Distribution of native forest in the upper Clutha district, Otago, New Zealand

Transcription

1 New Zealand Journal of Botany ISSN: X (Print) (Online) Journal homepage: Distribution of native forest in the upper Clutha district, Otago, New Zealand Peter Wardle To cite this article: Peter Wardle (2001) Distribution of native forest in the upper Clutha district, Otago, New Zealand, New Zealand Journal of Botany, 39:3, , DOI: / X To link to this article: Published online: 17 Mar Submit your article to this journal Article views: 278 Citing articles: 9 View citing articles Full Terms & Conditions of access and use can be found at

2 New Zealand Journal of Botany, 2001, Vol. 39: W01/ $7.00 The Royal Society of New Zealand Distribution of native forest in the upper Clutha district, Otago, New Zealand PETER WARDLE Landcare Research P.O. Box 69 Lincoln, New Zealand Abstract The upper Clutha district extends from steep, glaciated mountains along the South Island Main Divide to broad plateaus and terraced valleys further downstream, and covers an annual precipitation gradient from 4000 m to 400 mm. all forest prevails from the valley floors to the subalpine tree limit in n0fi-weste-n headwaters, but southwards down the rainfall gradient becomes increasingly confined to small pockets. Nothofagus is overwhelmingly dominant, with N. menziesii prevailing in the north-west and N. solandri vu. cliffortioides in drier country to the east. Pockets of forest in the south of the district cm consist of ei- &er species. Nothofagus fusca co-do&ates with the other Nothofagus species at low altitudes through part of the Matukituki catchment, and Over a small area by Lake Hawea. Low-altitude N. menziesii forest in the Makarora Valley has a similar composition to forests west of the Main Divide, and includes several conifer species and a wide range of broadleaved trees, notably Weinrnannia racemosa. The hardiest conifers, Podocarpus hallii and Phyllocladus alpinus, are widely distributed in the Nothofagus forests of the district and also dominate small stands of native trees on otherwise treeless mountains. In the moister part of the district Kunzea ericoides and Leptospemum scoparium are successional to broad-leaved forest, whereas in the drier parts they are self-perpetuating. Grey scrub, dominated mainly by Discaria toumatou, is widespread on slopes where rainfall is low, and on river flats under higher rainfall. Small trees of Sophora microphylls and Olearia spp. occw locally in this scrub. B00021 Received 22 June 2000; accepted 22 May 2001 Keywords forest distribution; Nothofagus; Phyllocladus alpinus; Podocarpus hallii; precipitation gradient INTRODUCTION The upper Clutha district comprises the UPWr Part of the catchment of New Zealand's largest river. It extends from the South Island Main Divide to Cromwell at the confluence with the Kawarau River, and encompasses New Z~aland's steepest rainfall gradient. Down this gradient, native forest decreases from a COntinUOUS Cover in Valleys near the Main Divide, to small, scattered patches on the driest mountains. The present paper maps broad forest types, describes the distribution of the main tree species, and briefly discusses relationships between this vegetation and climatic patterns. Its purpose is to provide information relevant to COnSerVatiOn and land management, and a background to a Paper presenting information about the extent Of forest in the recent Past and hough the Holocene (Wudle 2001). Topography and geology The north-western tributaries (Matukituki, Makarora, and Hunter rivers) of the Clutha rise on the Main Divide and, along with many smaller Streams, flow into the glacial troughs that contain lakes wanaka and &wea. A wide valley extends 50 km from the lakes to CrOmWell? where the Clutha River is joined by the Kawarau River which drains Lake watipu. At ~romwell the Upper Clutha basin terminates in a deep, ~~~rrow gorge which has recently been dammed for electricity generation. Upstream from the outlets Of the lakes * the m~ntains are high and rugged. TOwards the Main Divide, ice-clad peaks exceed 1800 m. The sides of the main valleys have been glacially steepened, and most side streams plunge from U-shaped hanging valleys, but for most of their lengths the main rivers flow as braided streams over flats of alluvial gravel and silt. Downstream from moraines that dam lakes

