Insect herbivory in an experimental agroecosystem: the relative importance of habitat area, fragmentation, and the matrix

Habitat area, fragmentation, and the surrounding matrix influence levels of herbivory in various ecosystems, but the relative importance of these effects has rarely been assessed. We compared levels of herbivory and densities of dominant arthropod herbivores (the hemipteran insects Agallia constricta, Empoasca fabae, Therioaphis trifolii, Lygus lineolaris and Halticus bractatus ) among experimental plots that varied in the area and fragmentation of clover habitat and the composition of the matrix (bare ground or grass) surrounding clover habitat. To assess levels of herbivory, we compared clover biomass within herbivore exclosures to the biomass accessible to herbivores. The area and fragmentation of clover habitat, as well as matrix composition, significantly influenced the collective densities of herbivores, although each species exhibited unique responses to habitat structure. Herbivory was strongest in plots with large (64  m²) as compared to small (16  m²) amounts of clover habitat. The difference in clover biomass between the inside and outside of exclosures increased significantly with increasing density of Empoasca fabae but was unrelated to the densities of the other herbivores, suggesting that Empoasca fabae was an exceptionally important herbivore in this system. This study supports the view that herbivore densities and herbivory generally increase with increasing area of plant monocultures, but emphasizes that levels of herbivory may be driven primarily by one or a few key herbivore species.     

Seeding tallgrass prairie in monospecific patches promotes native species establishment and cover

In tallgrass prairie reconstruction, the way desired seeds are arranged on the landscape may affect species establishment, species persistence, and the establishment and persistence of undesired (nonseeded) species from the local propagule pool. To test effects of species seeding pattern on how grasslands develop spatially, we seeded 20—4 × 4–m bare soil plots with 16 tallgrass prairie species. Treatment plots were divided into 16—1 × 1–m subplots, 64—0.5 × 0.5–m subplots, 256—0.25 × 0.25–m subplots, or 1,024—0.125 × 0.125–m subplots. Each species was hand broadcast into separate subplots (1 m² total area/species) within each plot. An additional treatment included uniformly mixing and broadcasting all seeds across a plot. We recorded species cover at the 0.125 × 0.125–m scale within each plot at the beginning of the second and third growing seasons. While species persistence was greatest within plots seeded with larger subplots, plots with smaller subplots were more spatially diverse and less occupied by nonseeded species over time than larger subplot and mixed plots. As is common in reconstruction efforts, establishment was variable among species and seeding with monospecific subplots enhanced colonization of desired rhizomatous species (e.g., Heliopsis helianthoides, Monarda fistulosa, Elymus virginicus) into unoccupied locations at the expense of species from the local propagule pool. Results suggest that seeding species in smaller, monospecific patches could result in grasslands with a more balanced native species composition than those established with a seed mixture approach.     

Direct and indirect effects of habitat area and matrix composition on species interactions among flower-visiting insects

Traditionally, ecologists have focused on direct effects of habitat area and arrangement on individual species or pairwise species interactions. Indirect effects of habitat heterogeneity on multiple interacting species are often neglected or lack experimental support. In a factorial field experiment, we explored the direct and indirect effects of habitat area, fragmentation, and matrix composition on a community of flower-visiting insects in red clover. Habitat area, fragmentation, and density of inflorescences of red clover all influenced the insect pollinators and, in turn, the production of clover seeds. The strongest direct effect was on pollinator visitation, which was substantially higher in small clover patches surrounded by bare-ground than in larger patches embedded within grass. Structural equation modeling indicated that the observed matrix-dependent changes in pollinator visitation propagated across a tri-trophic system: higher visitation rates positively correlated with a higher seed set, which in turn was positively correlated with abundances of seed predators and their parasitoids. Therefore, this study suggests that habitat area and matrix composition can strongly influence the structure of species interaction webs through indirect effects, and also emphasizes that these effects can be propagated through mutualistic as well as trophic interactions.     

