Trees for Street and Highway

Beautification

by W. W. WebsterFormer Director of Parks, Krugersdorp.

INTRODUcnONWith the turn of the century, seventy

years ago, came an upsurge of interestin street tree planting throughoutSouth Africa, particularly in the largertowns and cities along the reef and inPretoria. On the Highveld some veryuseful experimental work with exotictrees around this period soon revealedthe shortcomings of certain Europeanspecies under local climatic conditions.Among these were Fagus sylvaticapurpurea (Copper Beech) and Acerpseudo-platanus (Sycamore), whichfound conditions rather trying. On theother hand, many European and Ameri­can trees, particularly decidious species,proved to be valuable acquisitions whenintroduced to parks, private estates andtown gardens. Nevertheless their quali­ties as trees for the town and city side­walk had still to be assessed, and thiscould only be done by trial and error,i.e. by actually planting them on side­walks where the rigours of weather andsoil conditions would prove theirsuitability or otherwise. These experi­ments were carried out with varyingdegrees of success in the many townsand few cities that existed half a centuryor more ago on the Transvaal Highveld,and have resulted in some of the magni­ficent avenues of trees that grace somany streets today.

As was to be expected, a number ofthe kinds used in the early days provedto be unsatisfactory for a variety ofreasons: some did not thrive at all;others became too large for any butvery wide street reserves where the side­walks were correspondingly broad;some were brittle, their branches beingliable to crack and break off over thecarriageways or sidewalks, constitutinga danger to life and limb - especiallyduring high wind and rainstorms;others still were subject to insect attackand disease, rendering their mainten­ance along miles of sidewalks expensiveto an extent that became prohibitive inthe long run.

The rather lengthy process of estab­lishing trees and tending them over aperiod of perhaps a decade or two hadto be embarked upon before a decisioncould be taken as to whether or not theywere suitable for street and arterialroadway beautification. Thus work hadto be tackled on a long term basis,regardless of the vagaries of the weather- especially the occurrence of severedroughts. Although many of the speciesplanted fifty years ago were com­paratively fast-growing, it neverthelesstook half a lifetime before they could bedemonstrated not to become too largefor planting on a sidewalk of averagewidth. Some of the loveliest avenues of

Platanus acerifolia (London Plane)have, of dire necessity, had to bepollarded and otherwise severelyprunedto allow the passage of double-deckerbuses, pantechnicons and other hugevehicles along our streets.

Considering the complete absence ofdata at the beginning of the experiments,surprisingly few mistakes were made.Were it not so, the present lovelyavenues that adorn so many streets inour cities and towns would not havestood the test of time and the severityof public opinion and criticism.

Over the years, the pooling of practi­cal experience by many horticulturistsin this field has furnished the professionwith a tremendous fund of informationwhichwith the rapid development of ourtowns, cities, freeways and arterial roads,will prove invaluable. The future beauti­fication of what our American counter­part calls a "parkway" (i.e. a highwaywith surroundings reminiscent of apark) will demand knowledge and skillof a very high order if the mistakes ofthe past - however fewthey fortunatelywere - are not to be repeated on amuch larger scale in the future. It isobvious that larger trees can be plantedalong highways than in city streets,where the smaller subjects will be moresuitable.

Careful experimentation with a wide

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variety of species has provided us withvery extensive data which, unless pre­served in permanent form, may be lostto future generations with the passingof the veteran horticulturists of thisregion. With this in mind, I shallattempt to place on record whatknowledge I have gleaned from themagnificent work of my professional"elders" and from my personal observa­tions and practical experience over morethan forty years on the Reef.

REQUIREMENTSIt is debatable whether or not the

ideal tree for planting on sidewalks incities and towns has yet emerged or islikely to emerge in the future when oneconsiders what qualities such a treemust or must not have before it can beconsidered suitable for the prupose.

A tree must (1) be sufficiently largeand leafy to afford shade in summer;(2) be free from insect pests, especiallycaterpillars; (3) retain its foliage through­out the year or shed it rapidly in theautumn to minimize nuisance to house­holders; (4) produce a straight trunk forappearance sake, stand severe tests ofdrought, cold and storm; (5) thrive onpoor soil for the most part; and (6) belong-lived.

