Urban Forestry & Urban Greening

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1 Urn Forestry & Urn Greening 1 (211) Contents lists ville t SieneDiret Urn Forestry & Urn Greening jou rn l h omepge: Effet of rooting onditions on the growth nd ooling ility of Pyrus lleryn M.A. Rhmn,, J.G. Smith,1,P. Stringer,2, A.R. Ennos,3 Fulty of Life Sienes, University of Mnhester, Mnhester M13 9PT, UK Red Rose Forest, Dok Offie, Trfford Rod, Slford Quys, Slford M5 3XB, UK r t i l e i n f o Keywords: Evpotrnspirtionl ooling Growing onditions Sher strength Urn het islnd s t r t Urn forests pper to e n exellent wy of mitigting the urn het islnd nd dpting ities to limte hnge, s trees provide ooling y evpotrnspirtion. However, the effets of urn growing onditions on tree growth nd ooling performne hve not een widely investigted. The urrent study ddresses this shortoming y studying the growth nd lef physiology of the ommonly plnted urn tree Pyrus lleryn Chntileer. The study ws rried out etween Ferury nd Novemer, 21 on streets in Mnhester, UK, where P. lleryn trees hd een growing for five to six yers under three ontrsting growth onditions: in pvement; in grss verges; nd in Amsterdm soil. Trees in Amsterdm soil hd grown lmost twie s fst s those in pvements, the differene eing relted to their lower degree of soil omption, nd hene lower sher strength. Trees grown in Amsterdm soil lso hd etter performne in lef physiologil prmeters suh s stomtl ondutne, lef wter potentil, nd folir nutrient sttus. Phenologil oservtions were lso onsistent with the oserved differenes in growth. The lower soil moisture ontent t 2 m depth in Amsterdm soil lso suggested there ws higher infiltrtion rte nd more moisture ville to plnt roots. The enhned growth nd physiologil performne of trees grown in Amsterdm soil ment they provided pek evpotrnspirtionl ooling of up to 7 kw, 5 times higher thn those grown in pvements. 211 Elsevier GmH. All rights reserved. Introdution The omined effet of the urn het islnd nd ongoing limte hnge hs pushed reserhers into investigting nd quntifying the potentil enefit of urn forests s mitigtion nd dpttion tool (MPherson et l., 1997; Gill et l., 27; Jim nd Chen, 29; Shshu-Br et l., 21). Trees ool down the lol urn nopy nd oundry lyer through evpotrnspirtion nd y reduing the het storge of surfe strutures y shding them. Nowk (2) reported energy ost redutions of uildings of t lest 25%, nd s muh s 5% y plnting trees in ourtyrds. Experiments hve shown tht evportion is the dominnt mens y whih trees dissipte the dytime rditive surplus (Oke, 1978), leding to redution in temperture nd energy ost. However, in order to determine how muh ooling urn forests provide, it is ruil to understnd wht ontrols tree growth, nd the onsequenes of plnting trees in different onditions. Corresponding uthor. Tel.: ; fx: E-mil ddresses: mohmmd.rhmn-3@postgrd.mnhester..uk (M.A. Rhmn), jgs1989@hotmil.o.uk (J.G. Smith), pete@redroseforest.o.uk (P. Stringer), rolnd.ennos@mnhester..uk (A.R. Ennos). 1 Tel.: ; fx: Tel.: ; fx: Tel.: ; fx: Aording to reent survey (Britt nd Johnston, 28), the numer of street trees in Englnd is inresing, prtiulrly in residentil nd industril res. However, the hrsh eologil onditions of the urn environment nd the tree plnting tehniques used there ple trees under inresed stress. This ompromises their potentil growth (Roerts et l., 26) nd my redue their effetiveness in ooling. In lrge ity suh s Mnhester, UK, thousnds of vehiles nd pedestrins use the streets every dy whih ffets tree growth in mny wys. Among the limiting ftors re soil omption (Rndrup, 1996; Smiley et l., 26; Brtens et l., 29), soil moisture vilility in the rooting zone (Rhodes nd Stipes, 1999), nutrient defiieny, nd ontmintion y pollutnts (Jim, 1998). All these ftors led to poor growth in urn street trees in omprison to trees in prk or nturl settings (Kjelgren nd Clrk, 1993; Close et l., 1996, 1996; Ikovoglou et l., 21; Leuzinger et l., 21). In UK ities suh s Mnhester, trees re usully plnted using three min estlishment tehniques. In the onventionl method, trees re plnted in 1.5 m 2 ut-out pits in pvement nd topsoil is pled in the top 5 6 m; no mesures re tken to redue susequent soil omption. Another tehnique is to plnt trees in grss verges in etween the pvement nd rod. A more reent tehnique is to plnt trees in struturl soils, whih onsist of vrious mixtures of grvel, snd nd soil. Snd-sed soil, or Amsterdm tree soil (Couenerg, 1994), hs 7 8% snd /$ see front mtter 211 Elsevier GmH. All rights reserved. doi:1.116/j.ufug

