Climate Change Impacts: Vegetation
Published Online: 15 SEP 2009
Copyright © 2001 John Wiley & Sons, Ltd. All rights reserved.
How to Cite
Sykes, M. T. 2009. Climate Change Impacts: Vegetation. eLS.
- Published Online: 15 SEP 2009
Climate, more than any other factor, controls the broad-scale distributions of plant species and vegetation in general. This is true of the present-day climate, but past climates still influence current vegetation patterns, not least because generation times for many species, especially trees, can be hundreds of years. At finer scales, other factors such as local environmental conditions including micrometeorology, soil nutrient status, pH, water-holding capacity and the physical elements of aspect or slope influence the potential presence or absence of a species. However, intra- and interspecific interactions, such as competition for resources (light, water, nutrients), ultimately determine whether an individual plant is actually found at any particular location.
Rapid climate change associated with increasing greenhouse gas emissions (IPCC, 2007) influences current and future vegetation patterns. Other human-influenced factors are, however, also involved. Sala et al. 2000 identified five different drivers of change that can be expected to affect global biodiversity over the next 100 years. Globally, land use change was considered the most important driver of change, followed by climate change, airborne nitrogen deposition, biotic interactions (invasive species) and direct (fertilizing or water use efficiency effects) CO2. At different scales the relative importance of these drivers can change. In arctic biomes or ecosystems, for example, climate change is substantially more likely to affect biodiversity than any of the other drivers. However, in Mediterranean ecosystems both land use change and biotic interactions were considered most important.
The impacts of climate change on vegetation are complex and our understanding of these interactions is complicated by these other factors. This article concentrates on the role of climate change, exploring the evidence for the impacts of climate change on vegetation and plant productivity. At the species level this evidence mostly concerns changes in the timing of phenological events or changes in the ranges of species. Additionally, climate–vegetation interactions in the past are briefly discussed and finally some of the modelling methodologies and future projections of the effects of climate on vegetation are described.
Understanding the interactions among the different elements of global change (of which rapid climate change is among the most important), vegetation distribution and dynamics and the services provided by ecosystems to humanity is one of the major research challenges of the twenty-first century.
How do plants respond to climate change?
Establishment, growth, reproduction and indeed survival through its life cycle are directly related to the environmental conditions sensed by the plant. Changing temperatures and precipitation, especially when they occur rapidly or extremely, directly affect species, often differentially, and can therefore influence the course of competition among species. The degree of climate change is unlikely to be uniform over the globe and the outcomes for both species and plant populations responding to these changes are likely therefore to vary. For example, predictions from general circulation models (GCMs) suggest warmer winter (and to a lesser extent summer) temperatures, especially in northern latitudes (e.g. northern Europe), but less precipitation and increased droughts in some areas of, for example, southern Europe (IPCC, 2007).
Plants respond in general positively to change (increasing growth and population size), or negatively (decreasing growth with likely local extinctions) or by dispersal to new, more favourable sites.
Two plant processes, phenology and range shifting, are important in a plant's response to climate change.
Phenology is the timing of events over the annual cycle of plants and animals and is often a response to changing temperature, moisture and light levels that occur through the year. In plants phenological events include easily observed events such as leaf emergence, flowering and leaf drop. The recording of such events has until relatively recently been the preserve of naturalists. The earliest known long-term records in Europe were kept by the Marsham family in England from 1736 to 1947. They recorded the phenology of more than 20 different species of plants and animals (Sparks and Carey, 1995). The oldest known records are, however, from ad 801 from Japan and they record the flowering of cherry trees connected with the timing of the annual blossom festival (Anon and Kazui, 2007). There have been a number of reviews and meta-analyses about the influence of climate change on phenology (e.g. Menzel et al., 2006). Menzel and Fabian 1999 reported for the period 1959–1993 in Europe that events of spring were occurring earlier at a rate of 1.8 days per decade. By 1971–2000, earlier leafing, flowering and fruiting had increased to 2.5 days per decade with a delay in leaf fall by 0.2 days per decade (Menzel et al., 2006). Schwartz and Reiter 2000 examined changes in spring during the period 1900–1997 with regard to lilac (Syringa) across North America. They found regional variations but on average an advance of spring by 5–6 days between 1959 and 1993 driven by warmer spring temperatures, though there was a great deal of interannual variability.
