Ground-dwelling Spider Assemblages Research Articles

Can Gap-Cutting Help to Preserve Forest Spider Communities?

Continuous cover forestry maintains many characteristics of uneven-aged natural forests and aims to preserve biodiversity. Gap-cutting is a management option that may create a balance between timber production and continuous forest cover. We investigated the effect of newly created gaps on ground-dwelling spider assemblages in a managed oak forest, in the Pilis Mts., Hungary. Between 2018–2021 we sampled newly created elongated and circular-shaped gaps of two different sizes in a six-times replicated randomised complete block design. Pitfall samples of ~4600 spiders indicated that spider species richness was moderately higher in the gaps than in control stands. Spider assemblages did not respond in a specific way to the different gap implementations, but their variation in species composition was considerably higher in gaps than in the control plots. The excess spider abundance and species number in gaps, as compared to control, increased over the observation period, as did the dissimilarity of gap assemblages to control. Species responses imply that gaps create a variation in microhabitats and microclimatic conditions, resulting in spiders’ diversification. The overall effect of gaps on spider assemblages suggests that gap-cutting is a suitable management option that preserves forest spider assemblages.

A preliminary survey of the ground-dwelling spider assemblages of the Ndumo Game Reserve, South Africa (Arachnida: Araneae)

Ground-dwelling spider assemblages were sampled by pitfall trapping in four contrasting biotopes in the Ndumo Game Reserve, South Africa, situated in the Maputaland-Pondoland-Albany biodiversity hotspot. Over two years (2006 and 2007) in two seasons (mid-summer and winter, 10 days each) 1261 spiders were collected, representing 31 families and 121 species. Twenty-five taxa were recorded from Ndumo for the first time. Spider activity densities and species richness were highest in the deciduous broadleaf woodland (BW, n = 538, S = 106), followed by Albizia adianthifolia-Vachellia tortilis woodland (AW, n = 358, S = 70), sand forest (SF, n = 188, S = 74), and Mahemane thicket (MT, n = 177, S = 53). The four most abundant species were Asemesthes ceresicola Tucker, 1923 (Gnaphosidae, 27.8%), Arctosa sp. (Lycosidae, 8.4%), Pardosa crassipalpis Purcell, 1903 (Lycosidae, 7.4%), and Stenaelurillus guttiger (Simon, 1901) (Salticidae, 5.2%). Species richness and activity densities were strongly seasonal, with sharp decreases in winter. Conservation assessments could not be carried out on a sizable proportion of the species collected, as they represent new taxa or were only represented by immatures (30.6%), but of the remainder the majority had a conservation status of Least Concern (64.5%), with very few being Data Deficient (4.1%) and a single vulnerable species being collected, Massagris natalensis Wesołowska & Haddad, 2009. However, among the new taxa not assessed there may be several Maputaland endemics.

Effects of Fire on Ground-Dwelling Spider (Araneae) Assemblages in Central Indiana Forests.

Fire is a natural disturbance that occurs in many temperate and tropical ecosystems worldwide. As ubiquitous members of these ecosystems, spiders (Araneae) are often affected by fire, and their response to this disturbance has been shown to be dependent on taxonomy, functional diversity, seasonality, and a variety of environmental factors. We examined the effect of fire on ground-dwelling spider assemblages in temperate forests in central Indiana over 5 yr and found that spider assemblages were significantly affected by fire disturbance. Overall spider abundance decreased, whereas species richness and diversity remained unaffected. We also found that spider response depended heavily on the family and/or guild to which the spider belonged. We suspect that altered habitat heterogeneity, the patchy nature of fire's effect on leaf litter, and the high rate of recolonization by spiders all played important roles in these observed patterns.

