Earth Surface Processes and Landforms vol:34 issue:13 pages:1758-1771
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 (CaCO3), 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.