The goal of this study was to determine the effect of local and large-scale processes on fire frequency during the postglacial period in a subalpine ecosystem (Alps, France). Large-scale processes should produce homogeneous distribution of fire-free intervals and synchronicity of fire series, and dominance of local-scale processes, such as those triggered by differences in relief, slope aspect, human history, etc. should create heterogeneous fire regimes. Four ponds and peat were sampled at different elevations and exposures. Sedimentary charcoal was used as a fire proxy, and plant macroremains were used as a vegetation proxy. Synchronicity analysis was based on a transformed Ripley's K-function. Similar fire-free intervals during the early Holocene suggest that fire regimes were controlled at that time by large-scale natural processes such as climate and vegetation patterns and establishment. No fire was reconstructed before 9000 y cal BP. Infrequent fires occurred following establishment of the subalpine bio-climate belt. However, local-scale processes have dominated the pattern of fire intervals during the late Holocene, with more fires at lower elevation and on south-facing slopes. Although altitude, topography, and slope aspect certainly drove between-site differences during the early Holocene, these differences disappeared during the late Holocene, when fire frequency was related not to ecological features of the natural landscape but likely to human population density and activities, e.g., need for pastures (woody fuel suppression). Fires were certainly controlled at first by climate and vegetation (Pinus cembra), but human practices have affected the fire regime for centuries. A new fire epoch might result from both the current global warming and on-going land-use abandonment, which has led to a significant fuel build-up in the Alps.

Nomenclature: Tutin et al., 1968–1993.

Due to stresses resulting from their high altitudes, subalpine forests are sensitive to disturbances, including fire. This study analyzes the long-term relationships between fire and subalpine vegetation in the western Alps. High-resolution analyses of charcoal, pollen, macroremains, and other palynomorphs were performed on sedimentary cores from 2 small peaty ponds located above 2000 m asl. in the Maurienne valley, France. Results reveal similar long-term vegetation dynamics, with differences concerning the structure and composition of local and surrounding plant communities. The vegetation pattern appears partially related to local fire occurrence, which was most frequent between 8900 and 6500 cal. BP at one lake and between 4100 and 1800 cal. BP at the second. Fires notably triggered the development and occurrence of populations of Acer and Alnus incana-type during a 2000-y period and the asynchronous alteration of Pinus cembra forests at both sites. Results show that the low-competitive species, i.e., Larix decidua or Pinus uncinata, were never stimulated by increasing fire frequency. This highlights the past importance of local-scale processes such as fire, which favoured pioneer broad-leaved species but did not threaten the resilience of the subalpine forests dominated by the cembra pine.

Nomenclature: Tutin et al., 1968–1993.

Pedoanthracological studies are generally able to provide accurate spatial resolution on plant distribution. But what is the true spatial variability of the pedoanthracological data? This study uses high-resolution spatial sampling in two 0.5-ha sites (5 pits per 0.5 ha) to assess the heterogeneity of the results obtained by soil charcoal analysis at a small scale. The results show heterogeneous patterns of soil charcoal distribution in terms of concentrations and botanical assemblages. Soil charcoal concentration ranged between 128 mg·kg^-1 and 3369 mg·kg^-1. Plant identifications and anthracomass values were analyzed by principal component analysis (PCA). PCA showed that between 32% and 48% of variance can be explained by inter-pit variability. The high-resolution data obtained through a multisampling strategy is more reliable for the investigation of heterogeneity in soil anthracological assemblages. It is obvious that care is needed in the interpretation of data derived from the analysis of single samples.

Nomenclature: Tutin et al., 1964–1980.

Infrequent large-scale natural disturbance regimes are an integral component of Engelmann spruce (Picea engelmannii) forests of the central Rocky Mountains. Wildfires, bark beetle outbreaks, winds, and avalanches cause relatively drastic changes in community structure, composition, and function. These disturbances may occur independently or interact where the incidence of one may change the potential for another. We assessed potential wildfire behaviour change in the wake of a catastrophic, landscape-wide spruce beetle (Dendroctonus rufipennis) outbreak in southern Utah, USA. Using data collected in spruce forests affected by the outbreak, the Forest Vegetation Simulator and Fire and Fuels Extension were used to simulate long-term (100 y) stand dynamics and potential fire behaviour under 3 reconstructed scenarios: no spruce beetle outbreak (low-severity), 50% spruce beetle-caused mortality (mid-severity), and 95% spruce beetle-caused mortality (high-severity). Simulations suggested a likely reduction in probability of active crown fire for 1 or 2 decades on near-pure Engelmann spruce sites after high-severity mortality. This counterintuitive result suggested extreme fire behaviour is not an inevitable consequence of spruce beetle outbreaks. No change in potential fire behaviour was predicted in stands with the least reduction in spruce basal area (low- or mid-severity). In one stand with a history of surface fire, stand structure and potential fire behaviour from low- and high-severity simulations were influenced by surface fire ∼100 y ago. These results are indicative of complex disturbance interactions that were influenced by the host-specific spruce beetle, resultant stand structures and fuel profiles, and in one case antecedent disturbance.

