sign in sign up
<<
Home , Antarctic Convergence, Chionochloa, Climate of New Zealand, Near Oceania, Oceanic climate

Gillison, A.N. (1994 *Oo"*i"* of the Gtasslands of . In Ihtwai Taprate Grasslatf,s: Evasia, , tuuth Arerica and Oreania, etl. R.T. Corplantl In firaslestens of the l/orJd ed-in-chief D.ll. cmdalL, 88. pp. 303-313. Elserrier Scientific hrblishing Co., . Chapterl2

OVERVIEWOF THE GRASSLANDSOF OCEANIA

A.N. CILLISON

INT'RODUCTION foundedby variationin climatc,soils, tcrrain, is- land size and patternsof land use. Some of the The grasslandsof Oceania arc distributedin land areastreated here are outside Oceaniascnsrl fragmcntcd units over a region extending some stricto and includc "outlicrs" such as Hawaii, the 105degrees longitudinally [from (120'E) Philippinesand the sub-Antarcticislands. These to Pitcairn Island (13,5'W)]and 78 degreeslat- havebeen includcd to providc a morc appropriatc itudinally Ifrom thc Northern regional biogeographicframework. A broad indi- (23"N)to the sub-Antarcticislands (55'S)1. Within cation of the regional distribution of major grass this vast territory, the land arca of approximately tribcsis givcnin Thble12.1. 8 509400 km2 supports a human population of Comparativestudies of grasslandswithin Ocea- about 2-5060000,the area per head ranging from nia are made complex by extreme variation in nearly 0.3 ha in Tirvalu zrnd to 14 ha in physical environmcnts: although semiarid Aus- Papua Ncw and 44 ha in Australia.Al- tralia containsextensive areas of "pure" grassland, though thc proportion of land which has been the south-wcstPacific island grasslands are mostly convertedto grasslandtcnds to vary directly with fragmentedmosaics distributed along locally vari- populationpressure, clirect relationships are con- able - often steep - physical environmental

TABLE I2.I

Compositionof the grassflora (?, contributcd by cach major tribc) in sclectedlocalitics in and near Oceania.compared with the gkrbal avcragcl

Locality Agrostcac Andropogoncae Avcncae Eragrostoac Fcstuccire Paniceae Others

Ilawaii (belowr'. 1300n) 5.'7 | 1.4 6.8 8.{) 17.0 35.2 t-5.9 , Philippincs 2.3 33.7 l.l 7.4 2.9 -33.7 18.9 PapuaNew Guinea 5.5 29.6 1.6 8.3 11 22.2 22..2 Kimbcrlcv Dist., W Austrahir 28.2 10.9 9.I 3.6 29.1 19.I De Grel'. Wcstern Australia l.l 1-5.7 r0.l 22.5 27.(l 23.6 South-wcstcrnQueensland 1.1 10.6 8.0 2l .3 1.8 18.6 35.3 SouthernS. Alrstralia 10.,1 12.3 2.0 26.0 9.7 3-s.I Thsmania 21.2 3.0 14.1 2.0 :1.0 28.4 South-westernNcw Zcaland 25.3 29.3 30.7 | 1.7 Ave rage u.,+ 15.2 10.8 9.0 13.0 19.9 23.7

Normal distribution spectrum(global) 8.2 I 1.9 6.3 IJ.I r6.5 2.4.3 rThc valucs usedarc from Hartley (1950),cxccpt for ,which arc basedon listsof grassgencra extractcdfrom Henty (1969).Hawaii and the Philippincsarc not parts ol Oceania.tensu stri(to. but are of intcrcst for biogcographiccomprrisr)n.