3 436 New Zealand Journal of Botany, 2001, Vol. 39 Wanaka and Hawea, the Clutha valley is bordered by flights of terraces on the flanks of high, rolling plateaus that, in the Pisa Range, attain nearly 2000 m. Similar terraces are prominent in the Lindis, Cardrona, and Motatapu valleys. Almost throughout, the mountains are formed by Haast Series metamorphic rocks of Permian and Triassic age (Wood 1962). Schist predominates except for greywacke and weakly schistose greywacke in the Hunter Valley and Dingle Bum. Schist topography is characterised by numerous bluffs, and tors rise from upper slopes and summits not affected by glacial erosion. Greywacke topography, in contrast, exhibits long, even debris slopes. Climate The prevailing westerlies and north-westerlies are responsible for a precipitation gradient in which totals approach 4000 mm annually near the Main Divide and decrease steadily to only 400 mm at Cromwell (Fig. 1). Where precipitation is high there are distinct spring maxima and winter minima, but the seasonal distribution becomes irregular as total precipitation decreases. Southerlies and southwesterlies also bring significant rain, and are responsible for much of the snow-fall at high altitudes. The southern end of the upper Clutha valley falls within the Central Otago climatic district, which experiences the most continental climate in New Zealand. As well as low rainfall, the valley floor experiences low humidity and cloud cover, except for shallow inversion fogs during winter. At Cromwell, the mean daily temperature maximum during January (the warmest month) is 24.4"C and the mean daily screen minimum during July is -1.8OC. As precipitation and cloud cover increase towards the Main Divide, the temperature range might be expected to narrow, although valley floors experience hard frosts during fiie spells in winter. The presence of Cordyline australis and various forest species indicates milder climates near the two large lakes, although temperature data for Wanaka and Lake Hawea differ only slightly from Cromwell. A 12-km stretch of the Main Divide flanking the Makarora valley lacks peaks over 1800 m, and its lowest point, Haast Pass, is only 562 m a.s.1. This allows some penetration of mild, superhumid West Coast weather into the Makarora valley. The potential upper limit of native forest in New Zealand coincides with a mean January temperature of 10-l l C (Zotov 1938; McCracken 1980). Climatic gradients measured by Wells (1972) for the eastern side of the Pisa Range and by Mark (1965) for the eastern slope of the Old Man Range 40 km down the Clutha Valley from Cromwell indicate that the 10 C isotherm lies at around 1200 m. This requires a lapse rate between the summer-warm valleys and the cool upper slopes that is considerably steeper than the mean January lapse rate of 0.51"C per 100 m calculated for New Zealand overall by Norton (1985), since the mean January temperature at Cromwell (213 m) is 17.7"C. Mark's (1965) and Wells's (1972) data also indicate that precipitation on the slopes above the dry Central Otago basins should increase to around 1000 mm annually at the 1200 m level. No estimates are available for the wetter mountains of the district. s0i1s Mapping units are shown on Sheet 10 of the Soil Map of the South Island (New Zealand Soil Bureau 1968). The mature soils of the Upper Clutha district mainly fall into three orders of the New Zealand Soil Classification (Hewitt 1998), according to their position on the rainfall gradient. Semiarid soils predominate at low altitudes down-valley from Luggate, where precipitation is less than 550 mm annually. They include Lowburn soils on terraces, CONOY soils on rolling to hilly land, and Alexandra soils on steep land. Pallic soils extend up-slope and up-valley from the Semiarid soils until about the 800 mm isohyet where they grade into Brown soils. The main units of Pallic soils are Arrow and Blackstone soils on the hilly to steep land, and Wanaka and Shotover soils which comprise the deeper soils on terraces. Brown soils occupy most land beyond the 800 mm isohyet, including the higher slopes of the Pisa and Dunstan Ranges. Most Brown soils on hilly to steep land are mapped as Dunstan and Carrick soils. Brown soils (Dublin and Luggate soils) are also mapped below the 800 mm isohyet, on shallow and stony alluvium on Hawea Flat and towards Wanaka. Fig. 1 Topography and localities. Isohyets have been interpolated from climate station data (New Zealand j Meteorological Service undated). The following localities are indicated by numerals: 1, Fish River; 2, Rough Creek; 3, Station Creek; 4, Waterfall Creek; 5, adds Bush and Sawyer Burn; 6, Stevensons Island; 7, Quartz Creek; 8, Grandview Creek; 9, Hospital Creek; 10, Lagoon Creek; 11, Spotts Creek; 12, Locharburn Stream.

4 Wardle Native forest distribution in upper Clutha 437

5 438 New Zealand Journal of Botany, 2001, Vol. 39 Soils of all three groups, but especially the Brown soils, grade into Recent soils on steep, unstable slopes. Recent soils also occur on young alluvium, adjacent to streams. Small areas of Gley soils occur on poorly drained sites. On gentle slopes under the highest rainfall, acid-leaching has led to the formation of patches of Podzols, whereas, in the driest localities, low leaching of Semiarid soils has resulted in retention of bands of calcium carbonate within soil profiles and led to the formation of saline soils in depressions. METHODS Sources of information Forests of the upper Clutha district are mentioned in Holloway's (1954) discussion of forests and climate change in the South Island. Wardle (1970,1984) and Wardle & Guest (1977) provide information on composition, structure, regeneration, and effects of browsing mammals in the silver (Nothofagus menziesii) and mountain beech (N. sozandri var. clifsortioides) forests of the district. Mark (1977) described and mapped forests in the Makarora and Matukituki catchments that lie within Mt Aspiring National Park. Much of the published work was based on plot data assembled for the Matukituki, Hunter, Dingle Burn, and Timam valleys by the New Zealand Forest Service. There are also unpublished Forest Service plot data for Mt Aspiring National Park and unpublished DSIR Botany Division reports on the Hunter Valley (Wardle & Johnson 1987) and other localities. All this information is now held at Landcare Research, Lincoln. Seven of the district's scenic reserves and other protected areas contain stands of native trees, which are described in two volumes about the scenic reserves of Otago (Allen 1978; Ward & Munro 1989). A Protected Natural Areas Survey report covers isolated stands in the drier, southern parts of the district (Grove & Ward 1994). Wells (1972) studied the ecology of the mountain totara (Podocarpus hazzii) stands of the Pisa Range, and mapped pockets of silver beech there and in the Cardrona catchment, while Burrell (1965) studied kanuka (Kunzea ericoides) shrublands and woodlands. Existing topographical maps (NZMS 1, NZMS 260) adequately show the boundaries of significant areas of native forest, but do not differentiate forest types or show small remnants in the drier, generally treeless parts of the district. Personal communications regarding location of tree species and composition of forest remnants have been an invaluable source of information. Finally, my own notes and observations, made over many years, cover most of the district. c1assification Of forest types The broad forest types recognised in this paper are based on the abundance of the canopy-forming beech or conifer species. Quantitatively based classifications are available for the Hunter, Dingle, and Timaru catchments from Wardle (1970) and Wardle & Guest (1977), whereas Mark (1977) and other published and unpublished reports (cited above) present qualitative classifications. The unpublished plot data held at Landcare Research and my own observations provide information on composition of forest stands and remnants at specific points. Classification of the smaller forest remnants is scarcely practicable as their species content may represent chance survival. Mapping Field reconnaissance was based on maps of the NZMS 260 series (scale 1:50 000), and information about canopy composition, forest type boundaries, and location of outliers was recorded either on these or as field notes and sketches. In the office, forest boundaries shown on the NZMS 260 maps were copied manually on to the NZMS 262 series (scale 1: ). Forest type boundaries from the published and unpublished sources were then added, together with symbols showing the location and composition of outlying stands. A final version was prepared from an electronic data base, to produce Fig. 2. Grid references refer to the NZMS 260 map series. No systematic collection of herbarium specimens was carried out, as the trees native to the district are well understood taxonomically and the flora of the upper Clutha is already well represented in herbaria at Landcare Research (CHR) and University of Otago (OTA). Tree ages For age determinations on trees, increment cores were extracted as close to the trunk base as possible, and the growth rings were revealed by sanding or cutting. Counts were made under a dissecting microscope. Where cores did not reach the centre of the trunk, the counts were extrapolated according to the ratio between core length and stem diameter. ~i~. 2 Dishbution of forest types with beeches and conifers.