A tree must not: (1) be so large as todarken the street by obscuring streetlights; (2) be so large as to shadewindows unduly in winter; (3) haveroots that interfere with gardens, crackgarden walls and lift up sidewalkpaving or asphalt in streets; (4) grow solarge as to interfere with overheadelectricity and telephone lines (alter­natively, if pruning is resorted to, itmust not grow rapidly enough torequire frequent attention, which isexpensive); (5) be so brittle thattraffic or electricity and telephone linesare endangered during storms by break­ing branches; (6) deposit on sidewalksflowers, fruits, pods, or any juicysubstance that may cause pedestrians toslip; and (7) refuse to grow in sand­stone, shale, gravel, clay or quartz whenencountered.

It is well to remember that a tree is athing ofbeauty and not just a thing that

stands in the way of a motor vehicleout of control.

FUNCTIONSIn the 17th century during the reign

of Louis XIV, the practice of plantingtrees along streets and boulevards wasintroduced in France and elsewhere inEurope. Today trees along our streetsenliven and embellish the otherwise dulland dreary jungle of concrete structures,and aleDJ our highways they break themonotony of many a weary milethrough the featureless plains, lendingan atmosphere of serenity and beauty.In our towns they provide a sanctuaryfor birds, heralding the spring, makinglovely the summer scene and colouringthe autumn with gold and amber shades.They break the force of wind, conditionthe air we breathe, shade us from theburning noontide heat and relieve inmany ways the burden of our days. Asabsorbers of poisonous fumes ladenwith carbon dioxide, they perform apublic service. The capital city ofAustralia boasts a tree population offour million. These trees beautify themetropolis by their presence withoutunduly interfering with the life andeconomy of the inhabitants.

Street trees lend character to a cityor town, linking the streets to the privategardens, public parks and open spaces,and aesthetically blending them withthe landscape generally. As manyvarieties as possible should be plantedon the streets of any city or town,having due regard to climatic and soilconditions. Open spaces along streetsand boulevards should be planted witha variety of distinctive trees to intro­duce as much colour as possible in leaf,flower and berries.

Street trees may be used to conceal abuilding partially or entirely from viewand to accentuate its architecturalfeatures. They may also serve to framea view of the landscape either at closequarters or at a greater distance, asdesired.

As time goes on and increasedresearch reveals the value of ourindigenous trees for street plantingmore use will be made of some of the

more promising subjects, such as Com­bretum spp., Schotia spp., Rhus spp.,Zizyphus spp., Dombeya spp. andOlea spp.

SPECIES USEDWe now proceed to examine the

species already tried and note their meritsand demerits, individually, as learnedfrom practical experience on the Reef.

Evergreen species are denoted by (E)and deciduous by (D).

1. Eucalyptus spp. (E)Many frost hardy species grow in

almost any soil but are most unsuitableas street trees for the following reasons:they are too large and of rapid growth;roots are troublesome in gardens andunderpavements and roads; they re­quire pruning too often when situatedunder electricity and telephone lines.

2. Pinus radiata (syn. P. insignis) (E)Makes an excellent street tree up to

about the twentieth year. Grows rapidly,requires - but dislikes - considerablepruning under lines, always looks welland thrives in most soils. Later be­comes too big, darkens streets, shadeshouses, ruins gardens, pavements andasphalt roads. Because of its size, iscostly to prune, but suitable for arterialroads and parkways.

3. Pinus pinaster (E)Thrives in stoniest ground, withstands

drought. Does not grow too rapidly ortop large but lurches when youngduring storms and floods thus losingalignment. Does not take kindly topruning and shaping, and is heavilyattacked by Ross Scale. Most unsuitablefor street planting.

4. Pinus halepensis (E)Appears to struggle in most places

on the Highveld. Is drought resistant,not too large, not attacked by scale.Only suitable for streets in the earlystages. Tends to become woody andshabby at an early age.

5. Pinus canariensis (E)Too large for street planting, thrives

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in most soils, long-lived, handsome. Aperfect specimen for parks. Excellentfor arterial roads and parkways.

6. Pinus pinea (E)Verylarge, rather slow-growing,long­

lived, does well in stony ground.Quite unsuitable from all points of viewfor street planting, but excellent forparks, arterial roads and parkways.

