Aim
Species distribution models (SDMs) are widely used to make predictions on how species distributions may change as a response to climatic change. To assess the reliability of those predictions, ...they need to be critically validated with respect to what they are used for. While ecologists are typically interested in how and where distributions will change, we argue that SDMs have seldom been evaluated in terms of their capacity to predict such change. Instead, typical retrospective validation methods estimate model's ability to predict to only one static time in future. Here, we apply two validation methods, one that predicts and evaluates a static pattern, while the other measures change and compare their estimates of predictive performance.
Location
Fennoscandia.
Methods
We applied a joint SDM to model the distributions of 120 bird species in four model validation settings. We trained models with a dataset from 1975 to 1999 and predicted species' future occurrence and abundance in two ways: for one static time period (2013–2016, ‘static validation’) and for a change between two time periods (difference between 1996–1999 and 2013–2016, ‘change validation’). We then measured predictive performance using correlation between predicted and observed values. We also related predictive performance to species traits.
Results
Even though static validation method evaluated predictive performance as good, change method indicated very poor performance. Predictive performance was not strongly related to any trait.
Main Conclusions
Static validation method might overestimate predictive performance by not revealing the model's inability to predict change events. If species' distributions remain mostly stable, then even an unfit model can predict the near future well due to temporal autocorrelation. We urge caution when working with forecasts of changes in spatial patterns of species occupancy or abundance, even for SDMs that are based on time series datasets unless they are critically validated for forecasting such change.
•Many farmland birds and butterflies use forest clear-cuts.•Clear-cut characteristics of importance include size and landscape composition.•The fact that farmland species use clear-cuts opens ...exciting tracks for research.•The potential of clear-cuts is worth attention from a conservation perspective.
The intensification of agriculture has resulted in more homogeneous landscapes and declines of many species associated with farmland or other semi-natural open habitats. In parallel, forestry has also intensified causing declines in many species associated with old-growth forests. While intensive forestry negatively affects forest species, it inadvertently creates new habitats such as clear-cuts, which attracts some farmland species. To understand the potential of clear-cuts as alternative habitat for farmland species, we need to know what makes clear-cuts attractive and whether they are suitable for reproduction and survival. We reviewed literature on the occurrence of farmland birds and butterflies in forest clear-cuts and synthesise the current knowledge on factors and characteristics affecting their occurrence.
Many farmland birds and butterflies do indeed use clear-cuts, and have been found in clear-cuts up to ten years after felling. Clear-cut characteristics of importance include age, size, retention structures, land-use history and landscape composition. However, direct measures of resource abundance such as food and hostplants are often lacking. In addition to the potential benefit of individual clear-cuts, the total clear-cut area in forested regions is often large. Together with the fact that clear-cuts may be occupied by farmland species for several years, the potential of clear-cuts as alternative habitat for farmland biodiversity is substantial. Clear-cuts with a history as meadows, the presence of species of conservation importance, or shorter distance to farmland could for example be motivations for focusing conservation efforts on farmland species instead of forest species. Gaining more knowledge on how farmland species use clear-cuts, and what characteristics they depend on, could help inform management guidelines. We are no advocates for forest clear-cuts, but given their ubiquity in forested landscapes, the potential of clear-cuts as alternative habitats for species suffering from loss of suitable farmland habitats is worth serious attention from a conservation perspective.
AIMS: Climate change is known to drive both the reshuffling of whole assemblages and range shifts of individual species. Less is known about how local colonizations and extinctions of individual ...species contribute to changes at the community level. Our aim was to estimate the contribution of individual species to a change in community composition attributed to climate change and to relate these species‐specific contributions to species’ commonness, climatic niche characteristics and life history traits most likely to influence species sensitivity to climate change. LOCATION: Sweden. METHODS: Focussing on birds, we analysed changes from 1998 to 2012 in the Community Temperature Index (CTI), a measure of the average climatic niche of a community. Using a jackknife approach we assessed the contribution of individual species to the temporal trend in CTI in four different regions across Sweden, controlling for habitat distribution. We further tested whether species contribution was related to population trends and rarity to identify species most vulnerable to climate change. RESULTS: Community Temperature Index had increased over time with the greatest gains occurring in the north of the country, reflecting the larger temperature increases in this area. Changes in the regional CTI were driven both by warm‐dwelling species colonizing new sites and by extirpations of cold‐dwelling species. Furthermore, the community changes were influenced by both rare and common species. At the same time, the distribution changes of a large number of species were seemingly unaffected by climate change. MAIN CONCLUSIONS: Both range expansion and contractions contributed to the relative increase of warm‐dwelling species in Swedish bird communities. We successfully identified the climatic impacts on some of Sweden's rarest species, including cold‐dwelling species in the mountainous north. Our approach may be an efficient tool to use when characterizing the impacts of climate change on species and communities.
