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Article

Being Edgy: Ecotones of Ground Cover Vegetation in Managed Black Alder Habitats

by
Agnese Anta Liepiņa
,
Didzis Elferts
,
Roberts Matisons
*,
Āris Jansons
and
Diāna Jansone
Latvian State Forest Research Institute “Silava”, Riga Str. 111, LV-2169 Salaspils, Latvia
*
Author to whom correspondence should be addressed.
Forests 2025, 16(5), 846; https://doi.org/10.3390/f16050846
Submission received: 9 April 2025 / Revised: 14 May 2025 / Accepted: 16 May 2025 / Published: 19 May 2025
(This article belongs to the Special Issue Forest Disturbance and Management)
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Abstract

:
Retention forestry creates anthropogenic ecotones that diversify forest landscapes in terms of age and biomass. Such diversification can have ambiguous ecological impacts, raising uncertainties, particularly for black alder swamp woodlands, which are considered sensitive and are prioritized in EU conservation policy. This study aimed to examine the effects of adjacent clear-cutting on ground cover vegetation in 12 black alder stands in the hemiboreal zone in Latvia 11 to 120 years since the harvest. Ground cover vegetation was recorded by species along 40 m transects. The effects of the time since adjacent stand harvesting and exposure to the edge on species richness and Shannon diversity were assessed using linear mixed-effects models. A detrended correspondence analysis was used to explore the main environmental gradients. A total of 103 species were recorded: 15 in the tree and shrub layer, 66 in the herbaceous layer, and 22 in the moss and lichen layer. The exposure to the adjacent stand had a moderate positive effect on species diversity, while the effects of edge age were complex and varied by stand type. The scale of disturbance (the absolute length of the analyzed edge), rather than edge age or exposure, had the most pronounced effect on ground cover vegetation composition, suggesting persistent secondary edge effects that should be considered in forest management and conservation planning.

1. Introduction

Timber harvesting via retention forestry, which is an anthropogenic ecotone creation, as it fragmentates forest landscapes in terms of stand age and biomass [1,2,3], is common in Northern Europe; hence, there have been heated debates about its ecological effects [4,5]. Unlike natural disturbances, clear-cutting uniformly removes most of the biomass, potentially altering ecosystem dynamics even beyond the harvested areas [6,7], subjecting them to increased solar radiation, heat stress, and altered microclimatic conditions [8,9]. However, the edges affect environmental conditions on both sites, mitigating the effects of the disturbance in the harvested site [10,11,12].
At the forest edge, gradients of wind, light, temperature, and moisture create a dynamic zone where external conditions can alter the course of vegetation succession and ecosystem development [13,14,15,16]. The primary edge effect occurs as early-successional, light-demanding species colonize cleared areas but are later replaced by shade-tolerant species as the canopy regenerates and closes [17], and competition intensifies [18,19]. Several studies suggest that the secondary edge effect emerges later, as dense young tree stands alter microclimatic conditions and species interactions, leading to delayed impacts on shade-tolerant plants [11,20], which are constrained by structural changes and competition [21]. Moreover, the secondary responses, such as shifts in species composition, typically exceed the magnitude of primary structural changes in anthropogenic edges [15,16,22].
Ground cover vegetation can serve as a valuable indicator for edge effects due to sensitivity to light availability and organic debris chemistry, along with soil type and geogenic factors such as nutrient levels and moisture [23,24]. Plant communities are a vital component of forest ecosystems, supporting nutrient cycling, regulating soil moisture, and maintaining fertility while providing valuable habitats, food, and shelter for diverse species [25,26]. While primary microclimatic and vegetation edge effects develop rapidly yet are transient, secondary effects develop over time and reciprocally alter the environmental conditions at the edge, adding complexity to the process [20]. Furthermore, the interactions of changing microclimatic conditions and species composition highlight ground vegetation as a crucial mediator of forest health, particularly in ecotonal zones shaped by edge effects.
Black alder (Alnus glutinosa (L.) Gaertn) swamp forests of Europe, though often small and fragmented [27,28], sustain dynamic ecosystems along gradients of moisture, soil reaction, and climate [29,30] and provide a high richness in herbaceous species, which is why alder forest habitats are included in EU-scale conservation plans (EU Council Directive 91E0*,92/43/EEC; [31]). Characterized by annual or periodic flooding while remaining waterlogged for much of the year, black alder swamp forests typically grow in terrain depressions, the edges of lentic habitats, swamps, and mires, where they support distinct ecological niches [32]. In addition, black alder is one of the few species adapted to anaerobic conditions [33]. Therefore, alder stands tend to provide unique habitats. Despite conservation efforts, alder swamp woods remain prone to threats such as the amplifying effects of climate change, invasive species, and human-induced hydrological and landscape modifications (e.g., timber harvesting) [34,35,36,37].
The interactions of anthropogenic edge creation and species composition affect adjacent areas; however, the magnitudes of the effects differ on local and landscape conditions [38]. A better understanding of forest ecotone creation is crucial for management and conservation, with such insights increasingly applied in close-to-nature management strategies [39,40]. To contribute to this growing body of research, the present study aimed to investigate the effects of adjacent clear-cutting on ground cover vegetation in black alder forest stands. Black alder forests, although representing only 3% of the managed forest area in Latvia, offer a valuable model due to their scattered distribution and the pronounced edge effects they experience. By focusing on this unique forest type, this study aims to add to anthropogenic ecotone research in Northern Europe and provide insights relevant for conservation and adaptive management in similar temperate ecosystems.

