2. Geomorph. N. К 48 3 293-304 Berlin ■ Stuttgart September 2004 Hydrological response of Mediter... more 2. Geomorph. N. К 48 3 293-304 Berlin ■ Stuttgart September 2004 Hydrological response of Mediterranean gorse shrubland under extreme rainfall simulation event José Carlos González-Hidalgo, Martín de Luís, Josep Raventós, JoRDi Cortina and Juan Rafael ...
Departamento de Ecología y Recursos Naturales, Facultad de Ciencias, Universidad Nacional Autónom... more Departamento de Ecología y Recursos Naturales, Facultad de Ciencias, Universidad Nacional Autónoma de México, Mexico City, Mexico Departamento de Ecología, Universidad de Alicante, Alicante, Spain Departamento de Biología Comparada, Facultad de Ciencias, Universidad Nacional Autónoma de México, Mexico City, Mexico Departamento de Ecología de la Biodiversidad, Instituto de Ecología, Universidad Nacional Autónoma de México, Mexico City, Mexico
ABSTRACT Background: Epiphyte removal forms part of routine management in shade coffee plantation... more ABSTRACT Background: Epiphyte removal forms part of routine management in shade coffee plantations. Aims: Assess the current status of three population orchids growing in Mexican shaded coffee plantations and evaluate the effect of perturbing the transient behaviour of different life stages. Methods: We modelled the short-term response of eliminating I) non-reproductive juveniles, or II) reproductive adult plants from coffee bushes, on populations of Oncidium poikilostalix, Lepanthes acuminata and Telipogon helleri (Orchidaceae). First, we calculated the transient dynamics per se and second, we made a perturbation analysis on population inertia. Finally, we made a comparison with a traditional sensitivity analysis. Results: All three species showed different positive asymptotic growth rate: O. poikilostalix (λmax = 1.106), L. acuminata (λmax = 1.209), and T. helleri (λmax = 1.012). The effect of eliminating the major part of the juvenile or adult orchids gave population inertia in relation to steady state, respectively, (+19%, -24%) for O. poikilostalix, (+17%, -28%) for T. helleri and (+57%, -35%) for L. acuminata. Conclusions: Eliminating juveniles or adults affects in different ways the short-term dynamics due to differential impact on size stages that have the non-linear effects associated with important disturbances that currently affect orchids growing in coffee plantations.
Background and Aims: Biological invasions are considered as second to habitat loss as a cause of ... more Background and Aims: Biological invasions are considered as second to habitat loss as a cause of the extinction of species. The study of population dynamics is particularly relevant for species with expansive behavior. The aims of this study were to: (1) evaluate the population ecology of Oncidium poikilostalix in shaded coffee plantations in Mexico, (2) evaluate the reproductive behavior of O. poikilostalix in this habitat, and (3) determine whether this orchid should be considered as an invasive species.Methods: During 2013-2015, most of the individuals of the Mexican population of O. poikilostalix (located south of the state Chiapas) were marked and measured. Additionally, the flower and fruit production (first flowering and repeated flowering), mortality and recruitment of new individuals were registered annually, and its potential distribution was modeled.Key results: Within this period a population increase of 1.11% was observed, with a proportional increase in the number of f...
The expansion of invasive species is a global concern. Within the Orchidaceae there are a number ... more The expansion of invasive species is a global concern. Within the Orchidaceae there are a number of invasive species. One of the most widely distributed invasive orchids in Mexico is Oeceoclades maculata (Lindl.) Lindl. By examining the population dynamic variations of an invasive species in its range of expansion, we can identify the factors that have contributed to that variation. Life Table Response Experiments (LTRE) were used to describe the dynamic of four populations of O. maculata in different ecosystems in south Chiapas, Mexico. Our goals were to quantify the contributions of differences between years and sites, and their interactions, to overall differences in population growth rate (k), and to underlying vital rates. Fertility, survival and growth made the largest contributions, both positive and negative, to annual differences in k. Spatial variations in k were also found. The largest plants (S3 and S4) made the contributions of greatest magnitude each year and in each site. In seven of eight cases, the inclusion of the interaction term gave a better estimate of the population growth rate. This investigation highlights the need for taking into account life-history variations at different scales when the research goal is to study expansion of an invasive species in a heterogeneous landscape. The usefulness of LTRE studies was also demonstrated to better understand the natural history of the species and thus lay the groundwork for planning efficient management strategies, either for the conservation of rare, endangered species, or for the control of invasive species.
