Climate Change and Variability

Climate change is emerging as one of the most important issues of our time, with the potential to cause profound cascading effects on ecosystems and society. However, these effects are poorly understood and our projections for climate change trends and effects have thus far proven to be inaccurate. In this collection of 24 chapters, we present a cross-section of some of the most challenging issues related to oceans, lakes, forests, and agricultural systems under a changing climate. The authors present evidence for changes and variability in climatic and atmospheric conditions, investigate some the impacts that climate change is having on the Earth's ecological and social systems, and provide novel ideas, advances and applications for mitigation and adaptation of our socio-ecological systems to climate change. Difficult questions are asked. What have been some of the impacts of climate change on our natural and managed ecosystems? How do we manage for resilient socio-ecological systems? How do we predict the future? What are relevant climatic change and management scenarios? How can we shape management regimes to increase our adaptive capacity to climate change? These themes are visited across broad spatial and temporal scales, touch on important and relevant ecological patterns and processes, and represent broad geographic regions, from the tropics, to temperate and boreal regions, to the Arctic. 4.1 Validating and quantifying vegetation turnover A 5 to 10% change in plant composition in the same plot between two following censuses, or with different survey methods, is common without any environmental change (Archaux et al., 2006; 2007). But in such a case this change is not related to a specific gradient, as plants within a given group replace each other. In this study, the most mesophilous and xerothermophilous plants (Meso+ and sXT groups) were more concerned, respectively loosing and gaining more than intermediate ones. Meso and XT groups also showed a significantly unbalanced turnover. The real turnover did not concern only the species at the very limit of species distribution for each plot. More distributed variations along the gradient give a lower If shift on axis one, but the same trend as far as species appear and disappear symmetrically. It may explain why the observed turnover was weaker than the simulated one. Although observed patterns of flora turnover were more complex than the simulated ones, they validate the method used for the simulation. The observed trend is clearly biased towards heat and drought resistant plants. It is opposed to what is expected in aging forest structures. Indeed, in Southern Europe the Mediterranean ecosystems were transformed by several thousand years of disturbances and development (Blondel and Aronson, 1999). The natural evolution of the unmanaged stands of this study, most of them adult but far from senescence, should be a maturation process leading to an increasing dominance of mesophilous and shade tolerant plants and the reduction of light demanding, generally xero-thermophilous species, inherited from past land uses (Tatoni and Roche, 1994). Probably, the adverse climate conditions in the last decade also contributed indirectly to a hotter and drier microclimate in the undergrowth, limiting canopy density though tree mortality (Allen et al., 2009), low branching rates and reduced leaf area (Thabeet et al., 2009). The potential turnover (25%) simulated on plot scale in this study with the climate expected in the middle of the 21st century hold with previous studies on larger scales: Bakkenes et al (2002) showed that 32% of the European plant species that are present in a grid cell of a few square kilometres in 1990 should disappear from that cell before 2050. High rates of potential extinction among endemic species (average 11%, up to 43%) were forecasted by Malcolm et al. (2006) for the whole Mediterranean basin and other biodiversity hotspots in the world by 2100. 4.2 Flora resistance on landscape and local scales Plant composition turnover observed in the last decade was significant but not as considerable as simulated by the model. A resistance to climate variations was observed, which may be partly explained by landscape structure. Bi index mapped at any scale is laid out like a patchwork of fragmented bioclimatic classes. When topography and soil are added on local scale, six among the nine classes represented on regional scales with medium site conditions can be found on a single square kilometre of hilly landscape with steep slopes and only one or two hundred meters of difference in elevation. Thanks to that fine grain mosaic, xero-thermophilous plants are scattered everywhere even at high elevation, taking advantage of steep south-facing slopes, shallow and rocky soils. Most of the time, some of them simply remain from degraded ecosystems inherited form former land uses The main objective of this chapter was to show that computed yields give additional information about climatic variability compared with the traditional use of individual meteorological elements. Our results indicate that none of the observed separate meteorological factors sufficiently reflects the