore prevalent and more severe when low temperatures occur inearly fall or late spring, when there is little or no snow cover duringthe winter or when low temperatures are of prolonged duration.Pronounced fluctuations in temperature can be extremely detrimentalto plants throughout the fall, winter, or spring.

Figure 1. Repairing sun scald damage.

Sun Scald Sun scald is characterized by elongated, sunken, dried, or crackedareas of dead bark, usually on the south or southwest side of a tree.On cold winter days, the sun can heat up bark to the point wherecambial activity is stimulated. When the sun is blocked by a cloud,hill, or building, bark temperature drops rapidly, killing the activetissue. Young trees, newly planted trees, and thin-barked trees(cherry, crabapple, honey locust, linden, maple, mountain ash, plum)are most susceptible to sun scald. Trees that have been pruned toraise the lower branches, or transplanted from a shady to a sunnylocation are also sensitive because the lower trunk is no longershaded. Older trees are less subject to sun scald because the thickerbark can insulate dormant tissue from the sun's heat ensuring thetissue will remain dormant and cold hardy. Sun scald can beprevented by wrapping the trunk with a commercial tree wrap, plastictree guards, or any other light-colored material. The wrap will reflectthe sun and keep the bark at a more constant temperature. Put thewrap on in the fall and remove it in the spring after the last frost.Newly planted trees should be wrapped for at least two winters andthin-barked species up to five winters or more. To repair sun scald



damage, cut the dead bark back to live tissue with a sharp knife,following the general shape of the wound, rounding off any sharpcorners to facilitate healing (Figure 1). Wrap the trunk in subsequentwinters to prevent further damage. Do not use a wound dressing.Spraying the area with a fungicide may help prevent fungal infectionof the wound.

Winter Discoloration of Evergreens Browning or bleaching of evergreen foliage during winter occurs forfour reasons:

1. Winter sun and wind cause excessive transpiration (foliagewater loss) while the roots are in frozen soil and unable toreplace lost water. This results in desiccation and browning ofthe plant tissue.

2. Bright sunny days during the winter also cause warming of thetissue above ambient temperature which in turn initiatescellular activity. Then, when the sun is quickly shaded, foliagetemperature drops to injurious levels and the foliage is injuredor killed.

3. During bright, cold winter days, chlorophyll in the foliage isdestroyed (photo-oxidized) and is not resynthesized whentemperatures are below 28° F. This results in a bleaching ofthe foliage.

4. Cold temperatures early in the fall before plants have hardenedoff completely or late spring after new growth has occurred canresult in injury or death of this nonacclimated tissue.

Foliar damage normally occurs on the south, southwest, and windwardsides of the plant, but in severe cases the whole plant may beaffected. Yew, arborvitae, and hemlock are most susceptible, butwinter browning can affect all evergreens. New transplants or plantswith succulent, late season growth are particularly sensitive.

Figure 2. Protecting evergreens fromwinter burn with a burlap screen.

There are several ways to minimize winter injury to evergreens. Thefirst is proper placement of evergreens in the landscape. Yew,hemlock, and arborvitae should not be planted on south or southwestsides of buildings or in highly exposed (windy, sunny) places. Asecond way to reduce damage is to prop pine boughs or Christmastree greens against or over evergreens to protect them from wind andsun and to catch more snow for natural protection. Winter injury canoften be prevented by constructing a barrier of burlap or similarmaterial on the south, southwest, and windward sides of evergreens(Figure 2). If a plant has exhibited injury on all sides, surround it witha barrier, but leave the top open to allow for some air and lightpenetration.

Keeping evergreens properly watered throughout the growing seasonand into the fall is another way to reduce winter injury. Never stressplants by under- or overwatering. Decrease watering slightly inSeptember to encourage hardening off, then water thoroughly inOctober until freeze-up. Watering only in late fall does not help reduceinjury.

Anti-desiccant and anti-transpirant sprays are often recommended toprevent winter burn. Most studies, however, have shown them to be



ineffective. If an evergreen has suffered winter injury, wait until mid-spring before pruning out injured foliage. Brown foliage is most likelydead and will not green up, but the buds, which are more cold hardythan foliage, will often grow and fill in areas where brown foliage wasremoved. If the buds have not survived, prune dead branches back toliving tissue. Fertilize injured plants in early spring and water themwell throughout the season. Provide appropriate protection thefollowing winter.

Dieback Deciduous trees and shrubs can incur shoot dieback and bud deathduring the winter. Flower buds are more susceptible to injury thanvegetative buds. A good example of this is forsythia, where plantstems and leaf buds are hardy, but flower buds are very susceptibleto cold-temperature injury. Little can be done to protect trees andshrubs from winter dieback. Plants that are marginally hardy shouldbe planted in sheltered locations (microclimates). Plants in a vigorousgrowing condition late in the fall are most likely to suffer winterdieback, so avoid late summer pruning, fertilizing, and overwatering.Fertilize in the spring on sandy soil or in the fall on heavy soil afterthe leaves have dropped.

Root Injury Roots do not become dormant in the winter as quickly asstems, branches and buds, and roots are less hardy than stems.Roots of most trees and shrubs that grow in Minnesota are killed attemperatures at or below 0 to +10°F. These plants survive inMinnesota because soil temperatures normally are much higher thanair temperatures and because soil cools down much more slowly thanair temperature.

