Decomposition constants (k) for above-ground logs and stumps and sub-surface coarse roots originating from harvested old-growth forest (estimated age 400–600 y) were assessed by volume–density change methods along a 70-y chronosequence of clearcuts on the Wind River Ranger District, Washington, USA. Principal species sampled were Tsuga heterophylla and Pseudotsuga menziesii. Wood and bark tissue densities were weighted by sample fraction, adjusted for fragmentation, then regressed to determine k by tissue type for each species. After accounting for stand age, no significant differences were found between log and stump density within species, but P. menziesii decomposed more slowly (k = 0.015·y⁻¹) than T. heterophylla (k = 0.036·y⁻¹), a species pattern repeated both above- and below-ground. Small-diameter (1–3 cm) P. menziesii roots decomposed faster (k = 0.014·y⁻¹) than large-diameter (3–8 cm) roots (k = 0.008·y⁻¹), a pattern echoed by T. heterophylla roots (1–3 cm, k = 0.023·y⁻¹; 3–8 cm, k = 0.017·y⁻¹), suggesting a relationship between diameter and k. Given our mean k and mean mass of coarse woody debris stores in each stand (determined earlier), we estimate decomposing logs, stumps, and snags are releasing back to the atmosphere between 0.3 and 0.9 Mg C·ha⁻¹·y⁻¹ (assuming all coarse woody debris is P. menziesii) or 0.8–2.3 Mg C·ha⁻¹·y⁻¹ (assuming all coarse woody debris is T. heterophylla). Including coarse roots increases these loss calculations (averages of all decomposition classes for the study year) to 0.5–1.9 Mg C·ha⁻¹·y⁻¹ or 1.0–3.5 Mg C·ha⁻¹·y⁻¹, respectively. Our results support substitution of log k in C flux models when stump k is unknown. Substitution of log k for coarse root k could, however, substantially overestimate C flux back to the atmosphere from these forests.

Forest expansion (afforestation) is one of the main vegetation changes currently observed in peatlands worldwide in response to natural and anthropogenic disturbances. We examined the relationships between plant and bird richness and frequency and extent of the forest cover in bogs of southeastern Québec to evaluate the impact of forest expansion on typical bog species. A total of 154 plant species and 36 bird species were recorded in the 16 peatlands studied (2-189 ha). Richness and frequency of ombrotrophic plant species were negatively associated with an increase in forest cover. Yet, minerotrophic and minerotrophic-ombrotrophic species did not appear to take advantage of this decline. Afforestation influenced bird species composition by altering the vegetation structure in all strata of the bogs (fewer mosses and shrubs, more trees) and by homogenizing the spatial distribution of plant communities (open patches progressively replaced by forested patches). Peatlands of southeastern Québec remain islands of boreal vegetation in a matrix of deciduous forests and agricultural fields, but afforestation appears to progressively reduce the diversity of peatland habitats. Afforestation does not imperil plant or bird species across their entire range, but it contributes to impoverishing regional biodiversity.

Interspecific competition has been identified as a major structuring force in phytophagous arthropod communities. We would expect to find particularly strong competitive effects in communities with outbreaking components, where the joint food resource is depleted by a single super-abundant species. To assess how arthropod assemblages of the trembling aspen (Populus tremuloides, Salicaceae) respond to outbreaks by the forest tent caterpillar (Malacosoma disstria, Lepidoptera: Lasiocampidae), we sampled galls and leaf-mines in central Alberta, western Canada. Both the incidence and rank order of sympatric taxa varied with the abundance of M. disstria. While most species were “susceptible” to defoliation by M. disstria, declining in abundance with increasing densities of forest tent caterpillars, two species showed no response and one “resistant” species even increased. These patterns at the landscape scale appear to reflect competitive mechanisms acting at a local scale. In a laboratory choice experiment, M. disstria larvae were found to damage a higher proportion of “susceptible” galls than “resistant” galls. Patterns at the landscape scale were also indicative of large-scale movement of gallers and leaf-miners. Following a year of severe defoliation, population densities within an outbreak area declined with increasing distance from the outbreak edge. This finding identifies regional processes as important in the population dynamics of the target taxa. Our study suggests a major structuring role for M. disstria in local arthropod communities. As outbreaks regularly affect a large proportion of temperate forests, they create ample opportunity for competitive interactions among phytophagous arthropods.

