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When Europeans arrived in Australia in 1788, there were approximately 70 Mha of forests. Since then, 40% has been cleared and a similar amount has been affected by logging; only about 25% remains relatively unaffected (Graetz et al., 1995; State of the Environment, 1996). Nationally, land clearing still exceeds planting, although this varies greatly across the states, and is occurring mainly in areas defined as woodlands. Plantations have been expanding in Australia at an increasing rate since 1990, currently by more than 50,000 ha yr-1 (National Greenhouse Gas Inventory, 2000). Much of this planting is occurring on farmed land and receives federal government support (Race and Curtis, 1997). Additional plantings are occurring to ameliorate land degradation problems such as erosion, waterlogging, and salinization, and further plantings are associated with the establishment of carbon sinks (Howden et al., 1999d).
Forests cover about 8.1 Mha (29%) of New Zealand's land area. Of this, about 6.4 Mha are in natural forest and 1.7 Mha in planted production forests. New forest establishment increased markedly during the 1990s. Almost all areas of harvested forest are replanted; during 1998, 52,000 ha of new forest plantings occurred (Statistics New Zealand, 1999).
Climatic factors are well known to influence species distributions (Hughes et al., 1996; Austin et al., 1997) and productivity (Landsberg and Waring, 1997). CO2 concentrations also have a direct effect (Curtis and Wang, 1998). Kirschbaum (1999a,b) has used a forest growth model to assess response to climate change and CO2 increases for a site near Canberra.
Howden and Gorman (1999) review this and other work on the impact of global change on Australian temperate forests. Productivity of exotic softwood and native hardwood plantations is likely to be increased by CO2 fertilization effects, although the amount of increase is limited by various acclimation processes and environmental feedbacks through nutrient cycling. Where trees are not water-limited, warming may expand the growing season in southern Australia, but increased fire hazard and pests may negate some gains. Reduced rainfall in more recent scenarios would have adverse effects on productivity and increase fire risk. Increased rainfall intensity would exacerbate soil erosion problems and pollution of streams during forestry operations. In Pinus radiata and Eucalyptus plantations, fertile sites are more likely to have increased productivity for moderate warmings, whereas infertile sites could have decreased production. To date, large uncertainties have lowered the priority of climate change in management considerations.
Despite large year-to-year climatic variability, many Australian native species are confined in their natural climatic range to within 1 or 2°C average mean temperature (Hughes et al., 1996; Pouliquen-Young and Newman, 1999), so without human intervention their survival will be threatened by warmings outside these ranges (see Section 12.4.1).
Of New Zealand's 13 Mha of land used for pastoral farming, at current prices 3-5 Mha of hill country would yield higher returns under forestry. Such land is being converted to plantation forestry at a rate of 40,000 ha yr-1, from an initial rate averaging 60,000 ha yr-1 over the past decade (Statistics New Zealand, 1998); the recent decrease in planting rate reflects current lower wood prices. Carbon trading would facilitate increased planting rates, possibly up to 90,000 ha yr-1 (MAF, 1999). Steep land is particularly uneconomic to manage for pastoral farming and could be converted to forest or scrubland by planting or abandonment and regrowth. Control of possums (a pest introduced from Australia by early European settlers) to minimize transfer of diseases to farm animals has the added benefit of improving the health and regenerative capacity of some indigenous forests (Ministry for the Environment, 1997).
Biomass from forest residues and purpose-grown crops already provides 6% of New Zealand's primary energy supply (EECA, 1996) and significant energy resources for Australia. Biomass use is expected to increase substantially over the next decade (Sims, 1999), partly as a response to constraints on net carbon emissions. This also may encourage increased forestry planting rates.
The direct effects of elevated CO2 on yield from radiata pine plantations are expected to be small in New Zealand. However, regional uncertainties remain with regard to possible increased growth loss under warmer, wetter conditions as a result of existing and new pests and diseases and losses from wind and fire associated with extreme weather events. Biosecurity mechanisms are being improved in New Zealand and abroad to better manage risk. Long-term trends in forest nutritional status are being examined. Indicators of sustainable forestry practices are receiving increasing attention. Risks from fire and wind also are being investigated in New Zealand. Systems to measure and predict effects on carbon sequestration in plantation forests are being improved.
Australia specializes in high-value, low-tonnage fisheries such as lobsters, pearl oysters, prawns, abalone, and tuna. Totaling about AU$2 billion yr-1 (ABARE, 2000), these fisheries are a significant local primary industry. Tonnage produced is very small by world standards because Australian surface waters generally are low in nutrients as a result of prevailing winds and boundary currents (Kailola et al., 1993). New Zealand's Exclusive Economic Zone (EEZ) is one of the largest in the world (Statistics New Zealand, 1999), and its NZ$1.23 billion export revenues from fisheries in 1998 constituted 5.5% of total export revenue for that year (Seafood New Zealand, 2000).