CORRECCIÓN DE PRUEBAS: Será realizada por la redacción de la revista, aunque los autores deben en... more CORRECCIÓN DE PRUEBAS: Será realizada por la redacción de la revista, aunque los autores deben enviar un texto muy claro y definitivo. Si se hallan deficiencias notorias en el texto, el trabajo será remitido a los autores de inmediato. TABLAS: Cada tabla en página por separado, numeradas siguiendo el orden de aparición en el texto y llevarán leyenda. El método de escritura admitido puede ser WORD o EXCEL. GRÁFICAS y DIBUJOS: Presentados en papel blanco no reciclado, exclusivamente en blanco y negro. Las láminas en color deberán ser costeadas por los autores. Gráficas y dibujos deben ser presentados de forma que, modificando su dimensión, no se vea modificada su comprensión. Deberán acompañar las leyendas al gráfico, suficientemente grandes e incluidas en la caja del mismo. Es obligatorio acompañar archivo en disco compatible y formato TIF o JPEG. ILUSTRACIONES: Las fotografías, separadas del texto, con leyenda y número de orden, posición en el texto, etc. NOTAS: Excepcionalmente se incluirán notas a pie, pero éstas deben ir en hojas separadas y debidamente numeradas. EXTENSIÓN: El texto comprenderá una extensión de 5 (min.) a 25 (max.) páginas mecanografiadas. El numero de gráficos, dibujos y fotografías debe ser proporcional al tamaño del texto. La dirección de la revista se reserva el derecho de revisar los trabajos presentados con el fin de adaptarlos a la publicación. http://publicaciones.ua.es Notes for the authors SUBJECTS Ecology Natural Resources Landscape Environmental Management Manuscripts typed on duplicate on one side of the sheet only, should be sent to the magazine direction: Mediterranea. S.E.B.Dep. Ecologia. Universidad de Alicante. Ap. 99 (03080 Alicante) Spain. All authors are kindly requested to send their papers in writing, but namely on MS DOS/IBM compatible disks, using MS-WORD program. Every paper should conform to the following rules:
In the Caribbean basin, hurricanes represent a dominant disturbance force for the tropical coasta... more In the Caribbean basin, hurricanes represent a dominant disturbance force for the tropical coastal forests. Using an Integral Projection Model (IPM), we assessed the population status of Encyclia bocourtii (Orchidaceae) three years after damage caused by Hurricane Ivan during its passage through the peninsula of Guanacahabibes, Cuba. Based on the abundance of E. bocourtii recorded in permanent study plots, we know that the population declined by 63% after disturbance. Our results show that the estimated asymptotic growth rate from the fitted integral model was λmax=1.028 [0.9377 – 1.1399]; the uncertainty associated with this parameter is related to the process of estimating reproductive variables on epiphytic orchids. The elasticity surface showed that elasticities are high along the first part of the principal diagonal representing the birth and survival of small to medium-size individuals. A damping ratio close to 1 suggested that the current structure is far from equilibrium, wh...
Since the early 1990s, Mediterranean gorse shrublands have expanded significantly in the Mediterr... more Since the early 1990s, Mediterranean gorse shrublands have expanded significantly in the Mediterranean regions of Spain mainly as a result of the increase in the frequency and extension of forest fires. Mediterranean gorse (Ulex parviflorus), which has been described as a degradation stage of forest communities after fire, has also been described as a fire-prone community. Thus, its presence increases the risk that new fires might occur. In spite of this evidence, there is little information on both the composition and structural characteristics of these communities or the relationship that might exist between these vegetation characteristics and fire behaviour. In this paper we present the results of a characterization of the vegetative structure (plant density, specific composition, biomass fractions, and horizontal and vertical fuel distribution) in Mediterranean gorse. We also analyse fire behaviour using indicators obtained at different scales. Our results show mature Mediterranean gorse shrublands to be communities with high biomass values (3000-4000 g m −2) and high horizontal and vertical vegetation continuity, in which the proportion of fine dead fuel fractions with low moisture content is around 50% of the total phytomass present. Ulex parviflorus is the dominant species and its degree of dominance is a key element in the behaviour of fire. Both the fire-line intensity values and the fire severity values observed can be considered high with respect to those observed in other Mediterranean communities, thus confirming Mediterranean gorse as a high-risk community.