The search for general plant community patterns that explain plant responses to land use changes is at present a major focus of studies related to grassland conservation. Traditionally, vegetation change has been documented by identifying species-based changes over time. Recent studies suggest that species-based assessments should be complemented with functional assessments of species characteristics. We examined land use change along a successional gradient by comparing grasslands with long grazing history, abandoned formerly grazed grasslands, and pastures with a short grazing history by using i) species data, i.e., species richness, composition, growth form, and homogenization, and ii) functional characteristics, using three core traits, seed mass, specific leaf area (SLA), and plant height. Analyzing species data directly in terms of species richness, composition, or growth form was a more straightforward tool than analyzing species function based on selected core traits. No functional groups, based on the investigated traits, were supported. Functional response trends were, however, detected, as height increased and SLA decreased along the successional gradient. Analyses based on species data followed documented response patterns associated with grassland succession, i.e., decrease in species richness, decrease in the number of plant species favoured by grazing, and shifts in species composition and growth form towards less dominance of herbs. Due to idiosyncrasy of individual species responses, we question the benefit of using a small number of response traits or functional groupings compared to species-based analyses for documenting vegetation changes in grazing systems over time.

In many parts of the world, invasions of woody plants into grassland communities have been attributed to an increase in grazing pressure, which is hypothesized to reduce competitive interactions between grasses and woody seedlings. However, few experimental studies have attempted to determine the importance of the effects of grass clipping (= simulated grazing) on biotic interactions between plant species in the field. In this study we tested the hypothesis that the establishment of Pinus sylvestris and Pinus nigra seedlings would vary with grass clipping and also soil nutrient level, owing to changes in the nature and intensity of biotic interactions. For both Pinus species, we found contrasting effects of the herbaceous cover on seedlings according to the life stage and the nutrient level. The net effects of the herbaceous cover on seedling recruitment rate switched from facilitation to competition with soil fertilization. The soil nutrient level also modified the impact of grass clipping on pine seedlings. On fertilized soils, clipping decreased competition intensity and increased the recruitment of pine seedlings. On non-fertilized soils, clipping decreased Pinus sylvestris recruitment but did not affect Pinus nigra recruitment. In the study area, under natural conditions, the herbaceous cover had a net positive effect on seedling recruitment owing to higher emergence. Grass clipping should not favour pine invasion in the absence of fertilization, but moderate grazing could favour the recruitment of Pinus nigra compared to Pinus sylvestris. Although an exotic species, Pinus nigra had a wider range of favourable conditions for recruitment than Pinus sylvestris. The effects of grazing on woody plant invasion are expected to differ strongly according to grazing intensity, the abiotic conditions, and the target species.

Intra-population variations in home range size can be considerable among carnivores, especially in the red fox (Vulpes vulpes). In this species, variations are not necessarily sex or age dependent. Our aim was to test whether differences in home range size and stability could be related to red fox female reproductive status, considering that red fox populations exhibit variable proportions of barren vixens. We examined differences in size and stability of seasonal home ranges of 16 foxes (three males and 13 females) radio-tracked from June 2001 to June 2003, in the Ardennes, France. Mean individual home range sizes varied widely, from 31 to 311 ha, with an average of 109 ha. The smaller a home range was, the more stable it was. Home range size was not sex dependent, but female home ranges were more stable than male ones. Reproductive females, mostly 2 y old at least, had smaller home ranges (mean: 50 ha) than non-reproductive females (mean: 174 ha), all 1 y of age. However, there was no difference in female home range stability. We hypothesized that reproductive females monopolize the richest food patches at the expense of non-reproductive females, which are younger and assumed to be subordinate and/or less experienced. Therefore, home range size correlated to food richness may be an important factor for female reproductive success. Competition for food and space could thus explain female reproductive suppression.

Epiphytic soils derive from organic matter accumulation on trunks and canopy branches of large trees. We compared chemical and physical properties, rates of net N mineralization, and bacterial biomass carbon associated with epiphytic soils and the forest floor of an old-growth, temperate forest dominated by the long-lived Fitzroya cupressoides (Cupressaceae) in Chiloé Island, southern Chile. Epiphytic soils had lower density, higher moisture content, higher total carbon and nitrogen contents, and lower pH than forest floor; however, these differences were only slight. Microbial biomass and soil C/N ratios did not differ between soil types. We estimated similar N mineralization rates in epiphytic soil and in the forest floor, but there was a significant interaction between time of the year and soil type, resulting from higher N production in epiphytic soils in some months. Microbial net N mineralization in the epiphytic layer contributed ca 6% of the internal N circulation. Fitzroya trees may access these nutrients via adventitious root uptake and leaching to the forest floor, thus exploiting an alternative path of nutrient circulation in old-growth forests.

