Shade+trees+

Shade(trees(can(be(planted(around(buildings,(providing(shade(to(keep(buildings(and(surrounding( areas( (such( as( carparks( and( pavements)( cooler( as( well( as( increasing( the( scenic( amenity( for( workers((for(commercial(buildings,(via(windows)(and(the(general(public(in(viewing(the(building.((

Potential)to)reduce)building)energy)demand)

Akbari((2002)(described(direct,(and(indirect(mechanisms(by(which(shade(trees(reduce(energy( demand(for(cooling.(Direct(shading(of(the(building(reduces(heat(gain(by:((1)(reducing(heat(gain( from(solar(radiation,(and((2)(reducing(radiant(heat(gain(due(to(diffuse,(reflected(light(from(the( surrounding(area.(Indirect(mechanisms(include:((3)(evapotranspiration,(which(reduces(ambient( temperatures.( Some( other( aspects( may( have( the( potential( to( increase! cooling( energy( demand( including:( (4)( providing( a( windbreak( to( reduce( the( amount( of( outside( air( which( penetrates( buildings( (this( can( either( increase( or( decrease( cooling( requirements( depending( on( the( design( and( construction( of( the( building,( and( may( reduce( heating( requirements),( and( (5)( (in( some( instances)( increasing( the( latent( airEconditioning( load( by( adding( moisture( to( the( air( through( evapotranspiration.( Overall,( Akbari( found( tree( plantings( have( the( potential( to( reduce( peak( electricity(demand(by(between(5(and(10(per(cent(in(the(United(States,(saving(several(billion(US( dollars(each(year((Akbari,(2002).(

Experiments( with( residential( shade( trees( in( California( homes( found( that( eight( large( and( eight( small(shade(trees(could(reduce(cooling(energy(use(by(30(per(cent,(or(around(4KWh(per(day,(with( peak( energy( savings( of( 0.7kW( (Akbari,( Kurn,( Bretz,( &( Hanford,( 1997).( In( Florida,( a( similar( experiment( using( a( mobile( trailer( revealed( reductions( in( air( conditioning( electricity( consumption(of(50(per(cent((Akbari,(2002).(There(is(a(significant(difference(in(building(heating( and(cooling(benefits(depending(on(the(side(of(the(building(being(shaded((Akbari,(2002),(varying( between( latitudes( and( the( sun( path.( Studies( in( the( US( found( maximum( surface( temperature( reductions(of(11E25o_{C(for(the(walls(and(roofs(at(two(buildings(that(were(shaded(by(trees((Akbari,(}

et(al.,(1997).(

Other( studies( have( investigated( the( impact( of( trees( on( reducing( winter( heating( requirements( through(lowering(ambient(wind(speeds.(Simulations(based(on(findings(of(the(impact(of(trees(on( reducing(ambient(wind(find(that(a(30(per(cent(uniform(increase(in(urban(tree(cover(can(reduce( urban(winter(heating(bills(by(approximately(10(per(cent,(and(rural(heating(bills(by(20(per(cent( (Akbari,(2002).(Akbari((2002)(estimated(that(if(the(same(trees(were(strategically(planted(on(the( north(side(of(buildings((in(the(northern(hemisphere),(the(energy(savings(in(urban(areas(would( be(almost(doubled((20(per(cent(reductions).( Potential)to)mitigate)the)urban)heat)island)effect) Trees(mitigate(the(UHI(effect(by(shading(surfaces(to(prevent(absorption(of(radiant(energy,(and,( by( converting( incident( solar( irradiation( into( latent( heat( of( vaporisation( through( evapotranspiration.( Evapotranspiration( accounts( for( around( 75( per( cent( of( the( cooling( effect( from( a( tree( canopy,( which( overall( is( estimated( to( reduce( building( energy( consumption( by(

around( 30( per( cent( (McBride,( 2007).( Dixon( and( Wolf( (2007)( found( that( tree( plantings( are( amongst(the(most(costEeffective(UHI(mitigation(methods,(reducing(air(temperatures(by(2(to(4o_C(

in(some(observed(cases.(On(average,(air(temperatures(are(reduced(by(1o_{C(for(every(10(per(cent(}

increase(in(canopy(cover.((

Taha,(Konopacki,(and(Gabersek((1996)(found(that(large(scale(tree(planting(in(10(US(metropolitan( areas( resulted( in( average( cooling( of( 0.3E1.0o_{C( at( 2:00pm,( and( by( up( to( 3.0}o_{C( is( some( areas.(}

