Quantifying the effects of habitat fragmentation presents challenges due to the complexity of landscape-scale habitat configuration and its interaction with landscape and local processes. While patch-scale studies contribute valuable insights, extrapolating their findings to landscape scales is problematic due to the influence of landscape-scale processes. We used structural equation modelling to examine the direct and indirect effects of landscape-scale attributes around sampled forest patches including forest amount, edge density, number of patches, mean patch size, and mean interpatch distance, and patch- or plot-scale attributes including focal patch size, focal patch isolation, sample plot distance to forest edge, within-plot microhabitat heterogeneity, and plot soil pH, on species richness of woodland specialist plants in 16 sample plots within each of 97 British woodlands ('focal patches'). We find direct positive effects on woodland specialist richness of: (i) forest edge density in the landscape, suggesting positive effects of fragmentation per se, (ii) distance to forest edge of the sample plot, suggesting negative local edge effects, (iii) focal patch area, (iv) within-plot heterogeneity and (v) within-plot soil pH. We also find indirect positive effects of: (i) forest amount in the landscape through its indirect correlations to focal patch size and distance to forest edge, and (ii) number of forest patches in the landscape, through its correlation with edge density in the landscape. Synthesis. Our results suggest positive effects of fragmentation per se, that is fragmentation controlling for forest amount, on richness of specialist forest plants, despite their negative local edge response. This confirms that cross-scale extrapolation is not valid in habitat fragmentation research: negative patch-scale edge effects do not scale up to produce negative landscape-scale fragmentation effects. Cuantificar los efectos de la fragmentaci & oacute;n del h & aacute;bitat presenta dificultades debido a la complejidad de la configuraci & oacute;n del h & aacute;bitat a escala de paisaje y su interacci & oacute;n con los procesos locales y de paisaje. Aunque los estudios a escala de mancha aportan informaci & oacute;n valiosa, extrapolar sus resultados a escalas de paisaje es problem & aacute;tico por la influencia de los procesos que operan a esa escala. Utilizamos modelos de ecuaciones estructurales para examinar los efectos directos e indirectos de atributos a escala de paisaje en torno a las manchas forestales muestreadas-incluyendo la cantidad de bosque, la densidad de bordes, el n & uacute;mero de manchas, el tama & ntilde;o medio de mancha y la distancia media entre manchas-y de atributos a escala de mancha o parcela-incluyendo el tama & ntilde;o de la mancha focal, el aislamiento de la mancha focal, la distancia de la parcela de muestreo al borde del bosque, la heterogeneidad de microh & aacute;bitat dentro de la parcela y el pH del suelo-sobre la riqueza de especies de plantas especialistas de bosque en 16 parcelas de muestreo dentro de cada uno de 97 bosques brit & aacute;nicos (& laquo;manchas focales & raquo;). Encontramos efectos directos positivos sobre la riqueza de especialistas forestales de: (i) la densidad de bordes del bosque en el paisaje, lo que sugiere efectos positivos de la fragmentaci & oacute;n per se; (ii) la distancia al borde del bosque de la parcela de muestreo, lo que sugiere efectos de borde negativos a escala local; (iii) el & aacute;rea de la mancha focal; (iv) la heterogeneidad dentro de la parcela; y (v) el pH del suelo dentro de la parcela. Tambi & eacute;n encontramos efectos indirectos positivos de: (i) la cantidad de bosque en el paisaje, a trav & eacute;s de sus correlaciones indirectas con el tama & ntilde;o de la mancha focal y la distancia al borde del bosque, y (ii) el n & uacute;mero de manchas forestales en el paisaje, a trav & eacute;s de su correlaci & oacute;n con la densidad de bordes. S & iacute;ntesis. Nuestros resultados sugieren efectos positivos de la fragmentaci & oacute;n per se-es decir, la fragmentaci & oacute;n controlando la cantidad de bosque-sobre la riqueza de plantas especialistas de bosque, a pesar de su respuesta negativa al borde a escala local. Esto confirma que la extrapolaci & oacute;n entre escalas no es v & aacute;lida en la investigaci & oacute;n sobre fragmentaci & oacute;n del h & aacute;bitat: los efectos negativos de borde a escala de mancha no se traducen en efectos negativos de fragmentaci & oacute;n a escala de paisaje.

