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Open Access
Growth, allocation and leaf gas exchanges of hybrid poplar plants in their establishment phase on previously forested sites: effect of different vegetation management techniques
(Institut National de la Recherche Agronomique (INRA), 2007-04-11) Coll Mir, Lluís; Messier, Christian; Delagrange, Sylvain; Berninger, Frank
The effect of different vegetation control methods (mowing and cultivation between plantation rows, herbicide application and cover plant sowing) on hybrid poplar (P. maximowiczii $\times$ balsamifera) growth, biomass allocation and leaf carbon assimilation was investigated in two plantations (1- and 2-year-old) established in previously forested sites of south-eastern Québec. Any vegetation control treatment applied the same year in which the plantation was established did not have an effect on hybrid poplar aboveground growth. However significant differences among treatments were observed belowground, where the removal of the competing vegetation at the tree base increased the fine root:leaf biomass ratio of plants, thus probably facilitating their establishment. In contrast, 2-year-old plants grew better when treated with herbicides, but no positive effect of the mechanical treatments was detected. In both sites, trees growing on herbicide-treated plots showed considerably higher leaf carbon assimilation and leaf N concentration which were both strongly correlated. We conclude that a strong vegetation competition for nutrients takes effect on hybrid poplar plantations on previously forested sites since there was no water shortage for any treatment during the study period.
Open Access
Six-year time course of light-use efficiency, carbon gain and growth of beech saplings (Fagus sylvatica) planted under a Scots pine (Pinus sylvestris) shelterwood
(Oxford University Press, 2007-08-01) Balandier, Philippe; Sinoquet, H.; Frak, Ela; Giuliani, Rita; Vandame, Marc; Descamps, Sylvestre; Coll Mir, Lluís; Adam, Boris; Prevosto, Bernard; Curt, Thomas
Two-year-old Fagus sylvatica L. saplings were planted under the cover of a Pinus sylvestris L. stand in the French Massif Central. The stand was differentially thinned to obtain a gradient of transmitted photosynthetically active radiation (PARt; 0–0.35). Eighteen Fagus saplings were sampled in this gradient, and their growth (basal stem diameter increment) was recorded over six years. Over the same period, morphological parameters (leaf area, number and arrangement in space) were monitored by 3D-digitization. Photosynthetic parameters were estimated with a portable gas-exchange analyzer. Photosynthesis was mainly related to light availability, whereas sapling morphology was mainly driven by sapling size. Annual stem diameter increment was related to the amount of light-intercepting foliage (silhouette to total leaf area ratio (STAR) × total sapling leaf area (LA)) and light availability above the saplings (PARt). However, light-use efficiency, i.e., the slope of the relationship between STAR × LA × PARt and stem diameter increment, decreased over time as a result of a relative decrease in the proportion of photosynthetic tissues to total sapling biomass.
