The research team, led by Aleksandar Popović of the University of Belgrade, established twelve sample plots totaling 3.6 hectares across three representative localities: Veliki Stolac in Bosnia and Herzegovina for Serbian spruce, Beleg in central Serbia for Macedonian pine, and Zeletin in Montenegro for Bosnian pine. All plots sit within strictly protected areas where forestry interventions are prohibited, and all developed on the same limestone substrate, forming shallow calcareous-dolomitic rendzina soils classified as Leptosols. This shared geological foundation proved to be a scientific gift, because any differences between the forests could not be blamed on bedrock.

What the researchers found instead were three chemically distinct soil worlds. The Serbian spruce stands, growing on steep north-facing limestone slopes between roughly 1,165 and 1,200 meters, produced the most striking numbers: humus contents of 48 to 55 percent, total nitrogen between 1.37 and 1.80 percent, and the widest carbon-to-nitrogen ratios of all three sites. Such a wide C/N ratio signals slow decomposition and the accumulation of carbon-rich organic matter, hinting at a soil environment where nutrients are locked up rather than rapidly recycled. The spruce soils also held the most hygroscopic water, consistent with the water-retaining power of abundant organic material.

Macedonian pine told a different story. At Beleg, in the subalpine zone between 1,795 and 1,890 meters where mean annual temperatures hover around just 2.6 to 3.7 degrees Celsius, the soils were the most acidic and the poorest in available nutrients. Phosphorus levels ranged from only 1.15 to 4.45 milligrams per 100 grams, with similarly low potassium. These conditions act as a harsh environmental filter, and the understory flora that persists there, including Arctic-Alpine elements, reflects species tolerant of both cold and nutrient scarcity. Bosnian pine occupied the middle ground chemically, with moderate humus, a less acidic reaction, and an intriguing nutrient imbalance of relatively high phosphorus but very low potassium.

The correlation analysis revealed that these soil properties do not vary independently. One tightly linked group comprised the adsorptive complex parameters, including exchangeable bases, total exchange capacity, and base saturation. A second group bound together organic matter, nitrogen, the C/N ratio, available phosphorus, and hygroscopic water. Strikingly, soil depth ran counter to the second group: shallower soils held more humus, nitrogen, and moisture. In these thin mountain soils, depth is not just a physical attribute but a marker of where organic life concentrates.

Above ground, the three forests were equally distinct. Across all plots the team recorded 152 vascular plant taxa from 31 families, with Bosnian pine stands supporting the richest flora at 102 species. Hemicryptophytes dominated everywhere, but the proportions of chamaephytes rose toward the harsher high-mountain pine sites, and Sub-Mediterranean elements appeared only in the Bosnian pine stands of Montenegro, which receive up to 1,746 millimeters of precipitation annually, mostly peaking in November.

To capture structural diversity in a single measure, the researchers calculated a Forest Structural Complexity Index by standardizing variables such as tree density, basal area, canopy cover, and the Shannon diversity index. Serbian spruce scored highest at +1.42, reflecting tall, dense stands with regular structure and the greatest species diversity indices. Bosnian pine scored lowest at -1.24, but this masked a different kind of richness: its stands showed the greatest variability in trunk diameters and the highest Gini coefficient of heterogeneity at 0.66. The messy, uneven structure of Bosnian pine forest appears to generate a mosaic of microsites, and it is precisely these stands that host the most plant species.

The study’s central conclusion is that no single environmental factor explains these forests. Soil properties and forest diversity emerge from the interaction of orographic conditions, tree species identity, stand structure, and ground vegetation. Tree species are known from broader European research to account for roughly 30 to 36 percent of variation in forest-floor carbon-to-nitrogen ratios, and the contrasting litter inputs of these three relicts plausibly drive their distinctive soil chemistries, which in turn shape what can germinate and survive beneath the canopy.

The implications reach beyond academic curiosity. Serbian spruce survives on a total of roughly 305 hectares with fewer than 30,000 individual trees and is listed as Endangered on the IUCN Red List; at one peat bog site on Mount Tara, only two adult trees remain with no natural regeneration. Macedonian pine is Near Threatened. For such fragmented populations, the authors argue, conservation focused solely on mature trees risks missing the point. Protecting the shallow, organic-rich soils, natural stand structure, and ground vegetation that create suitable regeneration microsites may matter more than any single rescue effort.

