Chapter 3 Natural terrestrial ecosystems Co-Chairmen: R.B. Street, Canada S.M. Semenov, USSR Lead authors: Unmanaged forests and vegetation W. Westman, USA Biological diversity and endangered species R. Peters and A. Janetos, USA Wildlife H. Boyd and J. Pagnan, Canada Wetlands M. Bardecki, Canada Heritage sites and Reserves R. Wein and N. Lopoukhine, Canada Expert contributors: R.S. de Groot (The Netherlands); L. Menchaca (Mexico); J.J. Owonubi (Nigeria); D.C. Maclver (Canada); B.F. Findlay (Canada); B. Frenzel (FRG); P.R. Jutro (USA); A A. Velitchko (USSR); AM. Solomon (JJASA); R. Holesgrove (Australia); T.V. Callaghan (UK); C. Griffiths (Australia); J.I. Holten (Norway); P. Mosley (New Zealand); A. Scott (UK); L. Mortsch (Canada); O.J. Olaniran (Nigeria) Contents 1 Introduction 3-1 1.1 Reasons for concern 3-1 1.2 Sensitive species and ecosystems 3-3 1.3 Analytical methodologies 3-3 1.4 Historical evidence 3-4 2 Direct impacts of elevated C02 3-5 3 ' Changes in the boundaries of vegetation zones 3-6 3.1 Global overview 3-9 3.2 Specific vegetation zones 3-10 3.2.1 Boreal and tundra 3-10 (i) Global warming of 2°C 3-10 (ii) Global warming of 1°C 3-10 3.2.2 Montane and alpine 3-13 3.2.3 Temperate 3-13 3.2.4 Semi-arid and arid 3-14 4 Changes within ecosystems 3-14 4.1 Water balances in terrestrial ecosystems 3-14 4.2 Ecological interactions 3-16 4.3 Biological diversity and endangered species 3-17 4.4 Pests and pathogens 3-18 4.5 Disturbance variables 3-19 4.5.1 Fire 3-19 4.5.2 Soil and surface stability 3-20 4.6 Sea-level rise 3-21 5 Socioeconomic consequences 3-23 5.1 Unmanaged vegetation and forests 3-23 5.2 Biological diversity and endangered species 3-25 5.3 Wetlands 3-26 5.4 Wildlife and fish 3-27 5.5 Heritage sites and reserves 3-28 6 Future deliberations 3-28 Table Table 3.1 Current relative surface area and net primary productivity of various vegetation zones 3-12 Figures Figure 3.1a: Changes in climate zones currently associated with specific vegetation (Leemans, 1989) - Western Hemisphere 3-31 Figure 3.1b: Changes in climate zones currently associated with specific vegetation (Leemans, 1989) - Eastern Hemisphere 3-32 Figure 3.2a: Potential changes in the distribution of the main tree species as a result of projected increases in temperature in the European part of the USSR along a transect at 50°E longitude (Velichko et al., 1990) -increase in global mean temperature of 0.8°-l°C . 3-33 Figure 3.2b: Potential changes in the distribution of the main tree species as a result of projected increases in temperature in the European part of the USSR along a transect at 50°E longitude (Velichko et al., 1990) -increase in global mean temperature of 1.8°-2°C . 3-34 3-ii Figure 3.3a: Potential changes in the distribution of the main tree species as a result of projected increases in temperature in Canada along a transect at 100°W longitude (Velichko et al., 1990) - increase in global mean temperature of 0.8°-l°C 3-35 Figure 3.3b: Potential changes in the distribution of the main tree species as a result of projected increases in temperature in Canada along a transect at 100°W longitude (Velichko et al., 1990) - increase in global mean temperature of 1.8°-2°C 3-36 References 3-37 3-iii Natural terrestrial ecosystems 1 Introduction reached the level at which these anthropogenic increases in GHG gases have the potential to affect This report examines the ecological impacts of global climate. climate change on natural ecosystems (land areas and associated flora and fauna which are not inten• The increases in the atmospheric concentrations of sively managed) and the socioeconomic conse• GHG and the projected changes in climate resulting quences of these impacts. For this report, the from these increases pose a serious threat to natural definition of natural terrestrial ecosystems includes terrestrial ecosystems and associated socioeconomic unmanaged forests and other natural vegetation systems. It must be recognised that the temperature systems, wetlands, deserts, freshwater lakes, alpine changes suggested by climate scenarios would regions and protected areas such as natural heritage present natural systems with a warmer climate than sites and reserves. It does not include intensively has been experienced at least during the past managed ecosystems such as agricultural areas and 100,000 years (Schneider and Londer, 1984), and forest plantations (Chapter 2, Agriculture and that there is no equivalent during the period of forestry) nor does it include components of the recent development of the present vegetation. terrestrial cryosphere (Chapter 7, Seasonal snow Moreover, a global temperature rise of 4°C above cover, ice and permafrost). the present norm, for example, would make the earth its warmest since the Eocene, 40 million years The changes to climate are considered to be those ago (Barron, 1985; Webb, 1990). resulting from increased atmospheric concentrations of greenhouse gases (GHG). The climate change Such warming would not only be greater than recent scenarios that form the base reference for this