CMG GardenNtes #615 Pruning Mature Shade Trees Outline: When t hire a prfessinal certified arbrist, page 1 General pruning guidelines, page 2 Limitatin n diameter f cut, page 2 Limitatin n size relatinships with reductin cuts, page 3 Dsage: Maximum amunt f life wd/fliage t remve, page 3 Other general guidelines, page 4 Pruning bjectives, page 5 Pruning methds, page 6 Structural pruning, page 6 Subrdinate pruning cnsideratins, page 6 What is the purpse f pruning this tree? page 6 What is the structural integrity f the branch unin? page 7 What is the aesthetic value f the branch? page 7 Where shuld the pruning cut be made? page 8 Illustratins f subrdinate pruning situatins, page 10 Medium-aged tree with cdminant trunks, page 10 Vigrusly grwing branches chkeut the central leader, page 10 Yung tree runded with heading cuts, page 11 Upright grwing tree with numerus upright grwing branches, page 11 Cleaning, page 11 Thinning, page 12 Raising, page 15 Reductin, page 16 Restratin, page 18 Pllarding, page 18 Frequently asked questins abut pruning mature shade trees, page 18 What abut tpping a tree? page 18 What abut utility right-f-way pruning? page 19 I am cncerned abut my tree in strng winds, but really d nt want t lse the shade. D I really need t have the tree pruned r remved? page 19 Hw shuld strm damaged trees be pruned? page 19 Hw shuld trees with rt damage be pruned? page 20 Hw shuld declining trees be pruned? page 20 When t Hire a Prfessinal Certified Arbrist Pruning large trees is a safety issue beynd the training and experience f hme gardeners. Hiring a bnded prfessinal is the best apprach fr mst tree pruning jbs. Lk fr arbrists with certificatin frm the Internatinal Sciety f Arbriculture, ISA. Many are listed in the phne bk yellw pages and a list f ISA Certified Arbrists wrking in the area can be fund n the ISA web site at www.isa-arbr.cm. Als, ask abut liability insurance cverage. 615-1
This CMG GardenNtes is written t help the hme gardener understand issues arund pruning f mature trees and help with cmmunicatins with their certified arbrists. General Pruning Guidelines Limitatins n Diameter f Cut Ideally, all pruning cuts are tw inches in diameter and smaller. On tree species resistant t decay, the standard culd be pushed t tw t fur inches, maximum (depending n actual vigr and grwth f the tree). These small wunds minimize the ptential fr internal decay. The tw-inch diameter and smaller branch is primarily sapwd (newer xylem rings f living cells active in water transprt and strage f phtsynthates) that is nt prne t decay. Unless there is a strng justificatin, (taking int accunt the ptential fr a decay clumn and internal cracking) avid remving branches larger than fur inches in diameter. At apprximately fur inches, heartwd (lder xylem rings f nnliving cells n lnger active in water transprt) dminates the branch structure. The branch becmes prne t decay as heartwd has n resistance t the spread f decay and is prne t internal cracking. (Nte: Due t chemical changes in the cells, heartwd is ften darker in clr.) [Figure 1] Figure 1. Crss sectin f Duglas-fir. Light clred uter rings are sapwd. The dark wd in center is the heartwd. When a pruning cut r ther injury pens a branch t decay, the decay clumn will take the current seasn f xylem ring and everything lder. Decay creates a pipelike structure in the branch. The healthy, undecayed wd will be the xylem rings that grw in future years. [Figure 2] Figure 2. When injury (such as imprper pruning cuts) leads t decay, it takes the current seasn s xylem ring and everything lder (inward). New grwth (xylem rings that grw in future years) will be resistant t decay. Decay creates a pipelike structure. 615-2
Fr example, if a branch with eight-inch diameter xylem (wd) is pruned back t a trunk with 12-inch diameter xylem (wd) and decay results, the decay clumn in the trunk will be 12 inches wide (that is, the diameter f the trunk wd at the time the injury ccurred). The tree wuld have t add six inches f healthy new grwth t meet the minimum standards fr structural strength (33% shell). If annual grwth rings were ¼ wide, this wuld take 12 years! Fr additinal infrmatin n tree decay and percent shell, refer t CMG GardenNtes #611, Tree Grwth and Decay. [Figure 3] Figure 3. The diameter f the decay clumn will be the diameter f the current seasn s xylem ring fr the year that injury ccurred and inwards. Structural weakness frm the decay is ffset by the grwth f new wd (xylem rings) in future years. Limitatins n Size Relatinship with Reductin Cuts Pruning ften invlves subrdinating side branches r secndary trunks t a mre dminant leader. This can nly be achieved with reductin cuts (remving a larger trunk/branch back t a smaller side branch). In reductin cuts, the diameter f the side branch must be at least ne-third the diameter f the trunk/parent branch remved. If the side branch is smaller, it becmes a heading cut. [Figure 4] Figure 4. In reductin cuts (remving a larger trunk/parent