Strategies for Mixed-Grass Prairie Restoration: Herbicide, Tilling, and Nitrogen Manipulation

Large areas of North American prairie have been planted with grasses introduced from Eurasia. We examined three strategies (herbicide, tilling, and nitrogen manipulation) for enhancing the establishment of seedlings of native species and suppressing the introduced grasses Agropyron cristatum (crested wheat grass) and Bromus inermis (smooth brome). Plots (5 × 15 m) were subjected to one of three levels of tilling (none, intermediate, complete) and four levels of nitrogen (none, intermediate, high, and sawdust added to immobilize nitrogen). Treatments were applied in a factorial design with twelve treatments and ten replicates. Seeds of 41 native species were drilled into the plots in May 1992. Following the failure of seeds to establish in 1992, a subplot (5 × 13 m) within each main plot was sprayed with the herbicide glyphosate in April 1993. The nitrogen treatments were repeated in Spring 1993. In August 1993, the density of native seedlings in sprayed subplots was 20 times that in unsprayed subplots. Within sprayed subplots, native seedling density and the cover of bare ground decreased significantly with increasing nitrogen availability. Plots receiving sawdust had significantly higher mean cover of bare ground and significantly lower concentrations of soil available nitrogen. Native seedling density was significantly higher in plots receiving the highest intensity of tilling. The responses of native seedlings to all these factors point to the importance of neighbor-free establishment sites as a prerequisite for prairie restoration.     

Feeding Preferences in Greylag Geese and the Effect of Activated Charcoal

ABSTRACT Greylag geese (Anser anser) can cause serious damage to agricultural fields near wetlands that are attractive for resting and nesting but not for feeding. Alternative plantings or spraying fields may prevent goose damage. We randomly designed 64 plots in spring 2004 and prepared plantings of white clover (Trifolium repens), white clover with perennial ryegrass (Lolium perenne; mixture), fertilized perennial ryegrass (grass), or unfertilized perennial ryegrass. We measured goose-dropping densities in plots as a measure of feeding preference in autumn 2004 (7 weeks), spring 2005 (6 weeks), and autumn 2005 (7 weeks) following removal of a protective fence and vegetation sampling for content analysis in 2004. We also sprayed activated charcoal (20 kg/ha) in a suspension on 32 plots (8/planting) to deter geese in autumn 2004 only. In a second experiment we examined pairs of greylag geese in cages for preferences between grass treated with or without activated charcoal. Charcoal did not deter geese in either experiment. However, dropping density averaged highest for clover (1.01/m²), followed by the mixture (0.65/m²), then fertilized (0.23/m²) and unfertilized grass (0.16/m²). Preferences were consistent in all 3 experimental periods. Fertilized grass reached 31.8 cm in height on average in spring, whereas clover measured 15.4 cm. Crude protein and water-soluble carbohydrate content (g/kg dry matter) was 294 and 49, respectively, in white clover and 183 and 139, respectively, in fertilized grass. We found a positive partial correlation independent of vegetation type between dropping densities and crude protein and a negative correlation with water-soluble carbohydrate content. Thus, to prevent grazing damage to agricultural fields, we recommend planting white clover, strongly preferred by feeding geese, in areas (fallow agricultural or nonagricultural) adjacent to their habitat and not in agricultural fields under production.     

Experimental evidence that ground‐disturbance benefits Woodlark Lullula arborea

To determine whether ground‐disturbance increased Woodlark Lullula arborea abundance, we examined responses over 3 years to four treatments varying in establishment method (shallow‐ or deep‐cultivated) and complexity (homogeneous or ‘complex‐mosaics’ comprising fallow and recently cultivated subplots), plus controls, replicated across the largest lowland grass‐heath in the UK. Abundance increased through the study and was higher on plots closer to woodland and across all treatments. Within complex‐mosaics, Woodlark preferentially used recently cultivated subplots over 1‐ or 2‐year‐old fallows. Regardless of treatment detail, providing suitable foraging habitat within c. 45 m of woodland, through annual ground‐disturbance, can increase Woodlark abundance within lowland grass‐heaths characterized by closed swards.     