Positive impact of traditional coppicing restoration on biodiversity of ground-dwelling spiders in a protected lowland forest

Lowland forests of Central Europe had been managed by diverse traditional practices for millennia. Such management helped to maintain heterogeneous habitat conditions suitable for a wide variety of arthropod species. Modern approaches to conservation, however, with their strategies of nonintervention, unintentionally caused an overall habitat homogenization within protected areas in many ecosystem types during the20thcentury. As a result, the diversity of organisms, including several large groups of arthropods, has gradually declined. Active interventions that would diversify homogenized lowland forest reserves are increasingly being reintroduced. A question remains as to whether the traditional management restoration at various intensities will maintain conditions suitable for high diversity of functionally important groups of arthropods. Here,we studied the effect of canopy thinning, aimed at coppice restoration, on ground-dwelling spider assemblages. Sampling was based on experimental plots distributed equally in an abandoned coppice-with-standards among three canopy thinning intensities: strong thinning, moderate thinning, and nonintervention as a control. We recorded 116 species of spiders, including a high proportion of Red-listed and threatened species. The species richness and presence of rare and threatened species increased with the intensity of canopy thinning. The abundance of spiders was greater in plots with moderate thinning than in control plots. Functional richness was greatest in open habitats with strong canopy thinning, however functional traits were equally distributed across allhabitats. Although ordination analyses revealed that species of conservation concern tended to be associated with open habitats, some conservation-valuable species had affinities alsofor nonintervention plots. Overall, our results indicated that the best silviculture practice for biodiversity conservation is a combination of various management intensities that would support functional groups ranging from open habitat specialists to species typical for dense and more humid forest patches. We demonstrated that returning to active coppicing management can be a successful strategy for biodiversity restoration in lowland forests.

Can Mixture of Flowering Plants within Intensive Agricultural Landscape Positively Affect Ground-Dwelling Spider Assemblages?

Spiders are dominant predators in agroecosystems. Terrestrial semi-natural habitats, such as different field margins, can enhance the abundance and diversity of spiders in adjoining fields. We compared the effect of a mixture of flowering plants and an adjacent maize crop for ground-dwelling spiders (Arachnida: Araneae). It was assumed that occurrence of these beneficial arthropods will benefit from the adjacent strip of mixed plants. They were collected by using pitfall traps in a two-year study carried out in Poland during whole growing seasons. The species similarity between the two studied treatments was low, which was indicated with the redundancy analysis (RDA). Furthermore, the species richness and overall abundance of spiders were significantly higher in the mixture of flowering plants than in the adjacent maize field, therefore we assumed that this kind of habitat diversification might increase their role in biological pest control.

Spatial and seasonal patterns of ground-dwelling spider assemblages belonging to the retrolateral tibial apophysis clade (Araneae: Araneomorphae) in two remnants of pine-oak forest from Mexico

ABSTRACT We analyzed the spatial-seasonal patterns on the abundance, composition, structure (i.e. abundance distribution among species), and diversity of the ground-dwelling spiders belonging to the retrolateral tibial apophysis (RTA) clade in two pine-oak forest remnants from Mexico. Additionally, a short review to compare the RTA ground-dwelling communities from Mexican habitats was carried out. Spiders were collected monthly, from July 2010 to June 2011, using pitfall-traps at each site. Species composition was seasonally, but not spatially, different. Estimated diversity for the Hill number 1 was influenced by the sites, and a site–season interaction effect was yielded for the Hill number 2. Abundance and community structure were strongly influenced by both sites and seasons. Six species exhibited strong associations with spatial and seasonal-specific conditions (possible bioindicators). Bibliographic analysis showed the highest richness and the lowest number of undescribed species in desert habitats of northern Mexico, pointing those as possible species repositories for the RTA clade. Our results showed a heterogenous spatial-seasonal response in the RTA ground-dwelling spiders, together with a weak influence of the regional variation in temperature and precipitation on the abundance and species richness, suggesting a stronger influence of ecological drivers at the microhabitat scale.

Minimizing the Wallacean shortfall: a small sample reveals new occurrences of ground-dwelling spiders in native Cerrado and exotic pastures in the Midwestern Brazil

