Presence Of Grazing Research Articles

Pyric herbivory increases soil microbial diversity but has a site-dependent effect on soil mesofauna in the mid-term

Woody plant encroachment threatens grassland biomes at a global scale. Pyric herbivory combines prescribed burnings and targeted grazing to restore open habitats and has proved to be successful in promoting landscape and plant community diversity. However, less is known on the effects of pyric herbivory practices on belowground biodiversity. We evaluated the midterm effect on mesofauna, bacteria and fungi of prescribed burns and targeted horse grazing regimes implemented to restore a grassland encroached by gorse (Ulex gallii Planch.). We hypothesized that 1) low-intensity shrub-to shrub burnings had no effect or had a transient effect of low magnitude on soil microbial diversity, and that 2) targeted horse grazing after burning increased soil mesofauna and microbial diversity in the midterm. We established an experiment in two shrub-encroached grasslands in western Pyrenees with three treatments (no burning and no grazing as control, burning but no grazing, and burning and grazing). We measured soil properties and soil diversity of fungi and bacteria (DNA-metabarcoding) just after fire, and vegetation structure, soil properties and soil diversity of fungi, bacteria and mesofauna after two periods of targeted grazing (a year and a half after the burning). The response to pyric herbivory differed among soil organisms. Fungi were more sensitive to burning than bacteria, but both recovered a year and a half after burning –fungi only recovered in the presence of grazing–. Grazing increased soil fungi and bacteria diversity indexes (∼20 % and ∼5 % increase, respectively) at the two sites. A year and a half after burning, burned and ungrazed areas had a 30 % more mesofauna diversity than control areas whereas grazing of the burned areas decreased mesofauna diversity by 30 % at one of the sites compared to the control. Since the responses to pyric herbivory vary among soil organisms, a wide range of management intensities across space and time are recommended for maximizing soil biodiversity.

Changes in plant community assembly from patchy degradation of grasslands and grazing by different-sized herbivores.

Grassland degradation caused by increases in livestock grazing threatens a variety of ecosystem services. Understanding changes in plant community assembly during the process of grassland degradation in the presence of grazing is important to help restore degraded grasslands worldwide but has received little attention thus far. The grassland degradation process is typified by heterogeneous degradation, that is, gradual formation of degraded patches (hereafter "patchy degradation"). Here, we experimentally examined the effects of herbivore grazing and patchy degradation on plant community assembly using nine pairs of non-degraded (intact) and patch-degraded (fragmented) grasslands subject to grazing by different-sized herbivores (i.e., NG, no grazing; SG, sheep grazing; CG, cattle grazing) over 4 years. Using a null-model approach, we estimated the relative magnitude of deterministic processes of community assembly by comparing the observed and expected β-diversity. We found that in the absence of herbivore grazing, deterministic processes played a greater role in community assembly, regardless of whether patchy degradation had occurred. However, the deterministic processes resulted in plant communities being more spatially similar in non-degraded grasslands while being more dissimilar in patchy degraded grasslands. Compared with non-degraded grasslands, species with strong competitive abilities (i.e., Leymus chinensis) were less dominant in patchy degraded grasslands, indicating relaxed competition and a reduced role of species interactions over plant communities. Instead, patchy degradation added the role of environmental variables over plant communities. SG consistently promoted more stochastic plant community assembly in both non-degraded and patch-degraded grasslands, while CG promoted more stochastic plant community assembly only in the non-degraded state, having no effect in the patch-degraded state. Our study offers important insights into changes in plant community assembly during ongoing patch-degradation of grasslands, indicating the role of increased environmental filtering of soil and reduced species interactions in driving plant community dynamics with increasing grassland patchy degradation. We also uncovered an herbivore species-specific effect on plant community assembly during the process of grassland degradation, which will better inform and improve future grassland restoration planning efforts.

Grazing Behavior Hinders Weight Loss in Long-Term Post Bariatric Surgery: a Cross-Sectional Study.

