Impact of grazing on the species richness of plant communities in Mediterranean temporary pools (western Morocco)

Abstract

The impact of grazing on the vegetation of Moroccan temporary pools has been studied at 2 scales: regional (inter-pools) and local (intra-pools). Half of the 16 forest pools studied is located in a reserve and ungrazed. The other half, located within public forest, is grazed. Vegetation releve´s coupled to water-depths measurements were carried out in each pool. The results showed a significant effect of grazing on both scales of analysis. This effect was found in the species composition of the vegetation, which differed between the 2 types of pools, and in the lower species richness and abundance of plant species in the grazed pools. These differences are interpreted as resulting from the selection by herbivores and the differential tolerance of species to disturbance. These impacts are likely to expose certain species to local extinction by reducing their populations.

Livestock disturbances in Mediterranean temporary ponds: A mesocosm experiment with sheep manure and simulated trampling

“…Colonizing species (macroinvertebrates) were unaffected by livestock treatments, but richness and density were higher in agricultural ponds than forest ponds. This contrasts with other studies that have shown either a positive (Davis & Bidwell, 2008;Marty, 2005) or a negative (Bouahim et al, 2010;Davidson et al, 2017;Epele & Miserendino, 2015;Foote & Hornung, 2005) effect of grazing on the colonisation of ponds by macroinvertebrates. As these taxa arrived in mesocosms from the surrounding landscape, habitat choice becomes an important factor in their distribution and abundance (e.g.…”

“…Trampling can be beneficial for some plant species, by the formation of microhabitats in the sediment (Barry, ). This may have a positive effect on smaller fragile species with poor competitive abilities, as found with the rare pillwort Pilularia minuta (Bouahim et al., ). Lastly, it must be noted that R. baudotii , a deeply rooted tolerant species in Triops ‐disturbed mesocosms (Croel & Kneitel, ; Waterkeyn et al., ) flourished in undisturbed conditions in our study.…”

“…Many temporary wetlands are used for watering and grazing (Bouahim et al, 2015;Croel & Kneitel, 2011a;Schmutzer, Gray, Burton, & Miller, 2008) so research increasingly focuses on the effects of grazing on wetland plant and animal communities and ecosystem function (e.g. Bagella et al, 2010;Bouahim et al, 2010;Boughton, Quintana-Ascencio, Bohlen, Fauth, & Jenkins, 2016;Marty, 2005;Pyke & Marty, 2005;Rhazi, Rhazi, Grillas, & El Khyari, 2006). For example, livestock grazing can vary along an intensity gradient (Davidson et al, 2017;Epele & Miserendino, 2015), resulting in detrimental or beneficial effects on pond biodiversity (Bouahim et al, 2010;Davidson et al, 2017;Epele & Miserendino, 2015;Marty, 2005;Schmutzer et al, 2008).…”

“…The effects of defecation and trampling within aquatic habitat remain understudied experimentally (Croel & Kneitel, 2011a, 2013 relative to foliar removal effects. In the case of most Mediterranean temporary ponds (MTP), plant species richness in ungrazed habitats is not necessarily lower than grazed ponds in the region (Bouahim et al, 2010;Rhazi, Grillas, Médail, & Rhazi, 2005). The oligotrophic state of these habitats in combination with a yearly intensive drought naturally restricts biomass production and competition, limiting possible positive effects of grazing (Bouahim et al, 2010) and make them more sensitive to nutrient addition.…”

“…This can occur because livestock herds often gather around the littoral zone to drink (Foote & Hornung, 2005;James, Kleinman, Veith, Stedman, & Sharpley, 2007), or enter the wetland to graze, and because many sensitive and rare plant species are found in the wetland basin (Barbour et al, 2007;Bouahim et al, 2014;Rhazi et al, 2012). Therefore, some studies suggest that although grazing may be beneficial at landscape scale, it might be less favourable locally (Bouahim et al, 2010;Marty, 2005). However, effects may be species specific (Bovee et al, 2017) and much remains to be studied in K E Y W O R D S crustaceans, defecation, macrophytes, trampling, water quality detail for the whole community, including across multiple trophic levels.…”