natural fluctuations, but it would occur 15 to 40 report are generally those decided at the workshop times faster than past natural changes (Schneider, held in Villach during 1987 (WMO, 1988). The 1989; Gleick et al., 1990). Such a rate of change illustrative examples of the environmental impacts may exceed the ability of many species to adapt or and socioeconomic consequences, however, may be disperse into more favourable regions and many based on different scenarios. plant and animal species may become extinct (Lester and Myers, 1989; Pain, 1988). For widespread, Generally accepted vegetation zones (eg warm abundant species, such as the loblolly pine (Pinus desert, tropical forest, boreal forest and tundra) have taeda) (Miller et al., 1987), even a substantial range been used to stratify the discussions. Use of these retraction might not threaten extinction; however, zones recognises the spatial resolution limitations of rare localised species, whose entire ranges become the current understanding of global climate change unsuitable, would be extinguished unless migration and the likely responses of ecosystems and their or human interventions were successful. On the components. Further stratification is achieved by other hand, some species, rare or abundant, may focusing discussion on major and sensitive compo• thrive under a new climate regime. Even for widely nents of natural terrestrial ecosystems: biodiversity distributed species, major losses of important eco- and endangered species, unmanaged forests and types and associated genetic material is likely (Davis vegetation, wetlands, freshwater fisheries, wildlife and Zabinski, 1990). and heritage sites and reserves. Although the focus will be on the larger scale (approximately 1000 km), Temperature changes will be important for animals where available, local analyses will be used to and also insects. Mean temperature, for example, illustrate specific environmental impacts and socio• influences the ratios of males to females in some economic consequences. reptiles. Changes in extreme temperatures, such as freezing versus no freezing, or extreme high tem• 1.1 Reasons for concern peratures, can significantly effect the dynamics and distribution of animals and, in particular, insects Climate is naturally subject to long-term changes (Waller et al., 1989). (glacial and interglacial periods) and short-term fluctuations. Scientific and technological progress, Ecological stress will not be caused by temperature however, appears poised to accelerate climate changes alone. Global precipitation characteristics evolution significantly by increasing the atmospheric are also expected to change (Hansen et al., 1981; concentration of radiatively active gases. The Kellogg and Schware, 1981; Manabe and Wetherald, associated enhancement of the greenhouse effect has 3-1 1987; Schlesinger and Mitchell, 1987) and for many An important point in understanding species' re• species, precipitation and soil moisture are more sponse to climate change, is that weather is variable important determinants of survival than temperature. and extreme events, like droughts, frosts, floods, Indeed, except at the treeline, where minimum blizzards, the frequency of hot or cold spells and temperature is often the dominant limiting factor, associated fires and pest outbreaks, may have more precipitation plays a major role in determining the effect on species distributions than average climate distribution of vegetation with trees occurring mainly (eg Knopf and Sedgwick, 1987). Animals can adapt where annual amounts are in excess of 300 mm their behaviour during droughts and heatwaves by (Woodward, 1990). Complicating this response is timing activity to cooler parts of the day, restricting the fact that enhanced levels of atmospheric C02 their movements to conserve energy and water, or increases the water use efficiency of plants (Gifford, migrating to more favourable areas. Increased 1979). Therefore, although precipitation character• frequency or persistence of these conditions, how• istics are expected to change, plants' efficiency in the ever, can significantly influence an animal's health use of the available moisture will also change. and survival either directly or indirectly through loss of habitat, food and water. The breeding success of birds and small mammals (eg muskrats, beavers, weasels, reptilia, and amphi• Increasing concentrations of GHG in the atmos• bians) are often linked to seasonal precipitation, phere pose two different sorts of stresses on natural snow cover and snowmelt (eg Campbell, 1968; Davis terrestrial ecosystems. In addition to causing chan• and Cook, 1983). Small alterations in the amount, ges in climate, GHG can directly affect ecosystem timing and intensity of precipitation events can processes, thereby influencing ecosystem health and dramatically affect regional water balances, with composition. Primarily affected are biological and significant impacts on flora and fauna (Pain, 1988; geomorphological processes (eg photosynthesis and Kushlan, 1986).