Grazing behavior is common in patients undergoing bariatric surgery (BS); however, little is known about grazing behavior in operated patients in the long term. We aimed to estimate grazing frequency and its association with weight loss and surgery response in patients who had undergone BS. This cross-sectional study included 109 patients who had undergone Roux-en-Y gastric bypass at least 5 years previously. They answered questions about socioeconomic factors, surgical information, and adherence to treatment/follow-up. The Rep(eat) questionnaire was used for grazing assessment. Student's t-test and Pearson's chi-square test were used to evaluate differences between groups. Analysis of covariance and partial correlation were used to investigate grazing behavior, and weight loss outcomes were controlled for the elapsed time since BS, healthcare service type, current psychologist care status, and the presence of a constriction ring. The mean elapsed time since BS was 9.97 ± 2.39 years. Patients with grazing behavior (67%) comprised fewer surgery responders (p = 0.019), had lower total (%TWL, p = 0.005) and excess weight loss (%EWL, p = 0.029), and received less psychological counseling (45.5% vs. 54.5%, p = 0.042). Correlations were found between the presence of grazing and its subtypes and %EWL and %TWL (T = - 0.382, T = - 0.361, p < 0.001; compulsive grazing: T = - 0.358, T = - 0.342, p < 0.001, p = 0.001; non-compulsive grazing: T = - 0.333, T = - 0.311, p = 0.001, p = 0.003). No significant difference between patients with and without grazing behavior was found for previous/current diagnoses of psychological diseases or dietitian counseling. Grazing behavior is common in the long-term among patients who have undergone BS and is negatively related to weight loss parameters.

Interaction exposure effects of multiple disturbances: plant population resilience to ungulate grazing is reduced by creation of canopy gaps

The impact of multiple disturbances on populations could be synergistic or antagonistic via disturbance interaction and are considered to be provoked by alternation of the impact of an ecosystem disturbance due to the effect of a preceding disturbance. The impact of a focal disturbance can also change when a preceding disturbance alters the proportion of individuals in a population exposed to these disturbances (i.e., interaction exposure effects), although this effect has not been addressed to date. Herein, we propose and test interaction exposure effects by elucidating disturbance interactions between canopy gap formation and ungulate grazing. Based on a vegetation and seed bank survey conducted on an island in Hokkaido, northern Japan, we examined whether canopy openness changes the impact of ungulate grazing on the occurrence probability of palatable plant species through the facilitation of germination. Species occurrence in the seed bank significantly decreased with increasing canopy openness under the presence of grazing; however, it slightly increased under the absence of grazing, suggesting that gap creation, which facilitates germination, exposes the seed bank to ungulate grazing. Because disturbances of various types often modify the habitat structure, these proposed disturbance interactions are expected to operate within various ecosystems and taxa.

Niche dimensionality and herbivory control stream algal biomass via shifts in guild composition, richness, and evenness.

We developed a framework for the hierarchical pathways of bottom-up (niche dimensionality) and top-down control (herbivory) on biomass of stream algae via changes in guild composition (relative abundance of low profile, high profile, and motile guilds), species richness, and evenness. We further tested (1) the contrasting predictions of resource competition theory vs. the benthic model of coexistence on how the number of added nutrients constrains species richness, (2) the relationship between species richness and evenness, and (3) the biodiversity-ecosystem-function paradigm. Implementing a combination of field and lab experiments that manipulated for the first time in benthic algae herbivory and/or niche dimensionality, i.e., the number of added nutrients (NAN), including nitrogen, phosphorus, iron, and manganese, we made the following discoveries. First, important predictors of guild composition were herbivory (field) and NAN (lab); of richness, NAN (field) and NAN and guild composition (lab); of evenness, guild composition (field and lab) and herbivory (field); and of biomass, guild composition, NAN, and richness + evenness (field and lab). Herbivory increased the proportions of the low profile and motile guilds but decreased the proportion of the high profile guild. In the absence of grazing, greater proportions of the high profile guild resulted in elevated richness and biomass but diminished evenness, whereas in the presence of grazing, these relationships generally disappeared. Second, both experiments confirmed the prediction of the benthic model that species richness increases with NAN, a pattern inconsistent with resource competition theory. Third, supplementation with manganese and/or iron increased algal richness, indicating that micronutrients, which have generally been overlooked in stream ecology, added dimensions to the algal niche. Fourth, the richness-evenness relationship, observed only in the absence of herbivory, depended on the size of the species pool. It was positive at richness lower than 49 species (lab), implying complementarity and facilitation, while at higher richness (field and lab), this relationship was negative, consistent with negative interspecific interactions. Finally, the greater dependence of biomass production on guild composition and NAN than on richness and evenness suggests that more comprehensive, environmentally explicit, and trait-based approaches are necessary for the study of the biodiversity-ecosystem-function paradigm.

