Response to natural and simulated browsing of two Mediterranean oaks with contrasting leaf habit after a wildfire

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.
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Doi: 10.1051/forest:2006024

Resum:

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.

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Post-fire regeneration thinning, cone production, serotiny and regeneration age in Pinus halepensis

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.
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Doi: 10.1016/j.foreco.2006.05.041

Resum:

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.

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