Chapter

Plant Effects on Soils in Drylands: Implications for Community Dynamics and Ecosystem Restoration

DOI: 10.1007/1-4020-3447-4_6 In book: Tree Species Effects on Soils: Implications for Global Change, pp.85-118
    • "Indeed, a fairly common pattern in these environments is the existence of one or two dominant nurse species, with individuals of other species located under their canopy or in their close neighbourhood (Valiente-Banuet & Verd u 2008). In this classical facilitative mechanism, a nurse species provides shelter from herbivores, modifies the environment or soil conditions under its canopy, and generates feedbacks among vegetation clumps and soil properties (Cortina & Maestre 2005). In contrast to this expected pattern, the abundance of accumulators and the similarity among the ISAR curves did not support the existence of only one or a few key or engineer species controlling diversity patterns in this community (Fig. 2), but instead our results suggest that a different ecological process leads to a non-hierarchical multi-species clumping. "
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    ABSTRACT: QuestionsShrublands often exhibit very high levels of species richness. We ask which mechanisms underlie plant species co-existence in a hyper-diverse Mediterranean shrubland, and the scales at which individual species exert their effects during organization of diversity in these communities.LocationBrea de Tajo, Madrid, Spain.Methods We computed the individual species–area relationships (ISARs) in a completely mapped Mediterranean dwarf shrubland. Using appropriate species-specific null models, we evaluated how diversity was organized around individual species, covering a wide array of spatial scales.ResultsWe mapped 7858 individuals from 48 perennial species. Our analyses showed that most species (80%) acted as accumulators and exhibited more diversity than expected, whereas 20% were neutral at fine scales. At larger spatial scales, most species exhibited no significant effects in terms of diversity accumulation.Conclusions In contrast to other species-rich ecosystems such as tropical forests, our results suggest that positive interactions and niche complementarities are the main drivers of community assembly in these communities. The most important finding was the existence of non-hierarchical multi-specific clumping that was independent of the fine-scale environmental heterogeneity, which is a pattern that has not been described previously, to the best of our knowledge. The abundance of accumulator species and the similarity among the ISAR curves suggest that nurse-like species were not present, thereby indicating that a different ecological mechanism led to the emergence of this pattern.
    No preview · Article · Aug 2015 · Journal of Vegetation Science
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    • "Although changes in soil properties underneath shrubs are consistent across soil types, climatic conditions, and plant species, the magnitude of such changes is highly variable (Cortina and Maestre 2005). The formation and development of fertile islands are shaped by a range of interacting physical and biotic concentrating mechanisms that are closely related to a number of factors (Li et al. 2007; Schlesinger et al. 1996) that includes shrub species characteristics, canopy size, nutrient uptake via roots and litter deposition (Li et al. 2007), aeolian dust deposition, stem-flow (Whitford et al. 1997), microbial population and rhizosphere root activity, accelerated biogeochemical cycling underneath the canopy (Li et al. 2007), habitat, and climatic conditions (Cortina and Maestre 2005). Shrub species (Li et al. 2007; Titus et al. 2002) and habitat (Li et al. 2008; Su et al. 2004) represent the principle factors that affect the formation and concentration of resource islands. "
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    ABSTRACT: Shrub-induced soil property spatial heterogeneity is common in arid and semi-arid ecosystems and aids desertified land restoration. However, the effectiveness of this technique may rely on the plant species used and the habitat conditions present. To assess the degree to which planting two native species, Haloxylon salicornicum and Calligonum polygonoides, facilitates degraded land restoration, soil and herbaceous plant community properties were measured 7 years after planting. Soil samples were extracted at two depths (0-5 and 5-20 cm) from three sub-habitats, i.e., under the shrub canopy, from alleys between shrubs and from the open area. Shrub planting increased the quantity of silt + clay content (30-39 %); enhanced water holding capacities (24-30 %); increased the levels of organic carbon (48-69 %), available nitrogen (31-47 %), available phosphorus (32-41 %), and electrical conductivity (21-33 %); and decreased the pH (7-12 %) and bulk density levels (5-6 %) in the surface layer of soils beneath the canopy. Soil property changes were more significant at the surface (0-5 cm) than in the deeper layer (5-20 cm), and were more pronounced under H. salicornicum than under C. polygonoides. Furthermore, the density and biomass levels of herbaceous plants were 1.1 to 1.2 and 1.4 to 1.6 times greater, respectively, in the shrub alleys than in open area. H. salicornicum induced more robust soil amelioration and herbaceous plant facilitative properties than did C. polygonoides. Artificially planting these shrubs may thus be employed to restore degraded areas of arid regions.
    Full-text · Article · Sep 2014 · Environmental Management
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    • "Nevertheless, a shift from facilitation to competition under high-abiotic-stress conditions may occur when the levels of the most limiting resource are so low that the benefits provided by the facilitator cannot overcome its own resource uptake (Maestre and Cortina, 2004). Thus, despite the fact that in water-limited environments, plants generally improve soil fertility and microclimate under their canopies (Cortina and Maestre, 2005), these changes do not always translate into increased water availability in their immediate vicinity (Sala et al., 1989; Valladares and Pearcy, 2002). Canopy interception can reduce the amount of water reaching the soil, and root competition for water can make the understorey drier than open patches (Abrams and Mostoller, 1995; Valladares and Pearcy, 2002; Hamerlynck et al., 2011). "
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    ABSTRACT: Water relations are essential in plant–plant interactions, particularly in Mediterranean coastal sand dunes, owing to marked drought periods and the possibility of groundwater (GW) salinization. In this study, seasonal water use dynamics were explored in the interaction between a native–invasive species, Retama monosperma, and the endangered Thymus carnosus, in south-western Spain. The following variables were measured: xylem water isotopic composition to determine water sources, predawn and midday stem water potential and free leaf proline content as stress indicator. GW electrical conductivity and stable isotopes were also analysed to assess water table salinity. In late summer and spring, the warmest seasons, Thymus beneath Retama displayed significantly lower water potential and higher leaf proline content than isolated Thymus, whereas Retama showed the highest proline content in autumn and winter. Water sources showed different patterns depending on the Thymus situation: Isolated ones always matched the brackish GW, as well as Retama plants, whereas Thymus beneath Retama switched among rainfall, soil and water table, showing a seasonal change in the water-harvesting strategy. Overall, competition for water sources between both species was discovered, which led to a shift in water use and water uptake strategies of understorey Thymus. The results also demonstrate the importance and potential use of species interaction studies in the development of threatened species management strategies. Copyright © 2013 John Wiley & Sons, Ltd.
    Full-text · Article · Apr 2014 · Ecohydrology
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