Blaise Touzard
University of Bordeaux
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Featured researches published by Blaise Touzard.
Journal of Vegetation Science | 2008
Estelle Forey; Benjamin Chapelet; Yann Vitasse; Mathieu Tilquin; Blaise Touzard; Richard Michalet
Abstract Questions: 1. Is there a primary role of disturbance at local scale and of environmental stress at regional scale? 2. Does disturbance increase or decrease environmental stress at local scale? Location: The Atlantic coastal dune system of the Aquitaine Region (France). Methods: Species biomass and 16 environmental variables were sampled in 128 quadrats along a local beach-inland gradient and a regional North-South gradient. Environmental data were analysed with ANOVAs and vegetation-environment relationships with Canonical Correspondence Analysis. Results: At the local scale community composition was primarily driven by disturbance due to sand burial, whereas water and nutrient stress better explained regional differences. However, random biogeographical events are very likely to also affect community composition at the largest scale. The main interaction between environmental stress and disturbance was the mitigation of nutrient stress induced by disturbance at a local scale. This was due to a positive direct effect of sand burial and a positive indirect effect of wind (decrease in VPD by ocean spray). Although wind had also a significant effect on soil conductivity and pH, there was no evidence that these factors had any role in community composition. Conclusions: Our results support the hypothesis that disturbance had a primary role at local scale and environmental stress at regional scale but further research is needed to separate the effect of stress from that of dispersal at regional scale. We also demonstrated that environmental stress in primary succession may not always decline with decreasing disturbance. Nomenclature: Flora Europaea (Tutin et al. 1964–1980).
Flora | 2004
Bernard Amiaud; Blaise Touzard
Summary The study deals with the influence of land use and abandonment on species composition of vegetation and seed bank in grasslands and oldfields. We wanted to explore: (1)How the seed bank changes when agricultural practices cease? In convergence with proposals in the literature, we addressed in particular the following two questions that have been proposed by Symonides (1986), Pickett & McDonnell (1989) and Roberts & Vankat (1991) for seed bank characteristics under secondary succession: (i) Does species richness and species diversity in the soil seed bank decrease during succession? (ii) Does the density of buried seed decline during succession? (2)What is the role played by seed bank in the recolonisation of plots disturbed by experimental disturbances? We studied species composition of vegetation and seed bank in an experiment with grassland and oldfield plots in old embanked marshlands (called “Marais Poitevin”). In these wetlands, artificial disturbances (mowing) and natural disturbances (cattle, roebucks, coypus, voles) are very frequent. In order to mimic disturbances, experimental disturbances were generated in spring after the end of the winter flooding and emerged seedlings counted three months later. Data about the seed bank, the undisturbed vegetation and seedlings emerging in disturbed quadrats were sampled. Detrended Correspondence Analysis (DCA) of the undisturbed quadrats, disturbed quadrats and seed bank samples showed significant differences of species composition. Similarity between seed bank and undisturbed aboveground vegetation was low and not very different between grassland and oldfield. Very few seedlings emerged in the undisturbed vegetation both in grassland and oldfield, which potentially indicates the importance of gaps for seed bank expression. In Marais Poitevin, the seed bank contributed very little to the seedling flora, and vegetative regrowth clearly predominated recolonisation after disturbances. In the seed bank, few species lost after succession from grassland to oldfield vegetation were still present as seeds in the soil, but in most cases species lost were not recorded in the seed bank. The results have shown that species richness and species diversity in the seed bank decrease during succession. On the other hand, the density of buried seeds did not decrease significantly from grassland to oldfield.
Flora | 2002
Blaise Touzard; Bernard Amiaud; Estelle Langlois; Servane Lemauviel; Bernard Clément
Summary We studied the species composition of vegetation and seed bank in an experiment with grassland and oldfield plots in an eutrophic alluvial wetland (called “Marais de Redon”) of Western France. In this wetland, artificial disturbances (mowing) and natural disturbances (cattle, roebucks, boars, voles…) are very frequent. In order to mime these natural disturbances, experimental disturbances were generated in March 1996 after the end of the winter flooding and the seedlings counted three months later. The seed bank, the undisturbed vegetation and seedlings emerging in disturbed quadrats were sampled. Detrended Correspondence Analysis (DCA) of the undisturbed quadrats, disturbed quadrats and seed bank samples showed significant differences of species composition. Similarity between seed bank and undisturbed aboveground vegetation was low and not very different between grassland and oldfield. Very few seedlings emerged in undisturbed vegetation both in grassland and oldfield, which indicates the importance of gaps for seed bank expression. The great majority of seedlings emerging after experimental disturbances were mainly recruited from the soil seed bank. This result contrasts with other studies where the seed bank contributed very little to the seedling flora and vegetative regrowth clearly predominated recolonisation after disturbances. In the seed bank, few species lost after succession from grassland to oldfield vegetation were still present as seeds in the soil, but in most cases, species lost were not recorded in the seed bank. The two hypotheses about changes in the seed bank during secondary succession, predicting decrease in species richness or species diversity and seed density were only confirmed for seed density parameter.