303 304 A.N. GII-LISON

gradientswhich may be variously associatedwith islands.ln thc tropical Pacific, on thc woody species.Similarly, in thc sub-Antarcfic is- othcr hand, thc closcsterlilnitics of lands,grasslands are componentsof ecosystems are with the upper montane and sLrbalpincfbrma- rather than ccosystcmsin their own right. tionsof New Guinea. The fbllowing filur chirptersare concerncdwith Partly becauscof a sparsefossil record, thc ori- the grasslandsof Oceania:Australia (Chapter l3), gin of the gcne pool from which Occanic grass- Ncw Zealand (Chaptcr 14), the strr-Antarctic is- lands havc been dcrivcd is unclcar. Thkhtajan lands (Chapter 15) and the south-west Pacific (19{19)and othcrs have argucd a case for likely (Chapter16.) centrcs of origin for thc Attgiospcrms,one focal area being north-casternAustralia - a hypothesis which tends to be supported by thc more rcccnt ORIGINSAND AFFINITIBS findingso1' Audlcy-Charles (1987). A numericerl analysisof world grassgencra by Simon and Ja- Uncertainty surrounds the origins of grassland cobs(1990) postulates that, with the exccptionof in Oceania.Whatever the pre-humanevtllutionary the pooids,the currently recognize.lgroups of thc determinants.the close interaction between man Poaceacarc Condwanan in origin. Thc analysis and grasslandin both Australia (up to 40 000ycars by Simon and Jacobs(1990) has dcmonstratcd or r.rlorewith fire) and Papua New Guinea (at closeaffinitics between thc tropical Paciflcgrasses least 9000 ycars with slash-and-burnagriculture) ernd those of thc cold tempcratc (mesotherm/ suggcstsit is logical to include humans as a "nat- microthcrm) oceauic islands,whercas grasslands ", albeit reccnt, evolutionary component for of microthcrm/mesothermAustralia and New thcseareas (Cillison, 1972). Zcaland have closer ties with Hawaii and the As with large arcas of south-casternAsia and Antarctic zonc. The affinitiesof thc sub-Antarctic the ,in recent times many grasslands islandgrasslands with SouthAnterica (Gre mmen, have becn initiated by slash-and-burnagriculture 19t12;scc also Chapter 15) are also reflectcdirr and by fire-bascdhunting practiccs.ln Australia, thc findingsof Simon and Jacttbs,whcrc, at thc before thc arrival of European man in thc 1780s, genericlevel, therc are evidcnt links betweentrop- aboriginal huntcrs manipulatedthe spatial extcnt ical Asia, Australia and parts of the western Pa- and structural and floristic composition of many cillc. woodland savannasand grasslandsby "patch"- Although providing a useful lbcus firr regional burning in ordcr Io c()nccntralcgr()ups of grass- geographic studies. phytogcographiczrnalyses ol eating animals such as kangarclosand wallabies. grass gcncra alonc are inappropriatc for cctl- Although the use of hrc tbr hunting is also logical intcrpretation.Therc is a nced ttl take widespread in and ,thcre is into accountvariability in cnvironmentas well as no parallcl in Australia fbr aboriginal slash-and- in functions and floristics in orclcr to pro- burn subsistenccagriculture. vide clearcr insights into evolution zrnddevelop- This background, together with the uncertain mcnt and into responscsto envirttnmentalchange. origin of many so-calledexotics, also crcates prob- Throughout Oceaniathere are "grasslands"which lems in dcfining"naturalness". There is continu- arc closely associatedrvith, or sttmetimcs dom- ing debatc about thc origins of the New Zealand inirtcd by, cypcraceousor other graminoids.Thc alpine and grasslandbiotas that have developed pervasivedistributicln patterns of thesegraminoids only recently and continuc to evolve rapidly (scc and their close ecologicaltics with true grasses Chapter l4). The New Zealandgrassland vcgeta- suggestthat they should be included in studics tion dcveloped following a major orogerryin thc involvinggrasslands. Pliocene and Late Tertiary and was latcr subject Instcad of cclncentratingsolely on grass taxa to limiting climatcsunder Pleistoccneglaciation. (c.g. genera),somc of thc questionsconcerning The generallack of drought in New Zealand, and grasslandorigins may be bctter focuscdusing mul- the relatively cool oceanic , distinguishit tivariatc analytical techniqucs involving identifi- from the continentalenvironment of Australiaand able, rcsponsc-basedattributes of graminoidsas givc it a closeraffinity with Thsmaniaand the sub- a whole. Functional groups in granrinoiclscan bc 305 OVERVIEWOF THE GRASSLANDS OF OCEANIA

the islandsin the sub-Antarcticcon- characterized in part by specific forms of acid Miocene.For likely that the climate has remained decarboxylationand associatedenzymic pathways vergenceit is past 10000 years (see (Prendergast,1989) and by other functional char- relativelyconstant over the acteristics(Gillison, 1988).By examiningthe spa- Chapter15). tial and temporal distribution of these functional groups along defined physicalenvironmental gra- dients,potentially useful models cou,d be derivcd which woulcl assistin interpreting graminoid ori- Bioclimate classification gins. For Australia and the larger islands (New Zealancl, New Guinea) and parts of the sub- Within Oceania, present-day rangc Antarctic, various authors have argued that his- from extremes of seasonal tropical lowland on torical climatic fluctuations,and in particular os- the one hand and alpine on the other to cold cillatory glaciation, have profoundly influenced non-seasonalregimes in the sub-Antarctic' Be- the establishmentand maintenanceof grasslands' there are broad climatic similaritiesbetween Periglacialactivity in parts of the sub-Antarctic cause and low-altitude/high- (e.g. Macquarie Island) also affectsthe establish- high-altitude/low-latitude latitude domains,the use of terms such as "trop- ment of grasses(l-offler et al., 1983; see also ical" and "temperate" can misleadwhen compar- Chapter 15). These processesfuel speculation ing grasslandclimates between regions (Oliver, about grasslandorigins. Apart from geomorphic processeslgrassland domains have a broad his- 1919). The bioclimatic framework used in Chapter 16 iory of expansionand maintenanceby man-made (see also Gillison, 1983) to compare the grass- fire, except perhaps in the sub-Antarcticislands' lands of the south-westPacific has been extended In New Zealand it is argued that the origin of following discussionto apply to Oceania grasslandsfollowing the arrivalof early Polynesian in the categoriesof havebeen accom- as a whole. This is based on broad N settlersover 1000years ago may the whole plant to and not be purely py- optimal growth responsesof I panied by , of defined thermal domains.The use of a response- z rogenic.In PapuaNew Guinea, the connection approachof this kind makes possiblemore lowland with upper montane and subalpinegrass- based ecologicalcomparisons between grass- lands through the agency of man-made fire has meaningful regionswith broadly similar climatesthan can I facilitated the spread of lowland graminoids and land obtained with other, more arbitrary methods associatedintroduced plant and animal species' be (see Nix, 1983, and Table 12.2)). Nix's approach Little is known about the likely origins of sub- made possiblea simplisticbut relatively uni- Antarctic grassland.Although the earliestvegeta- has comparisonbetween grasslandsin high and tion is recorded from the Tertiary and Quaternar!, form low latitudes with similar bioclimates.Although there is some evidence in the Iles de Kergue- are broad similarities in such contrasting len of loss in overall floristic richnesssince the there

