Effects of trampling on beach plants at the Baltic Sea

In the last century, increases in human population and beach tourism have affected coastlines worldwide. Resulting pressures on beach ecological systems demand research concerning tolerance of beach plants to disturbance by humans. At three different Baltic Sea beaches, Atriplex prostrata, Honckenya peploides and Crambe maritima were planted and observed while subjected to trampling stress intensities of 0, 1 and 2 footsteps center dot m(-2)center dot d(-1). Plant height, leaf growth, number of leaves, chlorophyll content of leaves and fitness of photosystem II were measured at monthly intervals. Survival of plants was documented until the following summer. Linear mixed effect models fit the effects of trampling intensity, time and species on growth, photosynthetic productivity and reproduction of plants. Survival was fitted using general linear mixed models for binomial data. The results indicated that the annual species A. prostrata showed an initial decrease in growth at the first trampling treatment, but no effects on seed weight due to trampling pressure. Honckenya peploides was not affected by trampling. Crambe maritima showed a reduction in growth and survival under any level of trampling pressure. Experimental trampling pressure was compared to observed trampling intensities at beaches with low visitor frequency, which was ascertained to be between 3 and 8 footsteps center dot m(-2)center dot d(-1). Because of the greater potential of endangerment for C. maritima, we suggest that nature conservation focus on reducing human trampling on the upper beach area, e.g. by closing this area. This practice would allow tourists continued recreational access to the water as well as to the lower beach area.