Microrefugia for Small Mammals in European Forests

Abstract

This review examines how forest microrefugia (fine-scale thermal and moisture shelters formed by canopy complexity, deadwood, topography, and snow) protect small mammals from climate extremes in European forests. It synthesizes evidence on the physiological and behavioral sensitivity of rodents and shrews to near-ground abiotic environmental conditions and highlights methods for measuring and modeling microclimatic factors using LiDAR and sensor networks. These findings are integrated into a framework that links structural retention, coarse woody debris, and canopy heterogeneity to microclimate resilience. Despite global advances in microclimate research and the development of new research methods and equipment, empirical data from European forests remain scarce, particularly regarding operative temperature, humidity, and vapor pressure deficit near the ground and within subnivean habitats. By bridging the fields of microclimate physics, small mammal ecology, and silvicultural design, the review identifies the mechanisms and metrics recommended to sustain functional refugia. The synthesis identifies knowledge gaps, standardizes microclimate metrics, and outlines required forest management practices, revitalizing research and inspiring new approaches to small mammal ecology.

1. Introduction: Why Small Mammals and Microrefugia Matter

Small mammals (Rodentia and Eulipotyphla, further SMs) contribute to seed dispersal, soil aeration, and nutrient cycling, serve as prey for higher trophic levels, thereby linking vegetation and predators within food webs in terrestrial ecosystems [1,2,3]. Due to their small body size and high metabolic rates, SMs are highly sensitive to microclimatic variation. They often respond to changes in temperature and humidity at fine spatial scales that are invisible in coarse climatic datasets [4,5,6,7]. Consequently, SMs are effective bioindicators of environmental change, reflecting shifts in ecosystem stability and habitat suitability.

Microrefugia, which are localized areas with buffered microclimates, provide critical habitats that allow SM species to persist despite less favorable conditions [8,9,10,11,12,13]. Forest canopies, topographic depressions, and soil moisture gradients can moderate extreme heat and drought, creating thermally stable refuges that enhance local persistence [1,14,15,16], determining whether SMs can withstand accelerating climate change [3].

The conservation of microrefugia is recognized as one of climate adaptation strategies, offering “slow lanes” for the persistence of biodiversity [17]. Safeguarding the microrefugia that sustain SM populations can protect ecosystem functioning and maintain resilience [7,18]. Integrating the fine-scale ecological requirements of SMs with the landscape-level management of microclimatic refuges is essential for sustaining biodiversity in a warming world.

We link the physiological sensitivity and behavioral ecology of SMs to the spatial and temporal dynamics of microclimates and microrefugia. Due to their high surface-area-to-volume ratios and rapid metabolic rates, SMs respond quickly to fine-scale thermal and hydric variation [3,5,6]. Their ability to persist depends on regional trends as well as on local microrefugia, that is, sites where topography, vegetation, and soil moisture mitigate exposure to heat and drought [7,10,15]. These refugia influence distribution patterns and sustain ecological functions such as seed dispersal and predation. Integrating microclimatic heterogeneity into SM ecology links individual physiology and behavior to population and community processes. Conserving microrefugia that support SM can increase ecosystem resilience by maintaining trophic and functional diversity [17,18].

Although forest microclimates and microrefugia have been extensively reviewed in recent years, most syntheses remain plant- or climate-centric. These syntheses focus on understory vegetation, tree regeneration, or abiotic buffering at the stand or landscape scale. Syntheses focusing on animals are rare, and perspectives centered on organisms are particularly underdeveloped for SMs, despite their high physiological sensitivity to near-ground thermal and hydric conditions. In European forests, empirical evidence linking microclimate, behavior, and population processes in SMs is scattered across different disciplines and regions, and no integrative synthesis has been conducted to date.

The aim of this review is twofold: first, to analyze the role of microrefugia in protecting SMs from the effects of climate change and second, to explore how integrating microclimatic processes into conservation planning can enhance biodiversity resilience. We link animal microrefugia with forest management by translating fine-scale thermal and hydric metrics into silvicultural terms, bridging microclimate ecology and applied forestry. We address the limited understanding of animal use of microrefugia despite their importance for ecosystem functioning, filling a key conservation gap. Furthermore, we provide practical insights by identifying traits and habitats that promote SM persistence. This review is the first to provide an organism-centered, Europe-focused synthesis linking microclimate physics, SM ecophysiology, and forest management within a unified mechanistic framework (Figure 1).

2. Materials and Methods

The review is designed as a conceptual and mechanistic synthesis rather than a quantitative meta-analysis, reflecting the heterogeneity of available data and metrics. A systematic literature search was conducted using the Web of Science Core Collection and Google Scholar to capture both peer-reviewed and gray literature covering all years available in these databases from their inception up to 20 October 2025, that is, without limiting the time period. Search strings combined terms for forest microclimate and small mammals (Table S1). In Web of Science, searches were conducted within the title, abstract, and keyword fields, whereas Google Scholar queries retrieved matches across titles, abstracts, keywords, and full-text content.

Initial general search using (“small mammal*”) AND (“forest*”) OR (“microrefugia”) returned over 90,000 titles. This broad exploratory search was used only to identify the thematic scope of the literature and to structure the review; it was not screened in full. From these, we constructed the paper structure with six main chapters. We then refined the search using strings that combined terms for forest microclimate and small mammals (Table S1). Titles and abstracts were screened for relevance to forested systems and small mammal microclimate ecology. To reduce the number of citable sources, inclusion and exclusion criteria were defined (Table S2). If too many studies still covered the same or very similar topics, we further applied the following rules: (1) retain one or two seminal papers, (2) include one or two regional or methodological papers per subtheme, and (3) prioritize meta-analyses and large datasets over isolated case studies. Instead of weighting studies based on citation impact, the synthesis emphasizes consistency and convergence across independent studies as the primary basis for inference. Our aim was to prune the results to a citable amount (<150 references). All retained articles were analyzed in full, and relevant information, such as species studied, forest type, geographic location, and measured physical or physiological variables, was extracted as needed for the specific thematic focus of each subchapter. Because many seminal papers and review articles were broader in scope than individual sections of this paper, only the aspects relevant to the discussed mechanisms were incorporated into the synthesis. The literature searches and pruning workflow are summarized in Figure 2.