7. Pinus roxburgbii (syn. P. longifolia)(E)

Excellent street tree during the firsttwenty years, most handsome, of steadygrowth, becoming too large. Is long­lived and not likely to lurch during wetweather. Excellent for arterial roadsand parkways.

8. Pinus patula (E)One of the most attractive pines,

needles drooping, fast growing, droughtresistant, handsome and suitable forstreet planting, becoming too largeafter twenty years. Requires consider­able pruning under electricity and tele­phone lines. Excellent for arterial roadsand parkways.

9. Casuarina cunningbamiana (E) Beef­wood

One of the hardiest in all respects,fast growing, pest free, easily shapedand controlled at required height.Foliage is dark green. Roots trouble­some in gardens, otherwise an excellentstreet tree and most suitable for high­ways.

10. Ligustrum lucidum (E) PrivetHardy, of medium growth, attractive

glossy foliage and cream flowers. In­clined to become ragged in appearanceunder any but favourable conditionsand with age. Heavily attacked by RossScale. Recommended for narrow streets,if sprayed alternate years. Prunes well inmoderation.

II. Bracbycbitonpopulneum (syn. Ster­culia diversifolia) (E)

Frost and drought hardy, slowgrowing, appearance spoiled by under­cutting to clear pavements. Remains

comparatively small for many yearsafter planting. Blooms freely but ir­regularly. Excellent for highways in dryareas especially.

12. Cedrus deodora (E), C. atlantica(E), C. libani (E)

Although they thrive in most High­veld soils, they are not suitable forstreets owing to height and spread ofbranches and the fact that their sym­metry is spoiled if they are prunedeither from below or above. Excellentfor parkways, parks and gardens ofsize.

13. Rhus lancea (E) KarreeIndigenous tree, fairly slow growing,

inclined to a crooked stem, easilygrown from seed, needs no pruning andis perfectly hardy in all respeets.

14. Grevillea robusta (E) Silky orSilver Oak

Large, fast growing, not entirelyfrost hardy and suffers from drought.Attractive foliage, flowers freely butirregularly, inclined to litter pavementswith flowers and seed pods over longperiods. Too large under overhead linesand wood is brittle when grown in goodsoil. Grows rapidly after pruning.Unsuitable for streets. Excellent forhighways, parks and gardens.

15. Acacia spp. (E)The beautiful Acacia terminalis (syn.

Acacia elata) would be the most suitableas a street tree were it not for itsultimate enormous dimensions and thefact that it is not totally frost hardy inthe early stages. Acacia baileyana andA. decurrens are short-lived, brittle,subject to caterpillar and AustralianBug attack and generally unsuitable forstreets. A. dealbata is an excellentsubject for highways.

16. Cupressus spp. (E)These are attractive in the early

stages, but are so short-lived, brittle andsubject to termite attack at the root thatthey do not justify the labour entailedin establishing them on a street. Thesame remarks apply to the closelyallied Callitris or Widdringtonia.

17. Quercus ilex (E), Q. incana (E),Q. retieulata (E)

The evergreen oaks appear to havebeen somewhat slighted on the High­veld, but from my observations there ismuch to commend them as street andhighway trees. They make excellentspecimens for parks and large gardens.

18. Calodendrum eapense (E) CapeChestnut

A handsome tree suitable for widestreets and highways, beautiful inbloom. Is not sufficiently frost hardy forHighveld, but excellentwhere conditionsare favourable.

19. Cryptomeria japoniea (E)A tall, erect and handsome street

tree, really stately. Likes deep soil.Roots are not troublesome. Pruningspoils form. Hardy in all respects, andrecommended for parks and gardens aswell as highways.

20. Arauearia eunningbamii (E) More­ton Bay Pine

A tall, erect tree, steady and regularin growth. Hardy in all respects.Should succeed in most soils and rootsare not troublesome. Would enhanceany situation in or out of town.

21. Scbinus molle (E) Common PepperTree

A very hardy tree of medium size andsteady growth. At one time largelyplanted in arid and semi-arid districtsas a street tree. Like S. terebinthifolius,it is regarded as most unsuitable forstreets, principally because the pollen issaid to precipitate attacks of hay fever.It also exudes a sticky, pungent sub­stance which is unpleasant.

