DALY: ORDINATION OF GRASSl.AND IN OTAGO 63

ORDINATION OF GRASSLAND AND RELATED

COMMUNITIES IN OTAGO

G. T. DALY'

Botany Department, University of Otago

INTRODUCTION

Indigenous grassland and related vegetationcovers most of Otago east of the lake district. Thecommunities occur over a wide range of topog-raphy and altitude and are, in consequence, deter-mined by a considerable variety of climates andsoils. Additional variation has its origin in thecomplex grass and shrub successions which beganafter Maori fires removed montane beech-podocarpforests from much of the region within the lastmillenium (Holloway 1954, Molloy et at. 1963).These complicated patterns of stable and unstablevegetation have been subjected to further drasticchange by the animals, plants and pastoral prac-tices introduced by European man.

Extensive descriptions of the geography of themain plant communities in Otago were made earlyin this century by Cockayne (1928) and. later.Zotov (1938) assessed the condition of large areasof indigenous grasslands. Though a number oflimited areas of the province were relatively wenknown. detailed descriptions began with the sur-veys by the Otago C:ttchment Board (Wardle 1956,1960, Mark et aI. 1959, 1960, and Mark 1965a).In this work little complete sampling was done, forthe object was inventory mapping of main com-munity types, their condition and agriculturalpotential. Mark (1955), however, made a quanti-tative study of grass and shrubland vegetation onMaungatua and, with Billings in 1961, related thealpine cushion vegetation to patterned ground inOtago mountains. More recently (Mark 1965b),has used point analysis and similarity comparisonsof Chionochloa rigida grasslands on Maungatua,Old Man Range and Coronet Peak. In reporting onhis detailed clim:tte measurements, Mark (1965a)has successfully correlated contemporary climateswith the broad zonation of mountain vegetation inCentral Otago.

The only complete regional analysis of anindigenous grassland in New Zealand was made byConnor (1961, 1964, 1965) in the MacKenziecountry and Upper Rakaia Catchment, Canter-bury. His excellent description of the grasslandcommunities. their main environmental features

and present condition has allowed a plausibleexplanation of their history to be made.Alpine grasslands in a part of Fiordland were

described by Mark and Burrell (1966) who usedSorenson's similarity coefficients to group andseparate stands in an altitudinal sequence. Ordina-tion of stands of grassland based on their coeffi-cients of similarity or dissimilarity has been littleused in New Zealand. Techniques available forthis quantitative analysis include those of the Wis-consin school (Bray and Curtis 1957, Loucks1960) and, more recently, those developed atBangor, North Wales (Orloci 1966, Austin andOrloci 1966).In the analysis of Otago grasslands and related

communities being made at present. the relativelysimple Wisconsin methods are being used. Thiscontribution reports a preliminary treatment ofgrassland stands using data gathered during 1965-66. An attempt has been made to relate variationjn the gras'sland continuum to the principalenvironmental gradients.

METHODS

Stand selection

After reconnaissance of the region, 99 standswere sampled to represent the wide range of varia-tion exhibited by the grassland and related vegeta-tion. No attempt was made to select stands atrandom, though for future studies this would havesome value. Samples were taken from 300 to5,400 ft. altitude and from arid to semi-aquatichabitats. They varied in area from approximateJyhalf an acre for \Some graminoid swamps to hun-dreds of acres for some Chionochloa and F estucagrasslands.No undisturbed jndigenous vegetation was found

within the region. Consequently, the only criteriafor suitability of prospective stands were that:

(I) The vegetation was not visibly recoveringfrom recent disturbance by fire or severe

.

grazmg.

* Miss E. L. Hellaby, Indigenous Grasslands ResearchFellow, Lincoln College, Canterbury.

64 DALY: ORDINATION OF GRASSLAND IN OTAGO

(2) The physiognomic dominant was repre-sented throughout the stand.

(3) The stand had visibly uniform topog-raphy, soil, aspect and moisture status.