Road development has expanded globally, with growing recognition of the impacts on freshwater systems. We synthesized findings from 426 publications to assess (1) where and for which freshwater taxa road effects have been studied; (2) the types of roads and stressors examined; (3) the study designs and biological responses measured; and (4) the reported road effects on freshwater taxon. Most studies were conducted in North America (62.1%), with the overall evidence base focusing on amphibians (36.1%), fish (14.8%), and reptiles (10.9%) in ponds/wetlands, laboratory settings, and streams. Research primarily assessed the impacts of road density or proximity (20%), traffic (18.4%), and salt/de-icers (17.9%) stressors, mostly using impact-only (51.0%) and control-impact (46.5%) study designs, restricting causal inference. Demographic, diversity, and mortality responses were the most frequently measured outcomes. Road effects were predominantly negative, underscoring widespread road impacts on freshwater taxon. Major knowledge gaps included understudied taxa (avifauna, mammals, crustaceans, molluscs, insects, plants), life-stages (eggs, juveniles), and several stressors. Future research should focus on addressing the knowledge gaps and apply comparative approaches to improve understanding and management.

Habitat restoration is needed to increase total habitat area, and halt and reverse global biodiversity loss. While scientists and conservation practitioners generally agree that more habitat is better for biodiversity, the preferred spatial arrangement of that habitat in a landscape is debated. The weight of evidence from empirical studies indicates that we can expect biodiversity to be weakly but positively related to fragmentation per se (the spatial arrangement of habitat, independent of its amount) across landscapes that have undergone habitat loss. Can we expect the same in a restoration context? Spatial variation in forest gain and loss provides an opportunity for a ‘natural experiment’ to address the question posed above, allowing assessment of the interactive effects of fragmentation per se and the history of habitat change on biodiversity. Here we used a two‐decade time series of forest cover plus data on forest breeding birds from 1660 locations across the conterminous United States to test whether bird diversity (richness, Shannon diversity, Simpson diversity) responses to forest fragmentation per se depend on the history of forest gain/loss. The effects of forest fragmentation per se on forest bird diversity depended on whether forest had been previously gained or lost. There were stronger, more positive effects of fragmentation on bird diversity in landscapes where forest had been gained than in landscapes where forest had been lost. Critically, effects of forest amount on bird diversity were much stronger than fragmentation, regardless of the history of forest area changes. Synthesis and applications . Our results suggest that, at least for forest breeding birds, the benefits of habitat restoration to increase total forest area could be enhanced by distributing a given amount of restored habitat across multiple patches. Our study also highlights the overarching importance of habitat amount for biodiversity conservation. Taken together, these findings imply that, if we want to maximize the benefits of restoration for biodiversity, the focus should be on maximizing total habitat area and increasing the number of habitat patches.

A key aspect of the fragmentation debate in conservation biology is whether fragmentation effects on biodiversity should capture the combined or separate effects of habitat loss and fragmentation, i.e., breaking apart of habitat into multiple patches. A common argument for treating loss and fragmentation as a single phenomenon is that human-caused habitat loss almost always leads to fragmentation. Here we assessed whether forest loss consistently results in fragmentation, at a global extent and across spatial scales commonly considered in landscape ecology. We evaluated how often forest loss resulted in a decrease versus increase in fragmentation for 150,000 randomly-selected forest locations. We delineated landscapes of six sizes (radii of 0.25 to 10 km) at each location. For the subset of landscapes that lost forest between 2000 and 2020, we estimated the change in fragmentation using four different measures of fragmentation. A decrease in forest fragmentation was a common outcome of forest loss. Across four measures of fragmentation, six landscape sizes, and all forested biomes, we found forests were more fragmented after forest loss 51

To determine whether we can reduce the impacts of forest loss on biodiversity by altering forest pattern, we need to estimate the effects of forest pattern independent of forest amount. We evaluated the independent and interactive effects of forest amount, fragmentation, and connectivity (wooded corridors) on diversity of forest-associated plants, small mammals, and birds. We selected 70 forest sites in eastern Ontario, Canada with low correlations between these landscape predictors. We found positive effects of forest amount, neutral or positive effects of forest fragmentation, and an interaction effect between connectivity and forest amount. In landscapes with low forest amount, biodiversity increased with connectivity, while at high forest amount, biodiversity decreased with connectivity. Thus, forest patches should be protected regardless of size, and conservation actions aimed at improving connectivity by adding wooded corridors should be prioritized in areas where forest is scarce, for example agricultural and urban areas.

