Next Article in Journal
Development of a Portable Calibration Chamber for PM Sensors Equipped with Wireless Connectivity Controlled by a Graphical Interface in Python
Previous Article in Journal
Multiscale Geophysical Characterization of Leachate and Gas Plumes in a Tropical Landfill Using Electrical Resistivity Tomography for Environmental Analysis and Diagnosis
 
 
Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
Journals
Environments
Volume 12
Issue 9
10.3390/environments12090339
environments-logo
Submit to this Journal Review for this Journal Propose a Special Issue
► Article Menu

Article Menu

share Share announcement Help format_quote Cite question_answer Discuss in SciProfiles
first_page
settings
Order Article Reprints
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Article

Biodiversity Status of Pure Oak (Quercus spp.) Stands in Northeastern Greece: Implications for Adaptive Silviculture

by
Efthimios Michailidis
1,
Athanasios Stampoulidis
2,
Petros Petrou
3,
Kyriaki Kitikidou
1,*,
Elias Pipinis
4,
Kalliopi Radoglou
1 and
Elias Milios
1
1
Department of Forestry and Management of the Environment and Natural Resources, Democritus University of Thrace, 68200 Orestiada, Greece
2
Department of Forestry and Natural Environment Management, Agricultural University of Athens, 36100 Karpenisi, Greece
3
Department of Forests, Ministry of Agriculture, Rural Development and Environment, 1414 Nicosia, Cyprus
4
School of Forestry and Natural Environment, Aristotle University of Thessaloniki, 54636 Thessaloniki, Greece
*
Author to whom correspondence should be addressed.
Environments 2025, 12(9), 339; https://doi.org/10.3390/environments12090339
Submission received: 14 August 2025 / Revised: 15 September 2025 / Accepted: 18 September 2025 / Published: 21 September 2025
Browse Figures
Versions Notes

Abstract

The aim of this study is the estimation of the biodiversity of pure oak stands within the jurisdiction of the Forest Service of Xanthi in northeastern Greece. Using a published graded biodiversity index that operates on management-plan description sheets, we scored five stand-level attributes (total wood stock, age of trees, canopy density, presence of regeneration, and stand aspect/orientation) for every eligible stand and classified biodiversity as low, moderate, or high. These data were sourced from the description sheets of pure oak stands found in the management plans of public forest complexes. Moderate biodiversity predominates (63.4% of stands), followed by low (33.5%), while high biodiversity is scarce (3.1%). Forest practice can influence all the factors which were used for the assessment of the biodiversity characterization of the stands except the aspect of the stand. From these factors the total amount of wood stock and the canopy density were the main factors which determined the low percentage of high-biodiversity stands. On the other hand, the age structure and the regeneration existence were the main factors which counterbalanced the negative influence of the total amount of wood stock and of the canopy density and thus led to the dominance of the stands characterized as having moderate biodiversity score.

1. Introduction

Biodiversity refers to the diversity of life on Earth, including living organisms and the ecosystems in which they live [1]. Biodiversity encompasses ecosystems, communities, species, populations, metapopulations, demes, individuals, and genes as well as the interactions between them [2]. The Convention on Biological Diversity has been in force since December 1993, and one of its main objectives is the sustainable use and conservation of biological diversity. Moreover, it is recognized that the sustainable use of biological diversity is the key for its maintenance [1]. Recent European reviews link stand structure and management to multi-taxon biodiversity and stress the need to report population-level patterns alongside plot studies [3,4]. Moreover, advances in mapping 3D forest structure with spaceborne and airborne LiDAR support the operational use of structure-based indicators for management scale biodiversity assessments [5,6].
The conservation of forest biodiversity is a critical responsibility at global, national, and local levels [7]. A comprehensive biodiversity-conservation plan must incorporate both protected areas and areas that are not managed primarily for conservation of biodiversity but are available for extraction of resources and production of commodities [2]. Therefore, there are many analyses and indices aiming to assess and quantify forest biodiversity to incorporate the relevant information into the management plans [7,8,9,10].
Stand structural attributes are strongly related to biodiversity of forests [11,12,13,14]. Stand structure heterogeneity and complexity are related to forest biodiversity [2,10,15], while biodiversity indices are used for the quantification of stand structure diversity and heterogeneity [16,17]. Ref. [15] presented a methodology of comparing spatial heterogeneity of stand structures between two forests using the variances of biodiversity index values calculated by their breast heigh diameter (DBH) distributions. Ref. [10], based on stand structural characteristics, developed a biodiversity assessment index to evaluate biodiversity in Greek and temperate forests using measurements taken in sample plots. The index combined five parameters: species composition, vertical differentiation, standing dead trees, presence of large living trees, and basal area.
On the other hand, Ref. [9] constructed a biodiversity assessment index, using parameters obtained by management plants, for Greek forests and forests with analogous ecological and biological characteristics. The parameters that are used are the aspect of the stand, regeneration existence, canopy density, tree age structure, and total amount of wood stock m3/ha. Applying the index of [9] the biodiversity of huge forest areas can be easily estimated since the management plans of forests in Greece contain information about the abovementioned parameters.
In this context the objective of the present study is to estimate the biodiversity holding capacity of pure oak (Quercus spp.) stands in an area of tens of thousands of hectares in northeastern Greece using the biodiversity assessment index of [9].
The oak wood volume represents 17.5% of the merchantable volume in Greek forests, while oak type of forest occupies 22.6% of the country forests [18]. Oak species growing in Greek forests are generally light-demanding to semi-shade-tolerant, while they exhibit a range of site requirements [19,20,21,22].
Based on the analysis of the parameters used for the calculation of the biodiversity index and on the index value for each stand, forest management can develop appropriate treatment schedules to increase the biodiversity holding capacity of the analyzed stands. These treatments in almost all cases are related to silvicultural treatment and redistribution of growing space [23,24,25].
The present study applies the Graded Biodiversity Assessment (GBA) index of [9] to all pure oak stands within the Forest Service of Xanthi—an area exceeding 32,000 ha—to (i) quantify current biodiversity status and (ii) identify the stand attributes that most limit or promote biodiversity. By synthesizing these results, we propose an adaptive silvicultural framework aimed at elevating the biodiversity holding capacity of these forests. We operationalize the GBA of [9] using structure-based biodiversity surrogates (total wood stock, age structure, canopy density, presence of regeneration, and aspect), which are consistently recorded in management plans. These variables function as biodiversity indicators rather than yield metrics and enable transparent, full-coverage stand-level biodiversity grading.