Sampling method

A rapid survey of the stand was made during

which a list of the spocie.~ pre.~ent was compiled.Then an estimate of the relative cover by cachspecies was made from hits recorded on a pointedsteel wire placed at regular intervals along a 100 ft.tape. The initial placement of the tape wasparallel to the contour and well within the stand.Subsequent tape positions were parallel to the firstand separated from it by regular numbers of paces;usually 30 in such communities as Chionochlvagrassland and shrubland or 20 in short-tussock andAgropyron! Raoulia grassland.

Point positions were separated by regular inter-vals along the tape - 2 ft. for cushion plant andlow tussock stands and 4 ft. for Chionochloa grass-land, shrubland and Cortaderia swamp. As 200point placements were made per stand. the numberof tape-positions was 4 in low vegetation and 8where the physiognomic dominants were large. Ateach position of the pointed steel wire, two hitsonly were recorded - the first hit on a canopyspecies above 6 inches and the first hit on a groundspecies below 6 inches. Results obtained by thismethod are known not to constitute true speciespoint-cover estimates and consequently the termrelative cover has been used. True cover is difficultand time-consuming to measure; besides, a non-selective sampling method was required whichcombined light equipment with rapidity andaccuracy, in vegetation varying from flat cushionsto shrub1and.In practice, the results for all the single-layer

communities and for some of those with a canopycorrespond closely to true cover estimates. Dur-ing point-sampling all new species encounteredwere added to the presence list. Additional specieswere recorded during the measuring of every standand this demonstrates one of the intrinsic valuesof quantitative sampling.For each stand a brief description of the soil

profile was made and a volume-weight sample ofsurface soil collected. Additional notes taken ateach stand included aspect, slope, condition andprobable extent of past disturbance. All speciesnot recognised in the field were given a fidd nameand collected for positive identification later. Point-hits on bryophytes and lichens were recorded anda collection was made of all specie'-sencountered.

Analytical methods

Stands were sorted into groups representing com-munities recognised by particular physiognomi-cally-dominant species. All species presence values,ground cover estimates and site records were thencompiled and community averages obtained. Therelative ground cover for leading physiognomic

Jom;nants and several prominent ground species

was graphed so as to give an arrangement of thechief communities on mineral soils. These com-munities were placed along the ordinate in a linearcontinuum related to increase in altitude andmoisture status.

Ordering of stands

For computation of the indices of dissimilaritybetween stands, 181 vascular species were chosenon the basis of their relatively high constancy in atleast one community. Values of relative groundcover for the 181 species, plus relative estimates ofcanopy cover for 19 were used - after being puton to punch cards - in computing the value of theIndex of Dissimilarity,

200W(C= 100 )

a+bfor each stand. These calculations for a partialmatrix of Dissimilarity values were performed inthe IBM-360 computer at the University of Otago.The partial matrix consisted of comparisons with

stands likely to be the mathematical ends of theordinates. From this matrix the stand having thehighest sum of Dissimilarity values, Le., the onemost dissimilar from all the others, was selected asthe first end of the primary axis. The stand mostdissimilar from the first end stand was taken asthe other end of the primary axis. All other standswere then placed between these two end standsaccording to their interstand distances, calculatedby the geometric method of Beals (1960).Many of the stands placed near each other on

the primary axis were not very similar. The pro-duction of a second axis which separates them intwo-dimensional space was therefore needed. Thefirst end stand of the secondary axis was that whichhad the poorest fit on the primary axis, i.e., hadthe highest "e" value of Beals. The stand placedat the other end of the secondary axis had thehighest Index of Dissimilarity relative to the firstend stand and separated from it by less than 10%of the length of the primary axis. The primary andsecondary co-ordinates were then constructed andstands plotted with respect to these in two-dimensional "vegetation space". Actually, tertiary

DALY: ORDINATION OF GRASSLAND IN OTAGO

and higher order axes may be calculated untilthere is no increase in the separation of highlydissimilar stands.

