DOI: 10.1111/jvs.70177 ISSN: 1100-9233

Long‐Term Structural, Compositional, and Ecological Shifts in a Temperate Old‐Growth Forest: Insights From Six Decades of Vegetation Resurveys

Andrej Rozman, Thomas A. Nagel
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ABSTRACT

Aims

Long‐term vegetation resurveys are essential for understanding how forest ecosystems respond to interacting climatic, structural, and biotic drivers. We assessed six decades of vegetation change in a temperate old‐growth forest, focusing on shifts in forest structure, plant diversity, species composition, and inferred ecological conditions, while also evaluating the consistency of trends derived from different resurvey methodologies.

Location

Rajhenavski Rog old‐growth forest reserve (51 ha), Dinaric Mountains, Slovenia.

Methods

We analyzed two complementary long‐term vegetation datasets: (i) repeated surveys of 62 systematically arranged semi‐permanent 49‐m 2 plots conducted in 1983, 2015, and 2025; and (ii) a reserve‐level comparison of historical Braun–Blanquet relevés from 1967 with new Braun–Blanquet relevés recorded in 2025 on 400‐m 2 plots. Because the historical Braun–Blanquet relevés were not precisely localized, this second dataset was interpreted as complementary evidence for broad reserve‐level change rather than as a strict plot‐level resurvey. We quantified temporal changes in vegetation‐layer cover; alpha, beta, and gamma diversity; species composition; and community homogenization. Ecological shifts were inferred using community‐weighted Ellenberg indicator values. Multivariate analyses and beta‐diversity partitioning were used to disentangle species turnover and nestedness components.

Results

Forest structure shifted markedly over six decades, with increasing dominance of Fagus sylvatica and a persistent decline of Abies alba , particularly in canopy and regeneration layers, accompanied by a long‐term reduction in herb‐layer cover. Despite these structural changes, plot‐level species richness and diversity remained largely stable, showing only a transient decline around 2015. In contrast, beta diversity declined consistently across both datasets, indicating long‐term community homogenization driven primarily by species turnover rather than species loss. Ellenberg indicator values revealed significant thermophilization, decreasing moisture conditions, and increasing soil reaction, while light and nutrient indicators remained stable. Species‐level analyses identified consistent long‐term winners and losers, with A. alba regeneration strongly suppressed, likely due to ungulate browsing.

Conclusions

Our results demonstrate that even structurally complex old‐growth forests undergo pronounced compositional shifts and increasing homogenization under sustained climate warming and biotic pressures. The congruence of trends across contrasting resurvey designs highlights the robustness of long‐term vegetation monitoring for disentangling global and local drivers of forest change. The consistency in the main trends across the two datasets supports the interpretation of long‐term vegetation change in the reserve and indicates that historical resurveys, even when the exact original plot locations are unknown, can be useful but must be evaluated cautiously.

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