Shrubs affect soil nutrients availability with contrasting consequences for pasture understory and tree overstory production and nutrient status in Mediterranean grazed open woodlands

Abstract

Increases of woody plant cover in former savannas and managed savanna-like systems are currently considered one of the major components of global environmental change. Besides, shrub encroachment is frequently recommended as a practical tool to ensure tree regeneration. However, there is little evidence that this process affects neighboring plants-tree and pasture-production and nutrient status in Mediterranean open woodlands through the modification of soil properties. The effect of two contrasting, in terms relevant to nutrient cycling, shrub species, Cistus ladanifer and Retama sphaerocarpa, were investigated. Cistus, a shallow rooted shrub, reduced top-soil water content and enhanced P and K but depleted N and Mg availability under its canopy. It worsened consistently both tree overstory and pasture understory production and nutrient content. By contrast, Retama, a deep-rooted, N 2 -fixing shrub, increased top-soil water content and N and Mg availability, but diminished P availability. In addition, it affected distinctively to pasture (facilitation) and trees (competition) biomass production. Overall, pasture production, irrespective of the habitat, was mainly limited by P, whereas trees growing with Cistus were limited by Ca and N and those trees growing with Retama by P availability. Our results showed that shrubs are capable to affect consistently both pasture and tree production and nutrient status through the modification of soil nutrient availability. However, these effects depended on specific shrub-understory and shrub-overstory combinations, which have implications for managing grazed open woodlands.

Tree patch distribution drives spatial heterogeneity of soil traits in cork oak woodlands

“…This confirms that P availability in soils depends not only on the balance between mineralization and uptake but also on the interaction with soil minerals, and probably on the distribution and density of roots and mycorrhizas (Gallardo 2003;Sardans and Peñuelas 2013). The likely effect of tree patches on soil P distribution might be hampered by the irregular distribution of shrubs in the plot and its effect on creating microenvironments (Rolo et al 2012) and/or by the higher resorption efficiency of cork oak trees that leads to low P concentration in leaf fall (Andivia et al 2010;Caritat et al 1996;Robert et al 1996). We did not find any relationship between tree cover and soil texture.…”

Mineral nitrogen and phosphorus pools affected by water table lowering and warming in a boreal forested peatland

“…Three years of oxic conditions would have resulted in mineralization leading to increases in extractable and available PO 4 pools. The reversal could be due to the drained site's thick oxic zone that supported the growth of shrubs of extensive and deeper root system (Munir et al, ) that in turn required greater amounts of PO 4 (Cleve, Oliver, Schlentner, Viereck, & Dyrness, ; Rolo, Lopez‐Diaz, & Moreno, ), removing it effectively from the peat. Macrae et al () also reported no difference in PO 4 concentrations between control peatlands and those drained for ~10 years, a result that could be due to a more limited WT drawdown of only 20 cm in that study or a similar return to predrainage pools as observed in this study.…”

Plant-soil interactions in Mediterranean forest and shrublands: impacts of climatic change

“…Regional scale evidences of the tree density and mean annual precipitation suggest that the structure of these man-made ecosystems have adjusted over long-time and corresponds to an optimal functional equilibrium with water cycle (Joffre et al 1999). Frequently the major problem to maintain these ecosystems and maintain tree production is the shrub competition that strongly impacts soil nutrient availability (Rolo et al 2012). …”