Invasive plants can substantially modify wetland structure and animal distribution patterns. In eastern North America, a Eurasian haplotype of the common reed (Phragmites australis, haplotype M) is invading wetlands. We studied the invasion of common reed in freshwater wetlands of an urbanized landscape and its effects on the distribution of amphibians at different life stages. Specifically, we hypothesized that the probability of reed invasion would be greatest in wetlands near anthropic disturbances. We predicted that the probability of desiccation at sampling stations increases with reed cover. Furthermore, we expected that wetlands invaded by common reed would have lower amphibian abundances, apparent survival, and rates of recruitment. We conducted trapping surveys to compare anuran assemblages of tadpoles, juveniles, and adults in 50 wetlands during two field seasons. The probability of reed invasion in wetlands increased with the cover of heavily-managed areas within 1,000 m and the distance to the nearest forest, but decreased with the length of roads within 1,000 m. The probability of station desiccation increased with reed cover. We found no evidence of a negative effect of reed presence on anuran population parameters, at any life stage. Landscape variables, such as the percent cover of forest or heavily-managed areas within a given radius from each wetland, influenced the abundance or the apparent survival of juvenile frogs and the abundance of ranid tadpoles. Our results show that amphibian patterns depend more strongly on the structure of the landscape surrounding wetlands than on exotic reed invasion in wetlands. © 2013 Springer Science+Business Media Dordrecht.

Exotic species contribute to aquatic habitat degradation. In the context of declining amphibian populations, the introduction of alien species has been the subject of numerous studies but few have been dedicated to exotic plants. We hypothesized that the establishment of the exotic common reed (Phragmites australis) in North America would lengthen larval anuran development and decrease the survival rate by modifying habitat structure, changing water characteristics, and decreasing food availability. We tested these hypotheses by studying the larval development of the wood frog (Lithobates sylvaticus) during an experiment in field enclosures. Within each enclosure, we created habitats with three different reed densities (zero, medium, and high). Tadpoles were placed in the enclosures and were followed for six weeks up to metamorphosis, during which we monitored water quality and phytoplankton composition. At the end of the experiment, tadpoles at medium and high reed densities developed more slowly than under the control. However, tadpole survival was similar across treatments. For a given developmental stage, total body length did not differ among treatments. Phytoplankton abundance varied with reed density, and groups known to be consumed by tadpoles were negatively influenced by reed density. We found no impact of reed density on pH, total phenolic concentration, or conductivity. Our results suggest that common reed establishment can influence amphibians with rapid development such as wood frogs. Though larval survival rates were similar across treatments, slower development under high reed densities implies a longer exposure to the risk of the pond drying out and to predators. © 2013 Copyright Taylor and Francis Group, LLC.

To better understand the causes of sugar maple (Acer saccharum Marsh.) replacement by beach (Fagus grandifolia Ehrh.) in the Boise-des-Muir old-growth forest (Quebec), we studied, i) the effect of beech litter on soil properties, ii) the effect of low light availability on maple survival and iii) beech regeneration via root sprouts. Soil properties, understory light, seedling emergence and survival, height growth, and density distribution of maple and beech were compared between the old-growth stand and an adjacent managed stand where the abundance of maple regeneration was high. We did not observe any detrimental effect of beech litter on soil properties and maple early establishment. Overall light availability and maple stocking were lower. and maple density declined more markedly with increasing size in the aid-growth stand than in the managed stand. The deficient maple regeneration in the old-growth stand might be related to a lack of microsites where light availability is high enough for maple survival, and not to a lack of initial recruitment in this species. In the old-growth stand, beech was located in mon shaded microsites than maple hut had a higher growth. Size class distributions of maple and beech suggest that beech had a higher survival rate than maple and that beech sprouts had a higher survival rate than beech seedlings. Beech seems to be better adapted than maple to survive in the deep shade of the old-growth stand. However, we expect that maple will regain its dominance in the understory of the Boise-des-Muir with increasing stand breakup that is likely to occur in the future.

The age structure of two mixed red pine (Pinus resinosa Ait.) and jack pine (Pinus banksiana Lamb.) forests located at Lac Duparquet, northwestern Quebec, were correlated with mean annual temperature and total precipitation recorded at Iroquois Falls for the period between 1913 and 1986. The age structures of both pine species showed a common pattern of regeneration characterized by low regeneration before 1930, an important regeneration peak starting around the 1930s, a dip in the age structure around 1950, a second, though less important, regeneration peak in the 1960s, and an important drop, especially for red pine, after 1970. In general, high regeneration rates were positively correlated with precipitation and negatively with temperature, suggesting that pine recruitment is negatively affected by low snow cover and/or drought. The absence of correlation with temperature suggests that the red pine northern limit may be controlled more by a change in the fire regime than by increasing temperature.

In order to define more precisely the fire regime prevailing in red pine stands, and to evaluate its effect on the maintenance of marginal populations in the boreal forest, we documented the frequency, extent, and intensity of fires that affected red pine populations un northwest Quebec. We focused on two islands in Lake Duparquet, divided the islands into 5 X 5 plots, and recorded topography, soil moisture, and vegetation for each plot. We mapped stems and noted fire scars, took core samples and stem cross sections to determine the age of trees, and uses fire scars, post-fire regeneration, surviving trees, and changes in growth rates as indications of fire passage and intensity. Fire frequency was also estimated using fire history data from 13 stands.

Before 1906 the fire regime was characterized by: (1) a short but very irregular fire interval averaging 30 yr, (2) a large variation un burned area, including patches that were generally left unburned, (3) a low fire intensity, although some fires were locally very intense, and (4) the occurrence, roughly every 68 yr. of fires of sufficient intensity to kill most trees on the entire island. Since 1906 the frequency of fire has decreased dramatically.

The fire regime appears to be controlled by abiotic conditions. The high-frequency fires of variables intensity primarily affect the xeric habitats The less frequent, intense (possibly crown) fires that affect the entire island may depend on stand development from a less susceptible pine and hardwood forest towards a more typical spruce-fir boreal forest in more mesic habitats.

The fire regime described for these insular stands as the limit of the species' range is similar to that described for other parts of the range of red pine. We hypothesize that red pine is restricted to insular habitats at this northern limit of its range because of the particular fire regime that prevails there; the larger and more intense fires of the mainland here led to elimination if the species.