Succession of boreal forest spider assemblages following wildfire and harvesting

To test whether spider succession following harvest differed from succession following wildfire, spiders were collected by pitfall trapping and sweep netting over two years in aspen-dominated boreal forests. Over 8400 individuals from 127 species of spiders were identified from 12 stands representing three age-classes (stand origin in 1995, 1982, and 1968) and two disturbance types (wildfire and harvesting). The diversity of spider assemblages tended to be higher in fire-origin stands than in harvest-origin stands; the youngest fire-origin stands also supported more even distributions of spider species. Spider assemblages responded quickly to wildfire and harvesting as open habitat specialists colonized stands within one year after disturbance. Many web-building species common to older forests either survived harvesting, or re-colonized harvest-origin stands more rapidly than they re-colonized fire-origin stands. Cluster analyses and DCA ordination show faunal convergence by ca 30 years after wildfire and harvesting; trajectories in re-colonization, however, differed by disturbance type as the succession of spider assemblages from fire-origin stands lagged behind spider succession in harvest-origin stands. Comparison with cluster analyses using vegetation data and abiotic site conditions suggests spider assemblages recover from harvesting and fire more rapidly than do a variety of other site characteristics. Several spider species (e.g. Gnaphosa borea Kulezyński, Pirata bryantae Kurata, Arctosa alpigena (Doleschall)) appear dependent on some of the conditions associated with wildfires as they were absent or rarely collected in harvest-origin stands.     

Diversity and seasonal variation of ground and understory spiders from a tropical mountain cloud forest

We made intensive samplings to study the seasonal response of spiders across different forest strata (ground and understory) in a tropical mountain cloud forest from Mexico. We sampled spiders from ten plots in six sampling events during the dry and rainy season, to analyze their abundance, structure (distribution of abundance among species), diversity and the response of the five dominant species at each stratum. Results demonstrated that seasonal patterns of spider communities differed among strata, revealing a complex spatiotemporal dynamic. Abundance, structure, diversity of ground spiders, as well as the responses of four dominant species at this stratum, showed low seasonal variations. In contrast, a strong seasonal variation was observed for the understory assemblage, with lowest abundance and highest diversity in the rainy season, and different assemblage structures for each season. Seasonal patterns of each assemblage seem linked to the responses of their dominant species. We found high co‐occurrence among most of the ground dominant species with similar habitat use and with multivoltine patterns, contrasting with low co‐occurrence among most of the understory dominant species with similar habitat use and univoltine patterns. Our results showed that the spiders’ assemblages of tropical mountain cloud forest (opposed to what is found in temperate and boreal forests) increase their species richness with the height, and that their responses to seasonal change differ between strata. Management programs of these habitats should consider the spatial and temporal variations found here, as a better understanding of their ecological dynamics is required to support their sustainable management.     

Bark-dwelling spider assemblages (Araneae) in the boreal forest: dominance,diversity, composition and life-histories

We collected spiders from tree-bark, foliage and litter habitats in deciduous and conifer dominated stands in NW Alberta (Canada) to define these assemblages and consider their conservation significance. To establish habitat associations, we used Indicator Species Analysis (ISA) together with a species dominance metric (DV′) newly proposed here. Of the 116 species collected, 78 were collected from bark. Results support categorizing 16 species as true bark-dwellers, 16 as facultative bark-dwellers and 46 as accidental bark-dwellers or species of unknown association. Species that were strong indicators of particular microhabitats in analyses restricted to bark habitats lost their indicator value when foliage and ground habitats were also considered, suggesting that bark habitats are critical for specific life-history functions. Clubiona canadensis Emerton 1980, Callobius nomeus (Chamberlin 1919), Pocadicnemis americana Millidge 1976 and Enoplognatha intrepida (Sørensen 1888) were the most common bark-dwelling species but their dominance varied among forest cover-types and trapping techniques. Collecting period, forest cover-type, habitat, and trapping technique were generally important environmental variables influencing composition of bark-dwelling assemblages. Although less important in structuring assemblages, tree status (dead or alive) and decay class were important for particular species. Bark habitats are crucial for boreal forest spider assemblages and must be considered central to maintenance of spider diversity.     

