Brachypodium Retusum Research Articles

Restoring stone and dominant grass species cover in a Mediterranean grassland: 20‐year effects on soil, vegetation, and arthropod communities

Long‐term studies are needed to monitor recovery following restoration, as it may take decades or even centuries, particularly in the case of Mediterranean dry grasslands, for communities to reach their former equilibrium before the degradation occurred. A multi‐component approach is also needed to evaluate restoration success and better understand the complex impacts of former restoration projects on present‐day ecological interactions and ecosystem functions. The objective of this study was to address the restoration of a Mediterranean grassland in southern France, 20 years after implementation. Particularly, we examine the long‐term impact on soil, vegetation, and arthropods of the reintroduction of a dominant grass species (Brachypodium retusum) and the restoration of the natural stone cover on a degraded former cultivated field. Soil analyses revealed that reestablishing stone cover only slightly acidified the soil, while B. retusum presence enhanced soil fertility. Brachypodium retusum also decreased the nutritional value of forage and increased plant biomass and litter. Plant composition shifted with treatments: B. retusum and stone cover favored xeromesophilous species, while B. retusum alone encouraged less palatable species. The soil seed bank composition and abundance were positively influenced by stone cover but negatively impacted by B. retusum reintroduction. Negative outcomes on some arthropods and mesofauna were measured in treatments with both B. retusum and stones, except for Acari, which were positively impacted by the presence of stones. The findings emphasize that B. retusum is an ecological engineer with complex effects on the different ecosystem components.

Root traits rather than functional diversity of soil microorganisms respond to drought and plant species composition in Mediterranean shrubland species

Belowground responses are critical in understanding how plants cope with the predicted increase in drought intensity and frequency in the Mediterranean region, because plant root systems compete with each other and interact with soil microbial communities under limiting water availability. However, the combined responses of plant roots and soil microorganisms to drought are not well understood. Using an experimental approach, we addressed the question of how recurrent drought and different combinations of two individuals from three common Mediterranean plant species (Quercus coccifera, Cistus albidus, and Brachypodium retusum) affect root characteristics and soil microbial activity. We hypothesized that drought effects on root characteristics and associated soil microbial communities are stronger when plant individuals of the same species compete for limiting water compared to inter-specific competition. Root morphological traits were more affected by the species identity of the neighbor individual than by recurrent severe drought, particularly in B. retusum, which may in part explain the higher survival previously observed for this species. On the other hand, drought and plant composition had little effect on root-associated soil microbes’ ability to use a wide range of different carbon substrates. Overall, our results did not confirm stronger effects of intra- compared to interspecific competition on the root and microbial responses, but showed strong species identity effects.

Ecological restoration of solar park plant communities and the effect of solar panels

The construction of solar parks leads to soil degradation and the destruction of vegetation. Solar panels change the microclimate affecting plant survival and vegetation development. The increasing solar energy production requires solutions for ecological restoration from the beginning of electricity production. We compared three methods to restore Mediterranean dry grasslands as a target community not affecting solar energy production: seed material transfer, sowing of the target species Brachypodium retusum and an increase in soil organic matter by compost addition. The experiment was set up in a solar park located in South-Eastern France, both outside and below solar panels (SP). After four years, seed material transfer was the best method to initiate plant succession towards the reference community. SP hampered restoration success and strongly reduced plant species richness, in particular of species from the reference community. B. retusum survival decreased by 50% and phytometabolic indices revealed a light stress under SP. However, the species still maintained growth similar to plants outside SP suggesting shade tolerance. Long-term monitoring is required to evaluate whether communities better adapted to light reduction under panels need to be taken into account for successful restoration.