2. Materials and Methods

2.1. Description of the Study Sites

The study was conducted in the hemiboreal forest zone in the central part of Latvia (Figure 1). The last 30-year mean monthly temperatures ranged from −5 °C in January to 18.2 °C in July [41]. The annual mean temperature for the study region was 6.9 ± 0.7 °C, and the mean annual precipitation was 676.8 ± 74.9 mm [41]. The study region had flat topography characterized by lowland conditions.
To characterize the effects of adjacent clear-cutting on ground cover vegetation, 12 black alder forest stands, which had one clear-cut stand adjacent to them, were selected (Figure 1). Two types of black alder forest stands were distinguished based on hydrological modification: stands subjected to hydroamelioration and those remaining in an unaltered hydrological state. The first group was classified as black alder swamp woods (ASW), which had a natural origin and no management activities persisting (n = 6) (Myrtillosa turf. Mel. according to local classification [42] and the 9080_1* subgroup of Fennoscandian deciduous swamp woods, Habitats Directive Annex I [43]). The ASW stands were characterized by annually or temporally flooded depressions and a hummocky topography. The other type of alder stands was categorized as biologically old, black alder-dominated forest stands growing on eutrophic drained peat (EDP) soils (Dryopterioso-caricosa according to local classification [42] and the 9080_3* subgroup of Fennoscandian deciduous swamp woods, Habitats Directive Annex I [43]).
The age of the ASW stands ranged from 102 to 128 years, but for the EDP alder stands it ranged from 87 to 113 years (Table S1). The area of the alder stands ranged from 1.0 to 4.6 ha, with a mean of 2.4 ± 1.2 ha (mean ± standard deviation). The total stand basal area was more uniform among the ASW stands, ranging from 25.0 to 30.0 m2/ha, whereas in the EDP stands, the stand basal area ranged from 11.0 to 34.0 m2/ha. All selected stands were dominated by black alder in the canopy layer and had an admixture of either Norway spruce, Picea abies; birch, Betula pendula; or Scots pine, Pinus sylvestris. Additionally, no noticeable signs of forest management were observed in the alder stands at the time of sampling.
Timber harvesting in forest stands adjacent to alder stands has taken place for 11 to 120 years before this study, providing a set of differently aged (younger and older) forest edges (Table S1). The length of the mutually shared edge (between each set of alder and harvested stand) ranged from 54.4 to 178.0 m, while the area of the harvested stand ranged from 0.4 to 3.3 ha. The forest types of the adjacent forest stands were similar amongst the two black alder stand groups, mainly characterized as birch-, Norway spruce-, or Scots pine-dominated (or mixed) stands growing on mesotrophic, mineral, silty soils. However, three of the EDP stands had the same type of adjacent stand (stands on eutrophic drained peatlands), dominated by either birch or black alder.