Spiders (Araneae) associated with downed woody material in a deciduous forest in central Alberta, Canada

1 Spiders (Araneae) were collected on and near downed woody material (DWM) in a Populus‐dominated forest to determine if spiders utilize wood surfaces, and to ascertain the importance of DWM habitat and wood elevation for spider assemblages. 2 Over 10 000 spiders representing 100 species were collected. Although more spiders were collected on the forest floor, spider diversity was higher in traps located on wood surfaces than on the forest floor, and 11 species were collected more frequently on wood surfaces. 3 Spiders utilized DWM at different stages in their development. Female Pardosa mackenziana (Keyserling) (Lycosidae) carrying egg sacs were caught most often on the surface of DWM, possibly to sun their egg sacs. Additionally, the proportion of immature spiders was higher on the wood surface than on the forest floor. 4 Spiders collected on logs with and without bark were compared to assemblages collected on telephone poles to assess what features of DWM habitat may be important. Web‐building species were seldom collected on telephone poles, suggesting that they depend on the greater habitat complexity provided by DWM. In contrast, hunting spiders did not distinguish between telephone poles and logs. 5 Fewer spiders and a less diverse fauna utilized elevated compared to ground‐level wood. Additionally, Detrended Correspondence Analysis revealed that the spider community from elevated wood was distinguishable from the spider community from ground‐level wood, and from the forest floor spider community.     

Response of ground and rove beetles (Coleoptera: Carabidae,Staphylinidae) to operational oil sands mine reclamation in northeastern Alberta,a case study

Species loss caused by anthropogenic disturbance threatens forest ecosystems globally. Until 50 years ago, the major sources of boreal forest disturbance in western Canada were a combination of forest wild fire events, pest insect outbreaks, and forest timber harvesting. However, in the 1960s, when the oil boom started in Alberta, oil and gas development along with oil sands mining quickly became another major forest disturbance agent. In this case study we report the effects of operational oil sands mine reclamation on terrestrial arthropod communities and compare them with nearby burned and mature forest sites as a way to provide a benchmark from which to understand the long-term trajectory of recovery for these groups. During the summer of 2016 over 6700 epigaeic beetles were collected using pitfall traps. A total of 43 species of ground beetles and 118 species of rove beetles were collected. Epigaeic beetle assemblages differed between the reclaimed, burned, and mature forest sites. Partitioning of beta diversity in the reclaimed, burned areas and mature forests indicated that species turnover formed the largest component of diversity. Species richness patterns were similar among sites; however, cluster analysis indicated that epigaeic beetle assemblages were only 20% similar between the reclaimed and natural sites. Although ground beetles of the reclaimed area showed positive spatial autocorrelation among treatments, both ground and rove beetles showed responses to the reclamation treatments. The reclaimed areas were dominated by small- to medium-sized open-habitat eurytopic species, whereas the fire and mature forest sites were dominated by larger forest species. The reclaimed area of this case study constitutes a novel, reconstructed ecosystem that is clearly not equivalent in species assemblage to burnt stands of similar age or to mature forest stands.     

Influence of habitat and microhabitat on epigeal spider (Araneae) assemblages in four stand types

Studies based on presence/absence of a species may provide insight into habitat associations, allowing the distribution of species to be predicted across the landscape. Our objective was to characterise the epigeal spider fauna in three mature boreal forest types (conifer, mixedwood and deciduous) and a disturbed habitat (clearcut) to provide baseline data on the spider species inhabiting major forest types of boreal northwestern Ontario, Canada. Only spring-active epigeal spiders were considered for logistical reasons. We further identified the coarse woody debris structure and microhabitat characteristics within these stand types to try to refine our ability to predict the within-stand occurrence of spiders. We found the clearcut habitat strongly dominated by the Lycosidae with 55% of spiders represented by a single species, Pardosa moesta Banks. The forested habitats were more diverse, with web-building families forming a large component of the fauna and many species represented by only a few individuals. The spider composition of the deciduous stands (aspen and mixedwood) was very similar, and distinct from that of spruce stands. Species such as Agroeca ornata (Emerton) (Liocranidae) and Pirata montanus Emerton (Lycosidae) were strongly associated with deciduous leaf litter. Within the spruce stands, Agyneta olivacea (Emerton) (Linyphiidae) and Pardosa uintana Gertsch (Lycosidae) were associated with feathermoss rather than Sphagnum microhabitats. Many of the habitat associations observed at Rinker Lake do not conform well to those described in the taxonomic literature as typical for the species. Few associations with coarse woody debris or microhabitat attributes (other than ground cover type) were found.     

