Poden conviure el bosc i el foc? : nous avenços de la recerca en ecologia del foc

El foc és un factor ecològic natural en nombrosos ecosistemes, però la seva freqüència i extensió han estat modificades per l'home. Actualment el règim d'incendis en moltes zones de clima mediterrani es caracteritza per un augment en el nombre d'incendis, en la seva reiteració i en la seva grandària. Aquest fet, unit a l'augment de la temperatura i dels episodis de sequera induïts pel canvi climàtic en aquesta àrea, genera incerteses sobre quina pot ser la resposta funcional dels ecosistemes i quins canvis es poden produir en la distribució d'espècies i l'estructura de les comunitats. Malgrat la reconeguda resiliència de les comunitats mediterrànies al foc, estudis recents demostren que aquesta resposta no és extensiva a tot tipus de sistemes i que fins i tot aquelles espècies que presenten mecanismes que els permeten regenerar-se eficaçment davant aquesta pertorbació, com la rebrotada o el manteniment de bancs de llavors protegits, poden veure's greument afectades per un augment en la freqüència, intensitat o grandària dels incendis o la seva combinació amb altres pertorbacions (p. ex., sequera). Fins a quin punt aquests efectes poden ser mitigats mitjançant diferents estratègies de gestió requereix un considerable esforç d'investigació.Fire is a natural ecological factor, but fire frequency and fire expansion have been modified by human activities. The present wildfire regime in most Mediterranean-type climate areas is characterized by an increase in the number, recurrence and size of fires. Moreover, increasing warming and drought episodes due to climate change in this ecological scenario may challenge the functional response of ecosystems and induce changes in the structure and species composition of Mediterranean communities. In spite of the well known resilience of Mediterranean-type ecosystems to fire, recent studies have demonstrated that this response is not applicable to all communities and that, even species with a successful regeneration after fire, due to resprouting or the presence of seed banks, may be threatened by an increase in the frequency, intensity and size of fires and/or the occurrence of other disturbances (e.g. drought). To what extent these effects could be modified by different management strategies remains to be further investigated

Masting plants: Why combine abstinence and lust in reproduction?

La majoria de plantes perennes produeixen llavors cada any, però n’hi ha algunes que mostren un comportament reproductiu estrany: les seves poblacions produeixen extraordinàries collites de manera erràtica i sincrònica, però passen alguns anys pràcticament sense reproduir-se. Són les espècies anyívoles i el motiu d’aquest comportament sexual, com es produeix, i les conseqüències que té per a les xarxes tròfiques ha intrigat els ecòlegs. En aquest treball presentem un resum del coneixement actual sobre les causes evolutives i ecològiques que promourien aquest comportament. Les dues hipòtesis més versemblants de la seva evolució serien els avantatges de controlar les poblacions de depredadors de llavors i afavorir que algunes escapin (saciat dels depredadors) i/o una millor eficàcia en la pol·linització de plantes pol·linitzades pel vent (eficiència en la pol·linització). La variabilitat entre anys en la mida de les collites seria el resultat de la possibilitat que les plantes puguin dedicar més o menys recursos a la reproducció a partir de les condicions ambientals (p. ex. meteorològiques, de mobilització de nutrients) mentre que la sincronia entre individus, fins i tot a grans escales espacials, seria el resultat de l’anomenat Efecte Moran, és a dir, la resposta a una condició ambiental amb àmplia sincronia espacial com és la meteorologia i els seus efectes en la floració o la maduració dels fruits. Finalment, es presenta el coneixement més recent sobre les causes que determinen que una espècie com l’alzina (Quercus ilex), tan important i abundant al nostre país, sigui anyívola i les seves conseqüències.Most perennial plants produce seeds every year, but some species show a bizarre reproductive behaviour: they produce bumper crops randomly and synchronously in some years, while in other years they produce virtually no seeds. These are known as masting species and the benefits of this behaviour, how it occurs, and the consequences for trophic networks have long intrigued ecologists. Here we present a summary of current knowledge about the evolutionary and ecological causes that promote masting. The two most likely hypotheses for its evolution are the advantages of controlling seed predator populations and encouraging some seeds to escape (predator satiation) and/or better efficiency in the pollination of wind-pollinated plants (pollination efficiency). The variability between years in the size of crops results from the fact that plants devote more or fewer resources to reproduction depending on the environmental conditions (e.g. meteorological conditions and nutrient mobilization). In addition, the synchrony between individuals, even at large spatial scales, is the result of the so-called Moran Effect: i.e. the response to an environmental condition with a broad spatial synchronization such as meteorology and its effects on the flowering or maturation of the fruits. Finally, we present the most recent knowledge on the reasons why the holm oak (Quercus ilex), so important and abundant in Catalonia, exhibits masting behaviour, and its consequences