Annals of Botany | 2012
Jean-Paul Maalouf; Yoann Le Bagousse-Pinguet; Lilian Marchand; Blaise Touzard; Richard Michalet
BACKGROUND AND AIMS There is still debate regarding the direction and strength of plant interactions under intermediate to high levels of stress. Furthermore, little is known on how disturbance may interact with physical stress in unproductive environments, although recent theory and models have shown that this interplay may induce a collapse of plant interactions and diversity. The few studies assessing such questions have considered the intensity of biotic interactions but not their importance, although this latter concept has been shown to be very useful for understanding the role of interactions in plant communities. The objective of this study was to assess the interplay between stress and disturbance for plant interactions in dry calcareous grasslands. METHODS A field experiment was set up in the Dordogne, southern France, where the importance and intensity of biotic interactions undergone by four species were measured along a water stress gradient, and with and without mowing disturbance. KEY RESULTS The importance and intensity of interactions varied in a very similar way along treatments. Under undisturbed conditions, plant interactions switched from competition to neutral with increasing water stress for three of the four species, whereas the fourth species was not subject to any significant biotic interaction along the gradient. Responses to disturbance were more species-specific; for two species, competition disappeared with mowing in the wettest conditions, whereas for the two other species, competition switched to facilitation with mowing. Finally, there were no significant interactions for any species in the disturbed and driest conditions. CONCLUSIONS At very high levels of stress, plant performances become too weak to allow either competition or facilitation and disturbance may accelerate the collapse of interactions in dry conditions. The results suggest that the importance and direction of interactions are more likely to be positively related in stressful environments.
Plant Ecology | 2010
Estelle Forey; Blaise Touzard; Richard Michalet
It has been recently proposed that the decrease in diversity towards the severe end of the humped-back diversity–biomass model of Grime was driven by a collapse of facilitation due to extreme conditions of either stress or physical disturbance. In order to test the hypothesis that disturbance is the primary direct factor driving the collapse of interactions occurring along environmental severity gradients, we conducted a removal experiment in the highly stressed French coastal dunes along a gradient of disturbance due to sand burial. Four dune species were used as targets and transplanted with and without neighbours in four communities along the gradient. The experiment was conducted twice, a dry and an average year. Results of the experiment showed that during the dry year the effect of the environment was prominent and only one species was facilitated for survival in the least disturbed community. During the average year, interactions for growth were important only in the same community, with positive or negative responses depending on the natural position of the target species within the coastal dune gradient. In accordance with our hypothesis, most interactions for both survival and growth were observed in the least disturbed community exhibiting the highest diversity. There were no interactions in the most disturbed community with the lowest diversity.
Plant Ecology | 2008
Bernard Amiaud; Blaise Touzard; Anne Bonis; Jan-Bernard Bouzillé
Elymus repens (L.) Gould and Agrostis stolonifera (L.), are competitive grasses with guerrilla strategy that invade grasslands with a low stocking rate. In this work, we tested the hypotheses that grazing exclusion facilitates vegetative development of rhizomes and stolons of these clonal grasses and that such change is a key mechanism for their abundance in set-aside grasslands. The competitive capacities of these two guerrilla species were characterised by samples in plant community (species richness and biomass) and on the level of individual species (morphometric measurements on stolons and rhizomes) during a growing season. Compared to grasslands where grazing was excluded for three years, species richness was higher in grazed site and the plant community structure differed. Indeed, with grazing exclusion, a shift from annual species with a diversified growth-form to perennial species with a tall tussock and graminoid growth-form was monitored. In ungrazed situation, Elymus repens and Agrostis stolonifera were the dominant grasses, and the standing biomass for the lowland community showed a significant increase compared to the grazed site. Vegetative development increased competitive capacities of these two guerrilla species and led by phenomenon of competitive exclusion to the disappearance of annuals species. With grazing cessation, Elymus repens was found to increase the size of aerial traits (shoot length and the number of leaves per shoot) and this may both be propitious for achieving dominance within plant communities and also maintaining its competitive local advantage. By contrast, Agrostis stolonifera showed an increase in a root trait, i.e. rhizome length, in the fenced site, which provide good ability for spatial propagation and then to explore adjacent patches. We concluded that Elymus repens presented a morphological capacity to change its colonising strategy from a guerrilla strategy to a phalanx strategy, by morphological variability of aerial organs, when it was submitted to competitive stress and environment modifications. Agrostis stolonifera showed a capacity to escape aerial competition resulting from grazing cessation, than to increase underground propagation capacity. The present study highlighted the capacities of Elymus repens to respond in an adaptative way to competitive pressure.
