Search

Peatlands store disproportionally large amounts of carbon per unit area, a function that is dependent on maintaining high and stable water tables. Climate change is likely to negatively impact carbon storage in peatlands, in part due to increases in vapour pressure deficit (VPD) driving higher evaporation (E) rates. However, the response of E to increasing VPD depends on the dominant vegetation type within peatlands. In this study, we used multiple years of eddy covariance (EC) measurements to compare E regimes at two peatlands with contrasting vegetation types – Kopuatai bog in Aotearoa / New Zealand, dominated by the vascular wire rush Empodisma robustum, and Mer Bleue bog in Canada, a "typical" shrub- and moss-dominated Northern Hemisphere peatland. We examined seasonal variability in E and equilibrium E (Eeq), energy balance partitioning, and the response of E , evaporative fraction (EF), and canopy conductance (gc) to VPD. Mean annual E was 45 % lower than mean annual Eeq at Kopuatai but only 16 % lower at Mer Bleue, demonstrating much greater limitations on E at Kopuatai. In addition, the mean midday (10:00–14:30 local standard time) dry-canopy Bowen ratio (β) at Kopuatai was 2.0 compared to 0.8 at Mer Bleue; therefore, the sensible heat flux (H) dominated over the latent heat flux (LE) at Kopuatai and vice versa at Mer Bleue. The responses of E , EF, and gc to increasing VPD at Kopuatai demonstrated stronger limitations on evaporative water loss for VPD > 0.7 kPa compared to Mer Bleue. The observed limitations at Kopuatai were attributed to strong stomatal control by E. robustum due to the rapid decrease in gc with increasing VPD; however, surface E could also be limited by its dense standing litter. At Mer Bleue, however, E was only weakly limited at VPD > 2 kPa, likely due to weak stomatal control over transpiration by the sparse shrub canopy and relatively large surface E from Sphagnum carpets. As such, the results of this study suggest that E. robustum drives a greater "hydrological resistance" to increasing VPD than the vegetation at Mer Bleue, leading to greater water retention at Kopuatai. This may enable greater resilience of the carbon sink function at Kopuatai to climatic warming and drying than at Mer Bleue. [ABSTRACT FROM AUTHOR]

The vegetation of subantarctic Campbell Island consists mainly of lowland Dracophyllum scrub and upland tussock grassland and tundra. Soon after the island was discovered in 1810, occupation by sealers and whalers led to localized burning and cutting of scrub. Further burning and cutting took place as a result of sheep farming between 1894 and 1931. Since the earliest photographs and vegetation descriptions of the island in the late nineteenth century, scrub cover has expanded markedly. Also, since the 1960s, the island has become warmer and drier. The aim of this paper is to quantify scrub changes as depicted in photo-sequences from the island, and to establish if the spread of scrub is a result of the cessation of anthropogenic activities or a response to global warming. Campbell Island, an isolated island 600 km south of New Zealand mainland (52°33.7′S, 169°09′E). Changes in scrub cover in the island were established through analysis of 33 photographic sequences in the island, the earliest photos dating back to 1888. Visual estimates were made of percentage woody cover in matching areas of repeat photographs, and of changes in scrub distribution with altitude and landscape type. Dracophyllum scrub was restricted at the time of the first photographs (1888) relative to its present extent, and earlier written observations suggest that there had been little change from the 1840s. Scrub cover has subsequently increased in most areas. Most of the spread occurred after the cessation of farming. Change has mostly consisted of a thickening and expansion of pre-existing scrub patches. There is no indication that the upper elevational limit of scrub has increased. Initial reduction of scrub was probably due to anthropogenic fire in the early nineteenth century, although it is possible that less favourable climates had also restricted its distribution. Failure of the scrub to regenerate significantly between 1840 and c. 1895 may also have been a consequence of generally cooler, wetter climates at this time. Rapid scrub expansion began between the end of farming and burning in 1931 and 1988 when the remaining feral sheep were removed. Sheep grazing in the absence of fire reduced competition, and encouraged regeneration and growth of woody scrub. Spread was probably assisted by a pronounced shift to warmer, drier climates in the second half of the twentieth century. Upper elevational limits of scrub have not increased, suggesting that factors other than summer temperature are controlling scrub line in this superoceanic environment. [ABSTRACT FROM AUTHOR]

Avoiding the worst impacts of global warming is a matter of systemic change and political will. An easily adaptable political system would be resilient to the effects of climate change, since a government could maintain effective control by implementing incremental changes. However, except for the United Kingdom (UK), Israel and New Zealand, all other states have rigid codified constitutions. Drawing on cybernetics and variety engineering, the study of New Zealand's constitutional system presented in this article suggests that a rigid codified constitution has merits for addressing long-term problems, such as climate change and sustainable development. [ABSTRACT FROM AUTHOR]