TABLEI2.2

The bioclimaticclasses used by Nix (1983)

temP. Bioclimatic Photosynthetic Optimum temp' Lower tcmp. UPPcr thrcshold threshold class PathwaY CC) cc) ('c)

Megathcrm Ca and CAM 30-32 It) 4b 36-38 Megatherm Ll 26-28 10 Mesotherm Cr 19,22 5 33 25 Microtherm L.-l r2-14 U 25 Hekistotherm L-l 68 l0 306 A.N. GILLISON

climates of the sub-Antarctic convergenceand sis, Brachiaria, Cenchrus, Digitaia, Melinis, Pan- tropical alpine areas, significant dilTerencesex- icum, Pennisetum and Setaia). In this region, ist in rainfall seasonality,solar radiation inten- semi-permanentto permanent swamp formations sity, day-length and wind. These differencesare commonly contain indigenous oryzoid C-l "wild- reflected in different plant functional character- rice" genera (Leersia and Oryza) and arundinoid istics expressedin the same (pooid) genera; the Phragmites. sub-Antarctic grassesare mesomorphi.:and the Two andropogonoid Ca grassesImperata cylin- tropical alpine grassesxeromorphic. Other func- drica and Themeda triandra (formerly T. aus- tional characteristicsrelated to the photosynthetic tralis) typify much of the humid Australian and pathway of grassesreveal a strong concentration Papua New Guinean megatherm grasslands.For of Ca acid decarboxylationtypes (especiallyan- this reasontheir presencein southernmesotherm/ dropogonoid taxa) towards the megatherm - microtherm Australia,where Cj grassespredomi- sonal bioclimate and a converseincrease in the nate, is diflrcult to explain on functional grounds. proportion of Cj types along a decreasingther- In seasonallyor permanentlymoist environments, mal cline to complete Cr (pooid) dominance in membersof the andropogonoidsub-tribe Saccha- the sub-Antarctic.In applyingthis classification,a rinae (Miscanthus and Saccharum) are conspicu- bioclimate domain is defined as "seasonal"if the ous. lt is puzzling that, although Miscanthus is coefficient of variation in annual rainfall durins widespreadthroughout the south-westPacific, it is the year exceeds600/o. not indigenousto Australia despite the presence of an apparentlysuitable bioclimate. As with some Megatherm grasslands other grassgenera, the distribution of Miscanthus may be due largely to historical trading activities In generalterms the stronglyseasonal megath- (cf. Simon, 1988).Maritime megathermgrasslands erm grasslands include many CAM- and Ca- are the norm for many south-westPacific islands, based vegetation types. For grasslandsthis do- often with Imperata cylindrica, Ischaemum spp. main is dominated by C+ Andropogoneae (cf. and tall rottboellinoid species of Rottboellia and Johnson and Tothill, 1985). In northern tropical Ophiuros. Deliberate annual firing of these grass- Australia, perennial, chloridoid "spinifex" hum- landsby man is common. mock grasses,especially Plectrachneschinzii and The se;rsonal megatherm woodland savan- Tiiodia basedowii,occupy the drier seasonalinte- nas of southern and south-westernPapua New rior north of 22'S, whereas in areas with more Guinea are characterized by Eucalypttts spp. and than 1200 mm mean annual rainfall there tends Melaleuca spp. This reflects a structural and floris- to be a divergenceinto "seasonal" and "peren- tic continuum with the savannasof Cape York nial" andropogonoids, for example within the Peninsulain Australia.These mixed grasslandsare genus So4glruz. Some of the most extensive tus- unique within Oceania.In where sock grasslandswithin this Australian zone are Melaleuca("Niaouli") savannasoccur without Ea- those on cracking clays dominated by Astrebla ca lyp tus, taxa ( i nclud i ng M ela le uc a quinqueneruia) spp. (Mitchell grass). These are relatively pure which are common to both Australia and New grasslandswhere the botanical composition is Caledoniaexhibit much wider environmentalam- strongly influenced by rainfall seasonality.Like plitude. The structureand floristic compositionof the spinifex-dominatedgrasslands of the more grasslandsin the smaller islandsof the south-west arid interior, they are unique within Oceania. It Pacific reflect the combined effects of oceanic cli- is not surprisingthat, in northern megathermsea- matic buffering, relatively lower floristic richness sonal Australia, graminoids with Indo-malesian in the island domains, increasedvulnerability to affnities occur towards the warmer, more hu- invasive exotics, and varying and often intense mid extremes.These include in particular, mem- land use. bers of the tribes Andropogoneae (Arthravon, The fragmented nature of many megatherm Capillip edium, Chry s o p ogon, D icha nt hium, E ulalia, grasslandsmakes difficult their comparisonwithin