Climate change–induced pressures

2016

Our climate is changing. Climate records, such as for rainfall and temperature, continue to be broken—for example, widespread record December temperatures across 4 states in south-eastern Australia in December 2015, Australia’s warmest October on record in 2015, Australia’s warmest spring on record in 2014, Australia’s warmest September on record in 2013, temperature records set in every state and territory in January 2013, record high temperatures in November in 3 states in 2012, and Australia’s wettest 2-year period on record in 2010 and 2011 (BoM 2012a,b, 2013a,b, 2014, 2015, 2016).

Although these may be statistically interesting, of much greater significance is the impact that extreme weather conditions have on the land and the wider environment. For millennia, Australia’s climate has been characterised by huge seasonal variability (Moros et al. 2009, Stuut et al. 2014). Our landforms are shaped by extremes, and many species are adapted to infrequent and unpredictable boom times. However, the pressures exerted by climate change are likely to change both the distribution and abundance of native and exotic species, and these biological impacts, together with the effects of flood, drought and other weather patterns, will progressively change Australian landscapes. It is worth noting that the effects of climate change are felt most disproportionately by large landholders (through scale) and low socio-economic groups (through lack of capacity to respond)—Indigenous people, especially across the north of Australia, are in both these categories.

We are also increasing our understanding of the impacts of climate change on soils—for example, decreases in soil organic carbon are predicted as a result of increased rainfall variability (Forouzangohar et al. 2016).

Climate change will result in impacts in its own right, but will also exacerbate existing pressures and impacts. In particular, climate change will have implications for the distribution of species and biological communities, water availability, and impacts of natural disasters. In agriculture, declining ‘growing-season’ rainfall will likely produce less crop biomass to protect soils from erosion. Research and investment are now increasingly focused on adaptation to climate change as well as reducing emissions—for example, adaptive management approaches that anticipate responses and modify them as changes in climate take place with a particular direction and magnitude. These approaches include land-use change or conversion in addition to novel approaches to existing land uses.

Native vegetation

Australia’s native vegetation is extraordinarily adaptable, with a long history of transforming in response to new environmental pressures. Climate change is one such pressure, so change in native vegetation as the climate continues to change may be a positive sign that nature is adjusting. However, as revealed in the AdaptNRM project, a new type of analysis is highlighting that the amount and speed of change could challenge the way we think about and manage our native systems. Although many of Australia’s 77 major vegetation subgroups are projected, even under a high–greenhouse gas emissions scenario, to retain somewhat familiar distributions at a broad continental scale, the vegetation at any particular location is often expected to alter in character (Figure LAN1). Furthermore, the environmental conditions projected for some parts of Australia have no present-day analogue, suggesting the potential for the emergence of novel vegetation communities containing combinations of plant species unlike that of any present-day community on the continent (Figure LAN2).

Given the amount and speed of change, we need new ways to approach the management of our native vegetation. The principles we currently use typically focus on preventing change, restoring ecosystems to a pre-European state, or conserving rare and threatened species. New principles are needed that acknowledge change, including loss of some species, and guide us towards more, rather than less, desirable futures for our unique land; this might include recognition of novel communities based on new assemblages of native species. In some cases, non-native species will play a significant role in determining the structure and dynamics of such novel ecosystems, and, in some instances, these roles may be critical.

Legend for climate scenario maps

Note: RCP8.5 is 1 of the 4 greenhouse gas concentration trajectories adopted by the Intergovernmental Panel on Climate Change for its Fifth Assessment Report, which describe the radiative forcing values in the year 2100 relative to pre-industrial values.

Source: Prober et al. (2015), used under CC BY ND

Figure LAN1 Projected distributions of vegetation types derived by the AdaptNRM project by linking an ecological similarity model, developed for vascular plants, with an existing vegetation map and climate scenarios: (a) observed major vegetation subgroups, from Australia’s National Vegetation Information System database; (b) model predictions of subgroups for the baseline period (1990), indicating effectiveness of the modelling, and generalised maps of the projected distribution of subgroups by 2050 for (c) hot Canadian Earth System Model 2, and (d) mild Model for Interdisciplinary Research On Climate 5 climate models, under a high-emissions scenario (RCP8.5)

Note: RCP8.5 is 1 of the 4 greenhouse gas concentration trajectories adopted by the Intergovernmental Panel on Climate Change for its Fifth Assessment Report, which describe the radiative forcing values in the year 2100 relative to pre-industrial values.

