| 1. |
- Cornelissen, Johannes H C, et al.
(author)
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Global negative vegetation feedback to climate warming responses of leaf litter decomposition rates in cold biomes
- 2007
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In: Ecology Letters. - : Wiley. - 1461-023X .- 1461-0248. ; 10:7, s. 619-627
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Journal article (peer-reviewed)abstract
- Whether climate change will turn cold biomes from large long-term carbon sinks into sources is hotly debated because of the great potential for ecosystem-mediated feedbacks to global climate. Critical are the direction, magnitude and generality of climate responses of plant litter decomposition. Here, we present the first quantitative analysis of the major climate-change-related drivers of litter decomposition rates in cold northern biomes worldwide.Leaf litters collected from the predominant species in 33 global change manipulation experiments in circum-arctic-alpine ecosystems were incubated simultaneously in two contrasting arctic life zones. We demonstrate that longer-term, large-scale changes to leaf litter decomposition will be driven primarily by both direct warming effects and concomitant shifts in plant growth form composition, with a much smaller role for changes in litter quality within species. Specifically, the ongoing warming-induced expansion of shrubs with recalcitrant leaf litter across cold biomes would constitute a negative feedback to global warming. Depending on the strength of other (previously reported) positive feedbacks of shrub expansion on soil carbon turnover, this may partly counteract direct warming enhancement of litter decomposition.
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| 2. |
- Jägerbrand, Annika K, 1972-, et al.
(author)
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Plant community responses to 5 years of simulated climate change in meadow and heath ecosystems at a subarctic-alpine site
- 2009
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In: Oecologia. - : Springer Science and Business Media LLC. - 0029-8549 .- 1432-1939. ; 161:3, s. 601-610
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Journal article (peer-reviewed)abstract
- Climate change was simulated by increasing temperature and nutrient availability in an alpine landscape. We conducted a field experiment of BACI-design (before/after control/impact) running for five seasons in two alpine communities (heath and meadow) with the factors temperature (increase of ca. 1.5-3.0°C) and nutrients (5 g N, 5 g P per m 2) in a fully factorial design in northern Swedish Lapland. The response variables were abundances of plant species and functional types. Plant community responses to the experimental perturbations were investigated, and the responses of plant functional types were examined in comparison to responses at the species level. Nutrient addition, exclusively and in combination with enhanced temperature increase, exerted the most pronounced responses at the species-specific and community levels. The main responses to nutrient addition were increases in graminoids and forbs, whereas deciduous shrubs, evergreen shrubs, bryophytes, and lichens decreased. The two plant communities of heath or meadow showed different vegetation responses to the environmental treatments despite the fact that both communities were located on the same subarctic-alpine site. Furthermore, we showed that the abundance of forbs increased in response to the combined treatment of temperature and nutrient addition in the meadow plant community. Within a single-plant functional type, most species responded similarly to the enhanced treatments although there were exceptions, particularly in the moss and lichen functional types. Plant community structure showed BACI responses in that vegetation dominance relationships in the existing plant functional types changed to varying degrees in all plots, including control plots. Betula nana and lichens increased in the temperature-increased enhancements and in control plots in the heath plant community during the treatment period. The increases in control plots were probably a response to the observed warming during the treatment period in the region. © Springer-Verlag 2009.
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| 3. |
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| 4. |
- Selander, Helena, 1975-, et al.
(author)
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Older drivers: On-road and off-road test results
- 2011
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In: Accident Analysis and Prevention. - : Elsevier Science B.V., Amsterdam.. - 0001-4575 .- 1879-2057. ; 43:4, s. 1348-1354
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Journal article (peer-reviewed)abstract
- Eighty-five volunteer drivers, 65-85 years old, without cognitive impairments impacting on their driving were examined, in order to investigate driving errors characteristic for older drivers. In addition, any relationships between cognitive off-road and on-road tests results, the latter being the gold standard, were identified. Performance measurements included Trail Making Test (TMT), Nordic Stroke Driver Screening Assessment (NorSDSA), Useful Field of View (UFOV), self-rating driving performance and the two on-road protocols P-Drive and ROA. Some of the older drivers displayed questionable driving behaviour. In total, 21% of the participants failed the on-road assessment. Some of the specific errors were more serious than others. The most common driving errors embraced speed: exceeding the speed limit or not controlling the speed. Correlations with the P-Drive protocol were established for NorSDSA total score (weak), UFOV subtest 2 (weak), and UFOV subtest 3 (moderate). Correlations with the ROA protocol were established for UFOV subtest 2 (weak) and UFOV subtest 3 (weak). P-Drive and self ratings correlated weakly, whereas no correlation between self ratings and the ROA protocol was found. The results suggest that specific problems or errors seen in an older persons driving can actually be "normal driving behaviours".