6 +A +B A».-. :,: /! ~-p.-~ - r.:-e' 'ceo:.>?? ; A 'e.\ ".rj.ir'rf'r ufcrt."." r.-ji-s *""*"" Reflional boundaries Main roads 100Drr, contour line

7 Wardle Native forest distribution in upper Clutha 439 RESULTS The broad pattern of native vegetation In headwaters close to the Main Divide, almost continuous beech (Nothofagus) forest extends from the valley floors to the subalpine tree limit, where it gives way to grassland, mostly dominated by snow tussocks (Chionochloa spp.), that ascends to the limit of continuous vegetation. Smaller blocks of beech forest occur in the smaller catchments draining into lakes Hawea and Wanaka, as well as in headwaters of the Lindis River. Unforested lower slopes around the lakes are occupied mainly by bracken (Pteridium esculentum). Botanically modified grassland and swamps occupy alluvial flats in the lower reaches of valleys tributary to lakes Wanaka and Hawea. Drier grasslands extend down-valley from the lakes, though these have been reduced or greatly modified through fie, grazing, cultivation, mining, and weed invasion. Shrubs or small trees with small leaves and divaricating branchlets grow scattered and as dense thickets in the low-rainfall areas, especially on rocky ground and in gullies, and also extend far up the major valleys beyond the lakes, on river flats too frosty, poorly drained, or recent to support beech forest; the thorny matagouri (Discaria toumatou) is the main component. Thickets of kanuka and manuka (Leptospermum scoparium) are extensive. Ecological ranges of the beech species Silver beech is typical of the wettest localities, extending to regular upper forest limits which, in the Makarora valley, are usually around 1140 m but can be as high as 1220 m on spurs of north-west aspect. In the Hunter Valley the usual and maximum altitudes are about 1160 m and 1230 m, respectively, reflecting the rise in the altitude of forest limits towards the interior of the island. Mountain beech forest is usually in drier localities. Although it forms the highest forest limits in New Zealand, there are few points in the upper Clutha where it attains its potential maximum altitude. In the upper Lindis valley there is a grove at 1250 m, while in the Dingle Burn, the NZMS 260 map shows forest reaching 1260 m on northerly aspects, with an extension to 1300 m around G Mountain beech and silver beech overlap widely. They can form thoroughly mixed stands but usually there is local segregation, with silver beech tending to occupy mesic sites such as hollows, sides of gorges, and the bases of bluffs. Mountain beech is on drier and more exposed sites, and on terraces and other flattish areas with podzols or gley soils. In many hanging valleys, slopes of the lower reaches are occupied by mountain beech, whereas those of the upper reaches are occupied by silver beech. Especially at higher altitudes, silver beech may occupy outcrops of bedrock, whereas adjacent debris slopes support mountain beech. Some of the small beech stands lying furthest down the rainfall gradient consist of silver beech, an apparent anomaly that is explained by their locations in rocky gorges and on bluffs. Red beech grows on lower slopes, extending on to terraces and flats where these are well drained and not too frosty. Silver beech and/or mountain beech and hybrids between red beech and mountain beech are also present in these stands. Distribution Of beeches Silver beech prevails to the exclusion of mountain beech in the headwaters of the Hunter valley and along most of its western side, throughout the Makarora valley and its tributaries (apart from a patch of mountain beech at the confluence of the Makarora and Young rivers), above the eastern shores of Lake Wanaka to as far south as Waterfall Creek, west of Lake Wanaka to as far south as the Minaret Burn, and in the headwaters of both branches of the Matukituki River. On the eastern side of the Hunter valley, the first mountain beech trees are near the top fork, on glacial benches on the lower slopes. With increasing distance down valley its proportions increase until, about the point that continuous beech forest ceases, mountain beech is dominant except in ravines and towards the upper forest limit, where silver beech still prevails. There are several patches of silver beech above 800 m in the mountain beech forests of the Dingle Burn. No silver beech has been reported from the beech stands of the Timaru and Lindis catchments, but one of the small mountain beech stands in Grandview Creek contains at least two silver beech trees, and there is also a patch of pure silver beech (Fig. 3A). Mixed stands of mountain beech and silver beech occupy the slopes up to 800 m a.s.1. between Ferguson and Long Flat creeks on the western side of the Hunter valley. Mountain beech forms most of the forest on the north-western side of Lake Hawea, although silver beech persists in gorges, and is the only species that reaches the up-valley limits of beech forest in the high, U-shaped valleys of the Young and McKerrow ranges. Red beech occurs with mountain beech 2 km north-east of adds Bush,

