Additive and nonadditive effects of herbivory and competition on tree seedling mortality, growth, and allocation

The interaction between simulated cotyledon herbivory and interspecific competition was studied in a greenhouse experiment using two species of trees, Acer rubrum and Quercus palustris, which commonly invade abandoned agricultural fields. Herbivory treatments were applied as a gradient of cotyledon removal for A. rubrum with 0, 25, 50, 75, and 100% of cotyledon tissue removed. Cotyledons from Q. palustris were clipped and removed (control, early, and late removal) to create a gradient of seed reserve availability. The competition treatment consisted of plugs of old-field vegetation that filled the pots with perennial cover. Mortality of seedlings was higher with competition. There was a significant interaction between herbivory and competition with the highest mortality occurring with competition at the highest intensity of herbivory in both species. Herbivory reduced biomass for Q. palustris only, while competition reduced biomass in both species. Neither species showed an interaction between herbivory and competition for growth. There was a significant interaction between herbivory and competition on allocation patterns for both species, with greater allocation to roots with competition at the highest intensity of herbivory. This study demonstrates the potential for cotyledon herbivory and competition to interact, altering the invasion of tree seedlings into abandoned agricultural land.     

Tree seedling establishment under insect herbivory: edge effects and inter- annual variation

As the density and species composition of insects may change in relation to distance from the forest edge, the role of herbivory in tree establishment may also change across edges. To determine the importance of insect herbivory in tree establishment, insect densities were experimentally altered at different distances from the forest edge. Plots were established at three distances from the edge, with plots located in forest, edge, and field habitats. In half of each plot, insect densities were reduced by insecticide application. Seeds of two tree species, Acer rubrum and Fraxinus americana, were planted into each plot in 1995. The experiment was repeated in 1996 with the addition of Quercus palustris and Quercus rubra.Distance from the forest edge was the most important factor in determining seedling emergence and mortality. Overall seedling performance increased from field to edge to woods, although responses varied among species. In 1995, a drought year, insect removal increased emergence and decreased mortality of tree seedlings. In 1996, a year with normal precipitation, insect removal had much less effect on A. rubrum and F. americana. For the two Quercus species, mortality was reduced by insect removal. The tree species differed in their susceptibility to insect herbivory, with Acer rubrum the most susceptible and Fraxinus americana the least. Herbivory by insects was shown to have the potential to affect both the composition and spatial pattern of tree invasions. Herbivore importance differed greatly between the two years of the study, making the interaction between insects and tree seedlings variable both in space and time.     

Temporal consistency in the spatial pattern of seed predation across a forest – old field edge

Seed predation is an important factor in determining the rate of tree establishment in abandoned agricultural land. Edges, through altered habitat use by small mammals, may influence the spatial pattern of forest regeneration in these successional sites. To determine the spatial pattern of seed predation across a forest-old field edge, we used a grid that began 30 m inside the forest and extended 60 m into the old field. Seed stations were placed at regular 10-m intervals and were monitored for removal of Acer rubrum seed for 50 d. This design was repeated over four years (1995–1998). Small mammal trapping was conducted in the final year of the study to determine the spatial pattern of seed predators within the site. Removal rates varied among the four years of the study with years of high and low removal rates. However, the spatial pattern of seed removal rate was similar in all years. Final survival ranged from 0.7–15.5% of seeds, with lower final survival in years with faster rates of seed removal (1996 and 1998). Seed removal rates and rates of discovery were greatest at the forest edge and decreased with distance into the old field. The number of seeds surviving to the end of the experiment also varied across the edge gradient, with highest survival at greater distances into the old field in low predation years. Seed removal rate covaried with spatial pattern of Peromyscus leucopus captures within the site. Seed removal and discovery was also higher under the exotic shrub Rosa multiflora, which may have provided cover for foraging seed predators. These indirect effects of edges on plant communities can potentially alter the rate and spatial pattern of tree invasion into disturbed lands and illustrate the importance of understanding plant-animal interactions in the context of habitat fragmentation.     

