Rates of local colonization and extinction reveal different plant community assembly mechanisms on road verges in central Spain

Abstract

Question: Does community assembly on roadsides differ between two contrasting habitats along a stress–productivity gradient? Is establishment success determined by the regional pool, environmental filters or historical events? Location: Highway roadcuts and embankments in central Spain (40°29′N, 03°34′W). Methods: Species composition was recorded annually in 45 plots distributed on steep slopes with newly exposed surfaces (roadcuts) or newly built topsoiled substrates (embankments), for 4 years following hydroseeding with standard or native seed mixture. Frequency of appearance and local colonization and extinction rates of individual species were clustered in establishment success groups. We examined the correspondence between descriptive plant traits and species performance on both roadslope types. Results: Roadslope species richness showed a sustained increase over time, although at consistently lower levels and rates on the more productive embankments. Sixty per cent of the colonization events involved species from the surrounding vegetation. Hydroseeded species persisted through time, but did not modify community composition or dynamics. A higher establishment success rate was found in wind‐pollinated species with large seeds and in exotic species. Those species growing on embankments showed an equal or higher establishment success rate on roadcuts and, conversely, species from roadcuts exhibited an equal or lower success rate on embankments. Conclusions: At the initial stages of community assemblage on unproductive newly created areas, species richness was shaped by the regional species pool. Communities on less harsh topsoiled embankments were subjected, however, to the filtering effect of competitive exclusion. In a reclamation context, efforts to increase site productivity may have detrimental consequences for in situ conservation of local diversity.

Near‐natural methods promote restoration of species‐rich grassland vegetation—revisiting a road verge trial after 9 years

“…The poor ecological performance (low species number and low resilience) of the Standard revegetation procedure was not surprising, and similar results have been reported also by other authors (Zelnik et al ; de la Riva et al ). In this study, extremely species‐poor vegetation developed, almost totally dominated by the four sown species (three grasses and the forb Trifolium repens ).…”

“…Unfortunately, the standard method of revegetating road verges in grassland areas (adding commercial, species‐poor, and grass‐dominated seed mixtures, often by hydroseeding; Skrindo & Pedersen ) tends to result in species‐poor grasslands of low conservation value (Prach et al ). The standard method is nevertheless widely used as it has been regarded as a guarantee of rapid vegetation development and subsequent erosion prevention (de la Riva et al ; Oliveira et al ).…”

Identifying plant traits: A key aspect for species selection in restoration of eroded roadsides in semiarid environments

“…However, thus far, roadcut plant communities have received no attention as regards trait characterization. In the only attempt, to our knowledge, that aimed at identifying plant traits in both, roadfill and roadcut plant communities (but without considering slope aspect), de la Riva et al (2011) failed to find different specific traits associated to both types of roadslope plant communities under a wetter climate. After examining a set of easy-achievable traits from the literature, these authors reported that dominant species on both types of roadslopes shared common syndromes (wind-pollinated, large-seeded and non-native).…”

“…Notwithstanding, the ecological functioning of roadside plant communities has been scarcely studied yet (Schaffers and Sýkora, 2002;Valladares et al, 2008). Roadside plant communities represent a unique opportunity to test assembly rules and study plant trait filtering using applied ecology (de la Riva et al, 2011). They also represent a great challenge for ecological restoration and for the selection of suitable species for roadslope revegetation, especially in arid and semiarid regions where many restoration projects yield unsuccessful results (Bochet and García-Fayos, 2004).…”

Disentangling the relative importance of species occurrence, abundance and intraspecific variability in community assembly: a trait‐based approach at the whole‐plant level in Mediterranean forests

“…We found a large variation in the functional traits considered in this study along the explored environmental gradients, which suggest a non-random trait distribution at the community level (Weiher and Keddy 1999, Stubbs and Wilson 2004, Cornwell and Ackerly 2009, Freschet et al 2011, de Bello et al 2013). This means that only a particular set of trait values is advantageous under certain environmental conditions, thus limiting the range of trait space that species and communities are able to occupy (Díaz et al 1998, Holdaway and Sparrow 2006, Cornwell and Ackerly 2009, de la Riva et al 2011.…”