Heteropogon, Imperata, Ischaemum, Saccharum, the region. Apart from localized, repetitive pat- Sorghum and Themeda) and Paniceae (Alloterop- terns of mid-height to tall grasslands(typically OVERVIEWOF THE GRASSLANDSOF OCEANIA 307 of species of Heteropogon,Miscanthus, Themeda be dominatedby Ca andropogonoidand panicoid and members of the Rottboellinae), therc are groups, in semiarid Australia the largest propor- non-grassgraminoid componentswhich occur re- tion of grassesis representedby the chloridoid xe- peatedly throughout the region. Apart from typ- rophytic hummock (Plectrachne and Tiiodia) and ical herbaceouscyperaceous elements, these are tussock (Astrebla) grasses, which otherwise are woody, rosulategraminoids represented mainly by megatherms.Within this broad region, soil type Pandanaceae(Pandanus spp. and Sa-arangaspp.) is a critical determinant in grasslanddistribution. and palms, especiallyLivistona. Whereas Pan- This is especiallyevident in respectto speciesof danaceaeare distributedthroughout Indo-malesia Astrebla(see Chapter 13). and the megathermPacific generally, they appear There is an evident climatic correlation with to be particularly well developed in south-west vegetation change throughout most of the area Pacific grasslands. The genus Sararanga is re' of mesotherm/megathermoverlap. The "semi- stricted to the Philippines,the arid crescent",which stretchesfrom south-western and the New Province of Papua New through to the shadow Guinea where it occursin typicallyhumid habitats. west of the Great Dividing Range to north- Pandanus ranges acrossa wide spectrum of physi- ern Australia, lies within this area. This con- cal environments fr<.,mseasonal megatherm (Figs. stitutes an ecotone between the arid shrublands 16.3,16.10, 16.19 and 16.24)to cooler mesotherm and grasslandstoo dry for arable agriculture and situations. the higher-rainfalltemperate and tropical wood- The broad-leaf fan palm Livistona is repre- lands in which crops can be grown. The drier sented in Papua New Guinea by L. brassii (Fig. boundary of the crescentin southern and eastern 16.10), and another ten species(approximately) Australia approximatesthe limit for introduced occur in Australian savannas.The distribution pasturespecies (see Chapter 13). pattern of this palmoid grassland formation is Towardsthe cooler mesotherm region there is repeated in similar environments around the a gradual change from Ca to Cj grasses (es- megatherm seasonaltropics in various, presum- pecially Arundineae, Stipeae and Aveneae). In ably functional, analogues(e.g. Borassus,Mauritia lowland semiarid southern Australia these may and Sabal). As with Pandanus,the global distribu- be variouslyassociated with halophytic chenopod tion of this grasslandtype hasyet to be studied in shrubs- the saltbushes(Atriplex spp.) and blue- detail. Another feature of Australian and south- bushes (Maireana spp.) - often with scattered west Pacific grasslandsis the frequent association -form Eucalyptus spp. (Chapter 13; Car- of other woody rosulategrowth forms and, in par- nahan, 1990). These southern xerophytic grass- ticular, their distribution along thermal gradients. lands are often invaded by Mediterranean annu- In the lowland megatherm grasslandsthese are als (e.g. Hordeum leporinum and Medicago spp.). represented by the genus Cycas (C. media and C. In Australia, temperate (mesotherm) sl.rort-grass rumphii) (Fig. 16.11)and in montane,mesotherm/ vegetation occurs between 2J' and 42'S, with microtherm grasslandsby tree-fernsof the gcnus the proportion oi Arundineae,Pappophoreae and Cyathea (Figs. 16.14, 16.15 and 16.16).Apart Stipeae varying inversely with mean annual air from the Cyathea association which appears to temperature. In the montane and upper mon- be unique to New Guinea, the Cycasassociation tane grasslandsof Papua New Guinea, there is a is pantropical; yet its ecologicalconnection with parallel development in C3 groups - especially grasslanddoes not appearto havebeen examined Aveneae (Anthoxanthum, Deyeuxia, Dichelachne, in a global context. H ieroc hlo i:), Arundineae (Chio no c h loa) and Isach- neae (lsachne species. The "trunked" nature of Mesotherm grasslands some grasses,such as Chionochloa archboldii, is conspicuousin moist environmentsthat are fired Within the warmer part of the mesotherm episodically.This trunked habit has some struc- range there is considerable spatial overlap be- tural and possibly functional affinities with ro- tweengrasses with mesothermand cooler megath- sulate semi-ligneous [Cyathea spp. (Fig. erm growth optima. Whereas the latter tend to 16.15) and Pandanus spp.] associatedwith up- A,N. GILLISON 30u