The method for calculation of coefficient of dis-

similarity is such that stand position in the ordina-

tion is determined by composition of the vegetation.Vegetation structure and composition are largelyunder the control of environmental factors andthe interactions between them. Consequently, byplotting environmental parameters and the per-formances of species on an ordination, correlationsbetween vegetation and environment are obtained.The primary axis usually reflects the principalvariation of the vegetation and thus the environ-mental factor or factors related to this variation.Secondary and higher order axes relate to pro-gressively smaller amounts of variation in thevegetation as represented by the scatter of standpositions and therefore to environmental factorswith commensurately less influence.

A vailable moisture and seasonal temperatureappear to be the most important factors in theindigenous grasslands, though recent disturbanceoften obscures their controlling influence. At thistime, soil analyses are incomplete and accurateclimate records are available for the areas of onlya few stands. Despite fragmentary data on theenvironment it is useful to obtain some idea ofthe general relationship between environment andstand position on the ordination. Consequently.the moisture status for each stand was estimatedby a point-scoring system and altitude has beenused as an indirect measure of ambient temperaMture.

With the valuable advice of Mr E. J. B. Cutler,Pedologist, Soil Bureau, D.S.I. R.. each stand wasscored between 0 and 4 for position on a drainagecatena. average precipitation and the capacity forretaining soil moisture.

Using this system, a composite moisture scorewas derived for each stand. The moisture scoresranged from ° for the driest, most well-drainedstands to 12 for stands of semi-aquatic. poorlydrained vegetation. Any broad relation betweenmoisture supply and vegetation sampled should berevealed by plotting the scores on the stand ordina-tion determined by the vegetation. Similarly, someimpression of the importance of temperatureshould be obtained by plotting altitudes on thearrangement of stands in the ordination.

RESULTS AND DISCUSSION

The list of vascular species compiled in the studyapproached 400, including 50 exotic species. Over10;) species of bryophytes and lichens wererecorded.

Relative cover values for species graphed accord-ing to a linear arrangement of communities arepresented for important physiognomic dominantsin Figure I. some prominent ground sp~cies inFigure 2 and several important exotic species jnFigure 3. The arrangement of communities alongthe ordinate combines the gradients in altitude and

"moisture status. The curves for species. therefore.demonstrate their ranges of tolerance of differingmoisture and temperature levels. However. theydemonstrate also the relative resistance or Jack ofresistance of canopy species to burning and grazingon different sites.

FIGURE 1. Average re/alive ground cover contri-buted by leading physiognomic dominants to Otago

grassland commuJ1ities.

The physiognomic dominants form a replace-ment series in Figure 1. For exampJe, Festucal1ovae-zelandiae is weakened at the dry end to bereplaced by Agropyron scabrum and Ruoulia.ChioJ1ochloQ rigida at low altitudes tends to bemaintained against shrub encroachment followinglire and heavy grazing but on drier sites gives placeto Festuca J1ovae-zelandiae. Throughout a widesubalpine zone of weakness the narrow-leavedsnow tussock has been removed or greatly reduced

GROUND COVER BY PHYSIOGNOMIC DOMINANTS

65

DALY: ORDINATION OF GRASSLAND IN OTAGO

by fire and grazing. In moist situations, however,both the Chionochloa grassland and Hebe odorashrubland remain as remnants. Drier, exposedsituations now carry Festuca matthewsii grassland.and the fire-resistant Poa colensoi has increased

to overriding dominance in most of the zone. OnIhe exposed, cold and windswept alpine plateaux,

the highly adapted Celmisia viscosa, Dracophyllummuscoides and other mal and cushion plants havelong dominated. The scattered Chionochloa tus-socks in such vegetation may. however, remainfrom former alpine grassland.

FIGURE2. A verage relative ground cover contri-buted by some prominent ground species to Otago

grassland communities.

The cover by ground species fluctuates withboth degree of cover by canopy grasses and shrubsand the environmental gradients. For example.Raoulia hookeri is prominent in dry, eroding shortgrassland, Raaulia hectori in moist, cold, erodingalpine cushion/herbfield. Pernettya macro.,agmaand Pentachondra pumila contribute their highestcover to low- and mid-altitude Chionochloa rigidagrassland and Hebe odora shrubland. Such vegeta-tion flourishes on leached yellow-brown earth soils.containing abundant charcoal from former forests.The wide range of Raoufia subsericea is clearlySeen in Figure 2 but this species, together withothers such as Carex wakatipu, is most prominentin the low tussock swards at subalpine altitudes.These ground species may have increased on beingreleased from unfavourable conditions of illumina-tion beneath previously-intact snowgrass canopies.