Synergistic Interactions within a Multispecies Biofilm Enhance Individual Species Protection against Grazing by a Pelagic Protozoan.

Biofilm formation has been shown to confer protection against grazing, but little information is available on the effect of grazing on biofilm formation and protection in multispecies consortia. With most biofilms in nature being composed of multiple bacterial species, the interactions and dynamics of a multispecies bacterial biofilm subject to grazing by a pelagic protozoan predator were investigated. To this end, a mono and multispecies biofilms of four bacterial soil isolates, namely Xanthomonas retroflexus, Stenotrophomonas rhizophila, Microbacterium oxydans and Paenibacillus amylolyticus, were constructed and subjected to grazing by the ciliate Tetrahymena pyriformis. In monocultures, grazing strongly reduced planktonic cell numbers in P. amylolyticus and S. rhizophila and also X. retroflexus. At the same time, cell numbers in the underlying biofilms increased in S. rhizophila and X. retroflexus, but not in P. amylolyticus. This may be due to the fact that while grazing enhanced biofilm formation in the former two species, no biofilm was formed by P. amylolyticus in monoculture, either with or without grazing. In four-species biofilms, biofilm formation was higher than in the best monoculture, a strong biodiversity effect that was even more pronounced in the presence of grazing. While cell numbers of X. retroflexus, S. rhizophila, and P. amylolyticus in the planktonic fraction were greatly reduced in the presence of grazers, cell numbers of all three species strongly increased in the biofilm. Our results show that synergistic interactions between the four-species were important to induce biofilm formation, and suggest that bacterial members that produce more biofilm when exposed to the grazer not only protect themselves but also supported other members which are sensitive to grazing, thereby providing a “shared grazing protection” within the four-species biofilm model. Hence, complex interactions shape the dynamics of the biofilm and enhance overall community fitness under stressful conditions such as grazing. These emerging inter- and intra-species interactions could play a vital role in biofilm dynamics in natural environments like soil or aquatic systems.

Habitat management varying in space and time: the effects of grazing and fire management on marshland birds

Freshwater wetlands and marshes with extensive reed beds are important hotspots of biological diversity, but in the absence of proper management, they are subject to biotic homogenisation. We assessed the impact of spatiotemporally variable management by cattle grazing (for 4 years) and late-summer burning (1 or 3 years before the study) on both songbirds and non-passerines in a previously homogeneous reed bed. We surveyed birds using a combination of line transects and point counts in a quasi-experimental design comprising six treatment levels. Management increased both the diversity of marsh habitats and the diversity of bird species. The species richness and abundance of non-passerines (ducks and geese, wading birds, gulls and terns, rails, coots and grebes) was higher in recently burned than in unburned or old-burned patches. Species richness of farmland songbirds was higher in grazed than in non-grazed patches, and the richness and abundance of reed songbirds was higher in unburned, old-burned, and grazed patches than in recently burned patches. Total Shannon diversity and evenness of birds was lowest in areas with the most intensive treatment (patches grazed and twice-burned), whereas Simpson diversity was highest in these areas. Non-managed patches had fewer species and individuals of all groups except reed songbirds. The proportion of old reed was low in recently burned and grazed patches, and was similarly high in all other treatment areas. No other property of reed stands was influenced by management, and both the allocation and the effect of management were independent of water level. Spatiotemporally variable management by cattle grazing and late-summer burning may thus simultaneously benefit several groups of birds. The effect of burning alone disappeared in 3 years, even in the presence of grazing; thus it must be repeated every 2–3 years. We conclude that both management actions are necessary to establish and maintain highly diverse habitats for marshland bird communities.