22. Platanus aeerifolia (D) LondonPlane

One of the favourites with much tocommend it in the early stages. Becomestoo large for modern streets with over­head lines. Appearance is spoiled bypruning and pollarding. Is not verydrought resistant. Leaves fall rapidly inautumn and cause little inconvenienceto householders. Where overhead lines

8 SUID.AFRIKAANSE 80S80UTYDSKRIF No. 76

are to be contended with it is advisableto cut a channel through the branchesfor the wires rather than pollard theentire tree down below the wires. Themost attractive tree in any situationsuitable to its natural size and particu­larly for parks and highways

23. Platanus wrightii (D) Wright'sPlane

Similar in all respects to the precedingand equally attractive and suitable untilit becomes large enough to darken thestreet and shade houses. Naturallyasymmetrical. A lovely specimen treein parks, gardens or along the highway.

24. Acer pseudo-platanus (0) Syca­more

Does not thrive under Highveldconditions, mainly due to drought andheat. Bark subject to sunburn. Other­wise suitable. Being dwarfed by condi­tions, does not become large. Isattractive in leaf and when seeding. Nottroublesome in autumn. Needs deepground. Roots will not trouble gardens.Lovely specimen tree when climaticconditions are right.

25. Ulmus parvifolia (D) ChineseElm

Likely to be a favourite as growth issteady, moderate and not dense. Leavesare small and unobstrusive in autumn,being readily dispersed by wind. Prefersdeep soil but will grow fairly well inanything but rock and shale. Roots aretroublesome in shallow ground, whenit is liable to invade gardens. Excellentfor highways.

26. Ulmus pumila (D)The foliage of this tree is larger and

generally more striking than that ofUlmus parvifolia whilst it is in mostother respects very similar and equallyto be recommended.

27. Cercis spp. (D) Judas Tree orRed Bud

This very colourful tree has not beenused to the best advantage in thiscountry so far, yet there are severalvarieties that will serve our purpose for

narrow streets well and beautify ourparks, gardens and open spaces alonghighways admirably.

28. Fraxinus velutina (D) MexicanAsh

An attractive tree of moderate di­mensions inclined to seed heavily froman early age thus limiting its growth.Not troublesome in any way to pave­ments and streets. Suitable for fairlywide streets and highways. Subject toattack by aphids.

29. Fraxinus excelsior (D)A lovely tree with dark green foliage,

frost hardy but not heat and droughtresistant. Suffers severely on the High­veld from sunburn on the bark. Notrecommended here.

30. Fraxinus augustifolia (D) AshA bold tree with striking deep green

foliage, not troublesome, although need­ing some pruning to prevent interferencewith overhead lines. A likely tree for allpurposes, especially for parks andhighways.

31. Fraxinus pennsylvanica (D)A striking tree with bold foliage and

of medium growth. Fairly popular onthe Highveld for streets, parks andhighways.

32. Quercus robur (syn. Q. peduncu­lata) (D) English Oak

A good all-round street tree, where itis not necessary to prune, as pruningrobs it of its natural grace and form.Sheds its foliage irregularly over a longperiod. Prefers deep, moist soil butgrows fairly well in very indifferent soiland is perfectly frost hardy. Suffersfrom sunburn on the bark. Roots aretroublesome in gardens but not onpavements and streets. A lovely speci­men for parks, large gardens or high­ways.

33. Quercus palustrls (D) Pin OakMost attractive foliage and lovely

autumn tints in favourable weather.May develop too large for any but widestreets and form would be spoiled by

pruning. Thrives in most soils butprefers moist, deep ground. Needstraining in nursery to obtain straightstems. Excellent for parks, gardens andhighways. Avenue tree or specimensubject for a large estate.

34. Ginkgo biloba (D) MaidenhairTree

A beautiful tree in every respect andmost suitable for streets where the soilis deep, fairly fertile and moist. Freefrom insect pests, of medium growthand roots not troublesome in gardens.Hardy in all respects. Only malesshould be planted on sidewalks as thefruits offemales cause a nuisance under­foot when they drop.

35. Gleditsia triacanthos (D) HoneyLocust

A really tough tree, hardy in everyrespect, with attractive foliage. Cleanappearance, thorny, bears large shinypods which are attractive but inclinedto litter the ground when ripe unlesscollected as fodder for cattle. Excellentin early stages, too large and likely torequire too much pruning after thefirst twenty years. Ideal for parkways,if widely spaced for full development.