Summer wildfires and autumn torrential rainfall are the background to the development of one of t... more Summer wildfires and autumn torrential rainfall are the background to the development of one of the most important environmental problems in the western Mediterranean area: erosion, degradation of soil structure and desertification. These processes especially affect plant communities located in old abandoned fields where woody sprouters are practically absent. Under these conditions, post-fire vegetation cover is dependent on obligate seeders and, in the short term, especially on resprouting perennial grasses. Brachypodium retusum is a rhizomatous perennial grass that plays a particularly important role in the resilience of these fire-prone Mediterranean ecosystems. In Mediterranean gorse shrublands, during the first few years after a fire, this species represents 90% of plant cover and biomass. The recurrence or severity of fire does not seem to affect the regeneration capacity of this species. After two years, even under high fire frequency ͑12 years͒ and high fire severity ͑ Ͼ 400°C͒, it recovers both cover and biomass. Nevertheless, this species, a key factor in the control of soil erosion, is extremely affected by erosion processes. A single extreme rainfall event reduces the rate of regeneration of B. retusum by about 50%. The reduction in the protective cover of this species may result in degradation and eventual self-induced degrading process in the ecosystem.
In Western Mediterranean areas, fires are frequent in forests established on old croplands where ... more In Western Mediterranean areas, fires are frequent in forests established on old croplands where woody resprouting species are scarce and post-fire regeneration is limited to obligate-seeder species, such as Mediterranean gorse (Ulex parviflorus), that accumulate a great deal of fine dry fuel, increasing the risk of other severe fires. Under these conditions, fuel control techniques are required in order to prevent fires of high intensity and severity and the subsequent economic and ecological damage. Prescribed fires present an alternative to fuel control, and recent studies demonstrate that, under optimum climatic conditions, fire-line intensity values fall within the limits of those recommended for fire prescription. However, a better understanding of the consequences of fire on the regeneration of vegetation is needed in order to evaluate the suitability of prescribed fires as a technique for fuel reduction in Mediterranean gorse ecosystems. This paper analyses the factors controlling seedling germination after fire to make an evaluation from an ecological perspective of whether fire prescription is a suitable technique for fuel control in mature Mediterranean gorse shrublands. The results show that small differences in the composition of vegetation play a decisive role in fire behaviour, and have a decisive influence on the system's capacity for regeneration. Fire severity is low in mixed Mediterranean gorse communities with a low continuity of dead fine fuel (including Cistus sp., Rosmarinus sp., etc.) and fire creates a wide range of microhabitats where seedling emergence is high. In contrast, where U. parviflorus is more dominant, fire severity is higher and the regeneration of vegetation could be hindered. Our conclusions suggest that detailed studies of the composition of plant communities are required in order to decide whether prescribed burning should be applied.
... Study site. The Cal Carot badland area is located in the Vallcebre basin, south-eastern Pyren... more ... Study site. The Cal Carot badland area is located in the Vallcebre basin, south-eastern Pyrenees (north-eastern Spain) at 1230 m asl The climate is submediterranean, with mean annual rainfall of about 900 mm, much of which falls in autumn and spring. ...
Soil degradation and desertification are key problems facing Mediterranean ecosystems and these h... more Soil degradation and desertification are key problems facing Mediterranean ecosystems and these have worsened recently with the increasing frequency of fires. Moreover, rainfall in western Mediterranean areas is characterized by high intensity, and extreme rainfall events after fire strongly affect the equilibrium between soil erosion and vegetation recovery. These facts led us to carry out experimental fires in a fire-prone vegetation community (dominated by Mediterranean gorse, Ulex parviflorus Pourr.) to study the effect of a torrential rainfall event (through rainfall simulation) on the short-term vegetation regeneration process (seedling emergence and survival). The results indicate that, in Mediterranean gorse shrublands after fire, an extreme precipitation event does not affect seedling emergence (either through seed loss or from seed germination). In contrast, it has a significant effect on the reduction of seedling survival both from direct impact (seedlings buried by sedim...
