The Vegetation of Footpaths, , Cart-Tracks and Gateways Author(s): G. H. Bates Reviewed work(s): Source: Journal of Ecology, Vol. 23, No. 2 (Aug., 1935), pp. 470-487 Published by: British Ecological Society Stable URL: http://www.jstor.org/stable/2256132 . Accessed: 26/09/2012 14:08

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http://www.jstor.org THE VEGETATION OF FOOTPATHS, SIDEWALKS, CART-TRACKS AND GATEWAYS BY G. H. BATES.

(WithPlates XXXV-XXXVII.)

I. FOOTPATHS. THE contrastbetween the vegetationof footpathstraversing grassland and that of the surroundshas been commentedupon by observerson numerous occasions,while graziers have recognisedthe fact that horsesand sheep prefer to feedupon the footpathrather than the otherparts of the field. Apart from a passing speculationby Darwin ((I), p. 10), no detailed examinationof con- ditionsor of the factorsconcerned appears to have been made, in spite of the possibilityof the findingsbeing of economicvalue. The vegetationof the path is usually shorterthan that of the surrounding areas, thoughthis varies withthe intensityof grazing.The most outstanding phenomenonis the dark greencolour of the path in comparisonwith the other herbage. This deep colour is maintained throughoutthe year and is most conspicuousin winterwhen the path stands out in vivid contrastto the dead remainsof plant lifeon each side. With the exceptionof paths on very dry sandy soil, the dominantspecies are smooth-stalkedmeadow grass (Poa pratensis),perennial rye grass (Lolium perenne)and wild whiteclover (Trifolium repens). Poa pratensisis constantfor all examplesand Loliumperenne for the majority.Trifolium repens is extremely scarce in shaded positions,but is constantfor all paths exposed to sunlight. Crested dogstail (Cynosurus cristatus),cocksfoot (Dactylis glomerata)and plantains(Plantago spp.) are fairlyconstant. A distinctand constantzonation is found. In the centreof the path, if muchused, is an area ofbare earth.This is adjoined on eitherside by a zone of Poa pratensisfollowed by zones of Lolium perenneand Trifoliumrepens. An exampleis shownin P1. XXXV, phot. 1, thisbeing a path on a Lakeland fell. The surroundingvegetation is an Agrostis-Festucaassociation with Briza media, Vacciniummyrtillus, Molinia caerulea and Nardus strictaas sub-dominants. P1. XXXV, phot. 2 shows a small area of this and is a typical example of the contrastwhich occurs. On drysandy heathsin districtsof low rainfallthe dominantspecies of the path are usuallyFestuca ovina,Agrostis stolonifera, Galium spp., Plantagospp. and Hieraciumspp. On heaviersoils and in moistersituations, where puddling of the surfaceoccurs in winter,it is notable that areas dominatedby Poa JOURNAL OF ECOLOGY VOL. XXIII, PLATE XXXV ~~' ~ ~ ~ '

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BATS-VGETTIO O FOTPAHS,SIDWAKS,CAR-TRCK ANDGATEW~AYS Fae/0 7 G. H. BATES 471 pratensisand Lolium perenneare those where the surfaceis disturbed.The swardis not broken,but the mud oozes throughand almostcovers the surface. Footpaths are obviouslyof varying lengths but the widthis limitedaccord- ing to circumstancesand mayvary from a fewinches, as on a mountainside, to severalyards, as on a common.The lateral boundariesare not sharplydefined, but mergegradually into the surrounds,for treading is not evenlydistributed and is moreconcentrated in the centre.The boundaryusually occurs where the Lolium perenneand Trrifoliumrepens zone reachesits outerlimit.

Floristiccomposition of thevegetation of footpaths. The above statementswith regard to the floristiccomposition of footpath vegetationand the arrangementof species into zones is so patent to everyday observationthat elaboration in the formof statistical data is scarcelynecessary. To providesome illustration, however, eight examples are taken as follows: Example 1. Sheep Walk. Tarn Hows, Lancashire. 2. Larch Wood, GooseyfootTarn, Lancashire. 3. Mixed Wood, Walton, Derbyshire. 4. Paddock, Ashgate,Derbyshire. 5. Marsh Pasture, TerringtonMarsh, Norfolk. 6. Riverside,Gaywood, Norfolk. 7. Chalk Heath, MassinghamHeath, Norfolk. 8. Sandy Heath, Wooton Heath, Norfolk. Example 1 occurredon a hillsidewhere the soil was very acid (pH 4) and the rainfallhigh. Example 2 occurredunder similar conditions but in a shaded situation. Example 3 occurred on a medium loam with an acid reaction (pH 5). Example 4 occurredin the same neighbourhoodas Example 3, but the soil was neutralin reactionowing to heavy liming.All formsof grazing animals, includingrodents, were excluded fromthis site. Example 5 is found upon a pasture of renowned grazing value on the silt land borderingthe Wash. Example 6 was upon a black alluvialriverside soil, neutral in reaction. Example 7 was that of a footpathtraversing a heath overlyingchalk, the soil being comparativelymoist and neutralin reaction. Example 8 occurredupon a dry, sandy, acid heath (pH 5) overlyinga Lower Greensandformation. An intensivesurvey of the above exampleswas carriedout both in summer and in winter. Quantitativedata, both of areal percentageoccupied and of frequency,were collected both fromthe footpathproper and also for com- parativepurposes from the surrounds. Qualitativedata relatingto constancy, exclusiveness,vitality and periodicitywere obtained from100 examples. For the purposesof this article the publicationof the wholeof this informa- tionwould be superfluous,and, as alreadystated, the phenomena are familiaror are easily accessible to the observer. For the purposes of the subsequent examinationof the problem,however, the findingsare summarisedbelow. 472 Vegetationof Footpaths,Sidewalks, Cart-tracks, Gateways Quantitativedata. (1) Areal percentage. In all the eight examples bare groundoccurred where treading was most severe,and occupied an average of approximately18 per cent. of the ground coveredby the path. Poa pratensisoccupied an average of 34 per cent. ofthe area ofthe paths in Examples 1-8, but only 2 per cent. of the area in Example 8 on dry sandy heath. Lolium perenneoccupied an average of 18 per cent. of the area of the paths in Examples 1-8, but only 1 per cent. in Example 8 and was absent in Example 2. Trifoliumrepens occupied an average of 10 per cent. ofthe area ofthe paths in Examples 1-8, but was absent in Example 2 and onlycovered 2 per cent. of the area in Example 8. Plantagospp. and Bellis perenniswere present in two examples,and other species such as Dactylis glomerataand Cynosuruscristatus were present in others. Poa pratensis,Lolium perenne and Trifoliumrepens were the dominantson the paths on whichthey occurred. In all cases except Examples 5 and 8, the floraof the surroundswas mixed and none of the above species were dominants. In Example 5, however,Poa pratensis,Lolium perenneand Trifoliumrepens were co-dominantson the surroundsas well as on the path, and in Example 8 both the path and the surroundsconsisted of an Agrostis-Festucaassociation containing Galium saxatileand Plantago coronopusas sub-dominants. (2) Frequency. This was determinedby notingthe numberof times a species or a patch ofbare groundoccurred within a 10 x 10 in. quadrat framethrown 100 timesat random. Bare groundoccurred with an average frequencyof 33 per cent. over the eight examples. Poa pratensishad an average frequencyof 69 per cent., Lolium perenne55 per cent. and Trifoliumrepens 35 per cent. over the eight examples. No otherspecies possessed a frequencyof any magnitudein com- parisonwith the above. None of the above species displayeda highfrequency on the surroundsexcept again in Example 5, where Poa pratensis,Lolium perenneand Trifoliumrepens were high and in Example 8 whereAgrostis spp. and Festuca ovina had the highestfrequency. (3) Constancy. Both Poa pratensisand Lolium perennedisplayed 100 per cent. constancy upon paths, while Trifoliumrepens displayed 80 per cent. constancy. No otherspecies was comparablewith the above, the next in orderbeing Galium saxatile32 per cent.,and Bellis perennis25 per cent. G. H. BATES 473