Contrasting effects of fire severity on the regeneration of Pinus halepensis Mill. and resprouter species in recently thinned thickets

Many studies have outlined the benefits for growth and reproduction resulting from thinning extremely crowded young forests regenerating after stand replacing wildfires ("thickets"). However, scarce information is available on how thinning may influence fire severity and vegetation regeneration in case a new fire occurs. We investigated the relationship between thinning and fire severity in P. halepensis thickets, and the effects on the establishment of pine seedlings and resprouting vigour in resprouter species the year after the fire. Our results show a positive relationship between forest basal area and fire severity, and thus reserved pines in thinned stands suffered less fire damage than those in un-thinned sites (respectively, 2.02 ± 0.13 vs. 2.93 ± 0.15 in a scale from 0 to 4). Ultimately, differences in fire severity influenced post-fire regeneration. Resprouting vigour varied depending on the species and the size of individuals but it was consistently higher in thinned stands. Concerning P. halepensis, the proportion of cones surviving the fire decreased with fire severity. However, this could not compensate the much lower pine density in thinned stands and thus the overall seed crop was higher in un-thinned areas. Establishment of pine seedlings was negatively affected by the slope and positively driven by the number of cones and thus it was higher in un-thinned than in thinned stands (respectively, 2581 ± 649 vs. 898 ± 325 seedlings∙ha-1). Thinning decreases fire intensity, and thus it may facilitate fire suppression tasks, but retaining a higher density of pines would be necessary to ensure P. halepensis regeneration after a new fire even

History matters: previous land use changes determine post-fire vegetation recovery in forested Mediterranean landscapes

Land use changes and shifts in disturbance regimes (e.g. wildfires) are recognized worldwide as two of the major drivers of the current global change in terrestrial ecosystems. We expect that, in areas with large-scale land use changes, legacies from previous land uses persist and affect current ecosystem responses to climate-associated disturbances like fire. This study analyses whether post-fire vegetation dynamics may differ according to specific historical land use histories in a Mediterranean forest landscape of about 60,000 ha that was burnt by extensive fires. For that, we assessed land use history of the whole area through the second half of the XXth century, and evaluated the post-fire regeneration success in terms of: (i) forest cover and (ii) tree species composition (biotic-dispersed, resprouter species, Quercus spp. vs. wind-dispersed species with or without fire-resistant seed bank, Pinus spp.). Results showed that stable forest areas exhibited a higher post-fire recovery than younger forests. Furthermore, the longer since crop abandonment translates into a faster post-fire recovery. Results highlight that to anticipate the impacts of disturbances on ecosystems, historical land trajectories should be taken into account.Collaborative work was facilitated by the Consolider-Ingenio Montes CSD2008-00040 project by Spanish Ministry of Science and Innovation. Postdoctoral and predoctoral fellowships to CPP (EX2009-0703) and BSH (FPU) were provides by Spanish Ministry of Education

Unexpected consequences of a drier world: evidence that delay in late summer rains biases the population sex ratio of an insect

The complexity of animal life histories makes it difficult to predict the consequences of climate change on their populations. In this paper, we show, for the first time, that longer summer drought episodes, such as those predicted for the dry Mediterranean region under climate change, may bias insect population sex ratio. Many Mediterranean organisms, like the weevil Curculio elephas, become active again after summer drought. This insect depends on late summer rainfall to soften the soil and allow adult emergence from their underground refuges. We found that, as in many protandric species, more C. elephas females emerged later in the season. Male emergence timing was on average earlier and also more dependent on the beginning of late summer rainfall. When these rains were delayed, the observed weevil sex ratio was biased towards females. So far, the effects of global warming on animal sex ratios has been reported for temperature-dependent sex determination in reptiles. Our results show that rainfall timing can also bias the sex ratio in an insect, and highlight the need for keeping a phenological perspective to predict the consequences of climate change. We must consider not just the magnitude of the predicted changes in temperature and rainfall but also the effects of their timing.R.B. was funded by a contract of the Atracción de Talento Investigador Programme (Gobierno de Extremadura). A.M. was funded by a Juan de la Cierva contract (Ministerio de Educación). J.M.A. and M.H. were funded by the Spanish Research Council (CSIC). J.M.E. is contracted by the CREAF Institute. The work was financed by the projects: CONSOLIDER-MONTES CSD2008-00040 CONSOLIDER-MICINN, PII1C09-0256-9052 and PPII-2014-01-PJCCM ESF and CGL2008-00095/BOS MICINN.Peer Reviewe

Identificación de los anillos anuales de crecimiento de la encina (Quercus ilex. L.)