branch back t a smaller side branch), the side branch must be at least ne-third the diameter f the trunk/parent branch remved. If the side branch is less than ne-third the trunk diameter, it is a heading cut. Heading cuts are nt acceptable in pruning standards. A cmmn mistake in lwering branch height is the use f heading cuts, which release watersput (sucker) grwth frm the pruned branch. The regrwth will be structurally unsund, resulting in trees that may be mre prne t strm damage than befre pruning ccurred. When pruning maturing trees, heading cuts are nt acceptable in pruning standards! Fr additinal details n reductin cuts refer t CMG GardenNtes #612, Pruning Cuts. Dsage: Maximum Amunt f Live Wd / Fliage t Remve D nt indiscriminately remve branches with live fliage as this can add stress t the tree. The amunt f live wd and fliage t remve per seasn depends n the actual grwth rate f the tree. Yung, actively grwing, trees are rather tlerant f a heavy pruning dse. As trees becme mature, they becme intlerant f heavy pruning. Lk at six t 12 branches arund the tree t assess grwth rates. Lk fr what is the typical grwth rate fr mst branches, nt the fastest r slwest grwing branches. 615-3
Trees under severe stress putting n insignificant annual grwth Limit pruning t cleaning (remval f dead and damaged branches). Live wd shuld nt be remved n trees under severe stress (including drught stress). Heavy pruning simply remves the stred phtsynthates that the tree is living n during the stress perid! On mature trees (greater than 75% mature size fr the site), pruning dse shuld be limited t 5% t 10%, based n actual grwth and vigr f the tree. On medium aged trees, the dsage really depends n actual grwth. Typical range wuld be 10% t 25% depending n actual grwth and vigr f the tree. In situatins where trees are pruned annually (the ideal situatin), the apprpriate pruning dse wuld be n the lighter side. Hwever, in real wrld situatins, trees are ften pruned nly nce every several years. Here the apprpriate pruning dse may be heavier. In situatins where heavy pruning is needed, cmplete the wrk ver a perid f years. Excessive pruning can lead t waterspruts (upright, sucker-like shts emerging n the trunk r branches). Watersputs, a cmmn respnse t ver pruning and strm damage, are structurally unsund. Excessive pruning als creates a hrmne imbalance between Auxins (prduced in the terminal buds f the canpy) which stimulates rt grwth and Gibberellins (prduced in the rt tips) which stimulates canpy grwth. This puts the rt system int a multi-year decline, resulting in a multi-year decline in canpy grwth. Strm damage may take f excessive amunts f live wd leading t heavy canpy grwth and waterspruts the first year due t high Gibberellins. The natural rt generatin declines the first year due t lw Auxins. This decline in rt regeneratin leads t a multi-year decline in rt and canpy grwth. The strm damage cunts int the dsage f life wd remved. When strm damage takes ff mre than the apprpriate dsage fr the trees actual grwth, limit pruning t cleaning (remval f dead and damaged) until the tree rebalances and resumes nrmal grwth rates. Remval f dead wd des nt cunt int the dsage. Other General Guidelines T maintain trunk taper resilient t winds, at least ne-half f the fliage shuld be in the lwer tw-thirds f the tree. The lwest limb shuld riginate in the bttm ne-third f the tree s height. Pruning shuld maintain the tree s natural shape. Avid lin-tailing where the small twiggy inner fliage is cleaned-ut n the lwer scaffld branches and secndary trunks. This shifts weight t the ends f branches and reduces the damping effect n the branch; increasing the ptential fr wind damage. It reduces the taper (widening f the branch/trunk as it mves dwnwards) increasing the ptential fr branch/trunk failure. It 615-4
als reduces the stred phtsynthate reserves in the lwer branching structure decreasing resilience t stress factrs. Avid tpping a tree. Tpping pens the tree t internal decay and cracking. Regrwth f waterspruts (adventitius shts) is structurally unsund. Written specificatin fr any pruning jb shuld include the fllwing: Clearly state which tree(s) will be pruned. Clearly indicate the bjectives fr pruning (why prune), such as reduce risk f failure due t wind damage r snw lading, manage health, imprve aesthetics, prvide clearance, imprve view. Specify pruning methds (hw t prune) t meet the bjectives, such as structural pruning, cleaning, thinning, raising, reducing, restratin pruning. State the size specificatin fr the minimum and/r maximum branch size t be remved. Fr example, Cuts shuld be made n branches tw inches and less in diameter and In a reductin cut, the side branch pruned back t shuld be at least ne-third the diameter f the branch remved. Specify the dsage (maximum amunt, by percentage, f live wd/fliage t be remved per seasn). Fr example, Pruning shuld nt remve mre than 15% f the live crwn. In writing pruning specificatins, the wrd shuld refers