2 186 M.A. Rhmn et l. / Urn Forestry & Urn Greening 1 (211) frtion onsisting of medium orse snd with uniform prtile sizes, with dded orgni mtter nd ly (Buhler et l., 27). The effet of these plnting regimes on tree growth nd ooling hs not een widely investigted. Kjelgren nd Clrk (1992) investigted the effet of urn prk, plz, nd nyon spes on the physiology nd growth of even-ged sweet gum (Liquidmr styriflu L.) street trees. Close et l. (1996, 1996) lso ompred the growth nd phenology of sugr mple (Aer shrum Mrshll) trees growing in forest nd in tree lwns on urn streets. They found tht trees growing in prks or forests hd 5% higher growth inrement nd hd doule the stomtl ondutne of trees grown in the streets. Grosky et l. (21) showed tht street trees grown in struturl nd non ompted soils showed lmost twie the shoot nd root extension three yers fter plnting ompred to those grown in the stndrd pvement profiles. The ojetive of this study ws to investigte the impt of urn plnting onditions on the growth nd ooling effetiveness of ommonly plnted street tree, Pyrus lleryn, growing in the UK fter longer period of time (5 6 yers). Methods Site seletion nd P. lleryn trees The study ws rried out over period of 1 months etween Ferury nd Novemer, 21, period hrterised y old winter up to the end of Mrh, dry spring nd erly summer up to the end of June, nd wet summer nd erly utumn up to the end of Septemer. Monthly wether dt from the Met offie ( for the Northwest of Englnd nd North Wles re shown in Tle 1. We investigted 49 individul P. lleryn trees whih met ertin riteri. The riteri required the trees to e growing on n urn street; to e of uniform ge; to hve een growing under the sme onditions for the sme time spn; nd for the initil size nd plnting onditions of the trees to hve een reorded. These riteri were met on five streets, ll of whih were loted ner the Vitori Prk nd Rusholme re of South Mnhester. Within these streets the sites were tegorised into three different growing onditions: trees growing in 1.5 m 2 ut-out pits in pvements, in grss verges, nd in 1.5 m 2 ut-out pits in pvements whih hd een filled with Amsterdm soil. Among the streets, Conynghm Rod ( N, W) hd trees in mixture of grss verges nd pved res. Denison Rod trees ( N, W) were ll growing in pvements. Trees in Kent Rod West ( N, 2 13 W) nd Upper Prk Rod ( N, W) were ll growing in grss verges nd trees in Thornton Rod (53 27 N, W) were growing surrounded y pvements ut in Amsterdm soil. Trees hd een plnted in 24 nd 25 t the ge of 4/5 yers. In totl 15 trees were growing in pved street, 21 in grss verges nd 13 in Amsterdm soil. Trees on pved streets nd Amsterdm soil were plnted in 1.2 m 1.2 m pits nd those on grss verges were growing in long tree lwns long rows of different lengths ut t lest.5 m wy from the edge of the nerest sphlt surfe. All the street trees were in residentil res nd were plnted on the prtition line etween two houses. Plnted trees were t lest 7 1 m prt from eh other. They were plnted either on the grss verges or pvements, next to the ker. Minimum distne to uildings ws 2 m. All the studied trees were free of ny visul dey symptoms, dmge or diek. Tree growth nd phenology The tree height, DBH (Dimeter t Brest Height) nd nopy spred t the time of plnting were ll known. To ompre the growth inrement of trees, the totl height of eh tree, DBH, nd nopy spreds were ll mesured using mesuring tpe in Ferury nd Mrh, 21. Lterl shoot growth ws lso investigted y mesuring five rndomly seleted rnhes from the lower nopy. The shortest distnes etween the lterl growth srs for the previous three yers (27 9) were mesured using 3 m