Much of the research into climate interactions with phenology has been undertaken at the country level. Fitter and Fitter 2002 reported that first flowering in the United Kingdom advanced by 4.5 days per decade in the 1990s and Peñuelas et al. 2002 reported earlier leafing (3.3 days per decade), earlier flowering (1.2 days per decade), earlier fruiting (3.5 days per decade) and delayed leaf fall (2.7 days per decade) in Spain over the last half of the century. These changes are, however, not consistent across species with an advancement of 14.6 days per decade for Lippia triphylla but there was a delay of 7.8 days per decade for Fraximus angustifolia (Peñuelas et al., 2002). In Japan, Doi and Katano 2007 examined four tree species including Ginko biloba in four different locations, and found over the past 50 years, in locations with the greatest warming, budburst had advanced by up to 5.6 days per decade. The temperature in March was shown to be the most important factor driving these changes. Horticultural perennials such as lilac, apple and grape have also been used to study the first leaf and flower date changes over the last half of the twentieth century (Wolfe et al., 2005). They concluded in the northeastern United States that spring phenology had advanced for these species between 2 and 8 days over 35 years. Similar levels of advancement (1–2 days per decade over the past 50 years) were reported by Richardson et al. 2006 using data and models based on 14 years of observations of sugar maple, American beech and yellow birch. Most of these studies imply that changes in temperature are the main driver; however, this may not always be true. Keatley et al. 2002 using phenological observations of flowering from the 1920s to the 1980s for four Eucalypt species in Australia concluded that there were significant relationships between temperature and rainfall and commencement of flowering for all species. However, the responses differed among species; two species would flower later and two other species earlier under predicted increases in temperature and summer rainfall.
Additionally, as phenological events occur across a range of species and trophic levels, there is a possibility of mismatches in the timing of these events. Visser and Both 2005 discuss the ‘trophical decoupling of food web phenology’ among different species. For example, the food chain related to the oak tree–winter moth–great tit, where the bird (the great tit) feeds its young on the caterpillars, which are available only for a short time in spring and feed on new oak leaves (Visser and Holleman, 2001). In recent warmer springs, eggs from the winter moth hatched up to 3 weeks earlier than bud burst in the oak. However, newly hatched caterpillars can survive only for a few days without food. The great tits, however, have not consistently responded to the warmer springs by shifting their date of egg laying (Visser and Both, 2005).
As species, especially on different trophic levels, respond individualistically to their environment, climate changes are likely to promote disruptions of important relationships, but not always predictably, leading to loss of biodiversity and possible ecosystem degradation. However, new relationships between species may well emerge as new combinations of species coexist.
In summary, the timing of phenological events of many, but not all species, has responded to climate change. In addition, species also respond differently with the potential to change competitive relationships and thus to disrupt trophic interactions.