2.2. Measurements

To examine ground cover vegetation responses to edge effects, transects were established perpendicular to the boundary between each black alder stand and the adjacent clear-cut area. To assess changes in vegetation composition depending on the distance from the adjacent stand, square sampling plots measuring 1 × 1 m were placed along the transect at various intervals (0 m, 5 m, 10 m, 20 m, and 40 m) from the edge of the stands. The sampling plots were arranged at each distance interval boundary—one in the center on the transect line and one on each side, positioned 1 m away from the edge of the central sampling plot (Figure 2). A total of 15 sampling plots were established along each transect for vegetation assessment.
The placement of the transects within the black alder stands was based on several criteria:
(1)
The length of the established transect does not exceed the length of the shared edge between the managed stand and the black alder stand;
(2)
The length of the transect placed in the black alder stand does not exceed the distance to the edges of other forest stands bordering the habitat;
(3)
The distance between two transects is not less than the width of one transect (5 m).
Depending on the size, shape, and configuration of the black alder stands in relation to the managed forest stand, one to two transects were placed in each alder stand. The areas that were generally not characteristic of the stands (e.g., ditches, trails, etc.) were avoided.
In each grid plot, the relative projective cover (%) of ground vegetation was recorded by species, distinguishing between vascular plants, woody plants in the herbaceous layer, and bryophytes. The projective cover for each plot was averaged across the three layers, allowing the total to exceed 100%. Additionally, the projective cover of wood debris and forest litter was documented. Vegetation surveys were conducted in June–July 2022 and 2023.

2.3. Data Analysis

To assess the spatial influence of adjacent forest management, the exposure of ground cover vegetation in black alder stands was calculated as the angle between the center of each grid plot and the shared forest edge (Figure 2). The angle was calculated for each grid plot of the transect. The diversity of the ground cover vegetation species was characterized by species richness and the Shannon–Wiener diversity index, which was calculated for each grid plot.
To evaluate the effects of edge-related and stand-level factors on species richness and diversity, differences in the number of species and diversity index values were assessed using linear mixed-effects models (LMMs). In particular, the transect code was set as a random effect, while the fixed factors included the grid plot’s exposure to the shared edge (represented as an angle and expressed in degrees (°)), stand type (ASW or EDP), the age of the adjacent stand (in years), and interactions of stand age and exposure with black alder stand type. Hence, if any of the interactions in the model were not statistically significant, they were excluded, and the significant models were compared using AIC (Akaike’s Information Criteria) to identify the best model. Then, if any factor or interaction had a significant effect, a Post Hoc test was conducted to compare the levels. LMMs were used for the Shannon index, while Poisson generalized linear mixed-effects models (GLMMs) [44] were applied for the assessment of the number of species. Additionally, plots that contained only one or two species were excluded from the analysis.
To analyze the main environmental gradients affecting ground cover vegetation in the studied stands, a detrended correspondence analysis (DCA) was applied to the sample plot data [45]. This indirect method of assessing ecological gradients involved detrending with 26 segments and downweighing rare species according to [46]. The DCA was supplemented with a matrix of stand and edge properties, including exposure towards the adjacent stand, age of the alder stands, age of the adjacent forest stand, length of the mutual edge, basal area of the black alder stands, and basal area of the adjacent stands, to test for correlation with the principal two gradients in ground cover vegetation. The stand properties tested included data obtained from the National Forest Service database for each stand, as well as angle measurements for each of the grid plots.
The statistical analysis was performed in the program R version 4.4.1. [47] and packages “vegan” [48], “lme4” [44], “emmeans” [49], and “lmerTest” [50]. The spatial analysis was performed in the program QGIS version 3.26.