Open Access
Facilitation in plant communities: the past, the present, and the future
(John Wiley and Sons, 2007-09-06) Brooker, Rob W.; Maestre, Fernando T.; Callaway, Ragan M.; Lortie, Christopher L.; Cavieres, Lohengrin A.; Kunstler, Georges; Liancourt, Pierre; Tielbörger, Katja; Travis, Justin M. J.; Anthelme, Fabien; Armas, Cristina; Coll Mir, Lluís; Corcket, Emmanuel; Delzon, Sylvain; Forey, Estelle; Kikvidze, Zaal; Olofsson, Johan; Pugnaire, Francisco I.; Quiroz, Constanza L.; Saccone, Patrick; Schiffers, Katja; Seifan, Merav; Touzard, Blaise; Michalet, Richard
1. Once neglected, the role of facilitative interactions in plant communities has received considerable attention in the last two decades, and is now widely recognized. It is timely to consider the progress made by research in this field. 2. We review the development of plant facilitation research, focusing on the history of the field, the relationship between plant–plant interactions and environmental severity gradients, and attempts to integrate facilitation into mainstream ecological theory. We then consider future directions for facilitation research. 3. With respect to our fundamental understanding of plant facilitation, clarification of the relationship between interactions and environmental gradients is central for further progress, and necessitates the design and implementation of experiments that move beyond the clear limitations of previous studies. 4. There is substantial scope for exploring indirect facilitative effects in plant communities, including their impacts on diversity and evolution, and future studies should connect the degree of non‐transitivity in plant competitive networks to community diversity and facilitative promotion of species coexistence, and explore how the role of indirect facilitation varies with environmental severity. 5. Certain ecological modelling approaches (e.g. individual‐based modelling), although thus far largely neglected, provide highly useful tools for exploring these fundamental processes. 6. Evolutionary responses might result from facilitative interactions, and consideration of facilitation might lead to re‐assessment of the evolution of plant growth forms. 7. Improved understanding of facilitation processes has direct relevance for the development of tools for ecosystem restoration, and for improving our understanding of the response of plant species and communities to environmental change drivers. 8. Attempts to apply our developing ecological knowledge would benefit from explicit recognition of the potential role of facilitative plant–plant interactions in the design and interpretation of studies from the fields of restoration and global change ecology. 9. Synthesis: Plant facilitation research provides new insights into classic ecological theory and pressing environmental issues. Awareness and understanding of facilitation should be part of the basic ecological knowledge of all plant ecologists.
Open Access
Linking multiple-level tree traits with biomass accumulation in native tree species used for reforestation in Panama
(Springer Nature, 2007-12-12) Delagrange, Sylvain; Potvin, Catherine; Messier, Christian; Coll Mir, Lluís
To improve establishment yield and carbon accumulation during reforestation, analyses of species adaptations to local environments are needed. Here we measured, at the individual scale, links between biomass accumulation and multiple-level tree traits: biomass partitioning, crown morphology and leaf physiology. The study was carried out on one- and three-year-old individuals of five tropical tree species assigned to pioneer (P) or non-pioneer (NP) functional groups. Among the species, Cedrela odorata, Luehea seemannii and Hura crepitans showed the greatest biomass accumulation. On our seasonally dry site, species performance during the first year was dependent on a greater investment in above-ground foraging, while performance after three years was mainly related to water relations. However, large biomass accumulations were not simply associated with an efficient water use but also with contrasting water uses, based on inter-specific relationships. Generally, greater carbon isotope discrimination (Δleaf) was related to greater allocation to roots. Species with high Δ leaf generally showed high leaf potential nitrogen use efficiency (PNUE), suggesting that lower water use efficiency (WUE) increases the efficiency of photosynthetically active N. Also, PNUE was negatively correlated to leaf mass per area (LMA), implying that photosynthetically active N is diluted as total leaf mass increases. Finally, no distinction in measured traits, including biomass accumulation, was observed between the two functional groups.
Restricted
Mycelial abundance and other factors related to o truffle productivity in Tuber melanosporum - Quercus ilex orchards
(Blackwell, 2008) Suz, Laura M.; María P., Martín; Oliach, Daniel; Fischer, Christine; Colinas, C. (Carlos)
Relative quantification of DNA from Tuber melanosporum mycelia was performed by conventional and real-time PCR in soil from trees in three truffle orchards of different ages to determine: (1) whether burn appearance is related to the amount of T. melanosporum mycelium in soil, and (2) whether productivity onset and truffle production are related to (a) the amount of T. melanosporum mycelium in soil, (b) tree height and diameter, (c) burn extension and (d) surface rock cover. The burn seems to appear only after a certain amount of mycelium has formed. Precociously productive trees presented higher quantities of mycelium than nonproductive trees in the productivity onset study, while highly productive trees presented less quantities of mycelium than nonproductive trees in the productivity study. Trees with high but not excessive surface rock cover showed greater truffle production. Larger trees tended to display a burn earlier than smaller trees.