t a practice that is rutine and recmmended. The wrd shall refers t a practice that is mandatry. Include these generic safety statements t reduce the hmewner s and pruning crew s liability. All wrk shall be perfrmed in accrdance with American Natinal Standards Institute A300 Pruning Standards and Z133.3 Safety Standards. All wrk shall be perfrmed under the supervisin f a licensed, Internatinal Sciety f Arbriculture certified arbrist. Pruning Objectives Pruning shuld be based n pruning bjectives (why t prune). D nt indiscriminately remve branches. Pruning bjectives determine methds (hw t prune) t be used, which in turn determine the type f pruning cuts made. Table 1 lists cmmn bjectives, methds and types f pruning cuts. Table 1. Objectives and Methds fr Pruning Maturing Trees Objectives (Whys) Methds (Hw) Pruning Cuts Reduce risk f failure (wind and snw) Structural Remval cut Imprve structure Cleaning Reductin cut Maintain health Thinning Heading cut Imprve aesthetics Raising Prvide clearance Reducing Imprve view Restring Reduce shade Pllarding Influence flwering and fruiting 615-5
Pruning Methds Structural Pruning A cmmn pruning bjective with maturing trees is t reduce the ptential risk f failure frm wind and snw lading. Significant wind damage ccurs n structurally weak trees with wind gusts f 60 t 75 mph. Even structurally sund trees may fail with wind gusts abve 95 mph. In Clrad (and ther snwy climates), mst significant strm damage is due t cdminant trunks (trunks f similar size). Structural prblems f this type shuld have been crrected while the tree was in the early grwth stage. Arbrists have a limited ptential t crrect structural defects n middle-aged and mature trees withut predispsing the tree t internal decay, cracking, and creating an unsightly shaped tree. [Figure 5] Figure 5. Cdminant trunks (adjacent trunks f similar size) accunt fr the majrity f strm damage in Clrad landscapes. Structural pruning centers arund develping a dminant trunk with subrdinate side branches and secndary limbs. T be mst effective, it requires annual pruning ver a perid f years, rather than an ccasinal ne-time pruning. Written pruning specificatins fr structural pruning f maturing trees shuld include the fllwing: Identify branches where wrk will be dne (fr example, cdminant trunk n suth side f tree ). Identify the methds t be used in pruning (fr example, the secndary trunk n the suth side shuld be reduced by 10 feet ). Subrdinate Pruning Cnsideratins Structural pruning f maturing trees is ften referred t as subrdinate pruning, where secndary trunks (and side branches) with weak branch unins are subrdinated t a dminant trunk. T avid remving t much fliage/live wd in ne seasn, subrdinate pruning generally requires wrk ver a perid f years. In evaluating hw t prune the maturing tree, take int accunt the fllwing cnsideratins: What Is the Purpse fr Pruning the Tree? Structural pruning (subrdinating weak side branches t a mre dminant trunk) is mre effective in reducing failure ptential than general crwn reductin r crwn thinning. With general crwn reductin r thinning, regrwth simply replaces what was pruned ff in a few years. 615-6
Wind lading T reduce ptential f failure due t wind lading, the height f secndary trunks and side branches with weak branch unins must be lwered. This is dne with reductin cuts, and prper reductin cuts may nt be pssible n many maturing trees withut intrducing decay and internal cracking, and structurally unsund watersput grwth. Fr example, many cttnwd and ppular trees will nt have side branches f adequate size fr prper reductin cuts (side branch prune back t must be at least 1/3 the diameter f the trunk remved). A slight reductin in secndary trunk/branch height will nt achieve the bjective. T significantly reduce the risk f failure, reductin may need t be 1/3 r mre f the branch length. On maturing trees, this may be int braches t larger fr pruning by pruning standards. Nt all branches can be effectively reduced. Snw lading T reduce ptential f failure due t snw lading, the snw catching vlume f the branch needs t be reduced. This is best achieved with structural pruning f weak branches. What Is the Structural Integrity f the Branch Unin? T evaluate the structural integrity f the branch unin (crtch) lk at the Aspect Rati (that is the diameter f the side branch t the diameter f the trunk). Any side branch with an aspect rati larger than 1 t 2 (diameter f side branch greater than ½ the diameter f the trunk) will be structurally weak due. Fr example, if the diameter f the trunk is fur inches, all side branches shuld be less than tw inches. A structurally strng branch unin has a branch cllar (where the annual grwth rings f the trunk wrap arund the annual grwth rings f the side branch). Fr a branch cllar t develp, the side branch needs t be less than ne-half the diameter f the adjacent trunk. Less than ne-third is preferred. Branch unins with branch cllars are als mre resistant t the spread f decay. Fr mre details n branch cllars, refer t CMG GardenNtes #611, Tree Grwth and Decay. [Figure 6] Figure 6. T evaluate the structural strength f a branch unin, cmpare the diameters f the trunk and side branch. A branch unin is structurally strng when it has a branch cllar. Fr the branch cllar t develp, the diameter f the side branch needs t be less than ne-half the diameter f the adjacent trunk. Branch unins can als be cmprmised with narrw crtch angles, leading t included bark (bark against bark) and multiple branching riginating in the same area. What Is the Aesthetic Value f the Branch? Is the branch in questin imprtant t the tree s balance and appearance? If the branch were remved, wuld its remval create a majr gap in the canpy? 615-7