2. Materials and Methods

2.1. Study Area

The research area comprises pure oak (Quercus spp.) stands within the jurisdiction of the Forest Service of Xanthi in northeastern Greece (Figure 1). These stands are dominated by Quercus frainetto Ten., Q. petraea (Matt.) Liebl., Q. pubescens Willd., and Q. cerris L. [26]. These stands belong to public forest complexes: Thermes–Satres [27], Echinos [28], Kotyli [29], Myki [30], Oraio [31], and Gerakas Xanthis–Kimmeria [32].
The total area of pure oak stands is 32,175.22 ha, of which forest-covered area totals 20,812.76 ha. Elevations range from 60 to 1400 m, leading to diverse climatic conditions due to the substantial altitudinal variation (data sourced from management plan description sheets).
Most of the pure oak stands are on gneiss substrates, while some stands are established on flysch and other geological formations. Besides oak, these stands contain (secondary) species such as Fagus sylvatica L., Carpinus orientalis Miller, Fraxinus ornus L., Ostrya carpinifolia Scop., Cornus mas L., Juniperus spp.), and others (data from management plan description sheets).

2.2. Biodiversity Index Calculation

To assess biodiversity in pure oak stands, the biodiversity index developed by [9] was used. This index is calculated based on five stand parameters: (a) total wood volume of the stand; (b) age of trees within the stand; (c) canopy density; (d) presence of regeneration; and (e) stand aspect (orientation).
These data were sourced from the description sheets of pure oak stands found in the management plans for public forest complexes in the area of the Forest Service of Xanthi:
–
Thermes–Satres Public Forest Complex Management Plan (2020–2029) [27];
–
Echinos Public Forest Complex Management Plan (2019–2028) [28];
–
Kotyli Public Forest Complex Management Plan (2018–2027) [29];
–
Myki Public Forest Complex Management Plan (2022–2031) [30];
–
Oraio Public Forest Complex Management Plan (2015–2024) [31];
–
Gerakas Xanthis–Kimmeria Public Forest Complex Management Plan (2017–2026) [32].
The description sheets were obtained from the FOROAKS project website [33]. A stand was classified as “pure” if its entire forest-covered area was covered by oaks. This stand-level data processing relies exclusively on the official forest-management plan description sheets; consequently, we applied the published GBA index using the inventory attributes available therein (wood stock, age structure, canopy density, regeneration, and aspect). Variables not recorded in these archival sheets (e.g., tree-related microhabitats, faunal metrics, or plot-level trait inventories) were outside the scope of the present dataset. Our selection of structure-based surrogates (wood stock, age structure, canopy density, regeneration) follows current evidence that practical, stand-level structural attributes are informative for biodiversity assessment and planning [3].
Each stand received biodiversity scores per parameter based on specific criteria:
  • Total amount of wood stock:
    –
    <100 m3/ha: 0 (low or no biodiversity);
    –
    100–250 m3/ha: 0.5 (moderate biodiversity);
    –
    >250 m3/ha: 1 (high biodiversity).
  • Age:
    –
    Even-aged stands: 0;
    –
    Uneven-aged stands: 1 (moderate biodiversity not applicable).
  • Canopy density:
    –
    Both density values <1: 0;
    –
    One density value <1 and the other ≥1: 0.5;
    –
    Both density values ≥: 1.
In the canopy density parameter, in the case of a biodiversity value of 0.5, 1 was included as a canopy value at the upper limit. This was also the case for a biodiversity value of 1, where 1 was also included as a canopy value. One (1) as a canopy density value was not present in the limits proposed by [9].
  • Regeneration:
    –
    None or minimal regeneration: 0;
    –
    Moderate regeneration: 0.5;
    –
    High regeneration: 1.
Where the management plans employed diverse descriptors for regeneration, each term was matched to the most appropriate of our predefined categories.
  • Aspect:
    –
    Exposure to one direction: 0;
    –
    Exposure to two directions: 0.5;
    –
    Exposure to more than two directions: 1.
Aspect is related to the number of distinguishable directions a stand faces (south, north, west, and east). When the aspect is a complex aspect, like the southeast, we recorded it with the initial aspect (in the previous example, it is recorded as south).
If stand age data were unclear in the description sheets, additional information was gathered from other sections of the description sheets. Diameter class distribution data from the plot which corresponded to each stand were also utilized to infer tree ages. Moreover, an estimate of the age structure of the stand was made using both characteristics and information from neighboring stands when necessary.
For each stand, biodiversity parameter scores were summed to calculate overall biodiversity:
–
Total score <1.5: low biodiversity;
–
Total score 1.5–3: moderate biodiversity;
–
Total score >3: high biodiversity.
All pure oak stands in the area of the Forest Service of Xanthi were analyzed except for a small number lacking sufficient data for the parameters evaluated.

2.3. Statistical Data Processing

Analyses were performed at the stand level on data of all eligible stands (N = 481). We summarized counts and proportions (%) by level for each GBA parameter. Pairwise comparisons of proportions used two-proportion Z-tests (two-sided; α = 0.05), which rely on the large-sample normal approximation to the binomial rather than a normality assumption on raw data. We verified the adequacy of this approximation via the usual np and n(1 − p) thresholds and, where any cell count was small, checked results with exact tests (identical conclusions). Where normality was relevant for continuous summaries, we assessed it using the Jarque–Bera test and detected no departures (all p > 0.05). We report Z, two-sided p (exact or <0.001), and Δ = p1 − p2.