8 440 New Zealand Journal of Botany, 2001, Vol. 39 as remnant patches over an area of several hectares that has mostly been cleared, and there are hybrid trees within Kidds Bush. I have been unable to confirm a report of red beech near the confluence of Ferguson Creek and the Hunter River (L. Burrows pers. comm.), although two hybrid trees were found on the fan of Long Flat Creek 3 km down valley. In catchments draining to Lake Hawea from the range south of The Neck, the limited areas of beech forest continue the pattern of prevailing mountain beech but with silver beech present in gorges. At the southern end of this range, on the lower slopes of Mt Maude, there are two gullies with beech stands, one of which has only mountain beech. The other contains both species. Burning about 160 years ago (Wardle 2001) reduced this stand to trees near the stream, those of silver beech being in a rock-bound gorge and those of mountain beech being in a more open part of the gully. Subsequently, each species has spread from these survivors, decreasing in size up the slope, from trees to marginal seedlings. The catchments entering Lake Wanaka from the McKerrow Range south of Waterfall Creek have mountain beech in their steep lower portions and silver beech in the hanging valleys above. The species that form the small patches of beech high up in gullies south of The Neck have not been determined, but the largest stand of mountain beech in the east branch of Quartz Creek contains some silver beech (Ward 1984). Mountain beech joins silver beech in small patches of forest on slopes above Lake Wanaka south of Minaret Creek (R. P. & K. M. Wardle pers. comm.). In the West and East branches of the Matukituki River, red beech is abundant or dominant on the valley floors and lower slopes, reaching an upper limit at about 800 m. These red beech stands include both silver and mountain beeches, excepting on the west side of the East Branch where they include only silver beech. Above the red beech upper limit, mountain beech and silver beech dominate, with the proportion of silver beech increasing with altitude until, at the upper forest limit, it can be the only species, especially on southerly aspects. The southern side of the main Matukituki valley and its West Branch are largely devoid of forest to about 12 km upstream from the fork, and there are only patches of forest on the northern side of the valley from 6 km below the fork. All three beech species are present in these patches, but the proportion of mountain beech rises while that of silver beech falls as rainfall decreases down valley. In the Motatapu catchment, beech forest occupies side valleys, separated by mostly treeless interfluves. At least two of these side valleys contain the three beech species, but towards the Motatapu fork red beech drops out, leaving mainly mountain beech at the lower altitudes and silver beech at the higher altitudes (Fig. 3B). I have seen only silver beech in the North Branch and only mountain beech in the South Branch. Patches of beech forest occur in four of the western tributaries of the Cardrona valley, and there is a single large silver beech tree on the western side of the main valley. Most patches contain only silver beech, but two include some mountain beech. In Spotts Creek, the species segregate in a manner similar to that on Mt Maude, with silver beech extending up from narrow gorges, and mountain beech in a more open stretch of the catchment (Fig. 3C). On the Pisa Range silver beech occurs as a stand on the side of a gorge in Luggate Creek at 750 m, with trees scattered downstream to 430 m; as two trees and a few seedlings on a crag at 720 m above Kidd Creek on the eastern side of the range; and as several trees beside Roaring Meg Creek at 520 m, near its confluence with the Kawarau River. Low1and podocaqs Below 450 m in the Makarora valley, there are scattered miro (Prurnnopitys ferruginea) and, very locally, matai (P. taxifolia) and rimu (Dacrydiurn cupressinurn). On the valley floor, the Makarora Scenic Reserve is a remnant of a stand of silver beech, matai, miro, and kahikatea (Dacrycarpus dacrydioides) that supported saw milling for many decades. On a steep fan 600 m south of the mouth of Minaret Creek, a patch of coniferbroad-leaved forest contains about six kahikatea trees, seedlings of the same species, and single trees of matai and mountain totara (R. P. & K. F. Wardle pers. comm.). Aspinall (1993) reported occasional miro trees in the upper reaches of the Matukituki Valley. Two matai trees grow just north of the Matukituki road bridge, and one by Diamond Lake 4 km to the north. According to Holloway (1954), matai was milled from the mountain beech forest at Kidds Bush, Lake Hawea. Forest and scrub with up1and conifers Mountain totara is widely distributed within beech forests, although mostly as suppressed saplings. Well-developed trees are mostly in places where a dense beech canopy is precluded, especially bouldery terrain and the edges of ravines. The species occasionally reaches nearly 900 m, but from

