This study examined changes in individual tree height and diameter at breast height and stand-level gross total volume over time, comparing plantation-grown jack pine (Pinus banksiana) and black spruce (Picea mariana) to wildfireorigin, mixed conifer stands. Mensurational data were collected from fixed-area plots in 32 plantations (15 jack pine; 17 black spruce; age 6–64 y) and 21 fire-origin conifer-dominated stands (jack pine/black spruce mixtures; age 4–91 y). Using a generalized three-parameter modified-Weibull function, we described relationships for individual tree and standlevel measures of growth and age for managed and natural origin stands, separately, and then compared the functions to assess growth pattern differences between managed and natural stands. Both the black spruce and jack pine plantations consistently outperformed the natural stands based on all measured individual and stand-level parameters, and significantly lowered the age to operability of the trees. For example, the modeled gross total volume at age 50 resulted in “improved” volumes over the natural stands of 35% and 50% for plantation-grown jack pine and black spruce, respectively. The results from this study suggest that establishing and maintaining desired species at moderate and relatively uniform densities on productive boreal sites can significantly increase yields and shorten the age to operability by nearly 15 y.

This study was designed as a log-scale examination of the influence that decomposing coarse woody debris (CWD in situ for 15 y following harvesting) had on soil carbon and nutrient levels. The study included 4 study sites representing 2 soil types: loamy tills versus sandy outwashes. The mature, fire-origin mixed conifer stands occupying these sites were clearcut harvested in 1994. In 2009, estimates of both total soil carbon and total and available nutrient pools were compared in locations under versus away from CWD. The presence of decaying CWD (now decay classes 3–4) significantly increased soil carbon ( 85 %) and nitrogen ( 49 %) pools. Estimates of inorganic N from a fresh soil 2M KCL extraction, however, were lower underneath the logs, suggesting that N immobilization is occurring as part of the decomposition process. In contrast, the presence of CWD had no significant effect on P, K, Ca, or Mg soil pools. Although there were marked differences in soil nutrient pools between the 2 soil types, the patterns associated with the presence of CWD were largely the same, and suggest that the influence of CWD does not extend beyond the bounds of the CWD. The results suggest that it will be important that biomass harvesting guidelines consider and include CWD retention levels to ensure that this important ecosystem component, with its associated functions (e.g., soil fertility, nutrient cycling), is maintained in harvested landscapes.

Hydrothermal processes are key components of permafrost dynamics and hydrological and carbon cycles in northern forest ecosystems. A forest hydrology model, ForHyM, was used to evaluate these processes by determining how the depth and duration of frost penetration into the soil would vary daily over the course of several decades. This was done for chosen upland/wetland conditions within the Mackenzie Plain south of Fort Simpson, where permafrost is currently sporadic to discontinuous. The model calculations were done using daily weather records from November 1963 to 2010, starting with a hypothetical no-frost condition within the soil and subsoil. Model performance was evaluated by comparing modeled and measured temperatures at different soil depths (upland and peat plateau modelling, R² = 0.95 and 0.94, respectively). It was found that well-drained upland forests within the general area would experience deep and complete freeze—thaw cycles each year. In contrast, poorly drained wetlands would develop gradually deepening permafrost that would at first stabilize in depth over the course of 10 to 20 y, with thaw depth limited to <1 m each year. However, recent increases in recorded air temperature (more so in winter than in summer) would destabilize the permafrost layer, and this would especially occur in areas with insufficient surface insulation by local peat, moss, forest litter, and snow accumulations. These estimates are consistent with (i) reported thawing depths and (ii) the widening encroachment of collapse scars towards the poorly drained portions of the South Mackenzie Plain.

Forests and woodlands with a long, uninterrupted presence (continuity) are often associated with high biodiversity and many habitat specialist species. But the mechanisms by which, and the scales in time and space at which, populations are dependent on continuity remain debated. We examine the spatial and temporal scales at which occurrences of plants, fungi, and invertebrates are affected by continuity and consider whether they are restricted by time for colonization (continuity per se) or by habitat formation times. We give improved definitions of landscape and local levels of continuity and evaluate the empirical literature with respect to these. By critically examining the reported effects of continuity on the occurrence of species in forests and woodlands, we explore the mechanisms behind the patterns at local and landscape scales. We conclude that many species are dispersal-limited in the current fragmented landscapes and occur mainly in landscapes with surplus continuity, meaning that the availability of habitats was greater in the past than it is currently. Our review indicates that local continuity per se is important at least for many forest herbs and for certain species of epiphytic lichens, insects, and land snails, but to a lesser extent for fungi. Several studies show that landscape-level continuity affects the current occurrence of species, in particular for vascular plants, but also for particular lichen, bryophyte, and invertebrate species. For continuity-dependent species, a successful conservation strategy should include both extending the period of habitat duration in relict patches and promoting habitat formation in the immediate surroundings of potential source patches. Conservation strategies need to acknowledge the continuity dependence of many species. Research on how to shorten habitat formation times by forest restoration is an urgent priority.