Las caracteristicas de la madera de encina (Quercus ilex L.) hacen de muy difícil interpretación el patrón de crecimiento anual de esta especie. Con el fin de intentar encontrar un método práctico y, al mismo tiempo, fiable para la identificación de los anillos anuales de crecimiento de la encina, se han seguido dos aproximaciones: el estudio de discos enteros de troncos y el de testigos de madera recogidos con barrena Pressler. La utilización de discos plantea dos problemas: por una parte se destruyen los individuos muestreados y, por otra, con ninguno de los métodos de preparación de la madera (pulido o corte transversal) se aprecian de manera clara los vasos conductores, que son la caracteristica más clara para identificar los distintos anillos. Los testigos de madera tienen la ventaja de que su manipulación es sencilla y que aseguran la supervivencia de los árboles muestreados. Sin embargo, en los tradicionales testigos de 5 mm de diámetro, la presencia de radios medulares que atraviesan la muestra impide la delimitación de los anillos de crecimiento. Este problema se soluciona con la utilización de testigos de madera de 12 mm de diámetro que, una vez cortados, perrmiten mostrar claramente el patrón de vasos. A partir de los datos obtenidos con muestras de encina de edad conocida pertenecientes a rebrotes muestreados en zonas cortadas o quemadas, se constata que la diferencia entre el número de años y el número de anillos identificados en los testigos de madera es, como máximo, de dos o tres. Esto hace que el método propuesto pueda ser utilizado de manera fiable en el estudio de la edad y del crecimiento de esta especie.The growth pattem of the holm oak (Quercus ilex L.) is difficult to interpret due to varied features of its wood. In order to find a practical as well as reliable method for interpreting annual tree-rings of the holm oak, two approaches have been tried: the study of basal disks and the study of 5 mm-diarneter, and 12 mm-diameter cores taken with a Pressler borer. We do not recommend the use of disks because the sampled individuals are destroyed during collection, and because with none of the methods used for treating wood (polishing and cutting) is it possible to show the vessels, which are the clearest form of identifying different tree-rings. Cores are easily manipulated and allow the survival of sampled trees; nevertheless, the traditional 5 mm-diameter cores are not adequate because holm oak wood is crossed by many wood rays, which prevent the definition of tree-ring limits. This problem has been solved using 12 mm-diameter which, after cutting, clearly show the vessel pattem. By means of dated samples of holm oak wood it has been possible to establish that the number of annual growth rings and the number of years differ in fewer than two or three units. The high correlation between both variables makes the propossed method highly efficient for interpreting age and growth patterns of the holm oak

The interplay among acorn abundance and rodent behavior drives the spatial pattern of seedling recruitment in mature Mediterranean oak forests

The patterns of seedling recruitment in animal-dispersed plants result from the interactions among environmental and behavioral variables. However, we know little on the contribution and combined effect of both kinds of variables. We designed a field study to assess the interplay between environment (vegetation structure, seed abundance, rodent abundance) and behavior (seed dispersal and predation by rodents, and rooting by wild boars), and their contribution to the spatial patterns of seedling recruitment in a Mediterranean mixed-oak forest. In a spatially explicit design, we monitored intensively all environmental and behavioral variables in fixed points at a small spatial scale from autumn to spring, as well as seedling emergence and survival. Our results revealed that the spatial patterns of seedling emergence were strongly related to acorn availability on the ground, but not by a facilitationeffect of vegetation cover. Rodents changed seed shadows generated by mother trees by dispersing most seeds from shrubby to open areas, but the spatial patterns of acorn dispersal/predation had no direct effect on recruitment. By contrast, rodents had a strong impact on recruitment as pilferers of cached seeds. Rooting by wild boars also reduced recruitment by reducing seed abundance, but also by changing rodent's behavior towards higher consumption of acorns in situ. Hence, seed abundance and the foraging behavior of scatter-hoarding rodents and wild boars are driving the spatial patterns of seedling recruitment in this mature oak forest, rather than vegetation features. The contribution of vegetation to seedling recruitment (e.g. facilitation by shrubs) may be context dependent, having a little role in closed forests, or being overridden by directed seed dispersal from shrubby to open areas. We warn about the need of using broad approaches that consider the combined action of environment and behavior to improve our knowledge on the dynamics of natural regeneration in forests