Spiders have gained wide acceptance in ecological studies as indicators of environmental quality because they show a strong preference for habitat type and pattern of land use. Knowledge of the spider community in Neotropical landscapes is still incipient. In order to decrease such lack of knowledge, this study provides information on the ground-dwelling spider assemblages in remnants of native Brazilian Cerrado (savanna woodlands) and in exotic pastures (Urochloa spp.; Poaceae). We collected the spiders in two remnants of native vegetation and in four exotic pastures using pitfall traps in Aquidauana, Mato Grosso do Sul, Midwestern Brazil. A total of 141 adults were captured, belonging to 11 families and 22 species of spiders (Arachnida: Araneae). Sixteen species were found in the exotic pastures, 10 in the Brazilian Cerrado, and only four were common to both habitats. We found higher species richness in exotic pastures when compared to Brazilian Cerrado. In addition, four spider species were reported for the first time in the state of Mato Grosso do Sul: Apopyllus silvestrii (Simon, 1905) (Gnaphosidae) sampled in exotic pastures, and Eilica rufithorax (Simon, 1893) (Gnaphosidae), Lycosa inornata Blackwall, 1862 (Lycosidae) and Oxyopes salticus (Hentz, 1845) (Oxyopidae) captured in the remnants of native vegetation. With these results, we minimize the Wallacean shortfall by increasing knowledge on distribution of spiders in remnants of native Cerrado and exotic pastures in the Midwestern Brazil. Moreover, we demonstrate that the ground-dwelling spider assemblage is rich and abundant in exotic pastures, a structurally poor and homogeneous habitat compared to the native vegetation of the Brazilian Cerrado. Then, our findings may aid in understanding the complexity of effects generated by mixed ecosystems on this group of predatory arthropods widely used as bioindicators of environmental and land use changes.

Effects of reindeer grazing and recovery after cessation of grazing on the ground-dwelling spider assemblage in Finnish Lapland.

The effect of reindeer Rangifer tarandus L. grazing on the ground-dwelling spider assemblage in Northern Finland was studied. Changes in species richness, abundance and evenness of spider assemblages were analyzed in relation to changes in vegetation and environmental factors in long term grazed and ungrazed sites as well as sites that had recently switched from grazed to ungrazed and vice versa. Grazing was found to have a significant impact on height and biomass of lichens and other ground vegetation. However, it seemed not to have an impact on the total abundance of spiders. This is likely caused by opposing family and species level responses of spiders to the grazing regime. Lycosid numbers were highest in grazed and linyphiid numbers in ungrazed areas. Lycosidae species richness was highest in ungrazed areas whereas Linyphiidae richness showed no response to grazing. Four Linyphiidae, one Thomisidae and one Lycosidae species showed strong preference for specific treatments. Sites that had recovered from grazing for nine years and the sites that were grazed for the last nine years but were previously ungrazed resembled the long term grazed sites. The results emphasize the importance of reindeer as a modifier of boreal forest ecosystems but the impact of reindeer grazing on spiders seems to be family and species specific. The sites with reversed grazing treatment demonstrate that recovery from strong grazing pressure at these high latitudes is a slow process whereas reindeer can rapidly change the conditions in previously ungrazed sites similar to long term heavily grazed conditions.

Responses of ground-dwelling spider assemblages to changes in vegetation from wet oligotrophic habitats of Western France

While many arthropod species are known to depend, directly or indirectly, on certain plant species or communities, it remains unclear to what extent vegetation shapes spider assemblages. In this study, we tested whether the activity-density, composition, and diversity of ground-dwelling spiders were driven by changes in vegetation structure. Field sampling was conducted using pitfall traps in bogs, heathlands, and grasslands of Brittany (Western France) in 2013. A total of 8576 spider individuals were identified up to the species level (for a total of 141 species), as well as all plant species in more than 300 phytosociological relevés. A generalised linear model showed that spider activity-density was negatively influenced by mean vegetation height and mean Ellenberg value for moisture. Indices of diversity (ɑ, β, and functional diversities) increased with increasing vegetation height and shrub cover. Variables driving spider composition were mean vegetation height, dwarf shrub cover, and low shrub cover (results from a redundancy analysis). Spiders, some of the most abundant arthropod predators, are thus strongly influenced by vegetation structure, including ground-dwelling species. Although later successional states are usually seen as detrimental to local biodiversity in Europe, our results suggest that allowing controlled development of the shrub layer could have a positive impact on the diversity of ground-dwelling spiders.