Because the study is observational, the proposed feedback mechanisms remain hypotheses awaiting direct tests of litter chemistry, decomposition rates, and microbial activity. But the message from these ancient forests is already clear: the ground beneath a forest is not a passive backdrop. It is a partner in an ancient conversation, and in the Balkans’ refugial conifer woods, that conversation has been running since before the ice ages, in soils often barely deeper than a hand.

Subject of Research: Soil and vegetation relationships in refugial endemic coniferous forests of the Balkan Peninsula

Article Title: Soil–diversity relationships in refugial endemic coniferous forests of the Balkan Peninsula

Article References: Soil–diversity relationships in refugial endemic coniferous forests of the Balkan Peninsula. (n.d.). https://doi.org/10.3389/ffgc.2026.1869703

Image Credits: AI Generated

DOI: 10.3389/ffgc.2026.1869703

Keywords: Serbian spruce, Macedonian pine, Bosnian pine, Balkan Peninsula, refugial forests, soil properties, forest diversity, endemic conifers, Leptosols, plant-soil feedback, forest structure, conservation

The research team, led by Anastasia Christopoulou of the University of the Aegean together with colleagues from the National and Kapodistrian University of Athens, Aristotle University of Thessaloniki, and the Academy of Athens, focused on the two most significant Macedonian pine areas in Greece: Mount Voras on the border with North Macedonia and the Chaidou forest in the Rhodope mountains near the Bulgarian frontier. Both sites lie within the Natura 2000 network of protected areas, yet while Mount Voras hosts a formally mapped 76 hectares of the protected habitat type 95A0, the High oro-Mediterranean pine forests, the presence of Macedonian pine in Chaidou had never even been mapped in the site’s official documentation. Reaching these stands required permits from the Ministry of Environment and Energy and close coordination with local forest services, whose staff guided researchers through terrain where brown bears are common and previously unmapped pine groves hide among the ridges.

The methodological approach combined classical dendrochronology with modern forest inventory and vegetation science. The team established five sampling plots of 0.1 hectares each, measuring the diameter at breast height of every tree exceeding 8 centimeters, and using laser hypsometry to capture tree heights. From 29 individual Macedonian pines, they extracted 34 increment cores, preparing each sample in the laboratory and measuring ring widths to the hundredth of a millimeter using a LINTAB measuring table and TSAP-Win software. Cross-dating relied on both visual comparison and statistical indices, including the Gleichläufigkeit coefficient and the Baillie-Pilcher and Hollstein t-values, ensuring that each ring could be assigned to its exact calendar year. Where cores missed the pith, the researchers applied standard growth-rate curves to estimate the missing rings to the tree’s center.

The headline finding is one of youth. The oldest tree sampled on Mount Voras reached just 104 years, with an estimated maximum of 112 years once missing rings were accounted for. At Chaidou, the maximum estimated age was a mere 72 years. This stands in stark contrast to Macedonian pine populations elsewhere in the Balkans, particularly in Bulgaria’s Pirin Mountains, where the species can live up to 600 years, and to its compatriot the Bosnian pine, Pinus heldreichii, which has produced multi-century and even millennia-old trees in the Greek Pindos range. The Greek Macedonian pine forests, it turns out, are essentially new arrivals on the landscape, dominated by trees established within living memory.

What caused this demographic reset remains an open question. The authors consider several plausible explanations, including past exploitation for timber, fires set by shepherds to improve grazing land, and broader land-use change. Historical records do not specifically document heavy use of Macedonian pine in the study area, although the species has been valued for carpentry and furniture elsewhere. Intriguingly, the young and expanding stands observed on Mount Voras, where saplings are colonizing former grasslands, point to land abandonment and the reduction of livestock grazing in recent decades as drivers of natural afforestation. Warming winter temperatures may further favor the species’ expansion toward the treeline, a pattern already documented in Bulgaria. Whatever the precise cause, the absence of very old individuals suggests these forests are recovering cohorts rather than ancient survivors, though the researchers caution that old trees could still persist in inaccessible ravines and cliffs beyond the reach of systematic survey.

Despite their youth, the trees are recording climate history with remarkable fidelity. The two independent chronologies, one from each mountain, correlated strongly with each other despite their limited overlap, and marker year analysis identified 36 years of exceptionally high or low growth. Four marker years were common to both sites, and each corresponds to documented climatic extremes in Greece. The year 1970, the sole shared positive marker year, aligns with the cooling trend that gripped Greece from the early 1960s to the mid-1970s. The negative marker years tell a darker story: 1987 marks the historic heatwave when July temperatures exceeded 40 degrees Celsius for nine consecutive days and reached 44 degrees in some regions; 2000 brought a parched August and sustained summer heat; and 2020 delivered another early-summer heatwave. Density fluctuations detected in the Chaidou samples, present in more than 60 percent of cores and consistently dated to 2006 and 2007, correspond to two years of extreme temperatures and unusually mild winters in Greece.

