Pacific Science (1992), vol. 46, no. 2: 111-127 © 1992 by University of Hawaii Press. All rights reserved

Vegetation Ecology of Fiji: Past, Present, and Future Perspectives!

JULIAN ASH 2

ABSTRACT: The Fiji Archipelago comprises a Tertiary island arc with several hundred small and a few large mountainous islands near the northeastern corner of the Australian tectonic plate, 3000 km from continental Australia-New Guinea. Despite contrary prevailing winds and ocean currents, the flora is very largely derived from that of Malesia, and the largest component was probably dispersed by frugivorous birds or bats, of which several taxa are established in Fiji. About 25% of the native vascular plant species are endemic and, with exceptions such as the relictual Degeneria, most have apparently diverged from overseas conspecifics. There are a few cases where speciation has occurred within Fiji but virtually none where reproductive isolation is established, permitting cohabitation. Until the arrival of humans, perhaps 4000 and certainly by 3000 yr B.P., the vegetation was predominately rainforests with stunted cloud forest at high altitude, though some more open communities might have occurred in drier areas. The forests have a mixed species composition, including most ofthe 1769 native species, and demographic observations indicate peak population fecundities after several hundred years for canopy trees and 80 years for several subcanopy taxa. Flowering phenology offorest species is seasonal with predomi­ nately synchronous annual or, in a few species, biennial frequency, while fruit maturation is spread throughout the year. Cyclones cause frequent minor damage and infrequent major damage, especially to coastal and ridge vegetation, and cause landslides. Insect-induced dieback has been recorded but there are no extensive single-species rainforests, except swamp forests, so the effects are diffuse. The impact of humans has been to convert much of the drier forest to frequently burned sedge-fern-grasslands, to create garden-forest successional mosaics around settlements in wetter areas, and, more recently, to selectively log much ofthe remaining accessible forest. Many plants have been introduced and established in cultivated or disturbed areas, increasing the flora by about 50% and largely excluding native taxa from those areas. Habitat conversion is thus the major threat to the conservation of Fijian native vegetation.

THE FIJI ARCHIPELAGO LIES in the seasonal a volcanic base. The larger, older islands have tropics, with most islands between 16° and mountainous interiors rising to 1320 m, com­ 19° Sand 176° E to 178° W, about 3000 km east prising dissected volcanic landforms, uplifted ofcontinental Australia-New Guinea (Figure marine sediments, and limestones. Taveuni is 1). The total land area of 18,376 km2 is largely the product oflate Quaternary vulcanism and in the islands of Viti Levu (56%) and Vanua has a mountain range with scoria cones, Levu (30%), with a further 300 islands ex­ craters, surface ash layers, and Holocene lava 2 ceeding 2.6 km , numerous smaller rocky flows (most recently 2000 yr B.P.). Some is­ islets, and sand cays on reefs. The surrounding lands in the eastern Lau group are raised coral ocean is 2-4 km deep, and all the islands have reefs and have little or no surface exposure of the underlying volcanic rocks. Rotuma, a small island 500 km to the north, is not I Manuscript accepted 2 May 1991. 2 Botany & Zoology Division, Australian National considered in this review. Alluvial coastal University, GPO Box 4, Canberra, ACT 2601, Australia. plains extend from valleys, and their shores III 112 PACIFIC SCIENCE, Volume 46, April 1992 have fine muddy sediments where there is of only about 6°C. Rainfall and cloudiness is offshore protection by coral barrier reefs. strongly influenced by the prevailing south­ Coarser beaches occur where there is only a east winds, and annual rainfall typically rises fringing reef to impede wave action, and cliffs from about 2000-3000 rom on southeast 2 and dunes (2 km ) are restricted to a few coasts and small islands up to 5000-10,000 localities where deep water extends to the mm on mountain ranges, declining to as low coast. During the last glacial period sea levels as 1500 mm on the northwest coasts of the about 150 m below present levels would have larger islands. There is a marked seasonal exposed reefs and lagoonal sediments, espe­ pattern, and although localities with annual cially around the larger islands (Figure 1). Sea rainfalls exceeding about 5000 mm rarely level rose to slightly (45 cm) above present experience prolonged soil water deficits, areas levels in the mid-Holocene, 5000 yr B.P. (Ash with less than about 2000 rom usually experi­ 1987a), a situation that may be repeated by ence several months ofsoil water deficit within current projected rises in sea level. the June-November period. Cyclones, bring­ ing high rainfall and high winds, occur every CLIMATE. The climate is oceanic, with sea­ few years. During the last glacial period level temperatures averaging about 22°C in (20,000-14,000 yr B.P.) it is estimated that July and 26°C in January with a daily range temperatures were 3-4°C lower in summer,