Consumption rates and the evolution of diet-induced plasticity in the head morphology of Melanoplus femurrubrum (Orthoptera: Acrididae)

Summary Phenotypic plasticity may be an ecologically important evolutionary response to natural selection in multiple environments. I have determined the effect of diet-induced developmental plasticity in the head size of grasshoppers (Melanoplus femurrubrum) onfeeding performance on two types of plants. Full-sib families were divided and raised on either red clover, Trifolium repens, or rye grass, Lolium perenne. In three different stages of ontogeny, grasshoppers raised on rye grass had significantly larger heads, relative to body size, than full-sibs raised on clover. A principal components analysis indicated that two to five relative head size characters covaried as a block in their plastic response to the feeding environment. Regressions of adjusted consumption rates (mg/sec) against relative head size revealed that larger head sizes, induced by the rye grass diet, enhanced consumption rates of rye grass, but not clover. Unexpectedly, a similar positive association was observed between head size and consumption rate for grasshoppers raised on clover when they were feeding on clover. These results support the inference that grasshoppers exhibit adaptive phenotypic plasticity. However, the unexpected influence of head size on consumption rates of clover indicates that the functional relationship between head morphology and feeding performance is complex and that variation in this relationship among plant environments is not sufficient to explain the evolution of diet-induced phenotypic plasticity.     

Influence of conservation reserve program mid-contract management and landscape composition on northern bobwhite in tall fescue monocultures

The United States Department of Agriculture (USDA) authorized mid-contract management (MCM) in 2004 to restore and maintain plant species composition and structural diversity in aging Conservation Reserve Program (CRP) fields for the northern bobwhite (Colinus virginianus) and other grassland-dependent wildlife. We implemented 3 USDA-approved MCM regimes (i.e., strip disking, strip glyphosate spraying, and strip glyphosate spraying in combination with legume interseeding) in 60 tall fescue (Festuca arundinaceae) CRP monocultures in south-central Illinois, USA, during 2005–2008. We hypothesized that adult bobwhite relative densities and brood presence would increase following MCM that effectively restored early successional plant communities in otherwise monotypic stands of tall fescue. We estimated annual adult bobwhite relative densities and brood presence-absence in managed and unmanaged CRP. We modeled vegetation characteristics and landscape composition to identify factors influencing adult densities and brood presence. Adult relative densities were 2-fold greater in managed fields than in unmanaged fields, and were negatively correlated with greater percentages of grass cover. Adult densities were positively correlated with greater plant species diversity, and greater percentages of bare ground and legume cover. Logistic regression and odds ratio estimates indicated that fields managed with glyphosate-interseed and glyphosate treatments were 39.6% more likely to have broods than unmanaged CRP, whereas disked fields were 10.0% more likely than unmanaged CRP. These models indicated that the probability of brood presence was greater in fields with increased percentage of bare ground, greater plant species diversity, and decreased percentage of grass and litter cover. These findings suggest that a 3-year rotation of glyphosate or glyphosate-interseed treatments can enhance habitat conditions for adult bobwhites and broods in CRP tall fescue monocultures. © 2011 The Wildlife Society.     