In Figure 3 a line representing the average per-centage of bare soil in communities has beensuperimposed. The driest and the most elevatedcommunities have today the least vegetative coverand appear to offer conditions too severe for

vigorous establishment and growth of inlroducedspecies. Grasses such as Anthoxal1thum, Agrosti.,and Horcus reach Iheir highest cover values inDiscaria-dominated grassland, The presence ofabundant Discaria may indicate relatively fertilesoil and less severe compeHtion for light from

.canopy Species.

FIGURE3. A verage relative ground cover of someimportant exotic species in grassland communitiesof Otago. Average percel1tage of bare soil has been

superimposed.

The flatweed, Hypochaeris radicata has the dis-tribution of a species able to exploit open soil butwith low competitive ability in closed swards. Thecurves of Figure 3 show clearly that these intro-duced plants reach their ecological limit in sub~alpine vegetation. Bare soil areas on alpineplateaux thus remain largely unoccupied asjndigenous species, with few exceptions, appearunable to re-establish.

Ordination of stands

Figure 4 provides the ordination of standsaccording to the two pdncipal axes of variation.Symbols representing stand positions identify themwith the accompanying key to the physiognomicdominants. For the ordination to be an adequateabstraction of the vegetation, stands appearing

66

GROUND COVER BY PROM!NENT SPECIES GROUND COVER BYIMPORTA.NT EXOTIC SPECIES

LEGEND

x Pea caespi toso

.. AgropyronRaoulia

c OiscariaFestucQ

. Festucanovae zet

, LowAll.Chion. rigida

. Mid All.Chicn. rigida

- Hebe adomChicn. rigida

A Festu},a "matt ewsil

0 ~balPinea colensoi

IS! SubalpineChicn. rigida

~ Celmi sicDrac. muscoides

0 Chicn. rubra

V Carex/Chion. rubraCortcderia

" Sphagnum I CarexO.-eobotus

DALY: ORDINATION OF GRASSl.AND IN OTAGO 67

ORDINATION OF OTAGO GRASSLAND STANDS(BRAY & CURTIS METHOD)

PRIMARY AXIS

FIGURE 4. A two-dimensional ordination of stands of grassland and related vegetation in Otago. Sym-bols identify stand positions with the key to physiognomic dominants.

close together should be very similar in composi-tion. In general this appears to be so. For somestands such as those dominated by Poa caespitosa,a third axis might provide a more efficient group-ing. The ordination shows clearly that these com-munities form a continuum with both graduallymerging and with relatively clear changes from onecommunity to another. It is as well to note, though,that the Bray and Curtis method of ordinationusually over-emphpasises the continuum and is lessefficient than the more recently devised techniquesof Orloci (1966) and Austin and Orloci (1966).

The ordination places most of the subalpinestands in an apparently mixed group. Thisappears to result from the inadequacy of grouping

according to the physiognomic dominants whenthere is considerable similarity throughout inground species composition. The ordination thuslends support to the possibility that most subalpinecommunities of mineral soils are stages in modi-fication of Chionochloa rigida grassland.

An interesting feature of New Zealand's indigen-ous grasslands is the large group of species withbroad ranges of tolerance. Connor (196 I, 1964,1965), in his studies of indigenous grassland inthe Mackenzie Country and Canterbury, hasdefined them as "widespread species". In thispreliminary ordination of grasslands in Otagosome of the lack of discontinuity between com-munities is very likely caused by the degree of

DALY: ORDINATION OF GRASSLAND IN OTAGO

ORDINATION OF OTAGO GRASSLAND STANDS(BRAV&CIJRTlSMETHOD)

FIGURE 5. Stand moisture scores plotted on theordination of stands of grassland and related vege-tation in Otago (Range: 0 - arid. excessivelydrained to 12 - semi-aquatic, poorly drained).

similarity between many stands conferred by thesewidespread species.