Qualitativedata (from 100 examples). Exclusiveness.No speciescould be describedas exclusiveto thefootpath, but the followingare preferential:Poa pratensis,Lolium perenne, Trifolium repens,Bellis perennis, Hieracium spp., Plantago major and P. coronopus. Vitality.The followingspecies regularly accomplish their complete life cycle: Poa pratensis,Lolium perenne, Cynosurus cristatus, Trifolium repens, Galiumsaxatile, Plantago spp. and Luzulaspp. Manyother species found on thepaths only showed vegetative development. Periodicity.The followingspecies only were winter green: Poa pratensis, Loliumperenne and Cynosuruscristatus. Other species were dormant during the wintermonths.

Habitatfc4ctors. (1) Edaphicfactors. Generalphysical conditions. The soil of the footpathis in the firstplace similarto thatof the surrounds, and wouldexhibit the same characters upon mechanicalanalysis. Any differencesin the physicalcondition of the soil betweenpath and surroundare theresult of treading upon the path. It is obviousthat the soil of the path possesses a greaterdensity than that of the surrounds,and thishas a secondaryinfluence upon temperature and moistureconditions. Attempts to obtaindefinite measures of the respective densitieswere a failureand onlyapproximations were possible. This was due to the difficultyof exact excavation,owing to plant rootsand to stones. Severalfacts were, however, quite apparent from the investigation. In the surroundsthe top 5 cm. wereof lowerdensity than those below, owingto thelightening effect of plant roots, and also to thefact that there is no superimposedlayer of soil, and thatno treadingoccurs. On thefootpath the surfacesoil is ofgreater or equal densityto thelower soil. The lower soil of the pathswas ofabout the same density as thatof the lower soil of the surrounds. It wouldappear that in the case ofthe footpath, the denser or consolidated conditionof the soil, due to treading,exists only in aboutthe first 3-5 cm.,and thatbelow that level conditions are comparablewith those at a similardepth in theremainder of the field. The exactarrangement or textureof the particles in thesurface layer will differaccording to whetherthe troddensoils contain a certainproportion of clay or not. Clay whentrodden or "puddled" in the presenceof moisture becomesaltered physically, owing to deflocculationofthe particles. The result ofthis action is theretention of moisture on thesoil surface, and uponthe soil dryingby the evaporationof thismoisture, a "baked" or "poached" con- ditionarises, and a hard,"baked" crustof varying thickness is formed. Theproportion of clay in thesoil of the footpath and thecondition arising therefromcannot be ofany importance as a factorinfluencing the constitution Journ.of Ecology XXI1I 31 474 Vegetationof Footpaths,Sidewalks, Cart-tracks,Gateways of the footpathcommunity, for the communityis the same in its main features on othertypes of soil, except in the extremecase of drysandy heath. Experimentswere carriedout in 1929 ((2), p. 587) on a heavy loam soil (Chesterfield,Derbyshire), and again in 1932 on lightsandy loam (near King's Lynn, Norfolk)in an attempt to determinewhether consolidation in itself exerteddirect influence or selectiveinfluence on the species. A gardenborder was in each case divided into two, one half being consolidatedand the other leftloose. The followingspecies were sown in rows(duplicated and randomised) across both loose and solid areas: Lolium perenne,Poa pratensis,Holcus lanatus,Agrostis stolonifera, Festuca ovina,Trifolium repens and Plantagomajor. In the case of the 1929 experimentsoil was consolidatedto a depth of about 30 cm., by packingthe soil layer upon layer. In this experimentit was foundthat all the species were reduced to about half the size and weightof those upon the loose soil. The rootsystems were also restrictedby the solidsoil. In the 1932 experimentconsolidation was carriedout by surfacepressure afterthe species were established,care being taken not to crush any of the leaves or stemsof the plants. In thiscase the consolidationresembled the type effectedon the footpath,i.e. onlythe firstfew centimetres of soil wereaffected. In this experimentlittle result was noted, except in the case of Poa pratensis whichwas reducedin size in the consolidatedportion. Holcus lanatus,Agrostis stoloniferaand Festuca ovina wereslightly stunted. It is significantthat these species are comparativelyshallow-rooted. From the above resultsthere appears no reason to suppose that consolida- tion itselfis responsiblefor the " footpathflora ". Poa pratensisis the species most adversely affected,and yet this is the constant and most abundant species upon the consolidatedportion of a path. Soil moisture.On the whole the footpathis a moisterhabitat than the surrounds.The pressureof the soil particles into closer association should increasesurface tension and consequentlythe powerof a soil to retainmoisture, thoughin recentlypublished work (3) it has been shown that consolidation does not greatlyaffect water-holding capacity. The surfaceof the footpath, however,is presseddown to a lowerlevel than the surroundsand gravitation will increasewater