To improve coverage in chapters with limited initial search results (see Table S1), we incorporated the literature triage tool Undermind (https://www.undermind.ai/#overview, accessed 20 October 2025). The search topics were based on chapter and subchapter titles and further narrowed using limitations derived from the predefined inclusion criteria. The obtained lists were automatically ranked according to thematic relevance, methodological detail, and ecosystem focus, thereby prioritizing empirically strong and conceptually unique studies. We manually reviewed all Undermind-derived relevance scores and evaluated all candidate papers against the same inclusion and exclusion criteria applied during the manual screening. Algorithmic ranking may favor studies with higher keyword density, English-language publications, or well-represented research regions, potentially underrepresenting locally focused or non-Anglophone literature; therefore, relevance scores were not used as exclusion thresholds. We did not formally test the sensitivity of the ranking to alternative thematic weightings, and Undermind was used strictly as a complementary aid rather than a substitute for systematic manual screening. Unlike semi-automated tools designed for high-throughput exclusion (e.g., Rayyan or ASReview), Undermind was applied selectively to identify conceptually relevant studies within subtopics with sparse initial coverage.

This process yielded 15 additional references. These studies primarily represented empirical data or methodological perspectives not retrieved through conventional keyword-based searches, including regionally focused or thematically cross-cutting work, and contributed unique evidence relevant to forest microclimate and SM interactions. Undermind search parameters are provided in Table S3.

3. Microclimatic Drivers of Small Mammal Ecology and Seasonal Dynamics

This section synthesizes how fine-scale microclimatic variation in forests translates into physiological constraints, behavioral responses, and demographic consequences for SMs, with emphasis on organism-scale exposure rather than macroclimatic averages. In line with the first aim, Section 3 summarizes evidence on how forest microrefugia protect SMs from climatic extremes. It traces the mechanistic pathways from microclimatic exposure to physiological and behavioral responses, and ultimately, demographic consequences.

Where European small-mammal-specific evidence is sparse, review relies on mechanistic convergence across taxa to infer likely responses, while avoiding quantitative extrapolation and explicitly identifying such cases as hypotheses rather than established effects.

3.1. Ecophysiological and Behavioral Sensitivity to Microclimate

3.1.1. Thermal and Water Balance Constraints

Due to their high surface-area-to-volume ratios, SMs experience rapid heat and water fluxes, making them highly sensitive to microclimatic variation. Operative temperature (T_e), which considers radiation, air temperature, wind, and humidity, is a key measure of the thermal environment. It more accurately reflects energetic load than ambient temperature (T_a) [19]. Variations in T_e across exposed and sheltered microhabitats can cause significant physiological stress or relief [19,20].

Mechanistic approaches that model heat and water exchange between organisms and their environments provide robust predictions of performance and survival limits [20,21]. Forest canopies and vegetative cover can buffer temperature extremes and vapor pressure deficit (VPD), thereby maintaining stable, humid microhabitats [2,14]. However, such buffering depends on the local water balance and the integrity of the canopy, both of which are threatened by warming and drought [14].

Species differ in their physiological capacities to manage these constraints. For example, the red-backed vole (Clethrionomys gapperi) has higher water turnover and evaporative loss than the white-footed mouse (Peromyscus leucopus), which confines it to moist habitats [22]. Similarly, montane rodents have high basal metabolic rates and thermal conductance, yet they rely on evaporative water loss for thermoregulation [23]. Variation in metabolic and hydric traits underlies adaptation to local VPD gradients. Populations in drier environments show reduced water loss and lower thermal preferences [24]. Behavioral and physiological plasticity, such as microhabitat selection and metabolic modulation, further buffer climatic extremes [24,25].

3.1.2. Sheltering Behavior, Activity Budgets, Torpor and Subnivean Ecology

Behavioral thermoregulation is the primary defense mechanism against microclimatic stress in SMs. Sheltering and reduced activity mitigate overheating, dehydration, and energy loss [26]. SMs retreat to burrows or vegetated cover, where operative temperatures may be 10–30 °C lower than the ambient temperature [27]. These refuges reduce VPD-driven water loss, and burrowing offers protection comparable to surface sheltering [28].

Activity adjustments further buffer thermal stress. For instance, subarctic voles shorten activity bouts and limit movement until insulating subnivean spaces form; then, they increase foraging as conditions stabilize [29]. Subnivean habitats (air pockets beneath snow) maintain near-0 °C temperatures, conserving energy and reducing cold exposure [30]. Snow loss or crusting increases mortality, whereas deep, porous snow enhances survival [31]. Similar buffering occurs in forest litter and soil cavities, where microhabitats can reduce exposure to lethal heat by over an order of magnitude [5]. Camera trapping confirms that rodents and shrews become more nocturnal and reduce their movement during cold or snowy periods to conserve energy [32].

Physiological strategies complement these behaviors. Many SMs use torpor or hibernation to lower their metabolic rates and body temperatures, thereby conserving energy and water [33]. Torpor expression increases with falling temperature and barometric pressure, enabling real-time energetic adjustments [34]. Together, behavioral and physiological thermoregulation enable SMs to withstand microclimatic extremes and maintain population viability under changing snow and temperature regimes [35].

3.1.3. Demographic Links

Microclimatic constraints influence demographic outcomes by affecting energy balance, reproduction, and movement. Elevated operative temperatures and VPD limit foraging and hydration, thereby reducing reproductive investment and survival [25]. Access to buffered microhabitats, such as shaded burrows or vegetated talus slopes, enhances survival by alleviating heat and water stress [27]. Therefore, behavioral flexibility in shelter use and diel activity timing is a key determinant of demographic performance [24,26].

Habitat structure also governs demographic resilience. A dense understory and ample litter cover increase survival and reproductive success by providing refuge from predators and climatic extremes [36,37]. Bank vole (Clethrionomys glareolus) and wood mouse (Apodemus sylvaticus) populations exhibit higher densities and breeding rates in forests with abundant shrubs and deadwood [36,38,39]. In contrast, simplifying habitat structure or intensifying agriculture lowers abundance and increases turnover, particularly for forest specialists [37].

Fragmentation alters connectivity, constraining movement and gene flow. The persistence of SM populations in fragmented or regenerating forests depends on local vegetation structure and landscape connectivity [38,40]. Forest edges and hedgerows can act as dispersal corridors that mitigate isolation [39]. However, excessive edge creation or small patch size can elevate predation and pathogen exposure, reducing survival [40].

3.2. Evidence and Implications of Forest Microclimate Buffering

3.2.1. Canopy Effects Re-Interpreted at Organism Height

Forest canopies act as thermal and hydric filters, buffering climatic extremes through structural complexity, soil moisture, and topography. Near-ground air is usually several degrees cooler during the day and warmer at night than in open areas [41,42,43]. In Europe, sub-canopies were 0.8 °C cooler in summer and 0.1 °C warmer in winter on average [42], and canopy cover explained up to 2.7 °C of local variation in boreal forests [43]. Similar patterns occur globally: old-growth canopies in the Pacific Northwest were up to 2.5 °C cooler than simplified stands [1]. Canopy cover greater than 50% lowered maximum temperature and VPD by 5.3 °C and 1.1 kPa, respectively, across western North America [14]

At organism height (5–30 cm), these offsets directly influence metabolic and hydric balance [43]. Shading lowers VPD by maintaining cooler, moister air. Even within tens of meters, shaded valleys remain markedly more humid [44]. Soil moisture amplifies this buffering; understories averaged 2 °C cooler in wetter soils [45], while structural complexity, especially in the shrub and sub-canopy layers, stabilizes near-ground conditions [46].