Using various artificial soil mixtures to restore dry grasslands in quarries

Quarry restoration is difficult to implement due to the scarcity of the original soil. The restoration of Mediterranean dry grasslands to mitigate similar ecosystem/habitat loss is thus still a developing process. So far, very few studies have created artificial substrates to address the lack of soil. In the La Crau plain (Southeastern France), quarries were established in an ancient Mediterranean steppe‐like dry grassland. Once the remaining grassland zones were protected in 2001, quarries were extended over former intensive orchards established on the grassland in the 1990s before it was protected. Now, restoration has to be done without the unaltered protected grassland soil but with the soil from orchards, which contains fertilizers spread during the orchard exploitation. To recreate a more suitable substrate, the orchard topsoil was mixed with poor substrate materials directly extracted from the quarry (0–30 mm pebbles with sandy matrix). Different substrate mixtures were tested with or without sowing the dominant species of the grassland, a perennial grass: Brachypodium retusum (and an annual grass B. hybridum). After 5 years of monitoring, our results show that raw substrate materials (100%) limit the establishment of all species, and that, at the opposite, orchard topsoil (100%) favors a significantly higher species richness of target and non‐target species. The recommended substrate mixture to reach a compromise between high target species cover and low non‐target species cover is composed of 50% raw quarry material and 50% arable soil. Sowing Brachypodium not only limits non‐target species richness and cover but also reduces target species richness establishment.

Contributions to the smut fungi of Africa. 7. First records of Tilletia brachypodii-ramosi and Ustilago constantineanui

Two poorly known smut fungi are recorded for the first time from Africa: Tilletia brachypodii-ramosi on Brachypodium retusum (from Morocco) and Ustilago constantineanui on Sporobolus schoenoides (from Algeria). Descriptions and illustrations are provided for these taxa.

Litter as a filter for germination in semi-arid Stipa tenacissima steppes

Woody species play a key role in Stipa tenacissima steppes, they affect ecosystem functioning, facilitate establishment of other plants and increase plant richness. Among the mechanisms involved in facilitation, effect of litter on seed germination and seedling establishment is largely underexplored. We studied the properties of the litter layer under five woody species common in Stipa tenacissima steppes, and assessed its effect on the germination of seeds of two key species with contrasting ecological strategy and seed morphology (the perennial grass Brachypodium retusum and the resprouting shrub Pistacia lentiscus). Litter accumulation was highest under Quercus coccifera and Pinus halepensis, and lowest under Rhamnus lycioides. Pistacia lentiscus and Rosmarinus officinalis showed intermediate levels. Litter accumulation hampered germination, particularly when seeds were sown over the litter. Litter of all species but Rhamnus lycioides reduced germination when seeds were under the litter. Litter extracts had no effect on germination. The effect of litter was largely independent of seed type. Our results show that litter has an overall negative effect acting as a physical barrier for. Litter may influence the balance between facilitation and interference. Its relation with species traits and its impact on habitat heterogeneity and community assemblage deserves further attention.

Preference by Donkeys and Goats among Five Mediterranean Forest Species: Implications for Reducing Fire Hazard.

Simple SummaryDonkeys and goats are animals adapted to graze in understories, and thus contribute to the prevention of forest fires. In this work, the preferences of donkeys and goats have been determined for five key plant species of the Mediterranean forest, where large forest fires have increased as a result of global change. Using a multiple selection test, it has been observed that both species can complement each other, since donkeys consume more fine fuel, such as Brachypodium retusum, and goats, highly flammable woody species, such as Pinus halepensis. In this way, browsing becomes an ecosystem service, which, in the case of donkeys, can even help prevent their extinction.During the second half of the 20th century, European countries experienced an increase in their forest area due to the global change. Consequently, there has been an increase in large forest fires, mainly in the Mediterranean basin, and this has forced the development of several types of prevention programs. One of them is the control of the understory by livestock. In this sense, browsing with a combination of donkeys and goats could be a good option, as both animals usually feed on forest species. However, little is known about their preferences for the key species of the Mediterranean forest. Using a cafeteria test, the preferences and consumption of both animals have been determined for five typical species of the Mediterranean forest, such as Quercus ilex, Pinus halepensis, Phillyrea latifolia, Rubus ulmifolius, and Brachypodium retusum. Results showed that donkeys and goats could act complementarily in the reduction of the fuel biomass of forests. Donkeys appear to act more on fine fuel, such as B. retusum, and goats on the more pyrophyte species, in this case P. halepensis. In addition, given that donkeys are at severe risk of extinction in Europe, this role of providing ecosystem services could contribute to their conservation. Despite this study only showing that goats and donkeys would consume all five presented plant species and that there are some differences in consumption during a short-term test, it constitutes a useful first step for conservation and fire prevention in the Mediterranean forests.