Understory spider assemblages from a cloud forest in Chiapas,Mexico, and their relationships to environmental variables

Cloud forests have high ecological complexity, but their reduced area and exploitation by human communities, make them one of the most endangered ecosystems in Mexico. The spider assemblages of a cloud forest reserve in Chiapas, Mexico, were studied to analyze influence of environmental variables (forest stand structure, temperature and relative humidity) and their temporal variation, on the distribution, abundance, species richness and assemblage structure of spiders. Ten parcels were established for the sampling of spiders and the recording of forest and climatic variables. Spider sampling took place during the dry and rainy seasons. Vegetation data were recorded at the end of the study (except canopy cover, which was registered at the end of each season). Some differences were found among parcels in forest stand structure, but only the density of seedlings showed a high correlation with spider abundance, seemingly seedlings (by its size and architecture) offered numerous supports for the understory spiders’ webs and then promote the settlement of weaver spiders. Also there were some correspondences between the similarity patterns of forest structure and spider assemblages, giving some evidence of a forest structure influence on the integration of spiders’ assemblages. Spider abundance was notoriously higher in the dry season. Other environmental variables had only weak effects on spider variables (abundance and species richness) and assemblage structure. The most abundant families were Tetragnathidae, Theridiidae and Linyphiidae, which were also among the dominant families in other tropical cloud forests, with the latter two also being among the most diverse. As complex ecosystems, tropical cloud forests seem to have complicated interactions with their inhabitant animals, not easy to elucidate.     

On the Relationships between Ground-dwelling Spider (Araneae) Assemblages and Dead Wood in a Northern Sugar Maple Forest

Downed woody material (fallen logs) offers ground-dwelling spiders (Araneae) ideal sites for nesting and foraging, but little is known about what characteristics of dead wood influence spider assemblages. In a maple forest of Forillon National Park, in eastern Québec (Canada), spider assemblages on, adjacent to, and away from fallen logs were compared. We also tested how log type (coniferous vs. deciduous) and decomposition stage influenced spider assemblages. Sampling was done for an intensive four-week period using both litter samples and pitfall traps. A total of 5613 spiders representing 83 species from 16 families was collected. Spiders were affected by the presence of logs, as both species diversity and total number of individuals collected were significantly higher on the log surface compared to the forest floor. Ordination analysis revealed a distinct compositional difference between the spider fauna found on the wood surface compared to the forest floor. Wood type and decomposition stage had few significant effects on spider assemblages, except that less decayed logs supported higher spider diversity than logs in advanced stages of decay. Dead wood is clearly important for generalist predators such as spiders, further supporting the conservation importance of fallen logs in northern forest ecosystems.     

Spider (Aranei) assemblages in bog-forest ecotone of the northern taiga subzone (Eastern Fennoscandia)

Soil-dwelling and ground spiders were studied in oligotrophic and mesotrophic bog-forest ecotones of the northern taiga (Eastern Fennoscandia) in 2005–2007. The number of spider species was greater in the forest as compared to the bog. The spider assemblages of the bogs and swampy forests was characterized by the prevalence of Lycosidae both in abundance and in species richness, whereas members of the family Linyphiidae prevailed in the forest. The species diversity of soil-dwelling spiders was lower in oligotrophic bogs than in mesotrophic ones. In all the bog-forest ecotones studied, the spider assemblages showed no edge effect (an increase in diversity and abundance), indicating a high degree of interpenetration of the spider complexes from adjacent ecosystems. Stenotopic spider species were not found in the ecotones studied either. The major ecological factors responsible for the specific features of spider assemblages in the biotopes studied are the temperature regime and soil humidity.     