Mycorrhizal colonization and macronutrient status of cliff-edge Thuja occidentalis and Acer saccharum

This work was done to determine if suppressed growth of stunted old-growth Thuja occidentalis along Niagara Escarpment cliff edges was associated with low concentrations of tissue macronutrients and/or the absence of mycorrhizae, and if the restriction of Acer saccharum from cliff edges could be due to similar limitations Mycorrhizal colonization rates and foliar concentrations of N, P, K, Ca, and Mg were compared between the cliff face, cliff edge, deciduous forest and a swamp for T occidentalis , and between the cliff edge and deciduous forest for A saccharum There were statistically significant differences in tissue nutrient concentrations and mycorrhizal colonization between species but not among habitats This suggests that the stunted growth of T occidentalis on the cliff face, and the absence of A saccharum from the cliff edge are not due to limitations imposed by macronutrients or lack of mycorrhizae     

Spatial analysis of an invasion front of Acer platanoides: dynamic inferences from static data

It is an open question whether the invading tree species Acer platanoides is invading and displacing native trees within pre-existing forest stands, or merely preferentially occupying new stands of secondary forest growth at the edges of existing forests. Several threads of spatial pattern analyses were used to assess the invasibility of A. platanoides , and to link the invasion to the structure of a plant community in the deciduous forest of the northeastern United States. The analyses were based on maps of a contiguous 100×50 m area along an A. platanoides infestation gradient.
The distribution of A. platanoides was highly aggregated and the population importance value increased from 28.1 to 38.5% according to mortality estimated from standing dead trees, while the distribution of native tree species was close to random and importance value of Quercus spp. decreased from 33.4 to 26.9% over time. The size distributions of each tree species across distance indicated that A. platanoides was progressively invading the interior of the forest while the native species (including A. rubrum ) were not spreading back towards the A. platanoides monospecific patch. The null hypothesis of no invasibility was rejected based on quantile regressions.
There were negative correlations between A. platanoides density and the densities of native species in different functional groups, and negative correlation of A. platanoides density and the species diversity in forest understory. The null hypothesis that A. platanoides invasion did not suppress native trees or understory was rejected based on Dutilleul's modified t-test for correlation, consistent with experimental results in the same study site.
The combination of multiple spatial analyses of static data can be used to infer historical dynamical processes that shape a plant community structure. The concept of "envelop effects" was discussed and further developed.     

Carabid beetles (Coleoptera: Carabidae) at forest-farmland edges in southern Finland

We studied carabid beetle abundance at eight forest-farmland edges using pitfall traps across 60-m gradients (30 m into the forest, 30 m into the adjacent farmland) in southern Finland in May–August 2001. Carabid assemblages changed gradually across the studied gradients, the most drastic changes occurring right at the edge (5 m). Forest-associated carabids were often caught in farmland habitat within 20–30 m from the edges, and open-habitat carabids were also caught in the forest patches. However, these two groups responded to the edge in slightly different ways. Forest carabids were abundant all across the gradient from forest interior to the edge ( 80 m 9), while open-habitat carabids showed a drastic abundance decrease toward the forest, 5–10 m before the edge the abundance-change slope across the edge: gradient was steeper for open-habitat than for forest carabids. Wing-dimorphic and long-winged carabids increased more steeply from forest to farmland, compared to short-winged carabids. Moreover, carabids associated with dry and moist habitat showed indications of stronger response to the edge than did eurytopic species. The pair-wise comparisons between predatory/mixed-diet carabids and seed-eaters, spring and autumn breeders, and day- and night-active species did not indicate edge-response differences.     

哀牢山中山湿性常绿阔叶林木质藤本对边缘效应的响应

全球范围内森林片断化现象日益严重。与其他木本植物(乔木和灌木)相比, 木质藤本更趋向于分布在片断化森林的边缘, 因而了解木质藤本对边缘效应的响应对于进一步了解其对森林动态的影响极其必要。本文对哀牢山中山湿性常绿阔叶林林缘到林内环境梯度上木质藤本的变化进行了调查。在形成年龄分别为13年、35年和53年的3种类型的林缘, 设置从林缘向林内连续延伸的长方形样地(20 m × 50 m)各10个(总面积3 ha), 每个样地再划分为5个20 m × 10 m的样方。在每个样方内对胸径≥ 0.2 cm且长度≥ 2.0 m的木质藤本进行了每木调查。在3 ha的林缘样地中共记录到木质藤本植物2,426株, 隶属于14科19属31种。木质藤本的物种丰富度和多度均随距林缘距离的增加而降低, 边缘效应深度在35年林缘的边缘为30 m, 13和53年林缘的边缘则为20 m; 它们的胸高断面积在53年林缘的边缘效应深度为20 m, 但在13和35年林缘的不同距离上差异不显著。木质藤本对边缘效应的响应在物种水平上存在显著差异, 主要呈现正向和中性的响应格局, 包括只分布于林缘的物种, 和从林缘到林内环境梯度上密度逐渐降低的物种; 也有对边缘效应不敏感的物种。典范对应分析(CCA)表明, 林冠开度、边缘形成年龄和土壤水分是决定木质藤本在片断化森林边缘分布的重要影响因子。     

