Spatial pattern analysis of dominant species in the Prepuna: Gaining insight into community dynamics in the semi-arid, subtropical Andes

We conducted a point pattern analysis of dominant woody and cactus species in a permanent plot located in the little known semi-arid Andes (Prepuna region) for gaining insight into community dynamics and, specifically, to determine the microhabitat (beneath or away from shrubs) where shrubs and cacti tend to recruit. Several null models were employed. We found that small individuals of the shrub species did not show attraction for larger individuals, which may show that the former are not facilitated by the latter. One of the two columnar cactus species presented a markedly aggregated pattern, and showed attraction for shrubs at small spatial scales. This could be related to vegetative propagation of the cactus and a facilitative interaction with the shrubs. Adult shrubs (whether considering or not the species) were distributed randomly in the plot. However, when the evaluation considered the species and included seedlings/saplings, shrub species showed aggregation at some spatial scale. We found a progression from aggregation at young age to increasingly less contagious distributions at older stages, which might indicate self-thinning. The two dominant shrub species showed neither attraction nor repulsion between each other. Our results could in part be explained by the characteristic climate of subtropical, high altitude semi-deserts.