Early scrub development in De Westhoek coastal dunes (Belgium)

Abstract

Coastal dunes in Northwestern Europe were subject to substantial scrub expansion during the past decades, a process often considered as a major problem for conservation management. This paper explores this process in De Westhoek nature reserve (Belgium), focussing on the three major constituents of the early scrub: Salix repens, Hippophae rhamnoides and Ligustrum vulgare. We study changes in dominance pattern between 1953 and 2010 based on vegetation maps and the demography of these species based on growth ring counting. We relate this data to the edaphic factors soil moisture and soil age. Early scrub development occurred in three phases: (1) rapid, mainly secondary scrub expansion after release of grazing pressure, (2) a main shift in relative abundance of the three main species, and (3) further succession into tall scrub and woodland along with local scrub decay. Edaphic factors play a major role in vegetation dynamics, but their relative importance diminishes along with landscape ageing. Simultaneously, the outcome of competitive interaction between scrub species, in which population demography plays a key role, gains importance. Primary and secondary scrub development seem to converge in terms of dominance patterns of S. repens, H. rhamnoides and L. vulgare. Spontaneous decay of mainly L. vulgare offers an opportunity for dune managers for the restoration of herbaceous dune vegetation with high conservation value.