Where Shuld the Pruning Cut Be Made? If the three previus questins lead t the cnclusin that a secndary trunk r branch needs t be pruned, several cnsideratins are needed t determine where t make the actual cut. Smetimes nne f the ptins meet pruning guidelines, and the better f the bad ptins is chsen. Fr illustratin, lk at the tree in Figure 7. It has three trunks. If the branch unins d nt have branch cllars (that is, the secndary trunks are mre than half the diameter f the primary trunk), the tree is prne t strm damage. Figure 7. As drawn, the tree has three trunks. Evaluate the need fr subrdinate pruning by cmparing the diameters f the secndary (left and right) trunks t the center trunk. T be structurally strng with branch cllars, the left and right trunk need t be less than half the diameter f the center trunk. Cnsideratins fr the Secndary Trunk n the Left As drawn in Figure 8, there are fur sites where pruning culd ccur t lwer the height f the secndary trunk (wind lading) and reduce the snw lading ptential. Figure 8. As drawn, there are fur lcatins where pruning culd ccur. Cnsideratins fr lcatins A, B and C with reductin cuts (remving a larger trunk back t a smaller side branch) A B C D If lcatin A has a 2-inch trunk with a 1-inchside branch, it meets the pruning guidelines fr bth size (decay ptential) and reductin cut (watersput grwth). Hwever, as drawn, it may have little ptential t minimize strm damage, as the height is nt significantly lwered (wind lading), and the ttal ptential fr snw lading has nt been significantly reduced. If lcatin A has a 2-inch trunk with a half-inch side branch, it des nt meet the reductin cut guideline (watersput grwth), as the side branch is ne-furth the size f the trunk being remved. Due t the size relatinship, this becmes a heading cut. Waterspruts regrwth n the trunk culd make it mre prne t strm damage than befre pruning! If lcatin B has a fur-inch trunk and a 3-inch side branch it vilates the size (decay) guideline because the trunk is t large, predispsing the trunk t decay and internal cracking. This is typical when pruning maturing trees, as branches will be t large except in the uter canpy. The 3 side branch is within the reductin cut (watersput) guideline, making it a reductin cut. 615-8
If lcatin B has a 4-inch trunk and a 1-inch side branch it vilates bth the size (decay) and the reductin cut (watersput) guidelines. If lcatin C has a 6-inch trunk and a 3-inch side branch it vilates the size (decay) standard. The 3-inch side branch is within the reductin cut (watersput) standard. Cnsideratins fr lcatin D with a remval cut (remving a smaller side branch back t a larger trunk/parent branch) Is the branch imprtant t the aesthetics f the tree? As drawn, the remval f the entire branch wuld create a gap in the canpy. Remval f the left side secndary trunk plus additinal pruning n the right side t aesthetically balance the tree wuld remve t much f the tree s fliage/live wd in a single seasn. If lcatin D has an 8-inch trunk with a 6-inch side branch (secndary trunk), it vilates the size (decay) guideline. Being a remval cut (remving a smaller side branch back t a larger trunk/parent branch); it des nt have a reductin cut standard. Withut a branch cllar, the branch unin is prne t decay. Better f the Bad Optins In reality, it is cmmn that nne f the ptential cuts meets acceptable pruning guidelines, and the arbrist lks fr the better f the bad ptins. Due t the diameter f the limbs, large trees have few acceptable ptins based n the size guideline (ptential fr internal decay and cracking). It is cmmn that secndary trunks may nt have any side branches f an acceptable size relatinship fr a reductin cut. If the tree species is prne t decay, avid cmprmising n the size (decay) guideline, pening the tree t decay and internal cracking. If the tree is in a stressed site (including limited water r rt spread ptential) avid cmprmising n the size (decay) guideline, as the tree is mre prne t decay. If the tree is vigrusly grwing r the ttal amunt f fliage/live wd being remved is at the maximum allwed in pruning standards, avid cmprmising n the reductin cut (watersput) guideline, as the tree is mre prne t watersput grwth. With grwth, the tree may becme mre prne t strm damage than befre pruning. If the tree will be pruned each year (dealing with the watersput grwth) this becmes less f an issue. If tree failure wuld nt cause injury r significant prperty damage, n pruning may be the better ptin. If tree failure wuld cause injury r significant prperty damage, it may be better t accept limited decay and wrk with resulting structural issues frm regrwth than t leave the tree at high risk fr strm damage. 615-9