3. Results and Discussion

The Diversity of Forest Ground Cover Vegetation

The ground cover vegetation species richness in the studied stands was moderate, as a total of 103 ground cover vegetation species were identified across all studied alder stands, among which there were 66 in the herbaceous layer, 15 in the shrub and tree layer, and 22 in the moss and lichen layer (Table S2). The observed species richness was lower than that reported in previous studies of black alder swamp woodlands, which was recorded as 113 vascular plant species in Norway [31] and as many as 171 bryophyte species in Sweden [51]. However, the differences in species richness might be partially related to the implemented survey methodology and the assessed substrates, especially regarding the bryophyte assessment methodology [51]. The spatial complexity of alder swamp forests is crucial, as it fosters habitats for diverse species adapted to hummocks and depressions and related varieties of growing conditions [31,52,53]; thus, the given richness numbers are likely underestimates.
The overall richness of ground cover vegetation was somewhat higher in the ASW compared to EDP stands (Table S3), with 83 and 75 species observed, respectively. The site types differed in terms of the sets of common species (Table 1), indicating pronounced effects of melioration [54,55,56], likely as the chemical composition of organic debris, soil type, and geogenic factors like nutrient availability and moisture have been altered [23,57]. In the ASW stands, 53 species were recorded in the herbaceous layer (Table S3), with the most common being Oxalis acetosella L., Galium palustre L., Lysimachia vulgaris L., Dryopteris carthusiana (Vill.) H.P. Fuchs, and Carex elongata L. (Table 1), which had moderate-to-low mean cover values and are common ground cover vegetation species for alder-dominated swamp forests in the Baltic region [43,58,59]. In the shrub and tree layer, 10 species were identified, the most common being Frangula alnus Mill., Rubus saxatilis L., Rubus idaeus L., Sorbus aucuparia L., and Quercus robur L. Twenty species were recorded in the moss and lichen layer, with the most frequently observed being Calliergonella cuspidata (Hedw.) Loeske, Plagiomnium affine (Blandow ex Funck) T.J.Kop., Thuidium tamariscinum (Hedw.) Bruch, Schimp. & W.Guembel, Dicranum polysetum Sw. ex anon., and Eurhynchium angustirete T.J.Kop., also typical for alder swamp woodlands [51].
In the hydroameliorated EDP stands, the ground cover vegetation was dominated by ecologically more plastic, as well as ruderal and mesophilic species [35,60], while their distribution among life forms was comparable to that of ASW. In the herbaceous layer, 48 species were identified (Table S3), with the most frequently occurring being Oxalis acetosella L., Impatiens parviflora DC., Galeobdolon luteum Huds., Dryopteris carthusiana (Vill.) H.P. Fuchs, and Urtica dioica L. (Table 1). Impatiens parviflora D.C. is an invasive, alien species [61], which might have spread in the EDP stands due to large-scale disturbance and improved growing conditions, thus posing a threat of replacing flood-tolerating species characteristic of alder stands [62] and overall herbaceous plant diversity [63]. This was hinted by slightly lower overall plant diversity in the drained alder stands. Species that were frequent in the ASW, such as Galium palustre and Carex elongata, showed reduced frequency and cover in the EDP stands or were absent (Table S3), indicating a loss of species specialized to high moisture regimes. In the shrub and tree layer, species overlap between the two site types was more common, but differences in abundance were still apparent, as a total of 12 species were recorded, of which the most common were Rubus idaeus L., Rubus saxatilis L., Sorbus aucuparia L., Frangula alnus Mill., and Fraxinus excelsior L., similar to the set in the ASW stands. However, Rubus idaeus L. and Rubus saxatilis L. increased notably in frequency and cover in the EDP stands, reflecting their ability to exploit increased light and nutrient availability [64]. In the moss and lichen layer, 15 species were recorded, with the most frequently observed being Plagiomnium affine (Blandow ex Funck) T.J.Kop., Eurhynchium angustirete (Broth.) T.J.Kop., Plagiomnium ellipticum (Brid.) T.J.Kop., Calliergonella cuspidata (Hedw.) Loeske, and Plagiomnium cuspidatum (Hedw.) T.J.Kop., consistent with observations within the region [59].
The time since the large-scale disturbance (harvesting of the adjacent stand) had a complex effect [65] on the diversity metrics of ground cover vegetation, as indicated by the significant interaction of the effects of stand type, adjacent stand age, and exposure on species richness and Shannon diversity (Figure 3A,C; Table 2). In the ASW stands, both the number of ground cover species and species diversity decreased significantly (p < 0.05) with increasing adjacent stand (edge) age (Figure 3A,C). In contrast, the EDP stands exhibited the opposite trend, with species richness and diversity increasing as the age of the adjacent stand increased. This shows the variation in the secondary edge effects between the two stand types [11,20], likely due to the edaphic and hydrological conditions in alder stands [62,66]. The abiotic and biotic edge effects can extend deep into forest interiors, though the scale can vary [16]. Moreover, the measured exposure to the adjacent stand had a consistent effect on the total number of ground cover species and the Shannon diversity index (p > 0.05) in both alder stand types, though the magnitude of these effects varied (Figure 3B,D), as indicated by intercepts. While both species numbers and diversity increased with higher exposure angles, the relationship was statistically significant only for the total number of species (p < 0.05) (Table 2).
The life forms of ground cover vegetation (represented by herbaceous, tree, shrub, moss, and lichen layers) showed contrasting responses to the effects of stand type, adjacent stand age, and exposure to the adjacent stand (Figure 4). Such differences might apparently be related to competition as the ecosystem recovers from the disturbance [67,68,69]. In the herbaceous layer, the relationship between the species richness and the age of the adjacent stand was type-specific (Figure 4A,B; Table 2), while showing a uniform response to the exposure to the adjacent stand. In the ASW stands, the number of herbaceous species declines significantly with increasing age of the adjacent stand, whereas in the EDP stands, it shows a moderate increase. The observed contrasting patterns in species richness likely stem from differences in how secondary edge effects unfold in each stand type. For instance, older edges likely experience increased canopy closure, reducing light availability and intensifying competition for resources [18,19], thus potentially reducing herbaceous species richness in the ASW stands. No significant differences were found in the richness of herbaceous species based on plot exposure to the adjacent stand (Table 2).