In Figure 5 the moisture scores have been plottedon the stand ordination. Moisture scores increasefrom right to left along the primary axis. Altitudeappears more strongly related to the secondaryaxis as seen in Figure 6. However, the two environ-mental variables are not independent, each beingassociated with both axes, thus causing a skew inthe orientation of the cluster of points representingstands. Effects of local variation in topographyand cultural modification probably obscure someof the indirect influence of altitude on vegetation-level climates, particularly in montane areas. Therelatively small number of stands sampled inalpine communities probably magnifies the diverg-ence of extreme stands from the point-cluster.

The distributions of relative cover by individualspecies according to stand position emphasisesthe usefulness of the ordination. For example,Bulbinella angustifolia achieves its highest groundcover in montane grasslands of moderate moisturestatus (Fig. 7). There is an interesting discon-tinuity in its distribution, as it appears to besucces"ful also in wet Chionochloa rubra grassland.

FIGURE6. Stand altitude plotted on the ordination

of grassland and related vegetation in Otago. Alti-tude is related to variation along both axes as itinfluences both temperature and precipitation.

ORDINATIONOF OTAGO GRASSLAND STANDS

(BRAY & CURTIS METHOO)

68

ORDINATION OF OTAGO GRASSLAND STANDS

(!lRAV & CURTIS MET~OO)

BULBINELLA ANGUST1FOLIAReIQtive Ground Cover

MO!STUREREGlME

ALTITUDE

(F..t.Wt)

. ',""-'~'" ~..~

FIGURE 7, Distribution of Bulbinella angustifolia

on the stand ordination.

DALY; ORDINATION OF GRASSLAND IN OTAGO

FIGURE 8. Distribution of Raoulia subsericea on thestand ordinulion. The grouping of stands in whichR. subsericea reaches high relative cover has heen

emphasised.

The soils vary in moisture level but those in whichBulbinella thrives are all likely to have good drain-age and aeration.

The wide range of Raoulia subsericea is clearlydemonstrated in Figure 8, as is the grouping ofstands where the species has high cover values.Again, to demonstrate the almost discontinuousdistribution of some montane and alpine species,the relative cover estimates from Agropyron scab-rum and Anisotome flexuosa have been plotted inFigure 9. These two species were recorded togetherin only one stand. The dwarf herb Anisotomeflexuosa is limited to vegetation at higher altitudesbut over a wide range of moisture. The lax tussockgrass, Agropyron scabrum is most prominent in themontane sites but it, too, may grow successfully inmoist grassland, though limited possibly by com-petition.

Conclusion

Ordination techniques such as those used in thispaper appear to have considerable value in theecological analysis of New Zealand grasslands.

FIGURE 9. Relative ground cover by Aoistome

flexuosa and Agropyron scabrum on the standordin'.lfion, showing the almost discontinuous dis-

tribution of the two species.

More detailed sampling and methods of treat-ment of data such as the weighted similarity ordin-ation of Orloci (1966) could be used to relatevariation in vegetation with accurately measuredenvironmental parameters.

This report forms part of a study of indigenousgrasslands of Otago using continuum analysis. Anattempt has been made to relatc variation in grasslandand related vegetation to the principal environmentalgradients.

Stands were sampled throughout the grassland andrelated vegetation west of the coastal hills and eastof the Cromwell Gorge. In each stand rapid point-records were takcn to obtain relative values of coverfor all macroscopic plants. Average relative values ofground cover for the leading physiognomic dominantsand some prominent ground species are graphed foran arrangement of communities. These performancecurves emphasize species optima and ranges of toler-ance. The overlapping distributions indicate the con-tinuum of vegetation along a gradient of increasingaltitude and changing moisture.

69

ORDINATION OF OTAGO GRASSLAND STANDS(BRAV&Cu.ms METHOD).

