Beverley R. Clarkson

Vegetation and peat characteristics in the development of lowland restiad peat bogs, North Island, New Zealand

A chronosequence of restiad peat bogs (dominated by Restionaceae) in the lowland warm temperate zone of the Waikato region, North Island, New Zealand, was sampled to identify the major environmental determinants of vegetation pattern and dynamics. Agglomerative hierarchical classification of vegetation data from 69 plots in nine different-aged bogs, initiated from c. 600 to c. 15,000 cal yr BP, identified eight groups. Six of these groups formed a sequence from sedges through Empodisma minus, the main peatforming restiad species, to phases dominated by a second restiad species, Sporadanthus ferrugineus. The sequence reflected bog age and paralleled patterns of temporal succession over the last 15,000 years (from early successional sedges through mid-successional Empodisma to late successional Sporadanthus) derived from previous studies of plant macrofossils and microfossils in peat cores. This indicated that different-aged bogs in the Waikato region could be used to interpret temporal succession. The remaining two classificatory groups comprised plots from sites modified by drainage, fire, or weed invasion and currently dominated by non-restiad species. The relationships between environmental variables and the six groups representing restiad bog succession indicated that, as succession proceeds, von Post decomposition index and nutrients in the top 7.5 cm peat zone decrease. The most useful indicators of successional stage were von Post, total P, total N, and % ash. Environmental response curves of the dominant plant species separated the species along nutrient and peat decompositional gradients, with early successional species having wider potential environmental ranges than late successional species. Empodisma minus, a mid-successional species, also had a relatively wide environmental range, which probably contributes to its key role in restiad bog development.

Foliar 15N natural abundance indicates phosphorus limitation of bog species.

Foliar δ15N, %N and %P in the dominant woody and herbaceous species across nutrient gradients in New Zealand restiad (family Restionaceae) raised bogs revealed marked differences in plant δ15N correlations with P. The two heath shrubs, Leptospermum scoparium (Myrtaceae) and Dracophyllum scoparium (Epacridaceae), showed considerable isotopic variation (−2.03 to −15.55‰, and −0.39 to −12.06‰, respectively) across the bogs, with foliar δ15N strongly and positively correlated with P concentrations in foliage and peat, and negatively correlated with foliar N:P ratios. For L. scoparium, the isotopic gradient was not linked to ectomycorrhizal (ECM) fractionation as ECMs occurred only on higher nutrient marginal peats where 15N depletion was least. In strong contrast, restiad species (Empodisma minus Sporadanthus ferrugineus, S. traversii) showed little isotopic variation across the same nutrient gradients. Empodisma minus and S. traversii had δ15N levels consistently around 0‰ (means of −0.12‰ and +0.15‰ respectively), and S. ferrugineus, which co-habited with E. minus, was more depleted (mean −4.97‰). The isotopic differences between heath shrubs and restiads were similar in floristically dissimilar bogs and may be linked to contrasting nutrient demands, acquisition mechanisms, and root morphology. Leptospermum scoparium shrubs on low nutrient peats were stunted, with low tissue P concentrations, and high N:P ratios, suggesting they were P-limited, which was probably exacerbated by markedly reduced mycorrhizal colonisations. The coupling of δ15N depletion and %P in heath shrubs suggests that N fractionation is promoted by P limitation. In contrast, the constancy in δ15N of the restiad species through the N and P gradients suggests that these are not suffering from P limitation.

Vegetation recovery following fire in two Waikato peatlands at Whangamarino and Moanatuatua, New Zealand

Abstract After fires in 1984 and 1989 at Whangamarino wetland, and in 1972 at Moanatuatua Bog, peatland flora and vegetation were monitored to determine rates and patterns of recovery. Species with rhizomes that survived the fires were able to resprout and grow rapidly in the initial post-fire period. Species that were eliminated had to re-establish from seed and so recovered more slowly. The vegetation at Moanatuatua took almost 12 years to recover to pre-fire condition, twice as long as at Whangamarino. Adventive and early colonising native species were prominent only in the first 1-2 post-fire years, probably because of temporarily increased availability of nutrients and/or open habitat. Ordination techniques arranged the plots and species in a sequence from shrub-sedgeland (Whangamarino), through Empodisma minus restiad rushland (Whangamarino), to Sporadanthus traversii/ Empodisma restiad rushland (Moanatuatua) following a gradient of decreasing fertility with time. Fires reset the bog development pro...

Sphagnum in peatlands of Australasia: Their distribution, utilisation and management

In comparison to the northern hemisphere, Sphagnum peatlands are an unusual andinfrequent component of the Australasianlandscape. Most peatlands in Australasiaare primarily composed of eitherRestionaceous or Cyperaceous peats. Sphagnum peatlands in Australia and PapuaNew Guinea/Irian Jaya (now West Papua) arelargely located in montane and alpineenvironments, but also occur down to sealevel in New Zealand and as moss patches onsome subantarctic islands. Fire is a majordeterminant of the characteristics ofpeatlands in Australasia. Peatlandmanagement in Australasia is hindered bythe need for increased understanding ofpeatland processes to enable a sustainablebalance of conservation of a small resourcewith localised utilisation. Themanagement focus in Australasia has largelybeen on ensuring ecologically sustainable Sphagnum moss harvesting, withlimited peat mining. We have found thatgeneral recovery of Sphagnum after moss harvesting canbe enhanced by harvesting larger peatlands,and by leaving one-third of the acrotelm toregenerate. The largest upland peat swampin mainland Australia, Wingecarribee Swamp,suffered a major collapse in 1998 followingpeat mining. Environmental and managementconsequences of this collapse have majorramifications for rehabilitation options. Sphagnum peatlands in Australasia arelikely to be adversely affected bydrainage, burning, grazing, trampling,global warming and peat mining.