Yacata 0

Vatu Vara@

VsnU8 Vatu t!> ~ Vatulala (i) ~oala

(f!Jrotoya

@Matuku

• Vatoa 100 KILOMETRES - Ono-i-Lau

FIGURE I. Map of the main Fiji islands (black) and reefs including the -150-m underwater contour delimiting islands at the lowest sea level in the glacial period, about 18,000 yr B.P. Vegetation Ecology of Fiji-AsH 113 the cloud base was reduced by 100-200 m Geological Origins ofFiji and rainfall was 30-50% reduced (Souther~ 1986), leading to increased periods of soil The Fiji Archipelago is an emergent portion water deficit and fewer cyclones. of the Tertiary Vitiaz island arc-basin system (Green and Cullen 1973, Crook and Belbin 1978, Rodda and Kroenke 1984, Monger and HUMAN POPULATION. Archaeological evi­ dence suggests that humans first settled in Fiji Francheteau 1987) near the northeastern cor­ at least 3300 and perhaps 4000 yr ago (Shaw ner of the Australian tectonic plate. Fiji is 1975, Southern 1986, Allen et al. 1989), and about 800 km west of the Tonga Trench where the Pacific Plate is being subducted at genetic evidence (Serjeantson 1989) suggests 1 that the founder populations were Polynesian rates of about 8 cm yr- , and within the zone that has been subject to vulcanism with later immigration by Melanesians. Indi­ clockwis~ rect evidence of population growth is avail­ fracturing, westerly shearing, and able from geomorphic and palynological rec­ rotation associated with the northerly contact ords, which indicate that forest clearance has between the two plates (Figure 2). Immediate­ occurred throughout this period (Southern ly west ofthe archipelago is an extensive sub­ 1986), with consequent erosion from hills and merged fragment of Gondwanic sialic rock siltation of coastal habitats and nearshore the Fiji Plateau, bounded by the Vanuatu and coral reefs (Hughes et al. 1979, Ash 1987a). Vitiaz trenches. The plateau is thought to have Forest clearance was occurring at the center originated as part ofthe Norfolk Island-New ~aledonia-d'Entrecasteaux of Viti Levu by 2000 yr B.P. (Southern 1986), Ridge, then ad­ close to the present eastern limit of such Jacent to northeastern Queensland, and to clearance and at similar dates in Lakeba have been carried northeastward by sea floor (Hughes et al. 1979), and an early phase of spreading during the past 80 million yr. These expansion may have been followed by agricul­ events are poorly defined and it is not known tural intensification. Undated prehistoric irri­ for how much, if any, of this period the gation/drainage systems are evident on most plateau might have been emergent, nor how alluvial flood plains (e.g., Rewa and Navua these developments relate to older Mesozoic [Parry 1977, 1981]), probably associated with Melanesian island arcs in the region. Evidence taro (Colocasia esculenta) cultivation. By the ofvertical uplift is apparent from the exposure early nineteenth century the population was of early Tertiary marine pillow lavas and variously estimated as 110,000 to 200,000, limestones in Viti Levu, but it is not evident mostly living around fortified villages and that any substantial islands were created until subsisting upon intensive horticulture supple­ the mid-Tertiary, perhaps 50 Ma and more mented by coastal marine foods (Derrick certainly 30 Ma when the South Fiji Basin 1950, Frost 1974, Gibbons and Clunie 1986). floor was spreading. Volcanic rocks of 7.5 Europeans introduced a cash economy and million yr age are found in Vanua Levu ?iversified agriculture, bringing about 60,000 (Rodda and Kroenke 1984). Uplift ofthe Lau mdentured laborers, mostly from India, to Ridge may only date to the past 2.5 million tend plantations of sugarcane, coconuts, etc. yr, associated with sea floor spreading be­ High fecundity combined with reduced child tween the Lau and Tonga archipelagoes (Katz mortality has since caused the population to 1977). grow rapidly, reaching about 730,000 in 1990 1 and increasing by 1.8% yr- . Indian emigra­ Origins ofthe Flora tion, following recent racially discriminatory legislation, currently removes this increase, BIOGEOGRAPIDC PATTERN. There is little but it is anticipated that the population will known ofthe fossil flora ofFiji before the past double by about 2050 and, perhaps, stabilize 23,000 yr (Southern 1986), so the develop­ at about 2 million. A quarter of the popula­ ~ent ofth~ vegetation can only be inferred by tion is now urban and 80% is within Viti mterpretatlOn of the current distribution of Levu, and these proportions are increasing. taxa. Balgooy's (1971) tabulation of the bio- 114 PACIFIC SCIENCE, Volume 46, April 1992

Pacific Plate

Australia

~ Spreading ridge

~.. ' Island arcs 10 Age m.y. c:::> Plate motion t Subduction zone Antarctica ~ (inactive)

FIGURE 2. Simplified geological map of the southwestern Pacific showing the major tectonic features and dates of past ocean floor spreading (compiled from various sources listed in the text). Vegetation Ecology of Fiji-AsH 115

geography of Pacific seed plant genera pro­ decline in the number ofplant genera, consis­ vides a guide to such reconstructions, and it tent with a Malesian source. It is notable, is evident that Fiji has very strong floristic however, that 70 Fijian plant genera are not links with Malesia-Asia. Of the 476 Fijian recorded in the intervening archipelagoes, genera, 90% are present in New Guinea, with suggesting that either about 15% ofcoloniza­ about 65-75% occurring in Australia, New tion was by direct long-distance dispersal, or Caledonia, and intervening archipelagoes. that both colonization and extinction have The geological history ofFiji suggests that the occurred on intervening islands. MacArthur archipelago only emerged after it had reached and Wilson (1967) proposed that islands have close to its present location with respect to a species diversity that results from the dy­ Australia-New Guinea, so the flora must namic equilibrium between colonization and have established by long-distance dispersal, extinction and is strongly controlled by the including "stepping-stone" spread along the area of the island, which limits their carrying Melanesian island arcs. This view is sup­ capacity. A plot of the number of seed plant ported by the absence in Fiji of some typical genera against archipelagic area for the south­ continental Gondwanic genera, notably No­ ern Pacific (Figure 3) suggests such a relation­ thofogus and Araucaria, which were wide­ ship, but the pattern is confounded by a spread on southern continents but seem un­ decline in area and habitat diversity with able to disperse long distances overseas (Ash increasing distance from Malesia. There is 1982). There are, however, a number ofbetter­ little evidence to document plant extinctions dispersed genera with southern Gondwanic on these islands except that Southern (1986) affinities such as Citronella, Coriaria, Cordy­ suggested that Quintinia became extinct in Fiji line, Cryptocarya, Dacrydium, Dacrycarpus, and Dacrydium and Dacrycarpus became ex­ Decussocarpus, Passiflora, Peperomia, Podo­ tinct in Taveuni at the end of the last glacial carpus, and Weinmannia (Thorne 1978). period, though probably as a result ofclimatic Passing eastward from New Guinea change rather than reduced island area. It is through the Solomon Islands and Vanuatu not clear to what extent island species diversi­ to Fiji, and on to Polynesia, there is a sharp ty is limited by extinctions, habitat areas, and

New Guinea• Cll... ~. 1000 (1) Solomons 01 New CaledO:la •• c: • FIJI Bismarcks -Cll Samoa • C. • Vanuatu • • Loyanles -o Tonga Society• ...(1) Santa Cruz .0 Norfolk • • E 100 • Tubal Cook ::J Rapa• • Z

