Ramón Reiné

Effects of the allelopathic plant Artemisia herba-alba Asso on the soil seed bank of a semi-arid plant community

Aims Seed bank strongly influences composition and structure of aboveground vegetation. Little attention has been paid to the role of allelopathy driving soil seed bank dynamics, even though allelochemicals released by allelopathic plants might determine whether a species can or cannot germinate from the soil seed bank and, therefore, to co-exist in the neighborhood of the allelopathic species. Hence, the effects of allelopathic plants on community organization through the effects of allelochemicals on soil seed bank remain largely unknown. In this study, we assessed spatial heterogeneities in soil seed bank caused by the presence of allelopathic plants, and evaluated allelopathic effects on seed bank germination and seedling mortality. Methods We examined the effects of the allelopathic shrub Artemisia herbaalba Asso on the spatial structure (in terms of species richness and seed density) of the soil seed bank of a semi-arid ecosystem in NE Spain. Specifically, we evaluated seed bank richness and density at three microsites: under the canopy of A. herba-alba individuals, under the canopy of Salsola vermiculata L. (a non-allelopathic shrub) individuals, and in bare soil. In addition, we assessed the effects of aqueous extract of A. herba-alba on soil seed bank germination (seedling emergence and emergence timing) and seedling mortality. Important Findings We found that seed bank richness and density were higher under shrub canopy than they were in bare soil. A. herba-alba and S. vermiculata microsites had similar seed bank richness. However, seed bank density was higher under A. herba-alba because of the high abundance of A. herba-alba seeds. Aqueous extract reduced seedling emergence from the seed bank by 50%, and affected mortality of some emerged seedlings. On the other hand, aqueous extract did not influence the emergence timing of seedlings. We conclude that, although the presence of allelopathic plants does not cause relevant changes in seed bank structure relative to similar non-allelopathic shrubs, their presence can actually result in a reduction of seedling emergence from the seed bank, which leads to low plant species richness and density nearby. To our knowledge, this is the first study to examine the effect of an allelopathic plant on the structure and germination in an entire soil seed bank.

Changes in Land Use of Pyrenean Mountain Pastures — Ski Runs and Livestock Management — Between 1972 and 2005 and the Effects on Subalpine Grasslands

Abstract In recent decades, the use of some subalpine mountain grasslands in the Central Spanish Pyrenees has changed. Ski resorts have been developed and cattle herd management has shifted from the traditional “rotational-type” system in which grazing cattle are overseen by a herder to a “continuous-type” system that does not involve a herder. In 2005, the locations of 30 floristic inventories performed in 1972 were revisited and inventories were repeated in two adjacent similar areas, although one had been used for the development of ski runs and the other had not. The objective was to assess the effects of those changes on plant diversity and other characteristics of the grasslands. In both areas, plant diversity was significantly higher in 2005 than it was in 1972. Both areas had been grazed by cattle to a similar extent; thus, the results suggest that diversity was affected primarily by the change in the livestock grazing system. Livestock grazing within the skiing area appears to have counterbalanced any reduction in plant diversity that would have occurred because of the construction and use of ski runs. In the skiing area, legume cover and pastoral value decreased, the Ellenberg Nitrogen Index reflected lower soil nutrients available to plants, and the cover of plant species that regenerate by seeds increased between 1972 and 2005; such changes did not occur in the non-skiing area. The abundance of ruderal species increased more in the skiing area than in the non-skiing area. Between 1981 and 2000, the amount of bare ground increased only in the skiing area.