Furthermore,(the(tree(plantings(produced(annual(energy(savings(of(between(US$10E35(for(each( 100m2(_{of( roof( area( in( residential( and( commercial( buildings.( Factors( that( affect( the( cooling(}

capacity(of(trees(include(the(tree(location,(size,(canopy(coverage,(planting(density(and(irrigation( (Coutts,(et(al.,(2013).(

Potential)to)mitigate)climate)change)

Urban( trees( can( sequester( carbon( in( their( biomass,( and( can( reduce( carbon( emissions( by( reducing( ambient( and( internal( building( temperatures.( Trees( and( vegetation( fix( carbon( during( the(process(of(photosynthesis(and(store(excess(carbon(in(biomass.(As(trees(and(vegetation(die,( carbon(is(released(at(varying(rates(depending(on(the(process(of(removal(and(decomposition.(

Nowak(and(Crane((2002)(found(that(although(an(urban(area(with(trees(stored(less(carbon(per( land(area(than(a(forested(area(due(to(lower(tree(density,(individual(urban(trees(tended(to(store( four(times(more(carbon(than(a(forest(tree(due(to(a(more(open(urban(structure,(resulting(in(larger( tree( diameters.( Research( also( indicates( that( larger( trees( sequester( more( carbon( than( smaller( trees.( Nowak( (1993)( suggested( this( can( be( as( high( as( 1000( times( more,( while( Frelich( (1992)( estimated(that(on(average(a(tree(will(sequester(4.5kg(of(carbon(per(year(up(to(a(crown(of(50m2_,(

and(11kg(per(year(when(the(tree(has(a(crown(over(50m2_{.(Nowak((1994)(found(that(on(average(}

(from( 10( different( tree( north( American( species)( an( individual( tree( with( a( diameter( at( breast( height((dbh)(of(less(than(8cm(stored(3kg(of(carbon,(whilst(a(tree(with(76cm(dbh(stored(3100kg.( Trees(sequestered(on(average(1.0kg/year(of(carbon(for(a(dbh(of(less(than(8cm,(up(to(93kg/year( for(a(tree(with(a(dbh(greater(than76cm.((

Rosenfeld,(Akbari,(Romm,(and(Pomerantz((1998)(attempted(to(quantify(the(role(that(urban(trees( play( in( reducing( greenhouse( gas( emissions( due( to( lower( ambient( and( internal( building( temperatures,( finding( that( one( urban( shade( tree( in( Los( Angeles( can( avoid( the( combustion( of( approximately( 18kg( of( carbon( while( sequestering( a( further( 4.5E11kg( of( carbon( annually,( providing(between(3(and(5(times(the(greenhouse(gas(reduction(benefits(of(a(similar(forest(tree.(

Potential)to)improve)water)cycle)management)

Trees(assist(in(managing(the(water(cycle(by(intercepting(rainfall,(assisting(in(the(infiltration(of( some(and(slowing(the(remaining(runoff.(Trees(also(draw(moisture(from(the(soil(in(between(rain( events,( increasing( the( soil( water( storage( potential( (Stovin,( Jorgensen,( &( Clayden,( 2008).( This( allows( for( greater( precipitation( of( particulate( matter,( reduces( the( extent( and( expense( of( flood( control( and( mitigation( measures( needed( in( urban( areas,( and( protects( receiving( waterways( (Brack,( 2002).( Bartens,( Day,( Harris,( Dove,( and( Wynn( (2008)( found( that( tree( roots( increased( stormwater( infiltration( by( an( average( of( 153( per( cent( in( compacted( urban( soils.( Xiao,( McPherson,( Simpson,( and( Ustin( (1998)( found( that( the( urban( forest( canopy( intercepted( on( average(11.1(per(cent(of(precipitation,(with(the(greatest(benefits(occurring(for(trees(with(larger( leaves( –( such( as( the( large,( broadleaf( evergreens.( Their( study( found( that( the( role( of( the( urban( forest( in( intercepting( rainfall( gave( the( greatest( benefit( during( small( storms,( which( are( responsible( for( the( majority( of( the( issues( with( pollution( washout.( They( conclude( that( trees( in( urban( areas( give( the( most( benefit( in( protecting( receiving( waterways( from( pollution( and( the( impact(of(small,(frequent(rain(events(than(from(large(and(infrequent(flood(events.(

