Victoria's rainforests and the potential impacts of a changing climate.
The roots of today's rainforests have been traced back to when Australia was part of the Gondwanan super-continent (100 mya) (Peel 1999). At that time, most of Australia was covered by rainforest. Since then, however, the distribution and dominance of rainforest has varied as Australia broke free of the super-continent and underwent numerous climatic changes (Beadle 1981). It is thought that the Australian continent moved 30[degrees] of latitude north during the Cretaceous and Tertiary, causing significant climatic changes (Beadle 1981). The ancient climatic regime to which rainforests were adapted, i.e. dependable, high rainfall and low fire frequency, is now rare and Australia's rainforests have receded to isolated, protected patches (Peel 1999).
Rainforests can be defined according to rainfall, atmospheric conditions, soil and local topography. For the purpose of this article, a rainforest is characterised by a closed tree canopy that distinguishes it from other vegetation in areas of high rainfall, generally comprises many taxa and, perhaps most significantly, has canopy species with the ability to regenerate without the need for broad-scale disturbance (Busby and Brown 1994).
Five main types of rainforest occur in Victoria. Cool temperate rainforest occurs in the Otway Ranges, Wilsons Promontory, the Strzelecki Ranges, the Central Highlands and some parts of East Gippsland (Peel 1999). At lower elevations, the gradient from cool temperate rainforest to tall eucalypt forest includes a 'mixed' ecotone of cool temperate mixed forest. This blurred boundary from one vegetation type to another is unique in itself; it is characterised by an understorey of rainforest species with a eucalypt canopy (Busby and Brown 1994). Warm temperate rainforests are floristically rich and are most common east of the Mitchell River in East Gippsland, although other communities may be found in the Strzeleckis and at Wilsons Promontory (Peel 1999). Gallery rainforest is found in river valleys of East Gippsland, and dry rainforest, the least common of the five Victorian rainforest types, is found only in areas east of the Mitchell River and, due to its habitat, is relatively removed from fire danger (Peel 1999).
Rainforests occur as far west as Cape Otway and reach into the far corners of East Gippsland. They occupy less than 0.14% of Victoria, yet a disproportionate number of rare or threatened species may be found within them (Peel 1999). They have high levels of biodiversity, are valued for their water provision and are becoming increasingly more important for carbon capture and storage (Lindenmayer et al. 2011; Mackey et al. 2008). With this knowledge, it makes the need to protect them an even greater priority; however, climate change is a looming threat to the viability of rainforests in the future.
The distribution, health and abundance of Australian vegetation depend on consistencies in temperature, rainfall, fire regime and soil fertility as well as other factors (Beadle 1981). It is predicted that climate change will significantly alter three of these four parameters. Temperatures are predicted to continue to rise, annual rainfall will decrease and extreme weather events such as fire will increase in frequency and intensity (VCC 2008). Victoria's rainforests are particularly sensitive to such changes in the environment; key rainforest species such as Atherosperma moschatum Labill. c Labill. have low photosynthetic tolerance in high temperatures (Read and Busby 1990). Fire and climate are strongly correlated with the geographical limits of the prominent rainforest canopy species Nothofagus cunninghamii (Hook.) Oerst (Busby 1986). What will become of Victoria's rainforests?
In 2008, the Victorian Government released a summary of climate change predictions for Victoria prepared by CSIRO. This summary predicts that Victoria will become warmer and drier in the near future as a result of climate change. Victoria will experience more rapid warming than global trends, with a predicted temperature increase of 0.8[degrees]C per annum by 2030 (VCC 2008). The number of hot days will increase in frequency and intensity, more so in inland regions than coastal regions (VCC 2008a). Annual rainfall is expected to decrease by 4% by 2030 and 6% by 2070 (VCC 2008). Not only will the state become drier, but drought risk will increase by 10-80% by 2070 due to enhanced evaporation (VCC 2008a). Perhaps most threatening to Victoria's rainforests will be the predicted increase in fire frequency and intensity due to climate change. The warmer, drier climate will result in a greater number of 'extreme' fire danger days. By 2020, the number of 'extreme' fire days is estimated to increase by 5-40%, relative to the climate of 1974 to 2003 (VCC 2008). Under a low-emissions scenario, by 2050, the number of fire days may increase from 15-25% but under a higher-emissions scenario the risk of extreme fire danger days may increase by a staggering 120-230% (VCC 2008). This is grim news for Victoria, and especially for its unique rainforests. Some areas will be more at risk than others; for instance with the varying predictions for coastal versus inland sites, the rainforest of the Otways may be less affected than the rainforest of the Central Highlands.
