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The biology of coastal sand dunes.
MA Maun. 2009.
Oxford, UK: Oxford University Press. £37.50 (paperback). 288 pp.
Controls are the basis of science and nowhere are they more necessary than in ecology. Biologists are not as fortunate as physical scientists as we have as yet no other planet that can serve us in the search for appropriate comparisons, and we are therefore restricted to what can be found on Earth. The best that can be done is to search for communities that are reasonably ubiquitous in distribution and cosmopolitan in their species' composition so that meaningful comparisons can be made on a worldwide basis. Coastal sand dunes provide this opportunity and we must be grateful that Anwar Maun made a very fortunate choice when he decided at an early age to devote his life to making a worldwide study of coastal sand dunes. With the exception of the Polar Regions, coastal sand dunes are to be found from sub-arctic shores, through temperate and tropical zones, to the sub-antarctic islands of the Southern Pacific Ocean. The ecology and development of coastal communities is strongly linked by geographical continuity facilitating species' migration, which is further aided by maritime winds and ocean currents. This biological continuity provides an unending source of material for comparative ecological studies. Although Maun sadly did not live to see his book published, he did manage to complete most of this perceptive volume before his death in 2007. Dianne Fahselt added the final chapter on sea-level change and Irene Krajnyk collated and proofread the completed work.
This is primarily a biological work. Nevertheless all aspects of the physical features of sand dunes are discussed, from the action of wind on sand grains to their subsequent effects on the geomorphology and migration of sand dunes. The varying interactions of wind, water and sand in different climatic zones are also examined in detail with a global view of the ecological consequences for stability and water relations – including the internal condensation of dew and its role in sustaining vegetation.
The biological examination of dunes starts with the seeds, discussing dispersal, germination, seedling establishment and seed-bank longevity. This is followed by chapters on burial by sand, the effects of salt spray and salinity, mycorrhizal associations, animal and plant interactions, plant communities, and zonation and succession. Possibly the most absorbing chapter is provided by the historical account of the Ammophila problem. For decades ecologists have pondered over the curious fact that marram grass, whether it be the European Ammophila arenaria or the American A. breviligulata, invariably loses vigour when it is not supplied with fresh accumulations of sand. The problem is somewhat paradoxical as tolerance of sand burial for most sand-dune species is a negative factor that has to be overcome and not a requirement for survival. Maun traces the various interpretations of this phenomenon from early studies on nutrient deficiencies to inter-specific competition, lack of anatomical sites for the initiation of new adventitious roots, inhibiting effects of decaying organic matter, accumulation of harmful soil organisms (in particular nematode infections), decline of mycorrhizal fungi and even genetic degeneration. His carefully argued standpoint in this continuing debate favours a multivariate effect of a number of major factors, including soil volume for root and mycorrhizal expansion, and the physiological hormonal response of the plant as a consequence of episodic burial.
When discussing sand dunes from a plant-community and successional point of view we are saved the age-old division of yellow dunes and grey dunes, followed by dune heath and forest. Colour is, after all, merely a reflection of the nature of the local sand, and whether a lichen-rich grey dune-heath or a forest develops is also governed by local factors including propagule availability, grazing and human disturbance. The chapter on plant–animal interactions covers the entire gamut from nematodes to insects, birds and mammals, which is a surprisingly rich list given that it is not so much the dunes but their surrounding inland, littoral and maritime habitats that provide sustenance and shelter for the coastal fauna.
The final chapter on ‘Dune systems in relation to rising seas’ written by Dianne Fahselt opens up many fresh lines for future investigation as to how dune systems have responded to episodic changes in sea levels in the past and may do so in the future. Dune systems are historically mobile physically and also adaptable physiologically, and have survived many environmental changes in the past. Being widespread throughout the World, and with their coastal migration routes better preserved than inland communities, they should be expected to adjust to rising sea levels, provided negative human intervention can be avoided. However, as pointed out, a rapid rise in sea-level may be detrimental by imposing rates of burial that are higher than some species can tolerate.
No ecological book can ever cover everything that has to be said about a habitat. Topics that might have been broached could have included genetic variation in coastal species, together with a somewhat deeper metabolic treatment of the limits to survival in differing environments. Nevertheless, the book is a mine of information, especially from a historical point of view, and provides a refreshing reminder of the efforts of past researchers, which is always valuable if needless, uniformed repetition in future research is to be avoided. This posthumous work is to be greatly welcomed as it is the synthesis of a lifetime of perceptive observation and experimentation into coastal dune systems throughout the World, and is an excellent addition to any ecological library, public or private.