The Study of Land Potential: an Open-Ended Inquiry

The study of land potential: an open-ended inquiry $1. Latham and B. Denis =Centre ORSTOM Soumea yew Caledonia In the initial design of the Unesco/UNFPA The 'talasiga formation - the most extreme Project in Fiji, one of the stated objectives of a range of pyrophytic formations supported was scientific description of the agrological by very degraded soils - was either formed or qualities of the land resources, together greatly enlarged as a result of this inter- with an estimate of their capacity to with- ference. Soil erosion, and the creation of stand and support cultivation. Added to this large areas of colluvium, may also be presumed + was an emphasis on the dynamics of change in to have arisen from, or been accelerated by, the soil-vegetation complex, viewed as the the interference of man with natural environ- expression of interaction between variable mental process2. environmental conditions and the impact of In so far as the team was concerned with - changing human occupance. Following the evaluating the suitability of land for agri- conclusion of a mutually welcomed agree- cultural use, which was its pragmatic object- - ment between Unesco and ORSTOM, and ap- ive, the context had to be a search for the proval of this agreement by the Govern- optimal production capacity of these environment of Fiji, the present authors were char- ments, consistent with preservation or amelio- - ged with primary-responsibility for this ration of ecosystems that are already in a . task, in collaboration with other members very unstable condition. It was decided to directly recruited by the project. Fieid base the work on the task of classification - work was carried out on five islands (Lakeba, using the 'system for evaluation of soils' Taveuni, Nairai, Batiki and Kabara) among proposed by FAO (1976). Three stages of which four were also studied from other work are therefore. involved: points of view. In terms of their ecology, .- definition of ecological units; none of these islands was previously well- - evaluation of the agrological qualities described. The major source on the soil and of land; \%:etation of Fiji (Twyford and Wright 1965) - evaluation of land-use potential, taking 2s concerned principally with the two main account of the consequences which any par- islands - Viti Levu and Vanua Levu - and ticular form of use might have on the en- discussion of the smaller islands is based vironment. only on reconnaissance. The islands chosen for study in the present project were selec- - ted on the basis of their representativeness h terms of the range of ecological conditions encountered in the eastern part of Fiji. 'Based on work still in progress at the University of %ceover, all had been heavily affected by Auckland, and by this project. , human occupation, and hence were particular- 'In Fijian, the term 'talasiga' means 'sun-burnt land' ly appropriate for study in a pilot project (Parham 1972). The term designates both a pyrophytic Hthin the Man and the Biosphere Programe vegetation complex dominated by ferns, often in assoc- Of Unesco. On present evidence, i; would iation with Cas&na equisetifoolia, and also the very appear that these islands were first popu- degraded and often eroded soils which support the com- lated by about 3000 years ago1. Such plex. It is used in what follows as a generic term man for a soil-vegetation complex which, while not limited occupation must be presumed to have initia- to the eastern islands of Fijl, is particularly-well ted a range of environmental transformations, exemplified on some of these islands, outstandingly by clearing of the forest and use of fire. Lakeba. IJnesco, 1980. Papulation-enviromennent relations in tropical islands: the case ai eashm? Fiji. (MAB Technical Notes 13). -- --I , The emphasis given to each of these stages to the purposes of the project, which was varied according to the practical possibili- designed as a pilot study in this area. '&e ties of access to islands, to knowledge of approach adopted is represented diagramatrc- the environmental conditions as a whole, and ally in Figure 1. f ìEOMORPHOLOGY PEDOLOGY VEGETATION SOCIO- ECONOMIC CONDITIONS Definition of land- Study of soils and Description of lnvestmegt Crops grown or forms and their capable of being evqlu tion their characteristics vegetation types possibilities grown I/____ Land use ecology . \ DEFINITION OF ECOLOGICAL UNITS Environmental - consequences of t land use I I I r hrphodynamic constraints Edaphic constraints . Techn ícal Cropping - erosion -water / possibilities for possibilities - sedimentation - minerals terrain management I l I r AGROLOGICAL QUALITIES Chances of success Types of OF ECOLOGICAL UNITS of land use types land use Figure 1. FZm chart representing the method employed for the sf&y of land potential I. THE DEFINITION OF ECOLOGICAL UNITS The term 'ecological unit' is a compromise term 'ecological unit' seems more appropriate. between the ' land unit ' of most land-evalua- Even so, the task of defining such units de- i tion studies and the 