In contrast to the herbaceous layer, the species richness of the tree and shrub layer showed a uniform response to the age of the adjacent stand and type-specific responses to the exposure to the adjacent stand (Figure 4C,D; Table 2). As the exposure to the adjacent stand increased, the number of species in the shrub and tree layer increased in the EDP stands but showed a decline in tendency in the ASW stands (Figure 4C,D). The relationships between the richness of the moss and lichen layer and the age of the adjacent stand, as well as the exposure to the adjacent stand, were significant, positive, and uniform across the stand types (Figure 4E,F). This indicates the preference for moss and lichens, which are often considered biological indicators [70], for older ecotones, hinting at the positive effects of forest landscape diversity [71]. Most of the studied black alder swamps occur as small fragments in the landscape, which means that they are affected by microclimatic edge effects [28,38]. It is also likely that the distance to other black alder swamps or other types of forests is important for the dispersal of bryophytes among the black alder swamps [72,73].
As the responses of species richness to edge effects were specific for types (Table 2), separate ordination was performed for each stand type based on the projected cover of species (Figure 5A,B). In both stand types, two continuous gradients were estimated, which were generally comparable. In the EDP stands, a more distinct assemblage amongst sample plots was observed (Figure 5B), as they were arranged in two separate groups, while the ASW stands showed a greater dispersion (Figure 5A).
The environmental gradient assessment was difficult for the ASW stands, possibly due to the plasticity of and microrelief of the alder stands, where communities of species occur in a mosaic [32]. The first axis had a gradient length of 6.35, indicating the unimodality of the species cover data. The primary axis likely reflects a gradient related to soil fertility and potentially moisture conditions (Figure 5A), factors that have been identified as important drivers of species composition and diversity in floodplain forests [75,76], although soil moisture was not directly measured in this study. The right side of the graph likely includes sample plots from the hummocky areas of the ASW stands, as suggested by the abundance of species such as Hylocomnium splendens (Hedw.) Schimp., Vaccinium sp., Dicranum polysetum Sw. ex anon., and Rhytidiadelphus triquetrus (Hedw.) Ochyra & Stebel, which prefer semi-fertile, moderately moist soils [60]. Contrastingly, on the left side of the ordination space, species like Plagiomnium affine (Blandow ex Funck) T.J.Kop., Stellaria nemorum L., Lysimachia thyrsiflora L., and Impatiens parviflora DC., which thrive in wet, nutrient-rich, or waterfront areas [32], were more common, suggesting that temporary flooding occurred in the plots.
The second gradient was shorter (4.02) but strongly correlated with stand and edge properties, particularly the scale of disturbance, as highlighted by the correlation with the length of the mutual edge. This correlation with edge length exceeded that with edge age and the exposure of sample plots to the edge (Figure 5A), suggesting the effect of the scale of the ecotone [16]. Species positioned in the upper part of the ordination space included Carex elongata L., Carex acutiformis Ehrh., Lycopus europaeus L., Lycopodium annotinum L., and Plagiomnium ellipticum (Brid.) T.J.Kop., which generally thrive in wet, temporarily flooded areas or near water bodies [60]. The exception was Lycopodium annotinum L., which is more typical of well-drained coniferous or mixed forests, suggesting it may have originated from an adjacent, older stand. Contrastingly, species in the lower part of the ordination space, corresponding to shorter, younger edges with a smaller stand basal area, included Cirsium oleraceum (L.) Scop., Paris quadrifolia L., Circaea alpine L., and Rhodobryum roseum (Hedw.) Limpr. While these species also prefer wet conditions, they are more characteristic of shaded forests, hinting at the effects of light.
For the EDP stands, the lengths of the first and second gradients were similar (DCA1 = 3.19; DCA2 = 3.00) but shorter compared to the ASW stands, indicating a more homogeneous vegetation. The first gradient showed a modest correlation with edge length (Figure 5B). Nevertheless, in under-hydroameliorated conditions, the first gradient was likely related to light availability, as hinted by species ordination. On the right side of the ordination space, Urtica dioica L., Angelica sylvestris L., Crepis paludosa (L.) Moench, Padus avium Mill., and Galium palustre L., which can be characterized as shade-tolerant species [60], were abundant. Contrastingly, on the left side of the ordination space, species more typical of partial shade or moderate sunlight conditions, such as Rubus idaeus L., Trientalis europaea L., Solidago virgaurea L., and Corylus avellana L., were present.
Based on species abundance, the second gradient of the EDP stands likely represented a soil moisture gradient. Furthermore, the second axis correlated with several edge and stand properties, including the age of the adjacent stand and stand basal area in both the alder and the adjacent stands (Figure 5B). Species that prefer moderate to dry conditions, such as Vaccinium myrtillus L., Pleurozium schreberi (Willd. ex Brid.) Mitt., Hylocomium splendens (Hedw.) Schimp., Rhytidiadelphus triquetrus (Hedw.) Ochyra & Stebel, and Cirriphyllum piliferum (Hedw.) Grout., were positioned on the upper part of the ordination space. In contrast, the lower part of the ordination space seemingly indicates relatively wet soil conditions, as it was associated with moisture-adapted species such as Filipendula ulmaria (L.) Maxim., Iris pseudacorus L., Mycelis muralis (L.) Dumort., Geum rivale L., and Lycopus europaeus L. [29,60].
Moreover, in the EDP stands, the majority of the species characteristic of Fennoscandian deciduous swamp woods (Solanum dulcamara L., Iris pseudacorus L., Galium palustre L., Lysimachia vulgaris L., Thelypteris palustris Schott, Carex acutiformis Ehrh., etc. [29,43]) were positioned on the lower side of the ordination space (Figure 5B (highlighted in blue)). This implies that the species communities characteristic of alder habitats were more common in sample plots less exposed to the edge (i.e., smaller angle values). However, species commonly associated with Fennoscandian deciduous swamp woods in the ASW stands (Figure 5A; highlighted in blue) showed no clear trends along the first or second axis gradients, occurring in sample plots with both younger, shorter edges and older, wider edges. Accordingly, this suggests that hydroamelioration might increase the extent (distance from the edge) of the ecotone. It is likely that the ASW stands have already reached equilibrium, whereas the EDP stands have undergone drainage at some point in the past; therefore, the EDP stands are likely to exhibit a stronger response to adjacent environmental changes.

