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International audience; This study aimed to compare a neuropsychological test tapping into executive control function, the Wisconsin Card Sorting Test (WCST), performed in either traditional paper-and-pencil (PP) or virtual reality (VR) modality, and to determine the role of human factors (i.e., sense of presence, cybersickness, field (in)dependence and video game experience) as contributors to performance and perceived mental effort. Indeed, if virtual assessment might bring the ecological dimension to controlled laboratory research, it is often suggested that human factors might bias performance. WCST performance and its associated perceived mental effort were compared between the two modalities (N = 107). In the VR modality (N= 52), a correlation matrix was conducted as well as a cluster analysis in order to build two experimental groups, or profiles, based on their subjective experience of VR. WCST performance and perceived mental effort were then compared between these two groups while controlling for age and education. Results outlined a similar WCST performance and perceived mental effort between the PP and VR modalities. However, when comparing the two VR groups, results suggest that an unfavorable profile for VR, i.e., less sense of presence, more cybersickness, more visual field dependence and less video game experience, is associated with greater perceived mental effort. These experimental findings enable outlining a new conceptual and methodological framework for the assessment of executive control task performance in VR. Results could help users to take human factors into consideration in order to fully exploit or predict the benefits of this tool.

The complexity of natural ecosystems makes it difficult to compare the relative importance of abiotic and biotic factors and to assess the effects of their interactions on ecosystem development. To improve our understanding of ecosystem complexity, we initiated an experiment designed to quantify the main effects and interactions of several factors that are thought to affect nutrient export from developing forest ecosystems. Using a replicated 2 × 2 × 4 factorial experiment, we quantified the main effects of these factors and the factor interactions on annual calcium, magnesium, and potassium export from field mesocosms over 4 years for two Vermont locations, two soils, and four different tree seedling communities. We found that the main effects explained 56%–97% of total variation in nutrient export. Abiotic factors (location and soil) accounted for a greater percentage of the total variation in nutrient export (47%–94%) than the biotic factor (plant community) (2%–15%). However, biotic control over nutrient export was significant, even when biomass was minimal. Factor interactions were often significant, but they explained less of the variation in nutrient export (1%–33%) than the main effects. Year-to-year fluctuations influenced the relative importance of the main effects in determining nutrient export and created factor interactions between most of the explanatory variables. Our study suggests that when research is focused on typically used main effects, such as location and soil, and interactions are aggregated into overall error terms, important information about the factors controlling ecosystem processes can be lost.

We measured deciduous forest soil temperatures under control (unmanipulated) and snow-free (where snow is manually removed) conditions for four winters (at three soil depths) to determine effects of a snow cover reduction such as may occur as a result of climate change on Vermont forest soils. The four winters we studied were characterized as: 'cold and snowy', 'warm with low snow', 'cold with low snow', and 'cool with low snow'. Snow-free soils were colder than controls at 5- and 15-cm depth for all years, and at all depths in the two cold winters. Soil thermal variability generally decreased with both increased snow cover and soil depth. The effect of snow cover on soil freeze-thaw events was highly dependent on both the depth of snow and the soil temperature. Snow kept the soil warm and reduced soil temperature variability, but often this caused soil to remain near 0°C, resulting in more freeze-thaw events under snow at one or more soil depths. During the 'cold snowy' winter, soils under snow had daily averages consistently >0°C, whereas snow-free soil temperatures commonly dropped below -3°C. During the 'warm' year, temperatures of soil under snow were often lower than those of snow-free soils. The warmer winter resulted in less snow cover to insulate soil from freezing in the biologically active top 30 cm. The possible consequences of increased soil freezing include more root mortality and nutrient loss, which would potentially alter ecosystem dynamics, decrease productivity of some tree species, and increase sugar maple (Acer saccharum Marshall) mortality in northern hardwood forests.

We assessed the effect of a single, dormant season prescribed fire on soil enzyme activity in oak-hickory (Quercus-Carya) forests in southern Ohio, USA. Four enzymes specific for different C sources were chosen for monitoring: acid phosphatase, β-glucosidase, chitinase and phenol oxidase. Postfire acid phosphatase activity was generally reduced by burning and decreased with increasing longterm soil water potential. Postfire β-glucosidase differed little between control and burned plots. Chitinase activity increased after fire in proportion to fire intensity. Phenol oxidase activity was highly variable and did not correlate well with either fire or soil water potential. Enzyme activities tended to vary more between samples taken upslope vs. downslope of a given tree than as the result of fire or landscape position. Overall enzymes whose activities are controlled by microclimatic or edaphic factors were affected more than those controlled primarily by substrate availability. Single, dormant season fires may consume a large proportion of the forest floor and change the apparent character of the surface organic matter complex without having major effects on soil enzyme activity.