100 1000 10000 100000 1000000 2 Area of island(s) ( km )

FIGURE 3. Relationship between the area ofarchipelagoes and islands in the southern Pacific Ocean and the number of native seed plant general (data from Balgooy 1971). 116 PACIFIC SCIENCE, Volume 46, April 1992

30"N

.<:--

,,0 0_ Hawaiian b Islands Mariana Islands ~ ~ Saipan', Guam .. ~ .?? --.~~ <--- Line Islands •

Phoenix Islands - ~ Mar~uesas :. _,Islands

~ • Tuamotu ~ ..::.~ Archipelago

Soc'ieiy' '. .:" Cook Islands Islands

Australia

" Kermadec Islands --- ( ( -- w <.0 -- g -

FIGURE 4. Map of the western Pacific Ocean showing the prevailing ocean currents in January and the number of naturally occurring water-dispersed mangrove species (partly after Woodroffe 1987). competition, but disjunct distributions and able correlation with ocean currents, though the presence of primitive endemics such as a few species extend beyond the present nor­ Degeneria suggest that extinctions have modi­ mal range of easterly currents (Figure 4). fied island floras. Suitable habitats are less abundant in Poly­ nesia but, with human aid, mangroves have DISPERSAL VECTORS. Ocean currents now been established on many previously uncolo­ flow steadily in a westerly direction past Fiji, nized islands, and the pattern of mangrove though midsummer southeasterly currents in distribution may be taken as a model for the Solomon Islands region might occasional­ Malesian water-dispersed taxa with moderate ly penetrate nearer to Fiji (Figure 4). Man­ seed longevity. groves are water dispersed and their distribu­ Fijian strandline and beach species are tion illustrates the probable influence ofocean typically water dispersed and mostly show a currents. Of the approximately 30 mangrove wider distribution than mangroves through species in New Guinea and Australia, 19 the tropical Pacific (Guppy 1906, A. C. Smith extend through the Solomon Islands, 7 reach 1979,1981,1985, J. M. B. Smith 1990). These Fiji, and 4 reach an eastern limit in Samoa taxa apparently have more resistant and long­ (Woodroffe 1987). Evidently there is a reason- lived seeds than the precocious mangroves Vegetation Ecology of Fiji-AsH 117 and there are greater opportunities for their 1982, Gibbons and Clunie 1986). Certainly establishment in the central Pacific: the beach the prevailing patterns of ocean currents and flora ofone tropical Pacific island is much like winds are against dispersal from Malesia, and that of another and about 80% of Fijian overseas frugivore dispersal has not been beach species occur throughout the region. recorded, but it is evident that these events Overall only about 205% ofthe Fijian flora happen, probably much more frequently than is primarily water dispersed but a further 20% the minimum rate given above. Perhaps more may float and might be dispersed in this surprising is the minor contribution ofAmeri­ manner. Some taxa, such as Cerbera and can taxa to the flora, since water and wind Barringtonia, may have dispersed as strand­ both favor westerly dispersal and even igua­ line species and since evolved inland forms nas have made this journey successfully (Bal­ and species. gooy 1971, Gibbons and Clunie 1986). Despite the prevailing southeasterly winds, Polynesians and Melanesians evidently in­ occasional northwesterlies or cyclones could troduced a variety of crops and weeds, and transport some seeds and spores from Ma­ probably established at least a hundred spe­ lesia, and spore-dispersed pteridophyte spe­ cies, mostly in disturbed habitats associated cies (Brownlie 1977) and bryophytes (Whittier with gardening (Kirch 1983). With increasing 1975, Huerlimann 1978, Scott 1982) are wide­ international traffic during the past 150 yr, spread in suitable habitats in Fiji and neigh­ several hundred new species have been estab­ boring archipelagoes. The small seeds of or­ lished including many American and some chids and plumed seeds of Alstonia and As­ African taxa. About two new weed species teraceae are probably wind dispersed over and three new cultivated species are intro­ long distances. Small seeds from capsules and duced each year, such that the Fijian vascular small winged seeds, such as Gymnostoma, may plant flora has increased from about 1769 also be blown over considerable distances, but species before human arrival to at least 2600 it is unclear whether larger winged-seed taxa species: a 50% increase (Parham 1972, Smith such as Agathis and Gyrocarpus experience 1979, 1981, 1985). About 95% of introduc­ significant long-distance wind dispersal. It is tions are herbaceous. Itis observed that about difficult to determine which seed plants could 60% of introduced grasses, 40% of intro­ be transported long distances by wind but it duced herbs, but only 20% of introduced is probably at least 10% of the flora. woody taxa establish outside cultivation. As The majority of Fijian seed plants are ad­ yet, very few taxa have established in undis­ apted for animal dispersal, mostly with fleshy turbed native forests. In contrast, the floras of fruits, and the occurrence of several fruit bat heavily disturbed sites, subject to cultivation, and frugivorous bird genera (Watling 1982), grazing, or fire, tend to be dominated by principally pigeons and doves, suggests that introduced species and natives are infrequent these were responsible for much overseas or absent (Parham 1959, Ash and Ash 1984). plant dispersal, especially for forest species adapted to inland habitats. Endemism and Speciation Ignoring probable speciation events within Fiji, there have been at least 1400 successful Ofthe 1769 native vascular plant species in seed plant and 250 successful pteridophyte Fiji, about 75% are recorded from other colonization events over a period of perhaps archipelagoes, especially Samoa, Tonga, and 10-30 million yr, suggesting a minimum rate Vanuatu, and many of the ca. 400 endemics of one successful colonization event every have closely related species elsewhere, sug­ 6000-20,000 yr. Current rates ofnatural colo­ gesting that rates ofoceanic dispersal are high nization are unknown and may have fluctu­ relative to rates ofdivergence and speciation. ated in the past. Lower sea levels during At the generic level, endemism through diver­ glacial periods would have both increased gence is suggested in the Rubiaceae (Gillespiea island areas and created new island "stepping­ [one spo], Hedstromia [one spo], Readia [one stones" between Fiji and Malesia (Watling spo], Squamellaria [three spp.], and Sukunia 118 PACIFIC SCIENCE, Volume 46, April 1992