Rapid climate change-induced warming, especially in northern latitudes, is likely to lead to a suitable climate space that is available for species that require warmer conditions. Changes related to both latitude and altitude are possible. There is some evidence that species have already responded to climate change by range shifting and a number of reviews have summarized these (e.g. Parmesan and Yohe, 2003). In the Northern Hemisphere changes among the most studied groups, butterflies and moths, show range expansion in the north and sometimes contraction in the south (Parmesan, 2006). Range changes in plant species are less easy to observe though latitudinal movements have been recorded. For example, Holly (Ilex aquifolium), a species well known to have a close link to winter temperatures, has a northern limit closely associated with the location of the 0°C isotherm (Iversen, 1944). In the past 50 years this isotherm has moved north with a corresponding movement in the distribution of Holly, which now occupies new climate space along the more southerly coasts of Sweden (Walther et al., 2005a). Range changes related to altitude have also been observed, for example, in treelines moving upslope in the Scandinavian mountains (Kullman, 2001), whereas in Vermont the upper limits of the northern hardwood-boreal forest ecotone moved 91–115 m upslope between 1962 and 2005 (Beckage et al., 2008). Kelly and Goulden 2008 comparing two surveys (1977 and 2006–2007), along an elevation gradient in southern California found that the average elevation of the dominant plant species rose by 65 m between the two surveys and they attributed this to regional climate change involving both warming and changing precipitation variability. In the European Alps, Walther et al. 2005b report a trend in increasing species richness on alpine summits, which suggests an upward shift in species ranges as the climate becomes more favourable. This is likely to lead to more specialized alpine species facing local extinction as they are outcompeted by migrating species moving upwards in response to changing climate. Biome shifts have also been recorded in Mediterranean mountains. Peñuelas and Boada 2003 describe the upward migration by 70 m since 1945 of beech forest (Fagus sylvatica) and the replacement of beech and heathlands at lower levels by holm oak (Quercus ilex).
The situation with regard to the tropics seems to be more complicated, not just because data on the effects of climate change on tropical species are relatively scarce. However in a recent paper, Colwell et al. 2008 explored possible effects of climate change over a tropical elevation gradient using four insect and plant datasets in Costa Rica. They conclude that upslope movements of biota on mountainsides may be compensated as in higher latitudes by species from further down the mountain or the lowlands. However, replacements for current tropical lowland species from hotter sites are unlikely to be available as current species migrate upwards leading to ‘lowland biotic attrition’ and biodiversity loss.
Colonizing new areas not only depends on suitable climate space but also on the ability of each species to disperse or migrate to new areas. Rates of recent range shifts for nonplant species have already been shown to be substantial; for example, birds in Finland have moved at 16 km per decade (Brommer, 2004), and butterflies at 45 km per decade (Franco et al., 2006). Plants, however, respond substantially more slowly with treelines in Sweden moving at a rate of approximately 10 m per decade (Kullman, 2001) and alpine plants in Switzerland by 28 m per decade (Walther et al., 2005b). To date, there has been little published evidence of latitudinal range shifts for plant species, though Walther et al. 2005a describe (aforementioned) such a movement in southern Scandinavia as ‘a footprint of climate change’. If climate change is particularly rapid, then species with long generation times and limited dispersal may be unable to keep pace with it. Additionally some species need a vector to move their seeds, for example, jays effectively transport oak acorns and climate change may or may not affect these vectors in similar ways. Further, dispersal across a landscape substantially modified and fragmented by human developments (e.g. in Europe), may not be possible and also depends on the rate and extent of disturbances that may provide sites for regeneration en route. However it is also likely, given the extensive landscape management that is taking place in most countries, that specific choices can be made as to which species, particularly in the case of trees, can be planted in any particular site. This choice is likely to be made based on a number of factors: some economic, some related to biodiversity and some related to current and future environmental conditions.
A species may also survive in areas where the climate has changed because of a differential response to climate at different stages in its life cycle. Norway spruce juveniles, for example, seem to be more sensitive to warmer winters (>−1.5°C mean coldest month temperature) than established mature individuals (Sykes and Prentice, 1996). This sensitivity may be related to the reduced protective cover provided by snow at temperatures close to 0°C, especially in the spring when late frosts can be damaging to juveniles. This differential response implies that species may survive as mature individuals for hundreds of years outside their climate envelope until some disturbance (wind, fire) removes them, with no juveniles available to take their place.