supply in virtue of this fact. Anotherfactor is that the vegetationof the surroundsis frequentlymatted, and this surfacecovering of root materialretains water at the surfaceand rendersthe soil dry. On the footpath "mat " is eliminated by treading and a freeraccess of water is possible. On the otherhand a clay soil may, in the puddled state of the footpath, prohibitthe access of moisture,and may bake very hard in dry weather. Moistureconditions will be worse, in such cases, on the path than on the surrounds,yet the footpathstill possesses its distinctivevegetation. The speciesof the footpathsocies are not,as a whole,characteristic of a wet or dryhabitat. Loliumperenne thrives under good moistureconditions, but is G. H. BATES 475 deeprooted and fairly drought-resistant. Poa pratensis is shallowrooted, but possessesunderground runners and is drought-resistant.Thislatter grass is recognisedby agriculturalbotanists as one thattolerates dry situations. Trifoliumrepens, in virtue of its deep root system, is verydrought-resistant, andit is oftento be observedthat when pastures are burnt dry, this species is stillpresent in a greenstate. Actually a dry season favours the development of Trifoliumrepens. In viewof the above facts it doesnot appear that moisture initself can be regardedas a factorwhich is directlyresponsible for the existence of a distinct footpathsocies. It is assertedby somethat the distinct green colour of the footpathin winteris dueto moisture,but this may be explainedby the fact thatthe species of the footpath are all wintergreen. It isto be observed that the footpaths existing on dry sandy soil in districts oflow rainfall do not possess the characteristic flora of paths in other situations (Example8). Small coloniesof Poa pratensisand Loliumperenne may be foundin thedamp hollows, but thedominant and subdominant species are Festucaovina, Agrostis stolonifera, Galium spp., Plantagospp. (excluding Plantagomajor) and Hieracium spp. The phenomena were also noted where pathstraversed a cinder track and a slagheap (4). Onall othertypes of soils in moister situations the characteristic footpath communityexists on an area whichcoincides exactly with that which is puddledon the surface in winter. As already stated, the sward is notbroken, butmud oozes through and becomes mixed with the herbage. The occurrence of the typicalfootpath community of Poa pratensis,Lolium perenne and Trifoliumrepens on puddled areas is highlysignificant and goes to show that a moistcondition of the soil is important,though certainly an indirectfactor. Thepresence of moistureand a suitablephysical condition of the soil are essentialto puddling. Poa pratensisand Lolium perenne can tolerate puddling, whichis thus essential to the production ofthe footpath socies, because, as will be seenlater, it is lethalto speciesnot characteristic ofthe footpath. Chemicalcomposition. There is noreason why the chemical composition of thesoil of the footpath should vary from that of the surrounds. There is in somecases a greateraccumulation oforganic matter from decayed vegetation onthe surrounds than on the footpath, but this is notalways the case. It is alsonotable that grazing animals prefer the footpath, and thus it mayreceive moredroppings and urine than the surrounds. It isto be noted, however, that in the case of somepaths, livestock and evenrabbits are excluded,e.g. Example4. As regardssoil acidity a numberof investigations failed to revealany significantdifference inthe pH valueof the soil of the surrounds and the path, exceptwhere much " mat" waspresent on the surrounds, and here a difference wasrecorded, the earth below the "mat" beingmore acid than that of the path. 31-2 476 Vegetationof Footpaths,Sidewalks, Cart-tracks,Gateways Lightand aspect.Where a footpathtraverses grassland there is a greater illuminationon the path than on the surrounds,owing to the fact that the herbageis suppressedby treading,and its shadingeffect thereby removed. In many cases wherea path runs fromeast to west the northmargin of the path (which faces south) will be illuminatedby the direct rays of the sun at its maximumintensity. The oppositeside, especiallywhere overshadowed by tall grassor raisedground, will be shaded. The differencein illumination determined by actinometerwas for the shaded portion one-ninththat of the lighted northernside, in a typical example. Light intensityexerts a marked influenceupon Trifoliumrepens. In a shaded habitat, such as a wood or where other objects exclude sunlight, Trifoliumrepens is absent or very scanty, e.g. Example 2. Even aspect affectsthis species,and it will be foundthat wherethe southernside of a path is shaded fromdirect sunlightby tall grass or risingground there is a con- siderablylower scale of abundance, frequencyand dominancethan on the opposite side. 'When Trifoliumrepens is in flower,the relative abundance of whiteflower-heads on the side of a path witha southernaspect comparedwith the shaded northernaspect on the opposite side is very conspicuous. Light intensitydoes not appear to exertany markedinfluence on the otherspecies of the footpath,and they may all be foundin shaded situations.