For both countries, relationships have been established between recruitment of some fish species and climate variations, suggesting that fisheries in the region will be sensitive to climate change. However, it is uncertain how local winds and boundary currents that advect larvae and affect upwelling of nutrients might respond to GHG-induced climate changes, and downscaling from relevant global climate change model fields has not yet been done. Hence, this section concentrates on reporting studies of observed sensitivities of fisheries in the Australasian region to climate variability. There is insufficient information to date to project the impact of climate change on fisheries productivity.
Understanding of existing processes suggests that if El Niño were to become a more prevalent condition, the Indonesian throughflow and the Leeuwin current (Meyers, 1996) could weaken. If winds were favorable for upwelling, the west coast of Australia could undergo a dramatic shift from a low-production, high-biodiversity ecosystem to a more productive ecosystem typical of temperate shelves.
Australia's single largest fishery is western rock lobster (AU$260 million yr-1—ABARE 2000). Presently, settlement of larval lobsters (and adult catch rates some years later) is much higher in La Niña years (high coastal sea level, high SST, strong Leeuwin current) than in El Niño years (Pearce and Phillips, 1994). Because the mechanism appears to be through larval advection processes, however, it is unclear whether the species' spawning strategy would adapt to a sustained shift to a weaker Leeuwin current. Many other western Australian fisheries also correlate (some positively, some negatively) with ENSO (Caputi et al., 1996), through unknown mechanisms. Whether these mechanisms would continue to operate under the combined influence of a sustained weaker Leeuwin current (which tends to reduce temperatures) and a worldwide rise in SST is unknown. Southern bluefin tuna spawn where the Indonesian throughflow enters the Indian Ocean, but the impact of a possibly reduced throughflow also is unknown.
Conditions on the south coast of Australia also are influenced—but to a lesser degree—by the Leeuwin current, which tends to keep near-surface nutrient levels low. In addition, winds are favorable to downwelling, except during some summers, when Australia's only example of strong classical wind-driven coastal upwelling occurs off Portland, Victoria. Small meridional shifts of the subtropical high-pressure ridge modulate summer upwelling. Ecosystem impacts of this are poorly known.
On the east coast of Australia, the East Australian Current (EAC) is a dominant influence on coastal marine ecosystems. The EAC enhances upwelling and primary production (Hallegraeff and Jeffrey, 1993) and presumably fisheries, although this has yet to be demonstrated apart from its effect on the distribution of several tuna species (Lyne et al., 1999). Farther north, Vance et al. (1985) report a correlation of catches of banana (but not tiger) prawns with rainfall, probably as a result of runoff-driven export of juveniles from estuary nursery beds.
Post hoc analyses (Smith, 1996) of a dramatic decline in the late 1980s in the Australian gemfish fishery suggest a combination of fishery pressure and poor recruitments as the cause. Recruitment appears to correlate with climatic cycles (Thresher, 1994). Smith (1996) developed a quantitative framework to evaluate management strategies for this and other fisheries.
For New Zealand, there is some evidence that fisheries recruitment may be enhanced by more frequent ENSO events (Harris et al., 1988), although possible negative effects of increased incidence of toxic algal blooms also have been observed (Chang et al., 1998). Changes in ENSO and ocean variability may combine with ocean warming in ways that are poorly understood. Recent New Zealand studies on snapper (Francis 1993, 1994a; Francis et al., 1997), gemfish (Renwick et al., 1998a), and hoki have shown that climatic variations may have a significant impact on spawning success or failure and subsequent recruitment into marine fish populations. Growth rates of juvenile and adult snapper appear to increase when SSTs are warmer (Francis, 1994b). This may have significant effects on the timing and scale of recruitment (e.g., Francis et al., 1997). El Niño appears to have resulted in a westward shift of Chilean jack mackerel in the Pacific and subsequent invasion of this species into New Zealand waters in the mid-1980s (Elizarov et al., 1993). This species now dominates the jack mackerel fishery in many areas. Variations in the abundance and distribution of pelagic large gamefish species in New Zealand may be closely correlated with variability in the ocean climate, with implications for recreational fishers as well as the tourist industry operating from charter boats.
Environmental temperature has a major influence on the population genetics of cold-blooded animals, selecting for temperature-sensitive alleles and genotypes. In New Zealand snapper, differences in allele frequencies at one enzyme marker have been found among year classes from warm and cold summers (Smith, 1979). Such differences could impact survival, growth rates, and reproductive success.
Finally, it should be noted that, if the wildcard of possible reduction or cessation of North Atlantic or Antarctic bottomwater formation were to occur (Manabe and Stouffer, 1994; Hirst, 1999), this could lead to significant changes in deep ocean chemistry, ocean dynamics, and nutrient levels on century time scales. This could have wide, but presently unknown, ramifications for fisheries in Australian and New Zealand waters.
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