Topography and vegetation jointly generate fine-scale microclimatic diversity. In the Pyrenees, for example, canopy structure and slope predicted local temperature and VPD variation, defining high refugial capacity [47]. Similar outcomes have been observed in experimental manipulations: variable-density thinning increased canopy heterogeneity and SM diversity [48], while small canopy gaps had negligible effects on abundance in closed forests [49]. Canopy composition also shapes forest-floor microhabitats and herbaceous diversity [50,51].

Across biomes, canopy moderation slows understory warming [52], while in Mediterranean systems it can buffer maximum temperatures by over 14 °C [53], increasing mammal occupancy by ~50% in hot regions [54]. Similar effects occur in temperate Europe, where canopy cover reduces near-ground temperatures by over 10 °C during heat extremes [15,47]. However, fragmentation weakens this stability. Edges extending up to 20 m into tropical interiors reduce ground-level thermal insulation by one-third [55]. Thus, multilayered, moisture-retentive canopies sustain thermal stability and microrefugial capacity near the ground, which is critical under climate warming.

To synthesize the scattered quantitative evidence on near-ground microclimate buffering across forest types, seasons, and regions, we compiled indicative ranges of reported temperature and vapor pressure deficit offsets and included the basis of the evidence and its limitations (Table S4).

3.2.2. Vertical Forest Stratification and Microclimatic Variation

Forest canopies, understory vegetation, and detritus layers collectively regulate the microclimates near the ground experienced by SMs [56]. The canopy mediates shortwave radiation and turbulent energy exchange, creating steep vertical temperature and humidity gradients [41]. The strength of this attenuation depends on leaf area density, stand age, and canopy roughness. Old-growth forests, for example, reduce 1 m air temperature fluctuations by 30%–50%, relative to above-canopy conditions [57].

Understory vegetation traps cool air, limits wind exchange, and maintains high relative humidity. Coarse woody debris and litter act as thermal-hydric buffers, conserving soil moisture and lowering VPD. Removal of the canopy or litter through logging or thinning increases the diel temperature range and VPD, thereby diminishing the refugial potential [57,58]. Plots that retained more than 15% canopy cover after harvest remained significantly cooler and moister than clearcuts [57].

These microscale gradients directly influence activity, metabolism, and water balance. Buffered forest floors reduce evaporative loss and heat stress, thereby extending activity periods and supporting thermally sensitive species [59,60]. In fragmented or agricultural landscapes, structural complexity, including intact litter and understory, often has a stronger effect on SM abundance than patch size or isolation [37].

Litter and detritus provide insulating subsurface refugia. In Mediterranean forests, litter microhabitats were 1–5 °C cooler during the day and up to 3 °C warmer at night than the surrounding air temperature [53], which stabilizes VPD even during periods of extreme heat. Hydric coupling reinforces this buffering, canopy cover interacting with soil moisture enhances thermal stability [14]. As droughts intensify, the capacity of forests to sustain microrefugial conditions will depend on this soil–canopy linkage.

Fragmentation disrupts near-ground stability by increasing temperature variability and reducing humidity within 20 m of forest edges [55]. Similarly, narrow riparian buffers (less than 50 m wide) fail to maintain interior microclimates [61]. Therefore, maintaining multilayered canopies and intact litter is essential for preserving the thermal and hydric stability critical to SM survival. However, microclimatic data at the organism level remains scarce. There are no T_e measurements within 0–5 cm or inside detritus and coarse woody debris across diel or seasonal cycles in European boreal forests [2,62,63]. Similarly, there are few direct measurements of relative humidity and VPD within litter, bryophytes, or log cavities, and the pathways of humidity—interception, transpiration, detrital evaporation, and diffusion resistance—are poorly quantified [2,47]. Near-ground wind data (0–10 cm) is also limited, which constrains estimates of convective heat transfer and T_e. High-frequency observations of sunflecks, gusts, and post-rain humidity are also rare [2,62].

3.2.3. Ecological and Conservation Implications

Forest microclimate buffering is essential for the survival of temperature-sensitive species [1,6]. As climates warm, shaded and moist microhabitats act as refuges and stepping stones, reducing thermal stress and supporting the survival of SMs and other taxa [37]. In fragmented or agricultural landscapes, these patches serve as reservoirs of biodiversity, aiding recolonization and maintaining ecosystem function [37,61].

At broader scales, canopy-mediated buffering governs ecosystem resilience. Structurally complex and old-growth forests maintain stronger microclimatic stability [1], whereas simplified or degraded forests lose this capacity more rapidly. Models that integrate canopy and hydric data [14,52] suggest that intensified canopy loss and drought will cause nonlinear declines in microrefugia, thereby accelerating ecological turnover.

Effective conservation depends on preserving vertical heterogeneity, canopy continuity, and hydrological balance. Mixed-species, uneven-aged reforestation and riparian buffers greater than 50 m help maintain low operative temperatures and vapor pressure deficits (VPDs). As Tourani et al. [54] demonstrated, maintaining forest cover mitigates macroclimatic exposure and preserves organism-scale refugia, which are critical for species persistence.

3.3. Mechanisms and Microhabitat Types Used by Small Mammals

3.3.1. Categorical Review of Microhabitat Types

SMs exploit diverse microhabitats that fulfill their thermal, hydric, and protective needs. Key refuges in forested, rocky, and riparian ecosystems include tree cavities, coarse woody debris (CWD), dense understories, talus or rock voids, and snow or subnivean layers [64,65,66,67,68].

Tree cavities and hollows provide humid, thermally stable refuges that buffer diel temperature variation and reduce the risk of predation, thereby supporting the nesting and overwintering of species such as P. leucopus, eastern chipmunk (Tamias striatus), and garden dormouse (Eliomys quercinus) [64,69]. CWD stabilizes near-ground temperature and moisture, offering shelter from predators and desiccation. High log and litter cover promote species coexistence and spatial segregation [65,66,70].

Dense understory vegetation enhances concealment, foraging opportunities, and microclimatic stability. SM abundance generally increases with shrub density and vertical complexity [64,67,71]. Talus slopes and rock voids provide thermally inert, predator-protected refuges that buffer extreme heat and drought. These refuges facilitate persistence under warming or arid conditions [72].