3. Results

3.1. Total Number of the Stands

There were fewer high-biodiversity stands than moderate (3.1% vs. 63.4%; Z = −19.84, p < 0.001) or low (3.1% vs. 33.5%; Z = −12.18, p < 0.001), while moderate exceeded low (63.4% vs. 33.5%; Z = 9.29, p < 0.001). From the 481 analyzed stands, 15 (3.1%) stands were characterized as having high biodiversity (high-biodiversity stands), 305 (63.4%) were characterized as having moderate biodiversity (moderate-biodiversity stands), and 161 (33.5%) were characterized as having low biodiversity (low-biodiversity stands) (Figure 2). Moreover, from the 32,175.22 ha of the total area of stands, 881.57 ha (2.7%) were in high-biodiversity stands, 18,401.39 (57.2%) were in moderate-biodiversity stands, and 12,892.27 (40.1%) were in low-biodiversity stands, while from the 20,812.76 ha of the forested area of stands, 769,35 ha (3.7%) were in high-biodiversity stands, 12,705.15 (61.1%) were in moderate-biodiversity stands, and 7338.26 (35.3%) were in low-biodiversity stands (Figure 3a). Figure 3b displays the study area map divided into the three previously described biodiversity levels. The breadth of each gray shade reflects the total area of stands (ha) within that biodiversity level, with the exact values provided in Figure 3a.
In the full set of stands, those with total wood stock < 100 m3 ha−1 numbered 346/481 (71.9%), exceeding 100–250 m3 ha−1 (116/481, 24.1%) and > 250 m3 ha−1 (19/481, 4.0%); the 100–250 class also exceeded the > 250 class (see Table 1).
Uneven-aged stands numbered 338/481 (70.3%), exceeding even-aged (143/481, 29.7%) (Table 1).
For canopy density, the low class (both bounds < 1) included 374/481 (77.8%), exceeding the intermediate class (one bound < 1, the other ≥ 1; 88/481, 18.3%) and the high class (both bounds ≥ 1; 19/481, 4.0%); the intermediate class also exceeded the high class (Table 1).
For regeneration, the high class comprised 225/481 (46.8%), exceeding moderate (83/481, 17.3%) and none/minimal (173/481, 36.0%); there were fewer moderate stands than in the none/minimal category (Table 1).
For aspect, one direction accounted for 354/481 (73.6%), exceeding two directions (111/481, 23.1%) and > two directions (16/481, 3.3%); two directions also exceeded > two (Table 1).

3.2. High-Biodiversity Stands

From the 15 stands characterized as having high biodiversity, in one (6.7%) stand the degree for the total amount of wood stock is 0 (wood stock <100 m3/ha), in 11 (73.3%) stands the degree for the total amount of wood stock is 0.5 ([100, 250] m3/ha), and in three (20.0%) stands the degree for the total amount of wood stock is 1 (>250 m3/ha) (Figure 4). All (100%) stands are uneven-aged (degree 1) (Figure 4). Moreover, in three (20.00%) stands the degree for the canopy density is 0 (<1 for both bounds of the range), in six (40.0%) stands the degree for the canopy density is 0.5 (<1 for the lower bound, ≥1 for the upper bound of the range), and in six (40.0%) stands the degree for the canopy density is 1 density (≥1 for both bounds of the range) (Figure 4). In one (6.7%) stand the degree for the regeneration existence is 0.5 (moderate regeneration), and in 14 (93.3%) stands the degree for the regeneration existence is 1 (maximum regeneration) (Figure 4). Finally, in six (40.0%) stands the degree for the aspect of the stand is 0, in six (40.0%) stands it is 0.5, and in three (20.0%) stands it is 1.

3.3. Moderate-Biodiversity Stands

From the 305 stands characterized as having moderate biodiversity, in 188 (61.6%) stands the degree for the total amount of wood stock is 0 (wood stock <100 m3/ha), in 102 (33.4%) stands the degree for the total amount of wood stock is 0.5 ([100, 250] m3/ha), and in 15 (4.9%) stands the degree for the total amount of wood stock is 1 (>250 m3/ha) (Figure 5). A total of 30 (9.8%) stands are even-aged (degree 0), and 275 (90.2%) stands are uneven-aged (degree 1) (Figure 5). Moreover, in 212 (69.5%) stands the degree for the canopy density is 0 (<1 for both bounds of the range), in 80 (26.2%) stands the degree for the canopy density is 0.5 (<1 for the lower bound, ≥1 for the upper bound of the range), and in 13 (4.3%) stands the degree for the canopy density is 1 density (≥1 for both bounds of the range) (Figure 5). In 62 (20.3%) stands the degree for the regeneration existence is 0 (little or no regeneration), in 55 (18.0%) stands the degree for the regeneration existence is 0.5 (moderate regeneration), and in 188 (61.6%) stands the degree for the regeneration existence is 1 (maximum regeneration) (Figure 5). Finally, in 208 (68.2%) stands the degree for the aspect of the stand is 0, in 87 (28.5%) stands it is 0.5, and in ten (3.3%) stands it is 1.

3.4. Low-Biodiversity Stands

From the 161 stands characterized as having low biodiversity, in 157 (97.5%) stands the degree for the total amount of wood stock is 0 (wood stock <100 m3/ha), in 3 (1.9%) stands the degree for the total amount of wood stock is 0.5 ([100, 250] m3/ha), and in 1 (0.6%) stand the degree for the total amount of wood stock is 1 (>250 m3/ha) (Figure 6). A total of 113 (70.2%) stands are even-aged (degree 0), and 48 (29.8%) stands are uneven-aged (degree 1) (Figure 6). Moreover, in 159 (98.8%) stands the degree for the canopy density is 0 (<1 for both bounds of the range), and in two (1.2%) stands the degree for the canopy density is 0.5 (<1 for the lower bound, ≥1 for the upper bound of the range) (Figure 6). In 111 (68.9%) stands the degree for the regeneration existence is 0 (little or no regeneration), in 27 (16.8%) stands the degree for the regeneration existence is 0.5 (moderate regeneration), and in 23 (14.3%) stands the degree for the regeneration existence is 1 (maximum regeneration) (Figure 6). Finally, in 140 (87.0%) stands the degree for the aspect of the stand is 0, in 18 (11.2%) stands it is 0.5, and in 3 (1.9%) stands it is 1.