Changes in community and population responses across a forest-field gradient

The ground-layer vegetation of a forest-old field edge gradient was sampled to determine the effects of the edge on spatial patterns of plant species and community attributes. Species showed individualistic responses to the forest edge, with peak abundance at different spatial positions relative to the edge. Principal components analysis resulted in three axes which explained a total of 63.2% of the variation within the data set. The first two PCA axes were related to distance to the forest edge. The third separated plots into those that were dominated by Solidago canadensis. and those that were dominated by Solidago juncea. All population and community-level attributes varied along the edge gradient. Species richness, Shannon-Wiener diversity, and total percent cover increased from the forest to the edge, with slight declines 60 m from the edge in the field. Among-plot heterogeneity was higher at the edge than in either the forest or the field. Exotic species had peak abundance within 20 m of the edge inside the forest and are restricted to the edge. Most population and community-level attributes showed edge responses on both sides of the edge. This emphasizes the need to study edges as gradients that include both disturbed and undisturbed habitats.     

Interspecific variation in sapling mortality in relation to growth and soil moisture

To examine the causes of landscape variation in forest community composition, we have quantified sapling mortality as a function of growth and soil moisture for seven dominant species in transition oak-northern hardwood forests of the northeastern USA. We located saplings in sites that encompassed a wide range of variation in soil moisture and light availability. In mesic conditions, the probability of mortality decays rapidly with increasing growth among shade tolerant species and more gradually among shade intolerant species: the rank order of survivorship at low growth rates is Tsuga canadensis > Fagus grandifolia > Acer saccharum > Fraxinus americana > Acer rubrum > Quercus rubra > Pinus strobus . The relationship between probability of mortality and growth does not vary with soil moisture among species insensitive to drought: Tsuga canadensis , Quercus rubra, and Pinus strobus . However, probability of mortality increases substantially with decreasing soil water availability for the other four species. Acer saccharum and Fagus grandifolia have high mortality rates under xeric conditions even when their growth is not suppressed. Acer rubrum and Fraxinus americana exhibited a steady but more gradual increase in the probability of mortality with decreasing soil moisture. Among the five deciduous hardwood species we examined there is a weak inverse relationship between the ability to survive growth suppression, a measure of shade tolerance, and the ability to survive in xeric conditions, a measure of drought tolerance. Tsuga canadensis , however, is tolerant of growth suppression and exhibits high survivorship in xeric conditions, while Pinus strobus is intolerant of growth suppression but insensitive to soil moisture. Species differences in water-dependent mortality are consistent with the species distributions across landscape gradients of soil water availability.     

How forest edge-center transitions in the herb layer interact with beech dominance versus tree diversity

Aims Forest fragmentation and the associated augmentation of forest edge zones are increasing worldwide. Forest edges are characterized by altered plant species richness and community composition. As the tree layer and its species composition has been shown to influence herb layer composition, changes in tree species composition or richness may weaken or strengthen edge effects in forest ecosystems. We studied effects of the edge–center transition, tree species composition and their potential interaction on the understory vegetation in the Hainich National Park, Germany's largest connected deciduous forest, allowing to cover large edge–center transects.Methods We established 12 transects in an area of 75 km 2 of continuous forest, 6 beech-dominated and 6 in multispecies forest stands. Each transect reached from the forest edge up to 500 m into the forest interior. Vegetation relevés were conducted in regular, logarithmic distances along each transect.Important findings Herb species richness was influenced by an interaction of edge effects and tree diversity level. With increasing distance from the forest edge, herb species richness remained constant in multispecies forest stands but rapidly decreased in beech-dominated forest stands. Further, herb richness was higher in the interior of multispecies forest stands. Percent forest specialists increased and percent generalists decreased with distance from the edge and this contrasting pattern was much more pronounced in beech-dominated transects. By using structural equation modeling, we identified litter depth mediated by tree species composition as the most important driver of herb layer plant species richness.     

