Armenteras, D., Espelta, J.M., Rodríguez, N., Retana, J. (2017) Deforestation dynamics and drivers in different forest types in Latin America: Three decades of studies (1980–2010). Global Environmental Change. 46: 139-147.LinkDoi: 10.1016/j.gloenvcha.2017.09.002
Zavala M.A., Espelta J.M., Caspersen J., Retana J. (2011) Interspecific differences in sapling performance with respect to light and aridity gradients in mediterranean pine-oak forests: Implications for species coexistence. Canadian Journal of Forest Research. 41: 1432-1444.LinkDoi: 10.1139/x11-050
The relative abundance of two codominant Mediterranean tree species, shade-tolerant Quercus ilex L. and shade-intolerant Pinus halepensis Mill., is inversely correlated along aridity gradients, but this pattern is not explained by seedling responses to water or light availability, suggesting that subsequent life history stages may explain forest composition. To test this hypothesis, we calibrated statistical models of sapling growth and height-diameter allometry as functions of light availability and climatic variation as well as models of sapling mortality as a function of growth history. Contrary to the expectation of a sun-shade growth trade-off, P. halepensis grew faster than Q. ilex saplings at both low and high light levels. Low precipitation and aridity suppressed sapling growth rates, but no evidence of a shade-drought growth trade-off was found either. Pinus halepensis sapling mortality was strongly growth dependent, exhibiting high mortality rates at low growth, but the mortality of Q. ilex saplings was not. Height-diameter allometric variation was higher in low-than in high-light environments and was more pronounced with respect to changes in light than climatic water. Our results suggest that interspecific differences in sapling mortality and plasticity, rather than growth, may control species distributions at the mesic end of the aridity gradient. © NRC Research Press 2011.
Espelta J.M., Cortés P., Molowny-Horas R., Retana J. (2009) Acorn crop size and pre-dispersal predation determine inter-specific differences in the recruitment of co-occurring oaks. Oecologia. 161: 559-568.LinkDoi: 10.1007/s00442-009-1394-x
The contribution of pre-dispersal seed predation to inter-specific differences in recruitment remains elusive. In species with no resistance mechanisms, differences in pre-dispersal predation may arise from differences in seed abundance (plant satiation) or in the ability of seeds to survive insect infestation (seed satiation). This study aimed to analyse the impact of pre-dispersal acorn predation by weevils in two co-occurring Mediterranean oaks (Quercus ilex and Quercus humilis) and to compare its relevance with other processes involved in recruitment. We monitored the patterns of acorn production and acorn infestation by weevils and we conducted experimental tests of acorn germination after weevil infestation, post-dispersal predation and seedling establishment in mixed forests. Monitoring and experimental data were integrated in a simulation model to test for the effects of pre-dispersal predation in recruitment. In both oaks pre-dispersal acorn infestation decreased with increasing acorn crop size (plant satiation). This benefited Q. ilex which exhibited stronger masting behaviour than Q. humilis, with almost a single and outstanding reproductive event in 6 years. Acorn infestation was more than twice as high in Q. humilis (47.0%) as in Q. ilex (20.0%) irrespective of the number of seeds produced by each species. Although germination of infested acorns (seed satiation) was higher in Q. humilis (60%) than in Q. ilex (21%), this could barely mitigate the higher infestation rate in the former species, to reduce seed loss. Conversely to pre-dispersal predation, no inter-specific differences were observed either in post-dispersal predation or seedling establishment. Our results indicate that pre-dispersal predation may contribute to differences in seed supply, and ultimately in recruitment, between co-existing oaks. Moreover, they suggest that seed satiation can barely offset differences in seed infestation rates. This serves as a warning against overemphasising seed satiation as a mechanism to overcome seed predation by insects. © Springer-Verlag 2009.
Espelta JM, Gracia M, Molowny R, Ordoñez JL, Retana J, Vayreda J et al (2009) Els alzinars Manuals de gestió d’hàbitats. Diputació de Barcelona. Barcelona. 181 pp.
