The restoration of coastal shingle vegetation: effects of substrate composition on the establishment of seedlings.
Abstract
Shingle beach vegetation at Sizewell, Suffolk, UK, was extensively damaged by the construction of a power station. The feasibility of restoring the vegetation by directly sowing seeds of species important in the existing plant communities was investigated in the field and in glasshouse experiments. The species sown were Crambe maritima, Eryngium maritimum, Glaucium flavum, Lathyrus japonicus and Rumex crispus. The field experiment examined the effects of proximity to the sea, composition of the beach substrate, and its amendment with organic matter on seedling emergence and establishment. There was little emergence of seedlings during the first season and most occurred in the following spring, between February and April; G. flavum emergence was nearly confined to this period. A low percentage of the viable seeds of all five species had emerged even after two seasons. Greatest emergence was in the monocarpic G. flavum, whereas the relatively long-lived perennials showed lower emergence and slower growth. Only G. flavum produced reproductive plants, in the second year. Seedling emergence was greater in organic matter treated plots for all species and most emerged better from sandy plots than shingle dominated plots. Although G. flavum emergence was greater in sandy plots, seedling survivorship and growth were much greater in shingle plots; mortality showed evidence of density dependence. A glasshouse experiment examined the effects of sowing density and substrate texture on the survival of G. flavum. On shingle, survival was negatively density-dependent, but the much lower survival on sand was density-independent. Consequently, the higher mortality on sandy field plots was probably directly associated with substrate effects. Direct sowing of seeds on the beach cannot be recommended as a general technique for the restoration of shingle beach vegetation, except for annual or monocarpic species. Amendment with organic matter provided little benefit that could not have been achieved more simply by the addition of beach sand to the coarsest shingle substrates.