Open Access
Root architecture and allocation patterns of eight native tropical species with different successional status used in open-grown mixed plantations in Panama
(Springer Nature, 2008-04-19) Coll Mir, Lluís; Potvin, Catherine; Messier, Christian; Delagrange, Sylvain
We investigated biomass allocation and root architecture of eight tropical species with different successional status, as classified from the literature, along a size gradient up to 5 m. We focused on belowground development, which has received less attention than aboveground traits. A discriminant analysis based upon a combination of allocational and architectural traits clearly distinguished functional types and classified species according to successional status at a 100% success rate. For a given plant diameter, the pioneer species presented similar root biomass compared to the non-pioneer ones but higher cumulative root length and a higher number of root apices. A detailed study on the root system of a sub-sample of three species showed that the most late-successional species (Tabebuia rosea) had longer root internodes and a higher proportion of root biomass allocated to the taproot compared to the other two species (Hura crepitans and Luehea seemannii). Most pioneer species showed a higher leaf area ratio due to a higher specific leaf area (SLA). We conclude that the functional differences between pioneer and non-pioneer tree species found in natural forests were maintained in open-grown plantation conditions.
Open Access
Resource and non‐resource root competition effects of grasses on early‐versus late‐successional trees
(John Wiley and Sons, 2009-04-08) Messier, Christian; Coll Mir, Lluís; Poitras-Larivière, Amélie; Bélanger, Nicolas; Brisson, Jacques
1. This study assessed the effects of resource (i.e. nutrients) and non‐resource (i.e. interference for space) competition from fine roots of competing grasses on the growth, morphology and architecture of fine roots of four tree species of varying successional status: Populus deltoides ¥ P. balsamifera (a hybrid), Betula papyrifera, Acer saccharum and Fraxinus americana. We tested the general hypothesis that tree fine‐roots are affected by both below‐ground resource and non‐resource competition from non‐self plants, and the more specific hypothesis that this effect is stronger in early‐successional tree species. 2. The experiment was conducted in split‐containers where half of the roots of tree seedlings experienced either below‐ground resource competition or non‐resource competition, or both, by grasses while the other half experienced no competition. 3. The late‐successional tree species A. saccharum and F. americana were mostly affected by resource competition, whereas the early‐successional P. deltoides¥balsamifera and B. papyrifera were strongly affected by both resource and non‐resource competition. Non‐resource competition reduced fine‐root growth, root branching over root length (a measure of root architecture) and specific root length (a measure of root morphology) of both early‐successional species. 4. Synthesis. This study suggests that early‐successional tree species have been selected for root avoidance or segregation and late‐successional tree species for root tolerance of competition as mechanisms to improve below‐ground resource uptake in their particular environments. It also contradicts recent studies showing perennial and annual grasses tend to overproduce roots in the presence of non‐self conspecific plants. Woody plants, required to grow and develop for long periods in the presence of other plants, may react differently to non‐self root competition than perennial or annual grasses that have much shorter lives.
Open Access
Models for simulating the development of even-aged Pinus brutia stands in Middle East
(Instituto Nacional de Investigación y Tecnología Agraria y Alimentaria (INIA), 2010) Miguel Magaña, Sergio de; Pukkala, Timo; Shater, Zuheir; Assaf, Nabil; Kraid, Bassel; Palahí, Marc
Pinus brutia occurs in the Eastern Mediterranean region and is the most widespread conifer species in Middle East. It is important for multi-purpose forestry owing to its high ecological value and economic importance. To model the stand dynamics of P. brutia, 133 semi-permanent sample plots were placed in 10 to 166 year-old stands in Syria and Lebanon, covering the whole range of variation in site quality, stand age and stand density. Site index, distance-independent diameter increment, height and self-thinning models that included country effects were fitted to the data. The site index model was fitted using the guide curve method. The data for 10-year diameter growth model consisted of past growth measurements of all trees within the 133 plots. Diameter growth was modelled using variables representing site, size and competition. The self-thinning model was developed by estimating the maximum number of trees per hectare as a function of mean diameter and site index. These are the first cross-border models in Middle East enabling forest growth and yield predictions and stand dynamics simulations on an individual-tree basis. Such models will allow, with the aid of optimization techniques, finding the optimal forest management for P. brutia forests based on different management objectives.
