Forest dieback

Catastrophic breakdown of ecosystems can also be observed in natural ecosystems, without the influence of alien species. One such global problem is forest dieback (Mueller-Dombois, 1986), which is occurring over the globe without obvious cause. Hosking Hutcheson (1986) have made observation on dieback in the evergreen broadleaved forests of New... 

Betts R, Cox P, Collins M, Harris P, Huntingford C, Jones D. The role of ecosystem-atmosphere interactions in simulated Amazonian precipitation decrease and forest dieback under global climate warming. Theoretical and Applied Climatology, 2004. 78(1) pp. 157-175. doi 10.1007/s00704-004-0050-y... 

If, for example, S02 undergoes autoxidation on a wet leaf, the result might include not only acidification, but also the generation of highly reactive species, which should be considered when assessing the cause of such phenomena as forest dieback (28). 

These oxidants could be involved in the forest dieback this theory will be later discussed. 

Nihlgard, B. (1985). The ammonium hypothesis—An additional explanation for the forest dieback in F.urope. Amhio 14, 2-8. 

In this paper, we concentrate more specifically on the causes of the damage. Chemical analysis of needles and soil were perfomed in order to reveal possible nutritional imbalance able to explain the forest dieback.Physiological disturbances in yellowing trees were also analysed. Investigations were carried out in three areas of the Pyrenean massif the Luchonnais, vallee d Aure and Pays de Sault (figure 1) who show various climatic and edaphic features and different intensities of decay. 

In the last decades, an almost general consensus among scientists has emerged that forest dieback would not have occurred without the influence of air pollutants. The chronic impact of gaseous and dissolved pollutants, enhanced by the filtering action of tree canopies, has lowered the vitality of the forest ecosystems probably... 

Zealand. In the North Island, at moderate altitudes (300-600 m), the hard beech (Nothofagus truncata) may be the sole and dominant species of the forest. Since the mid-1970s there has been a marked dieback of Nothofagus, without replacement and particularly at lower altitudes. 

For a long time, dieback and decline of specific forest species, somewhere in the temperate zone, has been common. Age, climate, or biotic stress factors have frequently been judged to be the principal causes for declines. Again, however, it is difficult to assign responsibility for specific cause and effect. Trees are large and long-lived and their health integrates all the stresses to which they are exposed over time. 

These oxidants, obtained by photochemical reactions in the atmosphere, may be involved in the widespread dieback and decline of forests in both Europe and North America. The O3 and photooxidants theory, and its influence on acid deposition, will be shortly presented and discussed. 

Mueller-Dombois, D. (1987). Natural dieback in forests. BloSclence 37, 575-583. 

After about three decades of extensive research on acid deposition some of the effects of acidity in regions devoid of any buffering capacity are well known. Leaching of calcium and mobilization of toxic aluminum from soils and often profound changes of plant and heterotrophic species composition in lakes, including the demise of the most sensitive fishes, amphibians and insects, are the most deleterious and indisputably established impacts. In contrast, the exact role of acid deposition in the reduced productivity and dieback of some forests remains uncertain. ... 

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