4. Discussion

Moderate biodiversity predominates (63.4% of stands), followed by low (33.5%), while high biodiversity is scarce (3.1%). Conversely, high-biodiversity stands are less abundant than either of the other two classes. These patterns emerge from data processing at the stand level using the GBA index, and they are therefore descriptive of the entire population of eligible stands within the Xanthi Forest Service.
Forest practice can influence all factors used in the biodiversity assessment except aspect. Among the controllable factors, the total amount of wood stock and canopy density most strongly explain the scarcity of high-biodiversity stands. Stands with degree 0 in wood stock (346 stands) are more numerous than those with degree 0.5 (116) and degree 1 (19). The same pattern holds for canopy density: degree 0 (374) exceeds degree 0.5 (88) and degree 1 (19) (Table 1). Canopy characteristics are well known to influence stand biodiversity [34,35], and the observed prevalence of low canopy density is consistent with the relationship between canopy closure and wood stock embedded in the GBA scoring [9]. Young oak stands dominate in the study area ([26]; personal observations), and young, relatively sparse stands with both canopy-density bounds < 1 are expected to have low wood stock.
Historically, intense overgrazing and unsanctioned fuel-wood extraction were major disturbances in these oak forests ([36,37,38]; communication with residents and personal observations), which plausibly reduced both wood stock and canopy density. Overgrazing still disturbs many oak stands (information from description sheets of stands). Ref. [39] analyzing the effect of anthropogenic disturbance on the relationship between forest productivity and diversity of trees, in different ages of stands, suggested that the reduction in chronic anthropogenic disturbances is a key for the promotion of the positive effects of diversity on productivity.
Stand age structure and regeneration counterbalance, to a degree, the negative influence of low wood stock and canopy density and underpin the dominance of the moderate class. Age structure is linked to biodiversity [40], and uneven-aged structure is associated with biodiversity conservation [41,42,43]. In our dataset, uneven-aged stands (degree 1; 338 stands) are more numerous than even-aged stands (143). Regeneration is also favorable in many stands: degree 1 (225) exceeds degree 0.5 (83) and degree 0 (173), while degree 0.5 remains less numerous than degree 0 (Table 1). Anthropogenic disturbances and silvicultural treatments that release growing space [21,23,24,44] likely facilitated regeneration establishment and contributed to uneven-aged structures in numerous stands.
The scarcity of high-biodiversity stands thus stems primarily from legacy deficits in wood stock and canopy density. Similar legacy effects are reported in temperate oak systems in Europe [42] and Iran [35]. To maintain high-biodiversity status where it already occurs, forest practice should increase wood stock and canopy density in stands where the corresponding GBA components score 0 or 0.5, while preserving uneven-aged structure and sustaining regeneration at high levels.
Stands classified as moderate biodiversity would benefit from targeted improvements—primarily in wood stock and canopy density—while maintaining or expanding favorable age structure and regeneration. Within the moderate class, 30 stands are even-aged and 275 are uneven-aged; where appropriate, transitions toward uneven-aged structure should be encouraged. Regeneration should be increased where it is moderate (55 stands) or absent/very low (62 stands).
The stands that were characterized as low-biodiversity stands need interventions to improve their biodiversity characterization. The target of these interventions will be al-most all the parameters that influence the biodiversity characterization of the stands.
To increase the total amount of wood stock in pure oak stands, forest practice must remove only a very small amount of wood from the stands through cuttings and thinning, while in many stands no interventions must be performed. The increase in wood stock will lead to a canopy density increase. On the other hand, through regeneration cuttings the regeneration will increase, and the new age groups will be established [21,23,24,25] creating uneven-aged stands. However, to achieve the abovementioned silvicultural goals, grazing must be stopped since it destroys regeneration plants and can lead to a further deterioration of the stands [20].
The dominance of moderate-biodiversity stands suggests that relatively modest interventions could yield large gains. We recommend the following:
  • Stand densification through extended rotation periods or light thinning until wood stock exceeds 250 m3/ha.
  • Retention of legacy trees and standing dead wood to enhance habitat heterogeneity.
  • Strict regulation of grazing, which in many cases must be forbidden.
An analytical plan for the increase in biodiversity holding capacity of pure oak (Quercus spp.) stands in the area must be developed. In this plan, the stands on which the treatments must be light must be determined as well as those where no cutting or thinning will take place. On the other hand, the stands where regeneration cutting must be applied have to be selected.
There should be a prioritization of the measures to be taken in each stand since some interventions have a different impact on the goals we set. Thus, regeneration cuttings will increase regeneration and the uneven-aged structure of the stands, but at the same time they will reduce the wood stock. Also, there should be a prioritization of the stands in which specific interventions will be carried out according to their condition.
In the management of pure oak stands, more measures must be taken for the improvement of biodiversity holding capacity. An effort should be made to leave dead trees standing after interventions, where safety and phytosanitary risks are acceptable; in areas with active pest pressure or safety concerns, removal or treatment should be prioritized. Also, trees with large diameters as well as trees of other species should be favored, while treatment must aim at the enhancement of stand vertical differentiation to improve conditions for biodiversity [10].
More research is needed in forests with similar ecological conditions to determine the biodiversity status of stands using the surrogates of this study. This process will not only lead to measures for increasing biodiversity but will also increase the understanding of the forces which determined the status and dynamics of stands and thus will enhance their management.