Open Access
Assessing the ecological status in species-poor systems: A fish-based index for Mediterranean Rivers (Guadiana River, SW Spain)
(Elsevier, 2010-04-24) Hermoso, Virgilio; Clavero Pineda, Miguel; Blanco-Garrido, Francisco; Prenda, José
The assessment of the ecological status of freshwater ecosystems is a key issue for many international laws such as the Water Framework Directive (WFD) in light of the actual impoverished status of these ecosystems. Different multimetric approaches have been successfully developed in different freshwater environments. However, multimetric indices are difficult to apply to Mediterranean rivers basins, characterized by freshwater fish communities very low in species richness and support a high number of endemics with generalist and opportunistic life strategies. Here we follow a site-specific approach to develop an adaptation of the multimetric procedure usually used in Indices of Biotic Integrity (IBI), resulting in the Index of Community Integrity (ICI). We modeled the presence–absence of 10 native freshwater fish species from the Guadiana River basin using the Assessment of Nearest Neighbor Analyses (ANNA) model, to assess the deviation of the observed and expected community composition at reference condition. ANNA, which is a multi-species model, allowed incorporating in the index some rare species, though not all of them present in the basin. Deviations were transformed into probabilities of belonging to a reference site and species by species measures were then integrated in a final score. The use of presence–absence only data reduces potential errors associated with estimations of species’ abundance and its seasonal changes, which is especially important in Mediterranean environments. The ICI was sensitive to both habitat degradation and the degree of dominance of non-native species within the freshwater fish community (or biotic perturbation), which have been traditionally overlooked in IBIs, but was unresponsive to natural sources of variation. Given the site-specific nature and the simplicity of the index that we propose here, we expect it to be applicable to other Mediterranean basins for which predictive models can be produced.
Open Access
Building wood debris piles benefits avian seed dispersers in burned and logged Mediterranean pine forests
(Elsevier, 2010-04-28) Rost Bagudanch, Josep; Clavero Pineda, Miguel; Bas Lay, Josep M. (Josep Maria); Pons Ferran, Pere
Salvage logging is a common practice carried out in burned forests worldwide, and intended to mitigate the economic losses caused by wildfires. Logging implies an additional disturbance occurring shortly after fire, although its ecological effects can be somewhat mitigated by leaving wood debris on site. The composition of the bird community and its capacity to provide ecosystem services such as seed dispersal of fleshy-fruited plants have been shown to be affected by postfire logging. We assessed the effects of the habitat structure resulting from different postfire management practices on the bird community, in three burned pine forests in Catalonia (western Mediterranean). For this purpose, we focused on the group of species that is responsible for seed dispersal, a process which takes place primarily during the winter in the Mediterranean basin. In addition, we assessed microhabitat selection by seed disperser birds in such environments in relation to management practices. Our results showed a significant, positive relationship between the density of wood debris piles and the abundance of seed disperser birds. Furthermore, such piles were the preferred microhabitat of these species. This reveals an important effect of forest management on seed disperser birds, which is likely to affect the dynamics of bird-dependent seed dispersal. Thus, building wood debris piles can be a useful practice for the conservation of both the species and their ecosystem services, while also being compatible with timber harvesting.
