Estiarte M., De Castro M., Espelta J.M. (2007) Effects of resource availability on condensed tannins and nitrogen in two Quercus species differing in leaf life span. Annals of Forest Science. 64: 439-445.LinkDoi: 10.1051/forest:2007021
Seedlings of Quercus ilex and Q. cerrioides, an evergreen and a winter-deciduous oak co-occurring in western-Mediterranean forests, were grown at two light regimes (8 and 36% of photosynthetically active radiation), at two water regimes (500 and 800 mm) and with two nutrient availabilities (standard substrate and 7% increase in soil N). The concentrations of soluble condensed tannins (CT) and nitrogen in the leaves were analyzed to test the phenotypic plasticity of these commonly related parameters in two congeneric species with contrasting leaf habit. Q. ilex contains seven times more CT and a few less N than Q. cerrioides. Light increased CT, whereas neither fertilization nor water had an effect on CT. N concentration was decreased by light, increased by fertilization and not affected by water treatment. Plant growth was increased by light but not affected by fertilization or water treatment. CT were negatively correlated with N concentration. CT of the evergreen species exhibited greater plasticity than the deciduous one as reflected by a steeper negative correlation among nitrogen and CT concentrations in Q. ilex. Given the antiherbivory activity of CT, this implies that in less shaded environments, e.g. canopy aperture by disturbances, leaf tissue quality for herbivores will be much more reduced in Q. ilex than in Q. cerrioides. Higher leaf CT in Q. ilex and its higher plasticity to light availability may explain the higher browsing by sheep in Q. cerrioides than in Q. ilex resprouts, as well as the low recruitment rates of seedlings of the former species, reported in other studies. © INRA, EDP Sciences, 2007.
Moya D., Espelta J.M., Verkaik I., López-Serrano F., De Las Heras J. (2007) Tree density and site quality influence on Pinus halepensis Mill. reproductive characteristics after large fires. Annals of Forest Science. 64: 649-656.LinkDoi: 10.1051/forest:2007043
In Spain, many Pinus halepensis Mill. forests have been seriously affected by significant forest fires in the past decade, in 1994 alone, more than 100 000 ha were burned in Eastern Spain. In order to study the reproductive characteristics of P. halepensis after forest fires, six locations were selected in four areas affected by serious fires in the summer of 1994, and the following different precipitation zones were studied: dry-subhumid, dry and semi-arid. Ten years after the fires, data relevant to the production of pine cones: serotinous (grey), mature (brown), immature (green) and opened cones, was collected from areas with natural post-fire regeneration. Various cone and seed characteristics, such as pine cone seed number and weight, and germination percentage, were measured. The results showed greater production of cones and strobili in high-density sites. The biggest cone sizes (volume) and seed number per cone were related to site quality (dry-subhumid precipitation zone). Also, viability and germination percentages were higher with better site quality, with significant differences in values for serotinous and non-serotinous cones. Despite these differences, the canopy seed bank was large enough to ensure regeneration in this area for this age stand. © INRA, EDP Sciences, 2007.
Quevedo L., Rodrigo A., Espelta J.M. (2007) Post-fire resprouting ability of 15 non-dominant shrub and tree species in Mediterranean areas of NE Spain. Annals of Forest Science. 64: 883-890.LinkDoi: 10.1051/forest:2007070
Post-fire resprouting ability of the non-dominant tree and shrub species of the Mediterranean Basin has not yet been experimentally tested, although this group contributes to maintain the richness of Mediterranean plant communities. In this study, we have analyzed the post-fire recovery ability of 15 woody species that occur in relatively low abundance in dry and sub humid Mediterranean areas in NE of Spain. The main goals have been: (i) to determine experimentally the post-fire resprouting ability of these species and (ii) to compare the abundance of these species in areas affected by wildland fires and in unburned areas. We have observed a high resprouting ability after prescribed burning of most species except for Juniperus communis and J. phoenicea which showed a null resprouting. As the species with high resprouting ability showed similar presence in burned and unburned areas, we can conclude that wildfires are not a factor that constrains the presence of these species in Mediterranean woodlands. However, we found a reduction in the abundance of J. communis and J. phoenicea at the regional level after wildland fires. © INRA, EDP Sciences, 2007.
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.
Verkaik I., Espelta J.M. (2006) Post-fire regeneration thinning, cone production, serotiny and regeneration age in Pinus halepensis. Forest Ecology and Management. 231: 155-163.LinkDoi: 10.1016/j.foreco.2006.05.041
Many pines growing in fire-prone ecosystems exhibit an abundant production of cones and the retention of part of these cones as an aerial seed bank in the canopy (serotiny). The protection of seeds and their prolific release after fire facilitate the re-colonization of the burned area. However, over-stocking in this fire regenerated stands may constraint tree growth, as well as increase the risk of new wildfires. Therefore, thinning is strongly recommended both to reduce fire occurrence and to reduce intraspecific competition. Although the benefits of thinning for tree growth in fire regenerated forests have been thoroughly documented, less attention has been paid to the effects on reproductive traits such as the timing of reproduction, the size of the cone crop and the degree of serotiny. In this study, the effects of thinning on the reproductive traits of fire regenerated Pinus halepensis forests with different regeneration age (22-, 18- and 10-yr-old) were investigated. In the thinned plots, there was a greater increase in the percentage of pines that started producing cones for the first time (thinning = 50.4 ± 11.4%, control = 13.3 ± 4.0%), as well as an increase in the number of new cones produced per pine (between two- and six-fold compared to the control stands). Our results show that thinning may decrease serotiny depending on age. Thus, the number of pines bearing open cones did not change during the study in the thinned or control plots of the younger stands (10 yrs) or in the control plots of 22 and 18 yrs, while it increased in the thinned stands of 22 and 18 yrs. Not a single cone was observed to open during the study in the thinned or control 10-yr-old plots, while in the 22- and 18-yr-stands the number of old serotinous cones per pine opened was higher in the thinned plots than in the control ones. Therefore, we conclude that thinning in fire regenerated P. halepensis forests should be conducted in younger stands (10-yr-old, in our study), because thinning at this age shortens the juvenile (non-reproductive) period and greatly increases the number of new cones produced per pine in completely serotinous individuals. © 2006 Elsevier B.V. All rights reserved.
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 (2004) Dinàmica forestal. In Terradas J, Rodà F (eds) Els boscos de Catalunya: Estructura, funcionament i dinàmica. Documents dels Quaderns de medi ambient, Núm. 11. Departament de Medi Ambient i Habitatge, Generalitat de Catalunya, Barcelona, pp. 115-122.
Cortés P, Espelta JM, Savé R, Biel C (2004) Effects of a nursery CO2 enriched atmosphere on the germination and seedling morphology of two Mediterranean oaks with contrasting leaf habit. New Forests 28:79-88.
Espelta JM (2004) Els incendis forestals. In Terradas J, Rodà F (eds) Els boscos de Catalunya: Estructura, funcionament i dinàmica. Documents dels Quaderns de medi ambient, Núm. 11. Departament de Medi Ambient i Habitatge, Generalitat de Catalunya, Barcelona, pp. 123-136.
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