Comparison of neutral and adaptive differentiation in the Mediterranean grass Brachypodium retusum

Abstract The Mediterranean grass Brachypodium retusum is the dominant species of a vulnerable steppe habitat. Differentiation in phenotypic traits has been found in a previous study, but scales and drivers are largely unknown. In this study, we compared molecular and phenotypic variation between populations to (1) analyse spatial patterns of neutral genetic variation; (2) test for effects of selection on differentiation and (3) identify major drivers of adaptive differentiation. We collected plant material of 17 populations in the western Mediterranean covering a large part of the species range. Neutral population differentiation was estimated using AFLP markers. A regional-scale subset of pairs of French populations was sampled in close proximity from calcareous and red Mediterranean soils as major habitat types. Sampling sites differed in climate at a regional scale and in soil characteristics such as pH at a local scale. These populations were grown in a common garden experiment to measure phenotypic traits. To test for the effects of selection on phenotypic differentiation, we calculated pairwise θST values based on neutral AFLP markers and compared them to pairwise PST values using phenotypic traits. Global dataset θST indicated significant neutral genetic differentiation between western Mediterranean populations. In the French populations, PST of vegetative and reproductive traits were higher than θST, suggesting that directional selection contributed to phenotypic population differentiation. We also found significant local-scale differentiation between soil types, but differentiation was substantially higher at the regional scale, pointing towards climate as a stronger selective factor than soil type. Mean temperature of the hottest month and winter frost frequency were identified as major drivers of adaptive differentiation. The study demonstrated the importance of combining neutral marker and phenotypic trait analysis at different spatial scales to evaluate genetic structure. Despite relatively low differentiation in AFLP markers, environmental pressure was sufficient to maintain phenotypic differentiation at regional scales.

Functional similarity and competitive symmetry control productivity in mixtures of Mediterranean perennial grasses.

Competition is a major factor structuring plant communities and controlling their productivity. The functional similarity between the interacting species and the context resource availability are assumed to be most critical factors that modulate the strength, sign, and outcome of plant competition, yet their roles and interactions are subjected to debate. In a glasshouse experiment, we constructed monocultures and bi-specific cultures of three common perennial grasses of Mediterranean drylands, the short grass Brachypodium retusum and the tussock grasses Stipa tenacissima and Lygeum spartum, and investigated how the functional similarity between these species modulate their interactions and culture productivity under contrasting levels of water availability. Regardless the degree of functional similarity between the interacting species, B. retusum consistently exhibited a greater competitive ability than the other two species, followed by L. spartum, and with S. tenacissima behaving as the weakest competitor. Bi-specific cultures of B. retusum and either L. spartum or S. tenacissima produced higher biomass than the average biomass of the respective monocultures (i.e. overyielding), whereas the combination of the most similar species, L. spartum—S. tenacissima, which exhibited the highest competition symmetry (i.e., the more similar mutual impact), did not show any significant overyielding. Higher water availability increased productivity and promoted transgressive overyielding for the most dissimilar species, B. retusum and L. spartum, which however exhibited intermediate competition asymmetry. This study calls attention to the thin line between differences in functional traits and competition asymmetry that could eventually lead to either competitive exclusion or resource partitioning and coexistence.

Factors limiting early establishment of the Mediterranean grassland species Brachypodium retusum at disturbed sites