Strm failures are mre cmmn n yung and medium-sized trees as the c-dminant and secndary trunk reach 3-4 inches in diameter. Old, mature trees are actually less prne t strm damage, having had their weakness tested in previus mega strms. Illustratins f Subrdinate Pruning Situatins Medium-Aged Tree with Cdminant Trunks With cdminant trunks, ne trunk is subrdinated t a dminant trunk. Figure 9 illustrates this. It may require annual pruning ver a perid f years. a b c Figure 9. Befre and after pruning with cdminant trunks. a. Tree befre pruning. b. Cdminant trunk n right subrdinated t trunk n left. c. Tree balanced with ther, mre upright grwing branches n left subrdinated t the dminant trunk. Vigrusly Grwing Branches Chke-Out the Central Leader On species with ppsite branching patterns, vigrusly grwing lwer branches ften chke-ut the central leader. Figure 10 illustrates the pruning apprach. It may require annual pruning ver a perid f years. Figure 10. Befre and after views f a tree wh s vigrusly grwing branches chke-ut the central leader. a. Befre pruning b. Desired lk after pruning a b 615-10
Yung Tree Runded with Heading Cuts Trees shuld never be runded with heading cuts. Figure 11 illustrates the pruning apprach. It may require annual pruning ver a perid f years. a b c Figure 11. Befre and after views f a yung tree runded with heading cuts. a. Befre pruning b. Desired lk after pruning, subrdinating side branches t a dminant trunk. c. Tree with grwth. Upright Grwing Trees with Numerus Upright Grwing Branches Sme species f trees (including Callery pear and sme crabapple cultivars) have numerus upright grwing branches. Figure 12 illustrates the pruning apprach. It may require annual pruning ver a perid f years. Figure 12. Befre and after views f an upright grwing tree with numerus upright grwing branches. a. Befre pruning b. Desired lk after pruning a b Cleaning Cleaning is the remval f dead, diseased, cracked, and brken branches. This type f pruning is dne t reduce the risk f branch failure, imprve tree appearance, and t reduce the spread f insects and diseases. Mst pruning f middle-aged and mature trees falls int this type. Trees under stress r declining trees may need cleaning every few mnths t ever few years. All dead wd may be remved at ne time. It des nt cunt in the ttal f live wd/fliage remved. In cleaning, d nt remve healthy branches and live fliage. D nt clean ut healthy grwth in the tree s interir. [Figure 13] 615-11
Figure 13. This ld cttnwd needing cleaning t remve dead branches and reduce the risks assciated with branch failure. Remving dead branches T minimize risk if the branch were t fail, it is advisable t remve any dead branch larger than a tw-inch diameter and higher than 30 feet. Dead branches may als becme a surce f insect and disease pressure in the tree. Remve the dead branches using the three-step pruning technique. Fr details refer t CMG GardenNtes #612, Pruning Cuts. D nt cut int the branch cllar, which wuld pen a high ptential fr decay t spread int the trunk. If live wd has began t grw ut alng the dead limb, cut just beynd the live wd being cautius nt t nick the live tissue. Never flush cut the dead branch. [Figure 14] Figure 14. When remving dead branches, d nt cut int the living tissues. Written specificatins fr cleaning shuld specify the minimum size f dead branches t be remved. Fr example, Clean branches ne inch diameter and larger r Clean branches tw inches in diameter and larger that are 30 feet and higher abve the grund. The lcatin f the branch t be remved shuld be specific if the entire crwn is nt ging t be cleaned. Thinning Thinning is the selective remval f smaller branches (½ inch t 2.5 inches in diameter) t reduce crwn density. Because the majrity f small branches are in the uter canpy, thinning fcuses in this area. Thinning shuld retain crwn shape and size, and prvide an even distributin f fliage thrughut the crwn. Remval cuts are primarily used. [Figure 15] 615-12