ruler. The lef re index (LAI) ws mesured on My 24, 21 for eh tree using n AuPAR model LP-8 PAR/LAI Ceptometer (Degon Devies, WA). Bud urst; utumn olourtion nd lef fll were reorded ording to Close et l. (1996) t the initition of ud urst, initition of olour hnge, pek olour nd 1% lef fll. Soil sher strength nd moisture ontent To otin the mehnil properties of the soil, the sher strength ws mesured using sher vne tthed to torque meter (model RS ) in Ferury, 21. The vne ws pressed into the soil to depth of 5 mm nd slowly rotted mesuring the sher torque required. This ws done t five different positions in eh exposed tree pit. This gve mesurement of soil sher strength, whih is relted to omption (Zhng et l., 21). Soil moisture ontent ws mesured t two depths on two representtive dys of the eginning of summer nd the end of summer. Soil moisture ontent round the tree ses t depth of 2 m ws mesured using Professionl Soil Moisture Meter Lutron PMS-714 (Digitl Meter, Drwen, Lnshire, UK) on My 2, 21 nd Septemer 21, 21 etween 12: nd 16: h. The verge of two mesurements round eh tree se ws tken. Soil moisture ontent t depth of 8 m ws mesured using soil ugur from 17 rndomly seleted tree ses (5 from Amsterdm soil, 6 from pved streets nd 6 from grss verges) on Septemer, 21. Folir nutrient nlysis Nutrient vilility ws ssessed y investigting folir levels of essentil elements. Lef smples were olleted from the middle of the terminl shoot growth on August 12, 21 ording to Motsr nd Roy (28). Leves were oven dried t 7 C, ground with mortr nd pestle nd sieved with 5- m sieve. Totl N ws determined y dry omustion method using LECO TruSpe TM CN utonlyzer (LECO Corportion). Determintion of other essentil elements viz. P, K, C, Mg, Al, B, Co, Cu, Fe, Mn, Mo, Ni, Se, Zn nd N ws rried out following stndrd proedure using n tomi sorption spetrometer (AAS). Soil nutrient nlysis Nutrient vilility of soils ws ssessed y nlyzing soil ph, orgni ron, totl N, exhngele P, K, C, Mg, Mn nd N. Soil smples were olleted from the top 15 m of the soil ner the tree ses on Mrh 3, 211 nd ir dried t room temperture. Tle 1 Men monthly temperture nd rinfll dt for the Northwest of Englnd nd North Wles etween Ferury nd Novemer, 21. Ferury Mrh April My June July August Septemer Otoer Novemer Men temperture ( C) Men rinfll (mm)

3 M.A. Rhmn et l. / Urn Forestry & Urn Greening 1 (211) Stones, lrge roots nd other orse frgments were removed using 2- m sieve. Soil ph ws determined using ph meter (Mettler Toledo FE2). Orgni ron ontents were determined using the lorimetri method ording to Motsr nd Roy (28). Totl N ws determined y the dry omustion method using LECO TruSpe TM CN utonlyzer (LECO Corportion). Aville P ws ssessed using Bry s method, nd for ville C, Mg, K, N nd Mn, soil smples were extrted using mmonium ette (ph 7) (Motsr nd Roy, 28). Then soil extrtnts were nlyzed using n tomi sorption spetrometer (AAS). Lef physiology Physiologil nd meteorologil mesurements were mde on the trees on wrm, loudless dys My 25, 21, July 28, 21 nd August 27, 21 to investigte the wter sttus nd ooling potentil of the trees. Wter potentil in lef is mesure of tree wter stress. Lef wter potentil ws mesured on those 3 dtes etween 12: nd 16: h on 3 sunlit leves removed from the mid rown of eh tree, using pressure hmer tehnique (Digitl Plnt Wter Potentil Apprtus EL54-3 nd EL54-35, ELE Interntionl, Hertfordshire, UK). Stomtl ondutne is mesure of the regultory ontrol exerted y lef stomt to void wter stress. Mesurements of stomtl ondutne were rried out on the sme dtes etween 12: nd 16: h on 3 sunlit leves from the mid rown of eh tree using the lef porometer (model SC-1, Degon Devies, Wshington, USA). In July nd August, meteorologil mesurements tht would enle us to lulte evpotrnspirtion were lso mde. Air temperture nd reltive humidity were simultneously mesured in the shde, 1.5 m ove the ground using Temperture nd Humidity Dtlogger CEM DT-172 (Digitl meter, Drwen, Lnshire, UK). Lef tempertures were lso reorded using the porometer t the time of mesuring the stomtl ondutne. Atmospheri pressure dt for