Snow and subnivean layers maintain a near-constant temperature of ~0 °C and humidity, forming insulated winter refuges that reduce energy expenditure and the risk of predation [30,37].

Together, these microhabitat types form a mosaic of thermal and hydric refugia that support the survival, coexistence, and resilience of SMs under environmental change.

3.3.2. Thermal Inertia, Humidity Retention, and Predator Concealment

Thermal inertia reflects a substrate’s ability to buffer temperature changes. Materials with high heat capacity and low conductivity, such as soil, wood, rock, and snow, dampen diel fluctuations. Deep litter and coarse woody debris further stabilize temperatures, enabling species such as the northern short-tailed shrew (Blarina brevicauda) to endure intense diurnal variation [56]. Vegetation structure enhances this buffering effect by moderating microclimates [73].

Humidity retention depends on soil moisture, organic matter, and canopy shading. CWD, litter, and riparian substrates sustain high relative humidity and low VPD, which reduces evaporative loss [66,74]. Moist microhabitats also support invertebrate prey and fruiting plants, linking hydric stability to the food supply [75]. Seasonal shifts in moisture drive behavioral plasticity, prompting SMs to adjust their habitat use between dry and wet periods [69,70].

Predator concealment arises from dense undergrowth, debris, and cavities that obscure visual and olfactory cues [65,76]. In European forests, the concealment of SMs from predators is mediated by fine-scale structural features, including litter depth, ground vegetation density, coarse woody debris, and canopy continuity. These features strongly overlap with climatic microrefugia. Classic forest-floor studies have shown that species such as C. glareolus, P. leucopus, deer mouse (Peromyscus maniculatus), T. striatus, common shrew (Sorex araneus and congeners within Sorex spp.), and northern short-tailed shrew (Blarina brevicauda) preferentially use microsites with dense cover and high structural complexity that reduce exposure to predators [36,50,64]. Evidence from European forest systems further indicates that many widespread rodents and shrews, including A. sylvaticus, A. flavicollis, striped field mouse (Apodemus agrarius), field vole (Microtus agrestis), common vole (Microtus arvalis), Eurasian harvest mouse (Micromys minutus), Eurasian pygmy shrew (Sorex minutus), and S. araneus, respond positively to structurally complex habitats created by understory vegetation and coarse woody debris, which enhance antipredator cover [77]. However, responses differ among functional groups: semifossorial rodents rely heavily on litter layers and coarse woody debris, whereas more scansorial or generalist rodents show greater tolerance of open microsites, particularly near forest edges [30]. These findings suggest that predator concealment varies by species and guild and should be considered alongside microclimatic buffering as a co-benefit of microrefugia when evaluating habitat quality and persistence in forest landscapes [7,8,63].

Together, these thermal, hydric, and structural pathways allow small mammals to maintain homeostasis and persist in changing climates [70,72].

3.4. Seasonal Considerations

In temperate and boreal ecosystems, SMs face different seasonal challenges [78]. In summer, they face high metabolic demands, variable food availability, and risks of heat or drought stress. Winter brings cold exposure, scarce resources, and dependence on snow insulation [79,80]. These seasonal dynamics influence physiological constraints, community interactions, and conservation priorities in northern ecosystems [81].

3.4.1. Non-Snow Seasonal Adaptive Mechanisms and Management Implications

The seasonal dynamics of SMs in temperate and boreal ecosystems are shaped by physiological and ecological constraints throughout the year, which extend beyond merely surviving the winter. Outside of snow-covered periods, seasonal adaptation involves shifts in activity budgets, habitat use, and resource exploitation in response to changes in temperature, moisture, and food availability [78].

Elevated temperatures and episodic drought during the summer months reduce primary productivity and invertebrate availability, thereby constraining reproductive output and body condition in SMs [81,82]. However, fine-scale heterogeneity in vegetation structure, soil moisture, and microclimate buffering can mitigate these constraints, sustaining local abundance and diversity [83]. Behavioral adjustments, such as altered activity timing and increased reliance on shaded or humid microhabitats, play a central role in maintaining an energetic and hydric balance during warm periods. From a management perspective, it is particularly important to maintain canopy heterogeneity, understory cover, and soil moisture refugia in desiccation-prone or disturbed landscapes.

In autumn and early winter, SMs transition to energy conservation strategies, such as reduced activity, increased shelter use, and altered foraging behavior, as resources become scarce [78,81]. These seasonal adjustments influence survival and population trajectories independently of snow conditions and represent a critical yet often overlooked phase of the annual cycle. Management actions that preserve structural complexity and resource heterogeneity during these periods can enhance population resilience prior to the onset of winter.

3.4.2. Snow Insulation and Overwinter Survival

This section focuses exclusively on snow-mediated processes affecting overwinter survival. Winter SM dynamics depend on snow depth, continuity, and subnivean temperature. Deep, continuous snow provides a thermally buffered refuge that enhances SM survival and reproduction, whereas shallow or fragmented snow increases mortality [78,82]. Snowfall supports population growth in C. gapperi and other forest rodents in the winter [81,83]. Conserving forest and microtopographic features that maintain snow integrity and reduce compaction is critical.

Since the mid-20th century, snow cover has declined across Europe, with a later onset and earlier melt shortening the duration of snow cover [84]. The strongest declines are in western and southern Europe. Northern and alpine regions have experienced smaller, localized increases tied to higher snowfall. Overall, warming in autumn and spring and positive North Atlantic Oscillation (NAO) phases drive widespread snow loss, signaling a continued contraction of Europe’s seasonal snow cover in the context of climate change [85].

Snow insulation is essential for the survival of SMs, as the stability of the subnivium depends on snow depth, density, and persistence. These factors together determine winter habitat quality [31]. Reduced snow depth or duration increases temperature variability at ground level and cold stress. In contrast, continuous snow maintains subnivean temperatures near 0 °C, which supports energy balance and survival [78,86].

In boreal and temperate regions, snow continuity strongly influences SM demography. Deep, persistent snow enhances vole survival by lowering energetic costs and predation risk [83,86], whereas fragmented snow layers increase mortality and disrupt subnivean networks. Milder winters and positive NAO phases correspond with population declines [83]. Greater snow depth also limits predator access, stabilizing northern SM populations [87].

At broader temporal scales, overwinter SM survival and population cycles fluctuate in response to climatic variability. Yoccoz and Ims [78] demonstrated that SMs in Arctic ecosystems undergo greater demographic fluctuations due to harsh and unpredictable winters than alpine populations, which are buffered by consistent snowpack. Similarly, long-term European studies indicate that reduced snowfall and increasing winter irregularity have weakened vole cycles and decreased SM overwintering success [88].

