Frith C. Jarrad

Phenological response of tundra plants to background climate variation tested using the International Tundra Experiment

The rapidly warming temperatures in high-latitude and alpine regions have the potential to alter the phenology of Arctic and alpine plants, affecting processes ranging from food webs to ecosystem trace gas fluxes. The International Tundra Experiment (ITEX) was initiated in 1990 to evaluate the effects of expected rapid changes in temperature on tundra plant phenology, growth and community changes using experimental warming. Here, we used the ITEX control data to test the phenological responses to background temperature variation across sites spanning latitudinal and moisture gradients. The dataset overall did not show an advance in phenology; instead, temperature variability during the years sampled and an absence of warming at some sites resulted in mixed responses. Phenological transitions of high Arctic plants clearly occurred at lower heat sum thresholds than those of low Arctic and alpine plants. However, sensitivity to temperature change was similar among plants from the different climate zones. Plants of different communities and growth forms differed for some phenological responses. Heat sums associated with flowering and greening appear to have increased over time. These results point to a complex suite of changes in plant communities and ecosystem function in high latitudes and elevations as the climate warms.

Impacts of experimental warming and fire on phenology of subalpine open-heath species

The present study examined experimentally the phenological responses of a range of plant species to rises in temperature. We used the climate-change field protocol of the International Tundra Experiment (ITEX), which measures plant responses to warming of 1 to 2°C inside small open-topped chambers. The field study was established on the Bogong High Plains, Australia, in subalpine open heathlands; the most common treeless plant community on the Bogong High Plains. The study included areas burnt by fire in 2003, and therefore considers the interactive effects of warming and fire, which have rarely been studied in high mountain environments. From November 2003 to March 2006, various phenological phases were monitored inside and outside chambers during the snow-free periods. Warming resulted in earlier occurrence of key phenological events in 7 of the 14 species studied. Burning altered phenology in 9 of 10 species studied, with both earlier and later phenological changes depending on the species. There were no common phenological responses to warming or burning among species of the same family, growth form or flowering type (i.e. early or late-flowering species), when all phenological events were examined. The proportion of plants that formed flower buds was influenced by fire in half of the species studied. The findings support previous findings of ITEX and other warming experiments; that is, species respond individualistically to experimental warming. The inter-year variation in phenological response, the idiosyncratic nature of the responses to experimental warming among species, and an inherent resilience to fire, may result in community resilience to short-term climate change. In the first 3 years of experimental warming, phenological responses do not appear to be driving community-level change. Our findings emphasise the value of examining multiple species in climate-change studies.

Ecological aspects of biosecurity surveillance design for the detection of multiple invasive animal species

Complex surveillance problems are common in biosecurity, such as prioritizing detection among multiple invasive species, specifying risk over a heterogeneous landscape, combining multiple sources of surveillance data, designing for specified power to detect, resource management, and collateral effects on the environment. Moreover, when designing for multiple target species, inherent biological differences among species result in different ecological models underpinning the individual surveillance systems for each. Species are likely to have different habitat requirements, different introduction mechanisms and locations, require different methods of detection, have different levels of detectability, and vary in rates of movement and spread. Often there is a further challenge of a lack of knowledge, literature, or data, for any number of the above problems. Even so, governments and industry need to proceed with surveillance programs which aim to detect incursions in order to meet environmental, social and political requirements. We present an approach taken to meet these challenges in one comprehensive and statistically powerful surveillance design for non-indigenous terrestrial vertebrates on Barrow Island, a high conservation nature reserve off the Western Australian coast. Here, the possibility of incursions is increased due to construction and expanding industry on the island. The design, which includes mammals, amphibians and reptiles, provides a complete surveillance program for most potential terrestrial vertebrate invaders. Individual surveillance systems were developed for various potential invaders, and then integrated into an overall surveillance system which meets the above challenges using a statistical model and expert elicitation. We discuss the ecological basis for the design, the flexibility of the surveillance scheme, how it meets the above challenges, design limitations, and how it can be updated as data are collected as a basis for adaptive management.