Influence of boreal forest succession and dead wood qualities on saproxylic beetles

1 Saproxylic insects, a functional group dominated by beetles, are dependent on dead or moribund trees as habitat elements. 2 Although there are few studies of saproxylic insects from the North American boreal zone, European studies demonstrate that forest harvest can lead to a biologically significant decrease in saproxylic beetle diversity. 3 We studied saproxylic beetles in the North American boreal mixedwood forest using flight intercept traps established on naturally dead and girdled trembling aspen and spruce trees along a successional gradient of undisturbed stands from deciduous to coniferous overstory trees. 4 Composition and diversity of beetle assemblages differed among forest successional types. 5 Snag age class was an important determinant of composition for saproxylic beetle assemblages. 6 Multivariate regression analysis of these data indicated that saproxylic beetles are responding to changes in coarse woody debris, and not to the relative densities of canopy tree species, although these variables are strongly correlated. 7 Coarse woody debris management should be a primary concern in forest management plans seeking to conserve saproxylic organisms and the critical ecosystem functions (i.e. nutrient cycling) in which they participate.     

Understory spider diversity in two remnants of tropical montane cloud forest in Chiapas, Mexico

We evaluated the spider diversity of a tropical montane cloud forest understory in two nearby sites with different degree of human disturbance at the Biosphere Reserve Volcán Tacaná, Chiapas, Mexico. The study was conducted over a 24 days period distributed in 6 months in 2009, covering dry and rainy seasons. A total of 8,370 spiders (1,208 adults and 7,162 juveniles) were collected. Determined specimens (7,747) represented 112 species and morphospecies, 71 genera and 22 families. The results showed that human disturbance has an influence on spider communities: species richness was significantly higher in the preserved site as regards to the disturbed site. Despite their proximity, the composition of spider communities showed only a moderate similarity between the two sites. No differences in abundance were found among sites when considering the whole sample, but sites differed clearly when seasons were analyzed separately. The rainy season had a negative effect on the abundance of spiders in the preserved site. Although the spider community structure was very similar between sites, there was a trend towards a greater species evenness in the preserved site for the whole sampling period and for the dry season.     

甘肃子午岭天然次生林区三种植被类型中土壤蜘蛛群落的组成及多样性

2004年4—10月,在甘肃子午岭天然次生林区采用巴氏诱罐法采集土壤蜘蛛2164头,隶属于19科43种。研究表明辽东栎林(Quercusliaotungensis)、油松林(Pinustabulaeformis)和杨树林(Populusdavidiana)3种森林植被类型中土壤蜘蛛群落组成有明显的差异;不同生境蜘蛛群落的组成成分和多样性指数各异;从各生境中捕获的蜘蛛个体数量分析,皿蛛科、平腹蛛科和科狼蛛科的数量最多,优势类群的组成相似;各生境类型中蜘蛛功能集团的组成及多样性也有明显差异。同时,分析了影响蜘蛛群落组成和多样性的主要因子是生境的植被类型和生境异质性。     

Diversity of canopy and understorey spiders in north-temperate hardwood forests

1 We characterized and compared diversity patterns of canopy and understorey spiders (Arachnida: Araneae) on sugar maple ( Acer saccharum Marsh.) and American beech ( Fagus grandifolia Ehrh.) in hardwood forests of southern Québec, Canada.
2 We sampled canopies of 45 sugar maple and 45 American beech trees and associated understorey saplings in mature protected forests near Montréal. Samples were obtained by beating the crown foliage at various heights and by beating saplings around each tree.
3 Eighty-two species were identified from 13 669 individuals. Forty-eight species and 3860 individuals and 72 species and 9809 individuals were collected from the canopy and the understorey, respectively.
4 Multivariate analyses (NMDS ordination and NPMANOVA) showed the composition of canopy and understorey assemblages differed significantly, and canopy assemblages differed between tree species. Rank-abundance distribution models fitted to the canopy and understorey data indicated that different mechanisms structure the assemblages in both habitats. Three abundant spider species were significantly more common in the canopy; ten species were collected significantly more often in the understorey.
5 The forest canopy was shown to be an important reservoir for spider diversity in north-temperate forests.     