A current focus of ecology is the investigation of spatial effects on population and community dy... more A current focus of ecology is the investigation of spatial effects on population and community dynamics; however, spatiotemporal theory remains largely untested by empirical observations or experimental studies. For example, the segregation hypothesis predicts that intraspecific aggregation should increase the importance of intraspecific competition relative to interspecific competition, thereby enhancing local coexistence in plant communities. We applied recent methods of point pattern analysis to analyze a unique longterm data set on fully mapped seedling emergence and subsequent survival in a Mediterranean gorse shrubland after experimental fires and simulated torrential rainfall events. Our overall aim was to test if the observed spatial patterns were consistent with the segregation hypothesis during the entire community dynamics from early seedling emergence to the establishment of a mature community, i.e., we explored if the observed initial segregation did indeed prevent interspecific competition from becoming dominant. We used random labeling as the null model and specific test statistics to evaluate different biological effects of the spatial interactions that determine mortality. We found that mortality was clearly not random. Comparison of the probability of mortality in dependence on the distance to conspecific and to heterospecific plants showed that mortality was controlled almost entirely by intraspecific interactions, which is consistent with the segregation hypothesis. Dead plants were aggregated and segregated from surviving plants, indicating two-sided scramble competition. Spatial interactions were density dependent and changed their sign over the course of time from positive to negative when plants grew to maturity. The simulated torrential rainfall events and subsequent erosion caused nonspecific mortality of seedlings but did not reduce the prevalence of intraspecific competition. Our results provide support for the hypothesis that the spatial distribution of plants may profoundly affect competition and can be an important determinant in the coexistence of species and biodiversity.
Seedling emergence time is a crucial event in the life cycle of a plant, determining its fitness ... more Seedling emergence time is a crucial event in the life cycle of a plant, determining its fitness via different components including survival, growth, and fecundity. Precocious emergents usually survive, grow, and/or reproduce earlier in the life cycle, but for perennials it is unknown whether these benefits are maintained throughout the life of the plant. Here, we examine for the first time whether fitness benefits due to the early emergence of perennial plants are perpetuated or vanish with time. For nine years, in a Mediterranean gorse community, we followed the fate of 2118 seedlings belonging to the four dominant woody species. We estimated phenotypic selection gradients on emergence time for three fitness components (survival, growth, and fecundity), under two experimentally simulated scenarios (fire and fire þ erosion), at two different times in the life of the plant (3 and 9 years). Fire and erosion represent two potential selective forces constraining the temporal window of seedling emergence in Mediterranean habitats. All the species exhibited selection for early emergence, but through different fitness components. Directional selection favoring early emergence via survival in both fire scenarios was detected in the two Cistaceae species (Helianthemum marifolium and Cistus albidus), in which precocious emergents had higher fitness values late in the life cycle (9 years). In contrast, Fabaceae species (Ononis fruticosa and Ulex parviflorus) were not selected for early emergence via survival. Early emergents of all species in both fire scenarios had higher fitness values through growth early in the life cycle; these benefits decreased slightly with time but remained statistically significant, except in H. marifolium. Finally, late fecundity was enhanced by early emergence in both fire scenarios in C. albidus and U. parviflorus but not in H. marifolium. In conclusion, benefits acquired by emerging early are perpetuated for at least nine years.
We model the dynamics of grass plant growth as a collection of the individual dynamic behavior of... more We model the dynamics of grass plant growth as a collection of the individual dynamic behavior of shoots and leaves. The model is inspired in data for plants of three species (Elyonurus adustus, Leptocoryphium lanatum and Andropogon semiberbis) of common grasses in the Venezuelan savannas that were sampled monthly for 1 year. These species represent different architecture and regeneration response to fire. Modules (shoots and leaves) were counted in each cell of a square grid in each one of several vertical levels. Module density per cell provides the horizontal distribution within a level and is aggregated by level to obtain vertical distribution. Both distributions are simulated by a dynamical model based on shoot emergence and mortality, elongation of shoots and leaves given by Richards' equation, plus a few simple geometric considerations. For quantitative comparisons of model results to data, the transient and final values for vertical distribution plus two metrics of horizontal distribution at each level, were calculated for the simulation results and the field data. Proportion of occupied cells and maximum distance to the center of growth were the two metrics selected to capture the dispersion and range of the horizontal distribution. The model results indicate predictable final vertical profiles (of proportional density plus the two metrics) similar to the profiles of measured distributions for each species. A reasonable prediction of the transient behavior was also obtained but with larger deviations as evaluated by the root mean square error between model and data. Differences in vertical and horizontal patterns of module density among species are explained by changing a set of parameter values related to growth form and phenology. Thus, the model could be applied to generate plant functional types for analysis of savanna dynamics subject to fire. With modifications, the model is potentially applicable to other grass plants and other grassland ecosystems.
