Linking hydrological, geomorphological and biological properties in hyper-arid conditions: Distribution processes of a dominant clonal cactus by run-off

Abstract

The objective was to analyse the asexual spread of Tephrocactus aoracanthus (Cactaceae) related to run-off triggered by torrential summer rains in a hyper-arid desert. Through a manipulative essay, 30 joints (asexual dispersing stems) were placed in the mainstream of an alluvial fan and 30 joints out of the alluvial fan, without run-off influence (control). All joints were labelled, and their weight and diameter were measured. After each rain event with run-off, joints were surveyed identifying their spatial coordinates and environmental context. For this, two factors with two levels each one was selected: position respect to both microrelief (channels with concentrated run-off, or inter-channels as flat areas between channels, without run-off) and vegetation (entangled or not entangled in shrubs). Through a geographic information system, changes in slope angle and rugosity of terrain were analysed. Linear regressions were performed between the partial displacement of joints and their weight and diameter, grouped according to environmental context before each rainfall. None of the joints of the control treatment were moved, but all joints located in the mainstream were relocated. Three rainfall events triggered a mean displacement of 480.4 ± 210.0 m (SD); 103.0 ± 138.9 m (SD) and 33.2 ± 52.3 m (SD), respectively. The mean accumulated displacement of all joints during the experience was 577.12 ± 220.0 m (SD). As they moved, the joints passed through several different environmental contexts, increasing the proportion of joints entangled in vegetation and in inter-channel position. Until rooted, joints could be displaced by run-off in an anisotropic process, with an evident effect of slope angle and rugosity of terrain. On the other hand, no direct relationship was found between the displacement and the magnitude of the event, or both the size and the weight of joints. We assess the strategies related to the dispersal mechanism of clonal plants, related to conditions and enabling its agamic dispersal over long distances.