Because thinning is in the upper/uter canpy, it requires a trained arbrist with a high level f skill. Thinning is expensive, ften running $500 t ver $1,000 per large tree when dne crrectly. Figure 15. Thinning is the selective remval f small branches, grwing parallel t each ther, in the leafy upper/uter tree canpy. Thinning can include remval f suckers frm the base f the tree and sme watersputs n the interir. Excessive remval f waterspruts at ne time ften prmtes grwth f additinal waterspruts, and shuld be avided. Benefits f Thinning Thinning is a methd t minimize ptential damage caused by snw lading, a primary situatin leading t tree failures in Clrad. Thinning can reduce limb weight in rder t cmpensate fr structural defects. Thinning increases light penetratin int the tree interir. This can invigrate the tree and help retain the tree s natural shape. Thinning may adequately reduce shade fr shade tlerant under stry plants belw the tree. Hwever, thinning middle-aged and mature trees will nt adequately prmte grwth f sun lving plants like Kentucky bluegrass. Thinning is a technique t partially pen a view withut remving r structurally influencing a tree. This is ften referred t as vista pruning. On a tall tree, thinning may nt be an effective technique t reduce wind sail and ptential fr breakage in strng winds. Reducing is the mst effective way t deal with wind lading issues. Effectiveness f Thinning Researchers are questining the verall effectiveness f verall tree thinning. Depending n grwth rates, the tree may simply regrw the remved branches in a few years. Current thught in reducing strm lading is that structural pruning will be mre effective than general thinning. 615-13
Clarificatin n Thinning As a pint f clarificatin, thinning is dne n relatively small branches in the leafy upper/uter canpy. Thinning is nt remving large lwer branches, which culd create gaps in the crwn and encurage waterspruts. Thinning is nt remval f the small twiggy branches in the inner canpy. Thinning will nt significantly lwer a tree s height. [Figure 16] Figure 16. Left Thinning fcuses n small branches in the upper/uter tree canpy. Right Thinning des NOT remve large branches, creating a gap in the tree canpy. Avid lin-tailing which is the remval f the live small leafy twigs dwn in the tree s interir. Never clean ut these lwer branches and twigs n maturing trees. These small interir branches are critical t the trunk s structural integrity and vigr. They als serve t dampen tree sway in wind. Lin-tailing shifts the wind lading t the uter canpy increasing the tree s ptential fr wind damage. [Figure 17] Figure 17. D nt lin-tail trees as in the pht. Remval f the smaller twiggy wd in the inner tree canpy decreases vigr n the majr branches and trunk and shifts the weight t the tp increasing the ptential fr wind damage. Written specificatins fr a thinning jb shuld specify the fllwing: Clarify the dsage (percent f the tree s canpy may be remved). Fr example, Pruning shuld nt exceed 15% f the ttal live canpy. Clarify where in the tree the pruning will ccur. Fr example, Pruning shuld ccur in the uter third f the crwn. 615-14
Clarify size f branches t be remved. Fr example, Pruning shuld remve branches up t 2½ inches in diameter. Raising Raising is the remval f lwer branches t prvide clearance fr peple, traffic, buildings, r a view. When remving lwer branches, maintain at least ne-half f the fliage in the lwer tw-thirds f the tree. The lwest branch shuld riginate in the bttm ne-third f the tree s height (live crwn rati). [Figure 18] Figure 18. When remving lwer branches, maintain at least ne-half f the fliage in the bttm tw-thirds f the tree. The lwest branch shuld riginate in the lwer ne-third f the tree. Raising shuld be part f the tree s structural training while yung. Ideally raising wuld be dne befre branches t be remved exceed a tw-inch diameter. The ptential fr decay is high when the branch remved is larger than fur inches r when a tw-inch and larger branch is greater than half the diameter f the adjacent trunk (n branch cllar t suppress decay). On many trees, lwer branches make-up a significant prtin f the tree s entire canpy and cannt be remved withut significantly influencing tree health and appearance. When the branch t be remved is larger than tw inches, cnsider ther alternatives. Can the clearance required be achieved with remval and reductin cuts ut alng the branch rather than remving the entire branch? Leaving sme small diameter branches n the lwer trunk fr a year helps clse pruning wunds and lessens the ptential fr trunk cracking. [Figure 19] Figure 19. In raising branches n maturing trees, cnsider if required clearance can be achieved with remval and reductin cuts ut alng the branch rather than remving large branches entirely. Excessive remval f lwer branches increases the ptential fr tree failure by decreasing trunk taper, causing trunk cracks and decay, and transferring weight t the tp. Written specificatin fr raising shuld include the fllwing: Clarify the clearance required. Fr example, The tree s crwn will be raised t seven feet. 615-15