[one sp.]), Arecaceae (Neoveitchia [one sp.: shrubs, 35% are epiphytes (including many Gorman and Siwatibau 1975] and possibly ferns) and climbers, and the remainder are Goniocladus [one sp.]), and Sterculiaceae terrestrial ferns and herbs. Typically the single (Pimia [one sp.]), though several ofthese taxa most common species may account for up to are not adequately known (Parham 1972, about 15% of a vegetation stratum in a Smith 1979, 1981, 1985). The sole endemic particular habitat, and small clusters of each family, Degeneriaceae (two spp., Miller 1988), species are common but extensive stands are represents a primitive form ofangiosperm and rare except in swamps (see below). In general is presumably a relict from a wider, earlier the forests are taxonomically diverse, in keep­ Malesian distribution. ing with most tropical rainforests. Evidently most plant speciation in Fiji is at On the drier northwest side of the large the level of primary divergence from taxa islands and on small islands (Garnock-Jones elsewhere, together with some taxa showing 1978), what remains of the lowland forests divergence on different Fijian islands (e.g., suggests that the species diversity, particularly Degeneria, Homalium, Pandanus, and Veitch­ ofepiphytes, is lower and that species compo­ ia) and some diverging in different altitude sition is different. There are, however, few and climatic zones of the large islands (e.g., examples ofsuch forests, and these are mostly Aglaia, Alpinia, Balaka, Cryptocarya, Excoe­ restricted to rocky sites and have been caria, and Peperomia). Where an endemic disturbed. species occurs sympatrically, cohabiting with With increasing altitude there is a decline in a congener, their divergence generally appears species diversity of the forests and a gradual to have occurred outside Fiji, but cladistic and decline in canopy height. The cloud base is chronistic analysis of Fijian taxa has yet to be reached at about 600-800 m near southeast­ undertaken to confirm these patterns. Several ern coasts and at 900-1100 m inland, giving examples ofcohabiting endemics from within rise to cloud-shrouded mountain ridges sup­ a subsection of a genus (e.g., Psychotria) can porting cloud forests that have low rates of be identified from Smith (1979, 1981, 1985), photosynthesis, very low rates of transpira­ but mostly involve taxa that are poorly tion (e.g., 2 x 10-7 g cm-2 leaf S-1), and, known, so the probable time, place, and probably, low nutrient uptake (Ash 1987d). degree of divergence is uncertain. These ob­ Under these conditions, the trees are stunted servations suggest that for most taxa there has to 3-7 m height, climbing Freycinetia domi­ been insufficent time, selection pressure, or nates in the canopy, and epiphytes, especially opportunity for the evolution ofreproductive bryophytes, are abundant. Several endemics isolating mechanisms between plant popula­ (e.g., Ascarina swamyana, Medinilla specta­ tions within Fiji. In only a few families (e.g., bilis, M. waterhousei, and Paphia vitiensis) Arecaceae and Rubiaceae) does speciation are restricted to these conditions, each con­ appear to be relatively rapid. fined to a few adjacent mountaintops. At the generic level the cloud-forest flora has strong affinities to that on other neighboring Pacific Vegetation Structure and Dynamics archipelagoes, suggesting direct dispersal 2 RAINFOREST (8300 km ). The native terres­ rather than evolution from local rainforest trial vegetation of Fiji is predominantly rain­ taxa (Ash 1987d). forest, which varies principally in response to the climate (Berry and Howard 1973). On the FOREST DEMOGRAPHY. The population struc­ wetter southeastern side of the large islands, tures ofseveral forest tree, palm, and tree-fern the forests are diverse and mixed, including species have been examined (Ash 1985, 1986a, about 1350 vascular plant species (Smith 1979, b, 1987b,c, 1988a). Although some species 1981, 1985, Kirkpatrick and Hassall 1985, require the high light levels of tree-fall gaps Ash and Vodanaivalu 1989), of which about and clearings (e.g., Alpinia boia, Alstonia viti­ 20% are notophyll-mesophyll trees forming a ensis, Erythrina variegata, Macaranga vitien­ canopy at 20-30 m, 30% are small trees and sis, Parasponia andersonii, and Trema orien- Vegetation Ecology of Fiji-AsH 119 taUs), none seems to require extensive forest markedly seasonal, with some tree species disturbance for regeneration to occur. Repro­ being deciduous and many having a partial or duction in canopy-tree species generally com­ complete annual leaf flush. Most individuals mences when they reach at least half their of a species flower synchronously within a mature height coupled with high light levels, period of a few weeks. Endospermum macro­ whereas subcanopy species mostly reproduce phyllum is exceptional in flowering twice in once a certain size is attained together with a most years, and Barringtonia petiolata is ex­ moderate-to-fast growth rate. It appears that ceptional in flowering at irregular asynchro­ slow-growing individuals of subcanopy spe­ nous intervals 6-8 months apart. Most spe­ cies (e.g., Balaka microcarpa) may never re­ cies, though not all canopy individuals, flower produce. Using radiocarbon dating and once each year, but a few, notably those with growth ring and growth rate analysis to large slow-developing fruits, have a largely estimate ages, coupled with information on synchronous biennial pattern (e.g., Gonio­ seed production, the age-specific fecundity cladus and Pandanus). There do not appear to weighted by age-specific survivorship has be any species that normally have longer than been calculated for populations of several 2-yr intervals between flowering. species (Figure 5). A relatively large emergent, Generally, considering all forest species, Agathis vitiensis, reaches a peak in reproduc­ there is a peak in leafproduction near the start tion at about 300 yr; a smaller canopy tree, of the wetter season, about December­ Dacrydium nidulum, reaches a peak at about January, followed by a peak of flowering 200 yr, and the subcanopy palm Balaka micro­ in about January-March; fruit maturation, carpa and tree ferns Cyathea hornei and Lep­ which takes between 1 and 12 months in topteris wilkesiana all have reproductive peaks different species, is spread more evenly at about 80 yr. Evidently the factors control­ through the year with a peak in June­ ling fecundity and survival differ systematical­ September (Figure 6). The majority ofthe tree ly in different forest strata, and subcanopy species are apparently adapted for generalist longevity may be limited by local canopy-tree insect pollination, coinciding with the hotter longevity in addition to other factors. All wetter season. The major seed vectors, the these species, and others, appear to regenerate fruit bats and frugivorous birds, are depen­ frequently, though some local fluctuations are dent on the year-round supply of fruits, and apparent such that at a scale of 101 to 102 m2 their breeding seasons (Watling 1982) coin­ plants of similar age may occur together, cide with the peak in fruit abundance. This probably reflecting the scales of canopy dis­ essential community-level coordination of turbance, while at scales of 103 to 104 m2 such plant phenology with vector populations may peaks in regeneration are obscured. have arisen elsewhere in Malesia or it may have evolved within Fiji. At similar latitudes FOREST PHENOLOGY, POLLEN, AND SEED DIS­ in Australia many fruit doves and pigeons PERSAL. The phenology of Fijian forests is are migratory, following local trends in fruit availability (Crome 1975) while related spe­ cies in Fiji are relatively sedentary. Each Agathis vitiensis emergent tree major island has a different combination of Dacrydium nidulum • canopy tree frugivore species (Watling 1982), and there ~ubCanOpy Balaka microcarpa palm are typically only two to three fruit-bat species ~ubcanopy Cyathea hornei tree-fern and three to five pigeon and dove species on Leptopteris wilkesiana subcanopy tree-fern each Fijian island-far fewer species than in o 200 400 600 the larger islands of Malesia and only a part Age ( years) of the fauna present in Fiji, suggesting that area-related competitive exclusion might be FIGURE 5. Graph showing the relative age-specific fe­ cundity of various Fijian forest plants weighted by occurring between similar frugivores. This in population survivorship, standardized so that each spe­ turn suggests that the fruit resource is heavily cies has the same peak fecundity. exploited and limiting to the frugivores. There 120 PACIFIC SCIENCE, Volume 46, April 1992