Open Access
Predicting understory maximum shrubs cover using altitude and overstory basal area in different Mediterranean forests
(Springer Nature, 2010-05-20) Coll Mir, Lluís; González-Olabarria, José Ramón; Mola Yudego, Blas; Pukkala, Timo; Messier, Christian
In some areas of the Mediterranean basin where the understory stratum represents a critical fire hazard, managing the canopy cover to control the understory shrubby vegetation is an ecological alternative to the current mechanical management techniques. In this study, we determine the relationship between the overstory basal area and the cover of the understory shrubby vegetation for different dominant canopy species (Pinaceae and Fagaceae species) along a wide altitudinal gradient in the province of Catalonia (Spain). Analyses were conducted using data from the Spanish National Forest Inventory. At the regional scale, when all stands are analysed together, a strong negative relationship between mean shrub cover and site elevation was found. Among the Pinaceae species, we found fairly good relationships between stand basal area and the maximum development of the shrub stratum for species located at intermediate elevations (Pinus nigra, Pinus sylvestris). However, at the extremes of the elevation-climatic gradient (Pinus halepensis and Pinus uncinata stands), stand basal area explained very little of the shrub cover variation probably because microsite and topographic factors override its effect. Among the Fagaceae species, a negative relationship between basal area and the maximum development of the shrub stratum was found in Quercus humilis and Fagus sylvatica dominated stands but not in Quercus ilex. This can be due to the particular canopy structure and management history of Q. ilex stands. In conclusion, our study revealed a marked effect of the tree layer composition and the environment on the relationship between the development of the understory and overstory tree structure. More fine-grained studies are needed to provide forest managers with more detailed information about the relationship between these two forest strata.
Open Access
Aggregate Development and Organic Matter Storage in Mediterranean Mountain Soils
(Soil Science Society of China, 2010-10-27) Poch, Rosa M.; Antúnez Pujol, Montserrat
Soil aggregation and organic matter of soils from the pre-Pyrenean range in Catalonia (NE Spain) were studied, in order to assess their quality as carbon sinks and also to select the best soil management practices to preserve their quality. Aggregate stability, organic carbon and micromorphology were investigated. The highest amount of organic carbon was found in alluvial, deep soils (228 Mg C ha−1), and the lowest was in a shallow, stony soil with a low plant cover (78 Mg C ha−1). Subsurface horizons of degraded soils under pastures were the ones with smaller and less-stable aggregates. Fresh residues of organic matter (OM) were found mostly in interaggregate spaces. Within the aggregates there were some organic remains that were beginning to decompose, and also impregnative nodules of amorphous OM. Although OM was evenly distributed among the aggregate fractions, the larger blocky peds had more specific surface, contained less decomposed OM and had a lower organic/mineral interphase than smaller crumb aggregates, which were also more stable. Soil carbon storage was affected primarily by the OM inputs in the surface horizons. In order to store organic carbon over the mid- and long-term periods, the mechanisms favouring structuration through biological activity and creating small aggregates with intrapedal stable microporosities seemed to be the most effective.
Open Access
Invasive species and habitat degradation in Iberian streams: an analysis of their role in freshwater fish diversity loss
(Ecological Society of America, 2011-01-01) Hermoso, Virgilio; Clavero Pineda, Miguel; Blanco-Garrido, Francisco; Prenda, José
Mediterranean endemic freshwater fish are among the most threatened biota in the world. Distinguishing the role of different extinction drivers and their potential interactions is crucial for achieving conservation goals. While some authors argue that invasive species are a main driver of native species declines, others see their proliferation as a co‐occurring process to biodiversity loss driven by habitat degradation. It is difficult to discern between the two potential causes given that few invaded ecosystems are free from habitat degradation, and that both factors may interact in different ways. Here we analyze the relative importance of habitat degradation and invasive species in the decline of native fish assemblages in the Guadiana River basin (southwestern Iberian Peninsula) using an information theoretic approach to evaluate interaction pathways between invasive species and habitat degradation (structural equation modeling, SEM). We also tested the possible changes in the functional relationships between invasive and native species, measured as the per capita effect of invasive species, using ANCOVA. We found that the abundance of invasive species was the best single predictor of natives' decline and had the highest Akaike weight among the set of predictor variables examined. Habitat degradation neither played an active role nor influenced the per capita effect of invasive species on natives. Our analyses indicated that downstream reaches and areas close to reservoirs had the most invaded fish assemblages, independently of their habitat degradation status. The proliferation of invasive species poses a strong threat to the persistence of native assemblages in highly fluctuating environments. Therefore, conservation efforts to reduce native freshwater fish diversity loss in Mediterranean rivers should focus on mitigating the effect of invasive species and preventing future invasions.