Foraging behaviour of the root vole Microtus oeconomus in fragmented habitats

The effect of habitat fragmentation on spatial foraging behaviour in the root vole Microtus oeconomus was investigated in seven experimental populations. Four of the populations were established in large, continuous blocks (30 × 95 m) of meadow habitat (treatment plots), whereas the three remaining populations had six small rectangular habitat fragments (30 × 7.5 m) with variable inter-fragment distances (control plots). Both the small habitat fragments and the large continuous habitat were embedded in a non-habitat matrix area which was regularly mowed. Half-way through the study period, the continuous habitat in treatment plots was destroyed by mowing to give a configuration identical to the control plots. Dyed bait placed at the edges and in the interior of habitat fragments as well as in the matrix area was used to reveal differential use of these areas for foraging. Animals in the small-fragment plots fed more than expected along the edges, while edges were used according to availability in the large blocks of continuous habitat. In the fragmented plots, the frequency of foraging in the matrix decreased with increasing distance to the fragment border and with increasing inter-fragment distances. Furthermore, the frequency of use of more than one habitat fragment in individual foraging ranges decreased with increasing inter-fragment distances. Reproductively inactive animals of both sexes fed more often along habitat edges than reproductively active animals. Reproductively active females fed exclusively in one habitat fragment, whereas inactive animals and especially reproductively active males frequently included more than one fragment in their foraging ranges. The only effect of habitat destruction was less foraging in the matrix habitat in the post-destruction treatment plots compared to the permanently fragmented control plots. This was probably an effect of different matrix quality. Root voles in these experimental populations forage in edge and matrix habitat with great risk of becoming victims to predation, and the results are interpreted in this context. Received: 19 August 1998 / Accepted: 30 June 1999     

祁连山南坡植被景观格局及其破碎化

以扎麻什营林区的林相图和调查资料为基础,运用GIS手段,选取合适的景观格局指数,分析了祁连山南坡植被景观格局基本特征,并进行了破碎化评价.结果表明:研究区植被以草地和灌丛为主,景观基质已退化为裸地,各植被类型斑块密度远大于裸地,平均分维数较低,景观整体破碎化水平较高;草地和灌丛边界密度和破碎化指数均高于其他植被类型,反映出该区自然植被景观主要受放牧活动的影响;森林多以小面积零散分布,其中青海云杉林景观结构破坏较为严重,异质性较低,斑块形状趋于单一,显示出较高水平的破碎化,其他林种多以小面积集中分布于某些小的生境,受人类活动干扰较少,破碎化程度较低.

Abstract：

Based on the forest form map and investigation data of Zhamashi forest area, and by using GIS, appropriate landscape pattern indices were chosen to study the basic characteristics of vegetation landscape pattern on the southern slope of Qilian Mountain, with the landscape frag-mentation evaluated. In the study area, grass and shrub were the main vegetation types, and the landscape matrix had degraded to bare land. The patch densities of all vegetation types were far larger than that of bare land, and their mean fractal dimension was lower than that of bear land. All of these characters emphasized the highly fragmented condition of the vegetation landscape in this area. The total edge densities and fragment indices of grassland and shrub land were higher than those of other vegetation types, reflecting that the natural vegetation was mainly affected by grazing. The forests were more dispersed in small areas, and the landscape structure of Picea crassifollia forest was heavily destroyed, being induced that the heterogeneity became lower and the patch shape tended to single, suggesting a high fragmentation degree. Other forest types were centralized in a certain habitat and less disturbed by human activities, suggesting a lower frag-mentation degree.     

Effects of mixed cropping on population densities and parasitism rates of the diamondback moth, <Emphasis Type="Italic">Plutella xylostella</Emphasis> (Lepidoptera: Plutellidae)

Effects of mixed cropping and barrier crops on the population density and parasitism of the diamondback moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae), were evaluated in field plots of cabbage grown in Bali, Indonesia. The densities of P. xylostella at larval and pupal stages, as well as the overall density at larval plus pupal stages, were significantly lower in cabbage/coriander mixed cropping subplots than in cabbage monoculture subplots. Parasitism of P. xylostella by the larval parasitoid Diadegma semiclausum (Hellen) (Hymenoptera: Ichneumonidae) was not significantly different between the mixed and monocultural cropping systems. These results do not support the so-called enemies hypothesis, but suggest that disruption of the host searching behavior of female moths by neighboring non-host plants is the mechanism behind the associational resistance observed in the coriander mixed cropping system. The inclusion of a Napier grass barrier between mixed crop and monoculture subplots did not affect the influence of mixed cropping on larval and pupal densities. Therefore, Napier grass, which is used locally as a fence for preventing livestock invasion of fields, would not obstruct the pest-reducing effect of coriander/cabbage mixed cropping.     