Comparative study of ground beetle and ground-dwelling spider assemblages of artificial gap openings

Artificial gap openings cause significant changes in vegetation structure (in every forest level), thereby greatly influencing arthropod communities. Our study compared the data of two common forest floor arthropod groups, ground beetles (Coleoptera: Carabidae) and ground-dwelling spiders (Araneae) from two artificial gaps situated in a turkey oak forest. Our surveys were carried out in the Gyöngyös-plain, in Hungary. Sampling of the arthropod communities was done with pitfall traps arranged in two 70 m long transects, along the longitudinal axis of the gaps, with 15 traps in each transect, 5 m from each other. We measured the quantity and quality of the deadwood lying around within a radius of 2.5 m of each trap. We observed that the species and numbers of spider specimens were higher in the inner parts of the transects (in the gaps), while the numbers of ground beetle specimens declined in the same traps. Furthermore, the Shannon and Simpson diversity values of the ground beetles were generally lower than those of the spiders. The ordinations showed a distinct influence of the gaps on the communities. The numbers of specimens of exclusively edge-associated species were also higher in the gaps. The correlation analysis indicated significant positive correlations between the number of ground beetles and spiders and the quantity of deadwood. In addition, there were significant negative correlations between the numbers of species of both groups and the rate of decay of deadwood.

Both local and landscape-level factors are important drivers in shaping ground-dwelling spider assemblages of sandy grasslands

Earlier studies emphasized that landscape-level factors were essential in shaping arthropod assemblages of semi-natural grasslands. Recently, several studies demonstrated that local factors were more important than landscape-level factors. We examined the importance of several local and landscape-level factors on spider assemblages using pitfall traps from eight sandy grassland fragments between 2001 and 2003. We tested three hypotheses: (i) species richness decreases with grazing intensity; (ii) species richness increasing with fragment size; (iii) the higher isolation of fragments results in decreasing species richness. We found that species richness of spiders did not depend on the grazing intensity, but there were changes in species composition and abundance of species among the variously grazed fragments. Out of the other two studied local factors (fragment size, and the shape of fragment), only the fragment size was a significant predictor of the diversity of specialist spiders, since the number of these species increased significantly with fragment size. Out of the four investigated landscape-level factors (isolation, total area of croplands in the landscape, total area of forests in the landscape, and landscape diversity), only the isolation was a significant predictor influencing spider diversity. The total number of species, the number of generalist species and the number of hunting species increased significantly with the isolation of fragments. Our results suggest that both local and landscape-level factors are important drivers in maintaining spider diversity in sandy grasslands; therefore, these factors should be considered simultaneously during the restoration and/or management of grasslands.

Ground-dwelling spider assemblages in contrasting habitats in the central South African Grassland Biome

Background: Ground-dwelling spider assemblages in shrublands and cultivated pastures in the South African Grassland Biome have never been comprehensively studied.Objectives: Epigeic spiders were collected in eight different habitats in the Amanzi Private Game Reserve in the Free State to determine assemblages of different vegetation types.Methods: Three of the sampled habitats were contrasting low-lying shrublands; three were contrasting hill aspects (northern slope, southern slope and plateau) in the Buddleja saligna–Searsia burchellii–Olea europaea africana subcommunity; one habitat was cultivated Digitaria eriantha pastures, and the last habitat was an area in and around a freshwater dam. Spiders were sampled by pitfall trapping in early spring (Sept. 2012), mid-summer (Jan. 2013), mid-autumn (Apr. 2013) and mid-winter (July 2013).Results: A total of 2982 adult spiders were collected, representing 129 species and 33 families. Ammoxenidae was the most abundant family (40.85%), followed by Gnaphosidae (21.26%), Zodariidae (10.80%) and Salticidae (10.26%). Gnaphosidae was the most species-rich family (24.81%), followed by Salticidae (13.18%), Lycosidae (11.63%) and Zodariidae (6.20%). Spider activity densities and species richness did not differ significantly between habitats, although significant seasonal fluctuations were detected. The three hill aspects and cultivated D. eriantha pastures had the most distinct assemblages, while those of the three low-lying shrublands and freshwater dam showed considerable overlap.Conclusions: Our results indicate that the aspect of hills has a significant effect in shaping spider assemblages, while the vegetation composition of shrublands is not strongly influential. The unique spider assemblages of cultivated D. eriantha pastures can be attributed to the absence of woody plants.Conservation implications: This was the first study to investigate ground-dwelling spider assemblages in shrublands and cultivated pastures in the South African Grassland Biome. Our study confirms that hill aspects, shrublands and pastures harbour very different spider faunas. When identifying land for potential expansion or establishment of protected areas, conservation planners should ensure that the greatest diversity of vegetation units are included to optimise the conservation of biodiversity.