In summary, climate change is likely to change spatially the range or envelope that a species can occupy. Ranges may expand polewards in high latitudes as most warming is likely in these latitudes. It could lead to low-latitude boundaries that are contracting with possibilities of extinctions. To survive, a species may therefore need to be able to disperse to new and more suitable climates. This may or may not be possible, depending on the speed of climate change, the species-specific dispersal capabilities, the degree of landscape fragmentation and the possibility of human management.
Effects of climate change in the past
Climate changes have always occurred and vegetation always responds to such changes. Wyatt Oswald et al. 2007 showed that spatial patterns of vegetation across southern New England during the postglacial period are a response to the development of a regional climatic gradient. Environmental change can alter range and abundance of species, remembering that species respond in an individualistic way to their environment. Additionally climates from the past can give combinations of species not currently seen in present-day climates (nonanalogue communities) and, of course, plant communities can change through time as the environment changes. Climate has also been shown to closely control vegetation in another study from New England. Shuman et al. 2004, using lake sediments, found that rising temperatures approximately 14 600 years BP correlated with increases in spruce (Picea), shifts to warmer and drier conditions 2000 years later, correlated with a switch to pine (Pinus) species and 3000 years later with increased moisture availability a shift to Hemlock (Tsuga canadensis) and beech (Fagus grandifolia) occurred.
During the last ice age the range of many northern hemisphere species contracted away from the advancing ice sheet. Some species were restricted to refugia as a result, whereas others may have been scarce but widely distributed, for example, North American beech (Fagus grandifolia) (Bennett, 1985). However with the ending of the ice age and the retreat of the ice sheet, there were many elements, both environmental and geographical, that controlled the response of the vegetation to the changing climate. Using reconstructed forest composition maps, from fossil pollen, of eastern North America, Delcourt and Delcourt 1991 discuss the changes that occurred in species range margins and population centres influenced by climate as well as changes in the Atlantic coastline, the position of the Laurentide ice sheet and the changing locations of various proglacial and postglacial lakes.
In Europe, many species became restricted to small refugia in southern Europe (Bennett et al., 1991) leading to small populations genetically isolated (Willis and Whittaker, 2000). Recent evidence suggests, however, that some species survived further north than previously thought (Petit et al., 2003). Bhagwat and Willis 2008 concluded that typical traits or attributes of tree species restricted to southern refugia include large seeds and a current day reduced northerly distribution while more generalist wind dispersed species were found to be much more widespread into northern refugia. For example, European beech (Fagus sylvatica), which has large seeds and is one of the most important and widespread trees of present-day Europe, was restricted to very small populations in southern France and Italy and in the Pyrenees, Cantabrian mountains and Croatia-Slovenia (Magri et al., 2006) (Figure 1). However, Scots Pine (Pinus sylvestris) is wind dispersed with a current day northerly distribution and was found with a much wider distribution in the early Holocene in the Alps, the Hungarian plain and the Danube (Cheddadi et al., 2006).
The rate of migration or dispersal for species once the ice sheet began its retreat and the implications for the future response of species is much discussed. Estimates for the rate of migration for species vary and are species-specific depending in part on their mode of dispersal (e.g. wind or animal). Additionally if, as Bhagwat and Willis 2008 suggest, some species survived in more northerly refugia, rather than requiring long-distance dispersal events from refugia much further south in Europe, then for some species this rate may be substantially less than what has been previously suggested. This has implications for future climate change especially where fragmented landscapes are involved and suggest that some species may not reach new climate space without human intervention.
Our understanding of how climate may have influenced vegetation in the past and how it may do so in the future must include an awareness that species also respond to changes in year-to-year climate. Climate in all its aspects varies from year to year; some winters are colder than average, some warmer, some drier, some wetter, likewise in other seasons. This variability may well not influence the performance of a species in the middle of its climatic range, but for those species that inhabit climate space near the edge of their acceptable climate space, their climate ecotone, then variability could be important. Miller et al. 2008 show that at species boundaries or ecotones the competitive relationship between species in their response to climate can influence the nature and structure of the vegetation.