5. Conclusions

The stand-level assessment of all eligible pure oak (Quercus spp.) stands within the Xanthi Forest Service (N = 481) shows that moderate biodiversity predominates (63.4% of stands), while high biodiversity is scarce (3.1%), and low biodiversity accounts for 33.5%.
Forest practice can influence all the factors used to assess stand biodiversity, except the stand’s aspect. Among these factors, total wood stock and canopy density are the main determinants of the low proportion of high-biodiversity stands. By contrast, age structure together with the presence of regeneration counterbalanced the negative influence of total wood stock and canopy density, leading to the predominance of stands characterized as moderate in biodiversity. Raising wood stock and canopy density, while safeguarding uneven-aged structure and regeneration, offers the most direct route to biodiversity enhancement.
To maintain the biodiversity status of stands classified as high biodiversity, forest practice should increase total wood stock and canopy density in stands where the biodiversity index is 0 or 0.5. At the same time, it should primarily preserve the uneven-aged structure of stands and sustain high levels of regeneration. Moderate-biodiversity stands need improvement in certain parameters—chiefly total wood stock and canopy density. Low-biodiversity stands require interventions to improve their biodiversity characterization, targeting nearly all parameters that influence it.

Author Contributions

Conceptualization, writing—original draft preparation, E.M. (Efthimios Michailidis), E.M. (Elias Milios), K.K. and A.S.; methodology, validation, E.M. (Efthimios Michailidis), E.M. (Elias Milios), K.K., A.S., P.P., E.P. and K.R.; data curation, software, E.M. (Efthimios Michailidis), E.M. (Elias Milios) and K.K.; writing—review and editing, E.M. (Elias Milios), K.K., A.S., P.P., E.P. and K.R.; supervision; E.M. (Elias Milios). All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Data Availability Statement

The datasets generated during and/or analyzed during the current study are available from the corresponding author on reasonable request.

Conflicts of Interest

The authors declare no conflicts of interest.

