Bruce D. Clarkson

Taxonomy, ecology, and conservation of Sporadanthus (Restionaceae) in New Zealand

Abstract A new species, Sporadanthus ferru‐gineus (Restionaceae), is described from the peat bogs of the northern North Island, New Zealand. It is distinguished from S. traversii by its more robust, brittle culms with swollen bases, different coloured rhizome scales and culms, and smaller, dehiscent fruit. In the past S. ferrugineus has been referred to Sporadanthus traversii, which is now treated as a Chatham Island endemic. Because of this past confusion a detailed description for S. traversii is also provided and a lectotype for the species selected. The ecology of both species of Sporadanthus is reviewed. There are marked differences in their preferred habitats and response to fire. In particular, Sporadanthus ferrugineus is a late‐successional species of raised peat bogs. Within these ecosystems, S. ferrugineus is eliminated by fire and re‐establishment is from seed subsequently deposited by remnant plants. Following fire, S. ferrugineus takes five years to recolonise former habitat and requires 12 y...

Ecology of an elusive endemic shrub, Pittosporum obcordatum Raoul

Abstract The ecology of Pittosporum obcordatum Raoul (heart-leaved kohuhu), an endemic shrub or small tree, was investigated to explain its sporadic distribution. The species is characteristically found on lowland (<500 m a.s.l.) river flats where local climates have frequent summer drought and winter frost, and soils are waterlogged in winter. Population structures reveal no recent regeneration at some sites while at others there is recruitment in the smaller height classes. This pattern reflects mainly the frequency and intensity of browsing by domestic stock. The primary reason for the species uncommonness appears to be strict habitat specificity combined with habitat destruction and fragmentation. Factors potentially contributing to its vulnerability include slow relative growth rate, restricted seed dispersal, unbalanced population sex ratios, and inability of seedlings and small juveniles to survive heavy browsing.

Recent vegetation changes on Mount Tarawera, Rotorua, New Zealand

Abstract Vegetation changes over the period 1978–1992 on Mt Tarawera volcano are described and analysed in order to identify causes of species replacement. The most significant change has been an increase of tutu (Coriaria arborea), which has spread from the upper side of Kanakana Dome onto much of the top. Tutu colonisation appears to be limited by marginal habitat conditions, such as soil infertility, low water availability, and harsh climate, and the slow spread of its nitrogen-fixing endophyte. Habitat conditions may have become more favourable over recent decades because of increased soil fertility from weathering of the substrate and addition of organic material, and an overall warming of climate. Severe and unseasonable frosts cause dieback and periodically check tutu success; this facilitates replacement by more frost-tolerant, later successional species such as broadleaf (Griselinia littoralis). Preliminary analyses of dome-top soils reveal low levels of all nutrients tested, particularly nitroge...

Vegetation decline following recent eruptions on White Island (Whakaari), Bay of Plenty, New Zealand

Abstract Vegetation decline following recent (1976–90) eruptions on White Island (Whakaari) was assessed during 1986 and 1990 using historical accounts (1959 and 1967) as a baseline. More than two-thirds of the Metrosideros excelsa (pohutukawa) forest and scrub and all of the gannetry vegetation had declined markedly and several species had become locally extinct. The most probable causes of death of M. excelsa were toxic fumes, wet ash coating leaves, and “acid rain”. For the small herbaceous species, complete burial by tephra was probably the main cause of death. Size class structures of three forest plots and M. excelsa growth ring counts suggested several phases of forest development, with the most advanced forest older than 180 years. Data from M. excelsa forests on other volcanic islands indicate that mature M. excelsa forest develops in 250 years. The depauperate flora of White Island compared with other Bay of Plenty islands probably results from the extreme soil conditions and continuing volcanic...

Coprosma pedicellata (Rubiaceae), a new species from New Zealand

Abstract A new, diploid species of Coprosma, C. pedicellata (2n = 44) is described and illustrated. It has a close morphological affinity with the northern New Zealand hexaploid species C. parviflora (2n = 132), which may be an ancient amphidiploid derivative. C. pedicellata is readily identified by its distinctive growth habit, habitat, and pendant pedicellate violet drupes. It is known from a few disjunct localities along the foothills of eastern New Zealand where it is restricted to forest or forest margins, usually on moderately fertile soils with impeded drainage, in overflow and flood channels, and alongside small streams. It shares these cool winter‐wet/warm summer‐dry habitats with a select group of woody species, including other rare small‐leaved divaricate shrubs and dwarf mistletoes. C. pedicellata is considered to be a restricted taxon in need of active conservation management over the greater part of its present natural range.

Macrofossils and pollen representing forests of the pre-Taupo volcanic eruption (c. 1850 yr BP) era at Pureora and Benneydale, central North Island, New Zealand

Micro- and macrofossil data from the remains of forests overwhelmed and huried at Pureora and Benneydale during the Taupo eruption (c. 1850 conventional radiocarbon yr BP) were compared. Classification of relative abundance data separated the techniques, rather than the locations, because the two primary clusters comprised pollen and litter/ wood. This indicates that the pollen:litter/wood within-site comparisons (Pureora and Benneydale are 20 km apart) are not reliable. Plant macrofossils represented mainly local vegetation, while pollen assemblages represented a combination of local and regional vegetation. However, using ranked abundance and presence/absence data, both macrofossils and pollen at Pureora and Benneydale indicated conifer/broadleaved forest, of similar forest type and species composition at each site. This suggests that the forests destroyed by the eruption were typical of mid-altitude west Taupo forests, and that either data set (pollen or macrofossils) would have been adequate for regional forest interpretation. The representation of c. 1850 yr BP pollen from the known buried forest taxa was generally consistent with trends determined by modern comparisons between pollen and their source vegetation, but with a few exceptions. A pollen profile from between the Mamaku Tephra (c. 7250 yr BP) and the Taupo Ignimbrite indicated that the Benneydale forest had been markedly different in species dominance compared with the forest that was destroyed during the Taupo eruption. These differences probably reflect changes in drainage, and improvements in climate and/or soil fertility over the middle Holocene.

A new, rare species of Melicytus (Violaceae) from New Zealand

Abstract A new species of Melicytus, M. drucei, is described and illustrated. It has some features in common with diploid M. flexuosus and an un-described taxon which forms part of the tetraploid M. alpinus complex, and is believed to be a stable triploid hybrid between these two. M. drucei is known only from the Ahukawakawa Swamp and Pouakai Range, Egmont National Park, where it is restricted to the Pouakai volcano (250k yrs), and is associated with a small, distinct group of other shrubs. It is regarded as a unique, rare, and threatened species.

Hebe tairawhiti (Scrophulariaceae): a new shrub species from New Zealand

Abstract A new species of Hebe, H. tairawhiti, is described from New Zealand. It is a large shrub or small tree with a local distribution centred on the East Coast (Tairawhiti) region of the North Island and is considered threatened.