In Mediterranean dry grasslands, water availability and grazing strongly influence plant establishment. Although higher water availability and lower grazing pressure usually increase seedling recruitment in the beginning, higher competition may reduce seedling survival. In our study, we analysed this trade-off for the dominant species of Western Mediterranean steppes Brachypodium retusum which hardly recolonises restoration sites degraded by soil disturbance such as arable use.A split-plot experiment was set up on an ex-arable site in the “La Crau” steppe in order to test the effects of initial watering and sheep grazing on seedling recruitment, survival and early growth during two years. The watering treatment was applied in the first autumn and spring doubling the usual precipitation during this period and grazing was tested using exclosures. Survival and growth of seedlings established from field-sown seeds were compared to those of transplanted seedlings pre-grown in a growth chamber.Watering did not affect germination whereas the grazing effect was negative. Initial watering had a positive effect on survival only in grazed plots suggesting a compensatory effect under grazing disturbance. Significant main effects of watering on early growth disappeared in the second season. Grazing significantly reduced most measured growth traits whereas the effect on survival was only marginally significant. Planted seedlings (49%) survived better than seedlings emerged from field-sown seeds (36%). In conclusion, initial fencing increases establishment success of B. retusum in ecological restoration. Initial watering may help to mitigate negative grazing effects when fencing is not possible.

Effect of pre- and post-wildfire management practices on plant recovery after a wildfire in Northeast Iberian Peninsula

Fire and pre- or post-fire management practices shape the distribution and richness of plant species. Here, the effects of pre- and post-fire management on vegetation recovery were studied at different times, up to 18 months after a wildfire. Two months after a 2015 wildfire, 18 study plots were established (three 4-m2 plots for each treatment), vegetation regrowth was monitored and vegetal species richness (S), evenness (IT), density (D), diversity (H′) and maximum diversity (HMax) after 2, 10 and 18 months. The treatments were (1) control, unaffected by 2015 wildfire; (2) no treatment (NT), burned in 2015 wildfire and not managed; (3) managed in 2005 and burned in 2015 (M05B); (4) managed in 2015, 2 months before wildfire (M15B); (5) cut and manual removal after the 2015 wildfire (CR); (6) cut and no trunk removal randomly deposited on topsoil after the 2015 wildfire (CL). All the treatments were carried out in a Pinus halepensis Miller forest. At 10 and 18 months after the wildfire, vegetation recovery was greater in NT, CR and CL plots than in M05B and M15B the plots. By 18 months after the wildfire, Brachypodium retusum (Pers.) P. Beauv. and Rosmarinus officinalis L. were still dominant, especially in M15B, corroborating the belief that pre-fire treatment reduced ecosystem resilience and vegetal recovery compared to the NT and post-fire managed plots. Richness was significantly lower 10 months after wildfire in control plots, and IT was significantly higher in that inventory than previously in M15B. Eighteen months after the wildfire, H′ was significantly lower in M15B. Ten months post-wildfire, HMax was significantly lower in the control plots. Eighteen months after the wildfire, HMax, was significantly higher in CR, CL and M05B than in the control and M15B plots. Overall, pre-fire management was detrimental to post-fire vegetation recovery, while manual post-fire management proved beneficial.

Fire increases the reproduction of the dominant grass Brachypodium retusum and Mediterranean steppe diversity in a combined burning and grazing experiment

AbstractAimsWe assessed what the effects of fire and grazing are on vegetative growth and sexual reproduction of Brachypodium retusum, the dominant species of Mediterranean Thero‐Brachypodietea grasslands (“steppes”) and on species composition of the associated plant community.Location“La Crau”, southeastern France.MethodsWe set up a split‐plot experiment testing the effects of fire season (winter, summer) and grazing on plant cover, inflorescence number, seed set and germination of Brachypodium retusum in traditionally grazed grasslands. We further analyzed plant species composition and diversity in vegetation relevés. The same fire treatments were tested in a second experiment in long‐term grazing exclosures.ResultsBrachypodium retusum showed a rapid post‐fire recovery, but other species of the associated plant community, in particular annuals, recovered as fast or even faster. Fire increased Brachypodium retusum inflorescence production and seed set per inflorescence and this effect was stronger in the summer fire treatment. At the community level, fire significantly increased species richness, evenness and Bray–Curtis dissimilarity in the second post‐fire season and again, the summer fire effect was stronger. Grazing exclusion for two seasons had only a small effect on Brachypodium retusum and the associated plant community. The effect of both fire treatments on Brachypodium retusum was similar in long‐term exclosures. In these exclosures, fire resulted in a community shift towards the species composition of traditionally grazed steppes.ConclusionsThe concomitant positive effects of experimental burning on Brachypodium retusum reproduction and on plant diversity of Mediterranean steppe vegetation suggest that the system is adapted to fire as an important driver of community composition. Annual species surviving as seeds are as successful in post‐fire recovery as perennial resprouters. Prescribed burning may be an alternative strategy to restore community structure in abandoned (ungrazed) steppes showing a decline in typical grassland species after several years of grazing abandonment.