2. Geomorph. N. К 48 3 293-304 Berlin ■ Stuttgart September 2004 Hydrological response of Mediter... more 2. Geomorph. N. К 48 3 293-304 Berlin ■ Stuttgart September 2004 Hydrological response of Mediterranean gorse shrubland under extreme rainfall simulation event José Carlos González-Hidalgo, Martín de Luís, Josep Raventós, JoRDi Cortina and Juan Rafael ...
Departamento de Ecología y Recursos Naturales, Facultad de Ciencias, Universidad Nacional Autónom... more Departamento de Ecología y Recursos Naturales, Facultad de Ciencias, Universidad Nacional Autónoma de México, Mexico City, Mexico Departamento de Ecología, Universidad de Alicante, Alicante, Spain Departamento de Biología Comparada, Facultad de Ciencias, Universidad Nacional Autónoma de México, Mexico City, Mexico Departamento de Ecología de la Biodiversidad, Instituto de Ecología, Universidad Nacional Autónoma de México, Mexico City, Mexico
ABSTRACT Background: Epiphyte removal forms part of routine management in shade coffee plantation... more ABSTRACT Background: Epiphyte removal forms part of routine management in shade coffee plantations. Aims: Assess the current status of three population orchids growing in Mexican shaded coffee plantations and evaluate the effect of perturbing the transient behaviour of different life stages. Methods: We modelled the short-term response of eliminating I) non-reproductive juveniles, or II) reproductive adult plants from coffee bushes, on populations of Oncidium poikilostalix, Lepanthes acuminata and Telipogon helleri (Orchidaceae). First, we calculated the transient dynamics per se and second, we made a perturbation analysis on population inertia. Finally, we made a comparison with a traditional sensitivity analysis. Results: All three species showed different positive asymptotic growth rate: O. poikilostalix (λmax = 1.106), L. acuminata (λmax = 1.209), and T. helleri (λmax = 1.012). The effect of eliminating the major part of the juvenile or adult orchids gave population inertia in relation to steady state, respectively, (+19%, -24%) for O. poikilostalix, (+17%, -28%) for T. helleri and (+57%, -35%) for L. acuminata. Conclusions: Eliminating juveniles or adults affects in different ways the short-term dynamics due to differential impact on size stages that have the non-linear effects associated with important disturbances that currently affect orchids growing in coffee plantations.
Background and Aims: Biological invasions are considered as second to habitat loss as a cause of ... more Background and Aims: Biological invasions are considered as second to habitat loss as a cause of the extinction of species. The study of population dynamics is particularly relevant for species with expansive behavior. The aims of this study were to: (1) evaluate the population ecology of Oncidium poikilostalix in shaded coffee plantations in Mexico, (2) evaluate the reproductive behavior of O. poikilostalix in this habitat, and (3) determine whether this orchid should be considered as an invasive species.Methods: During 2013-2015, most of the individuals of the Mexican population of O. poikilostalix (located south of the state Chiapas) were marked and measured. Additionally, the flower and fruit production (first flowering and repeated flowering), mortality and recruitment of new individuals were registered annually, and its potential distribution was modeled.Key results: Within this period a population increase of 1.11% was observed, with a proportional increase in the number of f...
The expansion of invasive species is a global concern. Within the Orchidaceae there are a number ... more The expansion of invasive species is a global concern. Within the Orchidaceae there are a number of invasive species. One of the most widely distributed invasive orchids in Mexico is Oeceoclades maculata (Lindl.) Lindl. By examining the population dynamic variations of an invasive species in its range of expansion, we can identify the factors that have contributed to that variation. Life Table Response Experiments (LTRE) were used to describe the dynamic of four populations of O. maculata in different ecosystems in south Chiapas, Mexico. Our goals were to quantify the contributions of differences between years and sites, and their interactions, to overall differences in population growth rate (k), and to underlying vital rates. Fertility, survival and growth made the largest contributions, both positive and negative, to annual differences in k. Spatial variations in k were also found. The largest plants (S3 and S4) made the contributions of greatest magnitude each year and in each site. In seven of eight cases, the inclusion of the interaction term gave a better estimate of the population growth rate. This investigation highlights the need for taking into account life-history variations at different scales when the research goal is to study expansion of an invasive species in a heterogeneous landscape. The usefulness of LTRE studies was also demonstrated to better understand the natural history of the species and thus lay the groundwork for planning efficient management strategies, either for the conservation of rare, endangered species, or for the control of invasive species.