Roads, railways, power lines, and other linear infrastructure benefit the growing economy but also impact biodiversity. Environmental Impact Assessments (EIAs) are a key process that should guarantee that biodiversity loss is avoided or mitigated on linear infrastructure projects. Long-term population persistence can be compromised near infrastructure if their impacts are reducing population abundance. This is why the mere presence of an animal population near an infrastructure is not enough to infer that this infrastructure is or is not having an impact and there is a need to monitor population abundance trends. However, population-oriented approaches are rare in studies focused on the impacts of linear infrastructure. We suggest that the best way to evaluate genuine impacts is to include wildlife population abundance among the metrics to be measured in EIAs and monitored in follow-up studies. Population abundance and its trend are good proxies to evaluate the impact of linear infrastructure on the health of local populations and their persistence probability.

Increasing ecological connectivity among urban greenspaces is a global conservation priority to protect urban wildlife. However, effective monitoring remains a challenge, as connectivity models are rarely validated against biological data despite the need for these models to represent real wildlife movement. Here, we systematically reviewed the urban connectivity literature to assess (i) the extent of connectivity model validation; (ii) how validation varies by study objectives; (iii) where urban connectivity research is conducted; and (iv) what types of connectivity metrics, taxa, and biological data are used. Of the 430 studies reviewed, nearly half validated their connectivity models using biological data, but few used movement data. Structural connectivity metrics dominated, although use of functional metrics has increased in recent years. A clear taxonomic bias was also evident, with a disproportionate focus on birds. When validation was conducted, most relied on species richness or other biodiversity metrics. Such approaches offer ambiguous evidence for actual connectivity, as biodiversity patterns are often influenced by confounding factors like greenspace size and the speciesarea relationship. As such, direct empirical support for connectivity models capturing wildlife movement remains limited. Urban connectivity models are often applied without clear evidence that they represent actual ecological processes. To address this, future studies should incorporate a broader range of taxa and test multiple model types to disentangle how movement patterns align with different connectivity frameworks. Integrating biological validation, particularly movement data, into connectivity modelling is essential to tracking progress toward global goals for ecologically resilient cities.

Small habitat patches are commonly overlooked in conservation. This is partly due to the legacy of the SL > SS principle that few (or a Single) Large patches (SL) should protect species more effectively than Several Small patches (SS) of the same cumulative total habitat amount. Although most empirical studies have found either the reverse (SS > SL) or no difference (SL = SS), the original SL > SS principle is still widely assumed to be valid and particularly so for threatened taxa, such as most primates. Here, we tested the SL > SS principle using global data of primate patch occupancy in 1791 forest patches from 50 primate studies. We collated patch occupancy data across combinations of patches, and we evaluated whether combinations of SL patches have higher or lower primate occupancy (i.e., at least one patch occupied) compared to combinations of SS patches, while controlling for total forest amount. We find that, in most cases, SS and SL patches of the same cumulative habitat amount have equal occupancy. In the remainder of cases, we find a tendency for primate occupancy to be higher in combinations of SS than SL patches. This result holds regardless of a species' threatened status. These findings suggest that, even for threatened primates, the traditional SL > SS principle does not hold. They highlight the high cumulative importance of small forest patches for primates, and the need to increase their consideration in conservation.