36. Acer negundo(D) Manitoba MapleA. negundo var variegata

A delicate tree requiring deep fertilesoil and water. The foliage is pleasingto the eye but is shed early in autumn.Being of medium growth, is not difficultto control under overhead lines. Mostornamental for streets and highways.

37. Acer buergerianum(syn.A.trifidum)(D) Chinese Maple

In all respects the ideal street treewith attractive foliage, capable ofdeveloping beautiful autumn tints infavourable weather. It's never likely tobecome too large for the modern streetbut will not be a shade tree in theaccepted sense. It requires deep soil andmoderate fertility to thrive and beingof frail structure falls an easy victim tovandalism in the early stages. Willenhance any street, highway, park orgarden.

SOUTH AFRICAN FORESTRY JOURNAL No. 76 9

38. Ailanthus altissima (syn. A. glan­dulosa) (D) Tree of Heaven

A large tree of rapid growth withhandsome large foliage, curious whenladen with seed in the late summer andautumn. Resists smoke and grime incity streets better than most trees and isfree from insects. It is too large formost streets and suckers from the rootsvery freely. Not recommended exceptfor highways.

39. Jacaranda mimosaefolia (D)At an altitude of approximately

4,500 feet it thrives and blooms regu­larly, if not pruned or frosted, butcannot be recommended for plantingany higher. It is hardly a suitablestreet tree owing to large size andlittering of streets and sidewalks withcast flowers in November and largeleaves in winter. Pruning removes theterminals which bear the flowers. Mostsuitable for parks, large estates andhighways.

40. Populus spp. (D)Populus nigra var. italica (Lombardy

Poplar) is too slender in form and tootall to be suitable and the remainingvarieties of poplar grow too large,sucker from the root. Roots aretroublesome in gardens and on side­walks. Unsuitable for streets but mostattractive along highways. Autumnshades.

41. Aesculus hippocastanum (D) Com­mon Horse-Chestnut

Does not grow well enough underHighveld conditions to warrant its useon streets. Suffers severelyfrom droughtand heat.

42. Castanea sativa (syn. C. vesca)(D) Spanish Chestnut

A large, spreading tree of steady,stout growth. Too large in time for anybut wide streets. Very symmetical inform and not likely to be troublesomeexcept that children may climb forchestnuts. The 6 in. -7 in. catkins ofcream flowerrs are attractive and numer­ous in November. Excellent for parksand open spaces along highways.

43. Liriodendron tulipifera (D) TulipTree

A very suitable street tree in deepsoil. If not grown rapidly, wood shouldnot be too brittle. Attractive foliage andbeautiful in bloom. Natural grace ofform will be spoiled by pruning toleave overhead lines clear. Lovely parkand highway specimen.

44. Melia azedarach (D) Bead Tree orSyringa

A good shade tree with fragrant lilacflowers and handsome foliage. Fastgrowing and hardy, thriving in mostsoils. Too large for any but widestreets and unsuitable because it littersthe ground with an enormous crop ofpoisonous yellow berries annually.

45. Celtis australis (D) Nettle TreeA handsome tree of steady growth

and medium size. Does not sucker androots are not troublesome in gardens.An excellent street tree on the Highveld.Not likely to need much pruning underlines, splendid for open spaces, parksand highways.

46. Celtis africana (syn. A. rhamnifolia,A. kraussiana) (D) Witstinkhout

One of our indigenous trees. Growthis steady, the natural form irregular,and the size medium. It is droughtresistant, fairly frost hardy, long-lived,and the foliage is attractive. Roots arenot likely to be troublesome in gardens;but it is subject to aphid attack.

47. Albizzia julibrissin (D) Flat CrownA flat topped tree needing no pruning,

well branched and spreading, givingample shade on the sidewalk. The foli­age is attractive and the bloom fascinat­ing. A good subject for narrow streetsand under overhead lines. Roots giveno trouble at all, excellent for openspaces along highways. Not frost hardy.

48. Firmiana platanifolia (syn. Stercu­lia platanifolia) (D) Chinese Para­sol Tree

A striking, erect, well balanced treeof steady growth and medium size.

