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Povzetek: 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.
Ključne besede: floristic homogenization, forest disturbances, permanent vegetation plots, Quercus robur, Quercus petraea, resurvey study, Slovenia, thermophilization, tree layer cover
Objavljeno v DiRROS: 11.11.2024; Ogledov: 114; Prenosov: 54
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Povzetek: Bryophytes respond to a variety of environmental factors, including tree species composition and geological conditions, which are influenced by both natural and anthropogenic factors. Bryophytes growing on a variety of substrates were identified in ICP Forests monitoring plots in a wide range of close-to-nature managed forests, from lowland to high mountain areas in Slovenia. Based on data on tree layer composition (broadleaves vs. conifers) and on bedrock and soil type (calcareous vs. siliceous bedrock), all study plots were classified into five groups representing forest types. Different ordination analyses and statistical tests were used to represent differences between forest types in bryophyte composition, richness and functional traits. Almost 200 bryophyte species were identified in managed forests, with the most common being Hypnum cupressiforme, Brachytheciastrum velutinum and Polytrichum formosum. Bryophyte species composition varied considerably along the tree species composition and edaphic gradients represented by the selected forest types. Bryophyte species richness was significantly higher on calcareous bedrock than on siliceous bedrock. The higher occurrence of rocks on the ground surface may significantly increase the availability of various microhabitats for bryophytes. Bedrock had a significant influence on the functional diversity and composition of bryophytes, while tree species composition had less influence. Bedrock and tree species composition are important drivers of bryophyte species composition and diversity at taxonomic and functional trait levels. The high diversity of bryophyte species in Slovenian forests can also be attributed to close-to-nature and sustainable forest management practices that preserve favourable microclimatic conditions in forest stands and maintain diverse substrates.
Ključne besede: mosses, species richness, functional diversity, site conditions, overstory, sustainable managed forests, European temperate zone
Objavljeno v DiRROS: 31.07.2024; Ogledov: 313; Prenosov: 306
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Povzetek: V letu 2023 − eno leto po obsežnem požaru na Goriškem Krasu, ki je divjal julija leta 2022 − smo na izbranih gozdnih vzorčnih ploskvah popisali zeliščno, grmovno in drevesno vegetacijo in analizirali tla do globine 10 cm. Ploskve smo izbrali na lokacijah stalnih vzorčnih ploskev ZGS z različno stopnjo poškodovan osti zaradi požara. Na izbranih ploskvah smo skupno popisali 260 vrst praprotnic in semenk. V drevesni plasti smo popisali trinajst vrst (enajst domorodnih in dve tujerodni), v grmovni plasti trideset, v zeliščni pa 255. V drevesni plasti so bili najpogostejši mali jesen, črni gaber in črni bor, v grmovni mali jesen, navadni ruj in robide. V zeliščni plasti smo med drugimi popisali tudi devetnajst drevesnih vrst, ki so pomembna zasnova pri naravni obnovi požganega gozda na Krasu; najpogostejša sta bila črni gaber in rešeljika. Gradient poškodovanosti po požaru se jasno kaže v večini vegetacijskih in talnih spremenljivk. Statistično značilne razlike med skupinami ploskev z različno stopnjo poškodovanosti smo ugotovili za šest parametrov: pH-vrednosti in vsebnosti žvepla v organskem delu tal, zastiranje drevesne plasti, zastiranje mahov, število vrst v spodnji drevesni plasti, število vrst zeliščne plasti. Na ploskvah smo prepoznali devet (ter še tri vrste na požarišču zunaj ploskev) invazivnih ali potencialno invazivnih tujerodnih rastlinskih vrst; med drevesnimi sta bila najpogostejša robinija in visoki pajesen. Študija pomembno prispeva k razumevanju razvoja vegetacije, pomlajevanja ključnih drevesnih vrst in poškodb gozdnih tal v inicialni fazi po obsežnem požaru.
Ključne besede: gozdna vegetacija, poškodbe tal, gozdni požar, drevesne vrste, pestrost vrst, invazivne rastlinske vrste, Kras, Slovenija
Objavljeno v DiRROS: 21.05.2024; Ogledov: 587; Prenosov: 250
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Povzetek: 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.
Ključne besede: long-term vegetation change, invasive non-native plants, oak mortality, Quercus robur, Quercus petraea, canopy openness, Impatiens parviflora, Slovenia
Objavljeno v DiRROS: 19.04.2024; Ogledov: 459; Prenosov: 302
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Povzetek: Forests are important ecosystems that face threats from climate change and global environmental shifts, with invasive alien plant species being a significant concern. Some of these invasive species have already become established, while others are in the process of naturalisation. Although forests are a relatively stable ecosystem, extreme weather events increase their vulnerability to change, and clearings left after natural disturbances are particularly susceptible to invasion by alien plant species (IAPS). We created risk maps of two species that have spread rapidly in the last decade: American pokeweed (Phytolacca americana) and the tree of heaven (Ailanthus altissima). We prepared a generalised linear model based on the occurrence data collected within the LIFE ARTEMIS project. Eleven environmental variables were used to determine habitat characteristics. We constructed two models for each species: one covering the entirety of Slovenia and the other specifically for the forested areas in Slovenia, with the latter incorporating forest-specific variables (such as forest sanitation felling and monocultures). We observed the presence of both species at lower altitudes and in close proximity to water sources. American pokeweed tends to occur nearer to railways, while the presence of the tree of heaven is associated with areas lacking carbonate parent material and influenced by land use patterns. In forested areas, the occurrence of American pokeweed is influenced by forest habitat characteristics, such as disturbances caused by extreme weather events or the prevalence of Norway spruce monocultures. In contrast, the occurrence of the tree of heaven is influenced by more general environmental variables, such as altitude and proximity to railways. Consequently, we have generated risk maps for the entirety of Slovenia and separately for forested areas, both of which indicate similar levels of risk, particularly for the tree of heaven. The risk map for American pokeweed highlights numerous vulnerable areas, especially forest edges, which are highly susceptible to invasion. Furthermore, there is a higher likelihood of this species occurring in areas that have undergone sanitation felling. This study suggests that the production of risk maps of IAPS could be improved by focussing on habitat types and taking into account habitat-specific variables. This approach could enhance the early detection and management of these invasive species.
Ključne besede: American pokeweed, tree of heaven, species distribution modelling, forests, forest disturbance, habitat suitability
Objavljeno v DiRROS: 26.03.2024; Ogledov: 559; Prenosov: 1858
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