Tree Regeneration and Understory Woody Plants Show Diverse Responses to Forest–Pasture Edges in Costa Rica

ABSTRACT Edge effects along tropical forest–pasture margins are thought to cause a shift toward early successional characteristics of the understory forest vegetation. We tested this idea by sampling vegetation at five forest sites in northeast Costa Rica each of which had edges that were established over 20 yr earlier. Four of these sites had been selectively logged. We sampled woody plants >0.2 and ≤1.3 m height in 54 m² within 0.2 ha plots at edges (N=14), and at 150 m (N=11) and 300 m from edges (N=9). Composition and diversity did not vary with edge distance. Abundance of tree regeneration, mainly of canopy and emergent species, increased at edges. Abundance of lianas and slow‐growing tree species did not differ significantly across the sampling locations. Weighted mean wood density varied little, with a reduction at edges for canopy species. Palms were less abundant at edges, but not less species rich. At edges, these plant assemblages maintain many of the characteristics of forest interior vegetation, though the changes observed may indicate ongoing functional change. Degradation of forest–pasture edges is not a universal feature of tropical forest fragmentation, and forests with high rates of natural turnover might have a high capacity to maintain themselves within forest edges alongside pasture.     

Edge effect in different groups of organisms: vascular plant, bryophyte and fungi species richness across a forest-grassland border

Six transects were established on the edges of two deciduous forests near Krosno (Carpathian Foothills) to compare the species richness pattern of vascular plants, bryophytes and fungi. The transects had the shape of a cross with one arm 10 m along the forest edge and the other across the edge, 50 m into the forest interior and 12 m into the grassland. They consisted of 2×2 quadrats. The strongest edge effects were recorded for bryophyte, shrub and tree species richness, the weakest for herbaceous plant species richness. Overall vascular plant species richness and herbaceous species richness were higher in grassland than in the forest and peaked in grassland, 3 m from the forest edge. The shrub species richness was highest 1 m from the edge (in the forest) and the tree species richness 3 m from edge. Bryophyte species richness had roughly the same level across the grassland and within the first several meters of the forest, except for the 2 m zone on the edge itself where species richnes was as low as in the forest interior. Fungi species richness was low in the grassland and on the forest edge and rose dramaticaly a few meters from the edge, ramaining at the same level within the forest. The species composition across the forest-grassland border was analysed using detrended correspondence analysis. It revealed that in the case of bryophytes the increase in species richness did not correspond to a change in species composition, such as might have been caused by a general increase in bryophyte density.     

Forest edge contrasts have a predictable effect on the spatial distribution of carabid beetles in urban forests

Fragmented urban forest remnants are characterised by sharp edges and are bordered by various land-use types, which may have a considerable effect on the fauna and flora at forest edges, and into forest interiors. To investigate the effects of differentially contrasting edges (low vs. intermediate vs. high) on carabid beetle assemblages in urban boreal forests, we placed pitfall traps along a gradient from 6?m into three matrix types (secondary forest vs. grassland vs. asphalt) up to 60?m into urban forest patches in the cities of Vantaa and Helsinki, southern Finland. Individual species and carabid beetle assemblages were strongly affected by edge contrasts and distance from the forest edge. The strongest effect on individual species was caused by high contrasting edges: generalist and open-habitat species were favoured or not affected while forest specialists were affected negatively. Effects of the abundances of potential prey and competitors on the carabid beetles were also evaluated. Forest and moisture-associated carabid species were negatively to neutrally associated with springtail abundances while generalist and open habitat, and dryness associated species were more positively related to springtail abundances (a potential food source). In terms of potential competitors, forest and moisture-associated carabid species were negatively and/or neutrally affected by ant and wood ant numbers, while generalist and open-habitat species were neutrally to positively associated with these taxa. It appears that carabid beetle habitat associations are more important in the responses of these beetles across edges of different contrast than are the prey and competitor numbers collected there. We recommend the creation of “soft” or low-contrast urban edges if the aim of urban management is to protect forest carabids in cities.     

The Effect of Spatial Structure of Pasture Tree Cover on Avian Frugivores in Eastern Amazonia

The movement of frugivores between remnant forests and successional areas is vital for tropical forest tree species to colonize successional habitats. The response of these species to the spatial structure of pasture tree cover is largely unknown. We studied avian frugivores that were found in primary forest edges and large pastures in eastern Amazonia, Brazil. We determined how the small‐scale spatial structure of pasture trees at forest edges affects five response variables: bird presence, visitation rate, duration of visit, species richness, and an index accounting for species’ level of frugivory and abundance in forests. We used hierarchical linear models to estimate the effect of four predictor variables on response variables: (1) clustering of pasture trees; (2) percent canopy cover of pasture trees; (3) distance of pasture tree to forest edge; and (4) tree crown area. The study species, many of which are widely distributed in the Neotropics, were generally insensitive to percent cover and clustering of trees. Frugivore visitation to individual trees remained constant as cover increased. Visitation was positively correlated with focal tree distance to forest edge and crown area. The positive relationship between distance and visitation rates may be due to the increased abundance of some resource further from forests. If pastures were abandoned the distance from forest edges would not likely limit frugivore visitation and seed deposition under large pasture trees in our study (i.e., up to 200 m distant).     