Factors influencing natural regeneration of totara (Podocarpus totara D.Don) on grazed hill country grassland in Northland, New Zealand

There is increasing interest in establishing indigenous forests on marginal pastoral hill country in New Zealand to improve soil conservation, water quality and indigenous biodiversity. Large-scale reforestation using native seedlings is extremely costly. However, given suitable seed sources, it is possible to encourage natural regeneration of grassland into native plants. A grazed, sloping pasture site in Northland where totara (Podocarpus totara D.Don) regeneration had been allowed to develop over a 10-year period was assessed using a grid of 2-metre diameter plots. Counts of regenerating woody species and cover of herbaceous species were obtained in each plot. Plots were classified on the basis of herbaceous species cover using the TWINSPAN classification procedure. Regression analyses were used to identify site factors and characteristics of the herbaceous vegetation associated with totara regeneration. More than 7,000 stems ha−1 of woody species, mostly totara and gorse (Ulex europaeus L.), had accumulated over the 10-year period despite the presence of cattle grazing. Regeneration of totara was associated with steeper slopes and sites with the greatest diversity of herbaceous species but with lower overall levels of herbaceous cover. The regeneration pattern of the other main woody species was similar although gorse colonised a wider range of sites. Regeneration of woody species was absent on flatter sites, which were dominated by a few high-fertility tolerant herbaceous species and had high levels of herbaceous cover. This study has shown that regeneration of totara on a pastoral hill-country site was most prevalent on steeper slopes of lower fertility with typically sparse vegetation cover comprising low fertility tolerant herbaceous species. Conversely, totara regeneration was absent on flatter areas of higher fertility. It seems likely that grazing assists totara regeneration by keeping pasture cover short, thus increasing light levels near ground level for newly germinated seedlings. The propensity for totara to regenerate on pastoral hill country in the presence of grazing and where there is a nearby seed source could provide a practical option for re-establishing indigenous woody vegetation on erosion-prone marginal land.

Effects of long-term herbivore exclusion on the preservation of Thymus albicans, an endangered endemic Mediterranean species

In recent decades, the trend has been to exclude livestock in order to protect and conserve the vegetation. However, the response of a particular ecosystem need not be the same in every case. This study examines the effects of long-term grazing exclusion on a shrubland in Doñana Natural Park, Spain, and its impact on an endemic plant species in danger of extinction (Thymus albicans). We measured a range of biometric (plant height and total vegetation cover), chemical (soil P, N and C content) and physiological (chlorophyll fluorescence, photosynthetic pigments and shoot water potential) variables. Moderate grazing changed the plant species cover in the grazed area (reduction of 30%), but did not affect species diversity. The high mass of dead plant material found in the ungrazed area increased the risk of fire in this area. Goats enriched the soil with nutrients through deposition of faeces and urine. The clearing of vegetation by goat grazing had a potential positive impact on recruitment of T. albicans and the presence of grazing caused certain beneficial changes in physiological performance (better photosynthetic performance and less water stress during the summer). Our results indicated that, in the study area, exclusion of ungulates was not an appropriate measure and acted to preserve the existing vegetation: grazing decreased the presence of combustible material (prevented wildfire), decreased vegetation competition, improved soil fertility and contributed to the conservation of T. albicans. Under proper management, livestock grazing can therefore play an important role in the maintenance and conservation of elements of the Mediterranean ecosystem.