Post-fire nitrogen uptake and allocation by two resprouting herbaceous species with contrasting belowground traits

Immediately after fire, soil nitrogen availability increases due to ash deposition and the stimulation of mineralization by increased temperature. The coexistence of plant resprouters with contrasting root traits that grow soon after fire suggests different strategies operating for the re-acquisition of space, capturing resources and resisting additional stresses. Brachypodium retusum and Dactylis glomerata are two perennial grass species that co-occur in fire-prone Mediterranean basin ecosystems. B. retusum (Br) is a slow-growing grass with a developed rhizome, whereas D. glomerata (Dg) is a fast-growing grass that resprouts from rootstock buds. We hypothesized that the fast-growing grass would take advantage of the flush in available N after fire, whereas the aboveground growth of the slow-growing grass would rely on rhizome N reserves. The objective of this study was to ascertain the role of the root system characteristics and plant growth traits in relation to soil N uptake and plant N assimilation soon after fire followed by grazing. Therefore, in a pot experiment with plants and soil transplanted from the field, we applied 15N-NH4+ to the surface of the soil, immediately after cutting the aboveground plant biomass to simulate post-fire disturbance. Grazing defoliation was simulated using four successive cuttings. Both species resprouted quickly after the fire-simulation cutting, with the recovery of approximately 15% of the initial aboveground biomass only 5 days afterwards; 20 days later, the biomass reached 50% for Dg and 28% for Br. This regrowth was parallel to a reduction in belowground biomass. Later, the aboveground biomass remained approximately constant after four cuts over 75 days, maintaining the same total N content (close to 2.0 g N m−2 for Dg and 1.0–1.5 g N m−2 for Br). Both species showed high 15N atom % in their leaves after 20 days of 15N application, which slowly decreased over the successive cuts. After 55 days and two cuts, only Br showed a decline in the total plant 15N content. Plant growth and soil N uptake were higher in the non-rhizomatous species (Dg) showing greater root development and higher belowground/aboveground ratio. The rhizome of Br supported early resprouting but this species did not take much advantage of the initial N mineralization after fire. In Dg pots, the 15N-NO3- that leached out was lower than in Br pots. Dg showed higher nitrate reductase activity, in comparison to Br. In agreement with our hypothesis, the results suggest that the fast-growing strategy of Dg takes advantage of increased N availability after fire, whereas the slow growing Br relies on N rhizome reserves, which were slowly replenishing from available soil N. Both species showed high regeneration capacity after fire and high resilience to intensive post-fire grazing pressure.

Adaptive differentiation among populations of the Mediterranean dry grassland species Brachypodium retusum: The role of soil conditions, grazing, and humidity.

Genetic differentiation in plant species may result from adaptation to environmental conditions, but also from stochastic processes. The drivers selecting for local adaptation and the contribution of adaptation to genetic differentiation are often unknown. Restoration and succession studies have revealed different colonization patterns for Brachypodium retusum, a common Mediterranean grass. In order to understand these patterns, we tested population differentiation and adaptation to different environmental factors. Structured sampling of 12 populations from six sites and two soil types within site was used to analyze the spatial and environmental structure of population differentiation. Sampling sites differ in grazing intensity and climate. We tested germination and growth in a common garden. In subsets, we analyzed the differential response to stone cover, grazing and soil moisture. We found significant differences among populations. The site explained population differentiation better than soil, suggesting a dominant influence of climate and/or genetic drift. Stone cover had a positive influence on seedling establishment, and populations showed a differential response. However, this response was not related to environmental differences between collection sites. Regrowth after clipping was higher in populations from the more intensively grazed Red Mediterranean soils suggesting an adaptation to grazing. Final germination was generally high even under drought, but germination response to differences in soil moisture was similar across populations. Adaptive population differentiation in germination and early growth may have contributed to different colonization patterns. Thus, the provenance of B. retusum needs to be carefully considered in ecological restoration.