The influenceof thebiotic factor. Grazing. It is notable that livestockprefer to graze the footpathsrather than the surrounds.This applies mostlyto sheep and horses,as these animals bite closely. It mustbe obviousupon considerationthat grazingis a secondary influence.The species of the footpathare the best pasture plants in the agri- culturalsense, and owingto theirshortness they offer a succulentherbage. The droppingsand urinefrom the animals are sometimesheld responsiblefor the greencolour of the path, as is the case with water supply. No differenceis noted, however,on footpathswhere grazing animals, includingrabbits, are excluded,e.g. Example 4. Treading.The effectof treading upon the floraof a communityis threefold, and is both directand indirect.The indirectaction has already been studied, i.e. the consolidationof the soil and its influenceupon the species. It has been shownthat this is not responsiblefor the footpathsocies. The directinfluences are those of treadingand puddling upon the plant itself,and the mechanicaleffect or injurycaused thereby. It is very obvious that many species are damaged and are oftencompletely destroyed by the action of treading,while on the otherhand the species of the footpathsocies are comparativelyimmune to harmof this kind. The reason forthis immunity or resistancemust obviously be due to some peculiarityof structurewhich the species possess in common,and which is not possessed by the species sus- ceptibleto injury. G. H. BATES 477 An examinationof the habit of growthof the dominantgramineous species Poa pratensis and Lolium perenne,shows a very strikingand significant characterpossessed by these species and not by the species of the surrounds, i.e. the conduplicatestem and foldedleaf sectionas comparedwith the rolling of the leaf in other Gramineae (exceptingPoa spp., Dactylis glomerataand Cynosuruscristatus). An examinationof this structureof leaf and stemshows it to be an excellentadaptation to resistinjury, for the leaf and stem offera flatsurface to the crushingaction ofthe foot.The conduplicatearrangement of the shoot is of similarmechanical structure to the leaf springsof a carriage. The lifeform of the gramineousspecies ofthe footpathis also distinctfrom that of the most frequentspecies of the surrounds.The gramineousspecies of the path constitutea synusiaof cryptophytes, the buds beingburied just below the level of the soil. The Gramineaeof the surroundsare mainlyhemicrypto- phytes,the buds being at groundlevel, and two of the species, Agrostisspp. and Holcus mollis,may be chamaephytes. The arrangementof the gramineousspecies into life formsis a somewhat finepoint. It mightbe argued that some species describedin this thesis as cryptophytesor chamaephytesrespectively might all be grouped as hemi- cryptophytes,but adheringrigidly to the positionof theirperennating organs as the criterion,there is no doubt as to whichspecies tend to the cryptophytic habit and whichto the chamaephytic. It appears obvious that the double adaptation,i.e. the foldedleaf and the conduplicatestem with the cryptophyticlife form,enable the plant to with- stand injury.The leaf and stemare resistantto injury,while the growingpoint is protectedbelow the surfaceof the earth. It has been noted that Poa pratensisoccupies the zone of the most intense treadingand is followedby Lolium perenneon the less troddenarea. A com- parison of the two species shows Poa pratensisto be better adapted than Loliumperenne to resistinjury. In the formercase the growingpoint is buried deeperin the soil and the plantpropagates by undergroundstolons as wellas by seed. The leaves of Poa pratensisare short,tough and concave in longitudinal and cross section. The leaves of Lolium perenneare longerand moreflaccid. It is notable that Poa trivialis,though possessingmuch the same foliage charactersas P. pratensis,is veryrare on the well-troddenportion of footpaths. This speciesis definitelychamaephytic in lifeform. It has also been notedthat P. annua may occupy intersticeswhere it is protectedfrom treading, and it may also have a transientexistence where treadingis for some reason sus- pended ((2), p. 589). P. annua is a therophyte. Ofthe non-gramineousspecies Plantago major is well adapted to withstand treading.The leaves are broad and toughand occurin rosetteform, the upper ones protectingthe lower. On the footpaththe plant is an ecad occurringhere as a cryptophyte,whereas on untroddenareas it is a hemicryptophytewith semi-erectleaves. The average size ofthe plant is smalleron the footpaththan 478 Vegetationof Footpaths,SidewalJc, Cart-tracks, Gateways on the surrounds.Similar phenomena are noted in the case ofPlantago media, P. lanceolataand P. Coronopus. Trifoliumrepens is least adapted to treadingof any ofthe footpathspecies, and it is a significantfact that it occupiesthe outerzone and invades the foot- path fromthe surrounds.Light appears to offerthe greateststimulus to this speciesand to account forits presenceon the footpath.The plant is a chamae- phytewith prostrate runners, and in virtueof the toughand prostratenature of these runnersexhibits a certainresistance to treading.The leaves are often injuredby the processand are smallerin size upon troddenarea (4). Trifolium repensis not injuredby even pressure(as contrastedwith treading) to the same extentas are the Gramineae.