Source: Williams et al. (2014), used under CC BY ND

Figure LAN2 Degree to which environmental conditions are projected to become sufficiently novel by 2050 to potentially result in the emergence of vegetation communities containing combinations of plant species highly dissimilar from any present-day community on the continent, for (a) hot Canadian Earth System Model 2, and (b) mild Model for Interdisciplinary Research on Climate 5 climate models, under a high-emissions scenario (RCP8.5)

In addition to direct effects of climate on vegetation, there is also evidence of anomalously long fire-weather seasons, especially from 1996 to 2013 (Clarke et al. 2013, Jolly et al. 2015). These long fire seasons result from periods of benign weather during which fuel loads accumulate, followed by droughts, which permit intense bushfire activity and consequent impacts on vegetation structure, composition and recovery potential.

Understanding the impacts and consequences of climate change provides opportunities for novel or modified land management approaches, including managing vegetation and ecosystem processes for carbon sequestration, and managing land and ecosystems to help build resilience to impacts such as natural disasters.

Diseases, pests and weeds

Changes in climate will affect the viability, distribution and occurrence of diseases, pests and weeds in different ways. Many naturalised introduced plant species appear likely to become less of a threat as the habitat that they currently occupy becomes less suitable (Roger et al. 2015), but the large pool of naturalised species means that currently less invasive species may be poised to take over (see Box LAN1). Pests and diseases are likely to extend into new habitats that are currently unavailable to them (Roger et al. 2015), while native species may extend their range or their influence in concert with changing environmental effects (see Box LAN2).

The National Environmental Biosecurity Response Agreement (NEBRA) was signed by the Australian Government and all state and territory governments in January 2012. NEBRA operates in tandem with the Emergency Animal Disease Response Agreement (EADRA) and the Emergency Plant Pest Response Deed (EPPRD) in providing national arrangements for eradication responses to pest or disease incursions. While the EADRA and the EPPRD provide arrangements for responding to pests and diseases that affect agricultural industries, NEBRA facilitates responses to pest and diseases incursions where eradication primarily benefits the community. All 3 of the emergency response deeds, depending on the exotic pest or disease, may cover an incursion that could affect the environment or biodiversity.

Box LAN1 Scale of plant introductions to Australia

Since colonisation of Australia by Europeans, more than 41,000 plant species have been introduced into Australia, and 3175 of these have since become naturalised (Department of Agriculture and Food, Western Australia, [DAFWA], unpublished data, 2015; Figure LAN3).

Australia has at least 20,000 native plant species (Chapman 2009). Because more than half of these have been cultivated (DAFWA, unpublished data, 2015), many natives have become weedy outside their native range.

With more than 60,000 plant species in Australia (DAFWA, unpublished data, 2015), there are now 2 pools of potential weeds that could pose new problems in the future: introduced exotics (8108 species) and Australian natives that are known to be weedy overseas (1824 species). Many of these almost 10,000 species (DAFWA, unpublished data, 2015) may never become weedy in Australia, but for some it is just a matter of time and circumstance.

Box LAN2 Climate-related dieback in temperate woodlands

Forest boundaries move back and forth across the landscape in response to local climate variation, disturbance events, endemic insect outbreaks and other ‘natural’ events. Dieback, a gradual decline in tree health that often leads to premature death, is commonly associated with natural forest boundary retreats. With time, forests usually recover from these natural dieback events. However, dieback has been identified as an increasing problem beyond natural variation throughout Australia and the world.

Fossil evidence shows that, over the centuries, trees on the hilltops and ridgelines in the Monaro region of south-eastern New South Wales have moved onto the grassy plains in some centuries and retreated in others. During the past decade, however, the dominant ribbon gums (Eucalyptus viminalis) have suffered widespread decline, and almost all are now dead or suffering severe dieback symptoms. This dieback covers an area of around 2000 square kilometres between Bredbo, Numeralla, Nimmitabel and Jindabyne, with the most severely affected areas in a central region around Berridale. If all these trees die, there will be no remnant population to enable this important tree species to return to the area should conditions improve.

In the 1970s and 1980s, ‘rural dieback’ in the New England area of New South Wales was attributed to agricultural practices such as grazing, fertilisation and understorey clearing, which upset the balance of insects and their predators. The resulting insect population explosion led to repeated defoliation, which, over several years, exhausts the trees’ ability to recover. Other cases have been associated with a range of complex factors such as changed fire regimes, pollutants and fungal pathogens.