eh mesurement week were reorded from pulished dt of the Meteorologil sttion, Mnhester Airport, UK. To hek whether there ws ny signifint differene in wind speed mong the streets, wind speed t 1.5 m ove ground ws lso mesured using hnd held digitl nemometer (Omeg digitl nemometer, model HHF92A). The trnspirtion rtes (E, mmol m 2 s 1 ) of leves were then lulted for the two dtes in July nd August from the stomtl ondutne nd meteorologil dt using Fik s lw (Lmers et l., 1998): E = g v totl (e lef e ) P (1) where g v totl is the totl ondutne to wter vpour (mmol m 2 s 1 ), e lef is the vpour pressure inside the lef, whih ws ssumed to e the sturtion vpour pressure t lef temperture, nd e is the vpour pressure of the tmosphere, lulted y multiplying the sturtion vpour pressure t ir temperture y the reltive humidity of the ir. P is tmospheri pressure. From Eq. (1), the trnspirtion rte ws onverted to g m 2 s 1 nd multiplied y the ltent het of vpouriztion whih is 2.45 kj g 1 to lulte the energy loss per unit lef re (W m 2 ). Energy loss per tree ws then lulted ording to Eq. (2): Energy loss per tree = energy loss per unit lef re LAI A (2) where LAI is the lef re index of the tree nd A is the rown re of the tree lulted from its rown dimeter. Sttistil nlysis Dt were sujeted to ANOVA nd Tukey post ho tests using SPSS V 16 softwre. Differenes etween groups were onsidered signifint t p <.5. Results Tree growth nd phenology Trees in Amsterdm soil hd grown lmost twie s fst s those grown on the pvements nd 5% fster thn those grown in grss verges (Fig. 1), nd hd more lyers of leves in their nopy. A one wy ANOVA showed signifint differene etween trees grown in different plnting regimes in height inrement [F(2, 46) = ; p <.1]; in DBH inrement [F(2, 46) = 75.52; p <.1]; in rown dimeter inrement [F(2, 46) = ; p <.1]; nd in LAI [F (2, 45) = ; p <.1]. Post ho nlyses showed signifint differenes etween ll three groups in ll four hrteristis. Trees in Amsterdm soil lso hd higher lterl extension growth over the lst three yers (Fig. 2), though shoot growth hd generlly delined over the three yers. A two wy ANOVA showed signifint differene etween plnting regimes [F(2, 138) = ; p <.1], nd etween the growing yers [F(2, 138) = 9.55; p <.1]; however, no signifint intertion etween yers nd plnting regimes ws found. A post ho nlysis of plnting regimes showed tht the shoot extension of trees grown on Amesterdm soil nd grss verges ws signifintly higher thn tht of the pved streets. It lso showed tht the growth rte ws signfintly lower in 29 1 nd 28 9 ompred to Trees grown in Amsterdm soil nd grss verges roke ud round week erlier, etween 26 nd 28th Mrh, 21, ompred to 6 7th April, 21 in the se of trees grown in pvements (Tle 2). Autumn olour lso egn nerly two weeks lter in Amsterdm soil nd grss verges Otoer 1 versus Septemer 27. Pek olour ourred etween Otoer 14 nd 16 for pved street trees nd etween Otoer 26 nd 3 for grss verges nd Amsterdm soil trees. Soil sher strength nd reltionship with the growth prmeters There were signifint differenes etween the soil sher strength in the three different plnting regimes [F(2, 46) = 2.734; p <.1]. A post ho test showed tht soil sher strength ws signifintly higher in pved streets nd grss verges, more thn doule tht of Amsterdm soil (Fig. 3). Stter plots of DBH inrement nd LAI ginst soil sher strength, showed negtive ssoition (Fig. 4). A regression nlysis showed signifint effet of soil sher strength oth on DBH inrement (R =.574, p <.1) nd on LAI (R =.624, p <.1). Trees grown on less ompted soil showed higher growth nd greter LAI. Soil moisture ontent Soil moisture ontent nlyses showed lower moisture ontent in Amsterdm soil (Fig. 5) ompred to the pved streets nd grss verges soil. A one wy ANOVA showed signifint differene in soil moisture ontent etween the plnting regimes [F(2, 8) = 28.18; p <.1] in the top 2 m t the eginning of the growing seson. At the end of the growing seson there were lso signifint differene etween the plnting regimes [F(2, 14) = 3.679; p.5] in the top 2 m. However, no signifint differene ws found t 8 m.