This study examined foliar nutrient dynamics and nutrient resorption (retranslocation) in three species of Chilean Nothofagus (Fagaceae) that differed in leaf lifespan and elevational distribution. In our central Chile study area the elevations at which these three species are most abundant increase from N. obliqua (deciduous) at low elevations to N. dombeyi at intermediate elevation and N. pumilio (deciduous) at higher elevations up to treeline. We sampled a single stand at 1680 m in which all three species co-occurred. Nothofagus dombeyi leaves were structurally heavier, with specific leaf mass approximately twice that of the two deciduous species. On a concentration basis, foliar N increased in the order N. dombeyi < N. pumilio < N. obliqua and foliar P increased in the order N. dombeyi < N. obliqua < N. pumilio. However, when the differences in specific leaf mass among species were taken into account by calculating N and P content on a leaf area basis, N. dombeyi had the greatest N and P content. N and P remained relatively constant throughout most of the 4-yr N. dombeyi leaf lifespan, then decreased prior to abscission. Nothofagus dombeyi resorbed significantly less N (44-50%) than did the two deciduous species (63-78%), both on proportional and absolute bases. In contrast, N. pumilio and N. dombeyi resorbed similar amounts of P prior to abscission (40-50%), whereas no significant resorption of P from leaves of N. obliqua was noted. We use these results to clarify the relative importance of environmental gradients associated with elevation vs. genetically fixed leaf lifespans in controlling the nutrient dynamics of these congeneric tree species.

We evaluated the patterns of variation in the activity of four soil enzymes in oak forests soils at spatial scales from 10s of km to

We measured net nitrogen mineralization, net nitrification, proportional nitrification, and total inorganic nitrogen, available phosphorus, and soil organic carbon in five Andean forested stands in an attempt to resolve the relative influence of elevation and forest canopy composition on soil organic matter and nutrient dynamics in this ecosystem type. Our five forested study sites were within a contiguous Nothofagus forest that ranged from 1,280 to 1,700 m elevation in the central Chilean Andes. The five sites consisted of three single species stands, one each of the low elevation deciduous N. obliqua, the evergreen N. dombeyi, or the high elevation deciduous N. pumilio, as well as two mixed evergreen-deciduous stands. There was no statistically significant relationship of nitrogen mineralization or phosphorus with elevation. In contrast, there were statistically significant, though weak, negative relationships between elevation and net nitrification, proportional nitrification, soil pH and organic carbon. In general, soils from the N. obliqua stand had higher levels/rates of nitrification, soil organic carbon content, soil pH, and plant available phosphorus than soils form the other single species stands. In contrast, the N. dombeyi and N. pumilio stands had lower rates of nitrification and soil pH than did the N. obliqua stand. The evergreen-deciduous mixed stands tended to be intermediate in soil properties. These results demonstrate that vegetation, particularly the balance of evergreen and deciduous species, exerts stronger control over soil chemical and biochemical properties than the climate variations induced by 350 m in elevation, even where the evergreen and deciduous species are closely-related angiosperms.

in yellow-poplar; leaf [N] was significantly higher in red oaks grown at Ca:Al of 4 than 100. Yellow-poplar grew better in interspecific pairs than in intraspecific pairs. In contrast, competitive mode had no effect on red oak growth. Analysis of soil N pools indicated that red oak was unable to make use of the inorganic N added during biweekly nutrient solution additions. In contrast yellow-poplar was able to deplete soil N pools rapidly and its growth was probably N limited at Ca:Al ratio of 100. The critical Ca:Al threshold for growth decline appeared to be 4.0 for yellow-poplar. Yellow-poplar outcompetes red oak under N enriched conditions, but its competitive advantage decreases at lowered Ca:Al ratio. We hypothesize that the current shift in tree species composition observed in eastern North America may be the consequence of N enrichment, but that the direction of these shifts may reverse as lowered Ca:Al ratio and other effects of N saturation develop.