American ginseng (Panax quinquefolius) is an uncommon perennial understory herb found in eastern deciduous forest. The species is harvested for the international medicinal plant trade. While previous research has inferred that seed dispersal is limited, the production of bright red, fleshy berries suggests long-distance dispersal may be facilitated by songbirds. The objective of this study was to determine how songbirds interacted with ginseng and whether they dispersed or predated ginseng seeds. We used infrared, motion-activated cameras to observe animal—ginseng interactions in the field. To determine the disperser potential of songbirds observed visiting ginseng in the field, we conducted a captive feeding study at the Tennessee Aquarium. Thrushes removed berries from ginseng infructescences more frequently, compared to other potential dispersers, and regurgitated viable seeds 5–37 minutes after ingestion in feeding trials. By dispersing ginseng seeds, thrushes provide a mechanism for ginseng to improve its probability of persistence in the face of 3 primary threats to populations: deer browse, harvest, and climate change.

The association of the swollen-thorn acacia (Acacia cornigera) and ants is an example of defensive mutualism. It has been shown that some bird species prefer to nest in myrmecophyte acacias, suggesting that their nests are protected from predators by the associated ants. Based on previous knowledge regarding the existence of extended benefits for birds in the acacia—ant interaction, the role of the rufous-naped wren was analyzed within the ant—acacia system. Nest predation was assessed taking into account tree species with and without myrmecophytic interactions, tree cover and height, the presence and abundance of ants, predator type, and the distance between each nest and the closest myrmecophyte acacia. The probability of survivorship of artificial nests using a known fate analysis was calculated. The results showed non-significant differences in the probability of survivorship regardless of the presence and density of myrmecophyte acacias, tree cover and height, the presence and abundance of ants, or predator type. Interestingly, the highest degree of predation in the artificial nests was related to the rufous-naped wren. These results suggest that the acacia—ant—bird interaction is more complex than previously perceived.

A forager's willingness to trade off safety for food varies with its energetic state. Animals in a low energetic state should accept higher risk than animals with larger energy reserves. In mammals, energy expenditure by females on gestation and lactation may exceed the relatively low cost of sperm production by males. It follows, if reproductive costs are indeed higher for females than for males, that reproductive females may be more likely than males to trade safety for food. Thus, we evaluated the use of safe versus risky foraging patches by male and female meadow voles using putatively safe and risky habitats. We also used behavioural trials to assess whether sexual differences in personality could account for any differences in patch use. Voles preferred to forage in safe patches over risky ones. There was no difference between male and female voles, or between reproductive and non-reproductive individuals, in their respective use of safe versus risky foraging patches. Personality also had no effect on patch choice. The results are consistent with recent studies on other species that have failed to find differences in reproductive costs between the sexes. Experiments on foraging behaviour might thus provide simple and repeatable tests for sexual differences and similarities in reproductive costs.

Roads are linked to population declines in amphibians, primarily due to road mortality. Culvert-type ecopassages, along with fencing to direct animals to the passage, have been used to mitigate these impacts. However, the effectiveness of the ecopassage itself, independent of the associated mitigation fencing, is largely untested. In regions with heavy snowfall, long-term maintenance of amphibian-proof fencing is extremely costly. Therefore, it is important to know whether ecopassages alone (without fencing) mitigate amphibian mortality. We used a Before-After-Control-Impact design to experimentally test the hypothesis that pre-existing drainage culverts of the type typically used to mitigate road effects on herptiles mitigate anuran road mortality. Grates were installed at both ends of 6 culverts to exclude anurans from the culverts. At an additional 4 sites fencing was installed on either side of culverts on both sides of the road, to keep anurans off the road. Ten control culverts were left un-manipulated. Roadkill surveys were conducted 1 y before treatments were installed and in each of 2 y after. We predicted that, if culverts alone mitigate mortality, road kill should increase following installation of the grates. If fencing is effective for mitigation, road kill should decrease following installation of fences. We found no evidence for the first prediction: culverts alone did not mitigate road kill effects. In contrast, there was a large decrease in mortality at fenced sites, relative to control sites, indicating that fencing is effective at mitigating road mortality. These results suggest that culverts alone do not reduce anuran mortality; to reduce mortality, animals must be excluded from the road surface.

We studied ballooning spiders captured weekly over an 11-y period using a 12.2-m-high suction trap in an agricultural landscape of western Switzerland. We analyzed population trends, changes in phenology, and species composition. Yearly trends in population size of the most abundant species were studied with nonparametric correlations. We found that these trends were markedly different for ground-living (92% of all decreasing species) and upper-strata species (75% of all increasing species). These contrasting tendencies can be explained by a stronger effect of meteorological conditions on species living at ground level and by an observed decrease in habitat availability for open-habitat species. The phenology of ballooning spiders was analyzed using mixtures of Gaussian curves fitted to the yearly capture data; this was possible for the 7 most abundant species. From these, we estimated the dates of the ballooning peaks for each species and each year (1 to 4 peaks depending on the species). We found that the dates remained mostly constant: the timing of dispersal peaks showed no annual trend for all but 1 species. Using nonparametric correlation, we analyzed the relationships between the dates of the peaks and the meteorological parameters occurring before the peak dates. In line with the absence of trend, the dates of the peaks were only weakly related to meteorological conditions. The extreme climatic event of 2003 had a strong impact by reducing populations of ground-living species. Using Canonical Correspondence Analysis and clustering methods, we identified a strong shift in the phenological structure of the ballooning spider assemblage in that year. In all, despite noticeable trends in population size during the study period, the dispersal phenology did not change, which contrasts with observations from other arthropod groups.