Open Access
Nitrogen forms affect root structure and water uptake in the hybrid poplar
(Springer Nature, 2011-03-02) Domenicano, Susy; Coll Mir, Lluís; Messier, Christian; Berninger, Frank
The study analyses the effects of two different forms of nitrogen fertilisation (nitrate and ammonium) on root structure and water uptake of two hybrid poplar (Populus maximowiczii x P. balsamifera) clones in a field experiment. Water uptake was studied using sap flow gauges on individual proximal roots and coarse root structure was examined by excavating 18 whole-root systems. Finer roots were scanned and analyzed for architecture. Nitrogen forms did not affect coarse-root system development, but had a significant effect on fine-root development. Nitrate-treated trees presented higher fine:coarse root ratios and higher specific root lengths than control or ammonium treated trees. These allocation differences affected the water uptake capacity of the plants as reflected by the higher sapflow rate in the nitrate treatment. The diameter of proximal roots at the tree base predicted well the total root biomass and length. The diameter of smaller lateral roots also predicted the lateral root mass, length, surface area and the number of tips. The effect of nitrogen fertilisation on the fine root structure translated into an effect on the functioning of the fine roots forming a link between form (architecture) and function (water uptake).
Open Access
Bird Community Responses to Vegetation Heterogeneity Following Non-Direct Regeneration of Mediterranean Forests after Fire
(The Netherlands Ornithologists' Union, 2011-04-01) Zozaya, Elena L.; Brotons, Lluís; Vallecillo Rodríguez, Sara
Mediterranean forests are highly resilient to fires, showing a rapid recovery after disturbance. However, in some cases direct tree regeneration fails leading to radical changes in landscape composition. In this study, we evaluated the impact of landscape changes on the conservation value of bird species using the new landscape mosaic arising from non-direct regeneration after a fire. We used data from a large fire that occurred in central Catalonia (NE Spain) in 1998. The fire affected about 26,000 ha of a land mosaic mainly covered by Black Pine Pinus nigra forests and farmland dominated by cereal crops. We used line transects to estimate bird abundance and gathered information on dominant vegetation covers and landscape variables. Redundancy analysis (RDA) and generalized linear models were used to explore how the measured environmental variables explain bird species abundance and to analyze how post-fire heterogeneity in vegetation affected the conservation value of the bird community. Factors describing the main patterns in the post-fire landscape explained up to 31.2% of the total variability in bird community composition and described three main groups of bird species sharing similar ecological requirements. Additionally, 71% of the studied species significantly responded to one of the first three vegetation gradients distinguished in the study area. Finally, the conservation value of the bird community significantly decreased in areas dominated by Q. humilis resprouters and significantly increased in shrubland areas. Overall, our results suggest that large fires affecting non-direct regenerating forest types lead to a new and radically different mosaic landscape offering new opportunities to species with unfavourable European conservation status.