CORRECCIÓN DE PRUEBAS: Será realizada por la redacción de la revista, aunque los autores deben en... more CORRECCIÓN DE PRUEBAS: Será realizada por la redacción de la revista, aunque los autores deben enviar un texto muy claro y definitivo. Si se hallan deficiencias notorias en el texto, el trabajo será remitido a los autores de inmediato. TABLAS: Cada tabla en página por separado, numeradas siguiendo el orden de aparición en el texto y llevarán leyenda. El método de escritura admitido puede ser WORD o EXCEL. GRÁFICAS y DIBUJOS: Presentados en papel blanco no reciclado, exclusivamente en blanco y negro. Las láminas en color deberán ser costeadas por los autores. Gráficas y dibujos deben ser presentados de forma que, modificando su dimensión, no se vea modificada su comprensión. Deberán acompañar las leyendas al gráfico, suficientemente grandes e incluidas en la caja del mismo. Es obligatorio acompañar archivo en disco compatible y formato TIF o JPEG. ILUSTRACIONES: Las fotografías, separadas del texto, con leyenda y número de orden, posición en el texto, etc. NOTAS: Excepcionalmente se incluirán notas a pie, pero éstas deben ir en hojas separadas y debidamente numeradas. EXTENSIÓN: El texto comprenderá una extensión de 5 (min.) a 25 (max.) páginas mecanografiadas. El numero de gráficos, dibujos y fotografías debe ser proporcional al tamaño del texto. La dirección de la revista se reserva el derecho de revisar los trabajos presentados con el fin de adaptarlos a la publicación. http://publicaciones.ua.es Notes for the authors SUBJECTS Ecology Natural Resources Landscape Environmental Management Manuscripts typed on duplicate on one side of the sheet only, should be sent to the magazine direction: Mediterranea. S.E.B.Dep. Ecologia. Universidad de Alicante. Ap. 99 (03080 Alicante) Spain. All authors are kindly requested to send their papers in writing, but namely on MS DOS/IBM compatible disks, using MS-WORD program. Every paper should conform to the following rules:
In the Caribbean basin, hurricanes represent a dominant disturbance force for the tropical coasta... more In the Caribbean basin, hurricanes represent a dominant disturbance force for the tropical coastal forests. Using an Integral Projection Model (IPM), we assessed the population status of Encyclia bocourtii (Orchidaceae) three years after damage caused by Hurricane Ivan during its passage through the peninsula of Guanacahabibes, Cuba. Based on the abundance of E. bocourtii recorded in permanent study plots, we know that the population declined by 63% after disturbance. Our results show that the estimated asymptotic growth rate from the fitted integral model was λmax=1.028 [0.9377 – 1.1399]; the uncertainty associated with this parameter is related to the process of estimating reproductive variables on epiphytic orchids. The elasticity surface showed that elasticities are high along the first part of the principal diagonal representing the birth and survival of small to medium-size individuals. A damping ratio close to 1 suggested that the current structure is far from equilibrium, wh...
Since the early 1990s, Mediterranean gorse shrublands have expanded significantly in the Mediterr... more Since the early 1990s, Mediterranean gorse shrublands have expanded significantly in the Mediterranean regions of Spain mainly as a result of the increase in the frequency and extension of forest fires. Mediterranean gorse (Ulex parviflorus), which has been described as a degradation stage of forest communities after fire, has also been described as a fire-prone community. Thus, its presence increases the risk that new fires might occur. In spite of this evidence, there is little information on both the composition and structural characteristics of these communities or the relationship that might exist between these vegetation characteristics and fire behaviour. In this paper we present the results of a characterization of the vegetative structure (plant density, specific composition, biomass fractions, and horizontal and vertical fuel distribution) in Mediterranean gorse. We also analyse fire behaviour using indicators obtained at different scales. Our results show mature Mediterranean gorse shrublands to be communities with high biomass values (3000-4000 g m −2) and high horizontal and vertical vegetation continuity, in which the proportion of fine dead fuel fractions with low moisture content is around 50% of the total phytomass present. Ulex parviflorus is the dominant species and its degree of dominance is a key element in the behaviour of fire. Both the fire-line intensity values and the fire severity values observed can be considered high with respect to those observed in other Mediterranean communities, thus confirming Mediterranean gorse as a high-risk community.