grasslands per montane and subalpinegrasslands. Although Microtherm/hekistotherm the adaptive aspectsof this form require further restricted to very small study, there are clear implications for adaptive These grasslandsare mountains of southern Aus- convergencein a widc range of taxa - including areas of the high and New Guinean grasses- in other tropical high mountainsin the tralia, and the New Zealand The closebioclimatic world (suchas Africa and ). alpine and subalpinezones. sub-Antarctic Other montane mesotherm grassla,rdsin the afflnitiesbetween thc hekisttltherm microthcrm grass- south-westPacific are relatively few. But where grasslandsand the essentially subalpineareas suggest they exist - for example on Mount Thbwe- lands of these alpine and one entity. The broader- masana (11100m) in Espiritu Santo in they should be treated as grasses(mainly C3 arundi- - they are typicallyC4 megathermtypes with tall ranging microtherm common to the alpine, grasses(Rottboellinae) and andropogonoid Im- noid and pooid groups)are zones of Australia, perata cylindrica and Themeda triandra (see Fig. subalpine and high-montane Guinea. These form tus- 16.8).On the island of Savaii in Western , New Zealand and New height (0.2-1.2 m), and Imperata cylindrica occurs on montane lava flows sockformations of varying are influencedby soil with a short herb and moss layer, as well as on their growth fbrm and cover so in Papua New a montane cinder cone and ash plain' Other as- and aspect (this is not always - Although the ecolog- sociated species are Oplismenus compositu's and Guinea seeSmith, 1977). Ncw Guinean Paspalum orbiculare (Whistler, 1978). The appar- ical altnities of the high-altitudc (30' to -55'S) ent elevational"depression" ofvegetation in these grasslandsare with high-latitude woody elements smaller islandsmay be related to the Massenerhe- southern Oceania, they contain - (Rhododendron spp-) - bung effectr. especially Ericaceae links with the The New Zealand mesotherm grasslands re- which have strong biogeographic semblein floristic and structuralprofile the south- . ovcrlapping thcr- ernmost temperate short grasslandsof Australia Although there are closely grass genera common to (cf. Chapter 13). Differenccsderive from the pre- mal ranges, the only New Zealand and Papua dominantly of New Zealand and microtherm Ar-rstralia, pooids, , Festuca the lessbulTered of Australia. New Guinea are the C3 climate similar- Whereasin the is rcla- and Poa. Despite the apparent islands and the tively non-limiting,within the South Islandof New ities between the sub-Antarctic othcr areas, the rollcd, Zealand there is a marked rainfall gradient, which alpine grasslandsof the New Zealancl pooids decreasesto the east in the form of a xeromorphic leaves of the with the high-montane from the Southern Alps. This exerts a major in- suggest closcr affinities grassesrather than with thc fluenceon the structureand compositionof grass- New Guinean tussock sub-Antarctic species, lands and associatedvegetation types. Drought is mesomorphicforms of the laminae' Limited stud- not a feature of New Zealand vegetation, "de- with their broad, flattened indicate that these are sertic vegetation" being the only major plant for- ies of shoot/root ratios alpine zones than else- mation absent from the two islands.Below the much higher in tropical Other features of the New Zealand alpine grasslandslie mesothermtus- where (cf. Chapter 15). are unique in Oceania' sock or bunch grassesdominated by speciesof sub-Antarcticislands, that associatedwith grass- Poeae (Festuca and Poa),which reflect the growth are the large-leavedforbs these arc representcd forms of tropical mesotherm and sub-Antarctic land. On Macquarie Island and Stilbocarpa polaris microtherm grasses. by Pleurophyllum hookeri and, on the ilcs de Kerguelen, by Pringleaanti' scorbutica.lt is worth noting the convergencein form betwecn the rhizomatous Srilbocarpapolaris (Macquarie Island cabbage)and Rheum rhabar- | islands "Massenerhebungeffect" rcfers to situations on largc barum (domestic rhubarb) which is widespread ocourring at high elcvation inland' also where vegetation, in . Another large forb common in occurs at incrcasingly lower elevation towards the coast (sec Fennoscandiais Archangelica.Al- Chapter 16.p. a37). and sub-Arctic OVERVIEWOF THE GRASSLANDS OF OCEANIA 309 though large forbs are absent from New Guinea and phosphorusfrom -bornenutrients. Sig- microtherm grassland habitats (except Gunnera nificant atmospherictransfers of nutrients tiom - spp. along forest edgcs in moist sitcs), thcy oc- the sea to the land through aerosolsand pre- cur in alpine and subalpine areas of Africa and cipitation in oceanicclimates. Manuring South America (e.g. Lobelia and Espeletia,respec- by animals and sea birds also contributes signifi- tively). cantly,especially in the sub-Antarcticzone. Some Despite some similaritiesin tropical alpine and limited studiessuggest that there also may be sig- sub-Antarctic climates, there are significant dif- nificant nitrogen input to the soil by blue-green ferences (see Chapter 15). Radiation loads are algae.Nutrient pathwayshave been little studied, considerablyless in the sub-Antarcticzone. and but, due to the paucity of vertebrate herbivores photoperioclicamplitude is much wider' In the in some areas,energy may be channelleddirectly sub-Antarcticislands, precipitation is non-limiting through the detritus food chain (Chapter 15)-Nu- for plant growth and relative humidity is always trient transfersfrom vegetationto soil are reduced high. There are also strongyear-round winds aris- in the megatherm seasonalenvironments, where ing from anti-cyclonichigh-pressure systems which annual burning of grasslandremoves signi{icant - exert a dominant effecton the aspectof vcgetation amountsof labile nutrients especiallynitrogen, - (Lofller et al., 1983).Although winds reach gale potassium and sulphur whcreas phosphorus force in the high mountains of New Guinea, they ancl other macronutrientstend to be lost in ash are without the same intensity or persistenceas run-off. In New Zealand, earthworms play a sig- those in the sub-Antarcticconvergence. A notable nificantrole in soil-nutrientmobility (Chapter 14). feature of the sub-Antarcticclimate is its relative The conspicuouspresence of earthworm castsin stability throughout the year. Although Hnatiuk seasonallyflooded grasslandsof the Sepik Plains (Chapter 15) comments that tropical alpine ar- in PapuaNew Guinea and on the north-eastcoast eas of Papua New Guinea also show little cli- of also suggeststhat these inverte- matic variation, the high-montane,south-eastern brates play a significantrole in nutrient relation- extremitiesof the main cordillera of Papua New ships,where the store of soil nutrients is other-wise Guinea (e.g.Mount Sucklingat 3300m elevation) impoverished. do exhibit distinct seasonality(personal observa- Despitethis apparentrange of nutrient inputs,a tion). limited set of productivity data of annual herbage production from grasslandtypes acrossa range of Grassland productivity bioclimates(Thblc 12.5)indicates that mesotherm grasslandsare the most productive. There are no comparativestudies of grassland productionwithin Oceania.Most productivitydata Effects of humans and other animals are available in different forms, which complicates cross-tabulation.The data presentedin Chapters In recent times man has exerted a powerful l3 to 15 (summarizedin Table 12.3) indicate re- influencein the conversionof forest to grassland gional bioclimatic trends in herbage production by fire and agriculture. In the south-westPacific in defined grasslandtypes. Despite the paucity of the rate of spread of anthropogenic grasslands data,the mesothermnatural and introducedgrass- is increasingwith population pressureand forest land speciesappear to out-perform their megath- removal. erm and microtherm counterParts. In Oceania humans have been major agentsin Natural nutrient input varies with bioclimate extending and maintaining grassland.Influences and geographiclocation. Nutrient inputs appear range from primitive slash-and-burnagriculture to increase away from megatherm seasonalityto- throughout the south-westPacific, to purposive wards the highly buffered, oceanic, microtherm/ firing to drive game or else modify vegetation fbr hekistotherm environments. This may be due subsistence(e.g. firing to increaseproductivity of mainly to nutrient input in the latter from ma- the edible fern Pteidium esculentum by Maori). rine animalsand seabirds and to increasedatmo- In some areas - such as highland Papua New sphericdeposition of nutrients,especially nitrogen Guinea - as population pressurehas increased, 310 A.N. GILLISON