We initially speculated that non-tropical North American (USA and Canada) small mammal abundances might have increased over the past several decades due to declines in mammalian predators. To test this idea we assembled from small mammal researchers 818 time series of small mammal abundances, containing a total of 5317 individual abundance data points, for 66 species in 21 genera. The resulting database is the largest collection of multi-year abundance data for North American small mammals. We then used a hierarchical Bayesian modelling approach to estimate an overall abundance trend. Contrary to our initial speculation, we found strong support for an overall decline in North American small mammal abundance, with an estimated annual decrease of 3.6 %. Sixty species trends were negative while only six were positive. Given this decline and given that small mammals are important for ecosystem function as prey items, as predators, and for seed dispersal, we suggest conservation efforts should be directed to this generally neglected group. In particular, we need further work to uncover the causes and consequences of small mammal declines, and to develop mitigation strategies to avoid further declines in North American small mammals.

Understanding habitat fragmentation effects on wildlife is critical to promoting effective conservation practices. There are many metrics of habitat fragmentation, from simple (number of habitat patches) to complex metrics designed to summarize many aspects of landscape patterns. To make meaningful inferences, we must understand how complex metrics are related to landscape patterns, especially to habitat amount. Here, we examine the behavior of the Edge Influence index, a metric that has been used in several influential recent studies and is designed to assess fragmentation and edge effects. Contrary to expectation, this index does not primarily quantify fragmentation or edge but rather habitat amount. Therefore, researchers should take this into consideration when interpreting the results of studies based on the Edge Influence index. To guide meaningful conservation action in fragmented landscapes, we recommend using simple, direct measures of fragmentation and separating the effects of habitat configuration from the effects of habitat amount.

In a previous meta‐analysis, mammals with large home ranges, low reproductive rates and large body sizes were found to respond most negatively to roads. However, due to correlations among these traits, it is not known whether these responses were due to a subset or all three traits. We conducted a multiple meta‐regression of the effects of species traits on mammal responses to roads, using data from 92 studies, to determine whether an analysis with a larger sample size and controlling for correlations among traits will support the previous findings. The results reinforce the findings that mammals with larger home ranges and lower reproductive rates respond more negatively to roads. Surprisingly, we found that when controlling for the effects of home range size and reproductive rate, larger mammals respond less negatively to roads than smaller mammals. We speculate that the positive effect of body size is due to driver avoidance of collisions with larger mammals and/or differences in road attraction and car avoidance behaviours of larger versus smaller species that allow larger mammals to extract benefits of roads while avoiding oncoming vehicles We also found high variability of individual responses to roads, above what could be explained by the species traits model, most likely due to site‐ and/or species‐specific characteristics. Synthesis and applications. Road mitigation for mammals should ideally be informed by site‐level knowledge and generally involve prioritizing species with the combination of larger home ranges, lower reproductive rates and smaller body sizes. To protect these vulnerable mammals from roads, we should maintain low road densities and instal small‐mesh mitigation fencing along roads. This differs from current road mitigation efforts which are typically targeted towards large mammals (e.g. large‐mesh fencing along roads) and are often ineffective for smaller mammals.

Global conservation strategies aim to increase the area of nature reserves. To implement this goal, especially in fragmented landscapes like Central Europe, we must understand whether a Single Large (SL) reserve Or Several Small (SS) reserves has higher species richness (SLOSS), and why. To date, most studies find more species in SS than SL (SS>SL). The most commonly invoked explanation is higher habitat heterogeneity across SS than SL. We assessed SLOSS for beetles, spiders and birds in 44 forest reserves of three forest types in Central Europe, and tested several predictions based on this heterogeneity hypothesis. We assessed SLOSS in two ways: Quinn-Harrison-curves, and a new approach, the 'SLOSS ratio' of species richness standardized by sample coverage, in SL vs. SS. As habitat heterogeneity is challenging to measure directly, we indirectly tested the heterogeneity hypothesis through the following predictions: the SS>SL pattern should be stronger (1) for taxa with finer space use, (2) when there are more SS reserves, spread over more area, (3) when the reserves have been established for a longer time, allowing divergence among patches, (4) when the SS reserves include multiple forest types, and (5) for forest types with a lower frequency of stand-replacing disturbances. We found SS>SL for all taxa, and we found support for three of the predictions based on the heterogeneity hypothesis: (1), (2), and (4). We infer that a set of many small forest reserves is an appropriate objective for conservation planning and can make a strong contribution to global conservation goals.