The quality of the subnivium is thus a critical determinant of SM winter ecology. It functions as a seasonal refugium, and its degradation due to warming, rain-on-snow events, or compaction is a type of habitat loss [31,86]. Therefore, overwinter survival metrics should include snow depth and continuity, ground temperature stability, and physiological or demographic indicators, such as body mass retention and winter density change [83,89]. Monitoring these parameters provides early warnings of deteriorating subnivean conditions and helps forecast population responses to ongoing climatic shifts.

In northern and mid-latitude systems, management strategies should aim to preserve snow insulation and continuity by retaining forest canopies and mitigating surface disturbance. These conditions support stable subnivean microclimates and reduce the ecological costs of winter warming for SM populations [87,88].

4. Bridging Microclimate Measurements with Behavioral and Demographic Processes

Building on the ecological mechanisms outlined above, this section focuses on how organism-relevant microclimate conditions can be measured, modeled, and linked to behavioral and demographic processes, providing the methodological bridge between microclimate theory and population-level inference.

4.1. Measuring the Operative Environment

Accurately characterizing the thermal environment of SMs requires instruments to measure heat exchange via radiation, convection, conduction, and evaporation [90]. Standard meteorological data, such as air temperature and humidity at a height of 2 m, fail to represent microclimates at the height of the animals or within vegetation and soil [91,92]. Operative temperature (T_e) is the equilibrium temperature of a physical model that mimics an animal’s morphology and radiative properties, and it is a more biologically sound measure of environmental heat load [19,93]. Recent findings indicate that thermal balance operates around multiple thresholds, underscoring the importance of precise T_e measurements to define compensable and non-compensable limits [90].

4.1.1. Sensor Design and Deployment

Microclimate measurements should minimize radiative bias while capturing temporal and vertical variability. While traditional models integrate radiant and convective fluxes, compact loggers now enable high-resolution monitoring of air, soil, and surface temperatures across habitat strata [94]. Unshielded or poorly shielded sensors can record errors exceeding 25 °C in direct sunlight, which emphasizes the need for adequate shielding or aspiration [91]. Sensors should be positioned at biologically relevant heights (0–10 cm for SMs) to represent activity and rest conditions [91,95]. Standardized Gill-type radiation shields are still the preferred option because improvised or opaque designs can distort airflow and heat exchange [92].

4.1.2. Standardized Microclimate Metrics

Standardized microclimate metrics should include [47,96]:

• ΔT at organism height (difference between near-surface and reference air temperatures);
• VPD safe-hours (duration below vapor pressure deficit thresholds indicating dehydration risk);
• Thermal inertia of shelters, burrows, or nest chambers, reflecting habitat buffering capacity.

Frameworks such as myClim automate these computations and standardize metadata within hierarchical locality–logger–sensor structures [96].

To bridge conceptual definitions and practical implementation, we provide a concise, reproducible operationalization of organism-relevant microclimate metrics (ΔT, VPD safe-hours, thermal inertia) in Table S5, which facilitates adoption and cross-study comparability rather than prescribes universal thresholds.

4.1.3. Data Integrity and FAIR Compliance

Calibration against research-grade thermistors and metadata standardization are essential [92]. Adhering to the FAIR (findable, accessible, interoperable, and reusable) principles ensures comparability with global datasets, such as SoilTemp [97]. Comprehensive datasets should include information on the type of sensor, shielding, installation height, vegetation context, and calibration procedures.

Beyond temperature, physiological integration is necessary. The oxygen- and moisture-dependence of SM metabolism implies that operative conditions cannot be interpreted thermally alone. The temperature–size rule and associated oxygen-limitation hypotheses suggest that microclimate stress influences thermal load, metabolic scaling, and growth potential [98]. Thus, measuring operative environments (temperature and humidity combined) provides a mechanistic bridge linking habitat structure, physiology, and demographic response, not merely physical context [99].

4.2. Study Designs and Statistical Approaches

Linking microclimate exposure to demography requires integrated designs that connect environmental histories with population outcomes. Experimental frameworks, such as before-after-control-impact (BACI) and paired refugia versus non-refugia comparisons, are effective for testing the causal effects of microhabitat buffering [27,92]. Manipulating canopy cover or soil insulation can quantify the influence of refugial structures on demographic rates [53].

Monitoring approaches, including capture-mark-recapture (CMR), occupancy modeling, and reproductive indices, enable inference on survival and fecundity under variable thermal conditions [100]. Coupling these approaches with co-located sensors allows us to estimate time-varying exposure covariates, such as cumulative degree-hours above stress thresholds [101]. Analytical tools such as joint or integrated population models directly relate exposures to vital rates while accounting for environmental autocorrelation [91,94].

To generalize findings, analyses should incorporate nested spatial hierarchies (sensor → plot → habitat type) and align microclimate data with demographic events over time [96]. Integrating microclimate networks [102] with long-term population data bridges the gap between physiology and population dynamics.

4.3. Bio-Logging and Behavioral Validation

Bio-logging links organismal activity with real-time environmental data, bridging exposure and behavioral response. Miniaturized sensors that measure skin temperature, heart rate, and movement reveal how SMs exploit thermal heterogeneity [27,103,104]. Advances in telemetry and accelerometry allow for the continuous, minimally invasive monitoring of free-living individuals and quantify activity-temperature coupling and refuge-use thresholds [100,105].

Tri-axial accelerometers and magnetometers distinguish posture and orientation, linking fine-scale behavior to thermal exposure [105]. Integrating GPS, accelerometer, and microclimate data validates mechanistic models of thermoregulation and foraging behavior [103]. It is essential to adhere to ethical standards: devices should weigh less than 5% of body mass, comply with animal welfare regulations, and undergo pilot testing to minimize behavioral bias [92,106].

Bio-logging datasets, standardized under the FAIR and TRUST principles by the International Bio-Logging Society, are shared through repositories such as Movebank [107]. Global archives allow us to reconstruct exposure histories and behavioral adaptations and provide a mechanistic foundation for climate-responsive wildlife management [106,108].

5. Mapping, Modelling and Managing Small Mammal Refugia

In line with the second objective of this review, Section 5 transitions from mechanisms to applications. It demonstrates how microclimatic processes identified at the organism level can be mapped, modeled, validated, and incorporated into conservation planning and forest management.

5.1. Downscaling Climate to Organism Height

The microclimate conditions experienced by SMs, often a few decimeters above or below ground, are poorly captured by coarse climatic grids. However, recent advances in radiative transfer modeling and LiDAR-derived canopy structure now enable the realistic downscaling of temperature fields to the height of organisms [61,109,110]. These models integrate macroclimatic drivers, such as radiation and lapse rates, with modifiers like canopy transmissivity, understory density, soil moisture, and hydrology. This produces microclimate estimates with a resolution of 10–25 m.