Spider assemblages in floodplain forests along an urbanization gradient

Urban areas have been growing radically worldwide, causing considerable changes in biodiversity of natural habitats. In floodplain forests, we studied the effects of urbanization on ground-dwelling spider assemblages along a rural-suburban—urban gradient in Hungary. We tested three traditional hypotheses (intermediate disturbance hypothesis, habitat specialist hypothesis and hygrophilous species hypothesis) and two novel expectations (shade-preferring species hypothesis, and disturbance sensitive species hypothesis) on spiders. We found that the total number of species was higher in the suburban habitat than in rural and urban ones, supporting the intermediate disturbance hypothesis. We found a decrease in the species richness of forest specialist and shade-preferring species along the urbanization gradient. We found that the number of hygrophilous and disturbance sensitive species was the lowest in the urban habitat. The spider assemblages of the rural and suburban habitats were clearly separated from the assemblages of urban habitats. Based on our findings we emphasize that low and moderate intensity of forest management contributes to the preservation of the local species richness in floodplain forests.

Ground-dwelling spiders (Arachnida, Araneae) in different vegetational formations in a Neotropical floodplain

Spiders are generalist predators distributed in a wide variety of species found in tropical ecosystems, including wetlands such as the Brazilian Pantanal. We evaluated the composition, abundance and richness of ground-dwelling spider assemblage along a vegetation mosaic in the Brazilian Pantanal. For the evaluation, 30 transects were spaced 1 km apart in a 5 x 5 km2 area according to RAPELD methodology. Each sample point was characterized by a transect with five pitfall traps, which remained installed for eight days. A total of 724 spiders, distributed in 28 families and 50 species were collected. Lycosidae, Gnaphosidae and Salticidae showed the highest abundance, and Salticidae, Linyphiidae and Lycosidae had the highest richness. No differences were observed in the composition, abundance and richness of ground-dwelling spiders between the sampled vegetation units, however, the dominance of Lycosidae and Gnaphosidae highlighted a close association with vegetation formations composed of grasses, murundu fields and pasture. Hunting spiders were more prevalent than weavers in all vegetation types. Results demonstrate that the different vegetation types found within the Pantanal are similarly favorable environments to maintain the species richness of spiders in this important Brazilian wetland. Keywords: behavioral guilds, biodiversity, edaphic fauna, wetlands.

The effect of grassland management on diversity and composition of ground-dwelling spider assemblages in the Mátra Landscape Protection Area of Hungary

AbstractThe main objective of this paper is to report the effect of shrub removal and mowing on the diversity and composition of ground-dwelling spider assemblages in Natura 2000 habitats of Mátra Mountains. We found significant effects of shrub removal and mowing on spider communities. Diversity decreased in the year following shrub removal but increased in the following years. Spider diversity in the final year decreased due to the lack of additional treatments. During our study the hay meadows were the most diverse habitats compared to control shrubs and treated shrubs. Treatments caused changes in community structure: the highest number of generalist species was observed in the treated shrubs, and the highest density of rare and protected species in the hay meadows. The high species turnover observed between hay meadows and control shrubs reflects the importance of grassland management. We conclude that shrub removal an effective grassland management action to increase spiders diversity in Natura 2000 habitats. Finally, treated shrubs require additional treatments such as mowing to ensure the spider communities inhabiting them are as diverse as those inhabiting meadows.