20~ 320L-., 10 Deciduous 300~ I o -~~~ ~'" 80

>. 0 60 30 c: Leaf flush ,.. 0> \ ::l 20 0- \ ...0> 40 \ U. /I) CD 10 \ '0 Gl o""'-_"'-- ..L.__ Q. 20 /I) '0 ~ .c 30 0+----+----+--+----+----+ E o 5 10 20 40 80 ~ 20 Diameter ( em) 10 FIGURE 7. Histogram ofthe size-class frequency ofthe 0"'---"'------...... - shade-tolerant forest canopy tree A/una racemosa near 30 Suva showing deaths (black) due to an epidemic of bark-boring beetles in 1983. Ripe fruit 20 __ ... _ ~

10 ~ ~-- FOREST DIEBACK. There are no natural ex­ tensive single-species or single-genus stands o...... ------__-L._ of trees in well-drained Fijian forests (see ONDJFMAMJJASONDJFM swamps and mangroves discussed in follow­ month ing sections), and dieback is not obvious as an extensive forest-patch phenomenon, such as FIGURE 6. Graphs showing the average number of canopy-tree species deciduous, with leaf flushes, flower­ that in Nothofogus forests of New Guinea ing, and bearing ripe fruit each month, in a forest plot of (Ash 1988b) and in Metrosideros polymorpha 81 species and 500 trees near Suva from 1982 to 1985. forests of Hawaii (Mueller-Dombois 1985). However, individual species within diverse forests are affected, and an epidemic of bark­ does not appear to be much frugivore special­ boring beetles was noted in 1983 that caused ization, though some taxa feed primarily in mortality in subcanopy individuals ofpopula­ the canopy and some near the ground, and tions ofA tuna racemosa (Figure 7), a common most plant species of similar growth form canopy tree notable for its large seeds that probably experience similar patterns ofvector germinate and establish in clumps beneath dispersal. Excavations on Lakeba in the Lau and downslope of parent trees. Such dieback group and Naigani (connected to eastern Viti may explain why Atuna racemosa does not Levu in glacial times) have revealed various form extensive stands spreading from around extinct birds including large megapodes Me­ parent trees. gapodiusfreycinet and Proqura sp. and a large pigeon (Best 1984), all of which probably CYCLONES AND FOREST DISTURBANCE. Cy­ dispersed fallen fruits and seeds. With these clones, mostly coming from the northwest, are extinctions, coincident with human occupa­ a frequent source ofdamage to Fijian forests, tion, the dispersal of some large fruited and particularly near the coast and on ridges, understory species may have been reduced. where 150 km hr-1 gusts may be expected Introduced pigs and rats may have taken over every 5-10 yr, 200 km hr-1 gusts every 30-50 some of the dispersal functions, though they yr, and 250 km hr-1 winds might occur every are primarily seed predators. few centuries. Leaves, flowers, and fruits are Vegetation Ecology of Fiji-AsH 121 stripped off the trees every few years, and seeds for secondary succession (Nicholson major branches are broken and trees uprooted 1981). In higher-rainfall zones, cycles of gar­ every few decades. Certain emergents with dening and forest regeneration have been long spreading crowns are particularly susceptible and widely established around alluvial val­ to windthrow (e.g., Serianthes melanesica), leys, forming a mosaic ofseral stages in which but Agathis vitiensis is much more resilient species naturally favored by tree-fall gaps (see and apparently has the lowest rate ofcyclone­ above) are abundant. In the dry zone, fires lit induced mortality for a canopy species. The by man usually bum regenerating forest ex­ subcanopy environment is relatively fre­ cept in some fire-protected valleys and rocky quently subject to falling debris from canopy areas, and sedge-fern-grasslands, known as 2 trees, and this damage accounts for part ofthe talasiqa, now extend over most (3000 km ) of higher mortality ofsubcanopy plants and may the drier half of the large islands and over explain the similar fecundity patterns in the most small islands. It is debatable whether three species that have been examined (Ash there was any talasiqa land before humans 1986b, 1987b, 1988a). Heavy rainfall, asso­ arrived (Twyford and Wright 1965, Garnock­ ciated with cyclones, causes landslides on Jones 1978, Hughes and Hope 1979, Latham steep slopes, especially in the Serua hills of 1983, Southern 1986), though native taxa such southern Viti Levu where they are a significant as Cycas rumphii, Allocasuarina, and some component of forest disturbance, creating grasses apparently require fairly open con­ 2 4 2 bare patches of 10 -10 m . ditions. The 12 taxa Latham (1983) con­ sidered to be both native and restricted to LOGGING OF RAINFOREST. Selective logging talasiqa can, however, all be found in forest of old-growth rainforest, typically involving habitats, including rocky and coastal sites, in damage ordestruction of10-30% ofthe trees, Viti Levu. Southern (1986) considered that with extraction of the larger trunks for local during midglaci~l times the annual rainfall on (93 %) and export (7%) markets, is continuing the northwestern side ofthe larger islands may at a rate of about 60 km2 each year (yielding have been as low as 1000 mm, coupled with a 200,000 m3 timber), and it is estimated that all temperature decline of a few degrees, which of the accessible "production" forest will be might have favored these more-open vegeta­ logged by about 2020. This should leave about tion types. Subsequently, in the early Ho­ 2700 km2 ofunlogged, steep, catchment "pro­ locene, rainforests probably reoccupied much tection" forest, and about 5100 km2 of once­ of these areas. Many introduced species have logged or low-yield forest (Berry and Howard established in the talasiqa, and the flora typi­ 1973) that might provide a moderate sus­ cally includes Dicanthium caricosum, Miscan­ tained yield with a 50- to 70-yr logging cycle. thus floridulus, Panicum maximum, Pennise­ Logging operations give easy access to dis­ tum polystachyon, Sporobolus elongatus, and turbed forest and it is estimated that 5-10% the ferns Dicranopteris linearis and Pteridum of logged forest is subsequently gardened. A esculentum (Brownlie 1977, Smith 1979). Dur­ further 3-5% oflogged forest is being planted ing the past century much of the more fertile with Swietenia macrophylla (mahogany) or alluvial land in the dry zones has been culti­ Pinus caribea (Caribbean pine), and it is vated (Twyford and Wright 1965), especially intended that plantations of exotic species for sugarcane, and 750 km2 of Pinus caribea should gradually replace native rainforests as plantations are being established on the less the major source of timber. fertile hills: to date about halfthis reafforesta­ 2 SECONDARY VEGETATION (10,000 km ). Hu­ tion goal has been achieved. Currently (1990), man disturbance of the forests traditionally Fijian pine production is about 300,000 m 3 1 involved felling and burning to create gar­ yr , mostly from former talasiqa lands, and dens, or, perhaps, simply burning ofdry-zone supplies about 30% of Fijian timber needs. forests. The fate of such disturbed sites de­ pends very much upon subsequent distur­ FRESHWATER SWAMPS (55 km2). Several of bance and the presence of a local source of the craters on Taveuni, notably Tagimaucia 122 PACIFIC SCIENCE, Volume 46, April 1992