Soil physical attributes in integrated bean and sheep system under nitrogen levels

Integrated crop-livestock systems (ICLS) can promote higher grain and meat/milk yield as well as reduce soil degradation risks. Thus, this study aimed to evaluate the influence of grazing sheep with moderate intensity and nitrogen doses on soil physical attributes, and bean crop yield (Phaseolus vulgaris Lam.) under rotation with summer corn crop (Zea mays Lam.) and winter pasture with oats (Avena sativa Lam) and ryegrass (Lolium multiflorum Lam.) The experimental design was completely randomized blocks with split-plot; the plots were nitrogen doses and the split-plots were grazing presence or absence. The treatments were nitrogen doses of 0, 75, 150 and 225 kg ha-1 applied on ryegrass and white oat pasture in winter followed by bean crop. Soil density, macroporosity, microporosity and total porosity and bean grain yield were evaluated. When ICLS are managed under no-tillage with moderate grazing, sheep trampling did not affect negatively soil physical attributes, which did not reach critical levels for subsequent growth and development of the bean crop. The black bean yield in summer was not affected by antecedent presence of sheep grazing in winter.

Dissecting the Effects of Simulated Cattle Activity on Floristic Composition and Functional Traits in Mediterranean Grasslands

Livestock exerts direct and indirect effects on plant communities, changing colonization and extinction rates of species and the surrounding environmental conditions. There is scarce knowledge on how and to what extent these effects control the floristic and functional composition of plant communities in grasslands. We performed an experiment that included several treatments simulating trampling, defoliation, faeces addition and their combinations in a Mediterranean scrub community grazing-abandoned for at least 50 years. We monitored the plots for four years, and collected data on species composition, photosynthetically active radiation (PAR) and red∶far-red ratio (R∶FR), soil moisture and compaction. We estimated community weighted means (CWM) for height, habit, life cycle, seed mass and SLA. Neither compaction nor soil moisture were modified by the treatments, while PAR and R∶FR increased in all treatments in comparison to the Control and Faeces treatments. The floristic composition of all treatments, except for Faeces, converged over time, but deviated from that of the Control. The functional traits displayed the trends expected in the presence of grazing: loss of erect species and increased cover of short species with light seeds, with rosettes and prostrate habit. However, contrary to the results in literature, SLA was lower in all the treatments than Control plots. Like the results for floristic composition, all treatments except for Faeces converged towards a similar functional composition at the end of the four year period. The results of this study show the initial evolution of a Mediterranean plant community in the presence of grazing, driven primarily by the destructive action of livestock. These actions seem to directly affect the rates of extinction/colonization, and indirectly affect the light environment but not the soil conditions. However, their effects on floristic and trait composition do not seem to differ, at least at the small spatio-temporal scale.

Subhumid pasture soil microbial communities affected by presence of grazing, but not grazing management

Management-intensive rotational grazing has been shown to stimulate net primary production in subhumid pastures compared to extensive grazing strategies. The degree to which this represents a direct effect on plant developmental stage and community composition, and/or indirect effects of grazing on microbial community structure and nutrient feedback to production is an open question. To better understand whether the effects of pasture management on microbial communities led to indirect nutrient feedbacks, we analyzed microbial lipids and environmental and physical factors of surface soils under four pasture management treatments – management-intensive rotational grazing, continuous grazing, harvesting for hay, and an unmanaged control. Principal component analysis indicated microbial community structure under our two grazed treatments was different than that of ungrazed treatments. While there was no effect of treatments on total microbial biomass, guild comparisons revealed lower fungal-to-bacterial ratios, lower arbuscular mycorrhizal fungi concentrations, and higher actinomycete biomarkers in soils under grazing, irrespective of grazing management treatments. Gram-positive and anaerobic bacteria biomarker abundance was greater in treatments that included grazing and no management when compared to the treatment where biomass was harvested mechanically. There was no evidence of treatment effects on either Gram-negative bacteria or saprotrophic fungi. Regression tree analysis identified litter quality as the main correlate of differences in the microbial community between grazed and ungrazed treatments. Lower root C:N predicted lower F:B and biomarkers of the bacterial guilds Gm+ and actinomycetes, which were dominant in the grazing treatments, while higher root C:N predicted higher F:B and the guild biomarkers of AMF, which dominated in the ungrazed treatments. These results indicate that greater forage production observed in humid and subhumid regions under management-intensive rotational grazing likely stems from the direct effects on plant developmental stage and plant community composition rather than microbial mediated nutrient feedbacks from altered quantity and quality of plant litter. If the potential for a more favorable C balance in subhumid pastures is realized, greater biomass production and therefore greater litter inputs as a result of the direct effects of management-intensive rotational grazing on plant communities is the most likely mechanism.