Hardy and will make a good highwayand street tree. Excellent for parks andopen spaces.

49. Combretum spp. (D) Roode BlaarIndigenous just off the Reef. Hardy in

all respects. Handsome autumn tintsdevelop in autumn when the weather ismild. Grows to medium height, shapesand spreads well when pruned. Promiseswell for streets. Thrives with water inalmost any soil. Roots are not trouble­some.

50. Dombeya rotundifolia (D)Indigenous. Flowers appear before

leaves in spring. Medium height, slowgrowth, hardy, attractive in bloom.Worth a trial for narrow streets.Thrives in most soils and roots will notinterfere with gardens.

51. Tipuana tipu (syn. T. speciosa) (D)Thrives best at 4,500 ft. above sea

level or less, therefore the young woodis frosted occasionally on the Reef.Grows rapidly in the early stages andneeds special care in the nursery toprocure straight, stout stems beforeplanting on the street. The foliage isstriking, pale green and attractive. Inbloom and in seed it has a very pleasingeffect. On account of frosting down, isinclined to be flat crowned on the Reefand to develop a wider spread for thesame reason. A suitable tree for amedium or wide street if carefullygrown and trained from the start.Excellent for open spaces, parks andand highway planting.

52. Catalpa bignonioides (D)A small tree with striking foliage and

attractive bloom. Will not thrive underharsh conditions and is rather short­lived on streets as a rule. Useful inparks and open spaces.

53. Robinia pseudo-acacia (D)A large, handsome tree, too large for

our purpose and so prone to suckerfrom the root that it becomes a nuisancein any street, park and garden.

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54. Salix spp. (D) WillowSalix babylonica (Weeping Willow)

thrives in any moist and fairly deepground and is most attractive in a widestreet, but too large to plant underoverhead lines. Other species of willowsare worth a trial wherever moisture,deep soil and space are available andoverhead lines are absent. Attractivefor open spaces and in parks.

55. Sophora japonica (D)A large graceful tree with dark green

foliage and branches. The flowers arewhite and borne in fairly large paniclesin the late summer. Not troublesome inany way except that when the seed podsfall pavements may become slippery.Excellent for all decorative purposesand recommended for streets and high­ways.

56. Sophora tetraptera (D) KowhaiA lovely tree from New Zealand, with

bright yellow flowers and attractiveform when allowed to develop naturally.Needs time and careful training in thenursery before being planted on streets.Not likely to be troublesome. Hardyand suitable for open spaces and parksin particular.

57. Liquidambar styraciftua (D) SweetGum or Alligator Tree

A large, hardy tree of symmetricalform, with maple-like foliage whichassumes rich autumn tints in favourableweather. Free from insect pests anddiseases. Prefers deep, moist soil. Rootsare not likely to be troublesome. Areally handsome tree in winter. Equallysuitable for streets, open spaces andhighways.

58. Bolusanthus speciosus (D)A small, flowering tree, with hand­

some leaves and bright blue flowers.Thrives at 4,500 ft. above sea level orless. Would be suitable for narrowstreets, i.e. less than 50 ft. wide, but isnot sufficiently frost resistant for theHighveld. Lovely for gardens, parks andsmall open spaces.

PRODUCTION OF STREET TREESAll the trees mentioned in this paper

can be grown from seed with ordinarycare in the nursery, except the poplarsand willows, which are easily grownfrom hardwood cuttings.

The planes are most successful whengrown from cuttings as a uniformphenotype is thus assured. As seedlingsvary considerably in form and appear­ance, they should on no account beintermingled in a street where treesfrom cuttings are planted.

Deciduous trees should be grown togood size in the nursery before beingplanted out so as not be easily brokenby passing pedestrians who sometimesthoughtlessly and sometimes delibrate­Iy mutilate trees. In the nursery astraight, clear stem of 6 ft. before thecrown is reached, must be developed.Root pruning and shaping of the crownshould receive due attention prior toplanting out on streets. Moderatelyfertile soil is preferable to rich soil forthis purpose as it produces a sturdiertree. Deciduous trees are generallygrown in open ground. The evergreensare grown from seed, transplanted intoflats for a short period and should thenbe grown on in single tins without beingretarded. They should be planted outwhen 2 to 3 ft. high, dependent onspecies, and before becoming root­bound, otherwise they are likely todevelop a faulty and distorted rootsystem which will not hold againstwindstorms. The protection of suchsmall trees against the ravages ofanimals by means of suitable, nettedtreeguards is essential.