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| 5. |
- Selander, Helena, et al.
(author)
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The Nordic Stroke Driver Screening Assessment as predictor for the outcome of an on-road test.
- 2010
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In: Scandinavian Journal of Occupational Therapy. - : Informa UK Limited. - 1103-8128 .- 1651-2014. ; 17:1, s. 10-17
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Journal article (peer-reviewed)abstract
- The use of the cognitive test battery Nordic Stroke Driver Screening Assessment (NorSDSA) has increased, sometimes as a stand-alone test to evaluate fitness to drive, also for non-stroke patients such as patients suffering from cognitive deficits/dementia, approaches that may be questioned. The objective of the study was to determine whether the NorSDSA could predict an on-road test result, for large sets of stroke ( n=74) and cognitive deficits/dementia participants ( n=116), respectively. The percentage of correctly classified was 62% for the stroke group and 50% for the cognitive deficits/dementia group. A discriminant analysis with pass/fail on the on-road test as grouping variable could classify 62% of the stroke participants and the cognitive deficit/dementia participants. Hence, the NorSDSA could not predict the outcome of the on-road test. Therefore, NorSDSA should not be used as a stand-alone test to determine the fitness to drive of individual participants. Also, its use with participants suffering from cognitive deficits/dementia appears to be less successful than for clients with stroke.
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| 6. |
- Anund, Anna, et al.
(author)
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The effects of driving situation on sleepiness indicators after sleep loss : A driving simulator study
- 2009
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In: Industrial Health. - : National Institute of Industrial Health. - 0019-8366 .- 1880-8026. ; 47:4, s. 393-401
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Journal article (peer-reviewed)abstract
- Almost all studies of sleepy driving are carried out in driving simulators and with monotonous road conditions (no interaction with other cars). The present study investigated indicators of sleepy driving in a more challenging scenario after a night awake. 17 participants drove a high fidelity moving base driving simulator experiment while sleepiness was monitored physiologically and behaviourally. Short periods of situations of free driving (no other vehicles) alternated with short periods of following another vehicle (car following) with and without the possibility to overtake. The result showed that a night of prior sleep loss increased sleepiness levels at the wheel (eye closure duration and lateral variability) compared to after a night of normal sleep. Blink duration while overtaking was significantly lower compared to the other situations, it was at the same level as after night sleep. Speed when passing a stopped school bus was not significantly affected by sleepiness. However the warning caused a more rapid reduction of speed. In conclusion, a moderately challenging driving contest did not affect sleepiness indicators, but a very challenging one did so (overtaking). This suggests that it is important to monitor the driving situation in field operational tests of sleepy driving.
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| 7. |
- Jägerbrand, Annika K., et al.
(author)
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Responses of bryophytes to simulated environmental change at Latnjajaure, northern Sweden
- 2003
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In: Journal of Bryology. - : Taylor & Francis. - 0373-6687 .- 1743-2820. ; 25:3, s. 163-168
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Journal article (peer-reviewed)abstract
- We simulated a predicted environmental change in a subarctic-alpine plant community to study short-term growth in Hylocomium splendens, and three-year effects in abundance changes of the five most common bryophytes at Latnjajaure, northern Sweden. The experiment had a factorial design with increased temperature and nutrients, alone and in combination. Moss growth was measured during the 1995 growing season, and we measured species abundance before and after three years of environmental perturbation. The combined treatments of fertilizer and temperature enhancement caused a decreased growth in length and dry weight in H. splendens. There was a significant decrease in abundance of Rhytidium rugosum in the combined temperature and fertilizer treatment. The other four common bryophyte species (Aulacomnium turgidum, Dicranum groenlandicum, Hylocomium splendens, and Ptilidium ciliare) showed weaker, but not significant trends in the same direction. As the bryophytes are an important component of arctic and subarctic vegetation, we expect that they will play a key role in the impact of anticipated Global Change on the ecosystems.
