Topographic thresholds for plant colonization on semi‐arid eroded slopes

Abstract

Soil erosion plays an important role in plant colonization of semi-arid degraded areas. In this study, we aimed at deepening our knowledge of the mechanisms that control plant colonization on semi-arid eroded slopes in east Spain by (i) determining topographic thresholds for plant colonization, (ii) identifying the soil properties limiting plant establishment and (iii) assessing whether colonizing species have specifi c plant traits to cope with these limitations.Slope angle and aspect were surrogates of erosion rate and water availability, respectively. Since soil erosion and water availability can limit plant establishment and both can interact in the landscape, we analysed variations in colonization success (vegetation cover and species number) with slope angle on 156 slopes, as a function of slope aspect. After determining slope angle thresholds for plant colonization, soil was sampled near the threshold values for soil analysis [nitrogen, phosphorous, calcium carbonate (CaCO 3 ), water holding capacity]. Plant traits expressing the plant colonizing capacity were analysed both in the pool of species colonizing the steep slopes just below the threshold and in the pool of species inhabiting gentler slopes and absent from the slopes just below the threshold.Results show that the slope angle threshold for plant colonization decreased from north to south. For the vegetation cover, threshold values were 63°, 50°, 46°, 41° for the north, east, west and south slope aspect classes, respectively, and 65°, 53°, 49° and 45° for the species richness and the same aspect classes. No differences existed in soil properties at slope angle threshold values among slope aspects and between slope positions (just below and above the threshold) within slope aspect classes. This suggests that variations between slope aspect classes in the slope angle threshold result from differences in the colonizing capacity of plants which is controlled by water availability. Long-distance dispersal and mucilage production were preferably associated with the pool of colonizing species.These results are discussed in the perspective of a more effi cient ecological restoration of degraded semi-arid ecosystems where soil erosion acts as an ecological fi lter for plant establishment.

The fate of seeds in the soil: a review of the influence of overland flow on seed removal and its consequences for the vegetation of arid and semiarid patchy ecosystems

“…The role of erosion as an ecological driver that shapes the composition of plant communities had already been highlighted in previous studies in arid and semiarid environments (Guàrdia et al, 2000;GuerreroCampo andMontserrat-Martí, 2000, 2004;García-Fayos and Bochet, 2009;Bochet et al, 2009;Jiao et al, 2009). However, relatively little attention had been paid to the effect of erosion on seeds (mainly seed transport and germination) as compared to later stages of the plant life (seedlings and adult plants; de Luís et al, 2005;Tsuyuzaki and Haruki, 2008;Wang et al, 2014), even though seed stage is one of the most critical phases in vegetation development (García-Fayos and Cerdà, 1997).…”

“…According to all these results, it was concluded that seed loss by overland flow was not the key factor explaining the absence of vegetation on badland slopes as the probability of rainfall events of higher intensity and duration is low. Other possible alternative causes were suggested and further investigated, such as scarce water availability for plants, high salinity and the interaction of these latter factors with seed germination Bochet et al, 2009).…”

Ecological mitigation of hillslope instability: ten key issues facing researchers and practitioners

“…Bochet et al (2009) investigated topographic thresholds (slope angle and aspect) for plant colonization on semiarid eroded slopes in Spain, and observed that the slope angle threshold for plant colonization decreased from north-facing slopes (63°) to south-facing slopes (41°). Variations in slope angle threshold values between slope aspects resulted from differences in the colonization capacity of plants and was controlled by water availability, which was in turn controlled only by the solar radiation received (and not by soil hydrological properties).…”

GIS and Remote Sensing applications for abandoned quarries rehabilitation: A case study in the Akreuch Region, Rabat, Morocco.

“…South-facing slopes accentuate the natural aridity in Mediterranean regions (Lansiart & Odent, 1999). The colonization of plants varies in the northern hemisphere, from north to south (Bochet et al, 2009). North-facing slopes are wetter, and their soils are characterized by greater organic matter content (Poesen et al, 1998;Kutiel & Lavee, 1999;Hammada et al, 2004).…”