Terrestrial biological systems

Plants and animals can reproduce, grow and survive only within specific ranges of climatic and environmental conditions. If conditions change beyond the tolerances of species, then they may respond by:

1. shifting the timing of life-cycle events (e.g., blooming, migrating),

2. shifting range boundaries (e.g., moving poleward) or the density of individuals within their ranges,

3. changing morphology (e.g., body or egg size), reproduction or genetics,

4. extirpation or extinction.

Additionally, each species has its unique requirements for climatic and environmental conditions. Changes, therefore, can lead to disruption of biotic interaction (e.g., predator/prey) and to changes of species composition as well as ecosystem functioning. Since the TAR, the number of studies finding plants or animals responding to changing climate (associated with varying levels of confidence) has risen substantially, as has the number of reviews (Hughes, 2000; Menzel and Estrella, 2001; Sparks and Menzel, 2002; Walther et al., 2002; Parmesan and Galbraith, 2004; Linderholm, 2006; Parmesan, 2006).

Besides climate affecting species, there are many different types of non-climate driving forces, such as invasive species, natural disturbances (e.g., wildfires), pests, diseases and pollution (e.g., soluble-nitrogen deposition), influencing the changes exhibited by species. Many animal and plant populations have been under pressure from agricultural intensification and land-use change in the past 50 years, causing many species to be in decline. Habitat fragmentation (Hill et al., 1999b; Warren et al., 2001) or simply the absence of suitable areas for colonisation, e.g., at higher elevations, also play an important role (Wilson et al., 2005), especially in species extinction (Williams et al., 2003; Pounds et al., 2006).

1.3.5.1 Changes in phenology

Phenology - the timing of seasonal activities of animals and plants - is perhaps the simplest process in which to track changes in the ecology of species in response to climate change. Observed phenological events include leaf unfolding, flowering, fruit ripening, leaf colouring, leaf fall of plants, bird migration, chorusing of amphibians, and appearance/emergence of butterflies. Numerous new studies since the TAR (reviewed by Menzel and Estrella, 2001; Sparks and Menzel, 2002; Walther et al., 2002; Menzel, 2003; Walther, 2004) and three meta-analyses (Parmesan and Yohe, 2003; Root et al., 2003; Lehikoinen et al., 2004) (see Section 1.4.1) concurrently document a progressively earlier spring by about 2.3 to 5.2 days/decade in the last 30 years in response to recent climate warming.

Although phenological network studies differ with regard to regions, species, events observed and applied methods, their data show a clear temperature-driven extension of the growing season by up to 2 weeks in the second half of the 20th century in mid- and high northern latitudes (see Table 1.7), mainly due to an earlier spring, but partly due also to a later autumn. Remotely-sensed vegetation indices (Myneni et al., 1997; Zhou et al., 2001; Lucht et al., 2002) and analysis of the atmospheric CO2 signal (Keeling et al., 1996) confirm these findings. A corresponding longer frostfree and climatological growing season is also observed in North America and Europe (see Section 1.3.6.1). This lengthening of the growing season might also account for observed increases in productivity (see Section 1.3.6.2). The signal in autumn is less pronounced and more homogenous. The very few examples of single-station data indicate a much greater lengthening or even a shortening of the growing season (Kozlov and Berlina, 2002; Penuelas et al., 2002).

Altered timing of spring events has been reported for a broad multitude of species and locations; however, they are primarily from North America, Eurasia and Australia. Network studies where results from all sites/several species are reported, irrespective of their significance (Table 1.8), show that leaf unfolding and flowering in spring and summer have, on average, advanced by 1-3 days per decade in Europe, North America and Japan over the last 30 to 50 years. Earlier flowering implies an earlier start of the pollen season (see Section 1.3.7.4). There are also indications that the onset of fruit ripening in early autumn has advanced in many cases (Jones and Davis, 2000; Penuelas et al., 2002; Menzel, 2003) (see also Section 1.3.6.1). Spring and summer phenology is sensitive to climate and local weather (Sparks et al., 2000; Lucht et al., 2002; Menzel, 2003). In contrast to autumn phenology (Estrella and Menzel, 2006), their climate signal is fairly well understood: nearly all spring and summer changes in plants, including agricultural crops (Estrella et al., 2007), correlate with spring temperatures in the preceding months. The advancement is estimated as 1 to12 days for every 1°C increase in spring temperature, with average values ranging between 2.5 and 6 days per °C (e.g., Chmielewski and Rotzer, 2001; Menzel, 2003; Donnelly et al., 2004; Menzel et al., 2006b). Alpine species are also partly sensitive to photoperiod (Keller and Korner, 2003) or amount of snowpack (Inouye et al., 2002). Earlier spring events and a longer growing season in Europe are most apparent for time-series ending in the mid-1980s or later (Schaber, 2002; Scheifinger et al., 2002; Dose and Menzel, 2004; Menzel and Dose, 2005), which matches the

Table 1.7. Changes in length of growing season, based on observations within networks.

Location

Period

Species/I ndicator

Lengthening (days/decade)

References

Germany

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