4. Conclusions

In the studied alder stands, harvesting of the adjacent stand did not exhibit an explicit negative edge effect on ground cover vegetation, as the composition was neither altered nor decreased from the typical composition at the ecotones. Furthermore, the ecotones bear more diverse ground cover vegetation. However, the edge effects were complex, as mediated by edaphic (hydroamelioration) conditions and time since the disturbance (harvesting). In the undrained stands, the herbaceous layer exhibited a faster decrease in edge effects compared to the drained ones. The spatial extent of the edge effects was comparable between stand types, with exposure to the adjacent stand showing a moderately positive and consistent influence on species richness and diversity. The scale of the disturbance (the length of the mutual edge), hence the size of the ecotone, rather than the age and exposure to the edge, affected the ground cover vegetation. Distinct patterns in species composition with increasing adjacent stand age and exposure were observed between alder swamp woods and alder stands on eutrophic drained peat soils, highlighting the role of forest type and management history in determining edge vegetation diversity and resilience. Considering the observed dynamics of the estimated edge effects (recovery after), the retained stands would rapidly become a source of ground cover species for the harvested adjacent stands to recover.

Supplementary Materials

The following supporting information can be downloaded at https://www.mdpi.com/article/10.3390/f16050846/s1, Table S1: “Properties of the studied black alder stands (two types: EDP—black alder forest stands growing on eutrophic drained peat soils; ASW—black alder swamp woods) and the adjacent (managed) stands (two types: EDP; MS—birch, Norway spruce of Scots pine dominated (or mixed) stands growing on mesotrophic, mineral, silty soils). The abbreviations for tree species conducting the basal area of the studied forest stands (A—Alnus glutinosa, B—Betula pendula, S—Picea abies, P—Pinus sylvestris)”; Table S2: “A complete list of the acronyms and the full scientific names (including authorities) for the species surveyed within all of the sample plots (across ASW and EDP alder stands), listed according to their vegetation layer affiliation. A synonym of the species name is shown where applicable. * Total number of the recorded species across all vegetation layers”; Table S3: “The frequency, mean projected cover and standard deviation (±sd) of all of the recorded ground cover vegetation species within each of the distinguished vegetation layers (herbaceous layer, tree and shrub layer, moss and lichen layer) across both alder stand types. The frequency is displayed for each alder stand type—ASW and EDP, separately. The species, for which values are highlighted in red (not present) in case of ASW stands, were found only in EDP stands and vice versa”.