variations in the computed MPY series. We found significant linear correlations for only the western Estonian coastal zone, represented by the station at Kuressaare, because of the dominant limiting factor, the water deficit during the first half of summer in most years. Although the polynomial correlations were higher, indicating a dual influence of the factors, there was still high variance. The significant changes in MPY variability, as observed in Tartu in the second half of the period, were only weakly expressed in the precipitation series and were absent from the temperature and radiation data. Evidently, the combined effects of weather conditions on plant production processes have a more complex character than can be measured with longterm statistics for individual meteorological elements. Consequently, the use of MPY to express the agrometeorological resources available for plant production in yield units introduces additional information about the impact of climatic variability. The changes in MPY and their statistical distribution are better indicators of the impact of climate change on plant production than are changes in the time series of any individual meteorological elements. This holds particularly true if simulations for species adapted to local climatic conditions are used. If species are located at the borders of their distribution areas, some meteorological factors will predominantly limit their growth and will describe the climatic resources without being combined with other factors. The MPY series collected through 83106 years revealed no significant trends. However, significant trends do exist in terms of shorter periods. The variability of MPY has been increasing in the island regions of Estonia since the 1940s and in the continental areas since the 1980s. The above-described results have been further expanded into the future and future values of meteorologically possible potato crop yield have been generated. This allows to estimate the influence of climate change on agrometeorological resources for potato growth in Estonia. All of the four climate change scenarios projected the increase in annual mean temperature for Estonia, the highest warming during the cold part of the year. Average annual precipitation was also predicted to increase, however, changes in the annual range of monthly precipitation vary highly between models and scenarios and are less certain than changes in temperature. All the projected climatic tendencies have already been noted in observations during the last century (Jaagus, 2006), indicating evident climate warming in Estonia. Changes in MPY were calculated using historical weather variability and projected changes in mean monthly values. For early potato variety, all scenarios predict losses in potato yields, while the scenarios of more notable warming cause higher losses. For late variety, a The results of EFIMOD model simulations to specify a possible effect of forthcoming climate warming allowed for preliminary quantification of the effects of this environmental change on boreal forests in North America and Europe. In Central Canada, the black spruce and jack pine forests respond to climate warming, fire, harvesting and insects by significant modification of net primary productivity (NPP), soil respiration (Rs), net ecosystem production (NEP) and pools of tree biomass and soil organic matter (SOM). The simulated effects of six climate change scenarios demonstrated the similar increasing trends of NPP and stand productivity. The disturbances led to a strong decrease in NPP, stand productivity, soil organic matter (SOM) and nitrogen (N) pools with an increase in CO2 emission to the atmosphere. However the accumulated NEP for 150 years under harvest and fire fluctuated around zero. In jack pine forest, it becames negative only at a more frequent disturbance regime with four forest fires. In black spruce stands, it is slightly negative also in a case of four fire scenario as well as for harvest and two fires during the period of simulation. The results from this study show that climate warming and disturbance regimes might substantially change the NPP as well as the C and N balance, resulting in major changes in the C pools of the vegetation and soil under black spruce forests. Soil conditions, especially its productive potential determining by the N pool, modify the effect of climate change and disturbances: poor soils contrasting relative effect of climate change and damages, contrariwise more rich soil mitigates the effect of damages and climate change. In Russia, the effect of climate change in Norway spruce forests has the same dynamic patters as in Canadian black spruce forests. However, Scots pine forests on dry sandy sites lose both soil C and forest productivity. This reaction reflects a difference of environmental condition in Canadian jack pine stands in central boreal forest with harsh continental climate and Russian Scots pine stands in rather warm climate near the border of boreal and temperate broad-leaved forests. The results of selective analysis of EFIMOD simulations using experimental data of long-term ecological researches (Recognition project, Kahle et al., 2008) show the uniformity of forest