Experimentsupon theinfluence of treading. An experimentwas carriedout to test the theoryof resistanceto injury possessed by certain species and not by others ((2), p. 589). The following grasses were grownin separate and repeated strips: Poa pratensis,Dactylis glomerata,Lolium perenne,Anthoxanthum odoratum, Alopecurus pratensis and Agrostisvulgaris. The groundwas then utilisedas a gardenpath and trodden daily. Poa pratensisassumed a low dense habit,Dactylis glomerata and Lolium perennewere suppressed but persisted. The three remainingspecies were exterminatedby treading.The experimentwas carriedout in 1929 on a heavy loam (Chesterfield,Derbyshire). Puddling took place during wet weather, thoughthe workwas carriedout in summer. A furtherexperiment was carried out on a light loam (King's Lynn, Norfolk).The followingspecies were sown in rows and the trial duplicated. Trifoliumrepens, Dactylis glomerata, Poa pratensis,Lolium perenne,Festuca elatior,Agrostis stolonifera and Agropyrumrepens (the latterwas plantedin the formof runners). A pathway was troddenthrough the plots and the species were subjected to a severe treadingand puddlingduring a wet summerand autumn. Trifoliumrepens was affectedby the treadingbut not destroyed. Dactylis glomerata,Poa pratensis and Lolium perenne were somewhat restrictedin developmentbut persistedand quicklyrecovered from the bruisingaction of treadingby making freshgrowth during the restingstage. Festuca elatior offeredsome resistance,but eventuallythe buds in the centreof the plant, beingabove groundlevel, weredestroyed. Agrostisstolonifera and Agropyrum repenswere completelydestroyed and in the lattercase the runnersappeared dead and shrunken. It was noted that seedlingsof Poa pratensisappeared all over the trodden areas, but werevery dense in the regionof the P. pratensisstrips. It is possible that some ofthe seedlingswere those of P. annua, but ifso theydid not persist beyondthe seedlingstage, as no matureplants were identifiable. The exact effectof treading was as follows:The originalplants were broken G. H. BATES 479 down, and the leaves damaged in the case of all the species. In the case of Festuca elatior,Agrostis stolonifera and Agropyrumrepens the buds at the base of the plants were trampled in the mud and damaged, but with Dactylis glomerata,Poa pratensisand Loliumperenne, these were protected beneath the surfaceof the soil. It appeared that the damage to the bared buds of Festuca elatior,Agrostis stolonifera and Agropyrumrepens only took place when the earth was wet and treadingproduced a pulpy condition. Special influenceof treading. Festuca ovina and Agrostisstolonifera appear capable of withstanding treadingupon a dry footpath,but they do not tolerate puddling. The same applies to Galiumspp. These plants are extremelystunted by the treadingand the leaves are veryfine. It is obviousthat the stuntedleaf of Agrostisand the setaceousleaf of Festuca ovina must be resistantto treading,and it is significant that these species are the dominantson dry footpaths. Many other crypto- phyticspecies occur on the surrounds,but are not foundon footpaths,and are all of a type whichwould be damaged by treading,i.e. uprightor fragile. While Festuca ovina and Agrostisstolonifera are able to withstandtreading upon the leaf they are not able to withstandthe slight surfacedisturbance caused by puddling,and the damage done by the bruisingaction ofthe footor hoofwhen pressinginto the surfacesoil. These two species are chamaephytes and their growingpoints are on the surfaceof the earth: furthermorethey possess an extremelysuperficial root-system, forming a mat ofroot material at theirbase. Large-scaleexperiment on theinfluence of puddling. An experimentwas carriedout on a large scale in HardwickPark, Derby- shire,illustrating the effectof puddlingupon an association of Agrostisand Festuca (5). The aim was to imitatethe action of the hoof in wet weatheron about fouracres of very matted grassland.The compositionof the grassland, assessed on the percentagearea basis, was: Agrostisspp. 35-4 Cynosuruscristatus 24-6 Festuca ovina 23-1 Luzula campestris(agg.) 9-2 Lolium perenne Trifoliumrepens Ranunculus spp. 7-7 Moss Holcus lanatus ) 100-0 The swardwas cut frequentlyin two directionsby a disc harrow,drawn by a tractorwhile the groundwas very wet and rain was falling.The turfwas worked into a morass of mud and presented a puddled appearance. It was then heavilyrolled. The operationwas carriedout in March 1929, and in the followingsummer a completechange in the florawas noted. The analysisof the treatedportion was then as follows: 480 Vegetationof Footpaths, Sidewalks,Cart-tracks, Gateways Poa pratensis 50 9 Cynosuruscristatus 21*7 Agrostisspp. 9-1 Trifoliumrepens 12-0 Lolium perenne 10 Holcus lanatus Festuca ovina 5.3 Ranunculusspp. 100-0 The analyses of the herbage were carried out independentlyby Mr A. Roebuck of the Midland Agriculturaland Dairy College. The influenceof this puddlingaction, carried out on a large scale, shows a resultof such strikingsimilarity to that observedon the footpath,as to need no elaboration.The astonishingacquirement of dominanceby Poa pratensisin so shorta time must be explained by very widespreadpresence of the seed overthe area and the establishmentof a peculiarlyfavourable seedbed by the " puddling" operation.The plants wereyoung when examined in the summer, and hay had previouslybeen fedto cattle on the area. As willbe seen,the Poa mainlyreplaced Festuca and Agrostis,which were severely reduced. It would appear probable that the evergreenor "wintergreen" condition of Poa pratensisand Lolium perennemay be a factorin theirfavour in the footpathcommunity, in that they are in a growingstate duringthe puddling process.This may exertsome influence,but in the above experiment,the time ofthe operation(i.e. Marchin a moistwarm spring) allowed a good chance for Festuca ovina and Agrostisstolonifera to recuperate.