The effect of climate change on the rainforests of Victoria
The summary of predictions for climate change in Victoria divides the state into ten main regions (VCC 2008). Climate change will affect different parts of the state to different degrees and in varying ways. The five different rainforest types found across the state have different requirements and tolerances for rainfall, fire frequency and temperatures. Therefore, the impacts of climate change on Victoria's rainforests will vary not only according to the specific requirements of the rainforest type itself, but also with regard to its locations throughout the state.
Each rainforest type found in Victoria will experience raised temperatures and reduced rainfall by 2030 and 2070 compared to current levels; while cool temperate rainforest is found in more regions than any other rainforest type, curiously, it has more restricting climate limitations than other rainforest types. This means that changes in climate will significantly affect cool temperate rainforests. By 2030, cool temperate rainforests across the state may experience temperature increases averaging 0.8[degrees]C per year; and 3.6% less rainfall than current levels. The higher emission scenario for 2070 could see temperature rises in areas of cool temperate rainforests as high as 2.6[degrees]C per annum; and 10.6% less rainfall than present-day levels (Table 1).
To compare the effect climate change will have on temperatures and rainfall levels in the near future with regard to the rainforests of Victoria, the differences between current levels and predicted levels are expressed in percentage form in Table 2. In 2070, gallery and dry rainforests may experience winter temperature increases of 61% above current temperatures under a lower emissions scenario whereby C[O.sub.2] emissions increase until 2040, at which point they decline (VCC 2008). This is the minimum increase we can expect in 2070. Other rainforest types will experience an increase of about 40-44%. In summer, all rainforest types will experience a 12-13% temperature rise from current-day levels (Table 2).
Rainforests are characterised by fairly dependable temperature and rainfall thresholds. Cool temperate rainforests and cool temperate mixed forests currently require high to very high annual rainfall of 1200-2000 mm (Peel 1999). Warm temperate, dry and gallery rainforests require moderate to high levels of annual rainfall of 716-1200 mm (Peel 1999). Based on lower emissions scenario predictions for 2070, dry, gallery and warm temperate rainforest will be sitting well within the thresholds of their annual rainfall requirements (Fig. 1). Cool temperate rainforest and cool temperate mixed forest, on the other hand, will receive between 28 and 30% (on average) less than their minimum annual rainfall requirement (Fig. 1).
Changing fire regimes
Dry rainforest resists fire due to its location, while the proximity to fire-shielding landscape elements like estuaries or lakes often protects warm temperate rainforests from fire (Peel 1999). Unlike dry and warm temperate rainforest, the fire resistance of cool temperate rainforest is dependent on impermanent defences such as temperature and moisture levels, which make them the most vulnerable to climate change. Cool temperate rainforests form a closed canopy after long periods without disturbance, which then serves to foster a humid interior that not only keeps the forest moist, but also aids in the rapid decomposition of fine fuels (Busby and Brown 1994). Should rainfall levels fall and temperatures rise, this protective humidity eventually will decline, fuel loads will increase and any lichen-covered stags that stand in the forest will dry out, making them a flammable opening in the canopy (Busby and Brown 1994). As rainforests are characterised by long periods without fire, and since it appears that the cool temperate rainforests of Victoria will be most at risk of fire in the not-too-distant future, the potential effects of climate change on cool temperate rainforests are further examined here.