Rapid development of energy reserves in the boreal forest of western Canada has raised concerns about the potential impacts of forest fragmentation caused by seismic lines. Seismic lines are narrow linear corridors cut by the energy sector to access remote areas. Traditionally, seismic lines were cut using a bulldozer and averaged about 8 m in width. In response to concerns about conventional seismic line impacts, some energy companies have turned to new “best practices” that use lower-impact techniques to reduce their footprint (2- to 3-m-wide lines). Crucial to assessing the efficacy of this change in seismic policy for maintenance of biodiversity is determining how conventional and low-impact seismic lines are perceived by wildlife. We assessed the functional and numerical response of male ovenbirds (Seiurus aurocapilla) to conventional and low-impact seismic lines in mature aspen forest in northeastern Alberta. Based on radio-telemetry, ovenbirds perceived conventional seismic lines as creating a gap in the forest and used it as a territory boundary. In contrast, ovenbirds incorporated low-impact seismic lines within their territories. Spot-mapping data suggested no differences in ovenbird density in stands with a single conventional seismic line, multiple low-impact lines, or reference plots with no seismic lines. Despite the lack of numerical response to any seismic practice, we believe it is prudent to recommend that energy companies consider using new low-impact approaches in their seismic operations to minimize the ecological risks of energy sector activity for forest birds.

Seedling recruitment in temperate oaks is expected to depend mostly on biotic filters, given the relative independence from resource limitation conferred by large seed size. We investigated the magnitude and fine-scale spatial pattern of red oak (Quercus rubra) recruitment in a mature forest in southern Québec. We compared the scale of operation of experimentally assessed seed and seedling predation to that of several abiotic factors. We sought to interpret concordance or discordance between seed rain and seedling recruitment in terms of spatial heterogeneity in these environmental filters. Most of the demographic variables (adult leaf area index [LAI] and seed rain, newly emerged seedling, and recruited seedling densities) were highly heterogeneous and structured at fine spatial scales. Topography, soil moisture, and light, but not litter thickness, also showed significant spatial autocorrelation at fine spatial scales. However, most of the biotic filters (e.g., seed removal, seed germination, and seedling mortality) were not spatially structured, except for clipping by voles, which was significantly autocorrelated at small distance classes. Failure to detect autocorrelation in most of the biotic filters suggests that they may operate at scales different from that studied, e.g., at a coarser scale for seed predation, but at a finer scale for insect folivory. A path analysis revealed that a large proportion of the variance in seedling recruitment was the result of direct links between the demographic variables studied. Another path analysis, accounting for the effects of biotic filters, highlighted the critical role played by seed predators on recruitment. However, restricted seed dispersal was the major factor influencing the spatial distribution of recruits: indeed, spatial concordance between seed rain and recruit density suggested that even when they are heterogeneous at the same spatial scale, environmental filters are not strong enough to disrupt the patterns generated by primary seed dispersal. Hoarding by rodents accounted for a significant proportion of the spatially homogeneous seed removal; it also reduced potential recruitment limitation associated with microsite availability, thereby increasing the proportion of variation in the spatial pattern of recruitment accounted for by primary seed dispersal.

Litter characteristics of viviparous snakes presumably can be influenced by the mother's state (e.g., mass) at the onset of pregnancy, by food acquired during vitellogenesis, or by food eaten by the mother during pregnancy and delivered to the developing embryos via the placenta. Alternatively, food consumed while pregnant could be allocated to the female herself, potentially influencing her future survivorship and/or reproduction. We tested the effects of food consumption during pregnancy on litter traits of the garter snake, Thamnophis ordinoides, along with the effects of body size and age of mother. We also measured trade-offs between traits. Age was significantly correlated with body size of female snakes, but it had no direct influence on reproductive traits. Initial body size, by contrast, especially snout-vent length, significantly and positively influenced litter size and mass. Food intake by gravid females declined during pregnancy, and snakes became relatively anorexic prior to giving birth; their appetite resumed following parturition. Snakes offered smaller amounts of food while pregnant ate less than those fed ad lib, but had similar postpartum appetites. Higher food intake during pregnancy resulted in higher postpartum mass of females, but not higher litter mass or size of offspring. There was strong evidence of a trade-off between litter size and offspring size and between postpartum mass and litter mass. Overall, our data are consistent with the hypothesis that reproductive traits of viviparous snakes are determined proximately by previously accumulated stores (capital) and/or food consumed during vitellogenesis (income), but not by resources acquired during pregnancy.

Predation on flower-visiting insects can potentially reduce pollination levels and hence plant fitness. We tested this prediction in a field experiment with 10 matched pairs of milkweed patches in which one patch in each pair contained crab spiders and the other patch was predator free. Significantly fewer honeybees were observed in the spider than no spider patches, but there was no spider effect on the two species of bumblebees. A possible explanation for this difference is that the honeybees suffered three times higher predation rates than the bumblebees. There were no spider effects on either the rate of pollinia removal from milkweed flowers or the number and mass of seeds produced. The results suggest that crab spiders may have only small effects on bees and plant fitness, at least where bees are abundant.