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...

Dissolved organic carbon in New Zealand peatlands

Abstract We determined the concentration of dissolved organic carbon (DOC) and the specific ultraviolet absorbance (SUVA) of 193 samples of water collected from groundwater, porewater, drainage ditches, and streams at peatlands in New Zealand. There was a wide range in DOC concentration (from 7 to 184 mg litre–1), with the smallest concentrations in peatlands where there appeared to be large amounts of iron. Concentrations were large (generally >50 mg litre–1) in ombrotrophic (rain‐fed) peatlands and reached the highest values (averaging 81 to 129 mg litre–1) in water collected from the Torehape peatland (Waikato region), which is undergoing drainage and harvesting for peat and post‐harvest restoration. These high DOC concentrations suggest that New Zealand peatlands export 10 to 50 g DOC m–2 yr–1, a significant part of the overall carbon budget of peatlands. Most SUVA measurements ranged from 1.5 to 3.5 litre/mg DOC‐1/m–1) and suggest that the DOC contains 12 to 25% aromatics.

Restoring cut-over restiad peat bogs: A factorial experiment of nutrients, seed and cultivation

Abstract More than 75% of the original restiad peat bogs of the Waikato region, New Zealand, have been converted to agricultural use. Restiad bogs are also mined for peat but there is little information on methods for the post-harvest restoration of restiad bogs. We established a restoration trial on a mined bog with a full factorial experiment of four fertiliser additions (nitrogen, phosphorus, nitrogen plus phosphorus, and control), three seed additions ( Leptospermum scoparium , Sporadanthus ferrugineus , and no seed added [control] and three cultivation techniques (lightly-tilled, deeply-tilled and raised). All combinations were duplicated in 5×5 m plots. The first restoration goal was to establish rapidly a vegetation cover to minimise peat degradation. All plots in the raised cultivation treatments exceeded 88% cover by 2 years, whereas the other cultivation treatments had significantly less cover, ranging between 1 and 75%. The best combination within the raised treatments was nitrogen plus phosphorus fertiliser with L. scoparium seed, which reached 100% cover. A second goal was to establish the late successional species S. ferrugineus. Although cover of this species was greatest on the raised plots (up to 32%), the benefits of seed and fertiliser applications were not clear. Measured changes in nitrogen and phosphorus pools showed that nutrient status of the peat had returned to background levels within 2 years, minimising the potential for invasion by weeds with greater nutrient requirements.

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...

The pre-Taupo eruption (c. AD 130) forest of the Benneydale-Pureora district, central North Island, New Zealand

Abstract The composition and structure of three small areas of west Taupo forest, blasted down and buried during the c. AD 130 Taupo tephra eruption, are revealed by analysis of plant macrofossils, including leaves, seeds and wood. Data from these three sites and from the recently described Pureora buried forest were then used to interpret the pre-eruption vegetation along a 20 kilometre transect, from Pureora westward to Benneydale. All the stands were on flat or undulating terrain and dominated by podocarps, ranging from rimu (Dacrydium cupressinum)-tanekaha. (Phyllocladus trichomanoides) at Pureora to rimu at Benneydale. Broadleaved trees increased westward; on lower hillslopes in the Benneydale buried forest, northern rata (Metrosideros robusta) was an important canopy component. An amelioration of climate with decreasing altitude westward was indicated by a gradual change from prominence of horopito (Pseudowintera colorata) at Pureora to P. axillaris at Benneydale, and the presence of rewarewa (Knigh...

Vegetation and peat characteristics of restiad bogs on Chatham Island (Rekohu), New Zealand

Abstract Restiad bogs dominated by Sporadanthus traversii on Chatham Island, New Zealand, were sampled to correlate vegetation patterns and peat properties, and to compare with restiad systems dominated by Sporadanthus ferrugineus and Empodisma minus in the Waikato region, North Island, New Zealand. Classification and ordination resulted in five groups that reflected a disturbance gradient. The largest S. traversii group, which comprised plots from central, relatively intact bogs, had the lowest levels of total nitrogen (mean 1.20 mg cm‐3), total phosphorus (mean 0.057 mg cm‐3), total potassium (mean 0.083 mg cm‐3), and available phosphorus (mean 18.6 (Ag cm‐3). Modification by drainage, stock, and fires resulted in a decline of S. traversii and an increase of Gleichenia dicarpa fern cover, together with elevated peat nutrient levels and higher bulk density. Compared with peat dominated by Sporadanthus ferrugineus or Empodisma minus in relatively unmodified Waikato restiad bogs, Chatham Island peat under S. traversii has significantly higher total potassium, total nitrogen, available phosphorus, bulk density, and von Post decomposition indices, and significantly lower pH. Sporadanthus traversii and Empodisma minus have similar ecological roles in restiad bog development, occupying a relatively wide nutrient range, and regenerating readily from seed after fire. Despite differences in root morphology, S. traversii and E. minus are the major peat formers in raised restiad bogs on Chatham Island and in Waikato, respectively, and could be regarded as ecological equivalents.