The dynamic interplay between anthropogenic activities and biodiversity conservation necessitates a nuanced understanding of habitat change, especially in contexts marked by transitions from grasslands to forested areas. This investigation utilised three threatened butterfly species-the Marsh Fritillary, Apollo, and Large Blue-as models to explore how grassland associated species respond to altered environmental conditions. The methodology encompassed extensive field surveys and statistical analyses with ecological niche modelling to determine their current and future distributions on the Island of Gotland. The species were surveyed under distinct years from 2017 to 2020 in a total of 3333 hectares in a 6000 hectare area-the Marsh Fritillary in 2017 (1232 hectares), Apollo in 2019 (2346 hectares), and Large Blue in 2020 (2256 hectares). Results revealed that the estimated current extents of suitable habitats were 49,104 hectares for the Marsh Fritillary (15.6% of the island), 45,646 hectares for Apollo (14.5%), and 33,089 hectares for Large Blue (10.5%). In general, increased forest and shrub cover and decreased heterogeneity negatively affected butterfly occupancy, but each species exhibited unique habitat preferences. The predictive modelling demonstrated that continued succession would reduce the amount of habitats predicted to be suitable and generated alarming forecasts-a twofold increase in forest and shrub cover suggests habitat declines of 41%, 47%, and 65% for the Marsh Fritillary, Apollo, and Large Blue, respectively. Given these findings, proactive measures are imperative for strategically managing these habitats to preserve landscape heterogeneity and accommodate diverse ecological needs. This study is important to conservation management providing, crucial insights amid anthropogenic and ecological changes.

1. Established butterfly survey methods that are useful for monitoring species that are widely distributed and numerous may be less accurate for more rare species. We therefore need new monitoring approaches.2. We describe a plot-based survey method, where butterflies or larvae nests are counted within 1-ha grid cells. The aim was to compare this grid method with more traditional transect counts and evaluate both methods in relation to high-quality capture-mark-release (CMR) population estimates (reflecting the true population). We do this using data from a large population of the marsh fritillary butterfly in Sweden. Moreover, we followed the overall population trend from 2017 to 2021 for both adult butterflies and larvae.3. Results showed a higher detection probability using the grid method compared with transect counts, which for adult butterflies seem to be explained by time effort. Moreover, grid surveys of adult butterflies showed a clear significant relationship with the estimated true population size from CMR, while transect counts did not. For larvae, both methods showed significant relationships with the estimated adult population size, but the grid method found 5.7 times more larvae. The overall popu-lation fluctuated significantly across years. In years with low densities, the transect method largely failed to detect the species.4. The grid method seems more reliable for detecting the marsh fritillary and for estimating its population size, and thus, tracking the population trend. We propose this novel method to be integrated into surveys and monitoring of biodiversity, especially when focusing on rare habitat specialists that are normally underrepre-sented in monitoring based on volunteer counts.

Species-rich semi-natural grasslands have been lost during the last century due to agricultural intensification. This has had large negative consequences for many specialised species, including grassland butterflies. To prevent further loss, management regimes in the remaining grasslands must maintain habitat quality over time, and we therefore need to understand the habitat preferences of specialised species and how different management regimes affect their survival. We studied the egg-laying preferences of the threatened marsh fritillary butterfly in relation to host plant properties, microclimate and management (grazing) on Gotland, Sweden. Moreover, we followed the survival of eggs and larvae from 27 egg batches during a period of 8 months (from June 2020 to March 2021) in grazed and ungrazed areas. We found 92 egg batches in total and the average number of eggs was 184.5. Egg-laying probability increased with increasing host plant size and abundance, and environmental variables associated with a warm microclimate (low grass cover, low vegetation height and south-facing edges). The 27 egg batches that were followed over time had on average 203 eggs in June. Roughly 28% of the eggs developed into larvae, and about 17% of these survived over the entire study period, resulting in an overall 4.7% survival. Egg survival was higher in ungrazed habitats compared with grazed; in March (post-hibernation), there were almost nine times more eggs in ungrazed habitats. This study highlights the complex habitat ecology of specialised butterflies and underscores the detrimental impact of intense grazing, advocating for rotational grazing or mowing regimes. We study oviposition preferences and survival of both eggs and larvae (post-hibernation) for the marsh fritillary, in relation to host plant availability, microclimate conditions and grazing management Egg-laying probability increased with increasing host plant size and abundance, and environmental variables associated with a warm microclimate (low grass cover, low vegetation height and south-facing edges) Egg survival was clearly higher in ungrazed habitats compared with grazed; in March (post-hibernation), there were almost nine times more eggs in ungrazed habitats. image