Clarify what branch(es) will be pruned and the type f pruning cuts (remval r reductin cut) t be used. Fr example, The lwest branch n the suth side shall be remved back t the trunk with a remval cut. The lwest branch n the nrth side will be reduced with a reductin cut at the branch five feet ut frm the trunk and a remval cut t the lwest side-branch. Clarify what size f branches will be pruned. Fr examples, All cuts shall be tw inches in diameter and smaller. Reductin Reductin is the selective remval f branches t decrease the height and/r spread f a tree. It requires the use f reductin cuts, which remve larger branches back t smaller side branches. [Figure 20] Figure 20. Reducing is the selective remval f branches t decrease a tree s height and/r spread. Just being tall des nt indicate that a tree is structurally weak and prne t strm damage. Reductin is a methd t reduce ptential wind lading n large trees with structural defects. Reducing and thinning bth decrease ptential failure frm snw lading. Hwever, researchers are questining the effectiveness f verall tree reductin. Depending n grwth rates, the tree may simply regrw the remved branches in a few years. Current thught in reducing strm lading is that selective structural pruning n weak secndary trunks will be mre effective than general tree reductin. Nt all trees can be reduced withut predispsing the tree t decline and death. Crwn reducing requires the extensive use f reductin cuts, which can predispse the branch/trunk t internal decay. On lder trees shwing stress r decline, heading cuts can accelerate decline and death. [Figure 21] Figure 21. Nt every tree shuld be reduced. Ntice the dieback assciated with the previus reductin n this ld cttnwd. On ld trees and trees shwing stress r decline, heading cuts may accelerate the decline cycle. 615-16
In a prper reductin cut, the side branch pruned back t will be at least ne-third the diameter f the trunk/parent branch remved. Under American Natinal Standards Institute (ANSI) pruning standards, if the side branch is less than nethird, it is cnsidered a heading cut, which is generally unacceptable. Fr additinal details n prper reductin cuts, refer t CMG GardenNtes #613, Pruning Cuts. It is very difficult t use crwn reducing t permanently maintain a tree at a small size withut causing tree decline. Ideally, trees were selected with adequate space fr their mature size. Where size cntrl is necessary, it is best t begin reductin pruning as the tree reaches acceptable size, rather than when the tree becmes vergrwn. In crwn reducing, first visualize the new uter edge f the smaller canpy. Then prune the tree back t apprpriate branch unins fr a prper reductin cut r remval cut. Sme branches will be left taller than the visualized uter edge while thers will be cut back belw the visualized canpy edge. D nt make heading cuts and avid runding ff the tree canpy. [Figure 22] Crrect Incrrect Figure 22. Left In reductin, visualize the new uter edge f the smaller canpy. Prune back t branch unins that make prper reductin and thinning cuts. Sme branches will be taller than the new uter edge, sme shrter. Right This tree is incrrectly runded ff with heading cuts. In shrtening primary upward grwing trunks/primary branches t a lateral branch, a side branch that is smewhat upward grwing with a narrw branch unin angle may be strnger than a branch unin with a wide angle. [Figure 23] Figure 23. In shrtening a main upward grwing branch, pruning back t a narrw branch unin may be strnger than a wide branch unin. Just because a tree is tall des nt indicate that it is structurally unsund. Ptential risk f failure shuld be evaluated by an experienced arbrist based n branching structure, branch unin integrity, signs f internal decay, and previus damage. 615-17
Written specificatins fr reductin pruning shuld include the fllwing: Clarify the desired reductin in height/spread. Specify criteria fr reductin cuts. Fr example, All cuts shuld be made n branches less than tw inches in diameter. Diameter f the side branches pruned back t shuld be at least ne-third the diameter f the branch remved. Clarify the dsage (percentage f live wd/fliage t be remved). Fr example, Pruning shuld nt exceed 10% f the ttal canpy. Restratin Restratin is the selective remval f branches, spruts, and stubs frm trees that have been damaged by imprper pruning, vandalism, and strms. The bjective is t restre the trees structure, frm, and appearance t the extent pssible. Restratin generally requires annual pruning ver a perid f years. Actual pruning prcedures vary with the situatin. When dealing with situatins f excessive waterspruts, a rule t thumb is t remve ne-third and reduce nethird with each annual pruning. Remving all f the waterspruts at ne time ften stimulates the grwth f mre waterspruts. Pllarding Pllarding is a training system that invlves creating heads n secndary branches were small tertiary branches arise. The small tertiary branches are all remved back t the head every ne t three years (depending n grwth rates). Pllarding started as a methd t prduce shts fr fuel, shelter, and prducts made frm the yung shts. Tday, it is used as an art frm. Pllarding is cmmn in sme parts f Eurpe t keep tree small and shaped as living screens. Pllarding is nt tpping and shuld nt be cnsidered a rutine methd t keep large trees small. Due t annual labr invlved, it is uncmmn in the United States. Frequently Asked Questins Abut Pruning Mature Shade Trees What Abut Tpping a Tree? Shade trees shuld never be tpped. The regrwth f a tpped tree is structurally unsund. Tpping required by utility right-f-way pruning is starkly bvius and sets an unfrtunate cmmunity standard fllwed by thers. Instead f tpping, use cleaning, and/r prper structural pruning methds. [Figure 24] Figure 24. Never tp a tree, the regrwth is structurally unsund, making it very prne t wind and strm damage. 615-18
