Search

Understanding the factors that control grass–shrub interactions and coexistence is critical to the design of dryland management and restoration strategies. Using Stipa tenacissima tussocks as adult neighbor and Olea europaea var. sylvestris as target woody species, we performed a 5‐year‐long, large‐scale manipulative experiment to investigate the independent and combined effects of water and nutrient availability, and the modulating effects of O. europaea ontogeny on the net outcome of grass–shrub interaction. At two contrasting dryland sites, we conducted experimental plantings of Olea seedlings on two microsites: contiguous to a Stipa tussock (Stipa microsite) and on the intertussock bare‐soil areas (Open microsite), and manipulated resource availability by combining nutrient and water addition. The experiment followed a full factorial design, with all treatment combinations applied at each site. We monitored survival, height, and stem basal diameter of Olea individuals over a study period of 5 years. All across the wide range of conditions considered, negative effects of Stipa on Olea largely prevailed during the first 2 years after the plantation. We found that competition was stronger in the drier steppe, where extra inputs of water favored neutral interactions. Conversely, nutrient addition increased competition strength, particularly when combined with water inputs, pointing to the contrasting role of different resources and the importance of interactions between them in the control of plant–plant interaction outcome. The competition effects of Stipa faded with time and gradually shifted to neutral interaction as Olea individuals aged. Our results are particularly relevant to guide restoration efforts in formerly wooded xeric grasslands and rangelands. [ABSTRACT FROM AUTHOR]

Alpha grass (Stipa tenacissima) steppes are widely distributed within the semi-arid areas of the Mediterranean Basin, and represent a degraded stage of vegetation. We evaluated the effect of S. tenacissima tussocks and nursery inoculation with mycorrhizae on the survival of the native shrub Quercus coccifera. Experiments were carried out in three steppes located in semi-arid southeastern Spain. Survival during the first months after plantation was significantly higher in the surroundings of S. tenacissima tussocks than in open areas between the tussocks. We did not find any effect of nursery inoculation on seedling survival. This effect may be related to the fact that the used fungal strain did not survive the drought summer conditions in the study area. Our results support the idea of a facilitative effect of S. tenacissima on introduced shrubs, which may be related to improved environmental conditions in tussock microsites. However, this effect may not be enough for the establishment of seedlings in years with below-average rainfall and a strong summer drought. [Copyright &y& Elsevier]

The ecological functioning of dryland ecosystems is closely related to the spatial pattern of the vegetation, which is typically structured in patches. Ground arthropods mediate key soil functions and ecological processes, yet little is known about the influence of dryland vegetation pattern on their abundance and diversity. Here, we investigate how patch size and cover, and distance between patches relate to the abundance and diversity of meso-and microarthropods in semi-arid steppes. We found that species richness and abundance of ground arthropods exponentially increase with vegetation cover, patch size, and patch closeness. The communities under vegetation patches mainly respond to patch size, while the communities in the bare-soil interpatches are mostly controlled by the average distance between patches, independently of the concurrent changes in vegetation cover. Large patches seem to play a critical role as reserve and source of ground arthropod diversity. Our results suggest that decreasing vegetation cover and/or changes in vegetation pattern towards small and over-dispersed vegetation patches can fast lead to a significant loss of ground arthropods diversity in drylands. [ABSTRACT FROM AUTHOR]