Nomenclature: Wood, 1982; Flora of North America Editorial Committee, 1993.

We provide a study on long-term canopy gap dynamics in the Žofin Virgin Forest (total area 98 ha), which has been strictly protected since 1838. Our aims were i) to describe the size distribution of gaps at a given time; ii) to determine the area where dynamic processes occurred within a given period; and iii) to determine the role of deciduous versus coniferous trees in gap formation. The fate of individual gaps was followed in a 47-ha beech-dominated part of the reserve by analyzing aerial photographs taken in 1971, 1983, 1991, and 2004. The role of individual trees in canopy gap dynamics was studied by combining gap distribution maps with stem position maps of 1975 and 1997 for a 10-ha sample plot. We showed that i) total gap area (9–11%) and average gap size (88–99 m²) was stable during the 33-y study period; ii) canopy dynamics occurred in 0.1% of the area annually; iii) most gaps were created by the simultaneous death of 1–3 canopy trees; iv) death of deciduous trees played a more important role in the creation of gaps than their proportion among dead trees would suggest; and v) tree size and neighbourhood also determined if a dead tree became a gap maker.

Nomenclature: Jalas & Suominen, 1988.

An analysis of natural disturbances in the Julian Alps was carried out in the Jelovica-Pokljuka region (9627 ha) for the period 1979–2006. Data from salvage cuttings were used to examine the occurrence of windthrow, snow break, and insect attack disturbances in relation to site and stand characteristics, previous disturbances, and forest management. Forest stands at the site were characterized by a high growing stock (400 m3·ha-1 on average) and a large proportion of Norway spruce (87%). Salvage cutting due to windthrow, snow break and insect attacks was strongly related to altitude, aspect, topographic position, diameter structure, developmental phase of the stands, and forest landscape heterogeneity. Pole stands were more susceptible to snow breakage and less susceptible to windthrow and insect attack. A more heterogeneous forest landscape increased the risk of windthrow and insect attack occurrence, while the severity of all natural disturbances was lower in more heterogeneous forest landscapes. Natural disturbances and previous cuttings also significantly influenced the likelihood of occurrence and the severity of subsequent disturbances. To improve stand resistance, forest management measures considering the silviculture system and thinning are discussed.

Nomenclature: Pfeffer, 1995; Oberdorfer, 2001.

Wind damage of coniferous plantation forests containing hinoki (Chamaecyparis obtusa) and natural broad-leaved forests was studied in the Japanese mountains. Wind conditions determined using an air flow simulation model and historical wind disturbance records were integrated within a Geographic Information System (GIS). Based on the data set, the relationships between wind disturbance, wind speed, and stand height in plantation and natural forests were analyzed. A logistic analysis technique was applied to assess the probability of wind disturbance in stands that remained intact or were damaged as a result of the Isewan Typhoon. The results indicate that higher wind speeds and greater stand heights increase the probability of wind disturbance in both plantation and natural forests. Cross tabulation of the observed disturbance percentages in relation to wind speed and stand height in coniferous plantation forests and natural broad-leaved forests revealed that the former are more likely to be disturbed by strong winds than the latter. The logistic regression model enabled us to predict the likelihood of wind disturbance at our study site. Our results confirmed that it is possible, using wind condition prediction software, to analyze wind disturbance in mountain forests with complex terrain and steep slopes.

Nomenclature: Murata et al., 2004.

Habitat loss is the major phenomenon threatening species in the boreal forests. One example of a threatened species affected by habitat loss is the Siberian flying squirrel (Pteromys volans). We used mark-recapture data from 1992 to 2004 for 3 flying squirrel populations to estimate the demographic parameters of these populations. Average adult survival was 0.43–0.53, and probability of surviving and staying near the natal territory through the first winter was 0.23–0.30 in different populations. These values are low compared to survival estimates presented in the literature for other Sciurid species. The estimated population growth rates indicated population decline in all areas. In one of the areas, we found a decline in adult survival and population growth rate during the study. This decline was demonstrated to be linked to ongoing habitat loss due to logging. Low survival and emigration probabilities suggest that these populations are likely to be sinks. This highlights the need to ensure dispersal between the remaining patches of suitable habitat for successful conservation of this and other species associated with old-growth forests. The situation is worrisome as the studied populations are situated in an area where flying squirrel population densities have traditionally been high.