El riesgo de depredación y la competencia intraespecífica alteran el comportamiento de dispersión de semillas por parte de roedores

Los roedores tienen un importante papel como dispersores/depredadores de bellotas en los bosques Mediterráneos de Quercus spp. Existe abundante información del efecto de factores intrínsecos de las semillas (tamaño, composición) en la selección de las bellotas por estos animales, mientras que la influencia de otros procesos como el riesgo de depredación o la competencia intraespecífica han estado mucho menos estudiados. En un bosque mixto de encina y roble en el Parque Natural de Collserola, se ha investigado el patrón de dispersión/depredación de bellotas por parte del ratón de campo (Apodemus sylvaticus) en función del riesgo de depredación por parte de jineta (Genetta genetta) y la competencia intraespecífica (mediante un experimento en el que estos factores se simulaban a partir de olores). Un censo previo determinó que la población de roedores presente en el área de estudio estaba formada principalmente por Apodemys sylvaticus. Éstos respondieron al tratamiento de olor pues se observó un retraso significativo en la manipulación de bellotas de jineta respecto a los otros dos tratamientos. Asimismo, respecto a la distancia de dispersión se observó que las bellotas del tratamiento con olor a ratón eran dispersadas a menor distancia, a una distancia intermedia las de jineta y a mayor distancia las del tratamiento control. En todos los tratamientos, las bellotas dispersadas a zonas de microhábitat abierto fueron menos depredadas. Este trabajo sugiere que el patrón espacio temporal de dipersión/depredación de bellotas en bosques de encina y roble puede tener una elevada complejidad, a la vez que subraya el interés de mantener la integridad de las redes tróficas por sus efectos directos e indirectos sobre las poblaciones de organismos situados a diferentes niveles.Rodents may play an important role as seed dispersers/predators in Mediterranean oak (Quercus spp) forests. There exists much information about the influence of seed size or composition on the rodent choices while the influence of other environmental factors (risk of predation, instraspecific competition) has been barely addressed. In a typical Mediterranean mixed oak forest we studied how the pattern of acorn dispersal/predation by wood mouse (Apodemus sylvaticus) was influenced by the risk of predation by genet (Genetta genetta) or intraspecific competition (wood mice presence) by means of simulating their odour clues. According to a sampling campaign the dominant species of rodent in the study area was wood mouse Apodemus sylvaticus. Mice responded to odour treatment because there was a significant delay in the handling of acorns in the genet treatment in comparison to the other two treatments. Concerning the distance of acorn dispersal, acorns from the mouse treatment were dispersed at shorter distances in comparison to the control treatment, while those from the genet treatment were dispersed at intermediate ones. This work shows a highly complex spatial pattern of acorn dispersal while it emphasizes the importance conserving the integrity of the food web structure because of the direct and indirect effects among different organisms at different levels.Els rosegadors tenen un important paper com dispersors/depredadors d'aglans en els boscos Mediterranis de Quercus spp. Existeix molta informació de l'efecte dels factors intrínsecs de les llavors (mida i composició) a la selecció de les aglans per aquests animals, mentre que la influència d'altres processos com el perill de depredació o la competència intraespecífica han estat molt menys estudiats. En un bosc mixt d'alzina i roure al Parc Natural de Collserola, s'ha investigat el patró de dispersió/depredació d'aglans per part del ratolí de bosc (Apodemus sylvaticus) en funció del perill de depredació per part de la geneta (Genetta genetta) i la competència intraespecífica (mitjançant un experiment en el que aquests factors es simulaven a partir d'olors). Un cens previ determinà que la població de rosegadors a l'àrea d'estudi estava formada principalment per Apodemus sylvaticus. Aquests van respondre al tractament d'olor ja que es va observar un retard significatiu en la manipulació d'aglans de geneta respecte als altres dos tractaments. De la mateixa manera, respecte a la distancia de dispersió, es va observar que les aglans del tractament amb olor a ratolí eren dispersades a menor distancia, a una distancia intermèdia les de geneta i a una major distancia les del tractament control. En tots els tractaments, les aglans dispersades a zones de microhábitat obert van ser menys depredades. Aquest treball suggereix que el patró espai temporal de dispersió/depredació d'aglans en boscos d'alzina i roure pot tenir una elevada complexitat, al mateix temps que remarca l'interès de mantenir la integritat de les xarxes tròfiques pels seus efectes directes i indirectes sobre les poblacions d'organismes situats a diferents nivells