Avian Community Response to Grazing Intensity on Monoculture and Mixed Florida Pastures

Abstract Monoculture and mixed pastures in Florida provide habitat for a variety of resident and migratory bird species. The objectives of this study were to investigate the effects of grazing on vegetation structure and bird species richness and abundance in grazed monoculture and mixed pastures. Study pasture units were subject to four cattle grazing intensities: 0 = nongrazed (control), 15 = low, 20 = medium, or 35 = high animal units (AU) per pasture unit (no cattle, 1.3, 1.0, and 0.6 ha · AU −1 , on monoculture pastures and no cattle, 2.1, 1.6, and 0.9 ha · AU −1 , on mixed pastures). Monoculture pastures displayed a greater decrease in spatial heterogeneity of the vegetative community in the presence of grazing than mixed pastures. An increase in grazing intensity led to declines in total avian species richness and abundance and species richness within short-distance migrant, neotropical migrant, and permanent resident guilds on monoculture pastures. Declines in total species richness and abundance and neotropical migrant guild species richness and abundance were observed on mixed pastures subject to increasing grazing intensity. However, species richness within short-distance migrant and urban guilds and abundance within the grassland guild increased on this pasture type in the presence of grazing. Loss of spatial heterogeneity typically results in a lack of suitable habitat for birds that occupy the extremes of the vegetation structure gradient. This can lead to a loss of species richness and abundance. For the majority of avian guilds, a low grazing intensity of 1.3 ha · AU −1 and 2.1 ha · AU −1 on monoculture and mixed pasture, respectively, is recommended to maintain abundance. However, these grazing intensities may result in declines in species richness. Ultimately, if a range of avian species are to be supported on monoculture and mixed pastures, spatial heterogeneity of plant structure and composition must be maintained.

Prevalence of termites and level of damage on major field crops and rangelands in the Manasibu District, western Ethiopia

ABSTRACT: The current status of termite damage on maize ( Zea mays (L.)), teff ( Eragrostis tef (Zuccagni) Trotter), sorghum ( Sorghum bicolor (L.)) and rangelands was studied in five Kebele administrations (study sites) and on three farmers' fields in every Kebele, in Manasibu District, Wellega Zone of Oromiya Regional State. Termite samples were collected from infested crop fields and rangelands, identified to the genus level with keys to the Ethiopian termites, and percentage occurrence for each genus was determined. Six genera of termites: Ancistrotermes, Macrotermes, Microtermes, Odontotermes, Pseudacanthotermes and Trinervitermes were identified. The first five genera belong to the subfamily Macrotermitinae whereas Trinervitermes belongs to Nasutitermitinae. All of the genera belonged to the family Termitidae. Subterranean termites in general and Microtermes in particular, were found to be the most prevalent termites in the study area. The damage that termites caused to maize and sorghum were assessed by the use of quadrates and that of teff by laying wooden frames in the quadrates. For all the three crops, damage was assessed at vegetative, flowering, and maturity stages. It was found out that the levels at which the three crops were damaged by termites were significantly different from each other. Teff was the most seriously damaged crop in the study area, followed by maize, while sorghum was the least affected crop. Damage at different stages, within each crop, were also found to be significantly variable from each other. To evaluate the impact of termites on rangelands in the absence and presence of grazing by livestock, three plots of rangelands were fenced and protected for six months. It was found that the protected plot of the rangelands significantly had higher percent vegetation cover and lower number of termite foraging holes per m 2 . From the study, it can be concluded that the genus Microtermes was the major termite species attacking crops and rangelands in Manasibu district, implying that most control strategies should focus on this genus, especially to control termites on teff and maize.