Factors influencing the appearance of spider (Araneae) and beetle (Coleoptera) assemblages in nests of great reed warbler Acrocephalus arundinaceus

The appearance of spider (Araneae) and beetle (Coleoptera) assemblages found in nests of great reed warbler Acrocephalus arundinaceus was studied, firstly to investigate breeding success and the amount of precipitation as potential factors which might affect the abundance and species richness of both groups. In addition, we compared the diversity of spider and beetle assemblages between nests found in different reed habitats, and considered the position of nests (above water or dry ground). In this study we selected five different randomly chosen reed habitats: two mining ponds, two small canals and one large canal. Great Reed Warbler nests were collected either shortly after fledging, or after the clutch had failed. Altogether, 12 species of spider and 19 species of beetle were collected. In both groups there was no significant difference in abundance between successful, lost and cuckoo-parasitized nests; however, there was a significant difference in species richness between the three nest categories in spider assemblages, which was not the case in beetle assemblages. The amount of precipitation did not affect beetle or spider abundance; only the species richness of spiders showed significant growth. Furthermore, we found no significant relationship between vegetation cover and the species richness and abundance of spiders and beetles. The diversity of both groups differed significantly according to reed habitat: beetle assemblages were most diverse by the large canal and spiders at the mining ponds.     

Effect of forestry on the abundance and diversity of arboreal spiders in the boreal spruce forest

Spiders were sampled from spruce branches during late winter in northern Sweden, to investigate the effects of forestry on the community structure of arboreal spiders. Five lichen-rich, natural spruce Picea abies forests and adjacent mature, selectively-logged lichen-poor forests were selected as sample sites. Lichen-rich forests had over three times more spiders on the branches than the lichen-poor forests. The spider community was dominated by web spinners, i.e. the families Linyphiidae. Araneidae, Tetragnathidae and Theridiidae. Hunters, i.e. Philodromidae and Clubionidae. comprised < 3% of the individuals and > 82% of all spiders were juveniles.
Among the dominant species, only the orb-weaver Araneus nordmanni was found in all sites whereas the sheet-web spider Lepthyphantes suffusus was found in all five lichen-rich forests but only in two of the lichen-poor. Both species composition and dominance differed from spider communities in southern boreal spruce canopies. Small prey items, severe abiotic conditions and high predation pressure from birds are possible reasons why web spiders dominate the arboreal community in northern Sweden. These factors could also explain the observed shift in dominance from sheet-web spiders with large body size to those with a small body size, compared with arboreal spider communities in southern boreal forests.
Diversity indices (jack-knifing of Simpson index and Q statistic) showed a higher diversity of spiders in lichen-rich than in lichen-poor forests. The lichen-rich forest had more species and less dominance, in both rank abundance and the Berger-Parker index of dominance. However, rarefaction plots indicated no differences besides lower abundance of spiders on sampled branches in lichen-poor forests. It is suggested, that habitat structure (branch size and epiphytic lichen abundance) could be an explanation for the greater number of spiders in old, lichen-rich spruce forests.     

Habitat management by aboriginals promotes high spider diversity on an Asian tropical island

Orchid Island, 92  km off the southeast coast of Taiwan, has the northernmost tropical forests in East Asia. We assessed effects of habitat management by Orchid Island inhabitants, the Yami people, on spider diversity by comparing assemblages collected from the ground to canopy among four habitats (natural forest, cultivated woodland, second growth forest and grasslands) that receive different degrees of disturbance. Species and guild composition did not differ among replicates of habitat but differed significantly among habitats. Variation in spider diversity was inversely correlated with vegetation density. Cultivated woodland subjected to an intermediate level of disturbances had a lower understory vegetation density than natural forest, but higher spider diversity. Neither insect abundance nor biomass varied significantly among habitats suggesting little room for effects of prey availability on spider diversity. It appears that the Yami people maintain high spider diversity on Orchid Island by generating novel habitat types with different vegetation structures and disturbance regimes.     

Communities of ground-living spiders in deciduous forests: Does tree species diversity matter?