In a recent Opinion article, Watts and Hughes (W&H) suggest that habitat fragmentation is "generally bad for restoration." We found W&H timely given recent progress in the conversation on habitat fragmentation, and we agree on the importance of assessing habitat fragmentation in restoration ecology. At the same time, we found some claims in W&H to be unsubstantiated. We suggest that there likely are situations where fragmentation is "generally good" in a restoration setting, and we identify an urgent need to test empirically how biodiversity responds to fragmentation in a habitat restoration context. Such tests will tell us when the spatial pattern of restored habitat matters, informing the restoration efforts expected in the coming decades to fulfill recent historical commitments to sustain biodiversity globally.

The eastern migratory monarch butterfly (Danaus plexippus) population has declined by ∼84% between 1993 and 2024. Population recovery in the Midwestern United States is limited by the availability of the monarch's main host plant for egg laying—common milkweed (Asclepias syriaca). The extent to which common milkweed availability is limiting in other breeding regions is unknown. Our objective was to determine whether Canada has enough common milkweed to support its share of the trinational eastern migratory monarch population recovery target, given ∼29 stems of common milkweed are needed to contribute one adult monarch into the fall migratory population. To meet this objective, we estimated the number of common milkweed stems in Canada using published common milkweed availability estimates by land cover type. We also estimated the size of the Canadian monarch population if the recovery target was achieved using published estimates of wintering monarch density in Mexico, fall migration survival rates, and the relative proportion of monarchs entering fall migration from Canada. We estimate that Canada currently has 484 million common milkweed stems (range: 111 million–1 billion stems) and increasing this amount by 1.61 times (i.e., by ∼295 million stems), or equivalently, by 61%, would support the recovery target.

1. Restoration initiatives often target restoring the largest possible amount of habitat to provide the greatest benefits for biodiversity. However, the optimal configuration (e.g., the size and number of restored patches) of habitat, given a fixed total area, remains an unresolved question. 2. Here, we ask whether restoring a single large habitat patch or a mixture of smaller patches of the same total area supports higher plant diversity. To address this question, we measured taxonomic, phylogenetic, and functional diversity of all naturally recruiting woody species in 52 restored vegetation patches in Jambi Province, Sumatra, Indonesia. Thirteen restored patches of each of four sizes (25, 100, 400, and 1,600 m²) were established within conventional oil palm plantations six years before vegetation sampling. From these 52 patches, we generated 750 random comparisons between a single large patch vs. several small patches, ensuring equal total area (100, 400, or 1,600 m²). We evaluated taxonomic, phylogenetic, and functional diversity separately for all species, for native species, and for native forest species, using three diversity measures: species richness, the exponential of Shannon entropy, and the inverse of Simpson concentration. 3. Our findings indicate that restoring several smaller patches results in greater taxonomic, phylogenetic, and functional diversity of recruiting woody species than restoring a single large patch of the same total area. This result holds across the three total habitat areas (100, 400, and 1,600 m²), all species groupings, and all diversity metrics. As expected, species diversity also increased with total area in all cases. 4. Our findings challenge restoration strategies that focus exclusively on enlarging patches. Instead, biodiversity will be enhanced by increasing the total restored area across many patches of different sizes, including very small ones (e.g., 25 m²). ### Competing Interest Statement The authors have declared no competing interest. Deutsche Forschungsgemeinschaft, CRC 990, CRC 532776526

Abstract While habitat loss is a major threat to species, the effects of habitat fragmentation independent of habitat loss (fragmentation per se) are debated. Metapopulation studies often assert negative fragmentation effects, but they do not measure fragmentation per se. We evaluate the effects of fragmentation per se (patch density) across 20 years of patch occupancy patterns of the Åland Islands Glanville fritillary butterfly, Finland, a famous model system in metapopulation studies. Fragmentation per se had mainly positive effects on patch occupancy, the proportion of years occupied per patch, and patch colonization, and negative effects on patch extinction. These results suggest that fragmentation per se does not threaten persistence of the Åland Islands Glanville fritillary butterfly. Our results support the growing body of research challenging the paradigm that habitat fragmentation per se is mostly negative for species, highlighting the value of small patches for species conservation.