Quantity or Efficiency: Strategies of Self-Organized Xerophytic Shrubs to Harvest Rain

Canopy structure alters net precipitation inputs, partly governing the quantity of water recharging soil moisture. Clumped and scattered shrublands are structured with aggregated and isolated canopies, respectively, demonstrating contrasting self-organized patterns. However, the influence of self-organization on rain harvesting is largely unknown. Hence, we compared rainfall redistribution patterns of different self-organized shrubs of Vitex negundo and soil moisture responses during the 2020–2021 rainy seasons on the Loess Plateau of China. Our results indicated that the scattered shrubs harvested more throughfall (85.6% vs. 74.7%) and net precipitation (90.8% vs. 83.8%) than clumped shrubs. Comparatively, stemflow of clumped shrubs was initiated (57.2 vs. 60.4 min) and peaked (198.9 vs. 207.7 min) earlier, ceased later (84.4 vs. 54.5 min), lasted longer (8.9 vs. 8.4 hr), transported more swiftly (397.0 vs. 373.8 mm h⁻¹), and yielded a larger quantity (400.8 vs. 355.1 mL), respectively. This flux was funneled more efficiently (160.1 versus 140.5 fold compared to rain), and was more productive (1.768 vs. 1.346 mm g⁻¹) per unit biomass investment. For both self-organized patterns, more throughfall led to wetter soils, but more stemflow resulted in quicker response of soil moisture. Comparatively, the top-layer soil moisture remained more stable post rain under clumped shrubs. Therefore, via rainfall partitioning, the scattered organization was conducive for V. negundo to harvest more rain, but the clumped shrubs harvested rain more efficiently. This might relate to morphological adaptations of shrubs to resist drought and consequent formation and maintenance of self-organizations at the landscape scale.