NORTH CAPE SERPENTINE QUADRATS 1965-1987

by R.D. Reeves, A.J.M. Baker* and P.R. Shepherd

Department of Chemistry and Biochemistry, Massey University, Palmerston North * Department of Animal and Sciences, University of Sheffield, Sheffield, U.K.

SUMMARY

Two of the permanent quadrats (the unfenced, uncleared and cleared) established in the serpentine scrub vegetation of the North Cape Scientific Reserve in 1965 have been re-recorded. Some changes in the composition of both quadrats were detected but there had been little change in vegetation structure or species dominance. Records from the cleared quadrat confirmed the extremely slow rates of recolonization and diversification of the bared lateritic surface.

INTRODUCTION During the course of geobotanical and biogeochemical studies on the ultramafic/mafic areas of the North Cape plateau, carried out in August 1987, we have taken the opportunity to re-examine the permanent quadrats established by Gravatt in December 1965 in an area of 'plateau scrub' (Wheeler, 1963) on serpentine-derived, lateritic soil. Since the initial account of the vegetation within the quadrats, demographic changes have been reported by Johnstone (1967), Rae (1970) and Wright (1976). The present study allows an assessment to be made of further changes that have occurred, firstly 12 years after the last records were made, and secondly 22 years after the establishment of the permanent quadrats. However, records were made at only two of the five quadrats established by Gravatt - the unfenced, uncleared and cleared plots on the plateau scrub. The fencing originally erected to exclose the fenced quadrats no longer existed and had disintegrated at an undetermined date since the last records of the site had been made. Wright commented on the poor state of this fencing when he recorded the quadrats in November 1975, but no attempt had been made to reinstate the exclosures. Visual comparison of the fenced and unfenced quadrats on the cleared and uncleared plots suggested that there was now little difference in vegetation structure or species composition, confirming Johnstone's original belief that grazing pressures on the scrub vegetation were minimal since the establishment of the North Cape Scientific Reserve in 1964.

77 Tane, Vol. 33,1991 METHODS The quadrats were visited in late August 1987. Whilst it was generally possible to locate the reference corner posts without undue difficulty, almost all other corner markers for the quadrats had been removed or had rotted in situ. The area of the two unfenced quadrats was therefore re-measured and gridded in a similar manner to earlier recorders. Each of the subunits (9 for the uncleared and 16 for the cleared quadrat) was mapped individually, locating the position of each plant where it was rooted, and then all records were combined to produce distribution maps of the same type presented by Wright. No quantitative measurements of species cover were made. Figures la & b and 2a & b show the composition of the quadrats alongside the records made by Wright in 1975. Species abbreviations are those used by Wright; these are recorded in Table 1 with additional entries for 'new' species recorded in the present work.

Table 1. Abbreviations used in Figs 1-2.

Abbreviation Species

A Aira caryophyllea As (?Corybas sp.) Ca Cassinia leptophylla var. (C. amoena) Cj Cyathodes juniperina Co Coprosma rhamnoides ssp. (C. neglecta) Cy Cyathodes fraseri F Phormium tenax Gi Gonocarpus incanus H Hypochoeris radicata He Hebe ligustrifolia Hp Haloragis procumbens L Lepidosperma laterale Ls Leptospermum scoparium M Morelotia affinis R Rytidosperma sp. Pi Pimelea prostrata var. erecta Pm Pomaderris prunifolia var. edgerleyi Pt Pteridium esculentum T Thelymitra longifolia

78 THE UNCLEARED QUADRAT (Figure la & b) This quadrat was still dominated by a dense and more-or-less continuous cover of stunted manuka (Leptospermum scoparium), as originally reported by Gravatt (1966) and later by Wright (1976), suggesting that the plateau scrub had not been affected seriously by any fires in the intervening 12 years. The dominant shrubs (other than L. scoparium) were still Cassinia amoena and Hebe ligustrifolia. Although some changes in the relative cover of the two species were apparent, there was little change (reduction) in the number of established . There had been a marked decline in the numbers of Pomaderris prunifolia var. edgerleyi, only two of the original 12 plants still surviving as large, well-established individuals. In contrast, a marked increase (11 to 17) in living fronds of Pteridium esculentum was recorded. There has been a dramatic change in the population of Hypochoeris radicata; only one large rosette remained of the 30 individuals mapped by Wright. However, seedlings of H. radicata were noted in the ground layer of the quadrat and the change may be partly due to the fact that the present observations were made in August. The single plant of Phormium tenax close to the eastern corner of the quadrat noted by Wright was still alive, and its foliage now spread into the quadrat. New recruits into the community of established species include individual plants of Cyathodes juniperina and Coprosma rhamnoides. Losses of established plants were of Cyathodes fraseri and Thelymitra longifolia; both these species could still be found in the adjacent scrub. Species present as seedlings contributing minor ground cover (and therefore not plotted on the maps) were Cyathodes fraseri, Gonocarpus incanus, Coprosma rhamnoides, Pimelea prostrata, Acianthus sinclairii (or Corybas sp., the identity could not be confirmed at this early stage), Microtis unifolia, Morelotia affinis and Rytidosperma spp. (probably two species). The parasite Cassytha paniculata was noted trailing over shrubs within the quadrat. Bare ground had not decreased in area (less than 2%) since Wright's records but the position of the largest patch had moved and was now colonized partially by Cassinia amoena. Two new areas of bare ground had appeared under the Leptospermum cover. An abundance of Leptospermum litter had accumulated on the ground surface, probably a result of a combination of the impeded rates of litter breakdown in ultramafic soils and the resistant nature of the litter itself.