Habitat Associations of Ant Species (Hymenoptera: Formicidae) in a Heterogeneous Mississippi Landscape

Community assembly and the factors that influence it have long been a topic of interest to ecologists, but theory has yet to produce unequivocal evidence that communities assemble in predictable ways. The goal of this study was to document the relationship between ant communities and environmental variation between four habitat types. To accomplish this, ant communities and 16 environmental variables were sampled across four different habitat types in the Black Belt Prairie and Flatwoods regions in Mississippi. Furthermore, ant species were placed into functional groups for an analysis of the relationship between the assembly of ecological communities and variation in ecosystem function. A total of 20,916 ants representing 68 species was collected across the four habitat types. Nonmetric multidimensional scaling and analysis of covariance analyses both revealed three distinct ant communities, which can be characterized by habitat type: pasture, prairie, and woodland. Principle components analysis (PCA) simplified the 16 environmental variables into four principle components that explained 78% of the variation among sites. Results of multiple regression using the four PCA axes as predictor variables suggest that regional variation in soil structure, land cover type, and the presence of grazing have had major influences on ant community composition. Variation in flora and habitat architecture had smaller but significant effects on ant species diversity and functional group composition. Our results imply that restoration of native ant communities in disturbed habitats must consider how current disturbance regimens likely interact with the presence of Solenopsis to lower ant biodiversity.

Wide Ecological Amplitude of a Diversity-Reducing Invasive Grass

The goals of this study were to identify habitats occupied by the Eurasian grass Bothriochloa ischaemum (King Ranch bluestem) on the eastern Edwards Plateau of central Texas, USA, and to measure the effects of this invasive species on plant diversity. A set of descriptive field studies were conducted to determine the relationships between habitat characteristics (woody cover, slope, presence of roads and trails, history of prescribed burning, and presence of grazing) and the presence and abundance of this species. Species richness and diversity of perennial herbaceous species were compared between plots in which B. ischaemum was absent and plots that it dominated.

Indirect remote sensing of a cryptic forest understorey invasive species

Remote sensing has successfully been applied to map the distribution of canopy dominating invasive species. Many invaders however, do not dominate the canopy, and remote sensing has so far not been applied to map such species. In this study, an indirect method was used to map the seed production of Chromolaena odorata, one of the world's 100 worst invasive species. The study was executed in lowland Shorea robusta forest in Nepal, where Chromolaena invaded the understorey of degraded forest. A Landsat ETM+ image processed through a neural network predicted 89% and 81% of forest canopy density and light intensity reaching the understorey, respectively. We inverted these models to predict Chromolaena seed productivity. Light intensity determined 93% of the variation in log 10 seed production per plant. Chromolaena failed to produce seed below a light intensity of 6.5 mJ m −2 day −1. Further analysis revealed that Chromolaena was absent above this light intensity in case of a high biomass of other shrub and herb species, a situation occurring in the absence of grazing. We therefore suggest that other species control Chromolaena through competitive exclusion in the absence of grazing, whereas grazing breaks the dominance of these other species thus creating the conditions for Chromolaena attain canopy dominance. The presence of grazing was related to distance from the forest edge, a variable that together with light intensity allowed us to map 64% of variation in Chromolaena cover. Predicted Chromolaena cover and seed production per plant were combined into a map displaying the total seed production per unit area. Such map displaying seed producing sites could be used to significantly reduce the costs of controlling Chromolaena infestation by providing information on the spatial segregation of source and sink populations, which will support efficient habitat ranking to restore invaded areas and protect non-invaded ecosystems. This may prove particularly valuable when implementing control measures under circumstances of limited capital and manpower.