In forests, for example, canopy shading and evapotranspiration can buffer maximum temperatures by up to 3 °C, while soil temperatures may differ from open-air readings by over 7 °C [109]. LiDAR metrics of canopy height and gap fraction [111,112] and hydrological indices derived from digital elevation models further improve near-surface predictions. Downscaling couples mechanistic radiation-transfer models with machine-learning approaches, such as boosted regression trees and random forests, trained using sensor networks like ForestTemp and ForestClim [62,110]. These approaches now resolve “thermal landscapes” at the scale of refugia used by SMs.

5.2. Defining Refugia from a Small Mammal Perspective

From the perspective of SMs, this subsection addresses the second aim of the review. It defines microrefugia using biologically important thermal, hydric, and structural thresholds instead of purely climatic descriptors. Refugia are considered microsites that provide structural shelter and maintain favorable thermal and moisture conditions, enabling individuals to remain within physiological limits and reducing their exposure to predation. According to the microrefugia framework [63,113], the functionality of refugia can be quantified using the following:

• Thermal thresholds: cumulative “safe-hours” when operative temperature remains below upper critical limits [114];
• Hydric stability: VPD or soil moisture within species’ tolerance ranges. So far, no empirical tests in boreal systems link measured microhabitat VPD to SM abundance, behavior, habitat use, or physiology [14];
• Structural indices: presence of coarse woody debris, litter depth, or canopy closure providing shelter and insulation.

These indicators combine biophysical and behavioral components of habitat use. For instance, LiDAR and thermal modeling can estimate the year-round refugia provided by fallen logs, riparian shading, and snowpack persistence (the subnivium). Using these organism-centric metrics shifts the focus from purely climatic definitions to functional refugia that explicitly link energy balance, safety, and movement constraints.

5.3. Validation Workflows

According to N.A. Gilbert et al. [43], model validation must address both microclimate prediction accuracy and biological relevance. Independent datasets, such as telemetry, CMR, and fine-scale logger networks, are essential for testing predicted refugia occupancy across scales.

In order for microclimate models to be ecologically significant for small mammals as well as physically accurate, model validation must extend beyond statistical performance.

Table 1. Summary of model validation components addressing physical accuracy, biological relevance, and cross-site applicability in forest microclimate and refugia modeling.

Validation Component	Description
Physical accuracy	Validation involves comparing downscaled temperature and humidity estimates with independent sensor data across canopy layers and seasons. Because sub-canopy temperatures often differ by more than 2 °C from free-air conditions, models may have biases and seasonal offsets [62,92].
Behavioral validation	Testing evaluates whether individuals occupy predicted low-stress or buffered microhabitats. According to the climate proximity framework, validation should demonstrate the degree to which modeled temperatures align with the actual conditions experienced by animals, rather than merely their spatial or temporal patterns [115].
Cross-site transferability	To maintain ecological relevance, models should remain predictive across different forest structures, topographies, and hydrological regimes [62,115].

summarizes the key components of validation that integrate physical accuracy, biological relevance, and spatial transferability. Specifically, the table outlines how to evaluate downscaled microclimate predictions against independent sensor data, the behavioral occupancy of predicted refugia, and consistency across forest types and sites. By synthesizing these criteria, Table 1 establishes a conceptual link between microclimate modeling and assessing functional microrefugia for SMs. This approach supports inferences about persistence rather than presenting empirical results.

Together, these tiers ensure that microclimate models are statistically robust and ecologically interpretable for assessing SM refugia under climate change.

Illustrative validation workflow: Near-ground temperature and humidity are measured at a height of 5 cm using shielded sensors in retained forest patches and adjacent harvested stands. Physical accuracy is evaluated by comparing downscaled microclimate predictions with independent logger data to quantify bias and variance in ΔT at organism height across canopy classes. Next, biological relevance is assessed by testing whether predicted refugia (defined as locations with a sufficient number of VPD safe hours per day) correspond to higher SM occupancy, activity, or survival, as estimated from capture-mark-recapture or camera trap data. Concordance between accurate microclimate predictions and a positive biological response indicates the functional validation of refugia metrics. In seasonal contexts, validation can be extended by testing whether the cumulative number of VPD safe hours during the summer or winter correlates with demographic outcomes, such as body mass retention or overwinter survival. This links short-term exposure metrics to population-level persistence.

6. Management and Silviculture for Small Mammal Refugia

6.1. Structural and Spatial Elements of Refugia

Maintaining refugia for SMs in production forests requires sustaining structural complexity and diverse microhabitats that mitigate temperature, moisture, and predation risks. Key components, such as deadwood, large legacy trees, and multilayered canopies, regulate microclimates, support prey resources, and provide shelter [116,117].

Coarse woody debris and snags are essential structural elements that promote nutrient cycling, increase soil organic matter, and enhance thermal stability, while providing vital foraging and nesting sites [118]. Synthesis studies from Europe and North America suggest an optimal volume of 30–50 m³/ha of deadwood, with 20–80 m³/ha serving as an ecological baseline [119]. Long-term Swedish monitoring shows that small retention patches (0.03–0.5 ha) maintain 19–41 m³/ha of CWD two decades post-harvest, supporting stable microhabitat structures [120]. In the Białowieża Forest, SMs such as yellow-necked mouse (Apodemus flavicollis) and C. glareolus respond strongly to CWD thresholds near 0.75 m³/100 m² (approximately 7.5 m³/ha), where surface area and decay diversity rather than total volume determine refugia capacity [121].

Post-harvest management should integrate biodiversity and fire mitigation goals. Debris burning removes key habitats and releases greenhouse gases [118]. Constructed woody debris piles and windthrows can sustain C. gapperi, Microtus spp., and small mustelids for over a decade. Large-diameter trees serve as long-term “time bridges,” ensuring habitat continuity and carbon storage across rotations [116]. The continuous recruitment of such trees, uneven-aged canopies, and riparian buffers of at least 30 m are minimum functional thresholds to maintain microclimatic stability and connectivity of refugia [117,122]. Interior-like microclimatic conditions require wider, ≥50 m buffers [110].

6.2. Fuel Reduction, Production, and Refugia Protection

According to M.G. Betts et al. [123], balancing timber production with biodiversity conservation requires integrating structural retention and refugia protection into forestry operations. Continuous-cover and retention systems enhance habitat continuity and microclimatic buffering, sustaining SMs with minimal yield reduction [118]. When guided by adaptive, multi-criteria frameworks, retention forestry can balance carbon storage, fuel load, and biodiversity goals [122,124].

