Changing ecology


EcoTas13, the 5th joint meeting of the Ecological Societies of New Zealand and Australia, in Auckland, New Zealand, November 2013

From the moving opening welcome by the local Māori hapu (sub-tribe) Ngāti Whātua Ōrākei, it was clear that EcoTas13, the 5th joint meeting of the Ecological Societies of New Zealand and Australia had a unique flavour and contribution to make to ecology. This distinct character became yet clearer when the Māori welcome was reciprocated by O. Costello (University of Technology, Sydney, Australia), one of the stolen generations of the Bundjalung people of New South Wales with the presentation of a traditional message stick, conveying the Aboriginal legend of the rainbow serpent. Strong cross-Tasman indigenous collaboration was further developed in a symposium on indigenous ecology, exploring the novel insights that may be gained by merging the traditional knowledge of indigenous peoples with that from Western science.

Despite only being separated by some 1500 km, Australia and New Zealand have striking differences in ecosystems and cultures. In particular, Australia represents some of the world's oldest, most stable, and most nutrient-depleted soils, with a fire- and low-nutrient-adapted flora, some 40–50 000 yr of human presence, and a diverse mammalian fauna. New Zealand, by contrast, represents the last place on earth to enter the Anthropocene, with the first human colonists, the Māori, arriving only c. 740 yr ago. Many soils are young, with ongoing frequent volcanic and earthquake-related inputs, and the fauna is dominated by birds and insects with no native terrestrial mammals other than bats. Despite these differences, the ecosystems and cultures of Australia and New Zealand share many similarities, including strongly phosphorus (P)-limited soils, many plant genera in common, and similar issues with invasive species modifying ecosystems.

‘Ecology in the Antipodes is a science of change, a theme that runs strongly throughout the conference.’

Ecosystem development and retrogression

Ecology in the Antipodes is a science of change, a theme that runs strongly throughout the conference (Fig. 1). At the longest timescale, New Zealand and Australia have been disproportionately important in understanding the processes of ecosystem development and retrogression. At least five of the best-studied soil chronosequences occur in these two countries, where geologic and glacial processes have resulted in sequences of soil and biotic development and eventual nutrient loss and ecosystem retrogression (Turner & Condron, 2013). A chronosequence symposium organized by P. Bellingham (Landcare Research, Lincoln, New Zealand) focussed on similarities and differences among chronosequences in New Zealand and Australia. In both countries there is an increasing focus on organic P as an important nutrient source in retrogressive ecosystems, including a recognition that a great deal of this organic P may be in the form of DNA from fungi and microbes (Turner et al., 2012). Indeed, while early research on chronosequences focused on soil and plant community changes, there is a greatly increasing focus on soil biota in general (Dickie et al., 2013). Three of the six talks in the symposium focused on soil biota. D. Peltzer (Landcare Research, Lincoln, New Zealand) and colleagues showed that chronosequences in both Australia and New Zealand alternate between fungal dominance early and late in the sequences, while bacterial processes dominate the peak biomass stages, but that other soil biota (Collembola, Acari) follow more site-dependent trends (Doblas-Miranda et al., 2008). F. Teste (University of Western Australia, Crawley, Australia) and colleagues (presented by E. Laliberté, University of Western Australia, Crawley, Australia) and J. Tylianakis (University of Canterbury, Christchurch, New Zealand) and colleagues presented on the mycorrhizal component of soil biota, with both systems showing strong differences in the arbuscular mycorrhizal fungal communities found across different ecosystem ages.

Figure 1.

Aspects of change in southern-hemisphere ecology. The EucFACE site in New South Wales, Australia (a) studies the effects of elevated atmospheric CO2 concentrations (ambient +150 ppm) in a phosphorus-limited forest ecosystem. Invasive weeds (b) represent strong plant–soil feedbacks as in the invasion of Salix fragilis, Alnus glutinosa, and Cytisus scoparius in the Waiau river of New Zealand. At longer timescales, chronosequences of increasing ecosystem age (c) such as created by the retreat of New Zealand's Franz Josef glacier provide unique opportunities to understand the processes of ecosystem development and retrogression of plants, mycorrhizal fungi, and soils. Trends in global CO2 level, temperature anomalies, invasive species (Howell, 2008; Murray & Phillips, 2012), and soil nutrients (Richardson et al., 2004) shown (d) along with historical events. Land and sea surface temperature anomalies are shown for Australia and based on a 30-yr mean climatology (1961–1990). Source: the Australian Government, Bureau of Meteorology. Photograph credits: M. G. Tjoelker, R. Buxton, I. A. Dickie.

Human arrival and invasion ecology

While ecosystem change has always occurred, the rate of change in both Australia and New Zealand vastly increased following human colonization. In the closing keynote, R. Duncan (University of Canberra, Australia; Duncan et al., 2013) highlighted the role of human colonization in the loss of megafauna and birds in Australia and across the Pacific. As noted in a talk by G. Perry (University of Auckland, New Zealand), the relatively recent arrival of Māori to New Zealand c. ad 1270 resulted in the loss of an entire guild of birds, the moa, within 200 yr, along with deforestation of 40–50% of the country. European arrival resulted in further changes in both Australia and New Zealand, including the introduction of myriad new plant and animal species that have transformed ecosystems of both countries. Invasion ecology was a recurrent and strong theme throughout the meeting, including studies on invasive animals (toads, ants, deer, possum), plants (pines, willows, forest understory ground cover), fungi (Amanita muscaria, Rhizopogon spp.), and diatoms (Didymosphenia geminata).