In the case of the Monaro dieback, the ultimate cause of death seems to be an infestation of (native) eucalyptus weevils (Gonipterus sp.), which have been observed in large numbers on the few surviving trees. However, the underlying cause of this outbreak remains unclear. In a recent study (Ross & Brack 2015), ribbon gums appeared to be uniformly dead or showing signs of severe dieback regardless of their local environment. Areas that had been fenced off from grazing and with no other major disturbance might have been expected to be more resilient to dieback, but were as badly affected as those in paddocks that had been fertilised or grazed. Similarly, absence or presence of recent fire made no difference to the trees’ health.

Climatic factors may have played a role, given that the onset of the dieback coincided with the millennium drought. The Monaro region has a harsh climate, with extremes of temperature and low, unpredictable rainfall due to the rain shadow of the Snowy Mountains. Ribbon gums normally grow in wetter areas, and the Monaro is at the edge of their climatic range, so the millennium drought and ongoing climate change may have pushed the trees beyond a critical threshold.

With no evidence of recovery, it is likely that E. viminalis will disappear from the Monaro entirely, resulting in dramatic changes to the landscape and loss of biodiversity. Strategies for rehabilitation may include introducing species from more arid environments to accelerate adaptation to the changing climate.

Dead ribbon gums (Eucalyptus viminalis) in the Monaro region, New South Wales.

Dead ribbon gums (Eucalyptus viminalis) in the Monaro region, New South Wales.

Dead ribbon gums (Eucalyptus viminalis) in the Monaro region, New South Wales.

Photo by Kylie Evans, Biotext

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Source: Cris Brack and Catherine Ross, Australian National University

Agricultural and forestry production systems

The impacts of climate change on forestry and agricultural production will vary by crop, location and season. Under all climate change scenarios, seasonality is predicted to become more pronounced—for example, longer dry seasons, wetter wet seasons and hotter summers—and the intensity and/or frequency of extreme events are likely to continue to increase (Lewis & King 2015, Pepler et al. 2016).

New land uses such as carbon plantings, environmental plantings, and biofuels and bioenergy will need to be considered along with agricultural productivity and water resource maintenance, and potentially better governance approaches will be required to manage these uses (Bryan et al. 2016). Modelling suggests that market incentives that effectively price environmental services are needed, to ensure that efficient land-use arrangements are selected as the climate and society’s preferences change (Bryan et al. 2015). Climate change impacts will also mean that the productivity of some regions will change (some will become more productive, and some will become marginal or less productive), and some crops and varieties may need to change (Kelly 2014). However, although increased productivity is expected to maintain the level of agricultural production, despite the reduction in area brought about by new land uses and further urban development, this is predicated on significant investment in productivity improvements. The current evidence of decline in investment is therefore disturbing (Grundy et al. 2016).

Atmospheric carbon dioxide levels will increase, accompanied by increased temperatures and less predictable rainfall patterns (DoEE n.d). Reduced availability of water is to some extent offset by elevated carbon dioxide levels, which can increase transpiration efficiency—that is, plants are able to absorb sufficient carbon dioxide from the atmosphere more quickly when it is at higher concentrations, so they will lose less water during the process. As well, higher carbon dioxide levels also increase the efficiency of use of sunlight and consequently overall growth rates (Lobell et al. 2015). However, the increase in temperature and drought frequency will have detrimental effects on plant growth patterns, grain production and ripening. Drought and the impact of heat stress are likely to remain the key challenge for farmers for the next 50 years (Lobell et al. 2015).

Pinkard (2014) suggests that plantation productivity has already been detrimentally affected during the past 40 years by climate change. Direct impacts of climate change on productivity are changes in the incidence and severity of droughts, heatwaves and extreme weather events; increasing temperatures; and reduced rainfall. Indirect impacts are increased pest activity and increased fire hazard.

Increasing climate variability is also a major challenge for horticulture because growers depend on a predictable climate for water availability and seasonal temperature (seasonal changes trigger plant growth responses, so unpredictable changes can pose a threat to production; Horticulture Australia Ltd. 2006). Climate change also provides opportunities for new industries, such as carbon farming for sequestration, as well as challenges for changed management to avoid greenhouse gas emissions. Opportunities to reduce emissions and potentially achieve zero carbon emissions from agriculture through adopting existing management approaches and technology are outlined in a discussion paper by Beyond Zero Emissions, and the University of Melbourne’s Melbourne Energy Institute and Melbourne Sustainable Society Institute (Longmire et al. 2014).

Metcalfe D, Bui E (2016). Land: Climate change–induced pressures. In: Australia state of the environment 2016, Australian Government Department of the Environment and Energy, Canberra, https://soe.environment.gov.au/theme/land/topic/2016/climate-change-induced-pressures, DOI 10.4226/94/58b6585f94911