Many factors influence soil temperature. Moist soil holds more heatthan dry soil, so frost penetration will be deeper and soiltemperatures colder for sandy or dry (drought) soils. Snow cover andmulch act as insulators and keep soil temperatures higher. With newlyplanted trees, cracks in the planting hole backfill will allow cold air topenetrate into the root zone, reducing fall root growth or killing newlyformed roots.

To encourage fall root growth and to reduce root injury, mulch newtrees and shrubs with 6 to 8 inches of wood chips or straw. If the fallhas been dry, water heavily before the ground freezes to reduce frostpenetration. Check new plantings for cracks in the soil and fill themwith soil.

Frost Heaving Repeated freezing and thawing of soil in fall or spring causes soil toexpand and contract, which can damage roots and heave shrubs andnew plantings out of the ground. A 4- to 6-inch layer of mulch willprevent heaving by maintaining more constant soil temperatures.

Snow and Ice Damage Heavy snow and ice storms cause damage by bending and breakingbranches. Multiple leader, upright evergreens, such as arborvitae andjuniper, and multiple leader or clump trees, such as birch, are mostsubject to snow and ice damage. Relatively small trees can bewrapped together or the leaders tied with strips of carpet, strong clothor nylon stockings two-thirds of the way above the weak crotches(Figure 3). These wrappings must be removed in spring to prevent



Figure 3. Protecting trees from snowor ice damage.

girdling, and to allow free movement of the stem. Proper pruning, toeliminate multiple leaders and weak branch attachments, will reducesnow and ice damage. For trees with large wide-spreading leaders orlarge multi-stemmed trees, the main branches should be cabledtogether by a professional arborist.

Salt Damage Salt used for deicing walks and roads in winter can cause or aggravatewinter injury and dieback. Salt runoff can injure roots and beabsorbed by the plant, ultimately damaging the foliage. Salt sprayfrom passing autos can also cause severe foliar or stem injury.

To prevent salt damage, do not plant trees and shrubs in highly saltedareas. Avoid areas where salty runoff collects or where salt spray isprevalent, or use salt-tolerant species in these areas. Burlap barriers(Figure 2) may provide protection to some plants from salt spray.

Animal Damage Mice, rabbits (rodents), and deer can all cause severe damage toplants in the winter. These animals feed on the tender twigs, bark, andfoliage of landscape plants during the winter. They can girdle treesand shrubs and eat shrubs to the ground line. Deer can causesignificant injury and breakage by rubbing their antlers on treesduring the fall.

Figure 4. Protecting trees fromrodents.

Rodents Trees can be protected from rodent damage by placing a cylinder of1/4-inch mesh hardware cloth around the trunk. The cylinder shouldextend 2 to 3 inches below the ground line for mice and 18 to 24inches above the anticipated snow line for rabbit protection (Figure 4).Hardware cloth can be left on year-round, but it must be larger thanthe trunk to allow for growth. For small trees, plastic tree guards arealso effective. You can protect shrub beds from rabbits by fencing thebeds with chicken wire; however, check such fenced areas frequentlyto ensure a rabbit has not gained entrance and is trapped inside.

If you have many trees or shrubs to protect, using screens and wrapsmay be too expensive and time consuming. In such situations,repellents may be the best solution. Remember that a repellent is nota poison; it simply renders plants undesirable through taste or smell.

The most effective repellents for rodents are those containing thiram,a common fungicide. You can either spray or paint repellents on treesand shrubs. Repeat applications are necessary particularly after heavyprecipitation. If these methods are ineffective, commercial baitscontaining poisoned grain are available. However, baits may behazardous to humans, pets, and beneficial wildlife. Injury or death canresult for animals that eat the bait directly and for animals thatconsume bait-killed rodents. Shelter or containerize baits so they staydry and are accessible only to targeted rodents. Beverage cans laid on



their sides work well for this purpose. Trapping and shooting, wherelegal, will also control rodents.

Deer Deer feed on and damage terminal and side branches of small treesand shrubs. Repellents containing thiram provide some control iffeeding pressure is not extremely heavy. Plants can be sprayed orpainted with the repellent; however, the most effective procedure is tohang heavy rags near the plants to be protected that have beendipped in concentrated repellant. Repeated plant applications ordipping of rags is necessary. Deer can also be successfully excludedwith fencing. To be effective, fences must be high and constructedproperly. If deer are starving, there is little that will prevent feeding.Providing a more palatable forage may help, but it may also attractmore deer.

Conclusion Although plant cold hardiness and winter injury are common concernsassociated with Minnesota winters, appropriate plant selection,selecting the proper site, proper cultural practices, and preventivemaintenance will significantly reduce or prevent severe injury or lossof landscape plants. Even though plants respond differently to winterstress and each winter provides a different set of stressful conditions,plants possess a remarkable ability to withstand extremely severewinter conditions. Minnesota winters should not discourage planting oftraditional or new plant species. Learn to take advantage ofmicroclimates to enable interesting or different plants to be grown.Minnesota's list of landscape plant species needs to be expanded, notreduced.

Bert T. Swanson Professor Department of Horticultural Science University of Minnesota

Richard Rideout City Forester City of Milwaukee, WI

Reviewed by Jeffrey H. Gillman Nursery Management Specialist Department of Horticultural Science

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