Climate change is pushing species ranges and abundances towards the poles and mountain tops. Although many studies have documented local altitudinal shifts, knowledge of general patterns at a large ...spatial scale, such as a whole mountain range, is scarce. From a conservation perspective, studying altitudinal shifts in wildlife is relevant because mountain regions often represent biodiversity hotspots and are among the most vulnerable ecosystems. Here, we examine whether altitudinal shifts in birds’ abundances have occurred in the Scandinavian mountains over 13 years, and assess whether such shifts are related to species’ traits. Using abundance data, we show a clear pattern of uphill shift in the mean altitude of bird abundance across the Scandinavian mountains, with an average speed of 0.9 m per year. Out of 76 species, 7 shifted significantly their abundance uphill. Altitudinal shift was strongly related to species’ longevity: short-lived species showed more pronounced uphill shifts in abundance than long-lived species. The observed abundance shifts suggest that uphill shifts are not only driven by a small number of individuals at the range boundaries, but the overall bird abundances are on the move. Overall, the results underscore the wide-ranging impact of climate change and the potential vulnerability of species with slow life histories, as they appear less able to timely respond to rapidly changing climatic conditions.
Although climate change is acknowledged to affect population dynamics and species distribution, details of how community composition is affected are still lacking. We investigate whether ongoing ...changes in bird community composition can be explained by contemporary changes in summer temperatures, using four independent long-term bird census schemes from Sweden (up to 57 yr); two at the national scale and two at local scales. The change in bird community composition was represented by a community temperature index (CTI) that reflects the balance in abundance between low- and high-temperature dwelling species. In all schemes, CTI tracked patterns of temperature increase, stability or decrease remarkably well, with a lag period of 1–3 yr. This response was similar at both the national and local scale. However, the communities did not respond fast enough to cope with temperature increase, suggesting that community composition lags behind changes in temperature. The change in CTI was caused mainly by changes in species' relative abundances, and less so by changes in species composition. We conclude that ongoing changes in bird community structure are driven to a large extent by contemporary changes in climate and that CTI can be used as a simple indicator for how bird communities respond.
•Birds were counted on 300 forest clear-cuts over a large geographical area.•Several bird species typical to farmland were regularly found.•Their abundance depended on clear-cut age and size, and ...landscape characteristics.•Other farmland bird species clearly avoided forest clear-cuts.•The full significance of clear-cuts to farmland birds remains to be determined.
Many bird species typical to farmland have declined in numbers in recent decades. Some farmland bird species occur outside farmland in other open man-made habitats, such as forest clear-cuts. Given that in Sweden the total area of clear-cuts (5–6 %) almost equals that of farmland (8 %), clear-cuts have the potential to be an important habitat for some farmland birds. We investigated how bird community composition and species abundance on Swedish clear-cuts varied with geographical region, clear-cut characteristics and the surrounding landscape, with special focus on farmland species. Based on short visits in 2017–2019, we surveyed the occurrence of birds on 300 representative clear-cuts in Sweden, including six regions and 1300 km of latitude. We counted 1170 birds of 66 different species, including 10 out of 15 bird species in existing farmland bird indicators. Both bird community composition and species abundance varied with clear-cut size, age, vegetation height, region and proportion of nearby farmland, depending on species’ ecology. All six farmland species being proportionally common on clear-cuts are, when in farmland, dependent on residual habitats such as pastures and field borders with bushes and trees. In contrast, a third of the dedicated farmland species were scarce in clear-cuts, probably avoiding them because of predator-related avoidance of forest edges and/or a lack of suitable nest sites or food resources. To determine the full importance of forest clear-cuts for farmland species, and potentially make them more favourable for farmland birds, more studies are needed on the reproductive success on clear-cuts and which site features make them suitable habitat. This study did not determine the consequences of clear-cuts for forest birds across the forest cycle, consequences which needs to be balanced against any gains for farmland birds.
•Biodiversity assessments in dominant production forest types is often lacking.•We synthesized results of bird surveys in Sweden’s Norway spruce production stands.•Whereas common forest birds ...dominate, rare and decreasing species were also found.•Broadleaf trees and increased structural complexity increased bird species richness.•Some adjustments to forest management would readily benefit avian biodiversity.
