Germination of an obligate seeder (Ulex parviflorus) and consequences for wildfire management

In fire-prone ecosystems, reducing the risk of wildfire is generally attempted through vegetation clearing using controlled fires or, less often, mechanical techniques. Management practices, however, can be poorly efficient when the disturbances they introduce install environmental conditions that are similar to the ones under which the undesirable species evolved. Ulex parviflorus is a Mediterranean obligate seeder with physical dormancy forming large amounts of highly combustible standing necromass. In the present study, combining field and laboratory experiments, we determined the seedling recruitment of this species under different management practices (burning, mechanical clearing, slash/no slash on soil surface), we measured the environmental conditions (temperature, light, and moisture) enforced by these practices and we tested their individual and combined impact on germination in order to determine the most appropriate control method for this species. Germination is low under intact canopies, but it is strongly stimulated by both brush-chipping and fire. This is partly related to the inhibiting effect of the low red:far-red ratio of the light filtered by the canopy which is removed by brush-chipping and fire. The other factor involved is moderate heat, either fire-generated or resulting from solar radiation on bare soil, which breaks seed coat impermeability. Indeed exposing seeds on bare soil in summer resulted in a significant increase in their germination capacity and germination was reduced when the brush chips remained on the soil. Moisture fluctuations did not enhance germination. The summer heat impact affects management practices. When the brush-chipping treatment occurred before summer, the germination flush appeared the following autumn, but when the treatment occurred after summer, the germination flush did not appear until the autumn of the subsequent year, when interspecific competition with regenerating vegetation is likely to be more intense. We demonstrated that brush-chipping, especially when done after summer, is a better technique than fire for controlling U. parviflorus because it creates environmental conditions that are less favourable for its germination. This technique also has the potential to favour late-successional species less vulnerable to fire. By combining fuel reduction and land restoration, this technique is useful to the sustainable management policies that need to be developed. (C) 2008 Elsevier B.V. All rights reserved.