Post-fire recovery of Mediterranean ground ant communities follows vegetation and dryness gradients

Arnan X., Rodrigo A., Retana J. (2006) Post-fire recovery of Mediterranean ground ant communities follows vegetation and dryness gradients. Journal of Biogeography. 33: 1246-1258.
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Doi: 10.1111/j.1365-2699.2006.01506.x

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Aim: In the Mediterranean Basin, the main forest communities vary in their ability to recover after fire. In this study we analyse the effects of fire on ant communities occurring in various vegetation types distributed along a geographical gradient in the western Mediterranean region. Location: The study was carried out in burned and unburned habitats of 22 sites corresponding to eight vegetation types distributed along a gradient of dryness throughout Catalonia (north-east Spain). Methods: We placed five pairs of plots (one plot located in the burned area and the second one placed in the unburned margin) per site. We compared ant communities in these unburned and burned plot types 8 years after fire using pitfall traps. Traps were set out in mid-May and mid-July. We analysed the structure and composition of ant communities in the burned and unburned areas of these vegetation types using anova tests, correspondence analysis (CA) and linear regression. Results: The resilience of ant communities varies with vegetation type. Ant communities in forests with high resilience also recover rapidly after fire, while those in forests that do not recover after fire show the lowest resilience. Species richness does not depend on burning or vegetation type. The resilience of these Mediterranean ant communities to fire is related to the environmental characteristics of the region where they live. Accordingly, differences between burned and unburned habitats are smaller for ant communities in areas with higher water deficit in summer than for those in moister ones. Main conclusions: The structure and composition of ant communities after fire depends on the level of direct mortality caused by the fire. It affects ant species differently, as determined by the habitats used for nesting and foraging. The reestablishment of vegetation cover depends on forest composition before the fire. As vegetation cover determines resource and microhabitat availability and competitive relationships among species, forest composition before the fire also affects post-fire recovery of ant communities to the medium-term. Finally, ant communities living in drier areas recover more quickly after fire than those living in moister ones. This pattern might be because in areas with higher water deficit there are more species characteristic of open environments, which are habitats similar to those generated after fire. © 2006 The Authors.

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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

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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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A model of the recruitment of Pinus nigra from unburned edges after large wildfires

Ordóñez J.L., Molowny-Horas R., Retana J. (2006) A model of the recruitment of Pinus nigra from unburned edges after large wildfires. Ecological Modelling. 197: 405-417.
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Doi: 10.1016/j.ecolmodel.2006.03.027

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We have developed a simulation model for predicting the recruitment response of Pinus nigra from unburned edges in areas affected by large wildfires, where the regeneration of burned forests of this tree species is very low. We have simulated the distribution of P. nigra seedlings at different distances from the unburned edges by integrating empirical field data for the different processes affecting seed and seedling success. The simulation model determines the final number of seedlings established in any subplot, within the burned area, as the multiplication of a number of statistically independent processes, from cone and seed production and predation, to seed germination and seedling establishment. Probabilities are drawn at random at each time step from the experimental distributions that describe those processes. The model runs for a given number of years, thus simulating the accumulative effects on the total number of established seedlings of the different processes involved. That represents one model run, which is then repeated a sufficient number of times to calculate simulated distributions of established seedlings as a function of distance from the forest edge. The validation of those results with data from field measurements of seedling establishment in old-burned areas has demonstrated the ability of the simulation algorithm to reproduce observed results. Furthermore, the simulations carried out with the model for actual plots, located near the margins of the burned areas affected by the largest fires affecting P. nigra forests in Catalonia in recent years, have all shown striking similarities. The simulated values of established seedlings follow a Gaussian-like distribution in the first 100 m, with a wide range of 2000-25,000 seedlings/ha. There is also a clear trend for plots with medium and large trees to show an increment in increasing seedling establishment with tree density, whereas plots dominated by small trees give very low regeneration values. © 2006 Elsevier B.V. All rights reserved.

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Post-fire recovery of ant communities in Submediterranean Pinus nigra forests

Rodrigo A., Retana J. (2006) Post-fire recovery of ant communities in Submediterranean Pinus nigra forests. Ecography. 29: 231-239.
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Doi: 10.1111/j.2006.0906-7590.04272.x

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This study analyzes the variations in the structure and composition of ant communities in burned Pinus nigra forests in central Catalonia (NE Spain). Pinus nigra forests do not recover after fire, changing to shrublands and oak coppices. For this reason, we suggest that ant communities of burned P. nigra forests will change after fire, because the post-fire scenario, in particular with the increase of open areas, is different to the unburned one, and more favourable for some species than for others. In four locations previously occupied by P. nigra forests where different fires occurred 1, 5, 13 and 19 yr before the sampling, we sampled the structure and composition of ant communities with pitfall traps, tree traps and net sweeping in unburned plots and in plots affected by canopy and understory fire. The results obtained suggest that canopy and understory fire had little effect on the structure of ant communities. Thus, many variables concerning ant communities were not modified either by fire type (understory or canopy fire) or by time since fire. However, a number of particular species were affected, either positively or negatively, by canopy fire: three species characteristic of forest habitats decreased after fire, while eight species characteristic of open habitats increased in areas affected by canopy fire, especially in the first few years after fire. These differences in ant community composition between burned and unburned plots imply that the maximum richness is achieved when there is a mixture of unburned forests and areas burned with canopy fire. Moreover, as canopy cover in P. nigra forests burned with canopy fire is not completed in the period of time studied, the presence of the species that are characteristic of burned areas remains along the chronosequence studied, while the species that disappear after fire do not recover in the period of time considered. Overall, the results obtained indicate that there is a persistent replacement of ant species in burned P. nigra forests, as is also the case with vegetation. Copyright © ECOGRAPHY 2006.

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