RADULIA SUBSERICEARclalivOl Ground Cover

ORDINATION OF OTAGO GRASSLAND STANDS(BRAY & CURTIS METHOD)

ANISOTOME FlEXUDSA

ROlla!ivOl Ground CovOlr

AGROPYRON 5CA6RUM

Relative Ground Cover

70 DALY; ORDINATION OF GRASSLAND IN OTAGO

Coc/1icients of dissimilarity between stands were com-puted as a partial matrix and these dissimilarity valuesformed the basis for the construction of a tv.'o-dimen.sional ordination using the method of Bray and Curtis.

CONNOR, H. E., 1965. Tussock grasslands in the middleRakaia Valley. Canterbury, New Zealand. N.Z. J.B01. 3: 261-76.

The relationship between stand position and moistureand altitude is very marked. The ordination appearsto be an adequate characterisation of the vegetation.Cover values for Blilbinella--a/lgustifolia, Raoulia sub.seric('a, A lIisolome ffexllOsa and Agropyron sCllhntmhave been plotted and their distributions discussed.

HOLLOWAY,J. T.. 1954. Forests and climate in theSouth Island of New Zealand. Trmls. Roy. Soc.N .Z. 82: 329-410.

MARK,A. F.. 1955. Shrub land and grassland of Maunga-tua. Otago. N.Z. J. Sci. Tech. 37A: 349-366.

From these preliminary results it is considered thatordination methods are of value in the presentationand analysis of causal relationships between indigenousgrasslands, component species and their environments.

MARK, A. F.. 1965b. Central Otago: Vegetation andmountain climate. pp. 69-91 in: Celltral Otago.Special pub!. N.Z. Geog. Soc. Misc. Ser. 5. Christ-church. 1965.

REFERENCES

MARK,A. F.. 1965a. The environment and growth rateof narro\v-leavcd snow-tussock. Chionochloa rigida.N.Z. J. Bot. J: 180-93.

AUSTIN, M. P.. and ORLOCl, L. 1966. Geometric modelsin ecology. II An evaluation of ~ome ordinationtechniques. J. Eco/. 54: 217-27.

MARK, A. F.. and BURRELL, 1.. 1966. Vegetation studiesin the Humboldt Mountains. Fiordland. Part I.The alpine tussock grasslands. Proc. N.Z. £col.Soc. 13: 12-19.

BEALS, E., 1960. Forest bird communities in the ApostleIslands of Wisconsin. Wilsoll Bull. 72: 156-81.

MARK, A. F.. HILL, J. K.. and DOUGLASS, B., 1960. Alalld capability survey of the Moullt Benger di.~-Iriet, Central Otago. Un pub!. MS., Otago Catch-ment Board. 1960.BILLINGS, W. W.. and MARK, A. F.. 1961. Interaction

between alpine tundra vegetation and patternedground in the mount3ins of southern New Zealand.Ecology 42: 1R-31.

BRAY, 1. R., and CURTIS, 1. T., 1957: An ordinationof the upland forest communities of southern Wis-consin. Ecol. MOilOgr. 27: 325-49.

MOLLOY,B. P. 1.. BURROWS,C. 1.. Cox, J. E., JOHNSTON,J. A.. and WARDLE,P.. 1963. Distribution of sub-fossil forest remains. eastern South Island, NewZealand. N.2. J. Bot. 1: 68-77.

COCKAYNE, L. 1928. The vegetl1tioll of New Zealand.2nd cd. Engelmann, Leipzig.

ORLOCI, L., 1966. Geometric models in ecology r. Thetheory and application of some ordination methods.J. Ecol. 54: 193-215.

CONNOR, H. E.. 1961. A tall-tussock grassland com-munity in New Zealand. N.Z. J. Sci. 4: 825-35.

WARDLE, P.. 1956. Botanical survey of the upper Shot-over Catchment. OU1Ko Catchment Board Bull I:24-37.

CONNOR, H. E.. 1964. Tussock grassland communitiesin the Mackenzie Country. South Canterbury. NewZealand. N.Z. J. Bol. 2: 325-51.

ZO"rov, V. D.. 1938. Survey of the tussock-grasslandsof the South Island, New Zealand. N.Z. J. Sci.Tech. 20A; 212-244 and D.S.I.R. Boll. 73. 1939.