SELECTION OF TREES TO SUITCONDITIONS(a) Soil

Most of the deciduous trees will notthrive in any but deep soil and loosegravel. To plant them in shale, sand­stone or rock is to court trouble as timegoes on. There are a few deciduoustrees that will do moderately well inhard ground, notably, Ulmus spp.,Gleditsia spp., certain Fraxinus spp.and some indigenous species.

For hard ground, the following

evergreens are the most successful:Pinus pinaster, P. roxburghii, P.

radiata, P. canariensis, P. patula,P. pinea and Cedrus deodara.

(b) Width of StreetObviously the size of the tree should

correspond with the size of the street,i.e. a small tree for a narrow street, amedium stree for a wider street and soon.

In particularly wide streets, trees maybe planted in the centre as well as on thepavements or alternatively, in thecentre and not on the pavements. Thelatter course, is, however, not favouredin residential zones as it robs thepedestrian of a shady sidewalk andencourages the parking of motor carsin the centre of the street. Where treesare planted in the centre of the streetthey should be surrounded by a kerbedisland so that the possibility of parkingis eliminated. Planting in the centreshould only be resorted to in widestreets and in business zones where treesshould not or cannot be planted on thepavements on account of commercialconsiderations or the presence of veran­das.

PLANTING OF TREES ONSTREETS(a) Position of trees on sidewalk

Some definite policy must be decidedupon then adhered to by all partiesconcerned with the sidewalks of a town,namely, the Parks Department, TownEngineer's Department, Electrical Engi­neer's Department, Waterworks andSewerage Branches and the TelephoneDepartment, each service being allotteda position on the pavement for itsrespective use. The trees should be givena position as far from the building lineas possible without being too near thekerb, and the telephone and electricitylines should be kept as far from thetrees as possible.

The rule followed in Krugersdorp formany years is to place the trees adistance from the building line equal toone-fifth of the width of the entirestreet, e.g. if a street is 60 ft. wide frombuilding line to building line, the trees

SOUTH AFRICAN FORESTRY JOURNAL No. 76 II

are planted 12 ft. from the building line.This works admirably provided noservice is placed under or above thisposition.

It is questionable whether a streetnarrower than 50 ft. should be plantedwith trees. Personally, I would considerPrivet, Pride of India, Robinia hispidarosea or R. Kelseyi in the standardform rather than trees, unless Acerbuergerianum is considered smallenough to be admitted.

(b) Distance between trees on the side­walks

This will vary with the subject andwill also depend on whether or notoverhead lines are present. Where thereare no lines overhead and trees can beallowed to develop to natural size,small trees could be planted 30 feetapart and medium sized trees 40 ft.apart. Large trees should be spaced50 ft. apart, but are normally consideredtoo big for street planting.

Where overhead lines are present andpruning is to be resorted to, all smalland medium-sized trees could be planted30 ft. apart.

(c) Preparation of holes for treesExcavate one cubic yard of soil to a

depth of 3 ft. and replace same, beingcareful to consolidate the soil. Removeany large stones that may be presentand replace them with soil if this isnecessary to fill the hole. Do not addmanure or fertilizer as the tree will bebetter able to fend for itself in later lifeif it has to do so from the start in thenatural soil. Where practicable, holesmay be given approximately 10 gallonsof water each before the soil is replaced.

(d) Alignment of treesThis is important and each tree

should be carefully planted in a per­pendicular position, firmly settled inand kept in a perfectly straight linefrom one end of the street to the otheror at a constant distance from thebuilding line should the street make aturn at any point.

(e) WateringThis will be necessary immediately

after planting and from then onwardsat intervals of approximately 14days forat least 12 months, except whencopious rain renders watering unneces­sary for a period. In some instances itmay be necessary to water young treesduring dry periods for as long as 5 yearsafter planting. Watering of street treesis most satisfactorily carried out bymeans of a small barrel water cart of90 to 100 gallons capacity with tap andhose attachment drawn by a singlemule or horse. A larger vehicle is usefulwhen whole streets are to be wateredregularly soon after planting, but sucha vehicle is rather cumbersome.