4 188 M.A. Rhmn et l. / Urn Forestry & Urn Greening 1 (211) Height inrement (m) DBH inrement (m) Crown dimter inrement (m) d Lef re index (LAI) Pvement Grss verges Amsterdm soil Pvement Grss verges Amsterdm soil Fig. 1. Differenes in growth nd morphology of P. lleryn grown on three different plnting regimes. Annul growth inrements (24 1) in () height, () DBH nd () rown dimeter nd (d) LAI of the rown in My 21. Grphs show mens ± stndrd error (n = 15 for pved streets, 21 for grss verges nd 13 for Amsterdm soil). 1 Soil sher strength (kp) Pvement Grss verges Amsterdm soil Fig. 3. Sher strength of soil round P. lleryn trees grown in different plnting regimes. Grphs show mens ± stndrd error (n = 15 for pved streets, 21 for grss verges nd 13 for Amsterdm soil). Fig. 2. Annul lterl shoot extension in the previous three yers (27 9) of P. lleryn grown in different plnting regimes. Grphs show mens ± stndrd error (n = 15 for pved streets, 21 for grss verges nd 13 for Amsterdm soil). Folir nutrient sttus There were differenes in the nutrient sttus of severl elements etween trees grown in the different plnting regimes. Folir N ontent of trees grown on Amsterdm soil nd grss verges ws signifintly higher (Tle 3) thn the trees grown in the pvements [F(2, 15) = 5.553; p <.5]. Totl P ontent of trees grown in the grss verges ws signifintly higher (Tle 3) thn those grown in pvements nd Amsterdm soil [F(2, 15) = 6.227; p <.5]. B, Mn nd N were signifintly higher (Tle 3) in trees grown in Amsterdm soil ompred to those grown in pvements nd grss verges Tle 2 Phenologil oservtions of trees growing in the three different plnting regimes. Phenologil oservtions were rried out etween mid of Mrh, 21 nd mid of Deemer, 21. Growing onditions Bud rek Autumn olour nd lef fll 4th week of Mrh 1st week of April 1st week of Septemer 4th week of Septemer 2nd week of Otoer 4th week of Otoer 1st week of Novemer 3rd week of Novemer 1st week of Deemer Pvements Not strted Strted Autumn olour 1% 25% 45% Pek Lef fll 3% >8% Completed Grss verges Strted >6% Autumn olour 5% 1% 2% 3% Pek Lef fll >7% >95% Amsterdm soils Strted >7% Autumn olour Strted 1% 15% 3% Pek Lef fll >6% >95%

5 M.A. Rhmn et l. / Urn Forestry & Urn Greening 1 (211) y = -.7x R² =.329 DBH inrement (m) Lef re index (LAI) y = -.13x R² = Soil sher strength (kp) Soil sher strength (kp) 12 Fig. 4. Effet of soil sher strength on the growth nd morphology of P. lleryn () dimeter growth nd () LAI inrese. Tle 3 Folir nutrient sttus of tree leves growing in the three different plnting regimes. Leves were olleted on August 12, 21, 12 weeks fter the full loom. Plnting regimes Nutrients Men (%) Men ( g/g) N P K C Mg Al B Co Cu Fe Mn Mo Ni Zn N Pvements Grss verges 2.38 *.17 * Amsterdm soil 2.39 *.12 * * ** ** * Signifint differene t.5 level. ** Signifint differene t.1 level. [F(2, 15) = 4.75; p <.5; F(2, 15) = 6.613; p <.1; F(2, 15) = 8.325; p <.1]. Soil nutrient sttus There were