Summary 1. Forests are an important, yet poorly understood, component of the global carbon cycle. We develop a general integrative framework for modelling the influences of stand age, environmental conditions, climate change and disturbance on woody biomass production and carbon sequestration. We use this framework to explore drivers of carbon cycling in New Zealand mountain beech forests, using a 30-year sequence of data from 246 permanent inventory plots. 2. A series of disturbance events (wind, snow storms, earthquakes and beetle outbreaks) had major effects on carbon fluxes: by killing large trees, they removed significant quantities of carbon from the woody biomass pool, and by creating canopy gaps, they reduced the crown area index (CAI) of stands (i.e. canopy area per unit ground area) and woody biomass production. A patch-dynamics model, which we parameterized using permanent plot data, predicts that episodic disturbance events can create long-term ( c. 100-year) oscillations in carbon stocks at the regional scale. 3. Productivity declined with stand age, as shown in many other studies, but the effect was hard to detect because of canopy disturbance. Individual trees can increase productivity by adjusting the positioning, nutrient content and angle of leaves within canopies. We show that such optimization is most effective when trees are large and suggest it reduces the impact of water and nutrient limitation in old stands. 4. We found no evidence that forests were responding to changing climatic conditions, although strong altitudinal trends in biomass production indicate that global warming could alter carbon fluxes in future. 5. Synthesis.Our study emphasizes the critical role of disturbance in driving forest carbon fluxes. Losses of biomass arising from tree death (particularly in older stands) exceeded gains arising from growth for most of the 30-year study, moving 0.3 Mg C ha−1 year−1 from biomass to detritus and atmospheric pools. Large-scale disturbance events are prevalent in many forests world-wide, and these events are likely to be a driving factor in determining forest carbon sequestration patterns over the next century. [ABSTRACT FROM AUTHOR]

A representative temperature record for New Zealand based on station data from 1853 onward is used in conjunction with four coupled climate models to investigate the causes of recent warming over this small midlatitude country. The observed variability over interannual and decadal time scales is simulated well by the models. The variability of simulated 50-yr trends is consistent with the very short observational record. For a simple detection analysis it is not possible to separate the observed 30- and 50-yr temperature trends from the distribution created by internal variability in the model control simulations. A pressure index that is representative of meridional flow (M1) is used to show that the models fail to simulate an observed trend to more southerly flows in the region. The strong relationship between interannual temperature variability and the M1 index in both the observations and the models is used to remove the influence of this circulation variability from the temperature records. Recent 50-yr trends in the residual temperature record cannot be explained by natural climate variations, but they are consistent with the combined climate response to anthropogenic greenhouse gas emissions, ozone depletion, and sulfate aerosols, demonstrating a significant human influence on New Zealand warming. This result highlights the effect of circulation variability on regional detection and attribution analyses. Such variability can either mask or accelerate human-induced warming in observed trends, underscoring the importance of determining the underlying forced trend, and the need to adequately capture regional circulation effects in climate models. [ABSTRACT FROM AUTHOR]

If global warming is accelerating, then one might expect temperatures for most stations to be accelerating and perhaps variability to be increasing. In this study, we examine 57 New Zealand temperature time series for evidence of non-linearity and changing variability. These correspond to time series for annual minima, annual means and annual maxima for 19 stations. Estimation is by an extended least-squares method. We find a surprising diversity of behaviour of these series – presumably reflecting their different geographic factors as well as series length. We give evidence of regions where temperatures are decreasing. For series where a linear trend is significant, it is downwards in about one third of the cases. This proportion was higher in the South Island, especially for series of minima. Where a non-linear trend is significant, temperatures are decelerating in about one half of the cases. The ratio of downward to upward trends is highest among annual maxima and South Island minima and smallest in annual means. Where a linear trend in the variability is significant, it is decreasing in 13 cases and increasing in 5 cases, although possibly this is partly due to poorer quality data last century. Where a non-linear trend in the variability is significant, variability is decelerating in about two thirds of the cases. The results are used to project upper and lower return levels of minima, means and maxima for each of the series to the year 2010. [ABSTRACT FROM AUTHOR]

In contrast to the northern hemisphere where species of Chironomidae are usually the dominant benthic invertebrates in the coldest upper reaches of glacial streams, mayflies ( Deleatidium spp.: Leptophlebiidae) predominate in equivalent conditions in New Zealand. We examined the life histories and annual production of Deleatidium spp. at two sites on the Matukituki River (South Island, New Zealand) and at three sites in its glacier-fed tributary, Rob Roy Stream. Mean annual water temperature at the five sites ranged from 2.1 to 7.0°C. Monthly sampling showed that mayfly populations were poorly synchronised at all sites but were probably univoltine. The large Deleatidium cornutum was the dominant mayfly species found at the upper sites (Sites 1 and 2) on Rob Roy Stream, whereas above the confluence with Matukituki River (Site 3) it co-existed with a complex of smaller species we refer to as D. “ angustum”. Deleatidium “ angustum” also dominated at the Matukituki sites. Deleatidium production calculated for the five sites, assuming an 11-month nymphal life, ranged from 0.48 g dry weight/m2/year (Site 1) to 3.07 g dry weight/m2/year (Site 3). The values for D. cornutum at Sites 2 and 3 are high for a species of Deleatidium and reflect its large size. This species appears to be strongly adapted for growth at low temperatures. Climate change scenarios for New Zealand predict the gradual and ultimate loss of small South Island glaciers and a consequent warming of streams as runoff from rainfall and snow melt becomes more dominant in spring. As a result, suitable habitats will be lost for cold-water specialists such as D. cornutum, and they are likely to suffer reductions in their distributional range and local extinction. In contrast, species such as those in the D. “ angustum” complex may extend their ranges into streams formerly dominated by glacial meltwater. [ABSTRACT FROM AUTHOR]