TABLE 12.3

Net annualherbagc production (g . ') in variousgrassland types in selectedbioclimatos within Oceaniar

Region Bioclimate Grassland type Production

Australia megatherm tropical tall grass seasonal Themeda triandra I 12-t70 ThemedaI Sorghum 120 Heteropogon contortus 250-750

mcgatherm xerophytic tussock (Astrebla spp.) 128-18rJ

megatherm/ xerophytic hummock grass mesotherm Tiiodia pungens 94

mesotherm "Mediterranean" pasture (+ Trilolium subtenaneum) -s94

New Zealand mesotherm short tussock grass Chiono c hlo a cras s iusc ula 949 C. pallens 718 C. rigida 539 C- macra 346 C. oreophila 180

tall tussock grass Chionochloa 750-I 042

Sub-Antarctic: 2 Marion Is. microthcrm tussock grass Poa cookii 465

South microtherm Poa flabellata 6025

I Bascd on assumed total above-ground production in one growing scason. 2 Based on total above- and under-ground estimates in one growing (data from Moore, Ch. 13; Mark, Ch. 14; Hnatiuk, Ch. 15).

slash-and-burnagriculture has changedto seden- ter 13). In New Zealand, deer (Cervus elaphus) tary methods with accompanyingreplacement of are three times as efficient in energy use as sheep tall grassesby relatively short grasses(e.9. Imper- (Chapter 14). The impact of feral deer speciesin ata cylindrica and Themeda tiandra) - and often New Zealand has heen greatly reduced in recent with increasesin invasiveweeds and overall lossin yearsby culling for meat. In southern PapuaNew plant production. Guinea the population of introduced rusa deer In Australia, the extent of grasslandhas in- (Ceruus timorensis) has risen to a point where it creasedand undergonemodification since the ar- is competing significantlywith the indigenousag- rival of Europeans in 1788.Carnahan (1990) has ile wallaby (Mauopus agilis) for a highly seasonal estimatedsome of these changes(Thble 12.4),of grasslandfood resource. In a Hawaiian coastal which the conversion to graminoid crops (cere- grassland,Mueller-Dombois (1981) reported re- als and sugar cane) and pasture with introduced sults from a grazing exclosure where, afier one speciesis the most significant.Introduced - decade he identified four dynamic categoriesof ing animals in both New Zealand and Australia plant responses.One form ("persisters") could have had a major impact on grassland.Vast tracts be divided into stable and oscillatorytypes. The of semiarid Australia have been modified under latter can be comparedwith speciesshowing simi- grazing pressure over the last century (see Chap- lar behaviour in Mitchell grass(Astrebla) lands in OVERVIEWOF THE GRASSLANDSOF OCEANIA

