Flóra Tinya

Climate change mitigation and biodiversity conservation are key forest functions, but how to pursue them jointly in timber-managed forests is still unclear. We use a Europe-wide dataset of forest multi-taxon diversity and stand structure to (i) evaluate the importance of aboveground carbon stocks in determining species richness of six taxonomic groups; (ii) assess relationships between species richness and carbon stocks; (iii) discuss the potential to jointly enhance carbon and biodiversity and policy implications. Carbon-diversity relationships are positive for several groups, but mostly when deadwood pools are considered. Forest policies should consider the complex relationship between different carbon pools and taxonomic groups. Environmental policies emphasizing carbon sequestration in aboveground living biomass may conflict with biodiversity conservation by promoting homogeneous, fast-growing forests that fail to support species diversity of multiple groups. Sustainable forest management should acknowledge that deadwood carbon instead may translate into positive outcomes for both carbon storage and biodiversity conservation.

The species richness of vascular plants in forests can have contrasting effects on the occurrence of non‐native insects. The establishment of non‐native insect populations may be facilitated by low plant species richness, which reflects the availability of few but easily accessible resources, or hampered by high plant species richness due to spatial dilution of resources or biotic resistance (i.e., resistance against biological invasions). The relationship between the species richness of plants and non‐native insects is likely influenced by disturbance regimes, which, in European forests, mostly consists of timber harvesting. We investigated this relationship considering two major forest attributes: (i) species richness of non‐native vascular plants and (ii) forest management. From 1101 forest plots in Europe, we gathered occurrences of 1212 vascular plant species, including 160 non‐native species, and of 2404 beetle species, including 29 non‐native species. We tested the relationship between the species richness of non‐native beetles and plants using non‐linear quantile regressions. We disentangled the effect of non‐native plant species richness from that of management on the species richness of non‐native beetles, while accounting for forest structural variables, using structural equation models. We found clear evidence of a hump‐shaped relationship between non‐native beetle and plant species richness. The general shape of the relationship persisted when considering only woody or non‐woody plants, as well as only non‐native plants. The relationship was also similar between managed and unmanaged forests. However, the proportion of non‐native beetles in managed forests was higher than in unmanaged forests at the same plant species richness. Management had a direct negative effect on non‐native beetle species richness, whereas non‐native plant species richness had a direct positive effect. When considering all direct and indirect effects, management facilitated the occurrence of non‐native beetles indirectly via non‐native plants rather than directly. Synthesis and applications. Species richness of native and non‐native vascular plants modulates the species richness of non‐native beetles through relationships with opposite signs. The interplay with management regimes and forest structures determines whether non‐native beetles are promoted. Forest management aimed at reducing the intensity of disturbance while encouraging native plant species richness could promote the dominance of dilution effects and biotic resistance and could moderate the establishment of non‐native insects.

Managing forests to sustain their diversity and functioning is a major challenge in a changing world. Despite the key role of understory vegetation in driving forest biodiversity, regeneration and functioning, few studies address the functional dimensions of understory vegetation response to silvicultural management. We assessed the influence of the silvicultural regimes on the functional diversity and redundancy of European forest understory. We gathered vascular plant abundance data from more than 2000 plots in European forests, each associated with one out of the five most widespread silvicultural regimes. We used generalized linear mixed models to assess the effect of different silvicultural regimes on understory functional diversity (Rao's quadratic entropy) and functional redundancy, while accounting for climate and soil conditions, and explored the reciprocal relationship between three diversity components (functional diversity, redundancy and dominance) across silvicultural regimes through a ternary diversity diagram. Intensive silvicultural regimes are associated with a decrease in functional diversity and an increase in functional redundancy, compared with unmanaged conditions. This means that although intensive management may buffer communities' functions against species or functional losses, it also limits the range of understory response to environmental changes. Policy implications. Different silvicultural regimes influence different facets of understory functional features. While unmanaged forests can be used as a reference to design silvicultural practices in compliance with biodiversity conservation targets, different silvicultural options should be balanced at landscape scale to sustain the multiple forest functions that human societies are increasingly demanding.

Most broad-scale forest biodiversity indicators are based on data from national forest inventories and are used to assess the state of biodiversity through several regional initiatives and reporting. Although valuable, these indicators are essentially indirect and evaluate habitat quantity and quality rather than biodiversity per se. Besides, most of these indicators are applicable at regional or national scales, while their use at a more local level is difficult. Therefore, their link to biodiversity may be weak, which decreases their usefulness for decision-making. For several decades, Forest Europe indicators assessed the state of European forests, in particular its biodiversity. However, no extensive study has been conducted to date to assess the performance of these indicators against multitaxonomic data. We hypothesized that – as implied by the reporting process – no single biodiversity indicator from Forest Europe can represent overall forest biodiversity, but that several – eventually combined – indicators would reflect habitat quality for at least some taxa in a comprehensive way. We tested the set of indicators proposed by Forest Europe against the species richness of six taxonomic and functional groups (tracheophytes, epixylic and epiphytic bryophytes, birds, saproxylic beetles, saproxylic non-lichenized fungi and epixylic and epiphytic lichenized fungi) across several hundreds of plots over Europe. We showed that, while some indicators perform relatively well across groups (e.g. deadwood volume), no single indicator represented all biodiversity at once, and that a combination of several indicators performed better. Surprisingly, some indicators showed weak links with the biodiversity of the six taxonomic and functional groups. Forest Europe indicators were chosen for their availability and ease of understanding for most people. However, our analyses showed that there are still gaps in the monitoring framework, and that surveying certain taxa along with stand structure is necessary to support policymaking and tackle forest biodiversity loss at the large scale. Impact statement Biodiversity indicators used to assess the state of Europe’s forests perform unequally; a combination of indicators is more informative

Erdőökológiai kísérletünkben a vágásos és az örökerdő gazdálkodásban alkalmazott erdészeti beavatkozások aljnövényzetre gyakorolt kezdeti hatásait vizsgáltuk egy korábban vágásos üzemmódban művelt, egykorú gyertyános-kocsánytalan tölgyesben. A kísérletben kisméretű vágásterületeket, hagyásfacsoportokat, bontóvágással kezelt területeket, lékeket és kontrollként idős, záródott állományokat hasonlítottunk össze az aljnövényzet fajszáma, borítása és kompozíciója, valamint négy növényi funkciós csoport összegzett borítása szerint. Kimutattuk, hogy a beavatkozások utáni negyedik évre a fajszám és a borítás leginkább a vágásterületeken és lékekben nőtt meg, míg növekedésük a bontásokban közepes, a hagyásfacsoportokban mérsékelt volt. A kompozíció a vágásterületeken jelentősen átalakult; bennük főleg nem-erdei lágyszárúak, míg a lékekben inkább fény- és nedvességigényes erdei fajok nyertek teret. A növényzet erdei jellegének meg- őrzése mellett a fás szárú magoncok borításnövekedése is a lékekben és bontásokban volt a legnagyobb. Eredményeink alapján arra következtetünk, hogy a folyamatos erdőborítást fenntartó gazdálkodás természetvédelmi és faanyagtermelési szempontból is kedvező lehet.