Although fuel-reduction programs often remove coarse debris to reduce fire risk, evidence shows that deadwood rarely increases ignition; human activity is the primary cause [118]. However, its removal results in habitat loss, carbon emissions, and disrupted soil microclimates. Similarly, excessive salvage logging and biomass extraction impede biodiversity recovery after disturbance [125,126]. Maintaining at least 30% deadwood and designating uncut refugia zones during salvage operations preserves habitat integrity and carbon continuity [116,117].

At the landscape scale, heterogeneity in stand age, canopy density, and unharvested “anchor” patches supports SM persistence through spatial complementarity [116,117]. Artificial refuges cannot substitute for natural debris and vegetation complexity, which emphasizes the value of structural legacies [127]. The “Forest Biodiversity Artery” model implements these principles through micro-reserves, senescence islands, and habitat-tree corridors to reinforce resilience under climate and disturbance pressures [117,122,128].

6.3. Prescriptions and Adaptive Monitoring

Effective refugia management should be quantitative, adaptive, and multiscale, linking structural prescriptions to measurable biodiversity and microclimate outcomes. This requires maintaining legacy structures and functional refugia to sustain viable SM populations through disturbance cycles.

Operative temperature and VPD “safe hours” translate stress thresholds of organisms into silvicultural guidance. These metrics quantify how canopy cover and moisture balance buffer thermal and hydric extremes. They identify structures that maintain refugial conditions [14,47,96].

6.3.1. Prescriptions

To promote structural complexity, habitat continuity, and biodiversity within managed forest stands, the following prescriptions summarize recommended retention, restoration, and disturbance management practices based on current literature and field standards (

Table 2. Summary of structural retention and disturbance management prescriptions for maintaining coarse woody debris (CWD), refugia, and ecological continuity in managed forest ecosystems.

Prescription	Description
Deadwood retention and recruitment	Maintain 30–50 m3/ha of CWD across species, sizes, and decay classes, including at least 10 m3/ha of standing snags [119]. Patches of high-decay CWD (~11 m3 per 0.03 ha) sustain SM activity [125]. The continuous recruitment of large logs and snags from retained live trees ensures long-term refugia and carbon storage [116,117]
Retention patches and legacies	Retain 10%–20% of the basal area in mesic patches of at least 0.25 hectares with decayed wood and a complex understory [120,129]. Indicator species, such as A. flavicollis and C. glareolus, can guide spacing and refugia density [122].
Riparian and moisture refugia	Leave ≥ 30 m unharvested buffers along streams and wetlands to maintain soil humidity, cover continuity, and movement corridors, thereby providing partial microclimatic buffering [117]. Interior-like microclimatic conditions generally require wider, ≥50 m buffers [110].
Variable retention and continuity	Combine dispersed and aggregated retention to preserve legacy trees, emulate natural gap dynamics, and maintain microclimate heterogeneity [116,124].
Disturbance and fuel management	Use small-gap or partial-windthrow analogs to mimic natural mortality, promote understory regeneration, and reduce thermal extremes [125,128]. During salvage, retain at least 30% of the deadwood and convert the residues into debris piles that can function as refugia for up to ten years [118,126,127].

).

6.3.2. Key Performance Indicators

To evaluate the effectiveness of refugia-oriented silviculture, we need consistent, quantitative key performance indicators (KPIs) that link habitat structure to biological response. The following KPIs integrate structural, climatic, and faunal metrics to guide adaptive monitoring and assess the long-term functionality of refugia under changing forest and climate conditions (

Table 3. Recommended Key Performance Indicators (KPIs) for monitoring small mammal refugia in managed forests. This table summarizes key measurement foci and supporting literature.

Indicator	Measurement	Justification
CWD Metrics	Total volume (m3 ha−1), decay-class diversity, areal coverage of high-decay logs	CWD volume–decay diversity directly predicts SM abundance [117,125].
Microhabitat Heterogeneity	Canopy gaps, litter depth, shrub density, moss/woody debris cover	Multi-layered vegetation moderates microclimate and provides trophic resources [122].
Faunal Indicators	Occupancy or capture rates of A. flavicollis, C. glareolus, total species richness	Key species function as rapid indicators of refugia integrity [122,125].
Microclimatic Buffering	Near-ground temperature and humidity variance across retained vs. managed plots	Quantifies functional refugia performance under warming [117].
Structural Persistence	Proportion of retained patches and debris structures surviving >15 years post-harvest	Long-term persistence maintains CWD continuity and faunal occupancy [116,120].
Fuel/Bioenergy Co-benefits	Fraction of residues reused for habitat vs. removed for fuel; smoke-event frequency	Integrates fire safety with biodiversity outcomes [118].

).

6.3.3. Implementation Rationale

Monitoring these indicators continuously through permanent plots, sensor arrays, and bio-logging tools enables evidence-based, adaptive silviculture. Monitoring structural persistence and functional occupancy ensures management interventions sustain operative refugia while achieving carbon stability and production targets. Embedding refugia performance metrics into certification or adaptive management frameworks allows forest managers to maintain SM biodiversity as a proxy for ecosystem resilience in the face of intensifying climate variability.

7. Knowledge Gaps and Research Priorities

Despite progress in understanding forest microclimate buffering, key gaps persist that limit our ability to predict the persistence of SMs under climate change. The most critical limitations stem from a lack of organism-level exposure data and weak causal links between microclimate conditions, behavioral responses, and demographic outcomes. Without direct measurements of operative temperature (T_e), relative humidity, and vapor pressure deficit (VPD) within the actual microhabitats used by SMs (0–5 cm), it is impossible to mechanistically link habitat structure to activity constraints, energy balance, or survival across seasons [2,45,47,62]. Similarly, the absence of quantified hydric and convective processes (e.g., interception, detrital evaporation, and near-ground wind) prevents robust inference on dehydration risk and thermoregulatory limits. Only a few studies explicitly connect microclimate exposure (T_e, VPD) to SM abundance, physiology, or demography, thereby constraining causal inference on persistence mechanisms.

Validation of LiDAR-based and downscaled microclimate models at organism height is limited. Most lack cross-site accuracy and behavioral validation [43,62,110,115]. Standardized metrics, such as ΔT, VPD safe hours, and thermal inertia, are inconsistently applied and rarely supported by FAIR-compliant metadata, and constrain synthesis and comparison across studies [47,94,96]. Winter processes are underrepresented; the temperature stability of the subnivean zone and its links to overwinter survival are poorly quantified [31,78,81,86].