Author Contributions

Conceptualization, Ā.J.; data curation, A.A.L. and D.E.; formal analysis, D.E.; investigation, A.A.L., D.E., R.M. and D.J.; methodology, A.A.L., R.M. and D.J.; supervision, Ā.J.; writing—original draft, A.A.L.; writing—review and editing, R.M. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by “The impact of forest management on forest and related ecosystem services”, JCS Latvia’s State Forests research program (agreement No. 5-5.9.1_007n_101_21_76), and “ForestBand—Climate smart solutions for enhanced biodiversity through increased presence of broadleaved trees in landscape”, Interreg VI-A Estonia-Latvia Programme, project No. EE-LV00188.

Data Availability Statement

The data are available upon request.

Conflicts of Interest

The authors declare no conflicts of interest.

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Forests 16 00846 g001
Figure 1. The location of the 12 studied black alder stands (EDP (n = 6) and ASW (n = 6)).
Figure 1. The location of the 12 studied black alder stands (EDP (n = 6) and ASW (n = 6)).
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Figure 2. The schematic representation of the transect used for ground cover vegetation surveying. The red dashed lines represent examples of the trajectories used to measure the angle (exposure) at which the centers of the sample plots (located in the alder stands) were in relation to the adjacent stand.
Figure 2. The schematic representation of the transect used for ground cover vegetation surveying. The red dashed lines represent examples of the trajectories used to measure the angle (exposure) at which the centers of the sample plots (located in the alder stands) were in relation to the adjacent stand.
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Figure 3. The Shannon diversity index values (A,B) and total number of ground cover vegetation species (C,D) for each alder stand type, depending on the age of the adjacent stand and the sample plots’ exposure towards the adjacent stand.
Figure 3. The Shannon diversity index values (A,B) and total number of ground cover vegetation species (C,D) for each alder stand type, depending on the age of the adjacent stand and the sample plots’ exposure towards the adjacent stand.
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Figure 4. The number of ground cover vegetation species for each alder stand type depending on the age of the adjacent stand ((A)—herbaceous layer, (C)—shrub and tree layer, (E)—moss and lichen layer) and the sample plot’s exposure towards the adjacent stand ((B)—herbaceous layer, (D)—shrub and tree layer, (F)—moss and lichen layer).
Figure 4. The number of ground cover vegetation species for each alder stand type depending on the age of the adjacent stand ((A)—herbaceous layer, (C)—shrub and tree layer, (E)—moss and lichen layer) and the sample plot’s exposure towards the adjacent stand ((B)—herbaceous layer, (D)—shrub and tree layer, (F)—moss and lichen layer).
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Figure 5. DCA ordination of ground cover vegetation species and sample plots according to their relative projective cover in black alder swamp woodland forest stands (on the left, (A)) and alder stands growing on eutrophic drained peatlands (on the right, (B)). Species’ acronyms are displayed according to [74]. The species highlighted in blue are considered characteristic to the habitat Fennoscandian deciduous swamp woods (9080) [43]. Vectors represent the correlation between the principal two gradients indicated by the scores of DCA and site properties. Abbreviations for corresponding vector names: Angle—exposure towards the adjacent stand (angle, °), Alder age—age of the alder stand (years), Edge age—age of the adjacent forest stand (years), Edge length—length of the mutual edge (m), Alder BA—stand basal area of the black alder stands (m2/ha), Adjacent BA—stand basal area of the adjacent stands (m2/ha).
