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Abstract: Due to a long history of various anthropogenic pressures, lowland forest reserves are scarce and lack historical datasets suitable for analysing long-term vegetation trends. This study investigated changes in plant diversity and species composition in the long-untouched Krakovo forest reserve, the only preserved remnant of lowland oak-hornbeam forests with primary status in Slovenia. The original vegetation sampling was conducted in the 1970s. In 2024, we resurveyed 30 semi-permanent plots capturing the natural variation in soil moisture gradient. We found the decline of Quercus robur in the upper tree layer and the expansion of shade-casting tree Carpinus betulus in the lower tree layer, a pattern mainly attributed to the lowering of the groundwater table. This shift in overstory dominance manifested in a directional change of herb-layer composition associated with high species turnover (61 %). The deterioration of light conditions at the forest floor resulted in significant decrease of species richness, accompanied by the process of taxonomic homogenization. The analysis of Ellenberg indicator values revealed a reorganization of the plant communities in response to the increasingly shaded and cooler understory environment, benefitting a limited number of perennial herbs preferring closed canopies. The change towards nutrient-demanding species was probably caused by improved litter quality, nitrogen input from agricultural areas and nutrient release from accumulated deadwood. In terms of soil moisture, the reserve still exhibits a mosaic of interchanging distribution between wetter and more mesic habitats. However, given that oak natural regeneration is very poor, we anticipate even more drastic vegetation changes in the future.
Keywords: lowland primary forest, Quercus robur dieback, Carpinus betulus, Light availability, taxonomic homogenization, semi-permanent plot
Published in DiRROS: 05.05.2025; Views: 165; Downloads: 55
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Abstract: Questions The long-term response of understorey vegetation to increasing tree mortality has rarely been addressed in resurvey studies. For two Quercus-dominated forest types, we asked: (a) How did overstorey alterations, induced by canopy mortality, affect understorey diversity and composition? (b) Is there a signal of global change effects on understorey communities? (c) Are these assemblages experiencing a homogenization process? Location Five sites in Quercus robur (QR) and four sites in Q. petraea (QP) forests, Slovenia. Methods We studied changes in vascular plants in the understorey layer from 1992/1993 to 2023 across 45 permanent 20 m × 20 m plots in QR and QP forests, respectively. Vegetation surveys were carried out following the standard Braun-Blanquet method. We compared original surveys with recent resurveys using multivariate analysis, ecological indicator values (EIV), plant traits and methods that quantify changes in individual species. Results Since the early 1990s, tree layer cover decreased from 95% to an average of 55% in QR, whereas it remained relatively high (77%) in QP plots. This resulted in denser understorey vegetation and a significant increase in plot-level species richness in QR forests, but a slight decrease in QP forests. The extensive loss of canopy cover and disturbance effects in QR forests caused significant changes in species composition. Species turnover in QR was driven by colonization of new disturbance-tolerant taxa characterized by ruderal traits, whereas the compositional shift in QP was to a greater extent due to species losses. We detected a process of vegetation thermophilization (increase in EIV-temperature), suggesting an effect of rapid climatic warming. Understorey communities are now more similar to each other than 30 years ago, indicating a decrease in beta-diversity (floristic homogenization). Conclusions Despite some common trends, vegetation responses were forest type-specific. Our study presents evidence of understorey vegetation changes triggered by increased canopy mortality (a strong local driver particularly in QR plots) and also points to the signal of global change symptoms (thermophilization, homogenization), which acted rather independently from the observed decline in tree layer cover.
Keywords: floristic homogenization, forest disturbances, permanent vegetation plots, Quercus robur, Quercus petraea, resurvey study, Slovenia, thermophilization, tree layer cover
Published in DiRROS: 11.11.2024; Views: 348; Downloads: 312
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Abstract: The spread of neophytes (non-native plant species) challenges the conservation status and ecological integrity of forests, especially in lowland areas. Long-term resurvey studies are needed to evaluate the temporal dynamics of neophytes in forests; however, such data are scarce. In 2023, we resampled a set of 45 permanent vegetation plots (established in 1992/93) in two forest vegetation types: oak–hornbeam forests dominated by Quercus robur and colline oak–beech forests dominated by Q. petraea. Over the last 30 years, oak forests have experienced extensive oak tree mortality, with the degree of habitat degradation being greater in Q. robur forests. In the early 1990s, only three neophytes with low abundance were recorded across all plots. In the 2023 resurvey, the total number of neophytes increased to 22 species (15 herbaceous and 7 woody species), comprising 6.9% of the total species pool in the understory layer. The increase in the plot-level number and cover of neophytes was significant in plots dominated by Q. robur but not in those with Q. petraea. The most frequent neophytes were Impatiens parviflora (present in 31% of plots), Solidago gigantea (27%), Erigeron annuus (16%) and Erechtites hieraciifolia (16%). The richness and cover of neophytes were significantly affected by the tree layer cover (negative correlation) and the degree of soil disturbance (positive correlation). All neophytes established in disturbed patches, whereas the occurrence of I. parviflora was exceptional as it was able to colonize less degraded, shaded understory environments. Habitat degradation (the mortality-induced loss of stand-forming oak trees resulting in extensive tree layer cover decrease) emerged as a key driver promoting neophyte proliferation, coupled with the impact of management-induced disturbances affecting overstory and soil conditions. The spread is expected to continue or even intensify in the future because novel light regimes and disturbances make forest habitats less resistant to neophyte proliferation.
Keywords: long-term vegetation change, invasive non-native plants, oak mortality, Quercus robur, Quercus petraea, canopy openness, Impatiens parviflora, Slovenia
Published in DiRROS: 19.04.2024; Views: 669; Downloads: 543
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Abstract: Tree-ring width (TRW), stable carbon isotope ratio (δ13C) and intrinsic water use efficiency (iWUE) data set chronologies were built for the period 1961–2000 for two oak species (pedunculate oak – Quercus robur L. and Turkey oak – Quercus cerris L.) in northwestern Serbia (Vojvodina province). We focused on the response of the two oak species to measured meteorological data (temperature, precipitation and cloud cover), drought events expressed by six meteorological drought indices, and river water level to better understand their drought tolerance and stress and to assess the reliability of the species response to climate and drought indices when using TRW or δ13C. Turkey oak exhibited better drought tolerance (and less drought stress) compared to pedunculate oak, as manifested, respectively, by less negative δ13C and lower iWUE values. Based on a generalised additive mixed model (GAMM) among the six drought indices studied, the standardised precipitation evapotranspiration index and the standardised precipitation index showed the best fit with both TRW and δ13C, while the Palmer drought severity index exerted a strong influence only on TRW. It was thus concluded that δ13C responds more strongly and rapidly to climate variations than TRW.
Keywords: dendrochronology, stable carbon isotope, tree ring, Quercus robur, Quercus cerris, drought, climate change
Published in DiRROS: 04.08.2022; Views: 1221; Downloads: 899
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Keywords: varstvo gozdov, morfološke analize, Quercus robur, dob, hrastova pepelovka, Erysiphe alphitoides
Published in DiRROS: 13.09.2021; Views: 1429; Downloads: 444
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