Nomenclature: Latin binomials are those used by original authors.

Understanding the subtleties of the dispersal process, such as how dispersers investigate or avoid different habitat types, is critical to gaining insight into colonization rates and other population processes that occur across landscapes. In central British Columbia, Canada, I examined red squirrel (Tamiasciurus hudsonicus) dispersal activity in second-growth pine (Pinus conforta) stands of varying ages. The main objective of the study was to determine whether i) the dispersing animals directed more attention towards relatively older serai forest stands that more closely approximated their natal habitat (mature forest stands) or ii) they did not discriminate against younger forest stands, at least during the exploratory foray phase of dispersal. To counter the difficulty in monitoring dispersers over a large number of sites placed across the landscape, track counts were used to index dispersal activity. Dispersal activity became noticeably greater in pine stands once they reached 14–18 y of age, whereas younger stands showed relatively little activity. Average tree height and cone production in the second-growth forests increased with age, so both of these characteristics along with others (such as conspecific sign) constitute attributes of the stands that the animals potentially were keying into. To elucidate the relative importance of these potential cues will require further study.

Nomenclature: Nagorsen, 2005.

Size-selective harvest occurs not only in some animal species in the wild, but in some plant species. Panax quinquefolius, a perennial plant of eastern North America, is one such species. As harvest of this species is fatal, there is potential for evolutionary change if selected traits are heritable. In this study, we compared traits potentially affected by selection among 12 populations with different harvest pressures. We used the recovery pattern of an experimentally harvested population to develop an index of harvest pressure: the proportion of seedlings and juveniles. Age was related to leaf area, sympodium (stem) height, and reproduction in populations across a range of harvest indices (HI = 0.4122-0.9583). We detected variation among populations with different harvest indices in the age-leaf area relationship in 2006. A 10-y-old plant would have 30% less leaf area in a population with high harvest pressure (HI = 0.9) than in a population with low harvest pressure (HI = 0.4). Similar results were observed with sympodium height in 2005 and 2006. Reproductive plants in populations with higher harvest indices had reduced seed set, likely due to Allee effects. A separate, related study showed that leaf area differences were maintained among plants from 8 populations 4 to 5 y after transplantation to a common environment. Reduced growth rates in populations with higher harvest pressure may be the outcome of appearance-mediated selection.

Nomenclature: Gleason & Cronquist, 1991.

The presence of spatial autocorrelation in abundance and richness patterns has been recognised for some time. Evaluation of the tools to quantify patterning often uses simulated data that may be unrealistic or empirical field data where the presence and cause of structuring are unknown. We examine the efficacy of spatial pattern analysis for detecting pattern in empirical data at a fine scale using a field-based mesocosm experiment of a Drosophilidae community associated with decaying fruit. The mesocosm comprised 2 microclimate treatments that generated a particular expected spatial pattern in abundance and species richness. The magnitude of Moran's autocorrelation coefficients (I) was < 0.3 (i.e., low). However, the detected pattern was unaffected. Low Moran's I values did not result from low sample sizes, neither was the significance of Moran's I falsely inflated by large sample sizes. Examination of published I values revealed that autocorrelation values between 0.1 and 0.3 are common in empirical data, particularly at fine (lag distance ≤ 1 m) spatial scales. Pooling temporal samples strengthened the detected output without affecting the form of spatial pattern. We conclude that “weak” responses provide a valuable basis for mechanistic hypothesis generation, especially at fine spatial scales, and that the strength of spatial structure is likely to be determined by the spatial scale of the study.

Nomenclature: McEvey et al., 1988.

Higher predation on birds' nests is often associated with habitat fragmentation and edges, but little research has addressed whether these predation patterns result from non-random habitat use by predators. Using 2 endangered bird species, black-capped vireo (Vireo atricapilla) and golden-cheeked warbler (Dendroica chrysoparia), and their primary nest predator, the Texas ratsnake (Elaphe obsoleta), we test the hypothesis that birds nesting in habitats preferred by ratsnakes suffer higher nest predation than those nesting in non-preferred habitats. Ratsnakes did not use their habitat randomly, instead preferring locations with more structure and closer to cover objects and edges. Despite large sample sizes (186 nests and 31 snakes with radio transmitters), however, we did not find clear relationships between snake habitat preference and avian nest survival. Our results, in conjunction with those of another study, suggest that warbler nests were at greater risk if edge was abundant near the nest. Thus, reducing edge could promote nest survival. Additionally, because ratsnakes preferred warbler habitat over vireo habitat, vireos might suffer less predation in larger habitat patches that would increase average distances of nests from the snakes' preferred habitat. In making one bird species' habitat less attractive to ratsnakes' however, we may increase snake predation on other species.

