Abstract
The grey heron (<em>Ardea cinerea</em>) is a good example of an engineering species that forms nesting colonies (called heronries) composed of up to a few hundred nests during the breeding season. It exerts strong pressure on surrounding vegetation, mainly because of the heavy input of organic matter and high eutrophication. The birds also alter light conditions through direct tree damage. We aimed to examine the influence of a grey heron breeding colony on the soil properties and functional composition of the herb layer in two different forest communities: a suboceanic pine forest and a riparian mixed forest. We also wanted to establish whether these changes would make the forest ecosystem more vulnerable to colonization by nonforest species with higher light and trophic demands. Small-seeded, light demanding eutrophic species showed a tendency to be more abundant under the nests in both forest types. The calculated odds ratio (OR) showed that the probability of the presence of nonforest species under the nests was 29.5 times higher than that in the control plots (56 plants species were analyzed). Additionally, the nonforest species appeared to have high light and trophic demand (OR of 12.3 for light demand; OR of 7.0 for trophic demand), which explains the species turnover observed in the bird-affected microhabitats.
Highlights
The term “ecosystem engineers” was first used in ecology by Jones et al [1,2]
The acidity of soil in the nesting sites decreased in the pine forest slightly, albeit insignificantly, whereas a significant increase was observed in the riparian forest
The study showed the influence of a breeding colony of the grey heron on the edaphic conditions and plant cover structure of two different forest communities: a pine forest and a riparian forest
Summary
The term “ecosystem engineers” was first used in ecology by Jones et al [1,2]. As defined by the authors, an ecosystem engineer is an organism that indirectly changes the availability of resources for other organisms through physical modifications of the habitat [1]. If not all, ecosystems owe their structure to the engineering activity of living organisms, this activity might be easy to overlook because of its indirect nature. While most organisms influence the abiotic conditions of their environment in some way, the scale of the impact depends on many factors, including the qualities of both the engineering species and the modified ecosystem [1,2,3]. The grey heron (Ardea cinerea L.) can be considered one such engineering species. The presence of a heronry exerts strong pressure on the surrounding vegetation, mainly because of the heavy input of organic matter
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