80 research outputs found

    Effects of climate on occurence and size of large fires in a northern hardwood landscape: historical trends, forecasts, and implications for climate change in Témiscamingue, Québec

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    Questions: What climate variables best explain fire occurrence and area burned in the Great Lakes-St Lawrence forest of Canada? How will climate change influence these climate variables and thereby affect the occurrence of fire and area burned in a deciduous forest landscape in Témiscamingue, Québec, Canada?\ud Location: West central Québec and the Great Lakes-St Lawrence forest of Canada.\ud Methods: We first used an information-theoretic framework to evaluate the relative role of different weather variables in explaining occurrence and area burned of large fires (4200 ha, 1959-1999) across the Great Lakes- St Lawrence forest region. Second, we examined how these weather variables varied historically in Témiscamingue and, third, how they may change between the present and 2100 according to different scenarios of climate change based on two Global Circulation Models.\ud Results: Mean monthly temperature maxima during the fire season (Apr-Oct) and weighted sequences of dry spells best explained fire occurrence and area burned. Between 1910 and 2004, mean monthly temperature maxima in Témiscamingue showed no apparent temporal trend, while dry spell sequences decreased in frequency and length. All future scenarios show an increase in mean monthly temperature maxima, and one model scenario forecasts an increase in dry spell sequences, resulting in a slight increase in forecasted annual area burned.\ud Conclusion: Despite the forecasted increase in fire activity, effects of climate change on fire will not likely affect forest structure and composition as much as natural succession or harvesting and other disturbances, principally because of the large relative difference in area affected by these processes

    Structural changes and potential vertebrate responses following simulated partial harvesting of boreal mixedwood stands

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    Partial harvesting, where different numbers and arrangements of live trees are retained in forest stands, has been proposed for maintaining late-successional structure and associated vertebrate species within managed boreal forests. Using the stand dynamics model SORTIE-ND, we examined 80-year patterns of structural change in response to different intensities (30–70% basal area removal) and spatial patterns (22–273m2 mean patch size) of harvesting. We also applied habitat models for seven late-successional vertebrates to the structural conditions present after harvesting to assess potential species responses. Partial harvesting increased understory and downed woody debris (DWD) cover and decreased overstory structure for the first 25 years after harvest, in comparison to unharvested stands, with this effect subsequently reversing as harvest-induced regeneration reached the canopy. Although harvesting enhanced long-term structural development in this regard, large trees, large snags, and largeDWDall remained below unharvested levels throughout the simulation period. Harvesting also produced transient increases in early-decayDWDand ground exposure. Most changes in structural attributes increased in proportion to harvest intensity, but structural differencesamongharvest patterns were generally small. Dispersed harvesting induced somewhat less pronounced decreases in vertical structure, and produced more post-harvest slash, than aggregated harvesting. All seven vertebrate species decreased in abundance as harvest intensity increased from 30 to 70%. In comparison to their pre-harvest abundances in old stands, vertebrates associated with DWD (redback salamander, marten, red-backed vole) showed neutral or positive responses at one or more harvest intensities, whereas those associated with large trees and snags (brown creeper, flying squirrel) consistently exhibited substantial adverse impacts

    Characteristics of voluntary-induced stepping response in persons with stroke compared with those of healthy young and older adults

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    Background: Impairment of protective steps to recover balance from external perturbation is evident after stroke. Voluntary-induced stepping response (VSR) can be used to practice protective steps by instructing an individual to voluntarily lean their whole body forward until they perceive a loss of balance and automatically induce a step. However, to improve protective stepping performance, detailed characteristics of VSR in healthy persons are required. Research question: What is the difference in VSR between healthy and persons with stroke? Methods: An observational study was conducted in 30 participants, (10 young, 10 older, and 10 persons with stroke). All participants performed VSR for 10 trials. Step length, step width, step duration, CoM position, CoM velocity, trunk-hip displacement, and strategies of response were recorded using a motion capture system and analysed using Matlab software. Statistical analysis was performed using One-way ANOVA and Chi-square. Results: On average, participants with stroke had shorter step lengths and step durations than young and older adults. Step width of older adults and participants with stroke was wider than that of young adults (p<0.05). While multiple steps and losing balance were reported more frequently in participants with stroke than the others, the percentage of trials in which participants grasped the handrails was not significantly different between older adults and participants with stroke. CoM position, CoM velocity, and trunk-hip displacement at foot liftoff were significantly smaller in older adults and participants with stroke than young adults (p<0.05). Participants with stroke tended to use trunk bending rather than trunk leaning strategies to generate VSR in contrast to healthy participant. The prevalence of the trunk bending strategy was also greater in older adults than young adults. Significance: Values obtained from healthy groups can be used as guidelines to set realistic goals during VSR training to improve protective steps in patients with stroke

    Half-Time Strategies to Enhance Second-Half Performance in Team-Sports Players: A Review and Recommendations

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    The competitive demands of numerous intermittent team sports require that two consecutive periods of play are separated by a half-time break. Typically, half-time allows players to: return to the changing rooms, temporarily relax from the cognitive demands of the first half of match-play, rehydrate, re-fuel, attend to injury or equipment concerns, and to receive tactical instruction and coach feedback in preparation for the second half. These passive practices have been associated with physiological changes which impair physical and cognitive performance in the initial stages of the second half. An increased risk of injury has also been observed following half-time. On the day of competition, modification of half-time practices may therefore provide Sports Scientists and Strength and Conditioning Coaches with an opportunity to optimise second half performance. An overview of strategies that may benefit team sports athletes is presented; specifically, the efficacy of: heat maintenance strategies (including passive and active methods), hormonal priming (through video feedback), post-activation potentiation, and modified hydro-nutritional practices are discussed. A theoretical model of applying these strategies in a manner that compliments current practice is also presented

    The value of plantation forests for plant, invertebrate and bird diversity and the potential for cross-taxon surrogacy

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    As the area of plantation forest expands worldwide and natural, unmanaged forests decline there is much interest in the potential for planted forests to provide habitat for biodiversity. In regions where little semi-natural woodland remains, the biodiversity supported by forest plantations, typically non-native conifers, may be particularly important. Few studies provide detailed comparisons between the species diversity of native woodlands which are being depleted and non-native plantation forests, which are now expanding, based on data collected from multiple taxa in the same study sites. Here we compare the species diversity and community composition of plants, invertebrates and birds in Sitka spruce- (Picea sitchensis-) dominated and Norway spruce- (Picea abies-) dominated plantations, which have expanded significantly in recent decades in the study area in Ireland, with that of oak- and ash-dominated semi-natural woodlands in the same area. The results show that species richness in spruce plantations can be as high as semi-natural woodlands, but that the two forest types support different assemblages of species. In areas where non-native conifer plantations are the principle forest type, their role in the provision of habitat for biodiversity conservation should not be overlooked. Appropriate management should target the introduction of semi-natural woodland characteristics, and on the extension of existing semi-natural woodlands to maintain and enhance forest species diversity. Our data show that although some relatively easily surveyed groups, such as vascular plants and birds, were congruent with many of the other taxa when looking across all study sites, the similarities in response were not strong enough to warrant use of these taxa as surrogates of the others. In order to capture a wide range of biotic variation, assessments of forest biodiversity should either encompass several taxonomic groups, or rely on the use of indicators of diversity that are not species based
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