9 Wardle Native forest distribution in upper Clutha fe Silver be& forest <f P Mountam beech forest ^^ > beedl sp. not defeimlned (55] Brosdleaf dominant? Vegetation not mapped F) Radiocarbon date S K G T t L Silver beech bees Kowhai trees Broadleaf trees Totara trees Young totara treas rotara fog Soil charcoal p podhcarp n beech 1 Kanuka, celery pine 2 Manuka, kanuka 8-5 Manuka 6 Hebe Fig. 3 Local maps of forest boundaries. A, Grandview Creek; B, Motatapu Valley; C, Spotts Creek; D, Estuary Burn. Locations shown on Fig. 1. Radiocarbon dates and soil charcoal are discussed in Wardle (2001). as low as 370 m there are hybrids between mountain totara and snow totara (Podocurpus nivulis). Celery pine (Phyllocludus alpinus) is locally abundant on gentle or moderate slopes with podzol or gley soils, mainly as an understorey shrub but sometimes becoming a tree. Where beech canopies open out towards the upper forest limit there is usually an understorey of celery pine, snow totara, and smallleaved coprosmas. Kaikawaka (Libocedrus bidwillii) grows in beech forest near the confluence of the Fish and Makarora rivers, at a few points in the Matukituki catchment upstream from the fork, and on a spur between the Hunter River and Ferguson Creek (R. P. & K. F.

10 442 New Zealand Journal of Botany, 2001, Vol. 39 Wardle pers. comm.). Pink pine (Halocarpus bifurmis) also grows near the last locality, with stunted silver and mountain beeches on a glacially scoured slope at 800 m (J. A. Wardle unpubl. data). Mark (1977) reported bog pine (H. bidwillii) in a similar site at the lower end of the Makarora Gorge. Beyond the up-valley limits of continuous silver beech forest in the Siberia branch of the Wilkin River and the East Branch of the Matukituki River, there are stands of celery pine, mountain ribbonwood (Huheria glabrata), and inaka (Dracophyllurn longifolium), from which project taller trees of kaikawaka and mountain totara (Mark 1977). Other shrubs and small trees include mountain holly (Olearia ilicifolia), broadleaf (Griselinia littoralis), three-finger (Pseudopanax colensoi var. ternatus), Archeria traversii, Brachyglottis buchananii, Myrsine divaricata, and Coprosma spp. Bog pine is present in the East Matukituki stand. Both stands include groves and isolated trees of silver beech, which tend to be young and vigorous. A stand of kaikawaka and broadleaf also occurs at the upper forest limit in the Albert Burn (L. Burrows pers. corn.). In the head of the Minaret Burn, some 8 km beyond the up-valley limit of silver beech, there are stands of celery pine 3-5 m tall, one of them extending over some 25 ha and from 970 to 1100 m a.s.1. Celery pine is accompanied by inaka and, locally, there are mountain totara trees. Other shrubs include Dracophyllum unzjzorum, snow totara, and hybrid totara. In the North Branch of the Wilkin River, just beyond the up-valley limit of silver beech forest, there are similar stands of celery pine that also contain mountain totara. At the fork near the head of the Estuary Burn and for 2 km downstream, groves of large celery pines alternate with groves of silver beech, and are being invaded by silver beech saplings. Avalanche paths separate these groves. Silver beech reaches its lower limit 50 m above the flat valley floor, but celery pine reaches the foot of the slope. The Rough Creek fan in the West Branch of the Matukituki River supports an open stand of celery pine, mountain totara, snow totara, and totara hybrids. Further down the West Branch, beech forest on a south-facing slope was burnt about 1891 (Aspinall 1993; Wardle 2001). In the nowregenerating forest the most abundant young trees are mountain totara and its hybrids with snow totara; a few larger totara trees survived the fire. There are also occasional celery pine, broadleaf, and other small trees. Silver beech occurs as isolated saplings and young trees, and as small clusters that are derived from parent trees in gullies that survived fire. Cores extracted from post-fire silver beech trees gave age estimates of 45,50, and 65 years, and cores from two totara trees gave estimates of 50 years. In the Hunter valley, downstream from Long Flat Creek and the limits of continuous beech forest, there are considerable areas on the lower slopes where small mountain totara trees grow among broadleaf, other broad-leaved trees, and, often, kanuka. These occupy the sites of much older fires (Wardle 2001). Beech is vigorously invading along the margins of beech forest and isolated clumps of beech trees, with seedlings being frequent up to 15 m from parent trees. Cores from totara trees gave estimates of 40, 100, and 210 years and one from celery pine gave 205 years. Invading saplings of mountain beech and silver beech gave 20,110, and 140 years, and 45 and 150 years, respectively. With increasing altitude, celery pine becomes more abundant and mountain totara is replaced by snow totara and hybrids. Above 900 m shrubs such as inaka, Dracophyllum uniflorum, and Coprosma pseudocuneata become increasingly prominent. Small patches of coniferbroad-leaved forest and scrub are scattered through the drier mountains down-valley from the major forest areas, and fallen totara logs show that they were once far more extensive. These remnants are floristically impoverished and vary in composition from stand to stand. The most frequent taxa are mountain totara, snow totara, and their hybrids. Celery pine, inaka, Olearia nummularifolia, 0. cymbifolia, Brachyglottis cassinioides, and Hebe subalpina are widespread, although often represented by single plants in situations protected from fire. Bog pine occurs in three localities on the Pisa Range, the main one being the ridge east of the Locharburn Stream. In the upper reaches of the north-westem valleys, tall scrub of inaka, Dracophyllum unijzorum, celery pine, and snow totara extends beyond the up-slope and up-valley limits of silver beech forest, in places where the latter has been depressed by cold air drainage (Wardle 1991, p. 83). With increasing altitude, this becomes low-growing and confined to steep slopes of northerly aspect on surfaces that have escaped recent disturbance, whereas gentler slopes show gradations to communities of shrubs among Chionochloa tussocks. Such vegetation is inflammable, and charred sticks show that C. rigida grassland has replaced it over large areas, which are gradually reinvaded by shrubs, especially Coprosma spp. and inaka.