In Europe, Natura 2000 sites should protect threatened target species and networks of habitats. The management of Natura 2000 grasslands is often financed by subsidized grazing as part of the Common Agricultural Policy (CAP). We studied the extent of CAP grazing for Natura 2000 management and how this affects a butterfly target species (the marsh fritillary) and floral resources. Based on extensive capture-mark-release studies from 2 years in >550 ha grid cells in a 225 km(2) landscape in Sweden that includes 15 Natura 2000 sites, we compared marsh fritillary occurrence probabilities and population densities in ungrazed and CAP-grazed habitats. Moreover, we analyzed how nectar resources and orchids were affected by CAP grazing based on plants records from 2347 sample plots. We estimated the proportion of butterfly habitats that were CAP-grazed within and outside Natura 2000 sites. In total, 10 453 and 4417 butterflies were marked in 2017 and 2019, respectively. The grid cell occurrence probability was 1.8 times higher and the population density was 2.3 times higher in ungrazed compared with CAP-grazed habitats in 2017, and the corresponding numbers for 2019 were 10 and 5.3 times higher, respectively. The number of flowering plants were on average 6.9 times higher and the density of orchids was 12.3 times higher in ungrazed habitats. Roughly, 30% (130 ha) of the marsh fritillary habitat was CAP grazed, and 97% of this grazing occurred within protected areas, of which 111 ha was situated within Natura 2000 area where the marsh fritillary is the target species. Alarmingly, we show that intense yearly CAP grazing, which is the dominant management strategy in all Natura 2000 sites, has devastating consequences for the target species and other aspects of biodiversity. Less intense management, which would benefit biodiversity, requires changes in the CAP, to allow more flexible payments for habitat management objectives and conservation of target species.

Questions

Do burn severity and soil chemistry drive species and trait composition on recently burned clear-cuttings? Does the spatial distribution of common, easily dispersed colonizers vary with distance to fire perimeter?

Location

A 13,000 ha production forest landscape in boreal southern Sweden burned in a wildfire in 2014.

Methods

Vascular plants and bryophytes were recorded in permanent plots on clear-cuts two and five years following fire, covering a burn severity gradient. Soil carbon content (reflecting burn severity), pH and nutrients were measured at plot level. Trait data were retrieved from the BIEN and LEDA databases and analyzed using community-weighted mean (CWM) trait values. Statistical analyses included generalized linear mixed models (GLMMs), non-metric multidimensional scaling (NMDS) and multivariate ANOVA.

Results

Low burn severity resulted in higher frequency of legacy species (e.g. Vaccinium myrtillus), while high burn severity facilitated colonizing species (e.g. Senecio sylvaticus). Vegetation varied with soil chemistry, expressed through pH. Species composition changed between years and deviated from unburned clear-cuts. After five years the most common taxa on burned plots were the vascular plants Chamaenerion angustifolium, Betula spp. and Populus tremula and the bryophytes Ceratodon purpureus and Polytrichum juniperinum. CWM specific leaf area (SLA) decreased markedly with time and root buds increased with total carbon content in the soil (i.e., toward less severely burned plots), while soil pH was not associated with any studied trait. Chamaenerion angustifolium decreased with distance to the fire perimeter, while Ceratodon purpureus increased.

Conclusions

Burn severity and soil pH weakly drive vegetation dynamics in the early phase following fire on clear-cuts, indicating a large influence of stochastic processes. Deciduous trees are common already after five years and their further expansion will affect light and nutrient availability. To understand future vegetation trajectories on burned clear-cuts, studies need to incorporate the light factor and links between tree species’ identity and soil nutrient availability.

1) Extreme weather events can be expected to increase in frequency in the future. Our knowledge on how this may affect species persistence is, however, very limited. For reliable projections of future persistence we need to understand how extreme weather affects species' population dynamics.

2) We analysed the effect of extreme droughts on the host plant Succisa pratensis, colonization–extinction dynamics, and future persistence of the threatened marsh fritillary Euphydryas aurinia. Specifically, we studied a metapopulation inhabiting a network of 256 patches on Gotland (Sweden), where the summer of 2018 was the driest ever recorded. We analysed how the frequency and leaf size of host plants changed between 2017 and 2019, based on 6,833 records in 0.5-m2 sample plots. Using turnover data on the butterfly from 2018 to 2019 we modelled local extinction and colonization probabilities. Moreover, we projected future population dynamics with an increasing frequency of extreme years under three different management strategies that regulate the grazing regime.

3) Our results show a substantial decrease in both frequency (46%) and size (20%) of host plants due to the drought, which taken together may constitute a 57% loss of food resources. The butterfly occupancy decreased by over 30% between 2018 and 2019 (from 0.36 to 0.27). The extinction probability increased with increasing ‘effective area’ of the patch (taking quality reduction due to grazing into account), and the colonization probability increased with increasing connectivity and ground moisture.