THE CLEARED QUADRAT (Figures 2a & b) The most obvious feature of this quadrat was the predominance of bare ground, estimated to occupy c. 75% of the quadrat area. This is very similar to Wright's 1975 estimate of 68%. The largest plants within the quadrat were

79 1 X Ls Ca He ( ~\ v .

01 • ( \

0 pt & <£>

0 Ls

Pt Ls pt Fig. 1 Vegetation map of unfenced uncleared quadrat, as recorded (a) by Wright in 1975, (b) in the present work in 1987. The length of each side is 1.8 m. See Table 1 for abbreviations. Dimensions of larger plants are outlined; others are seedlings. Dashed outlines enclose groups of the same species. All intervening space (other than bare ground - diagonally shaded) is occupied by Leptospermum scoparium.

80 Cy Pm^x* A Pm Pm Ls •Pt '

• R Hp Ls

Hp T Ls Pt Pm

Pm

•Pm Pm- Pt. Ca Pt Pm • Ls •Pm

.Pt "R Hp Pm Hp Ls •Ls Ls Pm Pm Pm

Ca M Ca X

H

LS H cf Pt pt

(—)

{cgV—4s

n I Ls J p 3/ % R Pm Ls

LS Cy Pt R —— R R R R R

RLs Pt 0 Pt c R Pm H \

Fig. 2 Vegetation map of unfenced cleared quadrat, as recorded (a) by Wright in 1975, (b) in the present work in 1987. The length of each side is 1.2 m. Dimensions of larger plants (underlined) are outlined; others are seedlings. AH intervening space is bare ground.

81 seven well-established individuals of Pomaderris prunifolia var. edgerleyi, the species noted by Wright to be the most common in 1975. The one large shrub of Cassinia amoena referred to by Wright and reported then to be in a healthy condition had expanded in area so that it was now the second largest shrub in the quadrat. A further eight new recruits of C. amoena were recorded. There had been a 33 % increase in the number of Leptospermum scoparium plants, and a similar increase in the number of Pteridium fronds. Even more marked was the increase in numbers of small plants of Cyathodes fraseri; many of these were clumped in discrete areas of the quadrat. Individuals of the orchid Thelymitra longifolia had increased from 3 to 5 in number. A noteworthy change was the large increase in numbers of the grass Rytidosperma (originally recorded by Wright as Notodanthonia pilosa) from 3 to 27. Wright commented on the abundance of the plant in the adjacent fenced plot. The population of the adventive Hypochoeris radicata had similarly increased (from 2 to 15 rosettes). Cassytha paniculata was also recorded on the bare soil of the quadrat. New species recruits were Lepidosperma laterale, Acianthus sinclairii (or Corybas sp.) and Morelotia affinis; the last-mentioned was recorded by Wright as an important species of the fenced quadrat. The only species loss was the adventive annual Aira caryophyllea, which may well be recorded at another stage of the year. No Poa annua, originally recorded by Johnstone (1966) and Rae (1970) but not seen by Wright (1976), was found.

DISCUSSION The observations reported in this paper confirm two fundamental properties of the plateau scrub vegetation, firstly that its rate of development is extremely slow, and secondly, that when fully established, there is little change in community structure and composition. The scrub thus probably represents an edaphic climax condition on the ultramafic soils of North Cape. It is perhaps of most general significance that the cleared quadrat recorded 22 years after its establishment still comprises 75 % bare ground. The changes in species density and rates of diversification for this quadrat are summarized in Table 2 and Fig. 3. A year after Gravatt cleared the plot, Johnstone (1966) recorded 10 species present, half of which were adventive or native weedy colonists. Subsequent records of the quadrat suggest only a very slow increase in species density, the present figure being 13 spp/1.44 nr. The totals presented conceal the gains and losses involved. Fig. 3 shows that the net gains result from a recruitment of 2-3 new species and a loss of 1-3 species between each recording. These losses are largely the weedy herbs. It is also important to note that the present dominant shrubs, Leptospermum scoparium and Cassinia amoena, are not early colonists on the bare ground surface; their ultimate

82 Table 2. Changes in the species composition of the Cleared, Unfenced Quadrat 1967 - 1987

Species 1967 1969 1975 1987

Dichondra repens + - - - Pteridium esculentum + + + + Cyathodes fraseri + + + + Pseudognaphalium luteo-album + + - - Thelymitra longifolia + + + Pomaderris prunifolia var. edgerleyi + + + + Hypochoeris radicata + - + + Parentucellia viscosa + - - - Pimelea prostrata var. erecta + + + + Poa annua + + - - Gonocarpus incanus - + + + Leptospermum scoparium - + + + Cassinia amoena - + + + Aira caryophyllea - - + - Rytidosperma sp. - - + + Morelotia affinis - - - + Acianthus sinclairii (? Corybas sp.) - - - + Lepidosperma laterale - - - +

Total species density 10 10 11 13

E 12-

v- 10- \ c 8-

6- o in u- o Ql 2- m 0 t t A B

Fig. 3 Diversification of species recorded in the cleared unfenced quadrat, 1965-1987. The number of species gained and lost in the intervals between recording is shown. A - Dec '65 (Gravatt 1966); B = Jan '67 (Johnstone 1967); C = Aug '69 (Rae 1970); D = Nov '75 (Wright 1975); E = Aug '87 (Reeves et al. 1991).

83 dominance must result from sustained slow growth once they have established successfully. The most recent additions to the community include the sedges Morelotia affinis and Lepidosperma laterale, both of which are notable components of the surrounding mature scrub vegetation (Fig. 2a). This would indicate that these two species are very immobile, largely spreading from isolated clumps by vegetative growth and rarely establishing by seed. The changes noted were largely in agreement with the predictions made by Wright for the successional sequence in the plateau scrub. The species density of the uncleared quadrat was 18 spp/3.24 nr\ Although direct comparison with the data for the cleared quadrat is not possible because of the different areas involved, one would predict that it will be many decades before the species density of the cleared quadrat reaches a stable value. The exposed situation of the open lateritic surface, alluded to by Wright, is clearly a major factor inimical to seedling establishment and survival. Observations on the uncleared vegetation suggest that the Leptospermum cover, once ultimately established, provides a sheltered microhabitat for low-growing associate species. The litter layer noted will also provide a buffer against surface desiccation, so facilitating seed germination and seedling survival. In view of the floristic richness of the North Cape region (Druce et al., 1979), it is surprising that the species composition of the plateau scrub vegetation is not more diverse. The conditions of exposure and the edaphic constraints result in a stressed environment in which only the most resistant and slow-growing species can ultimately survive. The effects of the edaphic conditions on plant distribution will be discussed in a future publication. Clearance of the quadrat on the plateau scrub suggests an extremely slow rate of recolonization, during which process such an area will be subjected to strong erosional forces. The extreme effects of erosion can be observed at the margins of the plateau, where deep gullying has resulted. These observations reinforce the view that the plateau vegetation of North Cape is both fragile and unable to regenerate readily on disturbance. There is thus an urgent need to minimize any further destruction of the vegetation cover if this small and unique area of serpentine vegetation is to persist. Further recording of the permanent quadrats is urged by the authors, but there still remains a need to reinstate the quadrat boundaries in accordance with Wright's suggestions.

ACKNOWLEDGEMENTS

We wish to record our thanks to the staff of the Department of Conservation, Kaikohe, particularly Miss L. Forester and Mr J. Beachman, for their assistance with our visit to the site, and to Mr A.E. Wright of Auckland Museum for his helpful comments on this paper.

84 REFERENCES

Druce, A.P., Bartlett, J.K. &Gardner, R.O. 1979: Indigenous vascular plants on the serpentine area of Surville Cliffs and adjacent cliff tops, north-west of North Cape, . Tane 25: 187-206. Gravatt, D.J. 1966: Establishment of permanent quadrats in plateau scrub at North Cape. Tane 12: 87-91. Johnstone, I.M. 1967: A report on the permanent quadrats at North Cape. Tane 13: 143-146. Rae, W.J. 1970: North Cape Quadrats 1969. Tane 16: 53-60. Wheeler, J.M. 1963: The vegetation of the North Cape area. Tane 9: 63-83. Wright, A.E. 1976: North Cape quadrats 1975. Tane 22: 107-118.

85 86