Summer wildfires and autumn torrential rainfall are the background to the development of one of t... more Summer wildfires and autumn torrential rainfall are the background to the development of one of the most important environmental problems in the western Mediterranean area: erosion, degradation of soil structure and desertification. These processes especially affect plant communities located in old abandoned fields where woody sprouters are practically absent. Under these conditions, post-fire vegetation cover is dependent on obligate seeders and, in the short term, especially on resprouting perennial grasses. Brachypodium retusum is a rhizomatous perennial grass that plays a particularly important role in the resilience of these fire-prone Mediterranean ecosystems. In Mediterranean gorse shrublands, during the first few years after a fire, this species represents 90% of plant cover and biomass. The recurrence or severity of fire does not seem to affect the regeneration capacity of this species. After two years, even under high fire frequency ͑12 years͒ and high fire severity ͑ Ͼ 400°C͒, it recovers both cover and biomass. Nevertheless, this species, a key factor in the control of soil erosion, is extremely affected by erosion processes. A single extreme rainfall event reduces the rate of regeneration of B. retusum by about 50%. The reduction in the protective cover of this species may result in degradation and eventual self-induced degrading process in the ecosystem.
In Western Mediterranean areas, fires are frequent in forests established on old croplands where ... more In Western Mediterranean areas, fires are frequent in forests established on old croplands where woody resprouting species are scarce and post-fire regeneration is limited to obligate-seeder species, such as Mediterranean gorse (Ulex parviflorus), that accumulate a great deal of fine dry fuel, increasing the risk of other severe fires. Under these conditions, fuel control techniques are required in order to prevent fires of high intensity and severity and the subsequent economic and ecological damage. Prescribed fires present an alternative to fuel control, and recent studies demonstrate that, under optimum climatic conditions, fire-line intensity values fall within the limits of those recommended for fire prescription. However, a better understanding of the consequences of fire on the regeneration of vegetation is needed in order to evaluate the suitability of prescribed fires as a technique for fuel reduction in Mediterranean gorse ecosystems. This paper analyses the factors controlling seedling germination after fire to make an evaluation from an ecological perspective of whether fire prescription is a suitable technique for fuel control in mature Mediterranean gorse shrublands. The results show that small differences in the composition of vegetation play a decisive role in fire behaviour, and have a decisive influence on the system's capacity for regeneration. Fire severity is low in mixed Mediterranean gorse communities with a low continuity of dead fine fuel (including Cistus sp., Rosmarinus sp., etc.) and fire creates a wide range of microhabitats where seedling emergence is high. In contrast, where U. parviflorus is more dominant, fire severity is higher and the regeneration of vegetation could be hindered. Our conclusions suggest that detailed studies of the composition of plant communities are required in order to decide whether prescribed burning should be applied.
... Study site. The Cal Carot badland area is located in the Vallcebre basin, south-eastern Pyren... more ... Study site. The Cal Carot badland area is located in the Vallcebre basin, south-eastern Pyrenees (north-eastern Spain) at 1230 m asl The climate is submediterranean, with mean annual rainfall of about 900 mm, much of which falls in autumn and spring. ...
Soil degradation and desertification are key problems facing Mediterranean ecosystems and these h... more Soil degradation and desertification are key problems facing Mediterranean ecosystems and these have worsened recently with the increasing frequency of fires. Moreover, rainfall in western Mediterranean areas is characterized by high intensity, and extreme rainfall events after fire strongly affect the equilibrium between soil erosion and vegetation recovery. These facts led us to carry out experimental fires in a fire-prone vegetation community (dominated by Mediterranean gorse, Ulex parviflorus Pourr.) to study the effect of a torrential rainfall event (through rainfall simulation) on the short-term vegetation regeneration process (seedling emergence and survival). The results indicate that, in Mediterranean gorse shrublands after fire, an extreme precipitation event does not affect seedling emergence (either through seed loss or from seed germination). In contrast, it has a significant effect on the reduction of seedling survival both from direct impact (seedlings buried by sedim...