Open Access
Quantifying the effect of nitrogen-induced physiological and structural changes on poplar growth using a carbon-balance model
(Oxford University Press, 2011-04-14) Coll Mir, Lluís; Schneider, Robert; Berninger, Frank; Domenicano, Susy; Messier, Christian
We evaluate the importance of changes in photosynthetic capacity, respiration rates, root shoot ratio, pipe model parameters and specific leaf area in the early-growth response of hybrid poplar to nitrogen availability. Juvenile growth simulations for trees with three different levels of leaf nitrogen concentration (Nleaf) (low (1.2%), medium (2.4%) and high (3.6%)) were conducted with the carbon-balance model CROBAS. Five-year growth simulations showed the diameter and height of poplar trees to be, respectively, four and three times larger in plants with 2.4% Nleaf compared with those with 1.2% Nleaf. Increasing Nleaf from 2.4 to 3.6% resulted in 34 and 16% higher diameter and height growth of trees. According to the model, changes in the photosynthetic capacity accounted for most of the differences in growth between trees with different levels of Nleaf; the other parameters were much less influential. This suggests that in fast-growing early-successional broadleaved species such as poplars, physiological rather than allocational and morphological traits predominate in determining growth, at least under non-limiting light conditions.
Open Access
Climate change or land use dynamics: do we know what climate change indicators indicate?
(Public Library of Science (PLoS), 2011-04-21) Clavero Pineda, Miguel; Villero Pi, Daniel; Brotons, Lluís
Different components of global change can have interacting effects on biodiversity and this may influence our ability to detect the specific consequences of climate change through biodiversity indicators. Here, we analyze whether climate change indicators can be affected by land use dynamics that are not directly determined by climate change. To this aim, we analyzed three community-level indicators of climate change impacts that are based on the optimal thermal environment and average latitude of the distribution of bird species present at local communities. We used multiple regression models to relate the variation in climate change indicators to: i) environmental temperature; and ii) three landscape gradients reflecting important current land use change processes (land abandonment, fire impacts and urbanization), all of them having forest areas at their positive extremes. We found that, with few exceptions, landscape gradients determined the figures of climate change indicators as strongly as temperature. Bird communities in forest habitats had colder-dwelling bird species with more northern distributions than farmland, burnt or urban areas. Our results show that land use changes can reverse, hide or exacerbate our perception of climate change impacts when measured through community-level climate change indicators. We stress the need of an explicit incorporation of the interactions between climate change and land use dynamics to understand what are current climate change indicators indicating and be able to isolate real climate change impacts.
Open Access
Valuing acorn dispersal and resprouting capacity ecological functions to ensure Mediterranean forest resilience after fire
(Springer Nature, 2011-08-21) Puerta-Piñero, Carolina; Brotons, Lluís; Coll Mir, Lluís; González-Olabarria, José Ramón
Ecological processes within forests provide vital ecosystem services to society, most of which depend on the persistence of tree cover that can be altered after the impact of a disturbance. The aim of the present study was to examine the role of seed dispersal and resprouting that mediate resilience to large fires and evaluate the economic costs that these ecological functions provide. We used field data from 412 plots of the Spanish National Forest Inventory providing information on pre- and post-fire conditions of Mediterranean Pinus spp. and Quercus spp.-dominated forests. Then, we determined the need for restoration (N Rest) and estimated the minimum pre-fire densities needed to ensure adequate post-fire cover. Economic valuations were assessed through three different scenarios (Sc) of possible human-management actions aimed at ensuring proper post-fire tree cover: Sc. 1) a pre-fire management scenario evaluating the costs of planting Quercus spp. seedlings in the understory, mimicking the whole dispersal function; Sc. 2) a pre-fire scenario in which enrichment plantations increased the densities of natural oaks; and Sc. 3) a post-fire scenario where the restoration is done through planting pines within the burned area. Approximately 90% of the burned area (371 out of 412 plots) was able to recover after fire supporting the view that Mediterranean forests are resilient to fire. This resilience was primarily mediated by biotic seed dispersal and posterior resprouting of tree species. These ecological functions saved between 626 and 1,326 €/ha compared to the human-management actions. Ensuring key ecological processes within forests increases forest resilience and recovery after fire leading to a generally significant saving of economic resources. In a perspective of increased future impact of disturbances and decrease availability of economic resources for forest management, the implications of the present study can be far reaching and extended to other forest planning exercises.