Cool temperate rainforest occurs in areas where fire-free intervals are greater than 400 years (Peel 1999), but with the risk of fire in Victoria predicted to increase by 15-70% in 2050, such long intervals may become a thing of the past (Table 3). Indeed, fire frequency in the Central Highlands of Victoria is already higher than that of the last century (Lindenmayer et al. 2011), and one of the largest areas of cool temperate rainforest and cool temperate mixed forest occurs in this region.
Should fire threaten areas in which cool temperate rainforests occur, it is predicted that a positive feedback system will begin wherein with each fire comes greater risk of more fire until, eventually, what we now define as cool temperate rainforest in these key areas will become sclerophyll forest. Once the normally-closed canopy of a cool temperate rainforest is penetrated by fire, it is recolonised by more fire-prone and also more fire-tolerant species such as Acacia and Eucalyptus. This is known as a landscape 'trap'; ecosystem modification occurs to an almost entirely irreversible extent due to natural and anthropogenic disturbances causing a series of feedback processes (Lindenmayer et al. 2011). As previously mentioned, the effects of climate change will threaten the resilience systems of the cool temperate rainforest by reducing humidity, increasing fuel loads and increasing temperatures.
Inland regions such as the North East, Strzeleckis, Central Highlands and parts of East Gippsland are more at risk than coastal rainforest areas such as the Otway Ranges and Wilson's Promontory. The inland rainforest of the Central Highlands, for instance, has coexisted with fire for the last 40 millenia, however the most recent 2500 years has seen fire frequency and intensity increase (Baker et al. 2012). Every century, one or two high-intensity crown fires would disturb the rainforest but the damage would be minimal. This is due to the damp and humid resilience of the rainforest and the adjacent Eucalyptus regnans F.Muell. forest towering above the rainforest canopy (Baker et al. 2012). A high-intensity crown fire in neighbouring E. regnans forests affords some protection in that the crown fires will travel slowly and with reduced heat energy toward the crowns of the rainforest species as they stand much shorter than the giant eucalypts (Baker et al. 2012). Despite these protective mechanisms, in 2009 47% of the cool temperate rainforest in the Central Highlands of Victoria was burnt (Worley 2012). This suggests that the rainforest's ability to protect itself from fire was reduced due to the intensity and extreme conditions of the burn. In fact, 8.5% of Victoria's cool temperate rainforests were burnt in the 2009 fires, with 50% of the fires classed as 'severe' (Worley 2012). Not only has the intensity of fires increased, the occurrence of major bushfires in Victoria has steadily become more frequent since the 1850s. From 1850 to 1900, Victoria experienced an average of 0.4 major bushfires per decade; from 1900 to 1950, this jumped to an average of 2.4 major bushfires per decade and from 1950 to 2000 the frequency increased again to an average of 3.4 major bushfires per decade (Bryant 2009).
Key species of cool temperate rainforests
To get a better understanding of the effects climate change will have on cool temperate rainforest, it is important to study the key canopy species that constitute the forest. The restrictions on distribution, required versus predicted rainfall parameters and fire adaptations of each species, give key insights into how climate change and broad-scale disturbance, such as fire, may affect each species, and the implications this will have for cool temperate rainforests (Table 4).
In 2070, at lower emissions predictions, Acacia melanoxylon R.Br. and Eucalyptus obliqua L'Her. will receive annual rainfall that sits well above their minimum requirements; 76% above minimum required annual rainfall in the case of Eucalyptus obliqua. By contrast, Atherosperma moschatum, Nothofagus cunninghamii and Dicksonia antarctica Labill. will all receive less rainfall than their current lower thresholds (Table 4; Fig. 2).
Acacia melanoxylon and Eucalyptus obliqua are both well adapted to fire and neither species is restricted to cool temperate rainforest or to Victoria. Therefore, should a fire occur, these two species are likely to persist and become dominant in the sclerophyll forest that will eventuate with climate change and increasing fire frequency.