To summarise, understanding how species have responded to past climate change can provide some indicators for how species and vegetation may assemble under future climate change. It is however unlikely, given the substantial degree of human modification of current landscapes, to provide a clear picture of future species patterns of movement and distribution.
Effects of climate change on plant productivity
Plant productivity is likely to increase in a climate that becomes warmer and where there is enough soil moisture. Precipitation per se has in general little direct effect on plants as they normally take up most of their water and nutrients from the substrate or soil on which they are growing, though precipitation is clearly important for the level of atmospheric and soil moisture. The humidity (or water vapour) of the air influences movements in the stomata or pores within leaves, a response that controls the flow of carbon dioxide in and water out of the plant. Plants need to maintain a balance between growth and survival. Plants require photosynthesis and the production of carbohydrates, which requires CO2, for growth; and stomata need to be open to allow carbon dioxide to diffuse into the leaves. However, open stomata also mean the loss of water through transpiration. In wet areas the balance between these two requirements is less of a problem than in drier areas, where survival and growth have to be balanced. Increasing atmospheric carbon dioxide has been suggested as having the potential to increase plant productivity and growth, both through the fertilization effect of more carbon dioxide available for photosynthesis and the role it may play in plant water use efficiency. There is much discussion about these aspects and various long-term free-air carbon dioxide enrichment (FACE) experiments are underway in different ecosystems to assess the effect of increased levels of carbon dioxide on ecosystems (see review by Ainsworth and Long 2005). Results are mixed but tend to show that there is a fertilization effect at least in young forests. However, long-term effects and the effect of plant acclimation to carbon dioxide are not clear. Additionally the reduced movement of water through the stomata under elevated carbon dioxide could be important, especially in drier areas. However, the subject remains controversial.
Forecasting responses to climate change for the distribution of species, ecosystems and biomes
Modelling background to forecasting
Exploring the response of species, ecosystems and biomes to future climate change usually involves some sort of simulation modelling. Models are not real life, but can help explore possibilities and aid understanding of the complex interactions among species in an ecosystem or biome under rapidly changing environmental conditions. There are many models operating at a range of spatial and temporal scales. Equilibrium climate-vegetation models provide snapshot future distributions of species or vegetation types. Climate-driven dynamic ecosystem models simulate the temporal dynamics of species and vegetation interactions as well as the flows of carbon, nutrients and water through ecosystems. All models have a range of assumptions, caveats and uncertainties that users must be aware of before attempting to interpret model outputs.
Models have some sort of climate data – past, current or future – at different temporal or spatial scales as input. Past climate data can at least in part originate from historical instrumental records that are either site-specific or have been interpolated onto a standard spatial grid. Instrumental records are usually no longer than 100 years or so. Much of the climate data used by impact models come, however, from GCMs, which model gridded climate data for the past and future for short time periods and at large scales (e.g. 3×4° grids). Different scenarios of possible futures are modelled; currently many of these are based on the IPCC Special Report on Emission Scenarios (SRES) (IPCC, 2000). These scenarios represent possible futures depending on the level of current and future greenhouse gas emissions. Emission levels are directly the result of different socioeconomic storylines, which tell of possible future levels of economic development, regional or global solutions, population growth, etc. GCMs use these storylines to provide different climate scenarios, which can then be downscaled to be more relevant for use with impact models. None of these scenarios is likely to be the future but they can be used as exploratory tools.
Different types of models of vegetation have been developed. Statistical bioclimatic, habitat or niche-based models explore statistical relationships between a range of climate variables such as coldest month temperature, annual precipitation, growing season length, etc., and the current day digitized spatial recorded presence of a species (e.g. plants, birds, animals and butterflies). Heikkinen et al. 2006 list a nonexhaustive list of 16 statistical methods.