'ecosystem' favoured by mands a large input of new research, since i the Man and the Biosphere Programme. Many of these island-environments are little-known g the ecological units would in fact be con- scientifically, in view of their isolation .i*- gruent with natural ecosystems, being land and small size. Moreover, the environments > units of relatively uniform environmental of the different islands are very varied, and? conditions capable of separate analysis in - many elements are unique to particular islandgk terms of their life-support systems, but to Within-island variation is often as marked as-. speak of ecosystems involves questions of between-island variation. A short descriptict?? bounding and the import and export of energy of each islan< will introduce the disucssion i- and matter, which are not faced in this work. which follows. That discussion is based pri-; For an essentially reconnaissance study, the marily on Lakeba, the most complex of the - _. c * fie study of land potential i. islands studied from aq ecological viewpoint, KABARA but draws also on condítions elsewhere in the archipelago. Kabara is representative of a group of uplift- ed atolls, and occupies 52 km2. In the north- west, however, is an outcrop of basalt of (LAKEBa Pleistocene age. Three principal environments Although only 56 km2 in area, Lakeba is an may be distinguished. Most of the island is island of quite unusual ecological complex- formed of a limestone basin, sloping inward ity. Basically, the island constitutes an from the encircling ridge toward the centre, andesitic massif of Miocene age, partly and containing some pockets of bauxitic soils covered by Pliocene limestones, of which (humic f erralsols) ; this whole area is covered only fragments remain. In the present era, in dense forest. Second is the small volcanic it experiences an oceanic tropical climate, hill which carries the principal cultivated t* with a mean rainfall at coastal sites of area, but where soils (eutric cambisols) are around 2000 "/yr. A succession of somewhat badly eroded. Third are the coastal plain different palaeoclimates , together with areas of sand or rendzinas, which are mainly general uplift, has led to the formation of under coconuts. Kabara's environment is there- I a range of morphological units, including fore quite simple, but very different from bauxitic plateau areas, eroded hills, large that of the other islands. \ colluvial zones in the valleys and lowlands, ! and alluvial coastal plains within which are TAVEUNI quite numerous valley and sub-coastal swamps. Awide range of soils has evolved on these Taveuni is much the largest of the islands morphological units, among which the most studied (264 kmz), and is not representative maturely developed are the 'talasiga' soils of any other island but itself. Geologically, (acric ferralsols and ferralic cambisols) , it is the most recent in formation. Major while the least mature are the soils of the eruptions have taken place within the past, plains (eutric fluyisols, rendzinas , histo- 3000 years, concluding perhaps within the $ást sols and humic gleysols). Great diversity 1500 years, and the whole volcanic mass is lof of vegetation is associated with these soil- upper Pleistocene and Holocene age. The cli- landform complexes: dense forest, reed thic- mate is unusually humid, mean annual rainfall ket, forb vegetation dominated by ferns (tal- exceeding 6000 mm in parts of the island. asiga vegetation) , and hydromorphic herbac- According to the age of the volcanic parent eous vegetation. Notwithstanding its small material, soils may be divided into an andic size, the range of ecological units encount- group and a ferralitic group with bauxitic , ered in Lakeba exceeds the range encountered tendencies. Except where cleared for coconuts on any of the other islands visited. or other cultivation, a dense. forest covers the whole island to the summits. Taveuni is &TI= AND NAIRA1 6 a young island, of fertile volcanic soils x characterized by a dense rain forest with These also are small volcanic islands, but of little or no evidence of degradation. hasaltic composition and Pliocene age. Batiki, the smallest island :tudied by the project, SUMMARY Covers only 9 km2, but Nairai covers 28 km2. - Both islands are hilly, and eutric cambisols, The environments of these islands are varied, ferralic cambisols and a few areas of rhodic and contain distinctive elements. Because of ferralsols are developed on the hills. Rend- its diversity, work on Lakeba alone occupied zinas are found on the coastal'plains. Reed half the time alloted to the ecological sur- thicket dominates the slopes, but the small very in the field. Maps have been prepared areas of plain, the valleyZbottoms and the for Lakeba at a scale of 1:25 O00 and of parts summit area of Nairai carry forestvegetation. of Taveuni at 1:50 000; sketch maps only were These two islands therefore constitute a prepared for Kabara, Nairai and Batiki, at Younger and less diversified environment than the 1:50 O00 scale.

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