In the increasingly important domain of insular invasion ecology, the role of facilitation between different introduced taxa has been mentioned, but rarely studied. This paper outlines facilitation between introduced mammals and the invasive succulents Carpobrotus edulis and C. aff. acinaciformis on offshore islands in southeast France. Rats and rabbits are the primary seed dispersers of Carpobrotus sp. on the islands studied. No such dispersal activity was detected on the adjacent mainland. Seed digestion by rats and rabbits also enhanced percent seed germination and speed, in spite of an associated reduction in seed size. In return, Carpobrotus provides a water/energy-rich food source during the dry summer season, thus demonstrating a clear case of mutualism between invaders.

This study analyzes the influence of temperature, light conditions, seed age, and seed position in the fruit on germination of four Coincya taxa endemic to the south-central Iberian Peninsula: C. rupestris subsp. rupestris (two populations), C. rupestris subsp. leptocarpa, C. longirostra, and C. monensis subsp. orophila (two populations). The first three taxa are endangered. Germination was considerably lower in darkness than with a photoperiod in all taxa analyzed. Freshly matured seeds of C. rupestris subsp. leptocarpa and C. rupestris subsp. rupestris from main population showed primary dormancy, failing to germinate at any temperature or light condition tested. In the other taxa and populations analyzed, fresh seeds showed conditional physiological dormancy, germinating at low and middle but not at high temperatures (32/18 °C). In most taxa and populations, germination capability increased with seed age, and dormancy was finally broken, which suggests that Coincya taxa have non-deep physiological dormancy. The hypothesis that seeds can be induced into conditional dormancy with seed age was confirmed in a population of C. monensis subsp. orophila, where seeds lost the ability to germinate at 5 °C from the fourth month of dry-storage. In most populations tested, short-aged seeds (≤2 months) showed a more pronounced dormancy level when they were collected from the valvar dehiscent portion than from the indehiscent beak. However, the hypothesis that thick-beaked taxa have beak seeds with higher germination than seeds from the valvar portion cannot be accepted as a general trend.

We examined the possibility that granular insecticides, used intensively in the Canadian prairies to control flea beetles (Phyllotreta sp.) in canola (Brassica napus and B. napa), could contribute to bird population declines. A retrospective analysis (1971–96) was done to investigate relationships between counts of 29 bird species made on Breeding Bird Survey (BBS) routes with a spatially explicit granular use index (derived from surveys made in 1980–85) and an index of land use change (derived from Principal Components Analysis of agricultural statistics) for 30 Census Agricultural Regions (CARs). Controlling for spatial location and the land use change index, abundance of American robin (Turdus migratorius), horned lark (Eremophila alpestris), house sparrow (Passer domesticus), mourning dove (Zenaida macroura), and western meadowlark (Sturnella neglecta) was negatively correlated with insecticide use; only two species showed evidence of a positive correlation. At a shorter time scale, for which we had direct estimates of pesticide use (1980–85), we also found evidence that the black-billed magpie (Pica pica), European starling (Sturnus vulgaris), and killdeer (Charadrius vociferus) were less abundant in areas where granular insecticide use was high. Population trends (% annual change between 1971–96) were negatively correlated with the granular index for horned lark, house sparrow, and western meadowlark. Although correlational only, our results suggest that granular insecticides may be an important factor influencing population changes in some bird species in prairie farmland.

Festuca rubra is an abundant supratidal grass on sub-arctic James Bay (Canada) shorelines, forming extensive near-monocultures that are used as forage by nesting and migrating geese. Studies at other, more northern North American locations have shown grubbing by geese can have severe consequences for intertidal and supratidal marshes, but these studies have focussed on plant communities that differ substantially in species composition, physical environment, and extent from James Bay's Festuca meadows. In this study, we examined the responses of this grass to natural and simulated goose grubbing in Festuca swards heavily used by lesser snow geese, Canada geese, and brant at Akimiski Island in James Bay. We transplanted Festuca into plots previously devegetated by geese, into plots where we removed vegetation to simulate goose grubbing, and into intact vegetation (controls). We found shoots transplanted into control and artificially grubbed plots survived well, but those transplanted into previously devegetated areas usually died. Growth initially was reduced in naturally devegetated sites, but the few survivors in the following year performed as well as plants transplanted into intact or artificially grubbed sites. Spot measurements suggested that naturally devegetated sites suffered from degraded soil conditions, such as hypersalinity and increased temperature. These results provide evidence that recovery of Festuca swards following loss of vegetation is likely to be difficult, probably as a result of deteriorating soil conditions. Models of goose–plant interactions developed at substantially more northern sites thus seem applicable to the significantly different plant communities of the James Bay shoreline.