Oceanicity and the ecological disadvantages of warm winters

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Abstract
Oceanicity is commonly considered as ecologically benign in permitting certain species to extend their northern distribution limits. Although extension of species range, particularly under oceanic conditions, can appear biogeographically striking, it has little influence at the community level as most of the dominant species, even in hyper-oceanic habitats, are of wider distribution and not confined to areas near the coast. Examination of the distribution of plant communities as opposed to individual species, reveals an opposing view, where oceanicity instead of enhancing species diversity through amelioration of potentially stressful environments, has a more powerful influence in creating habitats that are hostile to many species. Plant distribution projections that make an accurate estimate of seasonal temperature differences suggest that warm winters (the current meteorological expectation) may lead to a reduction of the distribution of some species in the UK and adjoining areas of Europe. Warm winters with oscillating temperatures can be harmful through reducing winter dormancy and depleting carbohydrate reserves, particularly in over-wintering woody species. Water-saturated soils, especially in winter and spring, can be particularly injurious to woody species by accelerating carbohydrate depletion leading to root die-back in spring and premature wind-throw of larger trees. In tree-less areas, soil leaching is accelerated, particularly after human disturbance, and leads to nutrient deficiencies and the establishment of oligotrophic communities with reduced productivity. The mild oceanic winter can therefore be viewed overall as ecologically disadvantageous, leading to the spread of bog and acid moorlands, and reducing biodiversity and the potential for productivity both in agriculture and natural communities.