Effects of a fast-burning spring fire on the ground-dwelling spider assemblages (Arachnida: Araneae) in a central South African grassland habitat

Fire is widely used as a management strategy in grasslands to maintain vegetation structure and improve grazing quality for large herbivores. The impacts of burning on invertebrates in South Africa remain poorly understood. A study was initiated in spring 2005 to determine the impact of a fast hot burn on ground-dwelling spider assemblages in a grassland habitat in the central Free State. Pitfall traps were set out at six sites in the reserve, with three sites each in the burnt and unburnt areas, to sample spiders over a 12-month period. A total of 5 253 spiders were collected, representing 33 families and 120 species. Spider abundance was significantly lower in the burnt (n = 1 956) than unburnt sites (n = 3 297), and burnt sites had, on average, considerably fewer species than unburnt sites. The dominant families in the burnt sites were Lycosidae (29.5%), Gnaphosidae (16.9%), Ammoxenidae (9.6%) and Zodariidae (5.7%), whereas Ammoxenidae (22.7%), Lycosidae (20.6%), Gnaphosidae (15.3%) and Amaurobiidae (10.2%) dominated the unburnt sites. Of the nine most abundant families collected, only Caponiidae were more abundant in the burnt than unburnt sites. Our data suggest that fast-burning hot spring fires cause a considerable initial post-fire decline in spider abundance, and have a negative influence on the abundance as well as the resistance of assemblages to disturbances other than fire (e.g. rain). However, most of the dominant families had abundances comparable to unburnt areas within a year post-burn.

Even the smallest non-crop habitat islands could be beneficial: distribution of carabid beetles and spiders in agricultural landscape.

Carabid beetles and ground-dwelling spiders inhabiting agroecosystems are beneficial organisms with a potential to control pest species. Intensification of agricultural management and reduction of areas covered by non-crop vegetation during recent decades in some areas has led to many potentially serious environmental problems including a decline in the diversity and abundance of beneficial arthropods in agricultural landscapes. This study investigated carabid beetle and spider assemblages in non-crop habitat islands of various sizes (50 to 18,000 square metres) within one large field, as well as the arable land within the field, using pitfall traps in two consecutive sampling periods (spring to early summer and peak summer). The non-crop habitat islands situated inside arable land hosted many unique ground-dwelling arthropod species that were not present within the surrounding arable land. Even the smallest non-crop habitat islands with areas of tens of square metres were inhabited by assemblages substantially different from these inhabiting arable land and thus enhanced the biodiversity of agricultural landscapes. The non-crop habitat area substantially affected the activity density, recorded species richness and recorded species composition of carabid and ground-dwelling spider assemblages; however, the effects were weakened when species specialised to non-crop habitats species were analysed separately. Interestingly, recorded species richness of spiders increased with non-crop habitat area, whereas recorded species richness of carabid beetles exhibited an opposite trend. There was substantial temporal variation in the spatial distribution of ground-dwelling arthropods, and contrasting patterns were observed for particular taxa (carabid beetles and spiders). In general, local environmental conditions (i.e., non-crop habitat island tree cover, shrub cover, grass cover and litter depth) were better determinants of arthropod assemblages than non-crop habitat island size, indicating that the creation of quite small but diversified (e.g., differing in vegetation cover) non-crop habitat islands could be the most efficient tool for the maintenance and enhancement of diversity of ground-dwelling carabids and spiders in agricultural landscapes.

Ground-dwelling arthropod community response to native grassland conversion in a temperate desert of northwestern China

Oases are common in desert regions of northwestern China and are major sites for human settlement. The implementation of oasis conservation planning has led to afforestation with appropriate shrubs and trees in the native grasslands surrounding inhabited oases. However, little is known about how this Land use change from native grassland to shrub and tree plantations influences the composition of ground-dwelling arthropod communities and the performance of their different trophic groups. To address this, we measured activity density, taxon richness, and relative abundance of four different ground arthropod trophic groups (spiders, beetle predators, beetle herbivores, and beetle detritivores) and several environmental variables affecting arthropod distributions (vegetation cover, ground temperature, soil moisture, soil properties, and leaf litter) along an experimentally established land use change gradient of a mature shrub (Haloxylon ammodendron) planation, a mature poplar (Populus gansuensis) plantation and a mature pine (Pinus sylvestris) plantation, as well as a native grassland from which all cultivated systems were converted. We found that converted shrub plantation had much lower activity density of predatory, herbivorous, and detritivorous beetles; similar activity density of spiders; and similar taxa richness of all four trophic groups relative to the native grassland. However, converted forest plantations regardless of tree species had much higher activity density of spiders, lower activity density of the three beetle groups, much higher richness of predatory beetles, and lower richness of herbivorous and detritivorous beetles. We also found a change in the composition of the ground arthropod community that was largely driven by changes in ground temperature and leaf litter mass. We conclude that conversion of native grassland to shrub and tree plantations can significantly affect ground-dwelling arthropod communities, reducing the activity of ground-dwelling beetle assemblages while increasing that of ground-dwelling spider assemblages. These findings are important for conserving native arthropod diversity in desert ecosystems.