Oecologia | 2014
Patrick Al Hayek; Blaise Touzard; Yoann Le Bagousse-Pinguet; Richard Michalet
Few studies have examined consequences of ecotypic differentiation within alpine foundation species for community diversity and their feedbacks for the foundation species’ fitness. Additionally, no study has quantified ecotypic differences in competitive effects in the field and in controlled conditions to disentangle genetic from plasticity effects in foundation/subordinate species interactions. We focused on a subalpine community of the French Pyrenees including two phenotypes of a cushion-forming species, Festuca gautieri: tight cushions in dry convex outcrops, and loose cushions (exhibiting high subordinate species richness) in wet concave slopes. We assessed, with field and shadehouse experiments, the genetic vs. plasticity basis of differences in: (1) cushion traits and (2) competitive effects on subordinates, and (3) quantified community feedbacks on foundation species’ fitness. We found that trait differences across habitats had both genetic and plasticity bases, with stronger contribution of the latter. Field results showed higher competition within loose than tight phenotypes. In contrast, shadehouse results showed higher competitive ability for tight phenotypes. However, as changes in interactions across habitats were due to environmental effects without changes in cushion effects, we argue that heritable and plastic changes in competitive effects maintain high subordinate species diversity through decreasing competition. We showed high reproduction cost for loose cushions when hosting subordinates highlighting the occurrence of community feedbacks. These results suggest that phenotypic differentiation within foundation species may cascade on subordinate species diversity through heritable and plastic changes in the foundation species’ competitive effects, and that community feedbacks may affect foundation species’ fitness.
Acta Botanica Gallica | 2010
Zouhaier Noumi; Saâd Ouled Dhaou; Fethia Abdallah; Blaise Touzard; M. Chaieb
Abstract The main objective of this study is to determine the possible reasons for regeneration failure of Acacia tortilis subsp. raddiana (Fabaceae). We conducted some laboratory experiments, simulating natural conditions. We estimated rate of infestation of seeds by Bruchidius raddianae and B. aurivillil and tested the autotoxicity effect of leaf extracts (different concentrations) of A. tortilis in the laboratory at 30 °C (optimum germination temperature). Results show that the inhibitory effect on germination increase with the increased leaf extract concentration. At 100% concentration, a significant reduction of germination rate was found compared to other concentrations. On the other hand, the study also revealed a high infestation rate of seeds by B. raddianae and B. aurivillil which reduces the possibility in inhibits natural regeneration in A. tortilis.
Journal of Ecology | 2015
Patrick Al Hayek; Jean-Paul Maalouf; Blaise Touzard; Richard Michalet
Summary Differences in effects between phenotypes of foundation species on subordinate species have been reported, but no study has separated their heritable and plastic components. In a subalpine community of the French Pyrenees, we observed two phenotypes of Festuca gautieri: tight cushions in dry convex outcrops with few subordinate species and loose cushions in wet concave slopes with many subordinate species, suggesting differences in effects of the two phenotypes on subordinates. Using two reciprocal transplantation gardens, we studied the responses of the two phenotypes to changes in environmental conditions, thus assessing the contribution of heritability and plasticity to the phenotypic variation. Using a target cross-transplantation experiment, we assessed the plasticity and heritability bases of their contrasting effects. We also quantified the recolonization of resident plants within the reciprocally transplanted cushions. We found that morphological differences between cushions had both heritability and plasticity bases. The two competition experiments showed heritable increase in competitive effects from loose to tight cushions. This was counteracted by plasticity effects, which decreased competition from the benign to the stressful garden. Synthesis. We conclude that heritable effects overcome plasticity effects resulting in higher diversity in the loose phenotype from the benign habitats.
Rangeland Journal | 2012
Zouhaier Noumi; Lotfi Abdallah; Blaise Touzard; Mohamed Chaieb
The geographic distribution of Acacia tortilis (Forssk.) Hayne subsp. raddiana (Savi) Brenan in Tunisia, is limited to the Bou-Hedma region (Bled Talah) where the National Park of Bou-Hedma, a UNESCO (1986) biosphere reserve, is located. We have tested the hypothesis that A. tortilis acts as a foundation species as a result of the improvement of soil conditions under its canopy (soil water availability and nutrient enrichment). The herbaceous community (floristic composition, species density, species richness) and soil characteristics (soil nutrients and soil water) were sampled using the quadrat method beneath and between 16 adult trees of A. tortilis with both northwards and southwards (south and north sides) and eight open areas among the trees. Results showed that A. tortilis trees improve soil water availability, the nutrient status of soil (organic matter, total carbon, total nitrogen, extractable phosphorus), and has a positive effect on the understorey vegetation under arid conditions. No significant differences in species richness were observed between the north subhabitats and the south subhabitats.