The relationships between species diversity and ecosystem functions are in the focus of recent ecological research. However, until now the influence of species diversity on ecosystem processes such as decomposition or mineral cycling is not well understood. In deciduous forests, spiders are an integral part of the forest floor food web. In the present study, patterns of spider diversity and community structure are related to diversity of deciduous forest stands in the Hainich National Park (Thuringia). In 2005, pitfall trapping and quantitative forest floor sampling were conducted in nine plots of forest stands with one (Diversity Level 1), three (DL 2) and five (DL 3) major deciduous tree species. Species richness, measured with both methods, as well as spider abundance in forest floor samples were highest in stands with medium diversity (DL 2) and lowest in pure beech stands (DL 1). The Shannon-Wiener index and spider numbers in pitfall traps decreased from DL 1 to DL 3, while the Shannon-Wiener index in forest floor samples increased in the opposite direction. Spider community composition differed more strongly between single plots than between diversity levels. Altogether, no general relationship between increasing tree species diversity and patterns of diversity and abundance in spider communities was found. It appears that there is a strong influence of single tree species dominating a forest stand and modifying structural habitat characteristics such as litter depth and herb cover which are important for ground-living spiders.     

The effects of habitat parameters and forest age on the ground dwelling spiders of lowland poplar forests (Hungary)

Forest management has highly modified the structure of the European forests. Harvesting and post-harvest regeneration leads to a simplified forest structure. Our main objective was to detect the effects of habitat structure and forest age on the ground-dwelling spider diversity and assemblage composition of poplar forests at the Hungarian Great Plain. Our results demonstrate that the rarefaction diversity and the number of forest specialists closely correlated with the structural parameters of the forest floor, however, the age and canopy closure did not influence these parameters. According to redundancy analysis, the composition of spider assemblages was determined solely by habitat structure, with habitat structure having a major effect on the species composition and diversity of spider assemblages. A direct effect of forest age on the spider assemblages was not detected, due to the presence of different habitat types in the surrounding landscape, which may serve as suitable habitats for source-populations of spiders with different habitat requirements. Our results highlight the importance structural complexity of forests for maintaining forest spider diversity and preserving the regional species pool of spiders.     

Ground-dwelling spiders (Arachnida, Araneae) in fragmented old forests and surrounding managed forests in southern Finland

We studied the structure of spider assemblages in fragments of old coniferous forest in the southern Finnish taiga We sampled spiders with pitfall traps in the interiors and in the edges of the old-forest patches and in the surrounding managed forests We surveyed assemblages of ground-dwelling spiders and the relation of species to formerly mentioned three forest-habitat categories We analysed spider assemblages in relation to vegetation structure as well As in forest spiders there are no habitat specialists, no strict old-forest species were found However, the spider assemblages of old forests were different from those in the surrounding managed forests The difference was attributable to habitat differences, mainly to reduced tree-canopy cover in managed forests Large hunting-spider species (Gnaphosidae, Lycosidae) benefitted from clearcutting and other management measures, whereas the catches of small forest-living species (Linyphiidae) decreased in plantations and open forests The hunters colonized the edges of old-forest fragments, and were seldom found in the interior of old forest Size of old-forest fragment did not affect significantly the spider assemblage The results indicate that a buffer zone of mature forest with closed canopy should be left to surround the old-growth reserves in order to minimize the edge effect in the fragments     

Changes in riparian forest composition along a sedimentation rate gradient

Riparian forests are highly valued for maintaining water quality through the retention of sediments and nutrients. They also provide some of the most diverse and species-rich habitats in the world. What is largely unknown, however, is how sediment deposition affects plant community composition in these forests. The objective of this study was to examine changes in plant community composition across a gradient of increasing rates of sedimentation in riparian forests in the southeastern Coastal Plain, USA. Seventeen plots were established within riparian forests receiving between 0 and 5.5 cm year⁻¹ of sediment deposits. Species density and biomass estimates were collected annually from 2002 to 2006 for overstory and mid-story plant species within each plot. Percent cover and nested frequency of understory plant species were determined annually during 2004–2006. Measures of community composition in the understory, mid-story, and overstory layers of forests were compared to changes in environmental factors associated with increased sedimentation. In the understory, annual, exotic, and upland species had higher importance values in plots receiving high sediment deposition. The densities of shade-intolerant and N-fixing species in the mid-story also increased with increasing sedimentation rates. Increased overstory mortality was associated with high sedimentation rates, though increases in understory light levels in these gaps were not the main driver of understory species changes. Edaphic factors, such as soil texture, moisture, and temperature, were significantly correlated to species composition in all three forest layers, suggesting that changes in soil physical structure due to sedimentation may drive community-level changes in these forests.