Potential)to)improve)air)quality)

Air( quality( is( improved( by( trees( (and( vegetation( more( generally)( by( absorbing( gaseous( pollutants( through( leaf( stomata,( binding( water( soluble( pollutants( onto( moist( leaf( surfaces,( intercepting( particulate( matter( on( leaf( surfaces,( and( reducing( ozone( formation( via( reduced( urban(temperatures(and(absorption(of(ozone((McPherson,(Scott,(&(Simpson,(1998).(In(Modesto,( California,(annual(airEpollutant(uptake(of(the(city’s(urban(forest(was(estimated(to(be(154(metric( tonnes( (1.68kg/tree),( which( equated( to( an( implied( value( of( US$1.48( million( ($16/tree).( The( value( of( improved( air( quality( was( estimated( using( transaction( costs( to( reflect( average( market( value( of( pollutant( emission( credits,( using( data( from( 1994( through( 1997( for( the( San( Joaquin( Valley(Unified(Air(Pollution(Control(Management(District(of(the(amount(that(corporations(were( willing(to(pay(for(a(credit(to(emit(air(pollutants.(_{This(is(compared(to(a(total(annual(budget(for(}

managing/planting( the( urban( forest( US$2.6( million( in( 1997E1998,( equivalent( to( US$14.36/resident,(US$28.77/tree,(including(sidewalk(and(curb(repair,(leaf(cleanEup,(and(claims( (McPherson,(Simpson,(Peper,(&(Xiao,(1999).((

McPherson,(et(al.((1998)(also(estimated(the(value(improved(air(quality(due(to(residential(yard( trees( in( Sacramento,( California.( This( included( the( direct( absorption( of( ozone( and( other( air( pollutants;( reduced( ozone( formation( due( to( lower( UHI( effect;( and( reduced( CO2,( SO2( and( NOx(

emissions( from( power( plants( resulting( from( reduced( residential( electricity( consumption( (by( keeping( the( house( naturally( cooler).( Average( annual( benefit( of( US$895( per( 100( trees( planted(

was(found,(with(the(cost(of(the(additional(release(of(biogenic(hydrocarbons((or(biogenic(volatile( organic( compounds,( BVOC)( US$512,( giving( a( net( pollutant( uptake( benefit( of( US$383( per( 100( trees.(Tree(species(selection(was(important,(as(some(species(release(more(BVOCs(than(others,( and(with(low(BVOC(species(giving(greater(benefits.(The(study(noted(the(difficulty(in(estimating( such(benefits(using(models,(with(the(number(of(variables(that(affect(the(outcome.(A(study(of(five( US(cities(found(that(the(average(US$13–(65(spent(annually(per(tree(was(recouped(with(benefits( of( US$31( to( $89( per( tree( (a( return( on( investment( of( US$1.37( E( $3.09( per( dollar( invested).( Air( quality(benefits((combined(with(CO2(reduction(benefits)(accounted(for(between($1(and($2/tree( of(this((McPherson,(Simpson,(Peper,(Maco,(&(Xiao,(2005).(( Potential)to)increase)urban)biodiversity) Overall(biodiversity(in(cities(can(be(high((Alvey,(2006).(In(Guangzhou(City,(China(higher(diversity( in(tree(species(was(found(in(the(city(than(in(the(degraded,(surrounding(forests((Jim(&(Liu,(2001);( and(in(Christchurch,(New(Zealand(higher(floral(diversity(was(found(than(in(surrounding(areas.( Throughout( Europe,( higher( plant,( mammal,( and( reptile( and( amphibian( species( were( found( in( areas(with(higher(human(populations((Araújo,(2003).(This(may(be(due(to(areas(that(are(suitable( for( human( settlement( also( being( suited( for( a( greater( number( of( other( species,( or( to( human( activities(increasing(the(diversity(of(species(living(there((Araújo,(2003).(These(studies(generally( do(not(specifically(consider(trees,(however(they(do(highlight(the(significant(potential(of(urban( areas(to(support(biodiversity,(and(critical(importance(of(this(as(surrounding(landscapes(become( degraded.(The(issue(of(“biotic(homogenisation”(is(of(concern,(however,(whereby(certain(species( become( dominant( in( urban( areas( globally( due( to( human( preferences( and( these( species( being( well(adapted(to(urban(conditions,(thereby(decreasing(global(biodiversity(despite(increases(at(a( local(level((Alvey,(2006).(

