4.3.3.2. Production Forestry

The production of wood and paper products is a major industry in the region. In New Zealand, the industry is primarily based on plantations of fast-growing exotic species, whereas in Australia there is still a considerable forest industry based on native eucalypt forests in addition to expanding plantation forests. A rising world population, combined with increased living standards, may (at current prices) demand more wood than can be supplied from global resources by the year 2050. Temperate forest products are expected to play an important role in meeting demand (IPCC 1996, WG II, Sections 15.2.3, 15.4.3). There also is an increasing trend to see plantation forests as a means of sequestering carbon in the region (Maclaren, 1996).

CO₂ fertilization is likely to increase growth, especially when trees are water limited. However, growth enhancements due to increased temperature may occur only in trees not subject to water limitations (Landsberg, 1996). As already noted, however, the CO₂ impact on tree growth decreases with time for many species (Gunderson and Wullschleger, 1994). Any overall reductions in rainfall or changes in seasonality that result in water limitations or prolongation of droughts would negatively affect production and plantation seedling establishment. On the positive side, in New Zealand forestry many of the worst exotic weeds are C₄ plants, so the competitive effects may be reduced if elevated CO₂ concentration favors growth of C₃ over C₄ plants in temperate zones. Again, however, this gain might be negated by the relative advantage of C₄ plants at higher temperatures. Changes in tree and forest water use would alter the catchment hydrological characteristics, particularly runoff and extreme events (IPCC 1996, WG II, Sections 14.2, 14.4).

The exposure of forests and forest operations to fire risk may increase, particularly in Australia, and there is potential for changes in the frequency and intensity of damaging events from wind and storm, particularly in New Zealand. More intense rainfall events would exacerbate soil erosion and pollution of streams during forestry operations and make these operations more difficult to carry out. Warmer and wetter conditions could provide the opportunity for increased incidence of arthropod pests and pine needle blight (Dothistroma pini). Pinus radiata constitutes 91% of the exotic plantation forests in New Zealand and 68% in Australia, so this blight is a major potential risk to production forestry.

An important distinguishing feature of forestry is the long time scale of the tree lifecycle and the very large investment in the standing crop relative to the annual yield. Whereas a wheat farmer stands to lose one year's production in a climatic disaster, a forester may have at risk a full 30 years' growth. Thus, more so than with agricultural crops, global change has the potential to adversely affect the substantial accumulated capital of a standing forest. Furthermore, the long time scale means there are less frequent opportunities to apply adaptation options to any particular forest. The slower growing indigenous forests will be even more affected than the fast-rotation exotic forest plantations.

4.3.3.3. Fisheries

Relatively little is known about how climate affects marine fishes-particularly in the Southern Hemisphere, where data series tend to be short. Thus, it is extremely difficult to predict how climate change may affect Australasia's fish stocks and fishing industry, particularly in the context of the present stresses on fish stocks. There is some evidence, however, that climate impacts can be quite profound. The IPCC Second Assessment Report (SAR) concluded that although global marine fisheries production may remain about the same-despite possible changes in dominant species-there are likely to be collapses and expansions of specific regional fisheries (IPCC 1996, WG II, Section 16.2.2). These conclusions may likewise apply to large oceanic regions like Australasia, though current knowledge is not adequate to predict the impacts-positive or negative-on total productivity for the region.

In these circumstances, mobile high-seas fishing fleets are less likely to be affected, provided that access regulation is not tied to geographical areas. However, among the more localized small-scale fishers, who are dependent on specific in-shore fisheries, there may be large gains and large losses if fish populations shift their areas of abundance (IPCC 1996, WG II, Chapter 16). In addition, in-shore fisheries and marine stocks that need to reproduce in freshwater, estuaries, or mangroves may be negatively affected by changes in terrestrial and coastal processes, such as increased pollution and sediment discharge or loss of habitat. The economic impacts are unclear but could be significant for some parts of the industry.

Climate conditions are a factor in the outbreaks of bloom-forming algae and shellfish diseases that periodically occur in Australasian waters. These organisms include naturally occurring species and exotic species introduced by discharge of ships' ballast water. In the region's nontropical waters, some of the organisms are likely to be at the margins of suitable temperature conditions, and warming may give them increased opportunities to survive, spread, and form problem populations (IPCC 1996, WG II, Section 16.2.4).

Aquaculture and freshwater fisheries at mid-latitudes may benefit from longer growing seasons, lower natural winter mortality, and faster growth rates. Studies for New Zealand suggest that rising sea level and temperatures may increase oyster farm areas and productivity-but that sea temperatures may become excessive for salmon farming. Any increases in rainfall intensity over land are likely to increase coliform bacteria counts in runoff and result in more frequent closures of shellfish beds (IPCC 1996, WG II, Section 16.2.3).

IPCC Homepage