Distribución de plantas vasculares a escala local. Taxones con mayor ocupación geográfica en Ambite y Utande (La Alcarria Occidental)

The method for performing Floral Cover Indices (FCI), presented in a previous article, is applied to two 100 km 2 U.T.M. grid cells (30TVK86, Ambite and 30TWL02,Utande). They are located in different sectors of the natural region of Western “La Alcarria”. The goal is to know and compare distributions of presence and abundance of vascular plants at local scale. Geographical factors affecting cover of the flora is widely exposed. Analysis method and chorological maps drawing with four spatial levels (1, 4, 25 and 100 km 2 ) are presented. Results of the twelve taxa with the highest FCI in the set of two grid cells and phytogeographical interpretations are shown: Genista scorpius, Quercus ilex subsp. ballota, Thymus vulgaris, Helianthemum cinereum subsp. rotundifolium, Brachypodium retusum, Thymus zygis subsp. sylvestris, Lavandula latifolia, Dactylis hispanica, Rosmarinus officinalis, Koeleria vallesiana, Quercus faginea y Salvia lavandulifolia .

Temporal changes in soil water repellency after a forest fire in a Mediterranean calcareous soil: Influence of ash and different vegetation type

Forest fires usually modify soil water repellency (SWR), and its persistence and intensity show a high variability both in space and time. This research studies the evolution of SWR in a Mediterranean calcareous soil affected by a forest fire, which occurred in Gorga (SE Spain) in July 2011, comparing the effect of the main vegetation cover between pine (Pinus halepensis) and shrubs species (Quercus coccifera, Rosmarinus officinalis, Cistus albidus, Erica arborea and Brachypodium retusum) and the relationship with soil moisture content (SMC). Also the study analyzed the effect of ash on SWR dynamics under field conditions. Six plots were established on the fire-affected area and the unburned–control–adjacent area to monitoring SWR with the water drop penetration time (WDPT) test, SMC through moist sensors (5cm depth) and three different ash treatments: ash presence, ash absence and incorporation of ash into the soil. An immediate increase of SWR was observed in the fire-affected area, mainly in pine plots. SWR changes in control (unburned) plots were quite similar between different types of vegetation influence, despite higher SWR values being observed on pine plots during the study period. A noticeable decrease of SWR was observed during the first months after fire in the affected areas, especially after the first rainy period, both in pine and shrubs plots. SWR increase was registered in all plots, and the highest levels were in March 2012 in burned pine plots. SWR decrease was higher in plots where ash was removed. Fire-affected soils became wettable 1year and a half after the fire.

Limiting processes for perennial plant reintroduction to restore dry grasslands

In restored grasslands of southern Europe, perennial plants remain highly underrepresented compared with the reference ecosystems. We tested various treatments to reintroduce common perennial plant species (Brachypodium retusum, Poaceae, and Thymus vulgaris, Lamiaceae), which are usually not or poorly reintroduced via soil and hay transfer. Treatments included microenvironmental manipulations (rock cover and plant interactions) and two grazing intensities. Target perennial species were transplanted in 2002 in the reference grassland ecosystem (intact grassland area used as a control) and in two abandoned fields. Survival was assessed in June 2003 and June 2004. Target species shoot and root biomass were measured in June 2004. Grazing greatly reduced the survival and biomass of both target species and its effects were reinforced by summer drought: plants that did not establish well enough during the autumn and spring did not survive summer. The restored rock cover had a mild positive effect, particularly on B. retusum. There were no negative or positive plant neighbor interactions in the steppe, while there was competition in both abandoned fields. Competition was particularly intense in the abandoned melon field, composed of a dense sward of annual grasses (Bromus sp.). In order to reintroduce perennial species to dry grasslands, the ideal combination of treatments is to exclude or reduce grazing during the first year to allow seedlings to establish and to recreate adequate microenvironmental conditions. Reducing competition from arable weeds may help but is not essential in such dry grasslands.