TABLE 12.4

Extent(l0l km2)of Australiangrassland fitrmations - pastand prcscntl

Structural form Beforo 17802 At prcsent

area o/"3 area

NATURAL GRASSLANDS Hummock grassland 45 0.6 4-5 0.6 Closedgrassland/sedgcland t4 0.2 25 0.3 Ti:ssock grassland/scdgeland 359 ^a 326 1.2 Opcn tussock grassland 115 1.5 348 4.5 14 0.2 15 0.2 Sparse grassland : Subtotal )+/ 72 859 9.3

GRASS UNDERSTOREY IN WOODLANDS Hummock grasses 2045 26.9 2065 26.8 2385 31.0 2308 30.0 Tirssockgrasscs : Subtotal 443[l )/.v 4313 563-

ARTIFICIAL CRASSLANDS Sown pasture (, 0.0 136 5.6

I From Carnahan(199t)). 2 That is, bcfore the arrivai of European settlers. I 7o of total land area.

semiarid megatherm/mesothermoverlap areasof islands of the tropical south-westPacific. In the Australia. former, 32 species of invasive plants have be- The influence of native animals on vegetation come persistentor naturalized (Chapter 15). Of in the sub-Antarctic islands is far more benign, these, Acaena magellanica continues to spread as none is a herbivore and most (e.g. seals and with disturbance and grazing by introduced an- penguins) contribute significantlyto the nutrient imals, especially rabbits. In the south-west Pa- resource.The introduced animals tell a different cific (Chapter 16), apart from introduced weeds, story. Mostly introduced as a source of food by which also increase under grazing pressure by early sealers and whalers, these are many and cattle,continual firing and removal of woody veg- varied, including cattle, cats,horses, mice, mules, etation by logging or gardening have paved the pigs, rabbits, rats, reindeer, sheep, and flightless way for invading exotic grasses. The two most rails (wekas). Whereas some populations have significant are Pennisetum polystachyon and Pan- been reduced, others persist. As with mainland icum maximum. The former continues to spread Australia, on Macquarie Island rabbits have cre- rapidly (Figs. 16.7and 16.26)with increasingland ated profound changesin grasslandfloristics and degradation.Associated with thesegrasslands are structure,and a concertedprogram of eradication two conspicuous woody weeds, Leucaena leuco' using a mlxoma virus has been under way for cephala (Fig. 16.7) and Psidium guayava, which, severalyears. together with Muntingia calabura, rapidly occupy overgrazedand frequently fired lands. Vulnerability to exotic species Although many exotic specieshave invaded the "natural" grasslandsof New Zealand, the richer As a general rule, the relative impact on in- and more diverseflora in Australia has rendered digenous biota by invasive exotics increaseswith the grasslandsless subject to the entrance of in- decreasingisland size and distance from main- vaders. However, the massive invasion of prickly land sources.In this respect,at least for plants, (Opuntia spp.) in the early 1900s is an ex- the sub-Antarcticislands are no different to the ception to this pattern, and more recently other 312 A.N. GILLISON

TABLE 12.5 In this respect a minimum set of biophysicalat- tributes using attributes of plant function as well Summaryof tribesin Australiawith morc than 1o/oof the total numberof grassentities r, showingthe relativeproportlon ol as structure and floristics should be developed naturalizedoxotics (in descendingordcr) 2 which can be directly related to temporal and spatialchanges in the physicalenvironment. Tiibe Native Naturalized entit ie s cntities No. % No. o/c REFERENCES