signifint differenes in soil nutrient vilility in three different plnting regimes. Orgni ron nd totl nitrogen ontent of soils in the grss verges were signifintly higher (Tle 4) thn those in the pvements nd Amsterdm soil [F(2, 16) = ; p <.1; F(2, 16) = ; p <.1]. Aville C nd Mg ontent ws signifintly lower in Amsterdm soil (Tle 4) [F(2, 17) = ; p <.1; [F(2, 17) = ; p <.1]. Aville K ws signifintly higher in grss verges ompred to those in pvements nd Amsterdm soil [F(2, 17) = ; p <.1]. Lef physiology Middy lef wter potentils of trees grown in Amsterdm soil were less negtive ompred to the trees grown in pvements nd grss verges (Fig. 6). One wy ANOVA nd post ho tests showed signifint differene etween the lef wter potentil of trees in My [F(2, 144) = 27.62; p <.1] nd in August [F(2, 144) = 61.1; p <.1], with the lef wter potentil of trees grown in Amsterdm soil eing less negtive thn tht of other streets. Stomtl ondutne of trees growing in ll three onditions ws lower in the dry My, thn in the wetter months of July nd August. However, on ll three dtes, trees in Amsterdm soil hd stomtl ondutne lmost twie tht of those grown in the pvements nd 5% higher thn those grown in grss verges (Fig. 6). One wy ANOVA s showed signifint differene in My [F(2, 144) = ; p <.1]; July [F(2, 144) = ; p <.1] nd in August [F(2, 144) = 17.92; p <.1]. Post ho tests showed tht the stomtl ondutne of trees grown on Amsterdm soil ws higher thn those grown in grss verges nd pvements t ll the three times mesured nd the stomtl ondutne of trees grown in grss verges ws higher thn those grown in pvements in My nd August. Fig. 5. Soil moisture ontent in the top 2 m nd t 8 m depth round the ses of P. lleryn trees grown in different plnting regimes. Grphs show mens ± stndrd error (n = 15 for pved streets, 21 for grss verges nd 13 for Amsterdm soil for 2 m depth nd n = 6, 6 nd 5 respetively for 8 m depth). Evpotrnspirtionl ooling The omintion of their lrger nopy size, higher lef re index, nd higher stomtl ondutivity, ment tht the trees grown in Amsterdm soil hd on verge five times the rte of estimted trnspirtion wter loss nd ooling thn trees grown in pvement, nd lmost twie tht of trees grown in grss verges (Fig. 7). One wy ANOVA tests showed signifint differenes in energy loss from trees grown in different plnting regimes oth in July nd August [F(2, 46) = 25.73; p <.1 nd F(2, 45) = 57.41; p <.1]. Post ho nlyses showed tht the energy loss from trees grown on Amsterdm soil ws signifintly higher thn trees grown in pvements nd grss verges oth in July nd August. Wter losses were slightly higher in August thn July for ll trees euse of the lower reltive humidity on the streets on the dys of mesurements in August thn July. However, on oth the dtes there were no signifint vritions in the wind speed t 1.5 m height mong the streets. This shows tht the higher trnspirtion rtes of trees grown in the Amsterdm soil were not used y differenes in wind speed.