Reducing Competitive Suppression of a Rare Annual Forb by Restoring Native California Perennial Grasslands

Populations of the rare annual forb Amsinckia grandiflora may be declining because of competitive suppression by exotic annual grasses, and may perform better in a matrix of native perennial bunchgrasses. We conducted a field competition experiment in which Amsinckia seedlings were transplanted into forty 0.64‐m² experimental plots of exotic annual grassland or restored perennial grassland. The perennial grassland plots were restored using mature 3 cm‐diameter plants of the native perennial bunchgrass Poa secunda planted in three densities. The exotic annual grassland plots were established in four densities through manual removal of existing plants. Both grass types reduced soil water potential with increasing biomass, but this reduction was not significantly different between grass types. Both grass types significantly reduced the production of Amsinckia inflorescences. At low and intermediate densities (dry biomass per unit area of 20–80 g/m²), the exotic annual grasses reduced Amsinckia inflorescence number to a greater extent than did Poa, although at high densities (>90 g/m²) both grass types reduced the number of Amsinckia inflorescences to the same extent. The response of Amsinckia inflorescence number to Poa biomass was linear, whereas the same response to the annual grass biomass is logarithmic, and appeared to be related to graminoid cover. This may be because of the different growth forms exhibited by the two grass types. Results of this research suggest that restored native perennial grasslands at intermediate densities have a high habitat value for the potential establishment of the native annual A. grandiflora.     

A study of spatial distribution and population dynamics of two sympatric species of trichodorid nematodes

The spatial distribution and population dynamics of Trichodorus primitivus and Paratrichodorus pachydermus were studied at a Scottish nursery site in replicated plots. Each plot was split and half was fumigated with dichloropropene. The numbers of males, females and juveniles under Scots pine (Pinus sylvestris), grass/clover (Lolium perenne/Trifolium repens) and fallow in non-fumigated and fumigated subplots were recorded at 10 cm intervals to a depth of 50 cm every 4 months for 3 years. In the non-fumigated subplots the population densities of T. primitivus under each crop and the fallow soil were similar at the beginning and end of the experiment but P. pachydermus responded differentially, decreasing in fallow soils and increasing under pine. The ratios of adult: juvenile and male: female for the two species were not significantly affected by crop or sampling depth. T. primitivus was the more numerous species except under pine where P. pachydermus gradually became dominant during the study. Both species were present in all the depth samples but showed an aggregated distribution with different modal depths. The depth at which most P. pachydermus were found was shallower than for T. primitivus. Differences in the distribution and behaviour of the two species were found indicating how the two species could co-exist or succeed each other. Fumigation with dichloropropene decreased the trichodorid populations to < 1 per 200 g soil to a depth of 50 cm. The relative development of the populations under the different crops and fallow soil were similar to those in non-fumigated soils.     

Behaviour of male and female parasitoids in the field: influence of patch size,host density,and habitat complexity

1. Two field experiments were carried out to examine the role of patch size, host density, and complexity of the surrounding habitat, on the foraging behaviour of the parasitoid wasp Cotesia glomerata in the field. 2. First, released parasitoids were recaptured on patches of one or four Brassica nigra plants, each containing 10 hosts that were placed in a mown grassland area. Recaptures of females were higher than males, and males and females aggregated at patches with four plants. 3. In experiment 2, plants containing 0, 5 or 10 hosts were placed in unmown grassland plots that differed in plant species composition, on bare soil, and on mown grassland. Very low numbers of parasitoids were recaptured in the vegetated plots, while high numbers of parasitoids were recaptured on plants placed on bare soil or in mown grassland. Recaptures were higher on plants on bare soil than on mown grassland, and highest on plants containing 10 hosts. The host density effect was significantly more apparent in mown grassland than on bare soil. 4. Cotesia glomerata responds in an aggregative way to host density in the field. However, host location success is determined mostly by habitat characteristics, and stronger host or host‐plant cues are required when habitat complexity increases.     