Atherosperma moschatum and Dicksonia antarctica are both found in multiple regions as well as beyond Victoria (RBG 2012) and neither is restricted to cool temperate rainforest. Where they occur on coasts, they may be at lower risk to fire but may become less dominant in inland rainforests. A. moschatum does, however, have foliage with low flammability due to high moisture and low energy content; studies show that its leaves do not combust until >60% of moisture content is lost (Baker et al. 2012). This is in contrast to the leaves of many eucalypt species that will ignite when <40-50% of moisture has been lost (Baker et al. 2012).
A key dominant species of Victoria's cool temperate rainforests is Nothofagus cunninghamii. This species is restricted to habitats in Victoria and Tasmania. It has some adaptation to fire in its fire-responsive coppice shoots and may have bursts of regrowth after a fire with reproduction occurring either sexually or vegetatively (Howard 1981; Baker et al. 2012); however, once a stand of Nothofagus is broken up by a fire, the remaining trees no longer have the protection of moisture, low temperatures and limited fuel on the forest floor that the dominant stand had, and are less resistant to the damaging effects of fire (Howard 1981). In the Central Highlands in the 2009 fires, the individuals of N. cunninghammi that grew in low numbers as understorey to E. regnans or in small patches of rainforest were all killed; Pappas (cited in Baker et al. 2012: 187) noted that rainforest taxa did not survive the fires unless they occurred in strips of rainforest that were 50 metres wide or more (Baker et al. 2012). These examples demonstrate that the resilience of the species is not necessarily found in the individual. The damaged stand is then likely to burn again, which will continue the process of degradation. Once this positive feedback loop has begun, the fate of the species is compromised.
It is predicted that Nothofagus cunninghamii will be receiving 25% less rainfall than its minimum annual requirements. The inability of Nothofagus to adapt to lower rainfall levels that came about in the Tertiary period, between 65 and 18 mya, confined it to cooler, wetter areas; so it is predicted that by 2070, the species will be forced to retreat once again to residual areas that are only a fraction of its current extent. Nothofagus cunninghamii also requires water, gravity and animals to transport its seeds rather than far-reaching wind or invertebrate vectors (Baker et al. 2012). It may persist in Tasmania and in the coastal sites of Victoria, but there is a high possibility that it will recede from its current locations in the inland Strzeleckis and Central Highlands, especially considering its limited dispersal mechanisms.
Factors such as slope, topographic position and competing vegetation must be considered to formulate a more comprehensive prediction of the effects climate change may have on the rainforests of Victoria (Lindenmayer 2009); however, it is still possible to predict the likely fate of Victoria's rainforests based on climate change predictions for 2030, 2050 and 2070.
Should fire, the risk of which is increased by climate change conditions, become more frequent and intense throughout Victoria, cool temperate rainforest will be greatly impacted. The dominant canopy species of Victorian cool temperate rainforests, Nothofagus cunninghamii, will be most at risk. Due to climate change, it will experience high water stress and be most susceptible to accumulated effects of increased fire events.
Rainforests, compared to other vegetation types of Australia, are relatively persistent; with the predicted temperature, rainfall and fire regime changes resulting from climate change and continued degradation by humans, Victoria's rainforests may be very different by 2070.
I would like to acknowledge the following people for their support and hard work: Dr Maria Gibson for her guidance, knowledge and for answering all my emails; Leah Martini for her support and help with research into fire; and Keryn Riddington for being my editor and for introducing me to rainforests.