References

  1. Secretariat of the Convention on Biological Diversity. Handbook of the Convention on Biological Diversity: Including Its Cartagena Protocol on Biosafety; Secretariat of Convention: Bonn, Germany, 2005. [Google Scholar]
  2. Lindenmayer, D.B.; Franklin, J.F. Conserving Forest Biodiversity: A Comprehensive Multiscaled Approach; Island Press: Washington, DC, USA, 2002. [Google Scholar]
  3. Burrascano, S.; Chianucci, F.; Trentanovi, G.; Kepfer-Rojas, S.; Sitzia, T.; Tinya, F.; Doerfler, I.; Paillet, Y.; Nagel, T.A.; Mitic, B.; et al. Where are we now with European forest multi-taxon biodiversity and where can we head to? Biol. Conserv. 2023, 284, 110176. [Google Scholar] [CrossRef]
  4. Uhl, B.; Schall, P.; Bässler, C. Achieving structural heterogeneity and high multi-taxon biodiversity in managed forest ecosystems: A European review. Biodivers. Conserv. 2025, 34, 3327–3358. [Google Scholar] [CrossRef]
  5. de Conto, T.; Armston, J.; Dubayah, R. Characterizing the structural complexity of the Earth’s forests with spaceborne lidar. Nat. Commun. 2024, 15, 8116. [Google Scholar] [CrossRef]
  6. Parisi, F.; D’Amico, G.; Vangi, E.; Chirici, G.; Francini, S.; Cocozza, C.; Giannetti, F.; Londi, G.; Nocentini, S.; Borghi, C.; et al. Tree-related microhabitats and multi-taxon biodiversity quantification exploiting ALS data. Forests 2024, 15, 660. [Google Scholar] [CrossRef]
  7. Gao, T.; Hedblom, M.; Emilsson, T.; Nielsen, A.B. The role of forest stand structure as biodiversity indicator. For. Ecol. Manag. 2014, 330, 82–93. [Google Scholar] [CrossRef]
  8. Heym, M.; Uhl, E.; Moshammer, R.; Dieler, J.; Stimm, K.; Pretzsch, H. Utilising Forest inventory data for biodiversity assessment. Ecol. Indic. 2020, 121, 107196. [Google Scholar] [CrossRef]
  9. Bourma, K.; Milios, E.; Radoglou, K.; Kitikidou, K. Development of a Graded Biodiversity Assessment (GBA) Index for the Assessment of the Biodiversity of Managed Natural Forests. Ecologies 2023, 4, 614–626. [Google Scholar] [CrossRef]
  10. Milios, E.; Kitikidou, K. Enhancing biodiversity assessment in forests: Integrating instrumented measurements for a robust graded biodiversity assessment (GBA) index. Environ. Ecol. Res. 2025, 13, 131–139. [Google Scholar] [CrossRef]
  11. Sullivan, T.P.; Sullivan, D.S.; Lindgren, P.M.F. Partial harvesting of dry Douglas-fir forests: Stand structure, range habitats and maintenance of biodiversity using small mammal indicators. Forestry 2011, 84, 247–257. [Google Scholar] [CrossRef][Green Version]
  12. Persiani, A.; Lombardi, F.; Lunghini, D.; Granito, V.; Tognetti, R.; Maggi, O.; Pioli, S.; Marchetti, M. Stand structure and deadwood amount influences saproxylic fungal biodiversity in Mediterranean mountain unmanaged forests. iForest 2015, 9, 115–124. [Google Scholar] [CrossRef]
  13. Parisi, F.; Innangi, M.; Tognetti, R.; Lombardi, F.; Chirici, G.; Marchetti, M. Forest stand structure and coarse woody debris determine the biodiversity of beetle communities in Mediterranean mountain beech forests. Glob. Ecol. Conserv. 2021, 28, e01637. [Google Scholar] [CrossRef]
  14. McElhinny, C.; Gibbons, P.; Brack, C.; Bauhus, J. Forest and woodland stand structural complexity: Its definition and measurement. For. Ecol. Manag. 2005, 218, 1–24. [Google Scholar] [CrossRef]
  15. Milios, E.; Kitikidou, K. How to improve forest biodiversity management by comparing broad-scale stands’ structural spatial heterogeneity between two forests. Ann. Silvic. Res. 2025, 50, 7–11. [Google Scholar]
  16. Kitikidou, K.; Milios, E.; Stampoulidis, A.; Pipinis, E.; Radoglou, K. Within-forest stand (or formation, or plot) and between-forest stand (or formation, or plot) biodiversity indices. MethodsX 2022, 9, 101919. [Google Scholar] [CrossRef]
  17. Kitikidou, K.; Milios, E.; Stampoulidis, A.; Pipinis, E.; Radoglou, K. Using biodiversity indices effectively: Considerations for forest management. Ecologies 2024, 5, 42–51. [Google Scholar] [CrossRef]
  18. Ministry of Agriculture. First National Inventory of Greek Forests; Diretorate of Forest Cadastre: Athens, Greece, 1992; pp. 1–134. [Google Scholar]
  19. Athanasiadis, N. Forest Botany: Trees and Shrubs of the Forests of Greece, Part II; Giahoudis-Giapoulis: Thessaloniki, Greece, 1986. (In Greek) [Google Scholar]
  20. Dafis, S. Forest Ecology; Giahoudis-Giapoulis: Thessaloniki, Greece, 1986. (In Greek) [Google Scholar]
  21. Dafis, S. Applied Silviculture; Giahoudis-Giapoulis: Thessaloniki, Greece, 1992. (In Greek) [Google Scholar]
  22. Korakis, G. Forest Botany. Trees and Shrubs Native in Greece; Athanasiou Altintzi Editions: Thessaloniki, Greece, 2019. (In Greek) [Google Scholar]
  23. Oliver, C.D.; Larson, B.C. Forest Stand Dynamics; McGraw Hill: New York, NY, USA, 1996. [Google Scholar]
  24. Smith, D.M.; Larson, B.C.; Kelty, M.J.; Ashton, P.; Mark, S. The Practice of Silviculture: Applied Forest Ecology; Wiley: Hoboken, NJ, USA, 1997. [Google Scholar]
  25. Stampoulidis, A.; Pipinis, E.; Petrou, P.; Kitikidou, K. Regeneration analysis of the Juniperus excelsa mixed stands in Prespa National Park of Greece as a base for the assessment of the appropriate silvicultural treatment for the conservation of the species. South-East Eur. For. 2023, 14, 47–52. [Google Scholar] [CrossRef]
  26. Kitikidou, K.; Milios, E.; Radoglou, K. Allometry, biomass, and productivity of deciduous oak forests in Xanthi, northern Greece. Banko Janakari 2024, 34, 48–60. [Google Scholar] [CrossRef]
  27. Theodoridis, P. Thermes–Satres Public Forest Complex Management Plan 2020–2029; Forest Directorship of Xanthi: Xanthi, Greece, 2019. (In Greek) [Google Scholar]
  28. Theodoridis, P. Echinos Public Forest Complex Management Plan 2019–2028; Forest Directorship of Xanthi: Xanthi, Greece, 2018. (In Greek) [Google Scholar]
  29. Theodoridis, P. Kotyli Public Forest Complex Management Plan 2018–2027; Forest Directorship of Xanthi: Xanthi, Greece, 2018. (In Greek) [Google Scholar]
  30. Theodoridis, P. Myki Public Forest Complex Management Plan 2022–2031; Forest Directorship of Xanthi: Xanthi, Greece, 2021. (In Greek) [Google Scholar]
  31. Theodoridis, P. Oraio Public Forest Complex Management Plan 2015–2024; Forest Directorship of Xanthi: Xanthi, Greece, 2015. (In Greek) [Google Scholar]
  32. Theodoridis, P. Gerakas Xanthis–Kimmeria Public Forest Complex Management Plan 2017–2026; Forest Directorship of Xanthi: Xanthi, Greece, 2016. (In Greek) [Google Scholar]
  33. ForOaks Project. Available online: https://foroaks.fmenr.duth.gr/ (accessed on 22 July 2025).
  34. Ishii, H.T.; Tanabe, S.-I.; Hiura, T. Exploring the relationships among canopy structure, stand productivity, and biodiversity of temperate forest ecosystems. For. Sci. 2004, 50, 342–355. [Google Scholar]
  35. Naqinezhad, A.; De Lombaerde, E.; Gholizadeh, H.; Wasof, S.; Perring, M.P.; Meeussen, C.; De Frenne, P.; Verheyen, K. The combined effects of climate and canopy cover changes on understorey plants of the Hyrcanian Forest biodiversity hotspot in northern Iran. Glob. Change Biol. 2021, 28, 1103–1118. [Google Scholar] [CrossRef]
  36. Koutoulas, G. Thermes–Satres Public Forest Complex Management Plan 1988–1997; Forest Service of Xanthi: Xanthi, Greece, 1988. (In Greek) [Google Scholar]
  37. Koutoulas, G.; Maragos, N.; Asimakopoulos, G. Kotyli Public Forest Complex Management Plan 1998–2007; Forest Service of Xanthi: Xanthi, Greece, 1998. (In Greek) [Google Scholar]
  38. Koutoulas, G. Echinos Public Forest Complex Management Plan 1999–2008; Forest Service of Xanthi: Xanthi, Greece, 1999. (In Greek) [Google Scholar]
  39. Lin, S.; Fan, C.; Wang, J.; Zhang, C.; Zhao, X.; von Gadow, K. Chronic anthropogenic disturbance mediates the biodiversity-productivity relationship across stand ages in a large temperate forest region. J. Appl. Ecol. 2024, 61, 502–512. [Google Scholar] [CrossRef]
  40. Correia, D.L.P.; Raulier, F.; Filotas, É.; Bouchard, M. Stand height and cover type complement forest age structure as a biodiversity indicator in boreal and northern temperate forest management. Ecol. Indic. 2016, 72, 288–296. [Google Scholar] [CrossRef]
  41. Bagnaresi, U. Stand structure and biodiversity in mixed, uneven-aged coniferous forests in the eastern Alps. Forestry 2002, 75, 357–364. [Google Scholar] [CrossRef]
  42. Redon, M.; Luque, S.; Gosselin, F.; Cordonnier, T. Is generalisation of uneven-aged management in mountain forests the key to improve biodiversity conservation within forest landscape mosaics? Ann. For. Sci. 2014, 71, 751–760. [Google Scholar] [CrossRef]
  43. Savilaakso, S.; Johansson, A.; Häkkilä, M.; Uusitalo, A.; Sandgren, T.; Mönkkönen, M.; Puttonen, P. What are the effects of even-aged and uneven-aged forest management on boreal forest biodiversity in Fennoscandia and European Russia? A systematic review. Environ. Evid. 2021, 10, 1. [Google Scholar] [CrossRef]
  44. O’Hara, K. Multiaged Silviculture: Managing for Complex Forest Stand Structures; Oxford University Press: Oxford, UK, 2014. [Google Scholar]
Environments 12 00339 g001