11 Wardle Native forest distribution in upper Clutha 443 Broad-leaved trees Kamahi (Weinmannia racemosa) forms an open subcanopy in beech forest on lower slopes in the Makarora valley. It also grows as small trees on the sides of ravines and ledges of bluffs along the northeastern side of Lake wan&a, in the podocarp stand south of Minaret Creek, up to 800 m in the Hunter valley (especially on the eastern side, opposite Long Flat Creek), and for short distances up the main forks of the Matukituki aver. Southern rata (Metrosideros umbellata) grows in ravines and on bluffs in the Makarora valley, on the north-eastern side of Lake Wanka, between Minaret B~~ and Station Creek on the western side, at Sawyer Bum at Lake Hawea, and along the eastern side of the Hunter valley. Its upper altitudinal limit is 850 m. pokaka (Elaeocarpus hookerianus) grows only in the Makarora valley, apart from an Occurrence downstream from the Matukituki fork. Broadleaf is common on bouldery slopes and bluffs. In the lower reaches of the Estuary Burn broadleaf trees up to 9 m tall, with single and compound trunks up to 80 cm and 1 m diameter, respectively, cover nearly 200 ha of bouldery debris. Accompanying species include putaputaweta (Carpodetus serratus), wineberry (Aristotelia serrata), and fuchsia (Fuchsia excorticata). The stand appears to coincide with an ancient fire margin, since it shares its up-valley boundary with silver beech forest and its down-valley boundary with old kanuka stands that contain young totara trees and saplings (Fig. 3.D). On the drier mountains, broadleaf is associated with totara at the lower end of the Motatapu gorge, in Hospital Creek on the Grandview Range, and in the Luggate Creek catchment, and a few trees line a gorge of Lagoon Creek. Lancewood (Pseudopanax crassifolius), putaputaweta, wineberry, fuchsia, and karamu (Coprosma lucida) are abundant on well-&ained, moist soils under open beech canopies, shallow gullies and at the foot of slopes being common locations. Mountain ribbonwood is abundant on similar sites at higher altitudes. It also grows as scattered trees and small groves along streams beyond the beech forest areas, including around the Pisa Range and in the Cardrcma valley. Mapou (Myrsine australis) and lowland ribbonwood (Plagianthus regius) grow in the Makarora valley, the latter being confined to river flats. Three-finger is widespread in beech forest but reduced by deer and possums. Pseudopanax simplex and Archeria traversii are important on the wet side of the 1800 mm isohyet, the former mainly at mid altitudes and the latter mainly on rocky ground towards the upper forest limit. Reports of DracoPhYllum traversii from west of the MakarOra River and in the upper reaches of the Matukituki va11ey need to be confirmed because Of the possibility Of COnfUSiOn With D. menziesii which is present Close to the Main Divide. Narrow-leaved mahoe (Melicytus lanceolatus) is sporadic in the Makarora, MatukitUkk and Hunter vdeys. Cornon mahoe (M. ram$oms) grows in ravines on the northeastern side of Lake Wanaka 2 near the mouth of Minaret Burn, and on Harwich Island. The tree fern Cyathea smithii grows in the silver beech forest of the Makarora val1ey and there is at least One Plant in mountain beech forest at Kidds Bush. Around lakes Wanaka and Hawea and for some distance UP the major valleys entering the lakes, bracken-covered lower slopes are invaded by small broad-leaved trees which sometimes escape fie long enough to form a continuous canopy. Pittosporum tenuifolium is the most abundant, but is accompanied by lancewood, fuchsia, karamu, broadleaf, wineberry, tree tutu (Con'aria arborea), and cabbage tree (Cordyline australis). The rare fierce lancewood (Pseudopanax ferox) grows on The Peninsula and Stevensons Island. Kanuka and manuka shrubland and woodland bnuka and m~~uka are most Prominent aroucd the two large lakes Where they Persistently invade bracken fernland and grassland, on sites drier than those invaded directly by seedlings of broad-leaved trees. At first, the two species tend to grow together but eventually kanuka overtops and suppresses manuka. As the stands mature, the density of stems decreases and broad-leaved species invade. Beech invades where there are parent trees in the vicinity, and locally there are totara seedlings and saplings. Around the lakes recurrent fires seldom allow the succession to reach the stage of broad-leaved dominance, but in the Hunter valley very large kanuka, emergent from a broad-leaved canopy or sharing the canopy with beech, indicate advanced succession. Self -perpetuating stands of kanuka are extensive on dry, shallow soils on gravelly terraces between Hawea, Wanaka, Queensberry, and Tarras, and form dark woodland on otherwise sparsely vegetated, rocky slopes above Bendigo. On the driest sites the plants remain short and separated by bare surfaces, although the soil is occupied by far-extending roots (Burrell 1965). In these areas manuka is confined to moist sites such as seepages and stream banks, but