Open Access
Determinants of fine‐scale homogenization and differentiation of native freshwater fish faunas in a Mediterranean Basin: implications for conservation
(Blackwell Publishing Ltd, 2011-08-31) Hermoso, Virgilio; Clavero Pineda, Miguel; Kennard, Mark J.
Aim: Increasing threats to freshwater biodiversity are rapidly changing the distinctiveness of regional species pools and local assemblages. Biotic homogenization/differentiation processes are threatening the integrity and persistence of native biodiversity patterns at a range of spatial scales and pose a challenge for effective conservation planning. Here, we evaluate the extent and determinants of fine‐scale alteration in native freshwater fish assemblages among stream reaches throughout a large river basin and consider the implications of these changes for the long‐term conservation of native fishes. Location: Guadiana River basin (South‐Western Iberian Peninsula). Methods: We quantified the magnitude of change in compositional similarity between observed and reference assemblages and its potential effect on natural patterns of compositional distinctiveness. Reference assemblages were defined as the native species expected to occur naturally (in absence of anthropogenic alterations) and were reconstructed using a multivariate adaptive regression splines predictive model. We also evaluated the role of habitat degradation and introduced species as determinants of biotic homogenization/differentiation. Results: We found a significant trend towards homogenization for native fish assemblages. Changes in native fish distributions led to the loss of distinctiveness patterns along natural environmental gradients. Introduced species were the most important factor explaining the homogenization process. Homogenization of native assemblages was stronger in areas close to reservoirs and in lowland reaches where introduced species were more abundant. Main conclusions: The implementation of efficient conservation for the maintenance of native fish diversity is seriously threatened by the homogenization processes. The identification of priority areas for conservation is hindered by the fact that the most diverse communities are vanishing, which would require the selection of broader areas to adequately protect all the species. Given the principal role that introduced species play in the homogenization process and their relation with reservoirs, special attention must be paid to mitigating or preventing these threats.
Open Access
How spatial heterogeneity of cover affects patterns of shrub encroachment into mesic grasslands
(Public Library of Science (PLoS), 2011-12-08) Montané, Francesc; Casals, Pere; Dale, Mark R. T.
We used a multi-method approach to analyze the spatial patterns of shrubs and cover types (plant species, litter or bare soil) in grassland-shrubland ecotones. This approach allows us to assess how fine-scale spatial heterogeneity of cover types affects the patterns of Cytisus balansae shrub encroachment into mesic mountain grasslands (Catalan Pyrenees, Spain). Spatial patterns and the spatial associations between juvenile shrubs and different cover types were assessed in mesic grasslands dominated by species with different palatabilities (palatable grass Festuca nigrescens and unpalatable grass Festuca eskia). A new index, called RISES (“Relative Index of Shrub Encroachment Susceptibility”), was proposed to calculate the chances of shrub encroachment into a given grassland, combining the magnitude of the spatial associations and the surface area for each cover type. Overall, juveniles showed positive associations with palatable F. nigrescens and negative associations with unpalatable F. eskia, although these associations shifted with shrub development stage. In F. eskia grasslands, bare soil showed a low scale of pattern and positive associations with juveniles. Although the highest RISES values were found in F. nigrescens plots, the number of juvenile Cytisus was similar in both types of grasslands. However, F. nigrescens grasslands showed the greatest number of juveniles in early development stage (i.e. height<10 cm) whereas F. eskia grasslands showed the greatest number of juveniles in late development stages (i.e. height>30 cm). We concluded that in F. eskia grasslands, where establishment may be constrained by the dominant cover type, the low scale of pattern on bare soil may result in higher chances of shrub establishment and survival. In contrast, although grasslands dominated by the palatable F. nigrescens may be more susceptible to shrub establishment; current grazing rates may reduce juvenile survival.