(Southern et al. 1986), contain lakes with Xylocarpus granatum) reach heights of 7-15 sedge swamps dominated by Lepironia articu­ m near the inland margins, declining in height lata growing around the margin on organic to 3-6 m and changing to a Rhizophora­ sediments and upon floating mats ofalgae and dominated seaward zone. On northwestern 2 cyanobacteria (5 km ). With annual rainfalls coastlines, with lower rainfall, soil salinities at of about 8000 mm, these swamps are rapidly the inland margin rise, through evaporation flushed by the very high run-off, and some during dry periods, and a zone ofhighly saline rain-fed surfaces support Sphagnum cusipi­ bare mud is replaced seaward by stunted datum hummocks. mangroves, principally Rhizophora, increas­ Frequently inundated areas of lowland ing in stature to 3-6 m height in the more floodplains apparently once supported stands frequently inundated seaward zone. Seeds and of Metroxylon vitiense, a monocarpic "sago" seedlings are generally abundant, frequently palm, perhaps commencing about 4300 yr B.P. germinating but generally not surviving out­ with the mid-Holocene stabilization and grad­ side the zone of parental trees, except on the ual fall in sea level (Southern 1986, Ash accreting mud flats ofthe estuaries where even 1987a). Metroxylon was apparently not used aged stands are formed and extend several as a source of sago in Fiji and stands do not meters each decade. seem to have been conserved or managed. The mid-Holocene marine transgression, to Some remaining Metroxylon stands occupy­ about +45 em (Ash 1987a), extended man­ ing several hectares near Deuba appear to be grove distributions across some low-lying predominantly ofeven age, their regeneration floodplains, and the subsequent fall in sea perhaps linked to changes in drainage and level induced a slow seaward successional flooding regimes. trend in the mangrove zonation, which may Prehistoric human disturbance of poorly now be reversed if sea levels rise. drained lowland areas with high rainfall ap­ Human impact on terrestrial ecosystems pears frequently to have followed a sequence has tended to increase siltation of adjacent of events commencing with forest clearance coastal regions, generally favoring mangroves for gardening, which, if abandoned, favored (Ash 1987a). Siltation of fringing reefs, lead­ sedge colonization and peat development ing to death of the corals and establishment (0-2 m deep), and, combined with occa­ of mangroves, is apparently reflected in the sional burning by man, created extensive changing composition of marine faunal re­ monocotyledon-dominated sedge-Pandanus mains in middens (Gifford 1951, 1955). Man­ 2 tectorius swamps (50 km ; Ash and Ash 1984, groves are one ofthe most intensively utilized Ash and Ash 1985, Southern 1986, Ash natural ecosystems in Fiji, being a source of 1987c). Recently, drainage of such sites fuel and of foods such as crabs, prawns, and is leading to their use for agriculture and fish. Near towns mangroves are, however, housing (e.g., Dreketi, Navua, and Rewa frequently under threat as Crown Land avail­ floodplains). able for infilling and redevelopment, while some rural mangrove stands have been en­ 2 MANGROVE SWAMPS (194 km ) AND SEA closed by dikes and drained for cultivation GRASS BEDS. Mangrove species are present (e.g., Dreketi Valley and near Labasa). Their around most of the more wave-sheltered acidic (sulfide-rich) soil has caused prob­ coastline growing both on fine silt and coarser lems for crops, and some reclamation schemes rocky substrates including silted fringing cor­ have been abandoned. Such interference with al reefs. With higher rainfall, on southeastern drainage and siltation has locally led to coasts and estuaries, the soil salinity is gener­ mangrove dieback in adjacent areas. ally maintained at about marine concentra­ Sea grass beds, principally comprising the tions. The trees (Bruguiera gymnorhiza, Ex­ widely dispersed Halophila ovalis, Halodule coecaria agallocha, Lumnitzera coccinea, Rhi­ pinifolia, H. uninervis, and Syringodium isoeti­ zophora stylosa, R. samoensis [plus infertile folium, are found seaward ofmost mangroves hybrids between the Rhizophora species], and and in shallow lagoonal areas. Although they Vegetation Ecology of Fiji-AsH 123

