Population dynamics of some major woody species in relation to long-term succession on the dunes of Voorne

Abstract

This study is a follow-up of medium-term succession studies based on a vegetation map, scale 1:2 500, of the dunes near Oostvoorne made in 1959 and 1980. The area has a marked zonation with partly very young dunes and inner dunes at a distance of >1 200 m from the beach which are 800 yr old. The overall succession trend is a development from a largely open vegetation (resulting from overgrazing in the 19th century, which ceased 1910), to a scrub/woodland complex with locally dying off of patches of woody vegetation. To understand the processes of change, the age structure of most of the major woody species was determined.

Two transects were followed in the area running from the seaward coastal ridge towards the inner dunes. 86 plots were analyzed as to represent the vegetation types distinguished in 1980. In each plot all trees and shrubs were estimated on age by means of increment boring and counting of annual rings. The abundance of seedlings and saplings (<4 yr old) of all woody species was estimated in all plots.

The most important woody species are Betula (most B. pendula + some B. pubescens). Crataegus monogyna, Rhamnus catharticus, Sambucus nigra, Alnus glutinosa, Quercus robur, Salix (most S. cinerea + S. aurita and their hybrid S. multinervis). Hippophae rhamnoides, Ligustrum vulgare, and Salix repens, three important early successionals, could not be aged easily.

Age distribution curves show a marked stand-still in development in the 1960s. Some species stopped rejuvenating at all. Cumulative development curves for different zones show a clear change in growth rate over the zones for Crataegus and a simultaneous rapid development for Crataegus.

Two examples of species sequence within a community type are shown. An explanation of these results includes three main factors: (a) overall changes in the whole area related to disturbance and relaxation, (b) soil moisture and (c) rabbit grazing. Two main events in the development of a population are considered: germination and early development of the seedling, and untimely death of a dominant.

Nomenclature follows Arnolds & van der Meijden (1976), Standaardlijst van de Nederlandse flora, 1975. Rijksherbarium, Leiden.

Research on population dynamics reported on in this paper was carried out by de Cock & de Wildt as MSc students and supervised by van der Maarel, then all at the Division of Geobotany, University of Nijmegen, Nijmegen, The Netherlands. The preparation of the paper including some new observations and calculations were done by the first author in the framework of the project ‘Population dynamics of woody species in primary successions’ supported by NFR, the Swedish Natural Science Research Council.