Selectiveinfluence of treadingand puddling. From a considerationof the above data it would appear that the species whichare foundon footpaths,in wetor drysituations, are enabledto persistby virtue of their leaf structure.When, however,puddling becomes a factor, Festucaovina and Agrostisstolonifera are obliterated,but all speciespossessing the cryptophyticlife form are able to persist. The influenceof treading and puddlingupon a gramineouscommunity may be readilydemonstrated by rubbinga givenarea witha rubbersqueegee during wet weatheror whenthe groundis in a wet condition. An experimentof this naturewas carriedout on MassinghamHeath, Norfolk(August 1932). Three quadrats were chosen, each 1 sq. metre in area, with Agrostisstolonifera, Festucaovina, and Holcus lanatusas co-dominants,and scatteredindividuals of Lolium perenne,Trifolium repens and Plantago spp. The areas were rubbed with a squeegee and with the foot until the vegetationwas bruised and the surfacepasted with mud. Several days later it was noted that the quadrats presented,as a whole, a dead appearance. It was observed,however, that whileAgrostis stolonifera, Festuca ovina,and Holcus lanatuswere apparently dead, the "stumps" of Lolium perenneand Plantago spp. stood out of the groundin a strikingmanner and were still green. The runnersof Trifolium G. H. BATES 481 repensalso remainedgreen. A fortnightlater it was noted that some of the Agrostisstolonifera showed signs of recovery,a fewfresh green shoots having arisen,but Festucaovina had not recoveredand Holcus lanatuswas obliterated beyondrecognition. Lolium perenne had made a good recovery,having grown leaves up to 10 cm. long. Trifoliumrepens was developingleaves and so was Plantago spp. Theformation of thefootpath socies. In the years 1929-30,in a grasspaddock (Hawkshead Hill), attemptswere made to studythe formationof a footpathsocies, by observationscarried out on several areas whenthe footpathwas divertedto freshground. Permanent quadrats wereunfortunately obliterated, but the followingfacts were revealed fromclose observation. Existingspecies not typical of the footpathsynusia were suppressedand bare groundpopulated by Poa pratensiswhich in some cases sprangfrom seed, but in othersproliferated from pre-existing individuals. Plantago spp. also appeared as seedlingsupon this centralarea and grew to maturity. Lolium perennedid not appear as seedlingsin the firstplace, but pre-existingspecimens persistedand proliferated,and in the second year seedlingswere observed. Trifoliumrepens invaded the outer marginsof the path vegetatively.The runnersappeared to be attractedtowards the unshadedarea fromindividuals existingin the surrounds.Runners of T. repenswere defoliated by the actionof treadingand were pressed into the puddled ground,but in many cases re- cuperated.

II. FLAGGED FOOTPATHS. Several types of flaggedpavements are in existence,the commonestbeing the ordinarystreet . In this case the flagsmay be ofstone or , but in both cases intersticesexist betweenthe flags. Garden paths and field paths are sometimesflagged and even asphalt paths possess a whichis composed of individualstones. Cobbled paths and roadways are now of un- commonoccurrence. Except in the centreof large citiesor in the presenceof chemicalfumes or similaragents destructiveto plant life,all flaggedpavements possess vegeta- tion,though this is in many cases extremelyscanty. Lower formsof plant life such as mosses and algae may cover the flagsor exist in the interstices,but theirdistribution is not consideredin this paper. The completefloristic list of the habitat is indefinitelylarge and ranges fromseedling trees to grasses,but the frequencyof the majorityis ofso low an orderas to be negligible.They are accidentals,occurring in odd shelteredor protectedplaces. The remarkablecharacter of the vegetationof this type of habitat is the predominanceof Poa pratensisover all otherspecies. This grass occupies the 482 Vegetationof Footpaths,Sidewalks, Cart-tracks, Gateways intersticesbetween the flags,sometimes dominating this area and sometimes occurringin scattered colonies. It is practicallyconstant for all examples occurringon flaggedpavements in the most varied localities. It has been observedas the dominantspecies of flags and kerbstonesfor miles along a crossingDerbyshire moors, on the promenadesof seaside resorts,and in the suburbsof citiesin all parts of the country. Subdominantspecies are Galium spp. and Sagina procumbens. Wherethe flaggedpath bordersa bank or waysidethe lattersituations may be populatedby a large varietyof species,yet Poa pratensisstill dominates all the intersticesof the flags. In a surveyof twentyexamples it was foundthat whereasP. pratensisoccupied an average area of only5 per cent. ofthe vegeta- tion of the surrounds,it composed95 per cent. of the vegetationof the inter- stices assessed on an area basis ((2), p. 585). Thereappear to be two reasonsfor the dominanceof this species, firstly the ability to invade the intersticesby means of its runners,and secondlythe adaptation to resist the injury caused by the very severe and concentrated treading.This power of resistance is due to lifeform and leafand stemstructure and has alreadybeen fullydescribed. In the case of disused flaggedpaths or those rarelytrodden, the floramay be extremelyvaried and possess no distinctcharacters; this also applies to cobbled paths. The colonisationof a newlylaid flaggedpath takes place by seed infectionof the soil of the intersticesand by invasionfrom the surrounds of runner-bearingspecies. The commonestubiquitous annuals may appear to- getherwith Agrostisor Agropyrum.Poa pratensismay appear as isolated seedlingsin the intersticesor fromrunners invading from the surrounds.The mechanicaleffect of treadingsoon exertsits selectiveinfluence, Poa pratensis survivingon the closelytrodden portions. P1. XXXVI, phot. 3 showsthe dominationof an intersticeby Poa pratensis whilethe immediatesurrounds P1. XXXVI, phot. 4 containa mixed flora.

III. CART-TRACKSAND GATEWAYS. Cart-tracks,frequently used , fen droves and gatewayscover a large area of the countryside,probably of greatermagnitude than that occupiedby footpaths.They are all subjectedto the same mechanicalinfluences, i.e. human treading,and in additionthe deep disturbanceand churningaction of horses' hoofsand of cart-wheelsduring wet weather. In summerthe surfacemay be hard and stable, but in wintercertain parts of it will become a morass. On cart-tracksand fen droves the characteristicspecies are knotgrass (Polygonumaviculare), swinescress (Senebiera Coronopus), silverweed (Potent- illa anserina),greater plantain (Plantago major), rayless chamomile (Matricaria suaveolens).The grasses are Poa annua, P. pratensis,Lolium perenne,while associated withthese theremay be Trifoliumrepens. Distinctzonation exists on these areas, and upon examinationit is found that the most disturbed JOURNAL OF ECOLOGY VOL. XXIII, PLATE XXXVI

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1: _- "50K -MIN

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Phot.4. Flagged path intersticesdominated by Poa pratensis