do not have a major direct role in marine ceptible to severe wind damage. Such distur­ herbivore food chains, they are an important bance apparently favors local dominance by food resource for turtles and act as a substrate particular species. These near-coastal forest for algae and provide protection for many habitats were often settled and cultivated by marine invertebrates, especially at juvenile Fijians and, in the last century, developed as stages. Fiji has a rich marine benthic algal coconut plantations, such that littoral forests flora with, perhaps, 70-100 genera and 120­ are generally fragmentary and disturbed. The 170 species, but it is not well known, nor are species are, however, well adapted to distur­ its dynamics and role in the marine food chain bance and although the undisturbed vegeta­ documented. tion type is scarce the flora appears to be reasonably widespread. BEACH AND ROCKY SHORE VEGETATION. As indicated in the discussion of seed dispersal, Future Developments the Fijian beach and coral cay vegetation is similar in floristics and dynamics to that of The human population of Fiji is expected most tropical Pacific islands. Beaches and to double or treble within the next century, rocky shores are subject to continual wave accompanied by a greater rise in demand for action and infrequently to the huge swells goods and services. The consequences are induced by cyclones that periodically scour both an intensification and extension of pro­ and reshape the beaches to considerable ductive activities. The increased rate of natu­ heights and distances inland. The seaward ral biological resource utilization is likely to edge of most beach vegetation is, therefore, a be met by raising the intensity and frequency successional community colonizing sand dis­ ofexploitation ofnative ecosystems, especial­ turbed by the last storm: creeping vines such ly forests for timber products and coastal as Ipomoea pes-caprae and Vigna marina dom­ ecosystems for marine foods. In both in­ inate this zone. On rocky substratesjustabove stances the age-class structure ofpopulations the normal wave range there is little soil will be forced to change, and slow-maturing material, drying winds, and salt spray, which species are likely to be disadvantaged. together exclude most taxa except a few ha­ Natural populations of primary forest lophytic succulents (e.g., Portulaca sp., Sesu­ plants reach peak fecundities at 80-300 yr vium portulacastrum, the sedge Fimbristylus and, though their growth is accelerated by cymosa, and the grass Lepturus repens). Far­ reductions in competition, faster maturing ther inland, out of the range of most waves, secondary species will be favored by the antic­ there is typically a zone of moderately salt ipated 20- to 40-yr logging cycles. This trend is spray-tolerant shrubs, such as Clerodendrum expected for most of the 65% of forest area inerme, Scaevola taccada, Wedelia biflora, and identified as production forest, though it may Sophora tomentosa, frequently supporting the be several cycles before the floristic changes parasitic Cassythafiliformis. The shrub zone become overwhelming. As these changes oc­ passes into a taller zone typified by Pandanus cur, it is likely that interplanting or replanting tectorius (Ash 1987c), and this passes into with exotic tree species will become prevalent. littoral forest vegetation often dominated by The future ofthe remaining 35% offorest set trees such as Barringtonia asiatica, Calophyl­ aside for catchment protection is dependent lum inophyllum, Cerbera mangas, Cocos nuci­ upon political considerations since many of fera, Cordia subcordata, Hernandia nymphaei­ these forests do contain exploitable timber folia, Hibiscus tiliaceus, Tournefortia argentea, resources. Over the past few decades much of Terminalia catappa, and Thespesia populnea. the interior of the large islands has been At Sigatoka on Viti Levu the beach vegetation penetrated by a network of roads, some a extends into partially forested dunes (Kirkpa­ consequence oflogging activities, others built trick and Hassall 1981). These coastal forests to villages and dams, all facilitating further and Pandanus are generally outside the zone logging initiatives. All-weather roads have ofcyclone-induced wave damage but are sus- generally attracted settlement and adjacent 124 PACIFIC SCIENCE, Volume 46, April 1992 forest clearance, a pattern that is expected to For most of the Fijian forest resource, continue. The trend to urbanization is strong, conservation concerns must focus on the man­ however, so population growth in remote agement of a forest that has been selectively areas may be slight while nearer to towns, logged once and is likely to be logged again. especially Suva, encroachment on the forests Logging procedures and management regimes is likely to accelerate. span the range from disturbance analogous to The more open habitats created by logging the infrequent ravages of cyclones to much and clearance favor exotic weeds. With the more frequent and intense practices that establishment ofa herbaceous vegetation cov­ transform the primary forest to a secondary er, whether horticultural, arable, or pastoral, and exotic-dominated community. The future the switch from a native to an exotic flora and of the extensive production forests and per­ vegetation type is virtually complete. Similar haps that of some protection forest will de­ changes are evident in the avifauna, with pend on the type oflogging thatis practiced. A the remaining native birds virtually excluded second major conservation concern is, there­ from secondary vegetation (Clunie and Morse fore, to develop and implement silvicultural 1984), and similar changes probably occur in practices that will satisfy the financial de­ other animal taxa. Conservation ofthe Fijian mands oflandowners and the timber needs of native biota and vegetation is, therefore, the community while conserving the native largely synonymous with conserving the na­ flora and fauna. Limited plantations of fast­ tive forest habitats and maintaining a high growing