What Abut Utility Right-Of-Way Pruning? Pruning fr utility line clearance des nt always fllw desirable pruning techniques regarding appearance and health f the tree. In this situatin, the needs f the utility right-f-way take pririty ver the tree. When a tree under a pwer line requires frequent reductin, cnsider having the tree remved. Utility cmpanies are generally eager t accmmdate. In planting trees, selectin criteria (i.e., size and placement) shuld be fllwed s that a tree s health and appearance will never be cmprmised by the need fr utility pruning. I Am Cncerned Abut My Tall Tree Breaking in Strms, But I Really D Nt Want t Lse the Shade. D I Really Need t Have the Tree Pruned r Remved? This is a tw-part questin. First, des the tree shw signs f being highly susceptible t strm damage, (i.e., previus strm damage, dieback r dead branches, structural prblems such as cdminant trunks, weak branch unins r internal decay)? This shuld be evaluated by an experienced ISA Certified Arbrist. Secnd, if yes, what wuld the tree r branch hit shuld it fail? If it wuld cause significant prperty damage r threaten life, the tree shuld be pruned r remved as a preventive measure. Cleaning and structural pruning may reduce the ptential strm hazard withut cmprmising the shade. In sme situatins, the risk f failure cannt be reduced withut remval. Remember that healthy structurally sund trees are generally windfast even when mature. Strm damage is usually, but nt always, related t structural prblems that culd have been addressed with prper structural training when the tree was yung. Cdminant trunks accunt fr the majrity f tree failures in Clrad. The hazard f wind damage is higher n the regrwth f trees that have been tpped. Cnsult an ISA Certified Arbrist fr additinal details. Hw Shuld Strm-Damaged Trees be Pruned? First, fcus n cleaning (remving brken and damaged limbs) keeping in mind the structural integrity f the tree. Realize that yu may have t accept less than ideal pruning techniques by Mther Nature. Secnd, fcus n structural pruning t restre the tree s structural integrity and shape t the extent pssible. This may take place ver a perid f years. The maximum amunt f tree canpy that can be remved withut putting the tree and its rt system under stress includes the live wd/fliage remved by the strm. When Mther Nature remves t much live wd/fliage, limit pruning t cleaning. On strm damaged trees where excessive live wd and fliage were remved by strm damage, wait until the rts and crwn stabilize (as measured in canpy grwth) befre ding thinning, reducing, r ther structural pruning. This may be a multi-year perid. 615-19
Keep the tree if it can be pruned back t structurally sund wd and will be esthetically pleasing. Often when ne side f the tree is gne, the best ptin is t remve the entire tree. [Figure 25] Figure 25. Keep strmdamaged trees when they can be pruned back t structurally sund wd and has an acceptable appearance. This yard wuld lk better if the tree was remved. Hw Shuld Trees With Rt Damage be Pruned? Fcus n cleaning. Avid remving live wd and fliage as this culd speed the decline. Remving live wd lwers the auxin cntent, which is the hrmne that prmtes rt grwth. Remving fliage reduces phtsynthesis and levels f stred carbhydrates that the tree is living n during the recvery perid. Trees in a cnstructin site with damaged rts may require cleaning every 3-12 mnths fr five plus years. Hw Shuld Declining Trees be Pruned? Fcus n cleaning. Avid remving live wd and fliage as this culd speed the decline. Remving live wd lwers the auxin cntent, which is the hrmne that prmtes rt grwth. Remving fliage reduces phtsynthesis and levels f stred carbhydrates that the tree is living n. Old declining cttnwds and pplars may warrant cleaning every ne t five years. Authrs: David Whiting (CSU Extensin, retired), with Alisn O Cnnr and Eric Hammnd (CSU Extensin). Artwrk by David Whiting; used by permissin. Clrad Master Gardener GardenNtes are available nline at www.cmg.clstate.edu. Clrad Master Gardener training is made pssible, in part, by a grant frm the Clrad Garden Shw, Inc. Clrad State University, U.S. Department f Agriculture and Clrad cunties cperating. Extensin prgrams are available t all withut discriminatin. N endrsement f prducts mentined is intended nr is criticism implied f prducts nt mentined. Cpyright 2006-14. Clrad State University Extensin. All Rights Reserved. CMG GardenNtes may be reprduced, withut change r additins, fr nnprfit educatinal use. Revised Octber 2014 615-20