In both Australia and New Zealand interactions among multiple nonnatives are creating entirely novel interactions and ecosystems. J. Wood (Landcare Research, Lincoln, New Zealand) and colleagues reported on how invasive Australian mammals are spreading northern hemisphere ectomycorrhizal fungal inoculum, facilitating the invasion of North American pines, and T. Lebel (Royal Botanic Gardens, Melbourne, Australia) reported on ectomycorrhizal fungal invasions in Australia onto native hosts (Dunk et al., 2012). The interaction between invasives and native species created some interesting conflicts among ecologists from different disciplines, as when a keynote talk by J. Ogden (Great Barrier Island Charitable Trust, New Zealand) suggested that invasive pines were not really a problem, in part because they support native birds.

While some invasive species are shifting in response to anthropogenic introduction, other range shifts reflect adaptation to changing climates. This increasingly raises the question of how to decide which new species should be treated as undesirable invasives, and which as adaptive range expansions given changing climates, as highlighted by C. Thomas (University of York, UK) in his keynote on invasive species in a changing climate. For other invasive species, there is evidence of evolutionary responses to novel environmental selection, as noted by A. Moles (University of New South Wales, Sydney, Australia) and colleagues.

Changing climate

Rising atmospheric concentrations of greenhouse gases are expected to increasingly influence climatic changes in the coming decades. In Australia, average daily mean temperatures have increased by 0.9°C since 1910 and are projected to rise 1.0–5.0°C by 2070 (CSIRO & Australian Bureau of Meteorology, 2012). In both Australia and New Zealand, climatic extremes are strongly influenced by the El Niño Southern Oscillation (ENSO). The influence of increasing atmospheric CO2 on terrestrial ecosystems in this region is perhaps best understood against a backdrop of high interannual climatic variability and soil P limitations.

In a symposium entitled ‘New horizons on CO2 impacts’, organized by D. Ellsworth and S. Power (University of Western Sydney, Penrith, Australia), speakers highlighted the role of interactive effects of climate change drivers in governing forest and grassland ecosystem responses. Australia is home to a new free-air CO2 experiment (FACE) established in a native Eucalyptus tereticornis (EucFACE) forest in the Sydney basin, which was the topic of presentations by S. Power and colleagues, T. Gimeno (University of Western Sydney, Penrith, Australia) and colleagues, and C. Macdonald (University of Western Sydney, Penrith, Australia) and colleagues. It is notable that the stand is a 20-m tall mature evergreen forest on a relatively low fertility, P-limited site. This raises the interesting question of whether or not effects of elevated atmospheric CO2 on productivity and biogeochemical cycles are constrained by nutrient limitations when compared with FACE studies in the northern hemisphere.

Rates of leaf-level net photosynthesis showed strong initial responses to CO2 enrichment, but no further enhancement at CO2 concentrations above 450 ppm, during the initial 5-month ramp phase in which CO2 levels were stepped up in 30 ppm increments to attain the ongoing treatment level of 150 ppm above ambient. This early evidence suggests a relatively quick saturating response of leaf level photosynthesis. The leaf-level response was accompanied by a reduction in leaf nitrogen concentration through time, but no change in the already low leaf P concentrations (< 0.1%).

Intriguingly, early soil measures indicate increased exchangeable P and P mineralization in response to CO2 enrichment, suggesting enhanced soil P availability at least in the short term. Concomitant measures of soil CO2 efflux during the ramp phase and beyond indicate both an immediate and persistent enhancement of respiratory CO2 loss in response to CO2 enrichment and temporal dynamics coincident with precipitation inputs and subsequent soil wetting and drying.

In another FACE experiment, M. Hovenden (University of Tasmania, Australia) reported that elevated CO2 effects on temperate grassland productivity in Tasmania (TasFACE) were mediated by seasonal differences in rainfall in this Mediterranean-type climate. Biomass production was enhanced by CO2 enrichment in drier summers compared with wetter spring and autumn throughout the 10-yr study, where pulse effects of soil wetting in drier soils and subsequent water savings under CO2 enrichment may play a role.

In both native and managed grasslands, grazing by herbivores constitutes an important biotic factor governing ecosystem responses; yet our knowledge of grazing in relation to climatic change drivers remains comparatively poorly understood. To this end, P. Newton (AgResearch, Palmerston North, New Zealand) reported on a FACE experiment established on pasture in combination with sheep grazing in New Zealand (Newton et al., 2014) to determine the impact of CO2 enrichment on grassland productivity and composition under grazing. Throughout an 11-yr study, the CO2 fertilization effect varied widely and interacted with grazing. Interestingly, although composition shifts were evident initially under CO2 enrichment, grazing preference for legumes and forbs drove composition shifts such that composition of grasses, legumes and forbs were comparable between CO2 treatments after 5 yr of treatment.

Changing ecology

At the end of the EcoTas13 conference it might be easy to conclude that ecosystems in both Australia and New Zealand are changing at unprecedented rates and that problems perhaps outnumber solutions. Nonetheless, Antipodean ecology contributes to applied science with a strong record of success, including the first island-scale removals of invasive mammals and the rescue of species such as the Chatham Island black robin from the brink of extinction. New approaches using next-generation DNA methods (A. Drummond, University of Auckland, New Zealand; J. Wood, S. Knight, University of Auckland, New Zealand; B. Drigo, University of Western Sydney, Penrith, Australia), airborne laser-based mapping of weed populations (J. Griffiths, Department of Conservation, Wellington, New Zealand), and sophisticated statistical analyses (R. Duncan) will continue to improve, giving perhaps some hope for ecological science changing the future for the better.


P. Bellingham, B. Burns (University of Auckland, New Zealand) and S. Power provided helpful input into this report. I.A.D. is supported by the Bio-Protection Research Centre, Lincoln University, New Zealand. M.G.T. is supported by the Hawkesbury Institute for the Environment, University of Western Sydney, Penrith, Australia.