Another family of models based on simulating important plant physiological responses to climate have been developed for both species and more generalized descriptions of vegetation types or biomes. Prentice et al. 1992 developed the first mechanistic or process-based equilibrium model of vegetation at the global scale (BIOME), based on the idea that a few bioclimatic variables, climate variables that interact with a species biology, can be used to describe vegetation at broad scales. These variables are then compared to various limits required by generalized descriptions of species with similar functions known as plant functional types (PFTs). PFTs that can survive within the specified climate are then amalgamated using a rule-base to give vegetation types or biomes. Such a generalization is required for continental to global scale descriptions and where required information on the bioclimatic responses of hundreds of species is absent. In a major advance, later versions of the model (e.g. BIOME3; Haxeltine and Prentice, 1996) used mechanistic approaches to the modelling of the carbon and water cycles in ecosystems to quantify the net primary production (NPP) within a biome and the impacts of climate change on this.
More mechanistic and generalized formulations in equilibrium models such as BIOME3 led to the development of mechanistic dynamic and generalized global vegetation models (DGVMs) which could be used to simulate both changing climates and concentrations of atmospheric carbon dioxide at continental to global scales (Cramer et al., 2001). They use time series climate data and simulate the impacts of a changing climate on vegetation and various ecosystem processes especially carbon and water flows. Most DGVMs use physiologically robust representations of important plant processes such as photosynthesis (Farquhar et al., 1980) and have been extensively benchmarked against data and against each other (e.g. Cramer et al., 2001). They have been used with climate model output to predict changes in the distribution of global biomes, vegetation dynamics and changes in biogeochemical cycling, such as changes in water and carbon fluxes from vegetation and soil (Sitch et al., 2003).
At local to landscape scales, forest ‘gap-models’ (Botkin et al., 1972) were originally used to explore forest community dynamics through time and were then further developed to include climate change responses though physiological processes, such as photosynthesis, were parameterized in a simple way and it was difficult to generalize beyond specific sites or regions (Sykes and Prentice, 1996). The physiological improvements developed for DGVMs were then coupled with gap model principles to give models that simulate ecosystems at policy relevant scales such as landscapes. LPJ-GUESS (Smith et al., 2001) is such a model developed for local to regional to global applications. It combines the process-based biogeochemistry of the widely used Lund–Potsdam–Jena dynamic global vegetation model (LPJ-DGVM; Sitch et al., 2003) with a detailed individual-based representation of forest stand structure and dynamics including age classes or cohorts of different species of PFTs. Individual tree species can be distinguished, accounting for differences in phenology, allometry, bioclimatic tolerances and life history strategy, etc. Physiologically based models of this type simulate a relatively restricted number of species or PFT dataset because relevant physiological data are lacking for many species and cannot thus simulate the distributions for hundreds of species (plants, animals, butterflies, reptiles, etc.) as has been done by statistical models.
A current strategy is tending to merge the different approaches as dynamic vegetation models can describe vegetation change in terms of habitats at a scale dependent on the scale of the climate data. These can then be used with, for example, statistical descriptions of other species distributions (e.g. birds) to explore climate change effects on both individual species and their habitats.
Projections with regard to species distributions have been made extensively, especially in Europe, where it is generally predicted to become warmer in the north and drier in the Mediterranean with a general shift of climate space from the south-west to the north-east (Ohlemüller et al., 2006). Thuiller et al. 2005 suggested that more than half of the 1350 European plant species that were modelled are vulnerable to climate change by 2080 through changes in growing season length and moisture availability, though results were climate scenario dependent (Figure 2). Mountain and Mediterranean species were most vulnerable, whereas boreal zones could expect immigration of species from the south; northern mountains could also lose their more specialized species as treelines move up in altitude (Rickebusch et al., 2007). In North America tree species are likely to undergo similar processes with local extinctions on their southern boundaries, due to increased drought mortality and reduced reproduction, but with improved exploitation of new habitats in the north (Morin et al., 2008). Tree species on their northern range limits in British Columbia are projected to gain potential habitat at 100 km per decade. However, the rate of dispersal is likely to be a problem in many places especially through fragmented landscapes (Hamann and Wang, 2006). Skov and Svenning 2004 suggest that forest herbs will be required to move 2.1–3.9 km per year (depending on climate scenario) to track their climate space. Moreover, this implies that suitable forest is available through which they might move. Whether migration delays are a real problem for trees is, however, debatable in areas where humans heavily influence the landscape as they may just plant a required species. The situation for other species, both plant and animal, may, however, be more problematic.