BATES-VEGETATION OF FoOTPATHS, SIDEWALKS, CART-TRACKS AND GATEWAYS Face P. 482 G. H. BATES 483 regionsare dominatedby the annuals, while perennialsdominate the more stable regions.The mostseverely trodden and compressedportion of the stable surfacedo not, as a rule,support grasses, but the less troddenand compressed part ofthe stable surfaceand the marginsof the habitat may be dominatedby the perennialgrasses and by Trifoliumrepens. This communitymay usually be definedas an associes. The magnitudeof the area and its separationby ditches or hedges fromthe surroundingcom- munitiesshould entitle it to thisrank. It containsconsocies, socies and colonies. It is obviouslyin an unstable state. Gatewaysexhibit a somewhatsimilar flora and the constancyof the species is the same throughoutthe country.The obviousreason is that the mechanical factoris again the most potent.The phenomenonof zonationis also observed, especiallywhere a gateway enters a grass field,and this zonation gives an excellentexample of specificchanges in responseto varyingintensity of com- pression. In the actual gatewaymidway between the posts is an area of bare groundwhere disturbance and treadingare so severethat no species can exist while these continue. Following upon this is a zone in which Polygonum aviculareand Matricariasuaveolens are dominants. Intermixedwith the latter species,but extendingfurther out, Plantagomajor is a constant. Transientindividuals of Poa annua may occur over any part of the area at certainseasons, most commonlyin winterand spring. In the gateway of a pasture,grasses exhibit a zonationconsisting of the same speciestogether with Trifoliumrepens and arrangedin the same way as on footpaths.The grass zones are furthestfrom the gateway and mergeinto the pasture. Gatewaycommunities may also be describedas associes,being subordinate communitiesin the midst of cultivated or semi-cultivatedvegetation com- munities. Quantitativedata. In fiveexamples composed of two gateways,two cart- tracks,and one fen drove a surveyrevealed the followingdata. The species Plantago major, Polygonumaviculare, Matricaria suaveolens,Senebiera Coro- nopus,Potentilla anserina, Poa pratensisand Agrostisstolonifera were present in all cases with the exception of one gateway where Potentillaanserina was absent. The relativeabundance, and also the areal percentageoccupied varied greatlywith each example,for the size of the individualplants was extremely variable. Frequencydid not varyto quite the same extent,which was probably due to a certainamount of zonation of the species. The fact that the above species were the co-dominantsis revealed by the fact that other species, groupedas miscellaneous,only showed an average abundance of 3-6 per cent. of the total. In a hundredexamples the followingpercentage constancy of the species was recorded:Plantago major 100, Polygonumaviculare 92, Matricariasuaveo- lens 89, Senebiera Coronopus79, Potentillaanserina 60. Poa pratensis 94, Agrostisstolonifera 54. One or moreother species occurredin all the examples. 484 Vegetationof Footpaths,Sidewalks, Cart-tracks, Gateways Qualitativedata. No speciescould be describedas exclusiveto the com- munity,but the first five in theabove list could be classedas preferential. As regardsvitality, miscellaneous species were accidental and did not multiply.Agrostis stolonifera, originating from adjoining situations on stable ground,showed restricted vegetative development. The remainingspecies of thecommunity regularly completed their life cycle. Theperiodicity of the species varied, in that Poa pratensiswas winter green whilethe other species were dormant (or absentin thecase oftherophytes) in the winteraspect. Polygonumaviculare and Matricariasuaveolens do not appearas seedlingsuntil late in thespring aspect. The distributionwithin the community,apart fromthe phenomenaof zonation,showed one outstandingfeature, i.e. that perennialsdo not exist uponthe areas which have beendisturbed and puddledin winter,except in a seedlingor "maiden" state. These areas are dominatedby the annuals Matricariasuaveolens and Polygonumaviculare and in somecases by seedlings and immatureplants of Plantago major. Habitatfactors. The habitatof the community under consideration bears some features of resemblanceto that of the footpath,in that it is a disturbedarea, and the disturbanceis due to puddling.In thiscase, however, the disturbance is ofa muchmore violent nature, the soil being puddled and disturbedto depthsof severalinches, or in the case of cart-rutseven to the depthsof the axles. Certainparts of the area aredisturbed during winter months when the ground is soft,other parts, as, forexample, the region between the cart-wheels and the horse'shoofs, remain undisturbed. During summer the ground becomes hard, and thoughstill subjected to pressure,comparatively or quitestable. Edaphicfactors. Sincethe gateway and footpathcommunities are constantfor all typesof soil,the chemical composition of the soil and to a certainextent its physical condition,i.e. humus,clay, sand or chalkcontent, cannot have any definite influenceupon the flora. On sandyheaths (Bawsey and Snettisham,Norfolk, Greensandformation) the sameflora is foundas uponheavy clays. On soils containinga clayfraction "poaching" and deflocculationof theclay particles occurs,but this is notthe case on sands. Light. Owingto theabsence of other vegetation the habitat is fullyilluminated, as wasthe footpath. There appears to be someconnection between the light factor andthe vegetation, as all thespecies except Matricaria suaveolens are prostrate or straggling,and unableto coxnpetefor light in otherhabitats. Matricaria suaveolensis a Compositewith dissected leaves, and it is well known that species ofthat family and withthat type of foliage are extremelyintolerant of shade. JOURNAL OF ECOLOGY VOL. XXIII, PLATE XXXVII

41R.-~

Phot. 5. Fen drove, aestival-autumnalaspect. Polygonumaviculare is dominant betweenthe tracks. 1~~~~~~~~~~~~~~~~~~~~42

Phot. 6. Fen drove with Potentillaanserina and Plantago major dominatingthe undisturbedregion between the cart-tracks.

BATES-VEGETATION OF FOOTPATHS, SIDEWALKS, CART-TRACKS AND GATEWAYS Face p. 485 G. H. BATES 485 In the above connectionobservations were made in severallocalities on the reaction of Matricaria suaveolensto light. The firstthree were cart- runningeast and west.When the hedgewas dense or the groundovershadowed by it or by trees,Matricaria suaveolens was absent or scanty. In one example, at Castle Rising,Norfolk, a buildingshaded the sidewalkup to the inneredge of the kerb. A little Matricaria suaveolensgrew under the wall and on the sidewalk,but it was abundant upon the kerb. It is a significantfact that Matricariasuaveolens, Senebiera Coronopus and Polygonumaviculare, all germinatecomparatively late when most places are overshadowedby vegetation. Seedlingsof these speciesare not to be observed on cart-tracksor in gatewaysuntil the end of May. It is highlyprobable that these are the onlyhabitats offeringlight and a suitable situationfor germina- tion at this season. Thus it appears that lightis a contributingfactor to the existenceof the cart-trackand gateway community.