The anatomical analysis yielded an unexpected bonus. Four trees from Chaidou displayed indented growth rings, known as hazelwood, a feature caused when external injuries to the cambium, whether from fire, rockfall, herbivores, or human activity, deform the wood structure. While experts have anecdotally noted hazelwood in Macedonian pine, formal documentation in the scientific literature has been sparse. Its prevalence in the younger portions of trees aged 59 to 63 years suggests that even recently established forests are sensitive to episodic stressors capable of leaving permanent anatomical imprints, underscoring the value of dendrochronology for reconstructing disturbance histories that leave no other trace.

Structurally, the two forests could hardly be more different. Mount Voras supports a heterogeneous, uneven-aged stand shaped by prolonged regeneration and episodic disturbance, with lower densities and smaller trees. Chaidou, by contrast, shows a uniform age structure indicative of synchronous establishment, combined with higher stand density and intense competition. These differences produced a striking divergence in the relationship between size and age: on Mount Voras, diameter and height correlated moderately with tree age, but at Chaidou the relationships were weak and non-significant, with diameter and height even trending in opposite directions. The practical lesson is that the largest trees are not necessarily the oldest, a rule the data confirm emphatically. Fitted diameter distributions reinforced the contrast, with a lognormal distribution best describing Mount Voras and a gamma distribution fitting Chaidou, both revealing positively skewed structures dominated by small and intermediate trees.

The floristic survey recorded 55 plant taxa across the two sites, with 42 on Mount Voras and 22 at Chaidou, including understory species such as Juniperus communis, Vaccinium myrtillus, and Fragaria vesca. Only Pinus peuce and Calamagrostis arundinacea were typical species of the habitat type found at both sites. Worryingly, despite minimal human pressure and evidence of active expansion, both forests were assessed as having an Unfavourable-Inadequate conservation status, mirroring the national assessment for habitat type 95A0. The culprit is inadequate regeneration of the dominant pine at certain sites, compounded by the species’ limited and fragmented distribution in Greece. Remoteness, the authors warn, is a double-edged sword: it shields the forests from everyday human pressures but hampers active protection against large-scale disturbances, particularly wildfires, which are increasingly affecting high-altitude conifer forests in Greece and are expected to intensify under climate change.

For a species classified as Near Threatened on the IUCN Red List, and for a habitat type whose Greek conservation status is formally assessed as Inadequate-Bad, these findings carry real weight. The young Macedonian pine forests of Greece may lack the romantic gravitas of millennia-old Bosnian pines, but they represent unique ecosystems at the southernmost edge of the species’ range, with demonstrated sensitivity to regional climate variability and clear signs of dynamic expansion. The researchers argue that long-term monitoring of stand dynamics, regeneration, and disturbance responses is essential for adaptive management within the Natura 2000 sites that host them. As climate and land use continue to reshape mountain landscapes across the Balkans, these slender, half-century-old pines may prove to be not remnants of a lost past but pioneers of an uncertain future, their rings faithfully inscribing whatever comes next.

Subject of Research: Ecology, age structure, and conservation of Pinus peuce forests in Greece assessed through tree-ring analysis and plant diversity surveys

Article Title: Revealing the ecology of Pinus peuce forests in Greece through tree rings forest dynamics and plant diversity

Article References: Christopoulou, A., Lasut-Zmudzka, D., Zikos, A., Chrysafis, I., Kapsomenakis, I., Paidi, C., Ntagkounakis, G., Zevgolis, Y. G., Zerefos, C., & Arianoutsou, M. (2026). Revealing the ecology of Pinus peuce forests in Greece through tree rings forest dynamics and plant diversity. Discover Conservation, 3(1), Article 31. https://doi.org/10.1007/s44353-026-00095-x

Image Credits: AI Generated

DOI: 10.1007/s44353-026-00095-x

Keywords: Macedonian pine, Pinus peuce, dendrochronology, tree rings, forest ecology, Natura 2000, habitat 95A0, Balkan endemic species, climate change, forest conservation, plant diversity, Greece