De Las Heras J., Moya D., López-Serrano F.R., Eugenio M., Espelta J.M. (2008) Aleppo pine regeneration after fire along an aridity gradient. WIT Transactions on Ecology and the Environment. 119: 289-295.EnllaçDoi: 10.2495/FIVA080291
In the Mediterranean Basin, the number of large-scale fires and, consequently, the area of regenerated forests after a fire have been increasing over the last few decades. Mediterranean pine tree stand regeneration shows differences in growth and reproductive characteristics depending on site quality. Aleppo pine (Pinus halepensis Mill.) is an important obligate seeder species occupying a large surface in this area. In order to study growth and reproductive characteristics depending on different climatic conditions, six sites with similar characteristics (edaphic, exposure, slope) burned in the summer of 1994 were selected along a climate gradient. Different precipitation values determined three different ombroclimates: dry-subhumid, dry and semi-arid. Ten years after the fires, data on growth and cone production were collected from these areas in order to study the pattern of growth and reproduction and the influence of site quality (climate) on them. Results showed significantly higher values for growth and several cone characteristics; furthermore, they were positively related to site quality. Viability and seed germination percentages were higher in sites located in dry-subhumid areas. Serotiny was highest in dry locations (southern sites), and lower percentages were found in low tree density sites. The number of reproductive trees was higher northwards and the reproductive phase was reached in younger stands with lower tree density. In conclusion, results showed a geographical gradient based upon growth and reproductive characteristics, decreasing southwards in contrast to serotiny, which increases in southern sites. Density was found to be a significant factor influencing overall pine stand development.
Espelta J.M., Cortés P., Molowny-Horas R., Sánchez-Humanes B., Retana J. (2008) Masting mediated by summer drought reduces acorn predation in mediterranean oak forests. Ecology. 89: 805-817.EnllaçDoi: 10.1890/07-0217.1
Temporally variable production of seed crops by perennial plants (masting) has been hypothesized to be a valuable mechanism in the reduction of seed predation by satiating and starving seed consumers. To achieve these benefits, coexisting species subjected to the same predator would benefit from a similar pattern of seeding fluctuation over time that could lead to a reduction in predation at the within-species level. We tested for the existence of an environmental factor enforcing synchrony in acorn production in two sympatric Mediterranean oaks (Quercus ilex and Q. humilis) and the consequences on within-species and between-species acorn predation, by monitoring 15 mixed forests (450 trees) over seven years. Acorn production in Q. ilex and Q. humilis was highly variable among years, with high population variability (CVp) values. The two species exhibited a very different pattern across years in their initial acorn crop size (sum of aborted, depredated, and sound acorns). Nevertheless, interannual differences in summer water stress modified the likelihood of abortion during acorn ripening and enforced within- and, particularly, between-species synchrony and population variability in acorn production. The increase in CVp from initial to mature acorn crop (after summer) accounted for 33% in Q. ilex, 59% in Q. humilis, and 60% in the two species together. Mean yearly acorn pre-dispersal predation by invertebrates was considerably higher in Q. humilis than in Q. ilex. Satiation and starvation of predators was recorded for the two oaks, and this effect was increased by the year-to-year variability in the size of the acorn crop of the two species combined. Moreover, at a longer time scale (over seven years), we observed a significant reduction in the mean proportion of acorns depredated for each oak and the variability in both species' acorn production combined. Therefore, our results demonstrate that similar patterns of seeding fluctuation over time in coexisting species mediated by an environmental cue (summer drought) may contribute to the reduction of the impact of seed predation at a within-species level. Future research should be aimed at addressing whether this process could be a factor assisting in the coexistence of Q. ilex and Q. humilis. © 2008 by the Ecological Society of America.
Moya D, Espelta JM, López-Serrano FR, Eugenio M, de Las Heras J (2008) Natural post-fire dynamics and serotiny in 10-year-old Pinus halepensis Mill. stands along a geographic gradient. International Journal of Wildland Fire 17: 287–292.
Espelta JM, Verkaik I, Eugenio M, Lloret F (2008) Recurrent wildfires constrain long-term reproduction ability in Pinus halepensis Mill. International Journal of Wildland Fire 17: 579-585.
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