Another limitation is the inadequate distinction between functional guilds, which obscures the species-specific mechanisms of microrefugia use [5,27,115]. Insectivores generally have higher metabolic rates and are more dependent on humid microhabitats. This makes them particularly sensitive to VPD and risk of dehydration [19,22,23,25]. In contrast, terrestrial rodents rely more heavily on litter, soil, and coarse woody debris to buffer thermal and hydric extremes at the forest floor [28,36,37,50]. Arboreal or scansorial rodents experience distinct exposure pathways linked to canopy structure and vertical microclimate gradients [41,48,52]. Treating all SMs as a homogeneous group masks interspecific variation in thermal and water tolerances, limiting the transferability of persistence predictions across taxa and forest types [6,21,59].

Behavioral and physiological thresholds for refuge use, torpor, and activity modulation are rarely measured via bio-logging [25,27,33]. The structural requirements of functional refugia, such as CWD volume, decay diversity, and canopy density, as well as the landscape influences of edges and riparian buffers, remain empirically unresolved [55,57,61,117,120,125]. Most studies lack BACI designs or standardized monitoring [53,92,124].

Advancing this field requires multi-scale, organism-centered studies that integrate microclimate physics, physiology, and behavior; implement standardized methods; and promote FAIR data sharing (

Table 4. Research priorities for advancing the study of forest microrefugia and small mammals in European forests.

Knowledge Gap	Research Approach	Expected Outcome	References
Lack of operative environment data (Te, RH, VPD) at 0–5 cm within litter, logs, and burrows	Deploy miniaturized, shielded microclimate sensors and physical models at SM height across diel and seasonal cycles	Quantified near-ground Te and VPD offsets; microrefugia maps at organism height	[2,45,47,62,130,131]
Unresolved humidity and wind dynamics at the microhabitat scale	Integrate high-frequency RH/VPD sensors with micro-anemometry and soil-moisture probes inside litter and CWD	Mechanistic understanding of convective and hydric fluxes driving forest microrefugia	[2,62]
Few direct links between microclimate exposure and SM performance	Combine co-located sensor arrays with capture–mark–recapture, occupancy models, and bio-logging	Dose–response curves between Te/VPD exposure and survival, reproduction, or behavior	[2,27,130,131,132]
Limited validation of LiDAR and downscaled microclimate models	Conduct multi-site validation using independent logger networks and telemetry data	Cross-site accuracy (°C bias) and biological relevance (refugia occupancy prediction)	[43,62,110,115]
Non-standardized microclimate metrics and metadata	Apply standardized metrics (ΔT, VPD safe-hours, thermal inertia) and FAIR data frameworks (myClim)	Harmonized datasets for synthesis and meta-analysis	[47,92,96,131]
Poor understanding of subnivean and winter refugia processes	Link snow depth/continuity sensors with overwinter CMR or density monitoring	Indicators of subnivean stability and winter survival (e.g., mass retention, density change)	[31,78,81,86,130]
Behavioral thresholds for refuge use not quantified	Use accelerometry and body-temperature loggers to identify Te or VPD limits triggering sheltering/torpor	Species-specific behavioral thresholds for heat, dehydration, and cold stress	[25,27,117,130,132]
Unknown structural thresholds for functional refugia (deadwood, litter, canopy complexity)	Manipulative field experiments varying CWD volume, decay class, and canopy retention	Quantified CWD/cover thresholds (m3 ha−1, % cover) sustaining microclimate buffering and occupancy	[117,120,125,133,134,135,136,137]
Insufficient data on edge, gap, and riparian design effects on microclimate buffering	Gradient studies across buffer widths and gap sizes; couple microclimate sensors with trapping	Minimum structural dimensions (m) preserving interior-like Te and RH for SMs	[55,57,61,131,136,138]
Lack of causal evidence from silvicultural interventions	Implement BACI or randomized retention experiments	Demonstrated causal pathways linking management → microclimate → demography	[53,92,124,133,134,135,136]
Heterogeneous data and weak synthesis capacity	Require FAIR-compliant data publication (SoilTemp, ForestTemp) and meta-analytical synthesis	Quantitative meta-models linking microclimate buffering to SM persistence	[91,92]

). These studies must be designed to experimentally validate how microrefugia sustain SM persistence under climate change [91,92]. As shown in Table 4, the research priorities are organized along a mechanistic pathway that links microclimate exposure to behavior, physiology, and demographic performance across spatial scales ranging from the microhabitat to the stand and landscape levels.

Collectively, these priorities call for:

• Sensor–demography integration (bridging physical microclimate and biological response);
• Standardized data frameworks (FAIR and myClim-compatible);
• Experimental management validation (BACI and retention forestry trials);
• Cross-seasonal, organism-centered scaling of microrefugia processes.

8. Conclusions

The heterogeneity of study designs, response variables, and microclimate metrics identified in this review suggests that a robust quantitative meta-analysis is not yet feasible. This review also highlights the urgent need for standardized, organism-relevant measurements as a prerequisite for future effect-size synthesis.

This review had two aims: (1) evaluating the role of forest microrefugia in protecting SMs from the effects of climate change and (2) assessing how organism-scale microclimate processes can be incorporated into conservation planning and forest management in Europe.

Regarding the first objective, the synthesis revealed that fine-scale thermal, hydric, and structural heterogeneity is essential for the persistence of SMs under climate change. Across seasons, microrefugia buffer operative temperature and vapor pressure deficit at the organism level, influencing behavioral and physiological responses and ultimately survival and reproduction. The strongest buffering effects occur near the ground and in habitats with high structural complexity, such as litter layers, coarse woody debris, dense understories, and subnivean spaces. However, heterogeneity in study designs, response variables, and microclimate metrics currently precludes robust, quantitative synthesis of effects.

Regarding the second objective, the review demonstrates that microrefugia can be operationalized for management purposes when defined using biologically understandable thresholds rather than broad climatic descriptors. Structural retention, canopy continuity, deadwood availability, and moisture refugia are defensible levers for maintaining microclimate buffering at the organism scale in European forests. Nevertheless, causal validation remains limited, and direct links between microclimate exposure and demographic performance are scarce.

Advancing research on forest microrefugia for small mammals in Europe requires a prioritized, staged approach. In the short term, progress can be made by improving methods, such as deploying organism-scale microclimate sensors, integrating microclimate and demographic data, and adopting standardized, FAIR-compliant frameworks (e.g., myClim) to enable cross-study comparability. In the medium term, resolving key uncertainties will require the experimental validation of microrefugia effects using BACI designs and retention forestry experiments as well as establishing direct links between microclimate exposure and demographic performance. Long-term population responses, climate-driven regime shifts, and management–policy feedbacks can only be detected through sustained monitoring, long-term datasets, and the integration of microrefugia concepts into forest management and conservation planning in the context of climate change.