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.LinkDoi: 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.
Espelta J.M., Habrouk A., Retana J. (2006) Response to natural and simulated browsing of two Mediterranean oaks with contrasting leaf habit after a wildfire. Annals of Forest Science. 63: 441-447.LinkDoi: 10.1051/forest:2006024
In this study, we explore the response to browsing of two co-occurring Mediterranean oaks, the evergreen Quercus ilex and the deciduous Quercus cerrioides, resprouting in areas affected by large wildfires in central Catalonia (NE Spain). We tested three hypotheses: (i) differences in the preference of browsers will cause a higher impact of browsing on the deciduous oak, (ii) the deciduous oak will show a lower response to browsing than the evergreen one, and (iii) the response to browsing of Q. ilex and Q. cerrioides will differ depending on the season of the year when browsing occurs. To test the first hypothesis, we undertook the monitoring of the degree of browsing on resprouting evergreen and deciduous oaks after fire, while the second and third hypothesis were tested by mean of an experiment with different intensities of simulated browsing in different seasons of the year. The results indicate that Q. cerrioides individuals were more heavily browsed than Q. ilex ones. Moreover, browsing matched the two species in most of the size variables considered, cancelling the advantage in height and crown projection of the deciduous oak at the beginning of the resprouting process. In the experiment of simulated browsing, Q. ilex and Q. cerrioides showed a similar response to the different intensities of simulated browsing applied, but differences between species occurred depending on the season of the year when browsing occurred: Q. ilex showed a higher growth rate of crown projection than Q. cerrioides when it was browsed in autumn and winter, while the opposite pattern was obtained when stumps browsing occurred in spring and summer. © INRA, EDP Sciences, 2006.
Espelta J.M., Cortés P., Mangirón M., Retana J. (2005) Differences in biomass partitioning, leaf nitrogen content, and water use efficiency (δ13C) result in similar performance of seedlings of two Mediterranean oaks with contrasting leaf habit. Ecoscience. 12: 447-454.LinkDoi: 10.2980/i1195-6860-12-4-447.1
Co-occurrence of winter-deciduous and evergreen oaks is common in some Mediterranean-type climate areas. However, whether these species show an overlap in their regeneration niche is still poorly understood. We explored experimentally the changes in survival, growth, biomass partitioning, leaf nitrogen content, and water use efficiency (δ 13C) in seedlings of a deciduous oak (Quercus cerrioides) and an evergreen oak (Quercus ilex) in response to co-variation in light and water availability. Quercus cerrioides exhibited higher root length, root area, leaf nitrogen content, and less negative δ13C, but lower leafiness than Q. ilex. The interaction between species and light in specific leaf area and root-shoot ratio indicated different mechanisms to overcome water stress in the two oaks, with Q. ilex relying on leaf hardening and Q. cerrioides relying on a high root-shoot ratio. However, the two species showed similar survival and growth in most of the light-water gradient. Ecological inference of these results indicates that seedlings of these species have a similar ability to cope with variations in light and water in spite of their contrasting leaf habit. This similar performance suggests a competition for similar micro-sites during establishment, rather than a partitioning of the regeneration niche.
Ordóñez JL, Retana J, Espelta JM (2005) Effects of tree size, crown damage, and tree location on post-fire survival and cone production of Pinus nigra trees. Forest Ecology and Management 206: 109-117.
Espelta JM, Lloret F, Díaz-Delgado R, Pons X, Calvo E, Retana J (2004) Interacció entre estructura del paisatge, usos del sòl i règim d’incendis. In Plana E (ed) Incendis forestals, dimensió socioambiental, gestió del risc i ecologia del foc. Xarxa ALINFO XCT2001-00061, Solsona, pp. 34-37.
Espelta JM, Retana J, Habrouk A (2004) Gestió de boscos menuts d’alzina i roure después d’incendis. In: Plana E (ed) Incendis forestals, dimensió socioambiental, gestió del risc i ecologia del foc. Xarxa ALINFO XCT2001-00061, Solsona, pp. 124-127.
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