exotic trees in already disturbed areas proportion of long-lived trees. There are bio­ may achieve this goal provided there is a logical and aesthetic arguments for retaining balance maintained between the two forest old-growth forests intact as perpetual reserves types, but ultimately sustainable timber and and as standards by which to judge managed floristic management ofthese native forests is forest, but, at present, such reserves amount perhaps desirable, coupled with a system of to only a few thousand hectares in a few permanent reserves. localities: these would be totally inadequate as Despite quarantine screening, accidental the sole forest reserves. Development of a as well as deliberate introductions of exotic representative system of protected reserves is plants are likely to continue at a rate ofseveral highly desirable and has been proposed to the species a year. The existing trend for these government (Secretary, National Trust for species to establish and dominate open habi­ Fiji, pers. comm.). tats is likely to continue, but it is also likely Cloud forests, in particular, are of very that more shade-tolerant species will establish limited extent and all should be placed in and could invade native forests. Domesticated reserves: their biological, aesthetic, and tour­ herbivore populations, notably cattle and ism value greatly exceeds any value to be ob­ goats, are increasing, and both goats and pigs tained from primary production (Ash 1987d). have uncontrolled feral populations. These A threat to cloud forests is the development herbivores consume woody regrowth and fa­ of mountaintop telecommunication facilities vor open-habitat grasses, restricting the re­ that, although of limited size, may inadver­ growth of native forests. Predatory mon­ tently disturb much of this community. The gooses, rats, dogs, and cats, as well as humans upland lake and swamp catchments ofTaveuni have already had a severe impact on ground­ (Southern 1986, Southern et al. 1986) and nesting birds and native lizards: their impact representative sustainable areas of Pandanus on the vegetation is indirect but could affect swamp (Ash and Ash 1984, Ash 1987c), man­ vectors of both pollen and seeds. Certain groves, dune (Kirkpatrick and Hassall 1981), predators are absent from smaller islands beach, and dry zone forest are all habitats of (e.g., mongoose on Taveuni), and it is to be limited extent or with a notable proportion hoped that they are not introduced. currently disturbed and deserving of immedi­ Global changes to the atmosphere and ate conservation measures (Ash and Vodo­ climate may increase temperatures, increase naivalu 1989). the frequency of cyclones, increase rainfall, Vegetation Ecology of Fiji-AsH 125 and cause sea levels to rise by 0.5-1.5 m in the my of Dacrydium (Podocarpaceae) in Fiji. next century (Pearman 1988). All these pro­ Aust. J. Bot. 34: 197-205. cesses would affect Fiji, especially coastal ---. 1986b. Demography and production areas, reefs, and cays, returning these to the ofLeptopteris wilkesiana (Osmundaceae), a situation of about 5000 yr ago. The littoral tropical tree-fern from Fiji. Aust. J. Bot. species are mostly capable ofrapid migration 34:207-215. and could track such sea-level changes inland, ---. 1987a. Holocene sea-levels in north­ except on cays that might become totally ern Viti Levu, Fiji. N.Z. J. Geol. Geophys. submerged. Some loss oflow-Iying agricultur­ 30: 431-455. alland is likely, increasing the need for more ---. 1987b. Demography and production intensive land use. Compared with the impact of Cyathea hornei (Cyatheaceae), a trop­ on the atolls of Polynesia, Fijian ecosystems ical tree-fern from Fiji. Aust. J. Bot. would be disturbed rather than destroyed, and 35:331-342. there may be negotiations to resettle Polyne­ ---. 1987c. Demography and production sians on certain Fijian islands. of Pandanus tectorius (Pandanaceae) in Fi­ ji. Aust. J. Bot. 35:313-330. ---. 1987d. Stunted cloud forest in Conclusions Taveuni, Fiji. Pac. Sci. 41: 191-199. Though some endemic vertebrates have ---. 1988a. Demography and production been lost through the impacts of man and of Balaka microcarpa (Arecaceae), a tropi­ most lowland dry zone and low island ecosys­ cal understorey palm in Fiji. Aust. J. Bot. tems are extensively disturbed, Fiji still retains 36:67-80. a variety of more or less natural functioning ---. 1988b. Nothofogus (Fagaceae) forest ecosystems. With proper management these on Mt Gi1uwe, New Guinea. N.Z. J. Bot. can be retained while production of timber 26:245-258. and food in other areas is increased. In partic­ ASH, J., and W. ASH. 1984. Freshwater wet­ ular, attention should focus on preserving land vegetation of Viti Levu, Fiji. N.Z. J. sustainable areas that include unusual or re­ Bot. 23: 377-391. stricted habitats or contain rare speCies. A ASH, J., and S. VODONAIVALU. 1989. Floristic longer-term goal is to manage remaining for­ inventory of tropical forests in Fiji. in D. ests to conserve species as well as to yield G. Campbell, ed. World strategy for the resources. Inevitably these goals will require floristic inventory of tropical forest. Mis­ government control and, probably, appropri­ souri Bot. Garden, New York. ation of some land: it should not be beyond ASH, W., and J. E. ASH. 1985. Holocene the power of government to do these things. marine deposits on the south coast of Viti Levu, Fiji. N.Z. J. Geoi. Geophys. LITERATURE CITED 28:571-573. BALGOOY, M. VAN. 1971. Plant geography of ALLEN, J., C. GOSDEN, and P. J. WHITE. 1989. the Pacific. Blumea Suppi. 6: 1-222. Human Pleistocene adaptations in the trop­ BERRY, M. J., and W. J. HOWARD. 1973. Fiji ical Pacific: Recent evidence from New forest inventory. Land Resources Study 12. Ireland, a Greater Australian outlier. An­ 3 vo1s. and 36 maps. Overseas Develop­ tiquity 63: 548-561. ment Authority, Surbiton, U.K. ASH, J. 1982. The Nothofogus Blume (Faga­ BEST, S. B. 1984. Lakeba: The prehistory ofa ceae) of New Guinea. Monogr. BioI. 42: Fijian island. 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