Direct versus indirect effects of habitat fragmentation on community patterns in experimental landscapes

Habitat area and fragmentation are confounded in many ecological studies investigating fragmentation effects. We thus devised an innovative experiment founded on fractal neutral landscape models to disentangle the relative effects of habitat area and fragmentation on arthropod community patterns in red clover (Trifolium pratense). The conventional approach in experimental fragmentation studies is to adjust patch size and isolation to create different landscape patterns. We instead use fractal distributions to adjust the overall amount and fragmentation of habitat independently at the scale of the entire landscape, producing different patch properties. Although habitat area ultimately had a greater effect on arthropod abundance and diversity in this system, we found that fragmentation had a significant effect in clover landscapes with ≤40 % habitat. Landscapes at these lower habitat levels were dominated by edge cells, which had fewer arthropods and lower richness than interior cells. Fragmentation per se did not have a direct effect on local-scale diversity, however, as demonstrated by the lack of a broader landscape effect (in terms of total habitat area and fragmentation) on arthropods within habitat cells. Fragmentation—through the creation of edge habitat—thus had a strong indirect effect on morphospecies richness and abundance at the local scale. Although it has been suggested that fragmentation should be important at low habitat levels (≤20–30 %), we show that fragmentation per se is significant only at intermediate (40 %) levels of habitat, where edge effects were neither too great (as at lower levels of habitat) nor too weak (as at higher levels of habitat).     

Plant composition in the Maya Biosphere Reserve: natural and anthropogenic influences

We studied the floristic composition and stand structure of lowland forests of the Maya Biosphere Reserve (MBR) of El Petén, Guatemala. Sampling was performed over a gradient of human influence, including a newly established returnee community (migrant), the cooperative Unión Maya Itzá, as well as an adjacent protected area within the core area of the MBR. Five 1-ha plots, each divided into 100 contiguous 10 × 10 m² subplots, were used to record presence of all tree and vine species. The study area is a low-diversity rainforest with a canopy layer dominated by species of Fabaceae, a shrub layer dominated by Rubiaceae, and vines dominated by Bignoniaceae. Vines were conspicuous both in number and in diversity. Variation in both tree life-form composition and canopy abundance pattern apparently reflect variation in intensity of forestry among the plots. The similarities between the plots in the cooperative (a logging plot and a settlement plot) with regard to species area curves, and mean number of tree and understory species per subplot, may indicate effects of disturbance (in general) on vegetation structure. Detrended correspondence analysis (DCA) was used to investigate gradients in species composition among the five plots (125 subplots) and to generate hypotheses about vegetation–environment relationships. The study area appears as a mosaic of site-specific forest types or associations determined by a particular species or groups of co-dominant species. The main environmental characteristics of the area determining species composition and structure are related to the drainage of soils and human disturbance.     

The Role of White Clover in the Loss of Diversity in Grassland Habitat Restoration

A field experiment was designed to recreate a species‐rich mesotrophic grassland community of conservation worth. Trifolium repens (white clover) was observed to increase significantly in both frequency and abundance in sown plots grazed by cattle, but not in plots cut in June and subsequently grazed by cattle. In both these treatments permanent quadrats containing clover patches were found to be lower in species richness than were quadrats without clover. In both treatments botanical diversity was seen to decline over time. In the grazed‐only treatment the loss of diversity may be linked to the increase in clover. In the cut and grazed plots, T. repens did not become so abundant but diversity was still seen to decline, possibly due to the loss of low growing species from the taller sward. A pot experiment which varied the sowing density of a mix of seven wild flower species in full factorial combination with cutting frequency was established on soils from an arable field also sown with a single density of clover. T. repens was seen to decline from initial high cover estimates in infrequently cut and uncut treatments. In the pot experiment where a grass component to the vegetation was absent, clover was seen to have less impact on the other forbs than it did in the field. It is suggested that, being a nitrogen fixer, T. repens may have a competitive edge in ex‐arable soils low in available nitrogen. The observed reduction in botanical diversity may be a result of this increase in available nitrogen, facilitating the spread of the sown grasses and preventing the recovery of the sown forbs that were excluded by the invasion of T. repens. It is suggested that reducing the proportion of grass in the seed mixtures during grassland habitat creation on these soils may help reduce or delay this effect.     