Rain Forest Structure at Forest-Pasture Edges in Northeastern Costa Rica

Land-use change in the Sarapiquí region of Costa Rica has resulted in a fragmented forest landscape with abrupt edges between forest and pasture. Forest responses to edge effects vary widely and can significantly affect ecosystem integrity. Our objective was to examine forest structure at 20+ yr old forest-pasture edges in Sarapiquí. Three transects with 0.095-ha plots at seven distances from forest edges were established in each of six forest patches. Stem density, basal area, and aboveground biomass in trees and palms ≥ 10-cm diameter at breast height were measured in all plots. In addition, hemispherical photographs were taken to determine leaf area index, understory light availability, and percent canopy openness. Linear mixed-effects models showed significantly higher tree stem density at forest edges, relative to interiors, a pattern reflected by increased stem density, basal area, and aboveground biomass in small diameter trees (≤ 20 cm) growing near edges. No differences in total tree basal area, aboveground biomass, or hemispherical photograph-derived parameters were detected across the forest edge to interior gradient. The recruitment of small diameter trees following edge creation has contributed to the development of dense vegetation at the forest edge and has aided in the maintenance of similar tree basal area and aboveground biomass between edge and interior environments. These data reflect on the robustness of forest edges in Sarapiquí, a characteristic that will likely minimize future detrimental edge effects and promote a number of high-value environmental services in these forests.     

Species traits and the response of open‐habitat species to forest edge in landscape mosaics

Human driven changes in land‐use have increased the need to understand how landscape structure affects species distribution. We studied how forest edges affected the distribution of birds in grasslands recently encroached by forest patches. We investigated how species’ biological traits influenced their response to vegetation change near forest edges. We censured birds along 300‐m line transects run into the open habitat perpendicularly to forest edges. We recorded habitat variables and landscape context along each transect and characterized edges and forest patches. We recorded 33 bird species in 153 transects for a total of 654 individuals. We analyzed species response to edges with generalized linear mixed models. Habitat preference was prevalent to explain species response to forest edges. The abundance of open‐habitat birds such as skylark Alauda arvensis decreased significantly in the vicinity of edges. This negative response extended within 150 m from the edge. The effect was disproportionately higher in open‐habitat species with high conservation concern. The abundance of species feeding or/and breeding in both forest and open habitat, such as woodlarks Lullula arborea, sharply increased near edges (positive edge response). Abundance of shrub and non‐shrub dependent species increased with distance to edge. The two species groups did no differ in abundance/distance to edge relationship. Intensity of species response to forest edges varied among transects in relation to transect vegetation characteristics. Edge length or aspect, diet and nest height had no direct effect. We discuss the possible role of variation in resources and nest predation risk to explain observed patterns.     

Leaf herbivory is more impacted by forest composition than by tree diversity or edge effects

Links between biodiversity and ecosystem functioning are well established. Beyond biodiversity per se, community composition can have strong effects on ecosystem functioning. Furthermore, spatial processes including edge effects, can impact the diversity-functioning relationship. These spatial processes are especially relevant within a food web context, such as the transfer of plant biomass across the food chain through herbivory. The relative importance of diversity, community composition and spatial context on herbivory pressure at the community and the species level is, however, poorly understood.To fill this gap in our understanding, we studied to what degree herbivory in temperate forest plots varies according to edge distance, tree diversity and forest composition. In contrast to the prevailing view of tree herbivory increasing at forest edges, we found that the effects of forest edge and tree diversity on leaf herbivory were masked by effects of forest composition, i.e. the specific contributions of the tree species. The strongest composition effect found was increased herbivory on Quercus robur in the presence of Fagus sylvatica.Our findings highlight that neither edge distance, tree diversity, nor the interaction affected one ecosystem function, namely herbivory, whilst tree community composition did. This warrants consideration of identity and composition effects in future studies if we are to deepen our understanding of the determinants of ecosystem functions across systems.     