Experimental warming and long-term vegetation dynamics in an alpine heathland

High mountain ecosystems are vulnerable to the effects of climate warming and Australia’s alpine vegetation has been identified as particularly vulnerable. Between 2004 and 2010, we monitored vegetation changes in a warming experiment within alpine open grassy-heathland on the Bogong High Plains, Victoria, Australia. The study was part of the International Tundra Experiment (ITEX Network) and used open-topped chambers (OTC) to raise ambient growing-season temperatures by ~1°C at two sites. We assessed the effects of experimental warming on vegetation composition, diversity and cover using ordination, linear models and hierarchical partitioning. Results were compared with vegetation changes at four long-term (non-ITEX) monitoring sites in similar vegetation sampled from 1979 to 2010. The warming experiment coincided with the driest 13-year period (1996–2009) since the late 1880s. At the ITEX sites, between 2004 and 2010, graminoid cover decreased by 25%, whereas forb and shrub cover increased by 9% and 20%, respectively. Mean canopy height increased from 7 cm to 10 cm and diversity increased as a result of changes in relative abundance, rather than an influx of new species. These vegetation changes were similar to those at the four non-ITEX sites for the same period and well within the range of changes observed over the 31-year sampling period. Changes at the non-ITEX sites were correlated with a decrease in annual precipitation, increase in mean minimum temperatures during spring and increase in mean maximum temperature during autumn. Vegetation changes induced by the warming experiment were small rather than transformational and broadly similar to changes at the long-term monitoring sites. This suggests that Australian alpine vegetation has a degree of resilience to climate change in the short to medium term (20–30 years). In the long term (>30 years), drought may be as important a determinant of environmental change in alpine vegetation as rising temperatures. Long-term vegetation and climate data are invaluable in interpreting results from short-term (≤10 years) experiments.

Subalpine plants show short-term positive growth responses to experimental warming and fire

Climate warming has the potential to directly affect plant growth rates by accelerating plant processes, and through intermediate affects associated with increased length of the growing season and changes to soil processes. Alpine and subalpine ecosystems may be particularly vulnerable to climate warming because species are adapted to a cold environment and have limited upslope refugia in Australia. In the present study, the vegetative growth of seven subalpine open-heath species was examined in response to 3 years of warming and a wildfire. The warming experiment was established in late 2003 on the Bogong High Plains, Australia, using the protocols of the International Tundra Experiment (ITEX). During the growing seasons (snow-free periods) in 2004/2005 and 2005/2006 leaves and stems were monitored on common or widespread species from each of the major vascular plant growth forms. Plants were monitored inside and outside passively warmed open-topped chambers, at sites that were burnt in early 2003 and sites that escaped fire. In the short-term, warming had significant positive relationships with relative growth rates of three species, including Celmisia pugioniformis (forb; P = 0.09), Carex breviculmis (graminoid; P = 0.004) and Asterolasia trymalioides (shrub; P = 0.02). Burning had significant positive effects (P < 0.05) on the relative growth rates of two of these species, C. pugioniformis and C. breviculmis, as well as for Plantago euryphylla, Poa hiemata and Pimelea alpina. For P. euryphylla and P. alpina, the interaction of warming and burning showed significant relationships with relative growth rates, a negative relationship in P. euryphylla (P = 0.03) and a positive relationship in P. alpina (P = 0.07). Year and season were also found to affect the relative growth rates of most species (P < 0.05). These findings agree with previous northern hemisphere ITEX and other warming experiment results; that is, warming has a positive effect on species’ growth responses. In the present study, it is likely that continued climate warming may result in positive growth responses in other subalpine species across growth forms. Our findings emphasise the value of examining multiple species in climate-change studies.

Hierarchical models for evaluating surveillance strategies: diversity within a common modular structure.

This chapter introduces a hierarchical modelling approach to biosecurity surveillance, arguing that this provides a common structure for representing many different existing models, ostensibly proposed within different quantitative paradigms. A Bayesian formulation is demonstrated to provide a natural framework for analyzing such hierarchical models. The chapter commences with a description of Bayesian models for estimation and prediction of pest prevalence as well as detectability, and uses this as motivation for describing the concept of Bayesian learning. The role of prior distributions in facilitating estimation with uncertainty is then discussed in detail. Attention then turns to the process of constructing hierarchical Bayesian models for surveillance, including how to model search effort, detectability, prevalence and other important features. The generality of the approach is illustrated through a commentary on stochastic scenario trees, via three-stage Bayesian hierarchical models, three-stage cluster sampling and four-stage multi-scale detection. The chapter concludes with comments on how to choose among quantitative methods, and a comparative discussion of features in the modular model-based view described here.