Responses of ground-dwelling spiders (Araneae) to variable retention harvesting practices in the boreal forest

Green tree retention has been embraced as an alternative to large scale conventional clear-cutting aimed at managing the boreal forest in a more sustainable way. Ground-dwelling spider assemblages were studied 6 years after the application of variable retention harvesting practices (dispersed to 2%, 10% and 75% retention vs. aggregated retention) in deciduous and coniferous dominated stands as part of the Ecosystem Management Emulating Natural Disturbances (EMEND) project in the mixedwood boreal forest of northwestern Canada. Overall, spider composition was dominated by open-habitat species, especially by the wolf spider Pardosa moesta Banks, in all harvest treatments. However, an important shift in species composition was observed in unharvested controls. Distinctive ground-dwelling spider assemblages were observed in each forest cover-type and these were highly affected by the various harvest treatments, especially in coniferous forests. From the 164 species collected, 37 were indicators for various combinations of forest type, harvesting treatment and retention level. Species richness was affected as harvesting intensity increased; however, greater impact was observed in dispersed retention than in aggregated retention, and in coniferous stands compared to the same treatment in deciduous stands. Dispersed retention, even at 10%, seemed to mitigate adverse effects of harvesting on spider assemblages, but only in deciduous forests; however, important effects on biodiversity were observed in coniferous forests even after 75% retention. Retention of aggregated patches was useful in maintaining forest specialist species after harvesting, but was more effective when applied together with dispersed retention. Responses of spider assemblages to harvesting seemed to be highly correlated with environmental changes. Green tree retention preserves some of the heterogeneity, structural features and environmental conditions required by forest specialist species and thus becomes an effective management practice to maintain forest biodiversity, especially when both aggregated and dispersed retention practices are applied together. However, the effectiveness of these practices varies depending on the forest cover-type prior to harvesting and the amount of post-harvest residual. This suggests that a single prescription is insufficient for maintaining landscape heterogeneity, and that a combination of prescriptions is supported for a more sustainable management of the mixedwood boreal forest.

Citrus-orchard ground harbours a diverse, well-established and abundant ground-dwelling spider fauna

Ground-dwelling spider assemblages comprise one of the most representative predatory groups to be found in manycrops. There is some evidence of the role that ground-dwelling spiders play in controlling certain citrus pests; however, thereare almost no studies about the abundance and composition of this predatory group in citrus orchards. A three-year surveyconducted using pitfall traps in three citrus orchards in Eastern Spain yielded more than five-thousand ground-dwellingspiders belonging to more than 50 species and 20 families. Wandering families such as Lycosidae, Gnaphosidae andZodariidaewere the most numerous in terms of captures. The generalist predator Pardosa cribata Simon (Araneae: Lycosidae) was the most common species, representing a quarter of all captures, followed by Zodarion cesari Pekar. (Araneae: Zodariidae) and Trachyzelotes fuscipes (Koch) (Araneae: Gnaphosidae). Spiders were active throughout the year with a peak population in summer. The species abundance data for the three spider assemblages sampled fitted a log normal statistical model which is consistent with a well-established community. The presence of a cover crop provided higher abundance of alternative prey and consequently higher abundance and diversity of ground-dwelling spiders. This work demonstrates that the citrus-orchard ground harbours a diverse and abundant ground-dwelling spider fauna, which is also active throughout the year. A challenge for future studies will be to establish conservation management strategies for these predators, that will improve biological control of those citrus pests that inhabit or spend part of their life cycle on the orchard floor.