Figure 5. DCA ordination of ground cover vegetation species and sample plots according to their relative projective cover in black alder swamp woodland forest stands (on the left, (A)) and alder stands growing on eutrophic drained peatlands (on the right, (B)). Species’ acronyms are displayed according to [74]. The species highlighted in blue are considered characteristic to the habitat Fennoscandian deciduous swamp woods (9080) [43]. Vectors represent the correlation between the principal two gradients indicated by the scores of DCA and site properties. Abbreviations for corresponding vector names: Angle—exposure towards the adjacent stand (angle, °), Alder age—age of the alder stand (years), Edge age—age of the adjacent forest stand (years), Edge length—length of the mutual edge (m), Alder BA—stand basal area of the black alder stands (m2/ha), Adjacent BA—stand basal area of the adjacent stands (m2/ha).
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Table 1. The most frequently recorded ground cover vegetation species in each of the distinguished vegetation layers (herbaceous layer, shrub and tree layer, and bryophyte layer) and the mean projected cover and standard deviation (±sd) of the presented species. The frequency is displayed for each alder stand type—ASW and EDP, separately.
Table 1. The most frequently recorded ground cover vegetation species in each of the distinguished vegetation layers (herbaceous layer, shrub and tree layer, and bryophyte layer) and the mean projected cover and standard deviation (±sd) of the presented species. The frequency is displayed for each alder stand type—ASW and EDP, separately.
Vegetation LayerAlder Swamp Woods (ASW)Alder Stands Growing on Eutrophic Drained Peat Soils (EDP)
SpeciesNumber of PlotsFrequency, %Mean Cover, %Sd, %SpeciesNumber of PlotsFrequency, %Mean Cover, %Sd, %
HerbaceousOxalAcet7666.110.410.9OxalAcet13398.523.112.0
GaliPalu5346.11.11.6ImpaParv9671.110.711.6
LysiVulg4942.61.42.3GaleLute6749.63.95.3
DryoCart4236.53.57.1DryoCart6548.15.37.9
CareElon4135.73.86.5UrtiDioi5641.55.09.6
Shrub and treeFranAlnu2017.40.51.4RubuIdae7454.88.912.3
RubuSaxa1916.51.03.0RubuSaxa3223.72.45.4
RubuIdae1311.30.93.0SorbAucu1914.10.52.1
SorbAucu119.60.21.0FranAlnu107.40.21.0
QuerRobu54.30.00.2FraxExce64.40.10.9
Lichen and mossCaliCusp6153.08.412.2PlagAffi5943.77.212.4
PlagAffi2521.72.26.4EuriAngu4130.45.711.9
ThuiTama1513.01.75.9PlagElli3123.03.48.2
DicrPoly1412.21.03.9CaliCusp1410.41.14.0
EuriAngu1412.21.75.5PlagCusp107.40.83.5
Table 2. Statistics of the generalized mixed-effects model (GLMM) and linear mixed-effects model (LMM). Each response variable has an individual column. Only the significant χ2 and F-values are displayed, and corresponding p-values are represented using significance-level abbreviations: 0.001 (***), 0.01 (**), and 0.05 (*).
Table 2. Statistics of the generalized mixed-effects model (GLMM) and linear mixed-effects model (LMM). Each response variable has an individual column. Only the significant χ2 and F-values are displayed, and corresponding p-values are represented using significance-level abbreviations: 0.001 (***), 0.01 (**), and 0.05 (*).
PredictorTotal Number of Species (χ2 Values)Number of Species in the Herbaceous Layer (χ2 Values)Number of Species in the Shrub and Tree Layer (χ2 Values)Number of Species in the Lichen and Moss Layer (χ2 Values)Shannon Diversity Index (F-Value)
Age of the adjacent stand4.3 *8.4 **-6.7 **-
Type of the alder stand10.7 **4.9 *--10.7 **
Exposure of the sample plots (angle)6.0 *--7.2 **-
Age of the adjacent stand by the type of the alder stand17.3 ***10.8 **--19.1 ***
Exposure of the sample plots (angle) by type of alder stand--5.5 *--
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Liepiņa, A.A.; Elferts, D.; Matisons, R.; Jansons, Ā.; Jansone, D. Being Edgy: Ecotones of Ground Cover Vegetation in Managed Black Alder Habitats. Forests 2025, 16, 846. https://doi.org/10.3390/f16050846

AMA Style

Liepiņa AA, Elferts D, Matisons R, Jansons Ā, Jansone D. Being Edgy: Ecotones of Ground Cover Vegetation in Managed Black Alder Habitats. Forests. 2025; 16(5):846. https://doi.org/10.3390/f16050846

Chicago/Turabian Style

Liepiņa, Agnese Anta, Didzis Elferts, Roberts Matisons, Āris Jansons, and Diāna Jansone. 2025. "Being Edgy: Ecotones of Ground Cover Vegetation in Managed Black Alder Habitats" Forests 16, no. 5: 846. https://doi.org/10.3390/f16050846

APA Style

Liepiņa, A. A., Elferts, D., Matisons, R., Jansons, Ā., & Jansone, D. (2025). Being Edgy: Ecotones of Ground Cover Vegetation in Managed Black Alder Habitats. Forests, 16(5), 846. https://doi.org/10.3390/f16050846

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