The arctic generally is expected to be one of the areas most affected by climate change including changes in biodiversity, treelines and biome shifts. Kaplan and New 2006, for example, using 6 GCMs with 4 emission scenarios and the BIOME4 equilibrium vegetation model project large biome changes with a 2°C warming. Forest area between 60°N and 90°N could increase by 55% (3×106 km2) with a reduction of 42% in tundra. Tundra vegetation moves north but with a significant loss in prostrate dwarf-shrub tundra. More specifically in the Barents region (northern Scandinavia, Russia, Novaya Zemlya, Svalbard and Franz Josef Land), model predictions indicate an increase in boreal needle leaved evergreen forest northwards and up mountains, increased NPP and leaf area index (Wolf et al., 2008). It remains unclear, however, if migration rates of trees could in fact match the climate change.
Changes in vegetation types can be seen as changes in habitats for many different species. Hickler et al. 2009 project possible changes in potential habitats (i.e. without land cover/use changes) under different GCMs and emission scenarios for Europe (Figure 3). One particular outcome from these simulations highlighted possible major changes in habitat types in many of the currently designated Natura 2000 sites in Europe. Projections of such habitat changes can also be related to changes in other species groups. Preston et al. 2008 incorporated biotic interactions (dependence on semiarid shrublands) into species distribution models of two endangered species (a butterfly and a bird) in southern California and projected their responses to climate change. Habitats were reduced at all levels of increased temperatures and both species were also sensitive to increasing precipitation. They concluded that reserve design that considers biotic interactions is important especially for habitat specialists. The interaction between habitats and climate change is also shown by Malcolm et al. 2006, who, using vegetation types or biomes as proxies for habitats, explored the effects of climate change on endemic species in biodiversity hotspots. Especially vulnerable areas include Mediterranean type ecosystems, the Caribbean, Indo-Burma and the tropical Andes.
Plant productivity is forecast to increase not only as a result of a longer growing season especially in the north but also as a result of the direct effect of elevated carbon dioxide. However in already dry areas such as southern and south-east Europe, where climate models predict warmer temperatures and reduced precipitation, productivity may be substantially reduced (Morales et al., 2007). However, if canopy conductance is reduced because of increased water use efficiency that can take place under high carbon dioxide levels, this reduction may be less or even not occur. With regard to forest productivity and the requirements of the forestry industry, changing climate and increasing carbon dioxide at the global scale is likely to increase productivity and affect a range of forest ecosystem services including timber supply. There are, however, regional variations as well as impacts on fires, insect outbreaks and extreme events (Kirilenko and Sedjo, 2007). In California, for example, all future climate scenarios used by Lenihan et al. 2008 project the area burned by fire increasing 9–15% above the historical normal by 2100.
In summary, climate zones are projected to move latitudinally towards the poles, particularly in the Northern Hemisphere; they are also expected to move up in altitude in mountainous regions. In the north, winter temperatures are likely to become warmer while precipitation in the south is likely to decrease. Species will respond to these changes in different ways and their ability to track these changes could depend on their dispersal ability and the degree of fragmentation in the land cover they have to move through. It is also likely that mismatches among interacting species such as pollinator–plant species could contribute to extinctions. Additionally there is the possibility that vegetation and thus habitats in currently identified conservation areas may change substantially, raising serious questions with regard to short- and long-term conservation policy in some regions.
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