A current focus of ecology is the investigation of spatial effects on population and community dy... more A current focus of ecology is the investigation of spatial effects on population and community dynamics; however, spatiotemporal theory remains largely untested by empirical observations or experimental studies. For example, the segregation hypothesis predicts that intraspecific aggregation should increase the importance of intraspecific competition relative to interspecific competition, thereby enhancing local coexistence in plant communities. We applied recent methods of point pattern analysis to analyze a unique longterm data set on fully mapped seedling emergence and subsequent survival in a Mediterranean gorse shrubland after experimental fires and simulated torrential rainfall events. Our overall aim was to test if the observed spatial patterns were consistent with the segregation hypothesis during the entire community dynamics from early seedling emergence to the establishment of a mature community, i.e., we explored if the observed initial segregation did indeed prevent interspecific competition from becoming dominant. We used random labeling as the null model and specific test statistics to evaluate different biological effects of the spatial interactions that determine mortality. We found that mortality was clearly not random. Comparison of the probability of mortality in dependence on the distance to conspecific and to heterospecific plants showed that mortality was controlled almost entirely by intraspecific interactions, which is consistent with the segregation hypothesis. Dead plants were aggregated and segregated from surviving plants, indicating two-sided scramble competition. Spatial interactions were density dependent and changed their sign over the course of time from positive to negative when plants grew to maturity. The simulated torrential rainfall events and subsequent erosion caused nonspecific mortality of seedlings but did not reduce the prevalence of intraspecific competition. Our results provide support for the hypothesis that the spatial distribution of plants may profoundly affect competition and can be an important determinant in the coexistence of species and biodiversity.
Seedling emergence time is a crucial event in the life cycle of a plant, determining its fitness ... more Seedling emergence time is a crucial event in the life cycle of a plant, determining its fitness via different components including survival, growth, and fecundity. Precocious emergents usually survive, grow, and/or reproduce earlier in the life cycle, but for perennials it is unknown whether these benefits are maintained throughout the life of the plant. Here, we examine for the first time whether fitness benefits due to the early emergence of perennial plants are perpetuated or vanish with time. For nine years, in a Mediterranean gorse community, we followed the fate of 2118 seedlings belonging to the four dominant woody species. We estimated phenotypic selection gradients on emergence time for three fitness components (survival, growth, and fecundity), under two experimentally simulated scenarios (fire and fire þ erosion), at two different times in the life of the plant (3 and 9 years). Fire and erosion represent two potential selective forces constraining the temporal window of seedling emergence in Mediterranean habitats. All the species exhibited selection for early emergence, but through different fitness components. Directional selection favoring early emergence via survival in both fire scenarios was detected in the two Cistaceae species (Helianthemum marifolium and Cistus albidus), in which precocious emergents had higher fitness values late in the life cycle (9 years). In contrast, Fabaceae species (Ononis fruticosa and Ulex parviflorus) were not selected for early emergence via survival. Early emergents of all species in both fire scenarios had higher fitness values through growth early in the life cycle; these benefits decreased slightly with time but remained statistically significant, except in H. marifolium. Finally, late fecundity was enhanced by early emergence in both fire scenarios in C. albidus and U. parviflorus but not in H. marifolium. In conclusion, benefits acquired by emerging early are perpetuated for at least nine years.
We model the dynamics of grass plant growth as a collection of the individual dynamic behavior of... more We model the dynamics of grass plant growth as a collection of the individual dynamic behavior of shoots and leaves. The model is inspired in data for plants of three species (Elyonurus adustus, Leptocoryphium lanatum and Andropogon semiberbis) of common grasses in the Venezuelan savannas that were sampled monthly for 1 year. These species represent different architecture and regeneration response to fire. Modules (shoots and leaves) were counted in each cell of a square grid in each one of several vertical levels. Module density per cell provides the horizontal distribution within a level and is aggregated by level to obtain vertical distribution. Both distributions are simulated by a dynamical model based on shoot emergence and mortality, elongation of shoots and leaves given by Richards' equation, plus a few simple geometric considerations. For quantitative comparisons of model results to data, the transient and final values for vertical distribution plus two metrics of horizontal distribution at each level, were calculated for the simulation results and the field data. Proportion of occupied cells and maximum distance to the center of growth were the two metrics selected to capture the dispersion and range of the horizontal distribution. The model results indicate predictable final vertical profiles (of proportional density plus the two metrics) similar to the profiles of measured distributions for each species. A reasonable prediction of the transient behavior was also obtained but with larger deviations as evaluated by the root mean square error between model and data. Differences in vertical and horizontal patterns of module density among species are explained by changing a set of parameter values related to growth form and phenology. Thus, the model could be applied to generate plant functional types for analysis of savanna dynamics subject to fire. With modifications, the model is potentially applicable to other grass plants and other grassland ecosystems.
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Papers by José Raventós