12 444 New Zealand Journal of Botany, 2001, Vol. 39 becomes more abundant with increasing altitude and finds an upper limit higher than that of kanuka. The major north-western valleys and the lesser valleys around the lakes lack kanuka in their upper reaches, even where destruction of forest would seem to give it ample opportunity to invade. Kanuka is also absent from the Cardrona valley except near Wanaka, and I did not notice it in the Motatapu valley; this foreshadows its absence from the catchment of Lake Wakatipu and southwards. Grey scrub and associated small trees In the north-western valleys, inaka and Coprosma spp. occupy slumped surfaces, boulder fields, and rocky fans, together with Hebe subalpina, H. salicifolia, Olearia avicenniifolia, Aristotelia fruticosa, and the large herbs Aciphylla horrida and Phormium cookianum. As rainfall decreases down the valleys, filiramulate shrubs increase at the expense of broad-leaved shrubs, in a transition to grey scrub (Wardle 1991), which remains extensive on stony flats and hillsides, despite over a century of attempts to destroy it. Matagouri is the most abundant species, and can become a small tree. Coprosma propinqua, Melicytus alpinus, and Carmichaelia petriei are also abundant and extend further up the north-western valleys than matagouri. Coprosma rigida, C. crassifolia, Corokia cotoneaster, Aristotelia fruticosa, Myrsine divaricata, and the introduced Rosa ncbiginosa are common in matagouri thickets in gullies. Colonies of Coprosma virescens grow on dry rock outcrops, a habitat that occasionally also supports Melicope simplex. Coprosma intertexta occurs sporadically, and the local endemic Carmichaelia compacta grows around Cromwell. There are old records of Teucridium parviflorum from Bendigo and Queensberry (Petrie in Cheeseman 1925). Four small-leaved Olearia species are associated with grey scrub, three of them being small trees. 0. lineata is locally dominant throughout the range of grey scrub, whereas the rare 0. hectovii is almost confined to the Matukituki valley where it occurs from the main fork to c. 1 km up the West Branch, and near the road bridge where 0. fragruntissima is also present (Rogers 1996). The shrubby 0. odorata is widespread around and down-valley from the lakes. Lianes include Rubus schmiedelioides, Parsonsia capsularis var. tenuis, Muehlenbeckia australis, M. complexa, occasional Scandia geniculata, and rare Curmichaelia kirkii. Kowhai (Sophora microphyllu) trees occur in scattered localities on the lower mountain slopes between the lakes and Cromwell, usually on northfacing rock outcrops. Despite the harsh sites, seedlings are often abundant. Trees resulting from water-borne seed grow around the shores of Lake Wanaka and along the banks of the Hawea River, and grew around Lake Hawea before it was raised for hydroelectric storage. DISCUSSION The beech forests of the upper Clutha district form part of a floristic gradient extending from the western seaboard to the interior of the South Island. At mid altitudes on the slopes nearest the Tasman Sea, silver beech is associated with a diversity of other tree and understorey species; these same species, in the absence of beeches, constitute the coniferhroadleaved forests of central Westland. These speciesrich forests grade towards pure mountain beech forest as rainfall decreases and the temperature range increases towards the eastern end of this gradient (Wardle 1984). North-west of the 1800 mm isohyet beech forest is almost continuous from valley floor to the subalpine limit of forest. Down to the 900 mm isohyet it occurs as separate blocks of various sizes, and there are only small, isolated stands in sheltered localities in drier parts. This fragmentation has been increased by fire (Wardle 2001). The broad pattern of silver beech dominating in north-western headwaters and high valley heads, and mountain beech dominating in drier eastern areas, especially at lower altitudes, conforms with the physiological differences between these species (Sun et al. 1995; Sun & Sweet 1996)). However, there is no obvious environmental explanation as to why the species that extends furthest down the precipitation gradient should be mountain beech in the Lindis Valley and the more mesic silver beech on the Pisa Range. Why should red beech be almost confined to the Matukituki and Motatapu catchments, with the only other verified locality being 40 km away on the north-western shore of Lake Hawea? The answers probably involve locations of beech refugia during the last glaciation and specific differences in responses to the climatic fluctuations of the Quaternary (McGlone et al. 1996). The fragments of conifer-dominated forest and scrub scattered through the upper Clutha district are remnants of vegetation that extended almost universally across the mountain slopes throughout the early and mid Holocene until it was displaced by