Disturbanceand compression. It is obvious that the chieffactor influencing the habitat is that of dis- turbanceof the groundduring winter and compressionof the surfacein summer whenthe groundis dry. The effectof the winterdisturbance is to destroyall specieswhich have becomeestablished during summer. These speciesconsist of the annuals Polygonumaviculare, Matricaria suaveolens, Senebiera Coronopus, and the seedlingsand firstyear plants of Plantagomajor, together with a few miscellaneousseedling perennials. The annualswould obviously die irrespective of the disturbance,but the perennialsare also destroyed. Observationsbows that runner-bearingperennials are crushedbeneath the wetsoil, while Plantago major is squeezed out and leftupon the surfaceto be destroyedby frostor otheragencies. In any of these communitiesthe perennialsof morethan one year'sstanding are foundon partsof the habitatwhich are stable duringwinter. Potentillaanserina, having its main rootstocksestablished upon stable undisturbedground, may duringsummer send runnersover an area whichwas disturbedduring winter. It does not, however,tolerate much treading. P1. XXXVII, phot. 5, showsthe aestival-autumnalaspect of a fen drove; the surfaceis colonised by Polygonumaviculare: in winterit was a morass devoid of vegetation. P1. XXXVII, phot. 6 shows Potentillaanserina and Plantago major dominatingan undisturbedregion between cart-tracks.

The structuralresistance to treading. Plantago major, Matricaria suaveolens,Polygonum aviculare, Senebiera Coronopusand Poa pratensisare all resistantto treading.The resistanceof Poa pratensisand Plantago major in virtue of their life formand structurehas alreadybeen discussed(p. 477). The remainingspecies are also adapted to this influence. 486 Vegetationof Footpaths,Sidewalks, Cart-tracks,Gateways Polygonumaviculare has hard wirystems which resist treading,and the prostrateform prevents snapping of the stem at any given point. The leaves are small and become much smallerwhen the plant is subjected to treading. The flowersare minuteand are protectedin the axils of the leaves. Senebiera Coronopusis prostrate,has small scale-likeleaves and small flowersand thus survivescompression. Matricaria suaveolens is normallyan uprightplant but can become prostrate.The abilityof this species to resisttreading appears to be due to the small area of finelydissected leaves, and the extremelypliable natureof the stem,which is toughand fibrousand does not snap ifbent double. The flowerheads are comparativelylarge, but ifcompressed they splay out and appear to escape injury. It must be made clear that the species of the communitydo not flourish undercompression, but are severelystunted in growthboth withregard to the shoot and the root system. They are also altered in habit, being converted fromthe uprightor semi-uprightto the prostratehabit. In spite ofthis severe stuntingthey are, however,capable of completingtheir life cycle.

GENERAL SUMMARY. I. The chieffactor concerned in the productionof the footpathsocies from the grasslandcommunity is the mechanicaleffect of treadingand puddling. This exertsa selectiveinfluence on the grasses,eliminating those not structur- ally adapted to withstandthe injury of treadingand puddling. The species adapted by virtueof lifeform and leaf and stem structureare able to persist. These dominantsare zoned accordingto the intensityof treading. Under dry conditionswhere no puddlingoccurs, treading alone produceslittle change. The plantainsare governedby the same factoras the grassesand owe their existence to their life form. Trifoliumrepens does not exhibit as great a resistanceto treadingas do the grassesand hence occupiesonly the outerzone ofthe footpath.Light appears to be a decisivefactor with this species, shading being eliminatedby the treadingdown of taller species. II. The intersticesof flaggedpaths and sidewalksare dominatedby Poa pratensis.This is because this species can invade the area by means of runners coupled withits structuraladaptations to resistinjury by treading. III. The characteristicflora of a cart-trackor gateway community,owes its existenceto a peculiar combinationof circumstances.Severe disturbance and churningof the groundin winterexterminates all perennialspecies which have seeded duringsummer, annuals dying naturallyor as a result of this disturbance.During summer the disturbedarea becomeshard and stable,but is stillsubjected to surfacepressure, and is thereforepopulated by annuals or by seedlingperennials (chiefly Plantago major and Poa pratensis). In virtueof theirlife formand habit, these are able to resistthe injury of treadingto a sufficientdegree to continuetheir existence through the summerand autumn. Otherspecies than the above may appear duringspring and summeras acci- G. H. BATES 487 dentals,but succumbto treading.The undisturbedareas between or around the disturbedregion are populatedby perennialswhich may resista severe degreeof treading, but cannot survive disturbance and churningof the ground duringwinter. All the speciesare ill adaptedto competefor light and thehabitat offers illuminationwithout competition. It also favoursspecies which germinate comparativelylate in spring.

REFERENCES. (1) Darwin, C. VegetableMould and Earthworms.Ninth Thousand, 1883, p. 10. (2) Bates, G. H. "Effectof consolidationupon the botanical compositionof poor grassland." J. Min. Agri. 37, No. 6, pp. 587, 585, 589, 589, 585, 1930. (3) Gupta, S. Parmeshwar. "Reaction of plants to density of soil." This JouRN.21, No. 2, pp. 452-74, Aug. 1933. (4) Bates, G. H. "The relationof leaf size to root structurein Trifoliumrepens." This JOURN. 22, No. 1, pp. 271-8, 1934. (5) Bates, G. H. "Mechanical improvementof grassland." J. MHn.Agri. 36, No. 4, p. 323, 1929.