Drivers of plant richness patterns of Mediterranean riparian forests at local and regional scales have bottom‐up and top‐down effects

Abstract

Questions: It has been long recognized that community species richness depends on factors operating at different spatial scales. Most frequently, across-scale studies have focused on the impact of regional factors on local richness (top-down effects) while few have analyzed the importance of local factors on regional richness (bottom-up) and even fewer have tried to integrate effects on both directions. Our objectives were to reveal the key factors shaping plant species richness of Mediterranean riparian forests and to test whether empirical models based on top-down or bottomup relationships are able to explain the spatial scaling of richness.Location: Southern half of Spain, SW Europe. Methods:We designed two structural equation models integrating relationships between biotic and abiotic variables at two spatial scales, local and regional. Our models incorporated observed richness of 689 riparian woody communities.Results: Local-scale richness depended mostly on local climate, lithology and sediment textures. Regional species richness was driven by climate, lithology and water regime. In the top-down model, regional to local effects were driven mostly by the influence of regional richness on local richness. However, we also detected several bottom-up effects linking local climate, abiotic habitat and vegetation structure with the regional richness. In the bottom-up model, results were very similar, adding an effect of regional climate on local richness.Conclusions: Local, regional and across-scales factors are crucial for understanding species richness of Mediterranean riparian forests. Some factors are inherent to riparian habitats whereas others are already known as relevant for upland habitats. We provide support for the top-down models relying on the concepts of species pool and environmental filtering. However, we also stress that local-scale processes influence regional species richness. Bottom-up effects should not be underestimated when studying the spatial scaling of biodiversity. K E Y W O R D Scommunity, diversity, modeling, riverbank, scales, SEM, southwestern Europe, species pool 486 |

Tree Species Composition and Diversity in the Riparian Forest of Lake Barombi Kotto, Cameroon

“…All over the world, land-water ecotones are characterized by a high biodiversity compared to their adjacent ecosystems, usually as a result of the heterogeneous habitats created by frequent disturbances [1] [2]. Occurring at a transition zone between the terrestrial uplands and aquatic ecosystems, these ecotones are highly productive and provide a habitat for a large range of co-existing plant and animal species [3].…”

“…This can be partly explained by greater water availability (higher soil moisture) and their unique soils which are frequently disturbed [6]. The multi-layered vegetation structure dominated by moisture-loving (hydrophilic) trees, shrubs and herbs, forms a distinctive physiognomy in the landscape [2].…”

Floristic composition, structure and diversity of riparian forests in southwestern Nigeria: conservation is inevitable

“…Globally, riparian forests are branded by high biodiversity compared to their adjacent ecosystems, usually as a result of the diverse habitat created by recurrent disturbances which are natural processes such as lithology, climate and water regimes (Leo et al 2019). Varying disturbances notably anthropogenic activities such as logging, livestock grazing, conversion of forest to agricultural lands, mining and exploration, construction of dams and houses have affected the structure, composition and diversity of plant communities.…”

Assessment of Two Adjacent Mountainous Riparian Areas along Nestos River Tributaries of Greece

“…Most Mediterranean riparian areas will be adjacent to intermittent and ephemeral streams due to climate change's impact [8]. These riparian areas have characteristics different to those adjacent to perennial streams [24][25][26]. Native riparian species are adapted to seasonal peak flows, and this alteration will retard their regeneration, lessen their growth and allow other species to be more competitive and move into the riparian areas (typically invasive species).…”