Community attributes determine facilitation potential in a semi-arid steppe

a b s t r a c t Studies on positive plant-plant relations have traditionally focused on pair-wise interactions. Conversely, the interaction with other co-occurring species has scarcely been addressed, despite the fact that the entire community may affect plant performance. We used woody vegetation patches as models to eval- uate community facilitation in semi-arid steppes. We characterized biotic and physical attributes of 53 woody patches (patch size, litter accumulation, canopy density, vegetation cover, species number and identity, and phylogenetic distance), and soil fertility (organic C and total N), and evaluated their relative importance for the performance of seedlings of Pistacia lentiscus, a keystone woody species in western Mediterranean steppes. Seedlings were planted underneath the patches, and on their northern and south- ern edges. Woody patches positively affected seedling survival but not seedling growth. Soil fertility was higher underneath the patches than elsewhere. Physical and biotic attributes of woody patches affected seedling survival, but these effects depended on microsite conditions. The composition of the community of small shrubs and perennial grasses growing underneath the patches controlled seedling performance. An increase in Stipa tenacissima and a decrease in Brachypodium retusum increased the probability of survival. The cover of these species and other small shrubs, litter depth and community phylogenetic dis- tance, were also related to seedling survival. Seedlings planted on the northern edge of the patches were mostly affected by attributes of the biotic community. These traits were of lesser importance in seedlings planted underneath and in the southern edge of patches, suggesting that constraints to seedling estab- lishment differed within the patches. Our study highlights the importance of taking into consideration community attributes over pair-wise interactions when evaluating the outcome of ecological interac- tions in multi-specific communities, as they have profound implications in the composition, function and management of semi-arid steppes.

Biological soil crust influence on germination and rooting of two key species in a Stipa tenacissima steppe

Background and aims In Mediterranean steppes, Stipa tenacissima tussocks facilitate the establishment of vascular plants. We hypothesized that this effect may partially reflect the indirect interaction between Stipa tenacissima, biological soil crusts (BSC), and seeds. Methods We explored the relationship between BSC composition and soil surface conditions (surface roughness and hydrophobicity by using the water drop penetration time test), and seed germination and seedling rooting in aS. tenacissima steppe in southeastern Spain. We explored the causal factors of seed germination at two spatial scales and used SADIE index to represents the soil surface heterogeneity. Results Microsites strongly differed in BSC compositionand soilsurface conditions. Germination of two key species, Pistacia lentiscus and Brachypodium retusum, was not affected by BSC type. In contrast, rooting was lower on soil from open areas covered by BSC than on soil from open areas dominated by bare soil and soil collected under the tussocks. The effect was similar in both species. Lichens were probably responsible for the decrease in rooting. Conclusions Our results suggest that lichen cover and the cover of bare soil and mosses may hamper and facilitate rooting, respectively. By affecting seedling rooting, BSC may contribute to the facilitative effect of Stipa tenacissima.

Influencia de la exposición sobre la producción de sedimentos y escorrentía en ambientes semiáridos

By means of experiments with simulated rainfall the influence of aspect on runoff and erosion dynamics is analysed in a basin where the vegetation is distributed within a mosaic of Stipa tenacissima L. shrubs and inter-shrubs. In the inter-shrubs areas three different types of areas exist: Stone pavement (with rack fragments), Crusted surfaces (with surface crust) and vegetation covered areas (Brachypodium retusum). 
 The erosion and runoff rates are very low beneath the vegetation (Esparto tussocks and Brachypodium retusum grass), while in the intershrubs areas (Crusted and Stone pavement) rates are higher. The vegetation controls runoff generation through its effect on the infiltration rates.
 Both runoff and erosion processes are influenced by aspect. The northjacing slopes have higher infiltration rates, and runojf is attenuated and reduced. The soil losses are neglegible in compararison to the southjacing slope. Vegetation cover is inversely and non-linearly related to the volume of overland flow, and the relationship exhibit a threshold due to the patch distribution of the vegetation. Modelling and predictioning the geomorphological processes under semiarid conditions is very complicated due to the high spatial variability of bis factors, specially the vegetation.