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| 8. |
- Vadeby, Anna, et al.
(author)
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Sleepiness and prediction of driver impairment in simulator studies using a Cox proportional hazard approach
- 2010
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In: Accident Analysis and Prevention. - : Elsevier BV. - 0001-4575 .- 1879-2057. ; 42:3, s. 835-41
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Journal article (peer-reviewed)abstract
- Cox proportional hazard models were used to study relationships between the event that a driver is leaving the lane caused by sleepiness and different indicators of sleepiness. In order to elucidate different indicators' performance, five different models developed by Cox proportional hazard on a data set from a simulator study were used. The models consisted of physiological indicators and indicators from driving data both as stand alone and in combination. The different models were compared on two different data sets by means of sensitivity and specificity and the models' ability to predict lane departure was studied.In conclusion, a combination of blink indicators based on the ratio between blink amplitude and peak closing velocity of eyelid (A/PCV) (or blink amplitude and peak opening velocity of eyelid (A/POV)), standard deviation of lateral position and standard deviation of lateral acceleration relative road (ddy) was the most sensitive approach with sensitivity 0.80. This is also supported by the fact that driving data only shows the impairment of driving performance while blink data have a closer relation to sleepiness. Thus, an effective sleepiness warning system may be based on a combination of lane variability measures and variables related to eye movements (particularly slow eye closure) in order to have both high sensitivity (many correct warnings) and acceptable specificity (few false alarms).
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| 9. |
- Börjesson, Maria, 1974-, et al.
(author)
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The value of time of car drivers choosing route: evidence from the Stockholm congestion charging trial
- 2007
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In: Proceedings of the European Transport Conference. - Leiden, Netherlands. ; , s. 14-
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Conference paper (peer-reviewed)abstract
- In applied travel demand forecasting (including network modeling), congestion charges are generally assumed to affect travelers in the same way as fuel costs and other travel costs do. However, there are several reasons to believe that congestion charges affect drivers differently than for example fuel costs: for exampel, it is more “visible”, since you (as a rule) pay each time you pass a cordon (or equivalent), and it is often connected with a certain amount of hassle to actually pay the charge (calling a customer service, for example). Moreover, the way car drivers actually weigh travel time versus monetary cost when they choose route is largely unknown, since time and monetary cost are in general so correlated (as opposed to values of time in mode choice etc.). Data from the Stockholm congestion charging trial allow us to explore this question in detail. Car drivers traveling between the northern part of the county and the southern part could choose either to go through the cordon (paying two charges – 20-40 SEK depending on the time of day) or use the Essinge bypass, which was free of charge – a considerable detour for some trip relations. We use a large panel travel survey conducted before and during the charging trial to estimate the charging cost sensitivity compared to fuel cost sensitivity, and also estimate the actual value of time car drivers reveal when choosing route. Note that due to e.g. selection bias or travelers’ imperfect information about costs, this value of tme may differ from the average value of time for all travelers and also from the average value time for car drivers. The results is very applicable, in that it is easily incorporated into widely used traffic models (network equilibrium models or equivalent), allowing us to make more precise forecasts of the effects of congestion charges. It should also allow us to make more precise route choice modeling in other cases where routes have clearly different monetary costs.
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| 10. |
- Börjesson, Maria, et al.
(author)
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Welfare effects of Stockholm congestion charges using dynamic network assignment
- 2011
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In: Proceedings of the 2011 Conference and the Summer School. - Stockholm, Sweden.
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Conference paper (peer-reviewed)abstract
- According to the standard textbook analysis, drivers as a group will be worse off with congestion charging if not compensated by revenues. This result is confirmed by an analysis of the Stockholm congestion charging scheme using a static model with homogenous users. However, both this static model and the standard textbook analysis omit three important factors: taste heterogeneity, effects of charges on the larger network arising from less blocking back of upstream links and behavioural adjustments in the temporal dimensions. Taking account of these factors, using a dynamic model with heterogeneous users in a large-scale network, we find that drivers as a group benefit directly from the charging scheme in Stockholm. This paper investigates the importance of the three factors omitted in the standard textbook and the static model analysis in the Stockholm case, finding that all three add significantly to the benefit of the charges.
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