13 Wardle Native forest distribution in upper Clutha 445 the spread ofnothofagus (McGlone et al.1996) and, finally, by the fires of the human era (Wardle 2001). It is curious that the main pockets of survival are either in valley heads near the Main Divide where precipitation is in the order of 2000 mm annually, or on the driest mountains of the district, albeit on sites where regional dryness is moderated by altitude and topography. The explanation may be that component species possess greater tolerance of environmental extremes than the beech species that displaced them in intermediate localities (Sakai & Wardle 1978). The record of the distribution of forest types and native tree species in the upper Clutha district provides reference points for ensuring their protection. The pattern of forest distribution has been remarkably stable in the district since European activity began in the 1850s (Wardle 2001), despite fire, grazing by domestic and feral mammals, and some exploitation for timber. Although these influences continue, the greatest threat may now be competition from introduced plants, including herbaceous species that may have been encouraged by episodes of fertiliser use and increased stocking, and, especially, introduced trees that are hardier and more vigorous as pioneers than native trees. ACKNOWLEDGMENTS This study was carried out under Foundation for Research, Science and Technology contract CO9313 at Landcare Research. I am grateful to many people for information, especially Robert and Kate Wardle, Larry Burrows, and the late Gerald Scaife. I am also grateful to landholders for access to properties and use of tracks and huts. Julian Cone, Hoani Horsfall, Terry Savage, Kirsty Cullen, and Anouk Wanrooy of Landcare Research prepared the maps. Bill Lee, Matt McGlone, and Trevor Webb provided helpful comment on aspects of the paper. REFERENCES Allen, R. B. 1978: Scenic reserves of Otago Land District. Biological Survey of Reserves Report 4. Aspinall, J. 1993: Farming under Aspiring. Wanaka, Aspinall family. 267 p. Burre, J. 1965: Ecology Of Leptospemzum in Otago. New Zealand Journal of Botany 3: Cheeseman, T. F. 1925: Manual of the New Zealand flora. 2nd ed. Wellington, Government Printer p. Grove, P.; Ward, C. M. 1994: Lindis, Pisa and Dunstan ecological districts. a survey report for the Protected Natural Areas Programme. New Zealand Protected Natural Areas Programme 36: Hewitt, A. E. 1998: New Zealand soil classification. 2nd ed. Lincoln, New Zealand, Manaaki Whenua Press. 133 p. Holloway, J. T. 1954: Forests and climates in the South Island of New Zealand. Transactions of the Royal Society of New Zealand 82: Mark, A. F. 1965: Central Otago: vegetation and mountain climate. In: Lister, R. G.; Hargreaves, R. P. ed. Central Otago: a symposium to mark the centenary of the "Golden Years" in Central Otago. Special Publication of the New Zealand Geographical Society, Miscellaneous Series 5: Mark, A. F. 1977: Vegetation of Mount Aspiring National Park New Zealand. National Parks Scientific Series 2: McCracken, I. J. 1980: Mountain climate in the Craigieburn Range, New Zealand. In: Benecke, U.; Davis, M. R. ed. Mountain environments and subalpine tree growth. Proceedings of IUFRO Workshop November 1979, Christchurch, New Zealand. Wellington, New Zealand Forest Service. Pp McGlone, M. S.; Mildenhall, D. C.; Pole, M. S. 1996: History and palaeoecology of New Zealand Nothofagus forests. In: Veblen, T. T.; Hill, R. S.; Read, J. ed. The ecology and biogeography of Nothofagus forests. Newhaven, Yale University Press. Pp New Zealand Meteorological Service (undated): Sumaries of climatological observations to New Zealand Meteorological Service Miscellaneous Publication 177. New Zealand s0i1 Bureau 1968: General survey Of the soils of South Island, New Zealand. New Zealand Soil Bureau Bulletin 27: Norton, D. A. 1985: A multivariate technique for estimating New Zealand temperature normals. Weather and Climate 5: Rogers, G. M. 1996: Aspects of the ecology and conservation of the threatened tree Olearia hectorii in New Zealand. New Zealand Journal of Botany 34: Sakai, A.; Wardle, P. 1978: Freezing resistance of New Zealand trees and shrubs. New Zealand Journal of Ecology 1: Sun, 0. J.; Sweet, G. B. 1996: Genotypic variation in light and temperature response of photosynthesis in Nothofagus solandri var. cliffortioides and N. menziesii. Australian Journal of Plant Physiology 23:

14 446 New Zealand Journal of Botany, 2001, Vol. 39 Sun, 0. J.; Sweet, G. B.; Whitehead, D.; Buchan, G. D. 1995: Physiological responses to water stress and water1ogging in Nothofagus species. Tree physiology 15: Ward, G.; 1984: Proposals for protected natural areas in the catchments Of the East Branch Quartz creek and of a small creek flowing south-west from Little Mt Maude. Unpublished report held at Department of Conservation, Dunedin, New Zealand. Ward, G.; Munro, C. M. 1989: Otago II. Biological Survey of Reserves Series 20: Wardle, J. A. 1970: The ecology of Nothofagus solandri. New Zealand Journal of Botany 8: Wardle, J. A. 1984: The New Zealand beeches: ecology, utilisation and management. Wellington, New Zealand Forest Service. 447 p. Wardle, J. A.; Guest, R. 1977: Forests of the Waitaki and Lake Hawea catchments. New Zealand Journal of Forestry Science 7: Wardle, P. 1991: Vegetation of New Zealand. Cambridge, Cambridge University Press. 672 p. Wardle, P. 2001: Holocene forest fires in the upper Clutha district, Otago, New Zealand. New Zealand Journul of Botany 39: Wardk, p.; Johnson, P. N. 1987: Botany Division excursion to the Hunter Valley, Lake Hawea, Otago, with notes on soil charcoals and forest remnants in the upper Clutha basin. Unpublished DSIR Botany Division report held at Landcare Research, Lincoln, New Zealand. Wells, J. A. 1972: Ecology of Podocarpus hallii in Central Otago, New Zealand. New Zealand Journal of Botany 10: Wood, B. L. 1962: Sheet 22 Wakatipu. 1st ed. Geological map of New Zealand 1:250,000. Wellington, DSIR. Zotov, V. D. 1938: Some correlations between vegetation and climate in New Zealand. New Zealand Journul of Science and Technology 19: