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Pachystegia rufa and allied rock
daisies: rarity and threats
DOC SCIENCE INTERNAL SERIES 17
Department of Conservation
P.O. Box 10-420
Wellington, New Zealand
DOC Science Internal Series is a published record of scientific research carried out, or advice given,
by Department of Conservation staff, or external contractors funded by DOC. It comprises progress
reports and short communications that are generally peer-reviewed within DOC, but not always externally refereed. Fully refereed contract reports funded from the Conservation Services Levy (CSL) are also included.
Individual contributions to the series are first released on the departmental intranet in pdf form.
Hardcopy is printed, bound, and distributed at regular intervals. Titles are listed in the DOC Science Publishing catalogue on the departmental website http://www.doc.govt.nz and electronic copies of CSL papers can be downloaded from http://csl.doc.govt.nz © Copyright November 2001, New Zealand Department of Conservation ISSN 1175–6519 ISBN 0–478–22174–6 This report originated from work carried out under Department of Conservation investigation no.
3283. It was prepared for publication by DOC Science Publishing, Science & Research Unit; editing and layout by Lynette Clelland. Publication was approved by the Manager, Science & Research Unit, Science Technology and Information Services, Department of Conservation, Wellington.
1. Introduction 6
2. Pachystegia rufa Molloy 6
3. Pachystegia minor (Cheeseman) Molloy 9
4. Pachystegia insignis (Hook. f.) Cheeseman 10
5. Pachystegia A 11
6. Pachystegia B 11
7. Acknowledgements 12
8. References 12 Pachystegia rufa and allied rock daisies: rarity and threats Brian Molloy 20 Darvel Street, Riccarton, Christchurch
ABSTRACTThis report provides additional information on Pachystegia rufa and allied rock daisies, with particular emphasis on rarity and threats. Pachystegia rufa, currently listed as a ‘Declining’ species, is reassessed on the basis of new information available and is now regarded as ‘Range Restricted’ and not under threat. P. minor s.s. and P. aff. minor require more information (‘Data Deficient’) to enable their true status and trend to be properly assessed. Of the two, P. aff. minor is certainly more restricted and threatened. Pachystegia insignis consists of two major disjunct populations; one essentially north of the Kaikoura ranges and not considered to be threatened overall; the other south of the Kaikoura ranges and especially vulnerable, although more information (‘Data Deficient’) is required to assess this southern population objectively.
Pachystegia A and B, the former essentially coastal, the latter an inland entity, are unnamed taxa which are relatively widespread and abundant and are not considered to be threatened overall.
Further effort is needed to determine the status of P. minor and southern populations of P. insignis, and outlying populations of all taxa should be monitored from time to time and their protection and management advocated.
© November 2001, New Zealand Department of Conservation. This paper may be cited as:
Molloy, B. 2001: Pachystegia rufa and allied rock daisies: rarity and threats. DOC Science Internal Series 17. Department of Conservation, Wellington. 12 p.
DOC Science Internal Series 17
1. Introduction This report attempts to build on the information provided in my preliminary report on Pachystegia rufa (Asteraceae) and allied rock daisies (Molloy 2001).
In that report, aspects covered in broad outline included current knowledge of the taxonomy and distribution of the constituent taxa, and their habitats, ecology, breeding system, recruitment, rarity and threats. Additional information on some of these aspects is provided in a taxonomic revision of the group now in preparation.
The present report focuses on rarity and threats, with particular emphasis on P. rufa, the only species at present listed among the threatened and uncommon plants of New Zealand (de Lange et al. 1999). However, further fieldwork since my preliminary report was prepared has revealed that another species, P. minor, may be more uncommon than P. rufa and worthy of attention in conservation management. Recent fieldwork also reveals that other rock daisies, and their regular native plant associates, are under increasing threat from competing plants, notably introduced grasses and broom (Cytisus scoparius). With this in mind, it is opportune to review the relative abundance of all the named and unnamed taxa of Pachystegia, and to assess the threats each is exposed to in their respective habitats throughout their known natural range.
2. Pachystegia rufa Molloy This species, illustrated in colour by Eagle (1982, Plate 246, as Pachystegia D), was described by Molloy (1987), and is perhaps the most colourful member of the genus, with its reddish petioles and inflorescences, especially on new season’s growth. It is also the best known in terms of its distribution, relative abundance and habitat. This is due partly to its recent recognition and its attractiveness, and partly to the threat of large-scale quarrying of a section of its natural habitat, proposed by Tranz Rail New Zealand Limited in the mid 1990s.
This proposal led to two developments: a joint field survey of P. rufa and associated plants by Ruth Bartlett (Kingett Mitchell & Associates for Tranz Rail) and Cathy Jones and Jan Clayton-Greene (Department of Conservation), carried out in 1996; and the formal protection of about 138 ha of P. rufa habitat by an open space covenant agreement between a landholder, Charles Waddy, and the Queen Elizabeth The Second National Trust. This covenant, initiated in 1997, now protects a substantial part, about 75%, of the known habitat of P. rufa, principally on rock bluffs and outcrops in the Blind (Otuwhero) River and Stace (‘Waterfalls’) Stream which drain the ‘Little Haldon Hills’, about 10 km south of the Marlborough township of Seddon.
6 Molloy—Pachystegia rufa and allied rock daisies The aforementioned survey confirmed an earlier one of mine which found P. rufa was confined to the fault-bound ‘Little Haldon Hills’, and sandwiched between the habitat of the larger rock daisy, P. insignis, on the main Haldon Hills to the south, and the banks of the Blind River to the north. Where the two species are in close proximity, small populations of hybrids occur, notably on the southern edge of the ‘Little Haldon Hills’ and along the Blind River. The ‘Little Haldon Hills’ occupy an area of about 5 × 2.5 km, and rise to a maximum altitude of 537 m. The basement rock consists of massive greywacke of Jurassic age, which has somewhat higher levels of natural fertility than the older (Triassic) greywackes further to the west. Four principal streams—Stirling Brook, Beaumont Creek, Stace Stream and Blind River—dissect the area and flow to the north through relatively narrow rocky gorges, with numerous rock outcrops above on the intervening ridges.
Throughout this dissected landscape there is a noticeable increase in the amount of exposed rock—the habitat of P. rufa—from east to west; i.e. from the broad catchment areas of Stirling Brook in the east to Blind River in the west. This is reflected in a corresponding increase in the number of plants of P. rufa from east to west recorded during the joint Tranz Rail/DOC survey in 1996 which, in turn, confirms my earlier visual assessment (see Table 1).
I revisited the habitat of P. rufa in December 2000 with Cathy Jones and Jan Clayton-Greene (DOC), landholder Charles Waddy, and others, and confirmed
the following features:
P. rufa is quite at home on rock faces surrounded by trees of native hardwood species; an indication of its natural habitat. Since deforestation in Polynesian times the species has expanded its area to some extent, but not all the available habitat has been taken up, especially the massive and somewhat smoother rock faces at higher altitudes and on sunny slopes. Most plants of P. rufa occupy the more irregular and fissured rock faces in the lower shaded gorges and on other shaded slopes. On these sites a range of plant sizes and seedling establishment is evident, and signs of animal browse are minimal. Current populations are at least stable, if not slowly expanding. Erosion of some rock faces has occurred from time to time, usually by the cleavage of large sections, and in some cases the newly-exposed surfaces have been colonised by P. rufa.
DOC Science Internal Series 17 Even on its most favourable site, the density of P. rufa is less than that of P. insignis on corresponding sites on the nearby Haldon Hills. This behaviour is difficult to explain. It may have something to do with the number of niches available to the two species, or some aspect of the plants’ behaviour. Certainly, the number of florets per head on P. rufa is much less than on P. insignis.
Following a pilot trial on the breeding system of P. insignis mentioned in my preliminary report (Molloy 2001), a similar trial with P. rufa cultivated at Lincoln was carried out during the last flowering season. The same trend emerged: namely, an increase in numbers of seed set in selfed flower heads, through cross-pollinated flower heads, to open-pollinated ones. This confirmed that P. rufa, like P. insignis and other rock daisies, is basically selfincompatible, but some ‘leakage’ occurs. Seedlots sown from selfed, crossed and open-pollinated heads of P. rufa yielded high germination percentages in the range 77–93%. This information is additional to that reported by Simpson & Molloy (1978), but confirms that P. rufa, along with other rock daisies, is not constrained by its breeding system or germination.
Another feature, unique to P. rufa, which may constrain its ability to spread and occupy all available niches with the same density as other rock daisies, is the collapse into the plant of flower stems before all the seed is fully ripened and ready to be shed. As a result, flower stems lose their turgor and the heads remain closed. Nonetheless, there is often an abundance of seedlings at the base of plants each autumn, as is the case with other rock daisies.
Compared with other rock daisies, P. rufa is exposed to very few threats.
Dilution of the gene pool through hybridisation with its nearest neighbour P. insignis is unlikely, except in local ‘hot spots’ already mentioned above. Its habitat is reasonably weed free, and its bare rock substrate less prone to invasion from introduced grasses. If anything, the vigorous resurgence of native ‘grey scrub’ and hardwood trees will cast more shade and perhaps favour P. rufa. The abundance of bracken on the surrounding slopes, an indication of the relatively high level of natural fertility, while not directly affecting P. rufa, may do so indirectly if burnt regularly and the fires spread across the rock faces.
Damage from herbicide is unlikely given current farming practice. A few wilding pines are present and need to be monitored or removed to avoid them shading-out P. rufa.
As noted above, evidence of current animal browse on P. rufa plants is minimal.
Most, if not all, plants of P. rufa are beyond the reach of domestic livestock.
However, the ‘Little Haldon Hills’ supports a significant population of feral goats, and has done so for years. While it is difficult to assign any actual damage to P. rufa to these animals, like the wilding pines they should, at least, be monitored and, at best, eradicated or controlled to low numbers.
There is no firm field or historical evidence that P. rufa is a ‘declining’ species as listed by de Lange et al. (1999). Certainly, it has the smallest range of all the species in the genus, approximately 12 km2, and its total population is estimated to contain about 3000 individual plants, the majority of which are capable of reproduction. A reassessment of its classification using the step-bystep process set down in Table 3 of the draft document Classifying species according to the threat of extinction by Molloy et al. (2000) indicates that P. rufa should be classed as ‘Range Restricted’ and listed accordingly. Even if 8 Molloy—Pachystegia rufa and allied rock daisies quarrying was to proceed, as proposed by Tranz Rail, only a small part of the total population would be removed, and only temporarily, as restoration of the species is also part of the proposal. The formal protection of about 75% of the population by an open space covenant, with an agreed management to safeguard the species, gives cause for comfort in the long-term security of this attractive species.
3. Pachystegia minor (Cheeseman) Molloy This species, long regarded as a variety of P. insignis, was elevated to species rank by Molloy (1987). Two distinct leaf forms have been recognised (Molloy & Simpson 1980); one with light green or yellowish green rhomboid leaves identical to the type specimen of Cheeseman’s Olearia insignis var. minor (Cheeseman 1916); the other a somewhat smaller plant with darker green broadly obovate leaves. Both forms are illustrated in colour by Eagle (1982, Plates 244, 245, as Pachystegia C var(i) and var(ii), respectively). For the purposes of this report the rhomboid leaf form is referred to as Pachystegia minor s.s., the obovate leaf form as Pachystegia aff. minor. The taxonomic status of the latter is still unresolved.