6 19 M.A. Rhmn et l. / Urn Forestry & Urn Greening 1 (211) Tle 4 Nutrient sttus of the three growth medi. ph Orgni C (%) Totl N (%) P ( g/g) N ( g/g) Mn ( g/g) C ( g/g) Mg ( g/g) K ( g/g) Pvements ** 2.4 ** 5.2 Grss verges **.25 ** ** 4. ** 8.7 ** Amsterdm soil ** Signifint differene t.1 level. Fig. 6. Lef physiologil prmeters of P. lleryn trees grown in different plnting regimes t three different times of the yer (My, July nd August, 21): () middy lef wter potentil; () stomtl ondutne. Grphs show mens ± stndrd error (n = 15 for pved streets, 21 for grss verges nd 13 for Amsterdm soil). Fig. 7. Evpotrnspirtionl ooling lulted for P. lleryn trees growing in three different plnting regimes (n = 15 for pved streets, 21 for grss verges nd 13 for Amsterdm soil). Disussion The results showed lrge differenes in oth the growth rtes nd wter reltions of trees grown in the three different onditions. Trees in Amsterdm soil grew twie s fst s trees in pvements nd 1.5 times s fst s trees in grss verges. They were lso under less wter stress in summer thn those in pvements nd grss verges. This ws proly euse of the different soil sher strengths, whih indites different levels of omption. Zhng et l. (21) hve shown using the Mohr-Couloms eqution tht ulk density nd soil pore wter pressure re the signifint determinnts of soil sher strength; the higher the soil ulk density, the higher the soil sher strength. The sher strength of Amsterdm soil ws less thn hlf of tht found in pvements nd grss verges, nd oth the dimeter growth inrement nd lef re index of trees were inversely relted to soil sher strength. These results re similr to those found in North Ameri y severl other uthors (Froehlih et l., 1986; Close et l., 1996; Grosky et l., 21; Ikovoglou et l., 21; Smiley et l., 26). They lso found tht urn trees hd redued investment in folige prodution in response to urn stresses nd this resulted in sustntil deline in rown spred, terminl shoot extension nd LAI (Ripullone et l., 29; Tognetti et l., 29). Our trees grown in the pvements nd grss verges proly hd diffiulty foring their roots through the strong, ompted soils. Urn soil omption usully ours in the shllow lens of soil tht would e the tree s preferred rooting zone. For this reson, omption of top soil ontriutes to insuffiient rooting volumes through inresing the soil strength, usully to levels whih hinder root growth (Grosky nd Bssuk, 1995; Rhodes nd Stipes, 1999). The diffiulty in root penetrtion in pvements nd grss verges proly ffeted the wter nd nutrient uptke of the trees. Results of soil moisture ontent suggested tht Amsterdm soil hd signifintly lower moisture ontent t 2 m, though not t 8 m. This most likely reflets higher infiltrtion rte down through the soil, nd fster removl of the wter y the roots in Amsterdm soil. The signifintly higher nutrient sttus of the leves in the trees grown on Amsterdm soil lso suggests tht their roots hd etter wter nd nutrient uptke. Severl other studies hve lso desried the effet of pvements nd omption on plnt ville moisture (Close et l., 1996, 1996; Gomez et l., 22; Grosky et l., 29) nd nutrient uptke (Smiley et l., 1985; Close et l., 1996) during the summer. Finlly, the etter ess of trees in Amsterdm soil to wter is lso evident from the less negtive lef wter potentil of their leves, t ll times exept in the wet July. The high degree of grss roots nd grsses in the topsoil of grss verges plnting regime might inrese the orgni ron with onomitnt totl N vlues. Exhngele P ws low in ll three growing onditions s P is nturlly ville in very smll quntities in soil solutions. Only.1% or less of the totl phosphorus in soils is ville to plnts (vn Strten, 27). Exhngele C, Mg nd K were signifintly higher in the topsoil of grss verges nd pved streets, so, there is possiility of exessive nutrient lehing from Amsterdm soil. However, folir nutrient sttus did not indite ny signifint defiieny of mronutrients in the se of the trees grown in Amsterdm soil. This might e due to the more fvourle rooting onditions for the trees grown in Amsterdm soil. This is further linked with the higher onentrtion of N nd Mn in the leves of trees grown in Amsterdm soil, wheres no