Forests used for timber production provide essential ecosystem services to society, as well as potential breeding habitat for bird communities. In southern Sweden, 90% of productive forest land is used for timber production and stands dominated by Norway spruce (Picea abies) constitute approximately 40% of the forested area. Due to their homogeneous structure, these spruce production forests are often regarded as depauperate. Despite this perception, knowledge about the biodiversity found in these stands is scarce. Here we synthesize the results of four separate bird surveys conducted within 35 spruce production stands of southern Sweden. The results are compared to recent population trends within the general study area. In total 49 bird species were recorded, with a strong difference in species composition between newly planted clear-cuts (forest age <15years) and forests older than 15years. The majority of species encountered in the older forest category were common forest birds, with a single red-listed species among the regularly occurring species. In contrast, three red-listed “farmland species” were frequently encountered in the newly planted forests, revealing the capacity of those birds preferring open and recently disturbed habitats to utilize clear-cuts. A higher diversity of tree sizes and the inclusion of even relatively small proportions (<15%) of broadleaved tree species had a positive effect on bird species richness. Several species encountered in spruce production forests are declining in numbers, but it is not clear whether these stands are acting as source or sink environments for their populations. However, our results indicate that relatively small adjustments to spruce forest management should improve the quality of this widespread habitat.
The effect that extreme natural events have on biological diversity is relatively poorly known. We used a before–after control‐impact (BACI) design to analyze changes in bird abundances and ...communities following Hurricane Gudrun, which struck southern Sweden in January 2005, felling 75 million m3 of forest and causing damage to 5% of forested areas (half a million hectares) in a few hours. We used recent measures of impact in combination with classical BACI contrasts to analyze bird count data from a monitoring program in Sweden. We investigated changes in the abundance of 17 species commonly found in forests, along with changes in species composition and functional structure of the bird community. In total, we considered 34 response variables and examined whether responses were immediate or long‐term. There was no evidence of a strong effect of the hurricane on the abundances of six species. Estimates of the effects on five species were too uncertain to draw inferences. We detected positive and negative effects of the hurricane on the abundances of the remaining six species, but the magnitude of effects often was small. Generally, the effects were in the expected direction: negative on birds associated with mature forest and positive on birds associated with open land or young forest. We found evidence of an increase in the proportion of species that nest on the ground and a decrease in the proportion of species that nest in cavities and trees. In contrast, the hurricane had no discernible effect on functional measures of diversity (richness, evenness or divergence), or on communities’ reproductive or morphological characteristics. Our results suggest that the hurricane affected bird populations and communities, but the magnitude of effects was generally small.
1. The widespread declines of farmland birds have generally been linked to agricultural intensification. We tested the hypotheses that (i) changes in agricultural policy, through its effects on ...agricultural intensification and (ii) regional differences in agricultural intensification affect temporal and spatial population trends of farmland birds in Sweden. 2. We analysed regional bird population trends (1976-2003) for seven common farmland bird species: the migratory lapwing Vanellus vanellus, skylark Alauda arvensis, starling Sturnus vulgaris and linnet Carduelis cannabina and the resident tree sparrow Passer montanus, house sparrow P. domesticus and yellowhammer Emberiza citrinella. We identified three periods of agricultural policy in Sweden between 1976 and 2003: the intensification period (i.e. 1976-87; promoting increased production), the set-aside period (1987-95; promoting extensification of farming) and the Common Agricultural Policy (CAP) period (1995-2003; promoting increased production). Population trends were compared between three types of Swedish farmlands: open plains (intensive farming with a marked intensification), mosaic farmlands (i.e. farmland-dominated forest mosaics, less intensive farming, but show moderate intensification) and forest regions (i.e. forest-dominated farmlands with low intensity farming and extensification/abandonment). 3. The four migrants displayed clear significant trend switches between the policy periods, with declines in the 'intensification period' and the 'CAP period' and less negative or even positive population trends in the 'set-aside period'. The population trends of the three resident species showed no clear pattern in relation to agricultural policy periods. 4. All species except tree sparrow displayed significantly different population trends between farmland regions. Four species (lapwing, skylark, linnet and house sparrow) declined most in the open plains and the forest regions, whereas two species (starling and yellowhammer) declined most in the mosaic farmlands. 5. Synthesis and applications. Large-scale changes in agriculture policy have a strong potential to change the present poor state of farmland biodiversity as shown by the generally positive population trends in the 'set-aside period'. It also suggests extensification to be beneficial to farmland birds. However, in regions of low profitability and an already ongoing extensification, a further extensification will lead to loss of both farmland habitat and bird diversity. In such regions mixed farming needs to be retained and hence should be supported.
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