Figure 1. Study area and location of pure oak (Quercus spp.) stands within the jurisdiction of the Xanthi Forest Service (NE Greece). Colorless (white) areas indicate privately owned forests, not included in the analyses. Stands belong to the public forest complexes Thermes–Satres, Echinos, Kotyli, Myki, Oraio, and Gerakas Xanthis–Kimmeria, as delineated in the official forest management plans. Elevation spans ~60–1400 m across the area.
Figure 1. Study area and location of pure oak (Quercus spp.) stands within the jurisdiction of the Xanthi Forest Service (NE Greece). Colorless (white) areas indicate privately owned forests, not included in the analyses. Stands belong to the public forest complexes Thermes–Satres, Echinos, Kotyli, Myki, Oraio, and Gerakas Xanthis–Kimmeria, as delineated in the official forest management plans. Elevation spans ~60–1400 m across the area.
Environments 12 00339 g001
Environments 12 00339 g002
Figure 2. Biodiversity classification of all analyzed pure oak stands (unit: stand; full coverage, n = 481) using the GBA index. Counts and percentages: high = 15 (3.1%), moderate = 305 (63.4%), low = 161 (33.5%). GBA thresholds: total score < 1.5 = low, 1.5–3 = moderate, >3 = high. This figure summarizes the status of the entire stand population assessed from management plan description sheets.
Figure 2. Biodiversity classification of all analyzed pure oak stands (unit: stand; full coverage, n = 481) using the GBA index. Counts and percentages: high = 15 (3.1%), moderate = 305 (63.4%), low = 161 (33.5%). GBA thresholds: total score < 1.5 = low, 1.5–3 = moderate, >3 = high. This figure summarizes the status of the entire stand population assessed from management plan description sheets.
Environments 12 00339 g002
Environments 12 00339 g003
Figure 3. (a) Area of pure oak stands by GBA biodiversity class. Light-hatched bars show the total stand area (full management plan polygon); dark-hatched bars show the forested (forest-covered) area within those polygons, as recorded in the management plans. Many stands include partially forested and bare/barren areas; hence, totals differ between the two area types. Values are reported in hectares, with percentage labels to enable direct comparison across the three classes. Totals: total stand area = 32,175.22 ha (high = 881.57 ha; moderate = 18,401.39 ha; and low = 12,892.27 ha; forested area = 20,812.76 ha (high = 769.35 ha; moderate = 12,705.15 ha; and low = 7338.26 ha). (b) Thematic map of pure oak stands classified into low, moderate, and high biodiversity classes by the GBA index. Polygons follow official stand boundaries from the cited management plans; classes correspond to the areas summarized in Figure 3a. The map depicts full coverage of the Xanthi Forest Service jurisdiction.
Figure 3. (a) Area of pure oak stands by GBA biodiversity class. Light-hatched bars show the total stand area (full management plan polygon); dark-hatched bars show the forested (forest-covered) area within those polygons, as recorded in the management plans. Many stands include partially forested and bare/barren areas; hence, totals differ between the two area types. Values are reported in hectares, with percentage labels to enable direct comparison across the three classes. Totals: total stand area = 32,175.22 ha (high = 881.57 ha; moderate = 18,401.39 ha; and low = 12,892.27 ha; forested area = 20,812.76 ha (high = 769.35 ha; moderate = 12,705.15 ha; and low = 7338.26 ha). (b) Thematic map of pure oak stands classified into low, moderate, and high biodiversity classes by the GBA index. Polygons follow official stand boundaries from the cited management plans; classes correspond to the areas summarized in Figure 3a. The map depicts full coverage of the Xanthi Forest Service jurisdiction.
Environments 12 00339 g003
Environments 12 00339 g004
Figure 4. Degrees of stands based on the total amount of wood stock, tree age structure, canopy density, and regeneration existence in stands with high biodiversity. Attribute profile of high-biodiversity stands (n = 15) by GBA parameter. Wood stock (m3/ha) (a): degree 0 (<100) = 1 stand; 0.5 (100–250) = 11; 1 (>250) = 3. Age structure (b): 100% uneven-aged (degree 1). Canopy density (per lower/upper bounds) (c): 0 (<1, <1) = 3; 0.5 (<1, ≥1) = 6; 1 (≥1, ≥1) = 6. Regeneration (d): 0.5 = 1; 1 = 14 (degree coding as defined in Methods).
Figure 4. Degrees of stands based on the total amount of wood stock, tree age structure, canopy density, and regeneration existence in stands with high biodiversity. Attribute profile of high-biodiversity stands (n = 15) by GBA parameter. Wood stock (m3/ha) (a): degree 0 (<100) = 1 stand; 0.5 (100–250) = 11; 1 (>250) = 3. Age structure (b): 100% uneven-aged (degree 1). Canopy density (per lower/upper bounds) (c): 0 (<1, <1) = 3; 0.5 (<1, ≥1) = 6; 1 (≥1, ≥1) = 6. Regeneration (d): 0.5 = 1; 1 = 14 (degree coding as defined in Methods).
Environments 12 00339 g004
Environments 12 00339 g005
Figure 5. Degrees of stands based on the total amount of wood stock, tree age structure, canopy density, and regeneration existence in stands with moderate biodiversity. Attribute profile of moderate-biodiversity stands (n = 305). Wood stock (a): degree 0 = 188; 0.5 = 102; 1 = 15. Age structure (b): even-aged (0) = 30; uneven-aged (1) = 275. Canopy density (c): 0 = 212; 0.5 = 80; 1 = 13. Regeneration (d): 0 = 62; 0.5 = 55; 1 = 188 (degree coding as defined in Methods).
Figure 5. Degrees of stands based on the total amount of wood stock, tree age structure, canopy density, and regeneration existence in stands with moderate biodiversity. Attribute profile of moderate-biodiversity stands (n = 305). Wood stock (a): degree 0 = 188; 0.5 = 102; 1 = 15. Age structure (b): even-aged (0) = 30; uneven-aged (1) = 275. Canopy density (c): 0 = 212; 0.5 = 80; 1 = 13. Regeneration (d): 0 = 62; 0.5 = 55; 1 = 188 (degree coding as defined in Methods).
Environments 12 00339 g005
Environments 12 00339 g006
Figure 6. Attribute profile of low-biodiversity stands (n = 161). Wood stock (a): degree 0 = 157; 0.5 = 3; 1 = 1. Age structure (b): even-aged (0) = 113; uneven-aged (1) = 48. Canopy density (c): 0 = 159; 0.5 = 2; 1 = 0. Regeneration (d): 0 = 111; 0.5 = 27; 1 = 23 (degree coding as defined in Methods).
Figure 6. Attribute profile of low-biodiversity stands (n = 161). Wood stock (a): degree 0 = 157; 0.5 = 3; 1 = 1. Age structure (b): even-aged (0) = 113; uneven-aged (1) = 48. Canopy density (c): 0 = 159; 0.5 = 2; 1 = 0. Regeneration (d): 0 = 111; 0.5 = 27; 1 = 23 (degree coding as defined in Methods).
Environments 12 00339 g006
Table 1. Pairwise comparisons of stand-level proportions across GBA parameter classes (one row per two-proportion test; unit of analysis: stand; full coverage of all eligible stands, N = 481). Z is the standardized normal statistic for the two-proportion test (H0: p1 = p2); positive Z indicates p1 > p2, negative indicates p1 < p2; larger |Z| reflects a larger standardized difference. Two-sided p-values are exact where necessary or reported as < 0.001.
Table 1. Pairwise comparisons of stand-level proportions across GBA parameter classes (one row per two-proportion test; unit of analysis: stand; full coverage of all eligible stands, N = 481). Z is the standardized normal statistic for the two-proportion test (H0: p1 = p2); positive Z indicates p1 > p2, negative indicates p1 < p2; larger |Z| reflects a larger standardized difference. Two-sided p-values are exact where necessary or reported as < 0.001.
ParameterContrast (Level A vs. Level B)A: Proportion % (n/N)B: Proportion % (n/N)Zp-Value
Wood stock (m3/ha)0 (<100) vs. 0.5 [100–250]71.9 (346/481)24.1 (116/481)14.84<0.001
Wood stock (m3/ha)0 (<100) vs. 1 (>250)71.9 (346/481)4.0 (19/481)21.72<0.001
Wood stock (m3/ha)0.5 [100–250] vs. 1 (>250)24.1 (116/481)4.0 (19/481)9.00<0.001
Age structure0 (even-aged) vs. 1 (uneven-aged)29.7 (143/481)70.3 (338/481)−12.57<0.001
Canopy density0 (both <1) vs. 0.5 (one <1, one ≥1)77.8 (374/481)18.3 (88/481)18.46<0.001
Canopy density0 (both <1) vs. 1 (both ≥1)77.8 (374/481)4.0 (19/481)23.28<0.001
Canopy density0.5 (one <1, one ≥1) vs. 1 (both ≥1)18.3 (88/481)4.0 (19/481)7.08<0.001
Regeneration0 (none/minimal) vs. 0.5 (moderate)36.0 (173/481)17.3 (83/481)6.57<0.001
Regeneration0 (none/minimal) vs. 1 (high)36.0 (173/481)46.8 (225/481)−3.400.001
Regeneration0.5 (moderate) vs. 1 (high)17.3 (83/481)46.8 (225/481)−9.81<0.001
Aspect0 (one direction) vs. 0.5 (two directions)73.6 (354/481)23.1 (111/481)15.68<0.001
Aspect0 (one direction) vs. 1 (>two directions)73.6 (354/481)3.3 (16/481)22.40<0.001
Aspect0.5 (two directions) vs. 1 (>two directions)23.1 (111/481)3.3 (16/481)9.05<0.001
Note: Proportions are computed as the count in the stated level divided by the total number of stands (n/N). Percentages are rounded to one decimal. Assumptions: adequacy of the binomial normal approximation was verified (np, n(1 − p)); exact tests confirmed the pairwise results. Where relevant, Jarque–Bera tests indicated no departures from normality (all p > 0.05).
Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content.