7 M.A. Rhmn et l. / Urn Forestry & Urn Greening 1 (211) signifint differenes in N nd Mn onentrtions were found in the soil. It lso implies higher vilility of nutrients for the trees grown in Amsterdm soil. All these ftors resulted in very different lef performne in the three plnting regimes. Stomtl ontrol seemed to e the most importnt step to respond to drought in the dry month of My, s losing stomt would redue the rte of wter loss nd so minimize wter stress. All the trees showed onservtive wter use in My ut with higher rinfll in July nd August stomtl ondutne inresed signifintly in ll the trees. The stomtl ondutne of trees grown on Amsterdm soil ws muh higher ompred to the other trees, however, showing tht they would hve greter wter loss per unit lef re nd onsequently higher rte of photosynthesis. Their longer-lsting leves nd erlier udding proly lso helped the trees grown in Amsterdm soil to hieve their higher growth rte. These results re lso in ordne with those of other uthors who relted physiologil performne to soil omption (Tognetti et l., 29; Zhrh nd Rzi, 29). The omintion of the fster growth, more highly lyered nopy, nd etter performne per unit lef re of the trees grown in Amsterdm soil, ment tht they evpotrnspired nd provided ooling t five times the rte of the trees grown in pvements. Wheres one tree grown in Amsterdm soil n provide out 7 kw of ooling in August, nd 5.7 kw in July, in grss verges the figure is 3 nd 2 kw in August nd July respetively, nd in pvements it is only 1.4 nd 1 kw. Considering tht the ooling pities of room ir onditioners rnge from 1 to 1 kilowtts, the performne of these smll trees is impressive, though the energy loss per tree ws lulted sed on the trnspirtion rte of sunlit leves. Sine mny of the leves would hve een shded y the outer leves in the nopy, energy loss per tree would proly hve een overestimted. Further reserh, exmining the wter loss of street trees using weighing tehniques (Montgue et l., 24) or sp flow guges (Ptki et l., 211) would help to determine the preise rte of wter loss. Averge evpotrnspirtionl energy loss per unit lef re from the trees grown in Amsterdm soil ws 284 W m 2 in July nd 335 W m 2 in August. If we multiply those results y the verge LAI of the trees grown in Amsterdm soil we get trnspirtionl losses per unit rown re of 943 nd 115 W m 2. These figures for ooling re extremely high. Using the Penmn-Monteith eqution nd the meteorologil dt for the middle of typil July dy in Mnhester, one would lulte pek energy loss per unit re of 315 W m 2 for n dequtely wtered referene rop (ET ) (Allen et l., 1998). Our trees were therefore 3 times s effetive. The reson our trees provided so muh more ooling thn pth of vegetted lnd, might e euse trnsport of hot ir msses ove flt, dry surfes would hve used high dvetive trnspirtion, just s wshing on line dries out fster thn wshing lid out on the ground. Our vlues were lso onsiderly higher thn the verge diurnl summer evpotrnspirtionl energy loss of well irrigted urn forest, mesured using n eddy orreltion pproh round 225 W m 2 reported y (Grimmond nd Oke, 1999) in Chigo, USA. This suggests tht lrge stnds of trees would e muh less effetive t providing ooling, per unit rown re, thn single trees, euse they would hve muh lower dvetive wter losses. In onlusion, trees grown in Amsterdm soil performed etter in mny wys thn trees grown in grss verges nd espeilly those grown in pvements. They grew fster, developed wider rown with more lef lyers, nd showed etter lef physiologil performne. As result they provided round five times the evpotrnspirtionl ooling ompred with trees plnted diretly into 1.5 m 2 ut-out pits in pvements. Kjelgren nd Montgue (1998) showed tht P. lleryn trnspire 3% more wter when growing in sphlt ut-outs thn surrounded y turf. Our trees, plnted in the Amsterdm soils were lso growing in 1.5 m 2 ut-out pits in pvements ut, hving een plnted in etter growing medium, they grew etter nd ould even withstnd short dry spells. This growing method ould prove useful for produing trees tht provide the ooling tht the ities of the future would need even more s onsequene of future limte hnge. There were, however, some inditions tht the dvntges of the Amsterdm soil might hve een diminishing. A redution in terminl shoot growth ws pprent over the lst three yers. Sine ll the other trees lso hd redued terminl shoot growth, however, this might hve een due to differenes in the wether etween the yers. In support of this ide, the trees in the Amsterdm soil were still showing etter physiologil performne in 21. It should e worthwhile monitoring to see if the improved performne in Amsterdm soil persists over longer period of time. Aknowledgments This projet ws supported y dotorl grnt funded y the Sustinle Consumption Institute (SCI), University of Mnhester nd the Europen Union INTERREG IVB fund s prt of the VALUE projet. Thnks re due to Red Rose Forest for providing the initil growth dt nd to Dr. Giles Johnson nd Dr. Andrew Peter Den for their ordil help during the experiment. Speil thnks to Mr. Smuel Prtey nd Mr. Dvid Armson for ll their help. The uthors lso ppreite the nonymous reviewers for their ttentive reviews nd relevnt suggestions for improving this mnusript. Referenes Allen, G.R., Pereir, S.L., Res, D., Smith, M., Crop Evpotrnspirtion Guidelines for Computing Crop Wter Requirements FAO Irrigtion nd Dringe Pper 56. FAO, Rome. 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