Changing landscape and grazing: macroremains from the terp Peins-east, province of Friesland, the Netherlands

This article seeks to contribute some new insights to the discussion about the colonisation of the North-Netherlands coastal area in the Iron Age. The aim of the study presented here was to investigate whether archaeobotanical research can demonstrate the absence or presence of grazing and the changes in vegetation that follow the development of the salt marsh and that may be related to activities connected with human occupation. The material studied was sampled in the terp of Peins in the Dutch province of Friesland during the 1999 excavation. The beginnings of this terp can be dated in the first century A.D., although a small dike and two parallel ditches preceded it. The macroremains from these ditches proved useful in describing the changes in the salt marsh vegetation. It was shown that the salt marsh was not used for grazing cattle prior to habitation. Grazing only started at the time the first terp podium was raised.

Microcolonies, quorum sensing and cytotoxicity determine the survival of Pseudomonas aeruginosa biofilms exposed to protozoan grazing.

This study was based on the hypothesis that biofilms of the opportunistic pathogen Pseudomonas aeruginosa are successfully adapted to situations of protozoan grazing. We tested P. aeruginosa wild type and strains that were genetically altered, in structural and regulatory features of biofilm development, in response to the common surface-feeding flagellate Rhynchomonas nasuta. Early biofilms of the wild type showed the formation of grazing resistant microcolonies in the presence of the flagellate, whereas biofilms without the predator were undifferentiated. Grazing on biofilms of quorum sensing mutants (lasR and rhlR/lasR) also resulted in the formation of microcolonies, however, in lower numbers and size compared to the wild type. Considerably fewer microcolonies than the wild type were formed by mutant cells lacking type IV pili, whereas no microcolonies were formed by flagella-deficient cells. The alginate-overproducing strain PDO300 developed larger microcolonies in response to grazing. These observations suggest a role of quorum sensing in early biofilms and involvement of flagella, type IV pili, and alginate in microcolony formation in the presence of grazing. More mature biofilms of the wild type exhibited acute toxicity to the flagellate R. nasuta. Rapid growth of the flagellate on rhlR/lasR mutant biofilms indicated a key role of quorum sensing in the upregulation of lethal factors and in grazing protection of late biofilms. Both the formation of microcolonies and the production of toxins are effective mechanisms that may allow P. aeruginosa biofilms to resist protozoan grazing and to persist in the environment.

RENDIMENTO DE MILHO EM ÁREA DE INTEGRAÇÃO LAVOURA-PECUÁRIA SOB O SISTEMA DE PLANTIO DIRETO, EM PRESENÇA E AUSÊNCIA DE TREVO BRANCO, PASTEJO E NITROGÊNIO

O trabalho experimental foi conduzido no campo, na Estação Experimental da Fundação Agrária de Pesquisa Agropecuária (FAPA), nos anos agrícolas de 1999 e 2000, com o objetivo de verificar a influência da adubação nitrogenada residual para a cultura do milho, em sistema de plantio direto, em presença e ausência tanto de trevo branco quanto de animais em pastejo. O delineamento experimental foi o de blocos ao acaso com três repetições. Os tratamentos foram arranjados em parcelas subdivididas. No inverno, nas parcelas, foram colocados quatro níveis de nitrogênio (N-TI = 0, 100, 200 e 300 kg.ha-1 de N) e, nas subparcelas, a combinação de presença e ausência de trevo branco e de pastejo (CT = com trevo; ST = sem trevo; CP = com pastejo e SP = sem pastejo). No verão, em cada subparcela proveniente do inverno, foram colocadas cinco doses de N, em cobertura, (N-TV = 0, 60, 120, 180 e 240 kg.ha-1 de N) e cultivado o milho. Dezoito dias após a retirada dos animais a máxima eficiência técnica de rebrote da cultura de inverno foi obtida com 231 kg.ha-1 de N (N-TI). As áreas CP/N-TI mostraram tendência de apresentar maiores produtividades do milho que as áreas SP. As áreas sem N-TI produziram mais milho em subparcelas SP. As parcelas que receberam 300 kg.ha-1 de N N-TI não mostraram resposta do milho ao N-TV, comprovando o efeito residual do N-TI. Conclui-se que a interação entre pastejo e N-TI contribui para a nutrição nitrogenada da cultura do milho.