Share and Cite

MDPI and ACS Style

Michailidis, E.; Stampoulidis, A.; Petrou, P.; Kitikidou, K.; Pipinis, E.; Radoglou, K.; Milios, E. Biodiversity Status of Pure Oak (Quercus spp.) Stands in Northeastern Greece: Implications for Adaptive Silviculture. Environments 2025, 12, 339. https://doi.org/10.3390/environments12090339

AMA Style

Michailidis E, Stampoulidis A, Petrou P, Kitikidou K, Pipinis E, Radoglou K, Milios E. Biodiversity Status of Pure Oak (Quercus spp.) Stands in Northeastern Greece: Implications for Adaptive Silviculture. Environments. 2025; 12(9):339. https://doi.org/10.3390/environments12090339

Chicago/Turabian Style

Michailidis, Efthimios, Athanasios Stampoulidis, Petros Petrou, Kyriaki Kitikidou, Elias Pipinis, Kalliopi Radoglou, and Elias Milios. 2025. "Biodiversity Status of Pure Oak (Quercus spp.) Stands in Northeastern Greece: Implications for Adaptive Silviculture" Environments 12, no. 9: 339. https://doi.org/10.3390/environments12090339

APA Style

Michailidis, E., Stampoulidis, A., Petrou, P., Kitikidou, K., Pipinis, E., Radoglou, K., & Milios, E. (2025). Biodiversity Status of Pure Oak (Quercus spp.) Stands in Northeastern Greece: Implications for Adaptive Silviculture. Environments, 12(9), 339. https://doi.org/10.3390/environments12090339

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

Article Metrics

Back to TopTop