Potential)to)enhance)property)values)

A(study(in(Athens,(Georgia,(found(that(a(large(tree(in(the(frontEyard(of(a(property(was(associated( with( a( 0.88( per( cent( increase( in( home( resale( value( (Anderson( and( Cordell,( cited( in( Maco( &( McPherson,(2003).(Dombrow,(Rodriguez,(and(Sirmans((2000)(found(that(the(presence(of(mature( trees(on(a(parcel(of(land(increased(the(home(sale(price(for(singleEfamily,(detached(homes(by(2( per(cent.((

Considerations)for)use)

E Species!selection:! The( ability( of( trees( to( withstand( harsh( conditions( often( present( in( urban( areas( in( Australia,( such( as( drought( and( high( temperatures,( differs( between( species.( Some( species(may(reduce(transpiration,(loose(foliage(and(die(under(such(conditions,(resulting(in( the( loss( of( necessary( benefits( (such( as( cooling( during( heat( waves),( and( may( potentially(

require(replacement.(There(is,(however,(as(yet(very(little(data(on(the(physiological(controls( and( responses( of( tree( species( to( various( climatic( conditions( in( Australian( urban( environments((Coutts,(et(al.,(2013).(

E Potential!to!increase!ozone!concentrations:(Whilst(trees(can(reduce(ozone(production(rates,( and( reduce( levels( of( many( air( pollutants,( some( species( can( also( emit( volatile( organic( compounds( (VOC)( including( ozone.( These( biogenic( emissions( are( partly( temperature( dependent(and(vary(between(species,(and(are(also(affected(by(sunlight(and(humidity((United( States(Environmental(Protection(Agency,(2008).(Trees(can(be(selected(based(on(their(ozone( forming(potential(and(VOC(emissions(to(minimise(this(effect.(

E Fire!risk:( Trees( and( vegetation( around( buildings( can( increase( fire( risk.( Predictions( for( the( impacts( of( climate( change( in( Australian( city( are( that( the( fire( risk( may( increase( (Victorian( Bushfires( Royal( Commission,( 2009),( and( thus( measures( need( to( be( taken( to( ensure( that( shade(trees(do(not(increase(this(risk.(Mitigation(measures( include(selecting(less(fireEprone( species,( and( siting( these( to( reduce( the( likelihood( of( fire( transmission( (United( States( Environmental(Protection(Agency,(2008).(₍

E Maintenance:( Urban( trees( require( regular( maintenance( to( protect( overhead( and( underground(infrastructure,(and(to(minimise(the(potential(for(damage(during(storms.(Tree( risk(management(protocols,(such(as(those(developed(in(the(US,(can(outline(best(practice(and( inform( homeowners( about( their( own( tree( maintenance( procedures( (Pokorny( &( Albers,( 2003).(Urban(trees(can(cause(leaf(litter(issues(and(air(pollution(can(result(from(maintenance( activities((Silvera(Seamans,(2013).(

E Public! health! and! safety! concerns:( Urban( trees( may( exacerbate( allergies( if( they( produce( certain( pollens( (Silvera( Seamans,( 2013).( Concern( is( expressed( at( times( by( residents( that( trees( can( be( safety( risk( due( to( providing( cover( for( potential( robbers( or( attackers( (Silvera( Seamans,(2013).( E Water!requirements:(Urban(tree(plantings(can(lead(to(significant(irrigation(requirements(and( costs(in(semiEarid(cities((Silvera(Seamans,(2013).(Periods(of(lowErainfall(and(drought(occur( periodically(under(Australian(climatic(conditions,(which(can(compromise(the(ability(of(trees( to(be(irrigated.(As(was(experienced(in(Melbourne(during(the(Millennium(Drought,(this(can( severely(compromise(tree(health.(The(careful(selection(of(species(to(be(resilient(to(lowEwater( conditions,(as(well(as(consideration(of(alternative(water(sources(is(essential(to(ensure(that( street( trees( and( other( urban( vegetation( are( part( of( a( holistic( response( to( urban( climate( resilience((Coutts,(et(al.,(2013).(