Distributions of lizard species across edges delimiting open‐forest and sand‐mined areas

Abstract The distributions of lizards across habitat edges delimiting open‐forest and regenerating sand‐mined areas as a function of distance from the edge were studied at Tomago, New South Wales, Australia. Pitfall‐trapping was used to survey lizards across the northern edges of four forest fragments, to determine if lizards displayed characteristic responses across the edge, and whether these could be explained by the different habitat conditions. At each site, 11 equally spaced drift fences (each parallel to the edge) were arranged in a transect running perpendicular to the edge, and stretching 50 m into each habitat type. Captures of Amphibolurus muricatus (Agamidae) decreased substantially across the edge from the mine‐path to the forest so that it was identified as a mine‐path specialist lizard species. Captures of two skink species decreased across the mine‐path before reaching the edge, and were not caught (Ctenotus taeniolatus) or were seldom caught (Ctenotus robustus) in the forest, so they were identified as mine‐path specialist, edge avoiding, lizard species. Captures of Lampropholis delicata (Scincidae) increased across edges into the forest, consistent with the expectation for a forest specialist. Regression analyses indicated the responses to edges of three lizard species (A. muricatus, C. robustus and C. taeniolatus) were negatively correlated with canopy cover (probably due to its influence on temperature, as captures of A. muricatus and C. robustus were also correlated positively with mean daily temperature). In addition, the response of C. robustus correlated negatively with a vegetation factor (dense, even vegetation in the first 50 cm from ground level). The response of L. delicata correlated positively with understorey height. We have identified edge response strategies for four species of lizards across edges delimiting temperate open‐forest and mined areas, and identified habitat and microclimate variables that may have driven these responses.     

Inflow of seeds through the forest edge: evidence from seed bank and vegetation patterns

To determine the influence of the proximity of a forest edge on seed bank composition and diversity, we performed a seed bank sampling at ancient deciduous forests bordering intensive arable fields. Also vegetation patterns were taken into account. We hypothised that forest edges may facilitate the entrance of diaspores of invasive species into the forest and the successive incorporation of these species in the forest seed bank. We noticed a substantial influence of the proximity of an edge on seed bank composition at as well the forested side of the edge as the field side. The forest edge zone was limited to 3 m into the forest and the field edge zone extended 3m into the field. The seed bank samples of field and forest edge are characterised by a higher species diversity and seed density and a higher similarity between seed bank and vegetation, compared to field or forest samples. The forest edges contains fewer pioneer species in comparison with the forest interior and more competitive species and species of edges and clearings compared with field and forest samples. The seed longevity index increases towards the forest interior. We can conclude from our data that the forest and edge seed bank are composed by both seeds from recent dispersal processes and local seed set and by seeds originating from past vegetation on the site. Near the edge, actual seed input seems of primal importance. Further towards the forest interior seed input decreases and long-living seeds of past vegetation become more important. Ancient forest edges thus act as a barrier for seeds of species of the surrounding arable field.     

Edge effects on epiphytic communities in a Mediterranean Quercus pyrenaica forest

Question: What are the edge effect responses of epiphytic lichen communities in Mediterranean Quercus pyrenaica forest? Location: Central Spain. Methods: We established ten transects perpendicular to a road dissecting a well conserved remnant of Q. pyrenaica forest into two sections. Transects extended from the forest/road edge to 100 m into the forest. Data were collected from seven plots in each transect at different distances from the edge. Variables were grouped into stand scale variables (distance to edge, number of trees per plot, mean diameter per plot, irradiance) and tree scale variables (diameter and height of sampled trees, aspect of the sampled square and relative height of the square). We used General Mixed Linear Models and constrained ordination techniques to test the hypothesis that the spatio‐temporal heterogeneity of light and water controls the occurrence of lichens and bryophytes along the edge‐interior gradient in the Q. pyrenaica forest. Results: Microclimatic parameters vary in a non‐linear way; edge and interior stands showed the most divergent and extreme values. Although the micro‐environment within Mediterranean forests is heterogeneous, interior conditions are apparently suitable for the performance of some specific forest epiphytes. Consequently, species richness does not show significant differences along the gradient. Total epiphytic cover increases towards the forest interior, but distance to the edge together with other predictors at the tree scale (aspect and height of the square) are the most relevant predictors for the composition and structure of these communities. Conclusions: Composition and structure of epiphytic communities in a Mediterranean semi‐deciduous forest are affected by the edge between the forest and the road constructed. Since some extremely rare lichens only occur at interior stands, the conservation of these threatened elements requires urgent conservation measures because well preserved and unmanaged forests in the Mediterranean region are very rare.