Nomenclature: Grzybowski, 1995; Ladd & Gass, 1999; Crother et al., 2003.

Parasitism is sex-biased in many animal species. In mammals, males often appear to be more severely affected, possibly as a result of costs associated with sexual selection. River otters (Lontra canadensis) and other members of the Mustelidae are definitive hosts for nematodes of the genus Skrjabingylus, which have been found to cause lesions and deformation of the frontal bones of the skull. Infection has also been shown to reduce braincase volume in 2 mustelid species; thus, we hypothesized that a similar relationship exists in otters. Furthermore, we predicted that this effect of nematode parasitism would be biased toward males, which are the larger sex in otters. We used 130 male and female otter skulls collected throughout Ontario to test whether skulls with lesions attributable to nematode infection would show a male-biased reduction in braincase volume and other changes to skull morphology. We found that braincase volume was reduced in male otters with lesioned skulls and to a lesser extent in female otters with lesioned skulls. There was no detectable effect of age on braincase volume. We concluded that parasite-induced damage to otter skulls includes reduced braincase volume, and that this effect appears to be male-biased. This might affect behaviour of otters, reducing survival, and contributing to a pattern of sex-biased mortality.

Nomenclature: Carreno, Reif & Nadler, 2005; Wilson & Reeder, 2005.

Woody plants generally exhibit more conservative water-use characteristics than herbaceous perennials and annuals, including lower stomatal conductance, net photosynthesis, and transpiration, but higher photosynthetic water-use efficiency. Under soil moisture stress, stomatal conductance usually decreases more than net photosynthesis, resulting in lower ratios of internal to atmospheric CO₂ concentrations and higher photosynthetic water-use efficiency. However, we found that shrubs of a semiarid grassland employed opportunistic water-use strategies, which likely evolved due to the short duration of soil moisture availability. We measured photosynthetic gas exchange, leaf reflectance, and foliar stable carbon isotope composition in Artemisia cana, Prunus virginiana, Rhus trilobata, and Ribes aureum in southern Alberta. Under moist conditions, net photosynthesis was very high in A. cana, R. trilobata, and R. aureum, but less so in P. virginiana. Declining volumetric soil moisture caused stomatal conductance to decrease in proportion with net photosynthesis in 3 of 4 species (P. virginiana, R. aureum, and R. trilobata). Consequently, ratios of internal to atmospheric CO₂ were unaffected by soil moisture depletion, and photosynthetic water-use efficiency declined. At the leaf level, the normalized difference vegetation index did not vary with season in these species, while the chlorophyll index decreased only slightly and the photochemical reflectance index showed a small mid-season peak. A. cana had the lowest stable carbon isotope ratio, highest stomatal conductance, highest late-season net photosynthesis, and highest leaf nitrogen (% dry weight). As soil moisture decreased, A. cana exhibited a decline in ratios of internal to atmospheric CO₂ concentrations but no change in photosynthetic water-use efficiency. This study shows that even long-lived, woody species of a semiarid grassland have evolved traits facilitating rapid water-use to maximize carbon gain during brief periods of soil moisture availability.

Nomenclature: Kartesz, 1994.

In this study we show that spatial scale of investigation affects the estimated strength of competition for pollinators between an invasive and a native plant species. The effect of the invasive herb Oxalis pes-caprae on pollinator visits to the native herb Diplotaxis erucoides was studied when the invader was (1) totally present, (2) present on a large scale (of hectares) but absent on a small scale (of square metres), and (3) totally absent. No difference in number of pollinator visits to D. erucoides was found between treatment 1 and 3, i.e., between total presence and total absence of the invader. However, when the invader was removed in the small scale while still remaining in the large scale, a higher number of visits to the native was recorded. Our study thus shows the importance of incorporating multiple spatial scales to allow for investigation of hierarchical effects on competition for pollinators, and it suggests that small-scale studies of effects of invasive plants on pollinator visitation might risk overstating negative effects of the invader.

Nomenclature: Fauna Europaea, 2004; Tutin et al., 2001.