(f) Protection of treesThis is most important and very often

necessary for a considerable number ofyears after planting. The best methodis, undoubtedly, the mild steel tree­guard, two types of which are in use onthe Reef, one designed for the protectionof deciduous trees and the other forevergreens. A treeguard should beplaced around each tree immediatelyafter planting and the tree must besecured at one point in a centralposition in the guard in such a waythat it does not chafe against the guardor against the binding which secures itto the guard. Trees should not bestaked but encouraged to develop afirm grip on the soil with their roots,being secured only at one point nearthe top of the guard to obviate unduemovement in the wind.

Treeguards must not be removedfrom around a tree until the latter islarge enough not to be easily- brokenoff by vandals or damaged by animals.All branches should be out of reach,which will necessitate a clear trunkfrom 7 ft. to 8 ft. Immense damage canresult from animals rubbing theirbodies or heads against the trunks oftrees, especially young deciduous trees,and this must be prevented on ourstreets if success is to be attained.

(g) Filling of blanksBlanks will occur In most streets

after the original planting, usually forthe following reasons, viz.:-

(1) Failure to survive transplanting.

(2) Lack of sufficient water.

(3) Damage by vandals, such as theremoval of bark.

(4) Damage by animals.

All blanks should be replaced as soonafter they occur as possible, to avoidtoo great a variation in size between theoriginal and subsequent plantings. Thelargest tree practicable should be usedto fill a blank for the same reason.

(h) Training and shaping of the treeIn the case of evergreens, natural

development on one straigh t stem is theideal, the lower branches being gradu­ally removed a few each season as thetree develops until a clear trunk of thedesired height is obtained. Should thetree be situated under overhead lines itwill be necessary to 'stop' it approxi­mately 5 ft. below the lines, or approxi­mately 20 ft. above the ground, byremoving the leader or top of the mainstem. Thereafter the tree is prunedregularly to the shape of a dome, withthe spread increasing but not the height.

With the deciduous tree naturaldevelopment is even more desirablethan in the case of evergreens becauseduring the winter the framework isentirely exposed, and in the absence offoliage every defect or abnormality dueto pruning or other damage detractsfrom appearance. However, since weare unfortunate enough to have tocontend with overhead lines, we must,of necessity anticipate this nuisance.Three courses are open to us wherelines are present above deciduous trees.The course that is usually followed is toallow the tree to develop as naturallyas possible, as in the case of an ever­green, to a height of approximately20 ft. from the ground to 'stop' it byremoving the leader, pruning it to adome shape and allowing only thespread to increase. The second course isto 'stop' the tree much earlier andallow it to increase in height and spreadat the rate of approximately 18 inches

12 SUID-AFRIKAANSE BOSBOUTYDSKRIF No. 76

A good example of highway beautification - Planus acerifolia in Empire Road, Parktown, Johannesburg.

per annum until the maximum dimen­sions desirable or permissable under thecircumstances are reached. Both courseshave points to commend them but ineither the resultant appearance leavesmuch to be desired, especiaIly when theskeleton is seen in silhouette. The thirdcourse is to allow the tree to developnaturally and, as it approaches thelines, to remove the leader at a height ofapproximately 20 feet from the groundthus creating a channel through thecentre of the crown for the wires. Thisresults in less distortion than theprevious two solutions.

(i) Pruning

The amount of pruning necessary inany street will vary with the- type andage of the trees and with circumstancesrelating to width of the street and thepresence or absence of overhead lines.

Pruning should be carried out regu­larly, as and when required, with dueregard to shaping a well balanced treeof the maximum size desirable orpermissible under the circumstances.

Where trees, because of their exces­sive height, must be pruned downbelow overhead lines it is advisable to

aim at symmetrical dome shape forboth evergreen and deciduous trees.

SUMMARYIn this paper an attempt has been

made to place on record what is knownto me of the subject of tree planting onthe Highveld and I wish to acknowledgemy indebtedness to those who havelaboured patiently and left no meanheritage to posterity, leaving at thesame time a monument to themselves.They, with us, will endorse the senti­ments of Joyce Kilmer's immortalpoem, "Trees".

SOUTH AFRICAN FORESTRY JOURNAL No. 76 13