Coastal Dune Succession Research Articles

Aphid herbivory as a potential driver of primary succession in coastal dunes

Herbivory is a major factor affecting both the performance and the fitness of the species composing a plant community and, ultimately, conditioning its temporal and spatial dynamics. Coastal dunes are a typical example of primary succession where different biotic and abiotic factors determine plant species occurrence; however, the effect of insect herbivory herein has remained little explored. To address this matter, we combined an observational study along a successional gradient with a green-house experiment to determine the occurrence and the impact of plant–aphid interactions. We focused on the species Schizaphis rufula, a widespread and abundant aphid associated with dune grasses in early stages of primary succession in Europe. Firstly, we studied aphid infestation rates on the dune grass Ammophila arenaria along a succession gradient in three locations of the North Sea coast to address the relationship between plant community composition and aphid occurrence; secondly, we tested the effect of aphid herbivory on a set of dune species typical for the different stages of succession. We found that the degree of aphid infestation was inversely correlated with the degree of dune fixation. The results of the experiment showed that aphid multiplication was significantly higher and its effect more pronounced on two early successional grass species, i.e. A. arenaria and Leymus arenarius. Here aphid multiplication resulted in a severe decrease in plant biomass; in late successional grass species, there was limited multiplication and no effect on biomass. The results of the field survey and the green-house experiment indicate that aphids show a clear preference for plants from early successional stages and, moreover, they have a greater impact on these plant species. All this supports the hypothesis of aphid herbivory as a driving factor of primary succession in coastal dunes.

Facilitation in multiple life-history stages: evidence for nucleated succession in coastal dunes

Understanding plant interactions during succession is a central goal of plant ecology. The nucleation model of succession proposes that facilitative interactions lead to outward radiations of colonization from established plants. I tested the nucleation hypothesis for early successional plants on the primary dunes of barrier islands in the southeastern United States. On the coast of Florida and Georgia, I sampled the above-ground vegetation and the seed bank, and conducted a seedling emergence experiment in the field. Vegetation sampling at both field sites showed more positive correlations in percent cover of adult species than expected by chance. At both sites, there were significantly more seeds under plants than in open microsites. Seeds of the same species as the adult plants in the vegetated microsites were removed from the analysis, so the accumulation of seeds under adults is not due simply to a seed shadow effect. Seeds of six species were added to plots under plants and in open microsites, and seedling emergence was significantly higher under plants than in the open. The findings support the predictions of the nucleation hypothesis for the early life-history stages of seed dispersal and germination, and help to explain the clumped distribution of dune plants seen in the field. The results add further support for the contention that facilitation is an important mode of plant interaction in stressful and disturbed habitats.

Nematodes in a coastal dune succession: Indicators of soil properties?

The nematode fauna of coastal sand dunes in the Slowinski National Park (Poland) were studied. Within the wet parts of dune hollows, vegetational succession starts from bare wet sand gradually colonized by grasses and mosses, and changes to plant communities dominated by sundew and heath. The aim of the study was to determine whether vegetation succession was accompanied by a parallel succession of the nematode fauna. Samples were taken from 12 subsequent stages of vegetational succession. The extracted nematodes were determined up to genus level after Bongers (1987). The percentage of nematodes of different feeding types (bacteriophagous, fungivorous, predators, plant-parasitic and omnivorous) was calculated for every site. Soil moisture (average water table and actual water content), the existence of an upper organic soil layer and pH seem to be the key environmental factors influencing nematode community structure. Multivariate analysis techniques were used to classify the nematode samples into four groups: A – the nematode community in sites at early succession stages without permanent colonization by plants. B – the nematode community in sites at stages with permanent plant cover (grasses and higher plants). C and D – the nematode communities in sites with a developing permanent and stable soil organic layer, but differing in water regime. Changes in the incidence of nematodes of different feeding types in relation to vegetational succession support this classification. Nematode community structure changed from a high percentage of predators to a dominance of bacterial feeders. Fungal feeding nematodes only occur in abundance in sites with a developed organic layer and higher moisture content (group D), and the nematode community may be a good indicator of the progress of ecological succession in the deflation hollows.

Development of the nitrogen cycle in the soils of a coastal dune succession

SUMMARY The development of the soil nitrogen cycle in a coastal dune succession (xerosere) on the East Frisian Island Spiekeroog was investigated. In 13 sites of different successional age the nitrogen pools in the topsoil (0–30 cm) and the organic soil layers were determined. The nitrogen mineralization was studied at the sites during the vegetation period in 1987 (38 weeks) and winter 1990-91 (14 weeks). Turnover rates and nitrification rates were calculated. The nitrogen pool of the soil was very low in the first stage of the succession (<100 kg N ha−1 30cm−1) and increased rapidly to more than 1500 kg N ha−1 within approx. 200 years. This accumulation rate was strongly exposition-dependent. Mineralization of nitrogen was low in the young sites (15 kg Nmin ha−1 year−130 cm−1) and increased to more than 100 kg Nmin ha−1 year−1 in sites covered by buckthorn (Hippophae rhamnoides) and in dune forest. Mineralization was also exposition-dependent. The annual nitrogen turnover rate was very high in the young dune sands (up to 18%) and was only 2% in the brown dune sand podsols under Empetrum heathland. Nitrification dropped as well in the course of the dune development from 80–90% to 20% nitrate of total mineral nitrogen production over a year. Some hypotheses on nitrogen accumulation and retention during ecosystem and plant cover development are discussed.

Biogeochemistry of nitrogen in a coastal dune succession on Spiekeroog (Germany) and the impact of climate

The nitrogen cycle of terrestrial plant-dominated ecosystems is explained by means of a compartment model. Its main parts are described: the plant-internal cycle, the ecosystem-internal cycle and the global N-cycle, including input-output relations and biological N-fixation. The distribution of total nitrogen (N t ) as well as the net mineralization of nitrogen in the soils of a dune succession on Spiekeroog Island (Germany) are described. Values for 13 different sites are given, ranging from foredunes to climax dune forests in a chronosequence from 0 to > 250 years. In the course of development, the N-pools in the soils increase from approximately 150 kg to more than 3000 kg N t . ha −1 . 30 cm −1