Landscape structure influences tree density patterns in fragmented woodlands in semi‐arid eastern Australia

Landscape and local‐scale influences are important drivers of plant community structure. However, their relative contribution and the degree to which they interact remain unclear. We quantified the extent to which landscape structure, within‐patch habitat and their confounding effects determine post‐clearing tree densities and composition in agricultural landscapes in eastern subtropical Australia. Landscape structure (incorporating habitat fragmentation and loss) and within‐patch (site) features were quantified for 60 remnant patches of Eucalyptus populnea (Myrtaceae) woodland. Tree density and species for three ecological maturity classes (regeneration, early maturity, late maturity) and local site features were assessed in one 100 × 10 m plot per patch. All but one landscape characteristic was determined within a 1.3‐km radius of plots; Euclidean nearest neighbour distance was measured inside a 5‐km radius. Variation in tree density and composition for each maturity class was partitioned into independent landscape, independent site and joint effects of landscape and site features using redundancy analysis. Independent site effects explained more variation in regeneration density and composition than pure landscape effects; significant predictors were the proportion of early and late maturity trees at a site, rainfall and the associated interaction. Conversely, landscape structure explained greater variation in early and late maturity tree density and composition than site predictors. Area of remnant native vegetation within a landscape and patch characteristics (area, shape, edge contrast) were significant predictors of early maturity tree density. However, 31% of the explained variation in early mature tree differences represented confounding influences of landscape and local variables. We suggest that within‐patch characteristics are important in influencing semi‐arid woodland tree regeneration. However, independent and confounding effects of landscape structure resulting from previous vegetation clearing may have exerted a greater historical influence on older cohorts and should be accounted for when examining woodland dynamics across a broader range of environments.     

Can landscape properties predict occurrence of grey-sided voles?

There has been a long-term decline in spring and fall numbers of Clethrionomys rufocanus in boreal Sweden in 1971–2005. Previous studies on permanent sampling plots in the centre of 2.5 × 2.5 km landscapes suggested that habitat fragmentation (sensu destruction) could have contributed to the decline. Therefore, we tested these findings in a field study and compared trapping results on the central sampling plots of landscapes with a low degree of fragmentation (LDF) and of “hot spot” type with trapping results in managed forest landscapes with a high degree of fragmentation (HDF). We predicted that C. rufocanus would be more common on the LDF plots. We used our permanent plots supplemented with a new sample of plots, mainly of the rare LDF type, inside or just outside the long-term study area. Very few voles were trapped on both plot types, and no difference was found. However, a subsequent pilot study with trapping in a national park with large areas of pristine, unfragmented forest yielded more voles than in the managed, more fragmented, areas. Consequently, the initial field study data and some other recent data were also re-analysed from a “local patch quality” perspective. This alternative approach revealed the positive importance of large focal patches of forest >60 years old and their content of old-growth (pine) forest (>100 years). Interestingly, at the landscape level, the frequency distribution of patches of forest >60 years old, old-growth (>100 years), and especially of old-growth pine forest (>100 years), relative to the properties of plots with C. rufocanus, suggested that there are few forest patches left that are suitable for C. rufocanus. Our current results suggest that habitat fragmentation cannot be excluded as a contributing cause to the long-term decline of C. rufocanus in boreal Sweden.