Structural equation modelling detects unexpected differences between bryophyte and vascular plant richness along multiple environmental gradients

Abstract

The relationship between plant species richness and other biotic and abiotic variables is a subject of substantial interest in modern vegetation ecology. Several studies have reported relationships between plant biodiversity and area (Malyshev, ABSTRACTAim The aim of this study was to develop and evaluate a structural equation model explaining the species richness of bryophytes and vascular plants along multiple environmental gradients. Our primary interests in developing this model were: (1) to evaluate the effect of tree canopy along an altitudinal gradient on bryophyte and vascular plant richness; (2) to determine to what extent lithology was able to explain richness in the two groups of plants;(3) to assess whether anthropogenic disturbances decrease richness; and (4) to explore, comparing competing models, the causal links connecting spring area, discharge and spring complexity and to assess how these variables are related to richness.Location Eighty-six springs were sampled in the south-eastern Alps of Italy, from the lowlands to high-mountain regions, and on different lithologies.Methods A structural equation model (SEM) was used to test certain hypotheses about the direct and indirect effects of altitude, canopy, lithology, disturbance, spring complexity, discharge and spring area on bryophyte and vascular plant richness. Competing models were evaluated and bootstrap simulation was used to determine the stability of parameter estimates.Results SEM analysis made it possible to disentangle the different effects of canopy and lithology on bryophyte and vascular plant richness: for the former it was demonstrated that the increased richness with altitude was related primarily to lithology, whereas the latter increased because of the reduction of canopy cover. In addition, the model predicted that spring discharge determined the size of the spring area and even the complexity of the spring; these latter two variables influenced to different degrees both bryophyte and vascular plant richness. Anthropogenic disturbances affected the richness of bryophytes more than that of the vascular plants.Main conclusions Our study demonstrates that several similarities in the patterns of bryophyte and vascular plant richness are in fact induced by different environmental variables.

Patterns of bryophyte and vascular plant richness in European subalpine springs

“…The patterns in b-diversity differed between bryophytes and vascular plants. Many studies have found differences in vascular plant and bryophyte richness pattern (Bruun et al 2006;Grau et al 2007;Spitale et al 2009). Spitale et al (2009) even demonstrated that apparent similarities in the patterns of bryophyte and vascular plant richness could be induced by different environmental variables.…”

“…In addition, ecological studies in springs have the advantage that their areas are clearly differentiated from the surrounding habitats, in particular with a constant presence of water, low temperature fluctuations and nutrient limitation (Cantonati et al 2006). Further, the spring diversity is, generally, also controlled by environmental factors such as hydrological and thermal stability as well as the high oxygen saturation of water, high air humidity and relatively mild winter conditions compared to the surrounding (Spitale et al 2009). The springs can also be helpful in answering questions about differences between bryophytes and vascular plant diversity in response to environmental gradients (e.g.…”

“…The springs can also be helpful in answering questions about differences between bryophytes and vascular plant diversity in response to environmental gradients (e.g. Spitale et al 2009), because both taxonomic groups are abundant and often strong competitors in springs (During and Van Tooren 1990;Bergamini and Peintinger 2002), but they differ in important traits such as nutrition or dispersal ability (Spitale et al 2009;Hájek et al 2011).…”

Phytosociological and ecological study of springs in Trentino (south-eastern Alps, Italy)

“…Floristic differences among the communities of the class Platyhypnidio-Fontinalietea antipyreticae are also conditioned by discharge. In general, as reported in Spitale et al (2009), discharge affects crenic complexity, area and species richness. The largest springs with higher discharge have maximal floristic richness and phytocoenological diversity.…”

“…Crenic vegetation is typically composed of a mixture of vascular plants and bryophytes, with the former prevailing in shaded sites at lower altitudes, and the latter dominating the communities of open habitats, from the subalpine to alpine vegetation belts (Zechmeister & Mucina 1994;Spitale et al 2009). …”