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Received 21 November 2013; accepted 19 June 2014
School of Life and Environmental Sciences, Deakin University, Burwood Campus, 221 Burwood Highway, Burwood, Victoria 3125
Table 1. Current and predicted future temperatures and annual rainfall in Victoria's rainforests (after Peel, 1999; VCC 2011a; VCC 2011b; VCC 2011c; VCC 201 Id; VCC 201 le). Rainforest Type Locations Cool Temperate North East Otways Wilson's Promontory Strzeleckis Central Highlands East Gippsland Cool Temperate Mixed Forest Central Highlands East Gippsland Warm Temperate Strzeleckis East Gippsland Gallery Rainforest East Gippsland Dry Rainforest East Gippsland Rainforest Type Current Temps 2030 Temps Winter/Summer * Cool Temperate 0-6[degrees]C/6-12[degrees]C 1.4[degrees]C/11.2[degrees]C +0.9[degrees]C 5[degrees]C/11.6[degrees]C +0.8[degrees]C 4[degrees]C/11.5[degrees]C +0.8[degrees]C 4[degrees]C/11.5[degrees]C +0.8[degrees]C 4.6[degrees]C/12[degrees]C +0.8[degrees]C 2.3[degrees]C/11.1[degrees]C +0.8[degrees]C Cool Temperate 0-6[degrees]C/6-12[degrees]C Mixed Forest 4.6[degrees]C/12[degrees]C +0.8[degrees]C 2.3[degrees]C/11.1[degrees]C +0.8[degrees]C Warm Temperate 4.8[degrees]C/14.1[degrees]C 4[degrees]C/11.5[degrees]C +0.8[degrees]C 2.3[degrees]C/11.1[degrees]C +0.8[degrees]C Gallery Rainforest 4.8[degrees]C/14.1[degrees]C 2.3[degrees]C/11.1[degrees]C +0.8[degrees]C 1.9[degrees]C/14.5[degrees]C 2.3[degrees]C/11.1[degrees]C +0.8[degrees]C Rainforest Type 2070 Temps - Current rainfall Lower/higher emissions (nun) Cool Temperate 1200-2000mm +1.572.9[degrees]C 1089mm +1.3[degrees]C/2.4[degrees]C 773mm +1.4[degrees]C/2.6[degrees]C 926mm +1.4[degrees]C/2.6[degrees]C 926mm +1.3[degrees]C/2.6[degrees]C 864mm +1.4[degrees]C/2.7[degrees]C 924mm Cool Temperate 1200-2000mm Mixed Forest +1.3[degrees]C/2.6[degrees]C 864mm +1.4[degrees]C/2.7[degrees]C 924mm Warm Temperate 734-1200mm +1.4[degrees]C/2.6[degrees]C 864mm +1.4[degrees]C/2.7[degrees]C 924mm Gallery Rainforest 734-1200mm +1.4[degrees]C/2.7[degrees]C 924mm 716-994mm +1.4[degrees]C/2.7[degrees]C 924mm Rainforest Type 2030 2070 rainfall rainfall Cool Temperate -3% -5%/-10% -4% -6%/-12% -4% -6%/-11% -4% -6%/-11% -4% -6%/-11% -3% -5%/-9% Cool Temperate Mixed Forest -4% -6%/-11% -3% -5%/-9% Warm Temperate -4% -6%/-11% -3% -5%/-9% Gallery Rainforest -3% -5%/-9% -3% -5%/-9% Table 2. The percentage differences in average temperatures and annual rainfall across Victoria's rainforest types according to lower emissions scenarios for 2030 and 2070 for the state of Victoria. Average Temperature Increase by % Rainforest type 2030 2070 Winter Summer Winter Summer Cool temperate rainforest 23 7 39-74 12-23 Cool temperate mixed forest 23 7 39-74 12-23 Warm temperate rainforest 25 7 44-86 12-24 Gallery rainforest 35 7 61-117 13-21 Dry rainforest 35 7 61-117 13-21 Average difference in annual rainfall by % Rainforest type 2070 Lower emissions Cool temperate rainforest -28 Cool temperate mixed forest -30 Warm temperate rainforest 14 Gallery rainforest 20 Dry rainforest 23 Table 3. Implications of fire on Victoria's cool temperate rainforest due to climate change according to location. (After BOM 2012; Hennessy et al. 2005; Anon in SMH 2009; Bushfire CRC 2006; CSIRO 2011; Forest encyclopedia 2008). Predicted fire risk increase with climate change Areas covered Current fire season 2020 2050 Risk due by Rainforest to location North East December-February 4-25% 15-70% High Otways December-May 4-25% 15-70% Low Wilsons December-February 4-25 % 15-70% Low Promontory Strzeleckis December-February 4-25 % 15-70% High Central December-February 4-25 % 15-70% High Highlands East Gippsland September-February 4-25 % 15-70% Low-High Impacts of climate change on fire Areas covered Intensity Frequency Extent by Rainforest (heat) (number) (size) North East + + + Otways + + + Wilsons + + + Promontory Strzeleckis + + + Central + + + Highlands East Gippsland + + + Areas covered Predictions by Rainforest North East - High risk of fire due to inland location - Should fire occur, intensity, frequency and its extent would increase due to climate change - Likely to be converted to sclerophyll forest Otways - Low risk of fire due to proximity to coast - Should fire occur, intensity, frequency and its extent would increase due to climate change - Possibility of being converted to sclerophyll forest Wilsons - Low risk of fire due to proximity to coast Promontory - Should fire occur, intensity, frequency and its extent would increase due to climate change - Possibility of being converted to sclerophyll forest Strzeleckis - High risk of fire due to land location - Should fire occur, intensity, frequency and its extent would increase due to climate change - Likely to be converted to sclerophyll forest Central - High risk of fire due to inland location Highlands - Should fire occur, intensity, frequency and its extent would increase due to climate change - Likely to be converted to sclerophyll forest East Gippsland - Low to high risk of fire due to inland and coastal location - Should fire occur, intensity, frequency and its extent would increase due to climate change - Low to high likelihood of being converted to sclerophyll forest Table 4. The potential effects of climate change on key species of Victoria's cool temperate rainforests. * CH = Central Highlands, EG = East Gippsland, NE = North East, OT = Otways, STRZ = Strzeleckis, WP = Wilson's Promontory. (After Boland et al. 1984; BoM and Walsh 1993; Conn 1993; Costermans 2009; Floyd 2008; Francis 1981; Jordan et al. 1992; Large and Braggins 2004; Wilkinson and Jennings 1993). N.B. Although these are key species, none are restricted to Cool Temperate Rainforest, or Victoria. Tree Species Region * Rainfall Required 2070 prediction annual (mm) at lower emissions (mm) Acacia CH, EG, 750-1500 820 melanoxylon OT, WP Atherosperma STRZ, WP 1000-2000 870 moschatum Eucalyptus EG 500-2400 878 obliqua EG Nothofagus CH, OT, 1100-2500 820 cunninghamii STRZ Dicksonia OT, STRZ, 900-1700 875 antarctica WP Tree Species Fire Acacia Requires disturbance melanoxylon to regenerate Atherosperma Limited fire resistance moschatum Eucalyptus Fire tolerant/requires obliqua EG disturbance to regenerate Nothofagus Limited fire adaptation/ cunninghamii resistance Dicksonia Fire resistant antarctica Tree Species Implications Plant species Acacia Due to regeneration of seed melanoxylon with fire and low water stress, A. melanoxylon will persist Atherosperma Due to high risk of fire and moschatum high water stress, not likely to persist in habitat Eucalyptus Due to tolerance of/and obliqua EG regeneration with fire and very low water stress, E. obliqua will persist Nothofagus Due to high fire risk and cunninghamii extreme water stress, extreme water stress, Dicksonia At risk due to water stress antarctica Tree Species Cool Temperate Rainforest Acacia Will persist in all melanoxylon regions as part of sclerophyll forest Atherosperma Will recede to the moschatum most sheltered pockets, topographically Eucalyptus Will become a dominant obliqua EG of sclerophyll forest in inland locations Nothofagus Will recede to the most cunninghamii sheltered pockets, topographically Dicksonia May recede to the most antarctica sheltered pockets
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|Date:||Dec 1, 2014|
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