4) Projections of future dynamics showed an increasing risk of metapopulation extinction with increasing frequency of years with extreme droughts. The risk, however, clearly differed between management strategies. Less grazing in years with droughts decreased the extinction risk considerably.

5) Synthesis and applications. Extreme weather events can have profound negative impacts on butterflies and their host plants. For the marsh fritillary, an increased frequency of extreme droughts can lead to extinction of the entire metapopulation, even in a large and seemingly viable metapopulation. Increased grazing, due to fodder deficiency in dry years, may lead to cascading negative effects, while active management that reduce grazing in years with droughts can almost completely mitigate these effects.

Insect pollinators are declining, which often is related to intensified agriculture. Less focus has been on the effect of forestry. In many boreal forests, clear-cutting has replaced fire as the main disturbance agent, which has been negative for many species. Therefore, prescribed burning is performed, often on clear-cuts. Knowledge on the effect of fire on pollinators is, however, scarce. We sampled pollinators and their resources in 22 burned and 15 unburned clear-cuts in and around a large wildfire area in Sweden, three years after fire. We compared potential pollinator resources as well as richness, abundance and community composition of four groups of pollinators: bees (totaling 583 individuals), wasps (1226), hoverflies (416), and butterflies (7 2 8) between burned and unburned clear-cuts. Moreover, we analyzed the effect of burn severity (depth of remaining humus). We show that the diversity and cover of potential nectar/pollen plants were clearly lower in burned clear-cuts, while potential nesting resources were higher. Butterfly richness was 67% lower and abundance 89% lower in burned clear-cuts. Differences in richness and abundance were smaller for bees, wasps, and hoverflies, but their species composition differed. We found no effect of burn severity on pollinators or their resources. We conclude that burned clear-cuts have fewer pollinators three years after fire, which is driven by a loss of butterflies. However, changes in species composition from clear-cut fires could complement the fauna of unburned sites when mixed at landscape level. Future studies should follow vegetation and pollinator communities over longer time periods following clear-cut burning

Grazing generally benefits grassland biodiversity as it prevents shrub and tree succession. However, too intense grazing may have negative effects for example many grassland insects. EU-subsidies for grazing of some habitats, aimed at promoting biodiversity, still require a relatively intense grazing, and could therefore have negative consequences for some species. We quantified how such grazing affects habitat quality for the marsh fritillary butterfly, and how this influence its colonization-extinction dynamics and persistence. Specifically, we studied a metapopulation on Gotland (Sweden), where the marsh fritillary occupies unfertilized calcareous grassland with a naturally slow succession. We quantified the difference in larvae autumn nests between grazed and ungrazed habitat, and used this difference to adjust the ‘effective area’ of 256 habitat patches in a 50 km2 landscape. We then parameterized a metapopulation model based on the occurrence pattern of the adult butterfly, and simulated future population development under different grazing regimes. The results showed that ungrazed habitat harbored 4.8 times more nests than grazed habitat. Reducing the ‘effective area’ of grazed patches accordingly increased the local extinction probability and decreased colonization. Grazing all suitable habitat reduced the occupancy by over 80%, while no grazing increased the occupancy by up to 40%, based on projections of future dynamics. Current grazing is clearly too intense, and EU-subsidies are here, thus, a conservation measure with negative consequences for a threatened butterfly. To prevent this, subsidies for grazing need to be more flexible and better adapted to the prevailing soil conditions and requirements of the target species.

Protected areas are a key component in biodiversity conservation strategies, but evaluations of how effective they are in capturing species diversity is lacking for many ecosystems. We compared different protection types (animal sanctuaries, nature reserves and unprotected areas) using data on species richness and occurrence of coastal breeding bird species in a large archipelago in the Baltic Sea. Data were from extensive inventories based on a grid with 1 × 1 km resolution covering 4646 km2 on the East coast of Sweden. We focused on specialist species breeding exclusively in coastal habitats since these species are of specific conservation concern, but considered generalists, which also breeds in inland wetlands, as well. Animal sanctuaries had significantly higher species richness of specialist species than unprotected areas and nature reserves. Nature reserves had even lower richness of specialist species than unprotected areas. Further, a rarity-weighted diversity index showed that animal sanctuaries were better in capturing hotspots of bird diversity compared to nature reserves and unprotected areas. Hotspots, both protected and unprotected, were scattered throughout the entire archipelago. The rarity-weighted richness is therefore useful to identify gaps in the protected area network. Overall, we conclude that the establishment of animal sanctuaries has been a successful conservation measure for protecting specialist species in several aspects. Ongoing human exploitation of the Baltic archipelagos prompt further consideration of protecting still unprotected but species rich shorelines for the benefit of many coastal breeding birds.