Paniceae r87 68.8 85 31.2 Audley-Charles,M.G., 1987.Dispersal of Gondwanaland:rel- Eragrostideae 154 88.t) 2l 12.0 evanceto evolution of the Angiosperms.In: TC. Whitmore Andropogoneae 130 88.4 17 I 1.6 (Editor), B iogeogra p hic al Evo luti o n of the M alay Arc hipelago. Danthonieae 107 95.5 5 /< '71.6 Clarendon Press.Oxlbrd Agrostidcae 76 22 a1 I Carnahan,J.A., 1990. Vegetation. In: J.A. Carnahan (Com- Aristideac 64 100.0 0 0.0 piler), Atlas oJ'AustralianResources. Third Series, 6, Aus- Stipeae 6l 92.4 5 7.6 tralian Land Surveying and Land Infbrmation Group, Poeae 55 55.0 45 45.0 Dept. of Administrative Serviccs,Canbe rra. Chlorideae 30 75.0 10 25.t) Gillison, A.N., 1972.The tractablc grasslandsof Papua New Pappophoreae 20 100.0 tJ 0.0 Guinea. In: J. Ward (Editor), Change and Development Sporoboleae l6 76.2 5 23.8 in Rural Melanesia. Fifth Waigani Seminar, University of Phakrrideae lf 60.0 10 40.0 Papua New Guinea and Australian National University. Aveneac 8 27.6 29 78.4 Port Moresby, pp. 16l-172. Micraircae 8 100.0 U 0.0 Gillison, A.N.. 1983.Tiopical savannasof Australia and the Tiiticeao 1 16.7 20 83.3 southwest Pacific. In: F. Bourliere (Editor), TropicalSavan- Bromeae I 4.0 a1 96.0 ,?c.r.Ecosystems of the World, 13, Elscvicr, Amsterdam' pp.183-243. I E,ntities include speciesand infra-specilic taxa. Gillison, A.N., 1988. A plant functional attribute prolirrma 2 From Simon (l98l). for dynamic vegctation studies and natural resource sur- veys. CS/RO Aust. Division ol Waler Resourc'es,Canbera' Tich. h'lemo..R8/.1. -12 pp. invaders have appeared (Chapter 13). Although Gremmen, N.J.M., 1982. The Vegetationof the Is- Australian grasslands have suffered invasion by lands Marion and Pince Edward. M.J.A. Werger (Editor)' native woody weeds,there are some conspicuous Geobotany,3, Junk, , 1'{9pp. Hartley, W., 1950. The global distribution of tribcs of tho exotics.The grasslandsof northern Australia are Gramineae in relation to historicaland cnvironmcntal fac- rub- currently being invaded by the Madagascan tors. ALtsl.J. Alric. Res., l: 35-5-373. ber vine (Cryptostegiagrandiflora), and in swampy Henty, 8.E., 1969.A manual of the grassesof New Gurnea. areas in the north-westby Mimosa pigra, fot which Papua New Guinea Dep. fttr. Bot. Bull., 1,215 pp- urgent control measuresare being sought.Simon Johnson, R.W and Tothill, J.C., 1985.Definition and broad geographicoutline of savannalands. In: J.C. Tothill and (1981) has provided an analysiswhich showsthe J.J. Mott (Editors), Ecologt and ManaEiementoJ the Workl's grass that relative proportion of the existing flora Sat'annas.Australian Academy of Science,, in as- is made up of naturalizedexotics (Table 12.5). sociationwith Lommonwealth Agricultural Bureaux,Farn- ham Royal, Bucks.,PP. 1-13. Lolfler, 8., Sullivan,M.E. and Gillison,A.N.. l9ll3. Periglacial CONCLUDINGREMARKS landfbrms on Macquarie Island, subantarcticregion. Z. G eomorphol., N.F,, 27: 223-236. Mueller-Dombois,D., 1981.Vegetation dynamics in a coastal future for grasslandsin the region is not The grasslandof Hawaii. In: P Poissonct' F. Romane, M.P promising given the present and likely continu- Austin. E. van der Maarel and W. Schmidt (Editors), ing levelsof disturbance.To develop better man- VegetationDynamics in Grasslands, Heathlands ancl Mediter- agement tools, a more comprehensiveand spa- raneanLigneous Formations. Junk, Thc Haguo. (Repr- from tially referenced regional data base is required Vegetatio,46: I 3 1-140.) Nix, H.A., 1983.Climate of tropical savannas.In: F. Bourlidre monitoring. This should include for inventoryand (Editor), Tiopical Savannas. Ecosystemsof thc World, 13' response-basedmodels built from a basic knowl- Elsevier,Amsterdam, pp. 37-62. edge of how grasslandsrespond to environmental Olivcr, J., 1979. A study of geographicalimprecision: thc change along local as well as regional gradients. tropics. lasl. Geog,rStud., 17'.3-17 . OVERVIEW OF THE GRASSLANDS OF OCEANIA 3r3

-260. Prendergast,H.D.V, 1989. Geographicaldistribution of Ca thc Austrafian flora. Aus trob a ileya, 3: 239 acid decarboxylationtypes and associatcdstructural vari- Smith, J.M.B., 1977.Vegotation and microclimatcof east-and ants in nativc Australian grassos (). Aust- J- Bot., west-facingslopes in the grasslandsof Mt. Wilhclm, Papua 1". )<2 f71 New Guinea.J. Ecol.,65: 39 -53. Simon, B.K., 1981.An analysisof the Australian grassllora. Thkhtajan, A., 1969. F'loweringPlants, Origin and Dispersal. Au.\lruhail(yd, | : .l5b-.r7 l. Oliver and Boyd, ,31t) PP. rcgion of Simon, B.K., 198tJ.Thc biogeography of the Australian Whistler, W.A., 1978. Vegctation of the montane grasses.Proc. Ecol. Soc.Aust., l5:261 269. Savai'i.Western Samoa. Pac. Sci.,32:'79-94. Simon, B.K. and Jaoobs,S.W.L., 1990.Gondwanan grassesin